JPH1098229A - Multistage amplified optical transmission system and optical amplifier - Google Patents

Abstract

(57) [Problem] To provide a multi-stage amplified optical transmission system capable of maintaining good transmission characteristics such as SN ratio and waveform distortion. SOLUTION: A signal light output from a transmitter 100 is sequentially amplified through optical amplifiers 310 _{1 to} 310 _N at respective stages. In each of the optical amplifiers 310 _{1 to} 310 _N , the input light monitoring unit 313 detects the power level of the input light, and the amplification factor adjustment unit 315 outputs the detection result and the amplification information input unit 314.
The amplification factor is determined from the output light power level target value stored in the storage unit and the intensity of the excitation light supplied by the excitation unit 312 is adjusted so as to obtain the determined amplification factor. Then, the amplification factor is effected at the determined amplification factor, and the optical amplifiers 310 _{1 to} 310 _{1 of} each stage are used.
From 0 _N , light having a power level substantially equal to the output light power level target value is output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-stage amplified optical transmission system and an optical amplifier used in optical communication.

[0002]

2. Description of the Related Art As an optical amplifier, from the viewpoint of high speed,
An optical fiber amplifier that supplies operating energy in the form of light and amplifies and outputs input signal light is suitable. In particular, an optical fiber amplifier using an optical fiber doped with a rare earth element such as Er is excellent in high speed and low noise.

[0003] From the viewpoint of controlling the gain of each optical fiber amplifier to be constant, "Aida et al .: Transactions of the Institute of Electronics, Information and Communication Engineers, BI, Vol. J75-BI, No.
5, pp. 298-303, May 1992 "(hereinafter referred to as Conventional Example 1).
Nakabayashi et al .: From the viewpoint of reducing the wavelength dependence of gain in each optical fiber amplifier for multi-wavelength batch amplification.
1994 IEICE Spring Conference C-390 ”
(Hereinafter referred to as Conventional Example 2) and "Mizono et al .: 1994 IEICE Autumn Conference B-943" (hereinafter referred to as Conventional Example 3) have been proposed.

The optical fiber amplifier of the prior art 1 is ASE
Focusing on the relationship between (Amplified Spontaneous Emission) and gain, ASE (Amplified Spontaneous Emis) from the side of an erbium-doped optical fiber as an amplification optical fiber.
sion), the excitation light intensity is controlled according to the detected power level, and the gain is kept constant.

In the optical fiber amplifiers of Conventional Examples 2 and 3, when a required gain is set in a signal wavelength band, erbium-doped amplification made of a material having an amplification characteristic in which the wavelength dependence of the gain in the signal wavelength band is reduced. An optical fiber is used to control the pump light intensity to maintain the required gain.

When long-distance optical transmission is required for optical communication from a transmitter to a receiver, the distance between the transmitter and the receiver is compensated for in order to compensate for optical loss due to an optical fiber for transmission. In addition, it is essential to arrange a multi-stage amplification optical transmission system in which optical amplifiers such as a plurality of optical fiber amplifiers are connected in a multi-stage series. In such a multi-stage amplified optical transmission system, it is an essential element that the deterioration of the SN ratio of the signal light is small.

The SN in such a multi-stage amplified optical transmission system
From the viewpoint of maintaining the ratio, in “Terahara et al .: 1992 IEICE Spring Conference B-942” (hereinafter referred to as Conventional Example 4), the power level of the signal light at the output time of each optical fiber amplifier is fixed. ALC (Automa
tic Level Control), and the average value method ALC that keeps the total output power at the output time of each optical fiber amplifier constant
Discloses a multi-stage amplified optical transmission system that obtains a higher SN ratio than the case of (1).

In prior art example 4, a pilot signal is superimposed on a signal light to control the power level of the pilot signal at the time of output of each optical fiber amplifier to be constant, so that the signal at the time of output of each optical fiber amplifier is controlled. The light power level is controlled to be constant.

[0009]

The conventional optical amplifier and the multi-stage amplified optical transmission system have the following problems since they are configured as described above.

When the optical amplifiers of Conventional Examples 1 to 3 are applied to a multi-stage amplified optical transmission system, the gain of each optical amplifier is controlled to be constant. The power level of the light also increases or decreases.

Therefore, when the transmission loss in a specific transmission section of the relay transmission section is small, the power level of the input light increases, so that the power level of the output light increases. However, if the output light power level is too high, transmission waveform distortion due to self-phase modulation and chromatic dispersion caused by the non-linear optical effect of the transmission optical fiber, which is the transmission path, will occur.

On the other hand, if the transmission loss in a specific transmission section of the relay transmission section is large, the power level of the input light decreases, and the power level of the output light decreases. But,
When the output light power level decreases, the output signal light power level also decreases, so that noise generated in the transmission optical fiber, which is the transmission path, becomes relatively nonnegligible, and the SN ratio deteriorates.

In the multistage amplifying optical transmission system of the conventional example 4,
Since the pilot signal is superimposed on the signal light, the usable transmitter becomes special, and the existing transmitter cannot be used, and a high-precision wavelength splitter or the like is required for detecting the pilot signal. The configuration of the amplifier becomes complicated.

Further, when the transmission loss in each relay transmission section is not substantially constant and the transmission loss varies depending on the relay transmission section, it is necessary to change the amplification factor of each optical fiber amplifier. However, in general, when the amplification factor of an optical fiber amplifier is changed, the wavelength dependence of the amplification factor also changes.In a multi-wavelength batch amplification system, it is possible to reduce the wavelength dependence of the gain of the entire system. Can not.

The present invention has been made in view of the above, and provides a multi-stage amplified optical transmission system capable of maintaining good transmission characteristics such as SN ratio and waveform distortion, and is suitable for such a multi-stage amplified optical transmission system. It is an object of the present invention to provide an optical amplifier that can be used for the optical amplifier.

[0016]

A multistage amplified optical transmission system according to claim 1 is a multistage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers, Each of the plurality of optical amplifiers has (a) the amplification characteristics of the light of the wavelength of the signal light corresponding to the excitation light intensity and the input light intensity, and the relationship between the amplification factor and the noise light generation level as the amplification characteristics. (B) an excitation unit for supplying excitation light to the optical amplification unit, (c) an input light monitoring unit for monitoring the input light power level, and (d) amplification characteristics and a plurality of optical amplifiers. Based on the transmission loss in the relay transmission line between the optical amplifiers, the indicated optical power level to be output,
An amplification factor is determined based on the input light power level detected by the input light monitoring unit, and an amplification factor adjustment unit that adjusts the excitation light intensity supplied by the excitation unit according to the determined amplification factor. Features.

In the multi-stage amplified optical transmission system according to the first aspect,
The output optical power level of each optical amplifier depends on the amplification factor of the signal light wavelength corresponding to the pumping light intensity, the amplification characteristics of each optical amplifier such as the amplification factor and the noise light generation level, and the relay transmission between the optical amplifiers. The output optical power level of each optical amplifier is determined based on the transmission loss in the path, and the determined output optical power level is set in each optical amplifier. In each optical amplifier, the input light is monitored, and the amplification factor adjusting unit adjusts the intensity of the pumping light supplied by the pumping unit so that the output light power level is set.

Therefore, with respect to the propagation light in each relay transmission line, (i) the light intensity is set to be too large.
Generation of waveform distortion due to the nonlinear optical effect in the relay transmission line,
And (ii) at the time of system design, the amplification characteristics of each optical amplifier and the type and length of the transmission optical fiber, in order to suppress a decrease in the S / N ratio in the relay transmission line due to excessively low light intensity. And, in consideration of the transmission loss of the relay transmission path between the optical amplifiers estimated from the connection point and the like, by determining and setting the amplification factor of each optical amplifier,
(I) Realization of signal light transmission between a transmitter and a receiver while suppressing the occurrence of waveform distortion due to the nonlinear optical effect of the relay transmission line, and (ii) maintaining the SN ratio of the entire system. I do.

In order to obtain the transmission loss value in each relay transmission line, it is possible to actually measure the transmission loss value when the system is installed. In this case, the output optical power level to be output from each optical amplifier is determined at the time of installation of the system, and is set thereafter.

A multistage amplified optical transmission system according to a second aspect of the present invention is the multistage amplified optical transmission system according to the first aspect, in which an initial optical power level to be output is indicated to each of the plurality of optical amplifiers, and a plurality of the optical amplifiers are provided. The information corresponding to the operating amplification factor is collected from each of the optical amplifiers, and the optical power level to be newly output to each of the plurality of optical amplifiers is calculated based on the operating amplification factor of each of the plurality of optical amplifiers. And an amplification management unit for instructing each of the plurality of optical amplifiers of the calculated optical power level to be output.

In the multistage amplified optical transmission system according to the second aspect,
Set the power level of the light to be output from each optical amplifier,
This is performed by the amplification management unit during the operation of each optical amplifier.

In the early stage of system operation, the amplification management unit instructs each optical amplifier of an optical power level to be output in the early stage of operation of each optical amplifier. Each of the optical amplifiers that receive the instruction monitors the input light, and the amplification factor adjustment unit adjusts the intensity of the excitation light supplied by the excitation unit so that the output light power level is instructed. Along with this adjustment, each optical amplifier reports information corresponding to the amplification factor determined by the amplification factor adjustment unit to the amplification management unit.

The amplification management unit obtains a transmission loss value in each relay transmission line from the gain of each optical amplifier that has received the report and the output optical power level of each amplifier that has been instructed by itself, and obtains the calculated transmission loss value in each relay transmission line. From the transmission loss value and the amplification characteristics of the optical amplifier, it is possible to (i) suppress the occurrence of waveform distortion due to the nonlinear optical effect of the relay transmission line, and (ii) reduce the power level of the noise light generated in each optical amplifier. In consideration of this, an optical power level to be output from each optical amplifier that can secure the SN ratio of the entire system is calculated, and the calculated output optical power level is instructed to each optical amplifier.

Upon receiving the new instruction, each of the optical amplifiers monitors the input light, and the amplification factor adjusting unit actually controls the intensity of the pumping light supplied by the pumping unit so as to obtain the newly specified output light power level. Adjust with time.

Thereafter, reports on the amplification factors of the respective optical amplifiers,
Calculation of the optical power level to be output from each optical amplifier of the amplification management unit and feedback control of instructing each optical amplifier of the calculated output optical power level are performed to realize suitable multistage amplified optical transmission.

In the multi-stage amplified optical transmission system according to claim 2,
In the multistage amplified optical transmission system according to claim 1, a time change in transmission loss of each relay transmission line due to environmental conditions or the like occurs due to environmental conditions or the like without assuming substantially constant time change of transmission loss in each relay transmission line. Even so, suitable multistage amplified optical transmission is realized.

It is not necessary that the control speed of the output light power level by the amplification factor adjustment unit and the control speed of the output light power level by the amplification management unit match. It is preferable that the control speed of the output light power level by the amplification factor adjustment unit is faster, but the control speed of the output light power level by the amplification management unit may be equal to or less than the change speed of the transmission loss of each relay transmission line.

According to a third aspect of the present invention, in the multistage amplified optical transmission system according to the first aspect, the optical power level to be output by each optical amplifier is equal to the power of the signal light component output by each optical amplifier. The level is almost constant,
The optical power level is to be output from each of the optical amplifiers.

In the multistage amplified optical transmission system according to the third aspect,
Since the power level of the signal light component output from each of the optical amplifiers is substantially constant, if the suppression of the nonlinear optical effect is sufficient for the light of the signal light wavelength, the absolute amount of the signal light component is secured. , Signal light transmission is performed.

According to a fourth aspect of the present invention, in the multistage amplified optical transmission system according to the first aspect, the optical power level to be output by each optical amplifier is equal to the power of the signal light component output by each optical amplifier. The output optical power level of each of the optical amplifiers increases as the level becomes later.

The transmission optical fiber used for the relay transmission line has a small but non-linear characteristic, and the higher the light intensity density of the propagation light or the longer the propagation distance, the larger the nonlinear optical phenomenon occurs. The optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fiber has chromatic dispersion, when the optical frequency is modulated by self-phase modulation,
Waveform distortion occurs according to the propagation distance. Therefore, in the optical amplification of the multi-stage amplification optical transmission system, the larger the power level of the light having the wavelength of the signal light output from the optical amplifier, or the longer the subsequent propagation distance, that is, the signal light of the optical amplifier of the preceding stage The higher the output power level of light of wavelength
The waveform distortion will increase.

In the multi-stage amplified optical transmission system according to the fourth aspect,
The power level of the signal light component output from the optical amplifier is reduced in the optical amplifier on the transmitter side, and the power level of the signal light component output from the optical amplifier is increased in the subsequent stages. A suitable optical transmission in which the occurrence of self-phase modulation and the influence of chromatic dispersion are suppressed and waveform distortion is reduced is executed.

A multi-stage amplified optical transmission system according to claim 5 is the multi-stage amplified optical transmission system according to claim 2, wherein (i) the signal light has a plurality of transmission channels of different wavelength components.
(Ii) As the amplification characteristics of each of the plurality of optical amplifiers, the amplification factor dependency of the wavelength dependency of the amplification factor in a wavelength range including a plurality of wavelengths is further known, and (iii) the amplification management unit Based on the wavelength-dependent amplification factor dependence of the wavelength-dependent amplification factors and the operating amplification factors of each of the plurality of optical amplifiers, the light of each wavelength component of the signal light in the output light of the final-stage optical amplifier,
An optical power level to be output from each of the optical amplifiers for reducing the wavelength dependence of the gain of the system is calculated.

According to the knowledge of the inventor, in an amplification optical fiber doped with a rare earth element, in a 1.55 μm band generally used as a wavelength band of signal light, when the amplification factor is small, the longer the wavelength, the longer the wavelength. , The amplification rate tends to be high.
On the other hand, when the amplification factor is large, the shorter the wavelength is, the higher the amplification factor tends to be.

In the multistage amplified optical transmission system according to claim 5,
From the viewpoint of the output power level and the S / N ratio, even when the amplification factor of each optical amplifier must have wavelength dependence, the amplification management unit appropriately indicates the amplification factor of each optical amplifier. Thereby, the wavelength dependence of the gain of the entire system can be flattened.

An optical amplifier according to a sixth aspect is an optical amplifier used in a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers in sequence. A) the amplification factor of the light having the wavelength of the signal light according to the intensity of the excitation light and the intensity of the input light, and the optical amplification unit whose amplification factor value and the noise light generation level are known; (C) an input light monitor for monitoring the input light power level, (d) an information input unit for inputting level information relating to the indicated light power level to be output, and (e) level information An excitation light control unit that determines an amplification factor based on the input light power level detected by the input light monitoring unit, and adjusts the intensity of the excitation light supplied by the excitation unit according to the determined amplification factor; (f ) Output amplification factor information about the determined amplification factor Characterized in that it comprises an information output section.

In the optical amplifier according to the sixth aspect, the amplification factor adjusting section controls the pumping section so as to set the specified optical power level to be output in accordance with the input light level, and the specified output level is to be output. 3. An optical amplifier for a multi-stage amplification optical transmission system according to claim 2, wherein information relating to an optical power level can be input at an information input unit, and an amplification factor determined by an excitation adjustment unit can be output via an information output unit. It can be suitably adopted as.

The optical amplifier according to claim 7 is the optical amplifier according to claim 6, wherein (g) an output light monitor for monitoring the level of the output light of the optical amplifier, and (h) amplification determined by the amplification factor adjuster. The apparatus further includes an excitation light fine adjustment unit that finely adjusts the intensity of the excitation light supplied by the excitation unit based on the rate and the level of the output light detected by the output light monitoring unit.

According to the optical amplifier of the present invention, in addition to the adjustment of the power level of the output light by the feedforward control in the optical amplifier of the present invention, the power level of the output light is monitored. Since the light power level is finely adjusted, the output light power level can be adjusted more accurately.

In the optical amplifier according to the sixth aspect, if the amplification factor dependence of the wavelength dependence of the amplification factor in the wavelength band of the signal light of the optical amplifier is further known, the multistage amplified optical transmission according to the fifth aspect is provided. It can be suitably used as an optical amplifier of a system.

The multi-stage amplified optical transmission system according to claim 8 is a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers in sequence, other than the first-stage optical amplifier. The optical amplifier of the post-amplifier is
(A) A first optical amplifying unit whose amplification characteristics are known, in which the amplification factor of the light of the wavelength of the signal light according to the excitation light intensity and the input light intensity, and the relationship between the amplification factor value and the noise light generation level are known. When,
(B) a first pumping unit that supplies pumping light to the first optical amplifying unit and has a controllable pumping light intensity, and (c) a first input light monitoring unit that monitors a power level of the input light. (D) an amplification information input unit for receiving input level information relating to the power level of the signal light and the power level of the noise light at the time of the output of the optical amplifier at the preceding stage; and (e) output according to a preset level diagram. The amplification factor is determined based on the power level of the signal light to be output, the power level of the input light detected by the input light monitor unit, and the input level information, and the pumping light is supplied according to the determined amplification factor. A first amplification factor adjusting unit for instructing the unit.

Here, the optical amplifiers of the post-stage optical amplifier other than the last-stage optical amplifier are: (f) the power level and noise level of the signal light at the time of output based on the input level information and the determined amplification factor. It is preferable to further include a first amplification information output unit that generates and outputs output level information related to the power level of light.

Also, the first stage optical amplifier has (a) amplification characteristics of light having a wavelength of signal light corresponding to the intensity of the pump light and the intensity of the input light, and the amplification factor and the noise light generation level. A second optical amplifying unit having a known relationship, (b) a second exciting unit for supplying the exciting light to the second optical amplifying unit and having a controllable intensity of the exciting light, and (c) a power level of the input light. And (d) the amplification factor based on the power level of the signal light to be output according to the level diagram and the power level of the input light detected by the input light monitoring unit. The power level of the signal light at the time of output based on the second amplification factor adjustment unit that determines and instructs the excitation unit to supply the excitation light according to the determined amplification factor, and (e) the determined amplification factor. And output level information on the power level of noise light. It is preferable, further comprising a second amplifier information output unit for.

In the multi-stage amplified optical transmission system according to claim 8,
Optical transmission is performed while controlling the output power level of the signal light determined by the system design among the output light power levels of the respective optical amplifiers.

That is, in the multistage amplified optical transmission system according to claim 8, the output power level of the signal light of each optical amplifier is:
Amplification rate of light of signal light wavelength according to pumping light intensity, and amplification characteristics of each optical amplifier such as amplification rate and noise light generation level,
It is determined as a level diagram at the time of system design according to the assumed transmission characteristics of each relay transmission line.
Then, according to this level diagram, the power level of the signal light to be output is instructed to each optical amplifier.

When light to be amplified is input to each optical amplifier,
Each optical amplifier has an input optical power level detected by an input optical power monitor, a power level of signal light and a power of noise light at the time of output of an optical amplifier of a preceding optical amplifier, which are input through an amplification information input unit. The power level of the signal light component in the input light is determined based on the input level information related to the level. From the power level of the input signal light component thus determined and the specified power level of the signal light to be output, the amplification factor of the signal light component is determined, and the pumping light supplied by the pumping unit so as to have the determined amplification factor. Adjust the intensity.

Each optical amplifier amplifies the input light at the determined amplification factor and outputs the amplified light. In addition, considering the power level of the noise light generated by itself, the power level of the signal light component and the noise light at the time of output are taken into account. Output level information relating to the power level of the component is generated and output.

The output level information includes (i) the power level value of the signal light component and the power level value of the noise light component at the output time of each optical amplifier, and (ii) the power level value of the signal light component at the output time of each optical amplifier. The value of the ratio between the value and the power level value of the noise light component can be suitably adopted.

In the first-stage amplifier, since the optical amplification in the previous stage is not performed, it is assumed that there is substantially no noise component in the input light. Therefore, the mounting of the information input unit is indispensable as in other optical amplifiers. is not.

In the last-stage amplifier, since it is assumed that optical amplification in the subsequent stage is not performed, the mounting of the information output unit is not essential unlike other optical amplifiers.

Therefore, regarding the signal light component in each relay transmission line, taking into account the noise component of the wavelength of the signal light to be superimposed, (i) the nonlinear optical optics of the relay transmission line due to excessively increasing the signal light intensity In order to reduce the S / N ratio in the relay transmission line due to the occurrence of waveform distortion due to the effect and (ii) the signal light intensity being too small, the amplification characteristics of each optical amplifier and the transmission In consideration of the type of optical fiber, the length, and the transmission loss of the relay transmission line between the optical amplifiers estimated from the number of connection points,
By determining and setting the power level of the signal light component to be output from each optical amplifier, (i) while suppressing the occurrence of waveform distortion due to the nonlinear optical effect of the relay transmission line,
(Ii) Transmission of signal light between the transmitter and the receiver is performed while maintaining the SN ratio of the entire system.

When obtaining the transmission loss value in each relay transmission line, it is also possible to actually measure the transmission loss value at the time of installing the system. In this case, the power level of the signal light component to be output from each optical amplifier is determined at the time of installation of the system, and is set thereafter.

In the multistage amplified optical transmission system according to the present invention, the transmission loss of each relay transmission line due to environmental conditions or the like is not assumed, and the transmission loss of each relay transmission line is not assumed to be substantially constant over time. Even if the loss changes over time, it is possible to execute a suitable multi-stage amplified optical transmission.

In the transmission of the signal light and the transmission of the level information between the optical amplifiers, (h) the transmission of the signal light between the optical amplifiers is mediated, as in the multistage amplification optical transmission system according to the eleventh aspect. Mediating the transmission of the signal carrying the level information between the first transmission medium and (i) the optical amplifier;
A second transmission medium may be further provided, and as in the multistage amplified optical transmission system according to claim 12, the signal light is transmitted to the first transmission medium.
And the level information light carrying the level information has the wavelength of the second wavelength band having no shared wavelength with the first wavelength band, and the signal light and the level between the optical amplifiers An optical fiber that mediates transmission of both information light may be further provided.

If a transmission medium for signal light and a transmission medium for level information are separately prepared as in claim 11, the relay transmission path is composed of two transmission media. Since the type of information can be identified, the configuration of each optical amplifier can be simplified. Further, transmission of the level information is not limited to optical transmission, and electrical transmission can be adopted.

On the other hand, when the transmission medium for signal light and the transmission medium for level information are the same optical fiber, the relay transmission line has a simple configuration, but the level information in each optical amplifier is In addition, a new optical transmitter is required for the output, and an optical splitter by wavelength discrimination is required for inputting the level information, so that the configuration of the optical amplifier is somewhat complicated.

The multi-stage amplified optical transmission system according to claim 13 is
9. The multi-stage amplified optical transmission system according to claim 8, wherein the optical power level to be output from each optical amplifier is such that the power level of the signal light component output from each optical amplifier is substantially constant. Power level.

In the multistage amplified optical transmission system according to the thirteenth aspect, since the power level of the signal light component output from each of the optical amplifiers is made substantially constant, it is sufficient if the nonlinear optical effect is sufficiently suppressed for the light of the wavelength of the signal light. For example, the signal light transmission is performed while securing the absolute amount of the signal light component.

The multi-stage amplified optical transmission system according to claim 14 is
In the multi-stage amplified optical transmission system according to the eighth aspect, the power level of the signal light component output from each of the optical amplifiers increases as the level increases.

The transmission optical fiber used for the relay transmission line has a slightly nonlinear characteristic. When signal light of high intensity propagates, the higher the light intensity density of the propagation light or the longer the propagation distance. The larger the nonlinear optical phenomenon occurs, the more the optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fiber has chromatic dispersion, waveform distortion occurs according to the propagation distance. Therefore, in the optical amplification of the multi-stage amplification optical transmission system, the larger the power level of the light having the wavelength of the signal light output from the optical amplifier, or the longer the subsequent propagation distance, that is, the signal light of the optical amplifier of the preceding stage The higher the output power level of the light having the wavelength is, the larger the waveform distortion becomes.

In the multistage amplified optical transmission system of the present invention, the power level of the signal light component to be output is reduced as the optical amplifier is closer to the transmitter, and the power level of the signal light component output from the optical amplifier is reduced as it goes to the subsequent stage. Since it is large, the occurrence of self-phase modulation and the influence of chromatic dispersion due to the nonlinear optical effect in the relay transmission line are suppressed, and suitable optical transmission with reduced waveform distortion is performed.

An optical amplifier according to a fifteenth aspect is an optical amplifier used in a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially. a) an optical amplification unit having a known amplification factor of light having a wavelength of signal light corresponding to the intensity of the excitation light and the intensity of the input light, and a relationship between the amplification factor value and the noise light generation level; and (b) an optical amplification unit. (C) an input light monitor that monitors the power level of the input light, and (d) the power of the signal light at the time of output from the optical amplifier in the preceding stage. An amplification information input unit for receiving input level information relating to the level and the power level of the noise light; (e) a specified power level of the signal light to be output; and a power level of the input light detected by the input light monitoring unit And the input level information A gain adjuster for determining the width factor and instructing the pumping unit to supply pump light according to the determined gain; and (f) a signal at the time of output based on the input level information and the determined gain. An amplification information output unit for generating and outputting output level information relating to the power level of light and the power level of noise light is provided.

In the optical amplifier according to the fifteenth aspect, in accordance with the input light power level and the input level information, the amplification factor adjusting section controls the pumping section so as to set the power level of the signal light component to be instructed to be output. 9. An optical amplifier excluding the first and last stages of the multi-stage amplifying optical transmission system according to claim 8, wherein input level information can be input via an input information section and output level information can be output via an output information section. It can be suitably adopted as.

The optical amplifier according to claim 16 is the optical amplifier according to claim 15, wherein (g) an output light monitor for monitoring the level of output light of the optical amplifier, and (h) an amplification determined by the amplification factor adjuster. The apparatus further includes an excitation light fine adjustment unit that finely adjusts the intensity of the excitation light supplied by the excitation unit based on the rate and the level of the output light detected by the output light monitoring unit.

According to the optical amplifier of claim 16, in addition to the adjustment of the output light power level by the feedforward control in the optical amplifier of claim 15, the power level of the output light is monitored, and based on the monitoring result, the output is controlled by feedback control. Since the light power level is finely adjusted, more accurate adjustment of the output light power level, and furthermore, the power level of the signal light component of the output light can be performed.

In the optical amplifier according to the sixteenth aspect, the amplification information input section selects one of the level information output from the preceding optical amplifier and the preset information as input level information. With input selection means,
The selection is appropriately set, and (i) the level information output from the optical amplifier at the preceding stage is selected, whereby the optical amplifier is preferably used as an optical amplifier excluding the first and last stages of the multistage amplified optical transmission system according to claim 8. A possible optical amplifier is realized, and (ii) the first-stage amplifier of the multi-stage amplified optical transmission system according to claim 8 can be realized by selecting preset information. Also, an optical amplifier excluding the first and last stages can be realized.

Further, in the optical amplifier according to the present invention, the amplification information output section includes output selection means for selecting whether or not to output the output level information, and the selection is appropriately set.
Claim 8: (i) selecting to output
An optical amplifier suitable for use as an optical amplifier excluding the first and last stages of the multistage amplified optical transmission system of (1) is realized, and (ii) no output is selected. Since the last-stage amplifier can be realized, it is possible to realize the last-stage amplifier and the optical amplifier excluding the first-stage and the last-stage using the same configuration of the optical amplifier.

A multi-stage amplified optical transmission system according to claim 17 is
A multi-stage amplified optical transmission system for transmitting a signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein (1) each of the plurality of optical amplifiers other than the last-stage optical amplifier Includes (1a) an output light monitoring unit that monitors the output light power level, and (1b) a power level information output unit that outputs power level information indicating the output light power level to a subsequent optical amplifier, (2) Each of the optical amplifiers other than the first-stage optical amplifier among the plurality of optical amplifiers,
(2a) an optical amplification unit that amplifies the signal light at an amplification factor according to the intensity of the supplied excitation light, (2b) an excitation unit that outputs the excitation light and supplies the optical amplification unit, and (2c) the input optical power An input optical monitor section for monitoring the level, (2d) a power level information input section for inputting power level information output from the optical amplifier in the preceding stage, and (2e) power level information input from the power level information input section. Based on the output optical power level and input optical power level of the preceding optical amplifier, the transmission loss in the transmission path from the preceding optical amplifier to the own optical amplifier is determined, and amplification is performed based on the transmission loss. Determine the rate,
And a gain adjusting unit that instructs the pumping unit to supply pumping light having an intensity corresponding to the determined gain.

The multi-stage amplified optical transmission system operates as follows. In the optical amplifiers other than the last-stage optical amplifier among the plurality of optical amplifiers, the power level information indicating the output optical power level monitored by the output optical monitor unit is transmitted to the subsequent optical amplifier by the power level information output unit. Output. On the other hand, in the optical amplifiers other than the first-stage optical amplifier among the plurality of optical amplifiers, the output optical power level of the previous-stage optical amplifier represented by the power level information output from the previous-stage optical amplifier and input to the power-level information input unit, Based on the input optical power level monitored by the optical monitoring unit and the amplification factor adjusting unit, the transmission loss in the transmission path from the optical amplifier at the preceding stage to the optical amplifier at the own stage is determined, and the transmission loss is calculated. The amplification factor is determined based on the amplification factor, and the excitation unit is instructed to supply excitation light having an intensity corresponding to the determined amplification factor. Then, the excitation light output from the excitation unit is
The signal light is supplied to the optical amplifier, and the signal light is
The signal is amplified and output at an amplification factor substantially equal to the determined amplification factor.

Therefore, in each optical amplifier, even if the wave number of the input signal light suddenly changes, the amplification factors of the multi-wavelength signal light are maintained substantially constant. Also, since the amplification factor of the own-stage optical amplifier is determined according to the transmission loss in the transmission path from the previous-stage optical amplifier to the own-stage optical amplifier,
Even if the transmission loss changes, the power level of each signal light output from each optical amplifier is maintained substantially constant.

A multi-stage amplified optical transmission system according to claim 18 is
18. The multi-stage amplified optical transmission system according to claim 17, wherein a first transmission medium mediating transmission of signal light between the optical amplifiers and a second transmission medium mediating transmission of a signal carrying power level information between the optical amplifiers. And a transmission medium. In this case, the signal light output from the optical amplifier is input to the subsequent optical amplifier via the first transmission medium, and the power level information output from the power level information output unit of the optical amplifier is: The signal is input to the power level information input unit of the subsequent optical amplifier via the second transmission medium. Note that the second transmission medium is not limited to optical transmission, but may be electrical transmission.

A multi-stage amplified optical transmission system according to claim 19 is
18. The multi-stage amplified optical transmission system according to claim 17, wherein the signal light has a wavelength in the first wavelength band, and the power level information includes a wavelength in the second wavelength band having no shared wavelength with the first wavelength band. And an optical fiber that carries the power level information light between the optical amplifiers and mediates the transmission of both the signal light and the power level information light between the optical amplifiers. In this case, the power level information light carrying the power level information output from the power level information output unit of the optical amplifier is input to the subsequent optical amplifier via the optical fiber together with the signal light. Here, since the signal light and the power level information light have different wavelengths, they can be separated from each other.

A multi-stage amplified optical transmission system according to claim 20 is
In the multi-stage amplified optical transmission system according to the seventeenth aspect, the amplification factor adjusting unit determines the amplification factor to a value substantially equal to the transmission loss. In this case, if the nonlinear optical effect is sufficiently suppressed for the signal light, the absolute amount of the signal light is ensured, and the signal light transmission is performed.

A multi-stage amplified optical transmission system according to claim 21 is
In the multi-stage amplified optical transmission system according to the seventeenth aspect, the amplification factor adjusting unit determines the amplification factor to a value larger than the transmission loss. In this case, even when the transmission path between the optical amplifiers has nonlinear characteristics, the occurrence of self-phase modulation and the influence of chromatic dispersion due to the nonlinear optical effect of the transmission path are suppressed, and the waveform distortion is reduced. Optical transmission is realized.

The multi-stage amplified optical transmission system according to claim 22 is:
18. The multi-stage amplification optical transmission system according to claim 17, wherein the amplification factor adjusting unit compares the input optical power level with a predetermined threshold, and determines the amplification factor to be 0 when the input optical power level is smaller than the predetermined threshold. It is characterized by doing. In this case, a sudden disconnection in the transmission path in the section before each optical amplifier is immediately detected, and the optical amplification operation is immediately shut down.

A multi-stage amplified optical transmission system according to claim 23 is
18. The multi-stage amplification optical transmission system according to claim 17, wherein the amplification factor adjusting unit has a period longer than a period for updating the intensity of the pumping light instructed to the pumping unit and a period capable of following a fluctuation in transmission loss. The update rate is determined.
In this case, the amplification factor is kept constant, and the output light power level of each signal light is also kept constant.

An optical amplifier according to claim 24 is an optical amplifier used in a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers in sequence. A) an output light monitor for monitoring the output light power level; and (b) a power level information output unit for outputting power level information indicating the output light power level to a subsequent optical amplifier. . This optical amplifier is suitably used as an optical amplifier other than the last-stage optical amplifier in the multiplex amplification optical transmission system according to the seventeenth aspect.

An optical amplifier according to claim 25 is an optical amplifier used in a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers in sequence. ) An optical amplifier for amplifying the signal light at an amplification factor according to the intensity of the supplied pump light, (b) an pump for outputting the pump light and supplying the same to the optical amplifier, and (c) an input optical power level. An input light monitor for monitoring; (d) a power level information input for inputting power level information output from the optical amplifier at the preceding stage; and (e) a previous stage represented by the power level information input by the power level information input. Based on the output optical power level of the optical amplifier and the input optical power level, the transmission loss in the transmission path from the previous-stage optical amplifier to the own-stage optical amplifier is determined, and the amplification factor is determined based on the transmission loss. Decide, A gain adjustment unit for instructing supply of the excitation light intensity corresponding to the determined amplification factor to the excitation portion, characterized in that it comprises a. This optical amplifier is provided in claim 17.
In the multiplex amplification optical transmission system described above, the optical amplifier is suitably used as an optical amplifier other than the first-stage optical amplifier.

[0079]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, terms used in this specification and an outline of the relationship between amplification and generation of noise light in an optical amplifier using an amplification optical fiber will be described. explain.

FIG. 1 shows the state at the time of output from each optical amplifier.
5 is a graph showing a general power spectrum. The output light at the time of output from each optical amplifier is composed of a signal light component and a noise light component, and the noise light component includes light having a signal light wavelength. Therefore, in this specification, the power level of the noise light of the signal light wavelength generated by the ASE is referred to as the noise light component power level, and the power levels of the light of the signal light wavelength other than the noise light are referred to as the signal light component power level and the noise light. The sum of the component power level and the signal light component power level is expressed as an output light power level. Hereinafter, when expressed as noise light, it refers to noise light having substantially the same wavelength as the signal light wavelength.

The power level of light having a wavelength other than the wavelength of the signal light generated by the ASE is substantially the same as the power level of the noise light component in the transmission wavelength range of the wavelength filter normally provided on the receiver side. Therefore, the SN ratio of the propagation light can be evaluated by the ratio between the signal light component power level and the noise light component power level.

FIG. 2 is an explanatory diagram of amplification and generation of noise light in an optical amplifier using an amplification optical fiber. As shown in FIG. 2, the input light input to the optical amplifier includes a signal light component and a noise light component generated up to the previous stage, and the power level _ITI of the input light is equal to the power level I _SI of the input signal light component. Power level I _NI of the input noise light component (= I _TI −I
_SI ).

When the input light is input to the optical amplifier having the amplification factor A, the following equation is obtained: I _SO = A · I _SI I _NO '= A · I _NI I _VO = I _SO + I _NO ' = A · (I _SI + I _NI ) Optical amplification.

With such optical amplification, the optical amplifier is AS
By E, the noise light itself is generated and superimposed on the amplified light. Therefore, assuming that the power level of the generated noise light is I _NO ″, the power level I of the noise light component at the time of output is
_NO becomes I _NO = I _NO ′ + I _NO ″, and the output light power level I _TO becomes I _TO = I _SO + I _NO .

The power level of the noise light generated by the optical amplifier is a function of the power level of the input light and the amplification factor, but can be measured before actual use in the system. Predictable with high accuracy.

Hereinafter, embodiments of a multistage amplified optical transmission system and an optical amplifier according to the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) FIG. 3 is a configuration diagram of a first embodiment of a multistage amplified optical transmission system according to the present invention. FIG.
As shown in FIG. 1, this system is a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter 100 to a receiver 200, and includes optical amplifiers 31 connected in a multi-stage series.
0 _{1 to} 310 _N , a transmission optical fiber 810 ₁ for optically connecting the transmitter 100 and the optical amplifier 310 _1, and a transmission optical fiber 810 ₂ for optically connecting the optical amplifiers 310 _{1 to} 310 _N. 810 _N , and a transmission optical fiber 810 for optically connecting the optical amplifier 310 _N and the receiver 200.
_{N + 1} .

FIG. 4 is a configuration diagram of the optical amplifier 310.
As shown in FIG. 4, the optical amplifier 310 includes (a) an amplification factor of a light having a wavelength of signal light corresponding to the intensity of pumping light, and an amplification factor and a noise light generation power level known as amplification characteristics. Optical fiber 311 and (b) optical fiber 3 for amplification
A pumping unit 312 for supplying pumping light to the input unit 11; (c) an input light monitoring unit 313 for monitoring an input light power level;
(D) an optical amplifier 310 ₁ to 310 _N transmission optical fiber between amplifier characteristics and the optical amplifier 310 ₁ to 310 _N 810 _2-81
An amplification information input unit 314 that stores an output light power level target value set based on the transmission loss at 0 _N ;
(E) The amplification factor is determined based on the output light power level target value stored in the amplification information input unit 314 and the input light power level detected by the input light monitoring unit 313, and according to the determined amplification factor. An amplification factor adjusting unit 315 for adjusting the intensity of the excitation light supplied by the excitation unit 312 is provided. And
(F) Optical isolator 316 arranged at the optical input unit
Further comprising _1, an optical isolator 316 ₂ disposed on the light output portion.

In the multi-stage amplified optical transmission system of this embodiment, the output optical power level of each of the optical amplifiers 310 _{1 to} 310 _N depends on the amplification factor and the amplification factor of the light having the wavelength of the signal light corresponding to the intensity of the pump light. Based on the amplification characteristics of the optical amplifiers 310 _{1 to} 310 _N , namely, the noise light generation power level and the transmission loss in the transmission optical fibers 810 _{1 to} 810 _{N + 1} , the output light power level target value of the optical amplifier is determined. Decide,
The determined output light power level target values are stored in the respective amplification information input sections 314 of the optical amplifiers 310 _{1 to} 310 _N.

As shown in FIG. 3, in the multi-stage amplified optical transmission system of the present embodiment, each of the optical amplifiers 310 _{1 to} 310 _N
Is the output light power level target value of the amplification optical fiber 31.
1 are set such that the power level of the signal light component output from each of the first and second components is substantially constant.

In the multi-stage amplified optical transmission system of the present embodiment, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 310 _{1 to} 310 _N at each stage. In each of the optical amplifiers 310 _{1 to} 310 _N , the input light monitor 313
Detects the power level of the input light, and adjusts the amplification factor
5 determines an amplification factor from the detection result and the output light power level target value stored in the amplification information input unit 314, and adjusts the intensity of the excitation light supplied by the excitation unit 312 so as to obtain the determined amplification factor. I do.

Then, optical amplification is performed at the determined amplification factor, and light having a power level substantially equal to the output light power level target value is output from each of the optical amplifiers 310 _{1 to} 310 _N.

Therefore, the transmission optical fibers 810 ₁ -810 _1-
Regarding the light of the wavelength of the signal light at 810 _{N + 1} , (i) the transmission optical fiber 81 due to excessively increasing the light intensity
Waveform distortion due to the non-linear optical effect of 0 _{1 to} 810 _{N + 1} and (ii) lowering of the SN ratio in the transmission optical fibers 810 _{1 to} 810 _{N + 1} due to excessively low light intensity. Therefore, when designing the system, the optical amplifiers 310 ₁ to 310 _{1 to} 3
10 _N amplification characteristic and transmission optical fiber 810 _{1 to} 81
The amplification factors of the optical amplifiers 310 _{1 to} 310 _N are determined and set in consideration of the transmission loss between the optical amplifiers 310 _{1 to} 310 _N estimated from the type, length, and number of connection points of 0 _{N + 1.} By doing so, (i) the transmission optical fibers 810 _{1 to} 810 _{N + 1}
While suppressing the occurrence of waveform distortion due to the nonlinear optical effect of
(Ii) The signal light is transmitted between the transmitter 100 and the receiver 200 while maintaining the SN ratio of the entire system.

In the multi-stage amplifying optical transmission system of the present embodiment, the power level of the signal light component output from each of the amplifying optical fibers 311 is made substantially constant, so that the nonlinear optical effect can be suppressed for the light having the wavelength of the signal light. If it is sufficient, the signal light transmission is performed while securing the absolute amount of the signal light component.

FIG. 5 is a configuration diagram of an optical amplifier 320 which is a modification of the optical amplifier 310. As shown in FIG. 5, in addition to the configuration of the optical amplifier 310, the optical amplifier 320 includes (g)
An output light monitor 321 for monitoring the power level of the output light from the amplification optical fiber 311;
15 based on the amplification factor determined in step 15 and the power level of the output light detected by the output light monitor 321.
Excitation light fine adjustment unit 3 for finely adjusting the intensity of the excitation light supplied by 2
22.

In the optical amplifier 320, in addition to the adjustment of the output light power level by the feedforward control in the optical amplifier 310, the power level of the output light is monitored. Based on the monitoring result, the output light power level is finely adjusted by the feedback control. Is performed, the output light power level can be adjusted more accurately.

The transmission optical fibers 810 _{1 to} 810
To obtain the transmission loss value at _{N + 1,} it is also possible to actually measure the value at the time of installation of the system. In this case, the output optical power levels to be output from the optical amplifiers 310 _{1 to} 310 _N are determined at the time of installation of the system, and are set thereafter.

(Second Embodiment) FIG. 6 is a block diagram of a multistage amplified optical transmission system according to a second embodiment of the present invention. FIG.
As shown in the figure, in this system, the output light power level target value stored in the amplification information input unit 314 of each of the optical amplifiers 310 _{1 to} 310 _N is different from that of the first embodiment. The difference is that the power level of the signal light component output from each is set so as to increase as it goes to the subsequent stage.

In the multi-stage amplifying optical transmission system of the present embodiment, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 310 _{1 to} 310 _N of the respective stages, as in the first embodiment. In each of the optical amplifiers 310 _{1 to} 310 _N ,
The input light monitoring unit 313 detects the power level of the input light, and the amplification factor adjustment unit 315 determines the amplification factor from the detection result and the output light power level target value stored in the amplification information input unit 314, Excitation unit 3 to obtain the determined amplification factor
The intensity of the excitation light supplied by 12 is adjusted.

Then, optical amplification is performed at the determined amplification factor, and light having a power level substantially equal to the output light power level target value is output from the optical amplifiers 310 _{1 to} 310 _N in each stage. The power level of the signal light component included in the output light output from the optical amplifiers 310 _{1 to} 310 _N increases as the level increases.

The transmission optical fibers 810 _{1 to} 810 _{N + 1} have a small but nonlinear characteristic, and the larger the light intensity density of the propagation light or the longer the propagation distance, the larger the nonlinear optical phenomenon occurs. The optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fibers 810 _{1 to} 810 _{N + 1} have chromatic dispersion, waveform distortion occurs according to the propagation distance. Therefore, in the optical amplification of the multi-stage amplification optical transmission system, the larger the power level of the light having the wavelength of the signal light output from the optical amplifier, or the longer the propagation distance afterward, that is, the signal of the optical amplifier 310 at the preceding stage The greater the output power level of the light of the light wavelength, the greater the waveform distortion.

In the multi-stage amplified optical transmission system of the present embodiment, the power level of the signal light component to be output is reduced in the optical amplifier 310 on the transmitter 100 side, and the signal light component output from the optical amplifier 310 is reduced in the subsequent stage. Since the power level is increased, the transmission optical fibers 810 ₁ -81 ₁
The occurrence of self-phase modulation due to the nonlinear optical effect at 0 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, the multi-stage amplified optical transmission system of the present embodiment is different from the first embodiment in that the waveform distortion accompanying the self-phase modulation due to the nonlinear optical effect is reduced. It is advantageous.

Incidentally, similarly to the first embodiment, the optical amplifier 3
Instead of 10, an optical amplifier 320 shown in FIG. 5 can be used.

Further, similarly to the first embodiment, in obtaining the transmission loss value in the transmission optical fibers 810 _{1 to} 810 _{N + 1,} it is possible to actually measure the transmission loss value when the system is installed. In this case, the output optical power levels to be output from the optical amplifiers 310 _{1 to} 310 _N are determined at the time of installation of the system, and are set thereafter.

(Third Embodiment) In the present embodiment, the output light power level target value of each of the optical amplifiers 330 _{1 to} 330 _N is instructed by the separately provided amplification management unit 400 as compared with the first embodiment. Is different.

FIG. 7 is a block diagram of a third embodiment of the multistage amplified optical transmission system of the present invention. As shown in FIG. 7, this system is a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter 100 to a receiver 200, and (a) optical amplifiers 330 ₁ to 330 ₁ connected in series. 3
_30N , (b) a transmission optical fiber 810 ₁ for optically connecting the transmitter 100 and the optical amplifier 330 _1, and the optical amplifier 3
30 _1-330 transmission optical fiber 810 ₂ ～810 _N that between _N optically connecting, and optical amplifiers 330 _N and a receiver 2
Transmission optical fiber 810 _{N + 1} for optically connecting 00 and 00
If, collects information corresponding to the time, the optical amplifier 330 ₁ to 330 _N amplification factor running from each of instructing initial output optical power level target value to each of (c) an optical amplifier 330 ₁ to 330 _N , based on the optical amplifier 330 ₁ to 330 _N amplification factor in each of the operation of, for each of the optical amplifiers 330 ₁ to 330 _N to calculate a new output optical power level target value, the calculated output light power level target The value of the optical amplifier 330 ₁
To 330 _N , respectively.

FIG. 8 is a configuration diagram of the optical amplifier 330.
As shown in FIG. 8, the optical amplifier 330 includes (a) an amplification factor having a known amplification factor of a signal light having a wavelength corresponding to the intensity of pumping light, and a known amplification factor and noise light generation power level. Optical fiber 331 and (b) optical fiber for amplification 3
A pumping unit 332 for supplying pumping light to 31; (c) an input light monitoring unit 333 for monitoring an input light power level;
(D) an optical amplifier 330 ₁ to 330 _N transmission optical fiber between amplifier characteristics and the optical amplifier 330 ₁ to 330 _N 810 _2-81
An information input unit 334 for inputting and storing a target output light power level set based on the transmission loss at 0 _N.
And (e) determining an amplification factor based on the output light power level target value stored in the amplification information input unit 334 and the input light power level detected by the input light monitoring unit 333, and determining the amplification factor. An amplification factor adjustment unit 335 that adjusts the intensity of the excitation light supplied by the excitation unit 332 in response thereto, and (f) an information output unit 336 that outputs amplification factor information regarding the amplification factor determined by the amplification factor adjustment unit 335. (G) An optical isolator 337 ₁ disposed in the optical input unit and an optical isolator 337 ₂ disposed in the optical output unit are further provided.

As shown in FIG. 7, in the multi-stage amplified optical transmission system of the present embodiment, each of the optical amplifiers 330 _{1 to} 330 _N
The output light power level target value of the
1 are set such that the power level of the signal light component output from each of the first and second components is substantially constant.

In the multi-stage amplified optical transmission system of the present embodiment, the amplification management section 400
As the output optical power level of each of the optical amplifiers 330 ₁ to 330 _N, the amplification factor of the light of the wavelength of the signal light corresponding to the excitation light intensity, and the amplification factor and the noise light generated power level of the optical amplifier 330 ₁ Determining output optical power level target values of the optical amplifiers 330 _{1 to} 330 _N based on the respective amplification characteristics of the 330 _N and the estimated transmission loss in the transmission optical fibers 810 _{1 to} 810 _{N + 1} , and , The determined output light power level target values L _{1 to} L _N are converted to optical amplifiers 330 ₁ to 330 3.
Instruct 30 _N.

Each of the information input sections 334 of the optical amplifiers 330 _{1 to} 330 _N inputs and stores the specified output light power level target value.

Thereafter, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 330 _{1 to} 330 _N at each stage. That is, in each of the optical amplifiers 330 _{1 to} 330 _N , the input light monitoring unit 333 detects the power level of the input light, and the amplification factor adjusting unit 335 outputs the detection result and the output stored in the information input unit 334. An amplification factor is determined from the target optical power level, and the excitation unit 3 is set to obtain the determined amplification factor.
32 adjusts the intensity of the excitation light supplied.

Then, optical amplification is performed at the determined amplification factor, and light having a power level substantially equal to the output light power level target value is output from each of the optical amplifiers 330 _{1 to} 330 _N.

In parallel with the above-described optical amplification operation, the optical amplifier 3
Each of the 30 ₁ to 330 _N outputs the determined amplification factor A ₁ to A _N from the information output unit 336 to the amplifier manager 400.

The amplification management section 400 determines the optical amplifiers based on the amplification factors of the optical amplifiers 330 _{1 to} 330 _N that have received the report and the output light power level target values of the optical amplifiers 330 _{1 to} 330 _N specified by the amplification management section 400. The power level of the signal light component at the time of output of 330 _{1 to} 330 _N is obtained. The power level diagram of the power level of the signal light component thus obtained is compared with the power level diagram of the power level of the signal light component to be realized, and if there is a difference, the power level of the signal light component to be realized is determined. A new output light power level target value of the optical amplifiers 330 _{1 to} 330 _N to be a power level diagram is calculated. Then, the calculated output light power level target values L _{1 to} L _N are converted into the optical amplifiers 330 ₁ to
Instruct 330 _N.

The optical amplifiers 330 ₁ to 330 3 receiving new instructions
30 _N, the input light power level monitors, in order to newly designated output optical power level target value L ₁ ~L _N, the excitation unit 332 gain adjusting unit 33 the intensity of the excitation light supplied by
5 adjust.

[0116] Thereafter, a report of the amplification factor A ₁ to A _N by the optical amplifier 330 ₁ to 330 _N, the output optical power level target value L ₁ ~ amplifying manager 400 by the optical amplifier 330 ₁ to 330 _N
Feedback control is performed to calculate L _N and to instruct the calculated output optical power level target value to the optical amplifiers 330 ₁ to 330 _N to execute a suitable multi-stage amplified optical transmission.

In the multi-stage amplified optical transmission system of the present embodiment, the transmission optical fiber 810 ₁ as a relay transmission line assumed in the multi-stage amplified optical transmission system of the first embodiment.
810 _{N + 1} Performs suitable multi-stage amplification optical transmission even if the transmission loss over time changes due to environmental conditions, etc. can do.

In the multi-stage amplified optical transmission system of the present embodiment, the power level of the signal light component output from each of the amplifying optical fibers 331 is made substantially constant, so that the nonlinear optical effect can be suppressed for the light having the wavelength of the signal light. If it is sufficient, the signal light transmission is performed while securing the absolute amount of the signal light component.

FIG. 9 is a configuration diagram of an optical amplifier 340 which is a modification of the optical amplifier 330. As shown in FIG. 9, the optical amplifier 340 includes (g)
An output light monitor 341 for monitoring the power level of the output light from the amplification optical fiber 331; and (h) an amplification factor adjuster 3.
Based on the amplification factor determined at 35 and the power level of the output light detected by the output light monitoring unit 351, the excitation unit 34
Excitation light fine adjustment unit 3 for finely adjusting the intensity of the excitation light supplied by 2
52.

The optical amplifier 340 monitors the power level of the output light in addition to the adjustment of the output light power level by the feed forward control in the optical amplifier 330, and based on the monitoring result, finely adjusts the output light power level by feedback control. Is performed, the output light power level can be adjusted more accurately.

(Fourth Embodiment) FIG. 10 is a configuration diagram of a multistage amplified optical transmission system according to a fourth embodiment of the present invention. As shown in FIG. 10, this system is different from the third embodiment in that the amplification management unit 400 instructs each optical amplifier 330
_The output light power level target values L _{1 to} L _N stored in the information input units 334 of _{1 to} 330 _N are set to increase as the power levels of the signal light components output from the respective amplification optical fibers 331 become later. Is different.

In the multi-stage amplified optical transmission system according to the present embodiment, similarly to the third embodiment, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 330 _{1 to} 330 _N at each stage. . In each of the optical amplifiers 310 _{1 to} 310 _N , the input light monitoring unit 313 detects the power level of the input light, and the amplification factor adjustment unit 335 receives the detection result and the information input unit 334 instructed by the amplification management unit 400. The amplification factor is determined from the output light power level target value stored in the... And the intensity of the excitation light supplied by the excitation unit 332 is adjusted so as to make the determined amplification factor.

Then, optical amplification is performed at the determined amplification factor, and light having a power level substantially equal to the output light power level target value is output from each of the optical amplifiers 330 _{1 to} 330 _N. power level of the signal light component contained in the output light output from the optical amplifier 330 ₁ to 330 _N of the extent to be later stage, increases.

The transmission optical fibers 810 _{1 to} 810 _{N + 1} have a small but nonlinear characteristic, and a larger nonlinear optical phenomenon occurs as the light intensity density of the propagating light increases or as the propagation distance increases. The optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fibers 810 _{1 to} 810 _{N + 1} have chromatic dispersion, when the optical frequency is modulated by self-phase modulation, waveform distortion occurs according to the propagation distance. Therefore, in optical amplification of a multi-stage amplified optical transmission system,
The higher the power level of the light of the wavelength of the signal light output from the optical amplifier, or the longer the subsequent propagation distance, that is,
The higher the output power level of the light having the wavelength of the signal light of the optical amplifier 330 on the preceding stage, the greater the waveform distortion.

In the multistage amplifying optical transmission system of the present embodiment, the power level of the signal light component to be output is reduced in the optical amplifier 330 on the transmitter 100 side, and the signal light component output from the optical amplifier 330 is reduced in the subsequent stage. Since the power level is increased, the transmission optical fibers 810 ₁ -81 ₁
The occurrence of self-phase modulation due to the nonlinear optical effect at 0 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, the multi-stage amplified optical transmission system of the present embodiment is different from the third embodiment in that the waveform distortion accompanying the self-phase modulation due to the nonlinear optical effect is reduced. It is advantageous.

As in the third embodiment, the optical amplifier 3
Instead of 30, an optical amplifier 340 shown in FIG. 9 can be used.

(Fifth Embodiment) FIG. 11 is a block diagram of a multistage amplified optical transmission system according to a fifth embodiment of the present invention. In this system, the signal light has multiple wavelength components, and each optical amplifier performs multi-wavelength batch amplification. This system is
Compared with the embodiment, (i) each of the optical amplifiers 330 _{1 to} 33 ₁
The 0 _N amplification optical fiber 331 has, as amplification characteristics, an amplification factor of light having a wavelength of signal light corresponding to the intensity of pump light, and
In addition to the amplification factor and the noise light generated power level, that the amplification factor dependency of the wavelength dependency of the gain is known, (ii) amplifying the management unit 400 instructs each of the optical amplifiers 330 ₁ to 330 _N
Is that the target value of the output light power level stored in the information input unit 334 is a value that reduces the difference in gain as a system relating to the light of each wavelength component of the signal light in the output light of the final stage optical amplifier. different.

According to the knowledge of the inventor, in an amplification optical fiber doped with a rare earth element, in the 1.55 μm band generally used as the wavelength band of signal light, when the amplification factor is small, the longer the wavelength, the longer the wavelength. , The amplification rate tends to be high.
On the other hand, when the amplification factor is large, the shorter the wavelength is, the higher the amplification factor tends to be.

FIG. 12 is an explanatory diagram of the dependence of the amplification factor on the wavelength. FIG. 12A shows a case where the amplification factor is small, and FIG. 12B shows a case where the amplification factor is large. Then, an amplification factor value indicating the characteristic of FIG.
There is an amplification factor having a flat amplification factor dependence of the wavelength dependence of the amplification factor with the amplification factor value showing the characteristic of (b).

In the multi-stage amplifying optical transmission system of the present embodiment, the amplification management section 400
Are the output light power levels of the optical amplifiers 330 _{1 to} 330 _N as the light amplification factor of the signal light wavelength according to the pump light intensity, the amplification factor and the noise light generation power level, and the wavelength dependence of the amplification factor. Amplifier 330 ₁ that depends on the amplification factor
To 330 _N and amplification characteristics of the respective, based on the transmission loss in the transmission optical fiber 810 ₁ ~810 _{N + 1} to be estimated, determining the output optical power level target value of the optical amplifier 330 ₁ to 330 _N, Then, to indicate the determined output light power level target value L ₁ ~L _N to the optical amplifier 330 ₁ to 330 _N.

Each of the information input sections 334 of the optical amplifiers 330 _{1 to} 330 _N inputs and stores the specified output light power level target value.

Thereafter, the signal light output from the transmitter 100 is sequentially amplified through the optical amplifiers 330 _{1 to} 330 _N at each stage. That is, in each of the optical amplifiers 330 _{1 to} 330 _N , the input light monitoring unit 333 detects the power level of the input light, and the amplification factor adjusting unit 335 outputs the detection result and the output stored in the information input unit 334. An amplification factor is determined from the target optical power level, and the excitation unit 3 is set to obtain the determined amplification factor.
32 adjusts the intensity of the excitation light supplied.

Then, optical amplification is performed at the determined amplification factor, and light having a power level substantially equal to the output light power level target value is output from each of the optical amplifiers 330 _{1 to} 330 _N.

In parallel with the above-described optical amplification operation, the optical amplifier 3
Each of the 30 ₁ to 330 _N outputs the determined amplification factor A ₁ to A _N from the information output unit 336 to the amplifying management unit 400.

The amplification management unit 400 determines the nonlinear optics from the amplification factors of the optical amplifiers 330 _{1 to} 330 _N that have received the report and the output light power level target values of the optical amplifiers 330 _{1 to} 330 _N specified by the amplification management unit 400. The gain of each of the optical amplifiers 330 _{1 to} 330 _N reduces the difference in gain as a system for the light of each wavelength component of the signal light, while suppressing the waveform distortion of the signal light component due to the effect and securing the SN ratio. Is calculated, and a new output light power level target value corresponding to the obtained amplification factor is calculated. Then, the calculated output light power level target values L _{1 to} L _N are instructed to the optical amplifiers 330 _{1 to} 330 _N.

According to the inventor's knowledge, in the amplification optical fiber doped with a rare earth element, in the 1.55 μm band generally used as the wavelength band of signal light, when the amplification factor is small, the longer the wavelength becomes, the longer the wavelength becomes. , The amplification rate tends to be high.
On the other hand, when the amplification factor is large, the shorter the wavelength is, the higher the amplification factor tends to be. By adjusting the amplification factors of the optical amplifiers 330 _{1 to} 330 _N at each stage based on this property, it is possible to reduce the gain gradient as a system relating to the signal light multi-wavelength collectively amplified.

Optical amplifiers 330 ₁ to 330 3 receiving new instructions
30 _N monitors the input light power level, and adjusts the intensity of the pump light supplied by the pump unit 332 to the amplification factor adjusting unit 335 so as to output light having a power level equal to the newly designated output light power level target value. Adjust.

Thereafter, reports of the amplification factors by the optical amplifiers 330 _{1 to} 330 _N and the amplification of the
Calculation of the output light power level target value of _{1 to} 330 _N , and the optical amplifier 330 ₁ to
A suitable multi-stage amplified optical transmission is performed by performing feedback control of instructing 330 _N.

In the multistage amplifying optical transmission system of the present embodiment, the gain of the optical amplifiers 330 _{1 to} 330 _N is reduced to reduce the gain difference as a system relating to the light of each wavelength component of the signal light. From the viewpoint of the ratio, the optical amplifier 33
Even when the amplification factor at 0 _{1 to} 330 _N has to have wavelength dependence, the amplification management unit 400
By appropriately designating the amplification factor of _{1 to} 330 _N , the wavelength dependence of the gain of the entire system can be flattened.

As in the third embodiment, the optical amplifier 3
Instead of 30, an optical amplifier 340 shown in FIG. 9 can be used.

(Sixth Embodiment) This embodiment is different from the first to fifth embodiments in that transmission optical fibers 810 _{1 to} 810 _{N + 1} used for signal light transmission are provided separately from transmission optical fibers 810 _{1 to} 810 _{N + 1.} In that power level information is transmitted by optical fibers for use 820 _{1 to} 820 _N−1 .

FIG. 13 is a block diagram of a sixth embodiment of the multistage amplified optical transmission system of the present invention. As shown in FIG. 13, this system is a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter 100 to a receiver 200, and (a) an optical amplifier 350 ₁ connected in a multi-stage series.
And to 350 _N, when the transmission of (b) signal light, to connect the transmitter 100 and the optical amplifier 350 ₁ and the transmission optical fiber 810 ₁ for optically connecting, between optical amplifiers 350 ₁ to 350 _N optically A transmission optical fiber 810 _{2 to} 810 _N , a transmission optical fiber 810 _{N + 1} for optically connecting the optical amplifier 350 _N and the receiver 200, and (c) an optical amplifier 350 ₁ for transmitting power level information. Optical fibers 820 _{1 to} 820 for optically connecting between 350 _N to 350 _N
N-1 .

FIG. 14 is a configuration diagram of the optical amplifier 350. As shown in FIG. 14, the optical amplifier 350 includes (a) an amplification factor for a light having a wavelength of signal light corresponding to the intensity of pumping light, and an amplification factor and a noise light generation power level known as amplification characteristics. An optical fiber 351, (b) an excitation unit 352 for supplying excitation light to the amplification optical fiber 351, and (c) an input light monitor unit 353 for monitoring an input light power level.
And (d) an amplification information input unit 354 for receiving input power level information on the power level of the signal light and the power level of the noise light at the time of output from the optical amplifier 350 in the preceding stage.
And (e) determining the amplification factor based on the specified output signal light power level target value, the power level of the input light detected by the input light monitoring unit 353, and the input power level information, and determining the determined amplification. (F) the power level and noise of the signal light at the time of output based on the input power level information and the determined amplification factor, and (f) the amplification factor adjusting unit 355 instructing the pumping unit 352 to supply the pumping light according to the amplification factor. An amplification information output unit 356 that generates and outputs output power level information related to the power level of light. (G) An optical isolator 357 ₁ arranged in the light input unit and an optical isolator 357 ₂ arranged in the light output unit are further provided.

The amplification information input section 354 includes an input selection means 358 for selectively selecting one of the power level information output from the optical amplifier 350 at the preceding stage and the preset information D as input power level information. Prepare.

The amplification information output section 356 includes output selection means 359 for selecting whether to output output power level information.

[0146] In the first stage of the optical amplifier 350 _1, in (i) amplifying the information input unit 354, selected by the input selection unit 358, as the information D input power level information and the noise light component without the information that has been set in advance (Ii) In the amplification information output section 356, the output selection means 359 selects whether to output the output power level information.

In the middle stage optical amplifiers 350 _{2 to} 350 _N−1 ,
(I) In the amplification information input unit 354, the input selection unit 3
58, the power level information output from the optical amplifier 350 at the preceding stage is selected as the input power level information. (Ii) In the amplification information output unit 356, the presence or absence of output of the output power level information is selected by the output selection means 359. Is done.

In the last-stage optical amplifier 350 _N , (i) in the amplification information input section 354, the power level information output from the previous-stage optical amplifier 350 is selected by the input selection means 358 as input power level information. ii) In the amplification information output section 356, the output selection means 359 selects whether to output no output power level information.

As shown in FIG. 13, in the multi-stage amplified optical transmission system of this embodiment, each of the optical amplifiers 350 _{1 to} 350 _{1 to} 35
The power level of the signal light component output by O _N is substantially constant. The power level information is stored in the optical amplifier 3 in the preceding stage.
The value of the ratio between the power level of the signal light component and the power level of the noise light component at the time of output 50 is adopted. In addition,
As the power level information, the power level value of the signal light component and the power level value of the noise light component at the output time of the optical amplifier 350 at the preceding stage may be adopted, or the signal level at the output time of the optical amplifier 350 at the preceding stage may be adopted. The power level value of the light component and the power level value of the output light may be adopted.

In the multi-stage amplified optical transmission system of this embodiment, the signal light output from the transmitter 100 is
0 is input to the _1. Optical amplifier 350 ₁ which is the first stage optical amplifier
In the case of (1), since no noise light is generated in the optical amplifier at the preceding stage, substantially only the signal light component is input. Optical amplifier 35
0 In _1, the input light monitor the power level of the input light 353
The amplification factor adjustment unit 355 determines the amplification factor from the detection result and the output signal light power level target value, and adjusts the intensity of the excitation light supplied by the excitation unit 352 so as to obtain the determined amplification factor. I do.

[0151] Then, the light amplification is performed at the determined amplification factor, the optical amplifier 350 _1, the light having substantially the same power level in the output signal light power level target value is output as amplified light.

With such an optical amplification operation, the optical amplifier 3
Reference numeral ₅₀₁ denotes a power level of noise light generated due to the optical amplification of the determined amplification factor, calculates a ratio between the power level of the signal light component and the power level of the noise light component at the time of output, and obtains amplification information. From the output unit 356 to the next stage optical amplifier 3
To be output toward 50 _2.

Each of the optical amplifiers 350 _{2 to} 350 _N receives the light to be amplified output from the preceding optical amplifier, and the amplification information input unit 354 receives the power level information output from the preceding optical amplifier 350. I do. Optical amplifier 35
O _{2 to} 350 _N input the amplification target light, and the input light monitor 353 detects the power level. From this detection result and the input power level information, the power level of the signal light component at the time of input is obtained. Then, the amplification factor adjusting unit 355 determines the amplification factor from the power level of the signal light component at the time of input and the target value of the output signal light power level, and the excitation unit 352 supplies the excitation value to obtain the determined amplification factor. Adjust the light intensity.

Then, optical amplification is performed at the determined amplification factor, and light including signal light having a power level substantially equal to the output signal light power level target value is output from the optical amplifiers 350 _{2 to} 350 _N as amplification target light. Is done.

In addition to such an optical amplification operation, the optical amplifier 3
50 _{2 to} 350 _N−1 are used to determine the power level of the noise light generated due to the optical amplification of the determined amplification factor, and calculate the ratio between the power level of the signal light component and the power level of the noise light component at the output time. The calculated value is output from the amplification information output unit 356 to the optical amplifier 350 at the next stage.

Thus, the signal light output from the transmitter 100 is amplified sequentially through the optical amplifiers 350 _{1 to} 350 _N at each stage.

In the multi-stage amplified optical transmission system according to the present embodiment, the transmission optical fibers 810 ₁ to 810 ₁ as relay transmission lines assumed in the multi-stage amplified optical transmission system according to the first embodiment.
810 _{N +1 It} is not assumed that the transmission loss is substantially constant with respect to the passage of time, and even if the transmission loss of the relay transmission line changes over time due to environmental conditions or the like, suitable multistage amplified optical transmission is executed. be able to.

In the multistage amplifying optical transmission system of the present embodiment, the power level of the signal light component output from each of the amplifying optical fibers 351 is substantially constant, so that the nonlinear optical effect can be suppressed for the light of the wavelength of the signal light. If it is sufficient, the signal light transmission is performed while securing the absolute amount of the signal light component.

FIG. 15 is a configuration diagram of an optical amplifier 360 which is a modification of the optical amplifier 350. As shown in FIG.
The optical amplifier 360 includes, in addition to the configuration of the optical amplifier 350,
(H) an output light monitor 361 for monitoring the power level of the output light from the amplification optical fiber 351; and (i) an amplification factor determined by the gain adjuster 355 and the output light monitor 361.
And an excitation light fine-adjustment unit 362 for finely adjusting the intensity of the excitation light supplied by the excitation unit 352 based on the power level of the output light detected in step (a).

The optical amplifier 360 monitors the power level of the output light in addition to the adjustment of the output light power level by the feed forward control in the optical amplifier 350, and based on the monitoring result, finely adjusts the output light power level by feedback control. Is performed, the output light power level can be adjusted more accurately.

(Seventh Embodiment) FIG. 16 is a block diagram of a multistage amplified optical transmission system according to a seventh embodiment of the present invention. As shown in FIG. 16, this system is different from the sixth embodiment in that the power level of the signal light component output from each of the optical amplifiers 350 _{1 to} 350 _N increases as the level increases.

In the multistage amplifying optical transmission system of the present embodiment, similarly to the sixth embodiment, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 350 _{1 to} 350 _N of each stage. . In the optical amplifier 350 _1, the input light monitor unit 353 detects the power level of the input light, the amplification factor adjustment section 355 determines the amplification factor from the detection result and the output signal light power level target value is determined The intensity of the pumping light supplied by the pumping unit 352 is adjusted so that the amplification factor becomes higher. In the optical amplifiers 350 _{2 to} 350 _N , the input light monitor unit 3
13 detects the power level of the input light, and the amplification factor adjusting unit 355 calculates the amplification factor from the detection result, the input power level information input at the amplification information input unit 354, and the output signal light power level target value. The intensity of the excitation light supplied by the excitation unit 352 is adjusted so as to determine the determined amplification factor.

Then, optical amplification is performed at the determined amplification factor, and light including signal light having a power level substantially equal to the target value of the output signal light power level is output from the optical amplifiers 350 _{1 to} 350 _{N at} each stage. However, the optical amplifiers 350 ₁ to 350
Power level of the output signal light component output from the 50 _N is enough to be a later stage, increases.

The transmission optical fibers 810 _{1 to} 810 _{N + 1} have slight but non-linear characteristics, and the larger the light intensity density of the propagation light or the longer the propagation distance, the larger the nonlinear optical phenomenon occurs. The optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fibers 810 _{1 to} 810 _{N + 1} have chromatic dispersion, waveform distortion occurs according to the propagation distance. Therefore, in the optical amplification of the multi-stage amplification optical transmission system, the larger the power level of the light of the wavelength of the signal light output from the optical amplifier 350 or the longer the subsequent propagation distance, that is, The greater the output power level of the light of the wavelength of the signal light, the greater the waveform distortion.

In the multi-stage amplified optical transmission system of the present embodiment, the power level of the signal light component to be output is reduced as the optical amplifier 350 on the transmitter 100 side, and the signal light component output from the optical amplifier 350 is reduced in the later stage. Since the power level is increased, the transmission optical fibers 810 ₁ -81 ₁
The occurrence of self-phase modulation due to the nonlinear optical effect at 0 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, the multi-stage amplified optical transmission system of the present embodiment is different from the sixth embodiment in that the waveform distortion due to the self-phase modulation due to the nonlinear optical effect is reduced. It is advantageous.

As in the sixth embodiment, the optical amplifier 3
An optical amplifier 360 shown in FIG. 15 can be used instead of 50.

(Eighth Embodiment) FIG. 17 is a block diagram of an eighth embodiment of the multistage amplified optical transmission system of the present invention. As shown in FIG. 17, this system is a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter 100 to a receiver 200, and (a) optical amplifiers 370 ₁ to 370 _1- connected in multi-stage series. 370 _N and (b) a transmission optical fiber 810 ₁ for optically connecting the transmitter 200 and the optical amplifier 370 _{1 in} transmitting the signal light, and the optical amplifiers 370 _{1 to} 370-3.
Transmission optical fiber 810 ₂ to optically connect between 70 _N
810 _N , and a transmission optical fiber 810 _{N + 1} for optically connecting the optical amplifier 370 _N and the receiver 200. In transmitting the power level information, transmission optical fibers 810 _{2 to} 810 _N are used.

FIG. 18 is a configuration diagram of the optical amplifier 370. As shown in FIG. 18, the optical amplifier 370 includes (a) an amplification characteristic of an amplification factor of a light having a wavelength of signal light corresponding to the intensity of pumping light, and an amplification factor and a noise light generation power level known as amplification characteristics. An optical fiber 371, (b) an excitation unit 372 for supplying excitation light to the amplification optical fiber 371, and (c) an input light monitoring unit 373 for monitoring an input light power level.
And (d) an amplification information input unit 374 for receiving input power level information on the power level of the signal light and the power level of the noise light at the time of output from the optical amplifier 370 in the preceding stage.
And (e) determining the amplification factor based on the specified output signal light power level target value, the power level of the input light detected by the input light monitor unit 373, and the input power level information, and determining the determined amplification. (F) the power level and noise of the signal light at the time of output based on the input power level information and the determined amplification factor, and (f) the amplification factor adjusting unit 375 instructing the pumping unit 372 to supply the pump light according to the amplification factor. An amplification information output section 376 for generating and outputting output power level information related to the power level of light; and (g) an optical demultiplexer for splitting input power level information of the input light sent from the preceding optical amplifier. 383, and (h) an optical multiplexer 384 for multiplexing the light output from the amplification optical fiber 371 and the output power level information. Further, (i) an optical isolator 377 ₁ arranged in the light input unit and an optical isolator 377 ₂ arranged in the light output unit are further provided.

The amplification information input section 374 includes an input selection means 378 for selectively selecting one of the power level information output from the optical amplifier 370 in the preceding stage and the preset information D as input power level information. Prepare.

The amplification information output section 376 includes output selection means 379 for selecting whether to output output power level information.

In the first-stage optical amplifier 370 ₁ , (i) in the amplification information input section 374, information D indicating that there is no noise light component, which is preset information, is selected as input power level information by the input selection means 378. (Ii) In the amplification information output unit 376, the output selection means 379 selects whether to output the output power level information.

In the middle stage optical amplifiers 370 _{2 to} 370 _N−1 ,
(I) In the amplification information input section 374, the input selection means 3
At 78, the power level information output from the optical amplifier 370 at the preceding stage is selected as input power level information. (Ii) In the amplification information output unit 376, the presence or absence of output of the output power level information is selected by the output selection means 379. Is done.

In the last-stage optical amplifier 370 _N , (i) in the amplification information input section 374, the power level information output from the previous-stage optical amplifier 370 is selected by the input selection means 378 as input power level information. ii) In the amplification information output section 376, the output selection means 379 selects whether to output no output power level information.

As shown in FIG. 17, in the multi-stage amplifying optical transmission system of the present embodiment, each of the optical amplifiers 370 _{1 to} 370 is connected.
The power level of the signal light component output by O _N is substantially constant. The power level information is stored in the optical amplifier 3 in the preceding stage.
The value of the ratio between the power level of the signal light component and the power level of the noise light component at the output point 70 is adopted. In addition,
As the power level information, the power level value of the signal light component and the power level value of the noise light component at the output time point of the preceding optical amplifier 370 may be adopted, or the signal level at the output time point of the preceding optical amplifier 370 may be adopted. The power level value of the light component and the power level value of the output light may be adopted.

The wavelength of the signal light is 1.55 μm.
Using the m band, the wavelength of the power level information transmission,
The 1.3 μm band is used.

In the multi-stage amplified optical transmission system of the present embodiment, the signal light output from the transmitter 100 is
Enter in 70 ₁ . Optical amplifier 37 as the first stage optical amplifier
If 0 _1, the generation of the noise light is not in the previous amplifier, substantially only the signal light component is input. In the optical amplifier 370 ₁ , the input light monitor 373 detects the power level of the input light, and the amplification factor adjustment unit 375 determines the amplification factor from the detection result and the output signal light power level target value, and the determined amplification factor is determined. The intensity of the excitation light supplied by the excitation unit 372 is adjusted so as to obtain an amplification factor.

[0177] Then, the light amplification is performed at the determined amplification factor, the optical amplifier 370 _1, the light including substantially equal power levels of the signal light to the output signal light power level target value is output as amplified light.

With such an optical amplification operation, the optical amplifier 3
70 ₁ is determined the power level of the noise light generated due to the light amplification of the determined amplification factor, to calculate the ratio between the power level and the noise light component power level of the signal light component at the output time point, the amplification information From the output unit 376 to the next-stage optical amplifier 3
70 toward the ₂ output.

Each of the optical amplifiers 370 _{2 to} 370 _N receives the light to be amplified output from the preceding optical amplifier, and the amplification information input unit 374 receives the power level information output from the preceding optical amplifier 370. input. Optical amplifier 3
70 _{2 to} 370 _N input the light to be amplified, and the input light monitor 373 detects the input light power level. From this detection result and the input power level information, the power level of the signal light component at the time of input is obtained. Then, the amplification factor adjusting unit 375 determines the amplification factor from the power level of the signal light component at the time of input and the target value of the output signal light power level, and the excitation supplied by the excitation unit 372 to obtain the determined amplification factor. Adjust the light intensity.

Then, optical amplification is performed at the determined amplification factor, and light including signal light having a power level substantially equal to the output signal light power level target value is output from the optical amplifiers 370 _{2 to} 370 _N as light to be amplified. Is done.

With such an optical amplification operation, the optical amplifier 3
70 _{2 to} 370 _N -1 find the power level of the noise light generated due to the optical amplification of the determined amplification factor, and calculate the ratio between the power level of the signal light component and the power level of the noise light component at the time of output. The calculated value is output from the amplification information output unit 356 to the optical amplifier 370 at the next stage.

Thus, the signal light output from the transmitter 100 is amplified sequentially through the optical amplifiers 370 _{1 to} 370 _N at each stage.

In the multi-stage amplifying optical transmission system of the present embodiment, the transmission optical fibers 810 ₁ to 810 ₁ as relay transmission paths assumed in the multi-stage amplifying optical transmission system of the first embodiment.
810 _{N +1 It} is not assumed that the transmission loss is substantially constant with respect to the passage of time, and even if the transmission loss of the relay transmission line changes over time due to environmental conditions or the like, suitable multistage amplified optical transmission is executed. be able to.

In the multi-stage amplified optical transmission system of the present embodiment, since the power level of the signal light component output from each of the amplifying optical fibers 371 is substantially constant, the nonlinear optical effect can be suppressed for the light of the signal light wavelength. If it is sufficient, the signal light transmission is performed while securing the absolute amount of the signal light component.

FIG. 19 is a configuration diagram of an optical amplifier 380 which is a modification of the optical amplifier 370. As shown in FIG.
The optical amplifier 380 has the configuration of the optical amplifier 370,
(I) an output light monitoring unit 381 that monitors the power level of the output light from the amplification optical fiber 371; and (j) an amplification factor determined by the amplification factor adjustment unit 375 and the output light monitoring unit 381.
And an excitation light fine-adjustment unit 382 that finely adjusts the intensity of the excitation light supplied by the excitation unit 372 based on the power level of the output light detected in step (a).

The optical amplifier 380 monitors the power level of the output light in addition to the adjustment of the output light power level by the feedforward control in the optical amplifier 370, and based on the monitoring result, finely adjusts the output light power level by feedback control. Is performed, the output light power level can be adjusted more accurately.

(Ninth Embodiment) FIG. 20 is a block diagram of a ninth embodiment of the multistage amplified optical transmission system of the present invention. As shown in FIG. 20, this system is different from the eighth embodiment in that the power level of the signal light component output from each of the optical amplifiers 370 _{1 to} 370 _N increases as the level increases.

In the multi-stage amplified optical transmission system of the present embodiment, similarly to the eighth embodiment, the signal light output from the transmitter 100 is sequentially amplified via the optical amplifiers 370 _{1 to} 370 _N of each stage. . In the optical amplifier 370 ₁ , the input light monitor 373 detects the power level of the input light, and the gain adjuster 375 determines the gain based on the detection result and the output signal light power level target value. The intensity of the pumping light supplied by the pumping unit 372 is adjusted so that the amplification factor becomes higher. In the optical amplifiers 370 _{2 to} 370 _N , the input optical monitor 373
Detects the power level of the input light and adjusts the amplification factor
5 determines the amplification factor from the detection result, the input power level information input from the amplification information input unit 374, and the output signal light power level target value, and the excitation unit 372 supplies the determined amplification factor. The intensity of the excitation light to be adjusted is adjusted.

Then, the optical amplification is performed at the determined amplification factor, and the optical amplifiers 370 _{1 to} 370 _{N at} each stage output light including signal light having a power level substantially equal to the output light power level target value. Are the optical amplifiers 370 _{1 to} 370 _{N in} each stage.
The power level of the signal light component included in the output light output from the optical disk becomes higher as it goes to a later stage.

The transmission optical fibers 810 _{1 to} 810 _{N + 1} have slight but non-linear characteristics, and the higher the light intensity density of the propagation light or the longer the propagation distance, the larger the nonlinear optical phenomenon occurs. The optical frequency is modulated by self-phase modulation. On the other hand, since the transmission optical fibers 810 _{1 to} 810 _{N + 1} have chromatic dispersion, waveform distortion occurs according to the propagation distance. Therefore, in the optical amplification of the multi-stage amplification optical transmission system, the larger the power level of the light of the wavelength of the signal light output from the optical amplifier 370 or the longer the propagation distance after the optical amplifier 370, that is, The greater the output power level of the light of the wavelength of the signal light, the greater the waveform distortion.

In the multi-stage amplified optical transmission system of the present embodiment, the power level of the signal light component to be output is reduced in the optical amplifier 370 on the transmitter 100 side, and the signal light component output from the optical amplifier 370 is reduced in the later stage. Since the power level is increased, the transmission optical fibers 810 ₁ -81 ₁
The occurrence of self-phase modulation due to the nonlinear optical effect at 0 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, the multi-stage amplified optical transmission system of the present embodiment is different from the eighth embodiment in that the waveform distortion due to the self-phase modulation due to the nonlinear optical effect is reduced. It is advantageous.

Incidentally, as in the eighth embodiment, the optical amplifier 3
Instead of 70, an optical amplifier 380 shown in FIG. 19 can be used.

(Tenth Embodiment) FIG. 21 is a block diagram of a tenth embodiment of the multistage amplified optical transmission system of the present invention. As shown in this figure, the system includes a transmitter 110
Is a multi-stage amplifying optical transmission system for transmitting signal light output from a receiver to a receiver 210, wherein (a) multi-stage serially connected optical amplifiers 510 _{1 to} 510 _N and (b) signal light transmission Optical fiber 810 ₁ for optically connecting the device 110 and the optical amplifier 510 _1, and the optical amplifier 510 ₁
Transmission optical fiber 81 that connects to 510 _N optically
0 _{2 to} 810 _N , and the optical amplifier 510 _N and the receiver 210
A transmission optical fiber 810 _{N + 1} for optically connecting
(C) In transmitting the power level information, the optical amplifier 5
And transmission optical fibers 820 _{1 to} 820 _N-1 for optically connecting between 10 _{1 to} 510 _N.

FIG. 22 is a configuration diagram of the optical amplifier 510. As shown in this figure, the optical amplifier 510 includes (a) an amplification optical fiber 511 for amplifying a signal light at an amplification factor corresponding to the intensity of the supplied excitation light, and (b) an amplification optical fiber 511 for the amplification. An excitation unit 512 for supplying light, (c) an input light monitor unit 513 for monitoring an input light power level,
(D) an output light monitor 514 for monitoring the output light power level, and (e) a power level information input unit 515 for inputting power level information output from the optical amplifier at the preceding stage.
(F) a power level information output unit 516 that outputs power level information indicating the output light power level monitored by the output light monitor unit 514, and (g) power level information input by the power level information input unit 515. Is transmitted from the upstream optical amplifier 510 to the upstream optical amplifier 510 based on the output optical power level of the upstream optical amplifier 510 and the input optical power level monitored by the input optical monitoring unit 513. Transmission loss of the signal light in the optical fiber 810 for use, determines the amplification factor based on the transmission loss, and instructs the pumping unit 512 to supply the pumping light of the intensity according to the determined amplification factor. Part 51
7 is provided. Then, further comprising an optical isolator 518 ₁ disposed (h) optical input and an optical isolator 518 ₂ disposed on the light output portion.

In the first-stage optical amplifier 510 ₁ , the input light monitor 513, the power level information input 515 and the amplification factor adjuster 517 are unnecessary, and the pump 512 outputs the pump light having a constant intensity to the optical fiber for amplification. 511,
Amplification optical fiber 511 may be optically amplify signal light with a constant gain G _1. In the optical amplifier 510 _N of the last stage, the power level information output unit 516 is unnecessary.

In the multi-stage amplified optical transmission system according to this embodiment, a plurality of signal lights having different wavelengths are output from the transmitter 110 at substantially the same intensity.
Then, each of these multi-wavelength signal lights enters a first-stage optical amplifier 510 ₁ via a transmission optical fiber 810 ₁ ,
The optical amplifier 510 ₁ collectively amplifies the signals at substantially the same amplification factor G ₁ and outputs the resultant signal to the transmission optical fiber 810 ₂ . Further, the output optical power level of the optical amplifier 510 ₁ is monitored by the output light monitoring section 514, power level information gain adjuster 5 which represents the output optical power level
It generated by 17, and its power level information is output to the transmission optical fiber 820 ₁ by a power level information output section 516.

The second and subsequent optical amplifiers 510 _i (i = 2,...,
N) operates as follows. That is, the transmission optical fiber 810 _i output from the optical amplifier 510 _{i-1 at the} previous stage.
The respective multi-wavelength signal light having arrived via receives an input to the amplification optical fiber 511 via the optical isolator 518 _first optical amplifier 510 _i of the own stage, the input light monitoring section 51
3 monitors the input light power level. Also, the power level information output unit 51 of the optical amplifier 510 _{i-1 at} the previous stage
The power level information output from the optical fiber 6 and arriving via the transmission optical fiber 820 _i-1 is input to the power level information input section 515 of the optical amplifier 510 _i of the own stage and received.

Then, based on the output light power level of the preceding-stage optical amplifier 510 _{i -1} represented by the received power level information and the input light power level of the own-stage optical amplifier 510 _i , the amplification factor adjusting section 517. Accordingly, the transmission loss alpha _i of the signal light obtained in the transmission optical fiber 810 _i. Further, the amplification factor adjusting section 517 determines the amplification factor target value G _i in the optical amplifier 510 _i of the own stage based on the transmission loss α _i .

[0199] Then, the amplification factor adjustment section 517, is instructed exciting unit 512 to output the excitation light intensity corresponding to the amplification ratio target value G _i that determined, the excitation light to the amplification optical fiber 511 Supplied. Therefore, the signal light each multi-wavelength, is optically amplified at substantially equal amplification factor in the amplification ratio target value G _i in the amplification optical fiber 511, through the optical isolator 518 _1, the transmission optical fiber 810 i + ₁
Output to

[0200] Incidentally, in the gain adjustment unit 517, if the relationship between the intensity of the excitation light supplied to the amplification optical fiber 511 and the amplification factor is known, the excitation to be supplied based on the amplification ratio target value G _i What is necessary is just to instruct | indicate the intensity | strength of light to the excitation part 512. In addition, even if not, the gain adjustment unit 517
The actual amplification factor is obtained based on the input light power level monitored by the input light monitoring unit 513 and the output light power level monitored by the output light monitoring unit 514. as it becomes substantially equal to the target value G _i, amplification optical fiber from the pumping unit 512 51
The intensity of the excitation light supplied to 1 may be feedback-controlled.

[0202] Further, the output optical power level of the optical amplifier 510 _i is monitored by the output light monitoring section 514, power level information representative of the output optical power level is generated by the amplification factor adjustment section 517, and the power level information that There is output to the transmission optical fiber 820 _i by a power level information output section 516.

Similarly, in the optical amplifier 510 _{N at the} final stage, the multi-wavelength signal light output from the amplification optical fiber 511 is output to the transmission optical fiber 810 _{N + 1} . However, the output of the power level information is not required in the optical amplifier 510 _N in the final stage. Then, each of the multi-wavelength signal lights is input to the receiver 210, branched and received.

[0203] Such overall gain of the multistage amplifying optical transmission system, each optical amplifier 510 ₁ to 510 _N each gain G ₁ ~G _N respectively, and each transmission optical fiber 81
Each of the transmission losses α _{1 to} α _{N + 1 of} 01 to 810 _{N + 1} is integrated.

Here, the gain target value G _i determined by the gain adjuster 517 of each optical amplifier 510 _i is preferably set to a value substantially equal to the transmission loss α _i . By doing so, each stage of the optical amplifier 510 _i compensates for the transmission loss α _i of the transmission optical fiber 810 _{i from} the previous stage optical amplifier 510 _i-1 to the own stage optical amplifier 510 _i. Thus, the intensity of the output multi-wavelength signal light can be maintained substantially constant (see the lower part of FIG. 21).

Alternatively, the amplification factor target value G _i is set to the transmission loss α _i
It is also preferable to set the value to a larger value. Thus, the intensity of the signal light output from the optical amplifier 510 _i according the subsequent increases, the transmission optical fiber 8
The occurrence of self-phase modulation due to the non-linear optical effect in 10 _{1 to} 810 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, it is advantageous in reducing the waveform distortion accompanying the self-phase modulation due to the nonlinear optical effect.

Next, the optical amplifiers 510 _i (i
= 2, ..., it will be described in more detail how the determination of the action and the amplification ratio target value G _i of N). FIG. 23 is an explanatory diagram of the operation of the optical amplifier 510.

[0207] The signal light each power level of the multi-wavelength output from the transmitter 110 is substantially equal to each other, also, the wave number of the signal light (FIG. 23 (a)) shall be reduced at time T _1. At this time, the power level of the signal light output from the preceding optical amplifier 510 _i-1 (FIG. 23B)
Is substantially constant in time T ₁ before, decreased suddenly at the time T _1, is substantially constant at time T ₁ or later. Pre-stage optical amplifier 5
The power level information input unit 5 of the optical amplifier 510 _i of the own stage which is output from the power level information output unit 516 of 10 _i-1
The power level information input to 15 indicates such an output light power level.

[0208] current stage of the optical amplifier 510 _i to the input to the input light monitoring section 513 by the monitor signal light power level (FIG. 23 (c)), the influence of the variation in transmission loss of the transmission optical fiber 810 _i At the time T
_It decreases as the wave number of the signal light at ₁ decreases. Further, in this figure, the transmission optical fiber 810 _i is disconnected at time T _2,, the input optical power level in the time T _2, after which a zero.

[0209] Then, the transmission optical fiber 810 _i transmission loss alpha _i in (FIG. 23 (d)), the output light of the previous amplifier 510 _i-1 represented by the power level information input to the power level information input unit 515 Power level (Fig. 23 (b))
And the input light power level monitored by the input light monitor unit 513 of the optical amplifier 510 _i of the own stage (FIG. 23C).
Is obtained by the amplification factor adjusting unit 517 based on
Thus, the transmission loss α of the transmission optical fiber 810 _i
i is substantially continuously changed even at the time T ₁ in which the wave number of signal light is reduced. However, after the time T _2, it is unnecessary to calculate the transmission loss α _i because it is detected that the input light power level has become 0.

The gain target value G _i of the optical amplifier 510 _i of the own stage
(FIG. 23 (e)) is determined by the amplification factor adjusting unit 517 to a value substantially equal to the transmission loss α _i (FIG. 23 (d)).
At this time, the period in which the value of the amplification factor target value G _i is updated,
In the feedback loop for maintaining the amplification factor of the optical amplifier 510 _i constant, the intensity of the pump light output from the pump unit 512 is longer than the cycle of updating, and the transmission loss α _i of the transmission optical fiber 810 _i varies. Preferably, it is short enough to be able to follow. Further, in the transmission optical fiber 810 disconnection _i is time T _2, after produced, as the fact that the input optical power level falls below a predetermined threshold is detected, the amplification ratio target value G _i is 0 You.

In the optical amplifier 510 _i , the pumping light having the intensity according to the amplification target value G _i (FIG. 23 (e)) determined in this way is supplied from the pumping section 512 to the amplification optical fiber 511.
23, the input multi-wavelength signal light (FIG. 23 (c)) is collectively amplified by the amplification optical fiber 511 and output. At this time, the signal light each multiple wavelengths, are amplified at substantially the same gain with each other, the output optical power level (FIG. 23 (f)) is substantially constant in time T ₁ before decreasing at time T ₁ , becomes substantially constant at time T ₁ after, and becomes 0 at time T _2, or later. In time T _2, before the disconnection, current stage of the optical amplifier 510 _i of the output light power level (FIG. 23 (f)), the previous amplifier 510
The output light power level substantially coincides with the output light level _i-1 (FIG. 23B).

In the present embodiment, as described above, since the amplification factor is controlled to be constant in each optical amplifier 510i, even if the wave number of the input signal light suddenly changes, each optical amplifier 51 _i
The amplification factor of each signal light at 0 _i is maintained substantially constant. Further, the amplification ratio target value G _i of the optical amplifier 510 _i of the own stage determined according the previous amplifier 510 _i-1 to the transmission loss alpha _i in the transmission optical fiber 810 _i to the optical amplifier 510 _i of the stage since the transmission loss alpha _i in the transmission optical fiber 810 _i is be varied, the signal light each power level output from each optical amplifier 510 _i is maintained substantially constant. Further, since the transmission loss alpha _i is always monitored in the transmission optical fiber 810 _i, a sudden disconnection also immediately detect the transmission optical fiber 810 _i, optical amplification effect is preferred because immediately shut down. Also, the period which the value of the amplification factor target value G _i is updated, if longer than the period in which the intensity of the pump light output from the pumping unit 512 is updated, the gain constant and the output optical power level of each signal light It is preferable because both can be compatible with constant.

(Eleventh Embodiment) FIG. 24 is a diagram showing the configuration of an eleventh embodiment of the multistage amplified optical transmission system according to the present invention. As shown in this figure, the system includes a transmitter 110
Is a multi-stage amplified optical transmission system for transmitting signal light output from a receiver to a receiver 210, comprising: (a) optical amplifiers 520 _{1 to} 520 _N connected in multiple stages in series; and (b) transmission when transmitting signal light. vessels 110 and optical amplifier 520 ₁ and the transmission optical fiber 810 ₁ for optically connecting the optical amplifier 520 ₁
Transmission optical fiber 81 for optically connecting between ~ 520 _N
0 _{2 to} 810 _N , the optical amplifier 520 _N and the receiver 210
And a transmission optical fiber 810 _{N + 1} for optically connecting the optical fibers 810 _{N + 1} . In transmitting the power level information, transmission optical fibers 810 _{2 to} 810 _N are used.

FIG. 25 is a configuration diagram of the optical amplifier 520. As shown in this figure, the optical amplifier 520 pumps (a) an amplification optical fiber 521 that amplifies signal light at an amplification factor corresponding to the intensity of the supplied pump light, and (b) an amplification optical fiber 521. An excitation unit 522 for supplying light, (c) an input light monitoring unit 523 for monitoring an input light power level,
(D) an output light monitor 524 for monitoring the output light power level, and (e) a power level information input unit 525 for inputting power level information output from the optical amplifier at the preceding stage.
(F) a power level information output unit 526 that outputs power level information indicating the output light power level monitored by the output light monitor unit 524; and (g) power level information input by the power level information input unit 525. Is transmitted from the preceding optical amplifier 520 to the own optical amplifier 520 based on the output light power level of the preceding optical amplifier 520 and the input light power level monitored by the input light monitoring unit 523. Transmission loss of the signal light in the optical fiber 810 for use, the amplification factor is determined based on the transmission loss, and the amplification adjustment for instructing the excitation unit 522 to supply the excitation light having the intensity corresponding to the determined amplification factor. Part 52
And (h) an optical demultiplexer 531 for branching the input power level information of the input light transmitted from the optical amplifier at the preceding stage.
And (i) an optical multiplexer 532 that multiplexes the light output from the amplification optical fiber 371 with the output power level information. (J) An optical isolator 528 ₁ disposed in the optical input unit and an optical isolator 528 ₂ disposed in the optical output unit are further provided.

[0215] In the first stage of the optical amplifier 520 _1, the input light monitoring unit 523, power level information input unit 525, the amplification factor adjustment section 527 and the optical demultiplexer 531 is not required,
The pumping unit 522 converts the pump light having a constant intensity into the optical fiber 5 for amplification.
Is supplied to the 21, the amplification optical fiber 521 may be optically amplify signal light with a constant gain G _1. In the final stage optical amplifier 520 _N , the power level information output section 526 and the optical multiplexer 532 are not required.

In the multi-stage amplified optical transmission system according to the present embodiment, a plurality of signal lights having different wavelengths are output from the transmitter 110 at substantially the same intensity.
Then, each of these multi-wavelength signal lights is input to the _first- stage optical amplifier 520 ₁ via the transmission optical fiber 810 ₁ ,
The optical amplifier 520 ₁ collectively amplifies the signals at substantially the same amplification factor G ₁ and outputs the amplified signal to the transmission optical fiber 810 ₂ . Further, the output optical power level of the optical amplifier 520 ₁ is monitored by the output light monitoring section 524, power level information gain adjuster 5 which represents the output optical power level
27, and the power level information light carrying the power level information is output by the power level information output unit 526 and output to the transmission optical fiber 810 ₂ via the optical multiplexer 524. The power level information light has a wavelength band (for example, 1.3 μm band) having no shared wavelength with a wavelength band (for example, 1.55 μm band) of the multi-wavelength signal light output from the transmitter 110. It has.

The second and subsequent optical amplifiers 520 _i (i = 2,...,
N) operates as follows. That is, the transmission optical fiber 810 _i output from the optical amplifier 520 _{i-1 at the} previous stage.
The multi-wavelength signal light and the power level information light that have arrived through the optical amplifiers 520 _i are respectively separated by the optical demultiplexer 53.
1 branch off from each other. Among them, each of the multi-wavelength signal lights enters the amplifying optical fiber 521 through the optical isolator 528 ₁ and the input light monitor 523.
Monitor the input light power level. Also, the power level information output unit 526 of the optical amplifier 520 _{i-1 at} the previous stage
Power level information light output from is received by entering the power level information input unit 525 of the optical amplifier 520 _i of the own stage.

Then, based on the output light power level of the preceding-stage optical amplifier 520 _i-1 indicated by the received power level information and the input light power level of the own-stage optical amplifier 520 _i , the amplification factor adjusting section 527 is determined. Accordingly, the transmission loss alpha _i of the signal light obtained in the transmission optical fiber 810 _i. Further, the gain adjusting section 527 determines the gain target value G _i in the optical amplifier 520 _i of the own stage based on the transmission loss α _i .

[0219] Then, the amplification factor adjustment section 527, is instructed exciting unit 522 to output the excitation light intensity corresponding to the amplification ratio target value G _i that determined, the excitation light to the amplification optical fiber 521 Supplied. Therefore, the signal light each multi-wavelength, is optically amplified at substantially equal amplification factor in the amplification ratio target value G _i in the amplification optical fiber 521, through the optical isolator 528 _1, the transmission optical fiber 810 i + ₁
Output to

[0220] Incidentally, in the gain adjustment unit 527, if the relationship between the intensity of the excitation light supplied to the amplification optical fiber 521 and the amplification factor is known, the excitation to be supplied based on the amplification ratio target value G _i What is necessary is just to obtain | require the intensity | strength of light and direct | indicate to the excitation part 522. Also, even if it is not so, the amplification factor adjusting unit 527
The actual amplification factor is obtained based on the input light power level monitored by the input light monitoring unit 523 and the output light power level monitored by the output light monitoring unit 524. as it becomes substantially equal to the target value G _i, amplification optical fiber from the pumping unit 522 52
The intensity of the excitation light supplied to 1 may be feedback-controlled.

The output light power level of the optical amplifier 520 _i is monitored by the output light monitor 524, and power level information indicating the output light power level is generated by the amplification factor adjuster 527. Then, the power level information light carrying the power level information is output by the power level information output unit 526, is output to the transmission optical fiber 810 _i through the optical multiplexer 532.

Similarly, in the final-stage optical amplifier 520 _N , the multi-wavelength signal light output from the amplification optical fiber 521 is output to the transmission optical fiber 810 _{N + 1} . However, the output of the power level information is unnecessary in the optical amplifier 520 _N of the last stage. Then, each of the multi-wavelength signal lights is input to the receiver 210, branched and received.

[0223] Such overall gain of the multistage amplifying optical transmission system, each optical amplifier 520 ₁ to 520 _N each gain G ₁ ~G _N respectively, and each transmission optical fiber 81
Each of the transmission losses α _{1 to} α _{N + 1 of} 01 to 810 _{N + 1} is integrated.

Here, the gain target value G _i determined by the gain adjuster 527 of each optical amplifier 520 _i is preferably set to a value substantially equal to the transmission loss α _i . In this way, each stage of the optical amplifier 520 _i compensates for the transmission loss α _i of the transmission optical fiber 810 _{i from} the previous stage of the optical amplifier 520 _i-1 to its own stage of the optical amplifier 520 _i. Thus, the intensity of the output multi-wavelength signal light can be maintained substantially constant (see the lower part of FIG. 24).

Alternatively, the amplification factor target value G _i is set to the transmission loss α _i
It is also preferable to set the value to a larger value. By doing so, the intensity of the signal light output from the optical amplifier 520 _i increases in the subsequent stage, so that the transmission optical fiber 8
The occurrence of self-phase modulation due to the non-linear optical effect in 10 _{1 to} 810 _{N + 1} is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. That is, when the gain of the entire system is the same, it is advantageous in reducing the waveform distortion accompanying the self-phase modulation due to the nonlinear optical effect.

[0226] Incidentally, the method of determining the amplification ratio target value G _i in each of the optical amplifiers 520 _i are the same as those in the tenth embodiment.

[0227] In the present embodiment, as described above, since the amplification factor is controlled to be constant in each optical amplifier 520 _i, even if the wave number of the input signal light is suddenly changed, the optical amplifier 52
The amplification factor of each signal light at 0 _i is maintained substantially constant. Also, the amplification factor target value G _i of the optical amplifier 520 _i of the own stage is determined according to the transmission loss α _i in the transmission optical fiber 810 _i from the optical amplifier 520 _{i-1 at the} previous stage to the optical amplifier 520 _i at the own stage. since the transmission loss alpha _i in the transmission optical fiber 810 _i is be varied, the signal light each power level output from each optical amplifier 520 _i is maintained substantially constant. Further, since the transmission loss alpha _i is always monitored in the transmission optical fiber 810 _i, a sudden disconnection also immediately detect the transmission optical fiber 810 _i, optical amplification effect is preferred because immediately shut down. If the cycle of updating the value of the gain target value G _i is made longer than the cycle of updating the intensity of the pump light output from the pump unit 522, the gain is kept constant and the output light power level of each signal light is maintained. It is preferable because both can be compatible with constant.

(Twelfth Embodiment) FIG. 26 is a block diagram of a twelfth embodiment of the multistage amplified optical transmission system of the present invention. As shown in this figure, the system includes a transmitter 130
Optical ADM on the path for transmitting the signal light from the
(Add / Drop Multiplexer) 600 is provided, and a transmitter / receiver 700 for transmitting / receiving signal light to / from the optical ADM 600 is a multistage amplified optical transmission system.

[0229] is provided with the optical amplifier 520 ₁ on the signal optical transmission path from the transmitter 130 to the optical ADM600,
These are optically connected by transmission optical fibers 810 ₁ and 810 ₂ . An optical amplifier 520 ₄ is provided on the signal light transmission path from the optical ADM 600 to the receiver 230, and these are optically connected by transmission optical fibers 810 ₃ and 810 ₄ . Optical ADM
An optical amplifier 520 ₆ is provided on a signal light transmission path from 600 to the transceiver 700, and these are optically connected by transmission optical fibers 810 ₅ and 810 ₆ . Also, on the signal optical transmission path from the transceiver 700 to the optical ADM600 is provided with an optical amplifier 520 _7, these are the transmission optical fiber 810 ₇ and 810 ₈
Are optically connected to each other.

The transmitter 130 has the wavelengths λ _{1 to} λ _i and λ
_{i + 1} and outputs a signal light to [lambda] _j. Optical ADM60
0 inputs the signal light output from the transmitter 130 and the signal light output from the transmitter / receiver 700, outputs the signal light of wavelengths λ _{1 to} λ _i to the transmitter / receiver 700, and outputs the wavelength λ _{i + 1 to} λ _j and λ _{j + 1 to} λ _k
Output to. The transceiver 700 is an optical ADM 600
Inputs the signal light output wavelength lambda ₁ to [lambda] _i from and output toward the optical ADM600 signal light of wavelength λ _{j + 1} ~λ _k. The receiver 230 inputs the signal light of the wavelength λ _{i +} 1 ~λ _j and λ _{j +} 1 ~λ _k output from the optical ADM600.

The optical ADM 600 includes optical amplifiers 520 ₂ , 5
20 ₃ , 520 ₅ and 520 ₈ , an optical demultiplexer 610, an optical multiplexer 620, and an optical fiber for optically connecting them. The optical amplifier 520 ₂ output from the optical amplifier 520 ₁ arrives through the transmission optical fiber 810 ₂ multi-wavelength signal light (wavelength _{λ 1 ~λ i, λ i +} 1 ~λ j)
And collectively amplify and output. Optical demultiplexer 610, among the signal light of the multi-wavelength, and output to the signal light of the wavelength lambda ₁ to [lambda] _i to the optical amplifier 520 _5, an optical multiplexing the signal light of the wavelength λ _{i + 1} ~λ _j And output it to the device 620. Optical amplifier 520 ₅
Inputs the signal light of wavelengths λ _{1 to} λ _i output from the optical splitter 610, collectively amplifies the signal light, and outputs the amplified signal light to the transmission optical fiber 810 ₅ . The optical amplifier 520 ₈ receives the multi-wavelength signal light (wavelengths λ _{j + 1 to} λ _k ) output from the optical amplifier 810 ₈ and arriving via the transmission optical fiber 810 ₈ , and collectively amplifies and outputs. The optical multiplexer 620, the signal light of wavelength λ _{j + 1} ~λ _k output signal light of the wavelength λ _{i + 1} ~λ _j outputted from the optical demultiplexer 610 and the optical amplifier 520 ₈ multiplexes Output.
The optical amplifier 520 _3, the light multiplexer 620 multi-wavelength of the signal light output from (wavelength _{λ i + 1 ~λ j, λ} j + 1 ~λ k) enter the batch amplified transmission optical fiber 810 Output to ₃ .

Therefore, in this system, the wavelengths λ ₁ to
The signal light of λ _i is transmitted from the transmitter 130 to the receiver 230 via the optical ADM 600 and the like, and the signal light of wavelengths λ _{i + 1 to} λ _j is transmitted from the transmitter 130 to the transceiver 700 via the optical ADM 600 and the like. And the signal light of wavelengths λ _{j + 1 to} λ _k is
The receiver 23 via the optical ADM 600 from the transceiver 700
0.

Each optical amplifier 520 used in the present system
Is similar to that described with reference to FIG. The optical amplifier 520 ₁ outputs the power level information light indicating the output light power level in the transmission optical fiber 810 _2, the optical amplifier 520 _2, and inputs the power level information light.
The optical amplifier 520 ₃ outputs power level information light indicating the output optical power level to the transmission optical fiber 810 ₃ , and the optical amplifier 520 ₄ inputs the power level information light. The optical amplifier 520 ₅ transmits the power level information light representing the output light power level to the transmission optical fiber 810 _5.
And the optical amplifier 520 ₆ receives the power level information light. The optical amplifier 520 ₇ outputs power level information light indicating the output optical power level to the transmission optical fiber 810 ₈ , and the optical amplifier 520 ₈ inputs the power level information light.

Next, a method for determining the respective gain target values G _{1 to} G _{8 of} the optical amplifiers 520 _{1 to} 520 ₈ will be described. Hereinafter, the optical amplifier 520 _p to the optical amplifier 52
The transmission loss in the transmission path up to 0 _q is represented by α _pq .

[0235] That is, represents the transmission loss in the transmission optical fiber 810 ₂ from the optical amplifier 520 ₁ up to the optical amplifier 520 ₂ at alpha _12, for transmission from the optical amplifier 520 ₃ up to the optical amplifier 520 ₄ It represents the transmission loss in the optical fiber 810 ₃ alpha _34, represents the transmission loss in the transmission optical fiber 810 ₅ from the optical amplifier 520 ₅ up to the optical amplifier 520 ₆ alpha _56, the optical amplifier from the optical amplifier 520 ₇ 520 the transmission loss in the transmission optical fiber 810 ₈ up to the ₈ represented by alpha _78. These transmission loss α _12, α _{3 4,} α
Each of ₅₆ and α ₇₈ is an optical amplifier 520 ₂ , 520 ₄ , 520 ₆ and 520 ₈ , similarly to the method described with reference to FIG.
Each of the gain adjusting units 527 outputs the output light power level of the preceding optical amplifier represented by the power level information light output from each preceding optical amplifier and input to the own optical amplifier, and the input of the own optical amplifier. It is determined based on the optical power level.

Further, the optical amplifiers 520 ₂ through 52 ₂
Represents the transmission loss in the transmission path up to the 0 ₃ (including the optical demultiplexer 610 and an optical multiplexer 620) in alpha _23, the transmission path from the optical amplifier 520 ₂ up to the optical amplifier 520 ₅ (Light the transmission loss at containing demultiplexer 610) expressed in alpha _25, represents the transmission loss in the transmission path from the optical amplifier 520 ₈ up to the optical amplifier 520 ₃ (including the optical multiplexer 620) at alpha _83. Each of these transmission losses α ₂₃ , α _25, and α ₈₃ is a transmission loss in the transmission path in the optical ADM 600 and can be easily measured. Further, since the length of the transmission path is short, The change in that value is so small that it can be almost neglected and can therefore be treated as a known constant value.

The gain target value G ₁ of the optical amplifier 520 ₁ is determined as follows. If another optical amplifier is not present between the transmitter 130 and the optical amplifier 520 _1,
Amplification ratio target value G ₁ is fixed to a constant value. Otherwise, by the amplification factor adjustment section 527, and the output optical power level of the previous amplifier representing the power level information light fed to the optical amplifier 520 ₁ is output from the previous amplifier, the optical amplifier 520 ₁ on the basis of the input optical power level, transmission loss alpha ₀₁ of the transmission optical fiber 810 ₁ from the previous amplifier to the optical amplifier 520 ₁ is obtained, the amplification ratio target value G ₁ is substantially in the transmission loss alpha ₀₁ Determined as equal.

[0238] Similarly, the amplification ratio target value G ₇ of the optical amplifier 520 ₇ is determined as follows. If there is no other optical amplifier between the transceiver 700 and the optical amplifier 520 ₇ , the gain target value G ₇ is fixed to a constant value. Otherwise, by the amplification factor adjustment section 527, and the output optical power level of the previous amplifier representing the power level information light fed to the optical amplifier 520 ₇ output from the previous amplifier, the optical amplifier 520 ₇ Based on the input optical power level, the optical amplifier 520
Transmission loss alpha ₀₇ of the transmission optical fiber 810 ₇ to ₇ is obtained, the amplification ratio target value G ₇ is determined as a value approximately equal to the transmission loss alpha _07.

The target gain G _{4 of the} optical amplifier 520 _{4 is} also set.
An optical amplifier 5 of the stage from the optical amplifier 520 ₃ of the preceding stage
Based on the transmission loss α ₃₄ of the transmission optical fiber 810 ₃ up to 20 ₄ , G ₄
= Is determined by alpha _34. Similarly, the amplification ratio target value G ₆ of the optical amplifier 520 _6, the transmission optical fiber 810 ₅ from the optical amplifier 520 ₅ of the preceding stage up to the optical amplifier 520 ₆ the stage
Based on the transmission loss alpha ₅₆ of, by the amplification factor adjustment section 527 is determined by the G ₆ = α _56.

Further, the respective gain target values G ₂ , G ₃ , G ₅ and G ₈ of the optical amplifiers 520 ₂ , 520 ₃ , 520 ₅ and 520 ₈ in the optical ADM 600 are given by G ₂ + G ₅ = α ₁₂ + Α ₂₅ G ₂ + G ₃ = α ₁₂ + α ₂₃ G ₈ + G ₃ = α ₇₈ + α ₈₃ That is, for the signal light of wavelengths λ _{1 to} λ _i transmitted from the transmitter 130 to the transceiver 700, the optical amplifier 520 ₂ , the optical demultiplexer 610, and the optical amplifier 52
0 ₅ and is considered a transmission path one optical amplifiers between them, the total amplification factor target value _{(G 2 + G 5 -α 25} )
Is determined based on the transmission loss α ₁₂ of the transmission optical fiber 810 _{2 in} the previous section. For signal light of wavelengths λ _{i + 1 to} λ _j transmitted from the transmitter 130 to the receiver 230, the optical amplifier 520 ₂ , the optical demultiplexer 610, the optical multiplexer 620, the optical amplifier 520 _3, and these The transmission path between them is regarded as one optical amplifier, and the overall gain target value (G ₂ + G ₃ −α ₂₃ ) is calculated based on the transmission loss α ₁₂ of the transmission optical fiber 810 _{2 in} the previous section. It is determined. Further, with respect to the signal light of wavelengths λ _{j + 1 to} λ _k transmitted from the transceiver 700 to the receiver 230, the optical amplifier 520 ₈ , the optical multiplexer 620, the optical amplifier 520 ₃ and the transmission path between them are 1 Are considered as one optical amplifier, and the overall amplification factor target value (G ₈ + G ₃ −α ₈₃ ) is determined based on the transmission loss α ₇₈ of the transmission optical fiber 810 _{8 in} the previous section.

However, each of the gain target values G ₂ , G ₃ , G ₅ and G ₈ cannot be uniquely determined by only the above three equations. Therefore, the gain target value G ₂ ,
Any one of G ₃ , G ₅ and G ₈ is determined first, and the other three are determined based on this. For example, the amplification factor target value G ₂ of the optical amplifier 520 ₂ may be determined to be a constant value, or the output light power level of the preceding optical amplifier 520 _{1 and} the input light of the own stage optical amplifier 520 ₂ may be determined. The transmission optical fiber 81 determined based on the power level
It may be determined to be equal to the transmission loss α ₁₂ of O ₂ .

[0242] Transmission Thus firstly when the amplification ratio target value G ₂ of the optical amplifier 520 ₂ is determined, information about the amplification ratio target value G ₂ and the transmission loss alpha ₁₂ from the optical amplifier 520 ₂ to the optical amplifier 520 ₃ The target gain G ₃ of the optical amplifier 520 ₃ is determined based on the target gain G ₂ and the transmission losses α ₁₂ and α ₂₃ . Moreover, information on the gain target value G ₂ and the transmission loss alpha ₁₂ is also transmitted from the optical amplifier 520 ₂ to the optical amplifier 520 _5, the amplification ratio target value G ₅ of the optical amplifier 520 _5, the amplification ratio target value G ₂ And transmission loss α
It is determined based on the ₁₂ and alpha _25. Furthermore, information on the gain target value G ₃ is transmitted from the optical amplifier 520 ₃ to the optical amplifier 520 _8, the amplification ratio target value G of the optical amplifier 520 _8
8 is the amplification factor target value G ₃ and the transmission losses α ₇₈ and α ₈₃
Is determined based on

Thus, the gain target values G ₂ , G ₃ , G ₅
And G ₈ are determined in association with each other, so that the optical amplifiers 520 ₂ , 5
20 ₃ , 520 ₅ and 520 ₈ are means for transmitting the amplification factor target value of the own stage and the transmission loss from the previous stage to the own stage to another optical amplifier, and the amplification factor transmitted from the other optical amplifier. It is necessary to provide a means for receiving the target value and the transmission loss. Specifically, these means may be configured to transmit the signal light through the same path as the signal light transmission path by the power level information output unit 526 and the power level information input unit 525, or to provide a dedicated transmission provided separately. It may be transmitted via a path, or the optical AD
The gain target values G ₂ , G ₃ , G _5, and G ₈ may be determined by a management unit separately provided in M600.

Next, the operation of the present system and a method of determining the amplification factor target value will be described in more detail. FIG.
It is an explanatory view of the operation of the present system.

It is assumed that the power levels of the multi-wavelength signal lights output from the transmitter 130 are substantially equal to each other. Also, before the time T ₁ , the wavelength λ
The signal light of _{i + 1 to} λ _j is output, and after time T ₁ , the wavelength λ ₁
Λ _i and λ _{i + 1 to} λ _j are output. That is, the output optical power level of the transmitter 130 (FIG. 27 (a)) is larger abruptly at time T _1.

Similarly, it is assumed that the power levels of the multi-wavelength signal lights output from the transceiver 700 are substantially equal to each other. In addition, the time T
The _second front, without the signal light is output at all, the time T _2, since it is assumed that the signal light of wavelength λ _{j + 1} ~λ _k is output. That is, the output light power level of the transceiver 700 (FIG. 27)
(B)) is, appear suddenly at the time T _2.

The transmission loss α ₁₂ of the transmission optical fiber 810 _2.
(FIG. 27 (c)) has a front side of the optical amplifier 520 ₁ of the output optical power level of the power level information input to the power level information input unit 525 of the optical amplifier 520 ₂ represents an optical amplifier 520 and _second input of the stage Based on the input light power level monitored by the light monitor 523, the gain is obtained by the gain adjuster 527, and the value is assumed to change with time.

Similarly, the transmission optical fiber 810 ₈
The transmission loss α ₇₈ (FIG. 27D) of the optical amplifier 520 ₈
An output light power level of the previous amplifier 520 ₇ power level information representative of input to the power level information input unit 525, the input light monitoring unit 52 of the optical amplifier 520 ₈ the stage
Based on the input light power level monitored by 3, the gain is determined by the gain adjuster 527, and the value is also assumed to change with time.

Under such conditions, the optical amplifier 520
The input optical power level ₂ (FIG. 27 (e)) changes under the influence of the fluctuation of the transmission loss α ₁₂ (FIG. 27 (c)) of the transmission optical fiber 810 ₂ , and the transmitter at the time T ₁ . It increases as the wave number of the signal light output from 130 increases. Further, the optical amplifier 520 ₂ amplification ratio target value G ₂
If the constant value, the time variation of the optical amplifier 520 _{and second} output light power level, becomes the same as FIG.

Of the multi-wavelength signal lights output from the optical amplifier 520 _2, the signal lights of wavelengths λ _{1 to} λ _i are separated by the optical demultiplexer 610.
And input to the optical amplifier 520 ₅ . Therefore, the input optical power level of the optical amplifier 520 ₅ (FIG. 27 (f))
Appears after time T ₁ and the transmission optical fiber 81
It changes under the influence of the fluctuation of the transmission loss α ₁₂ (FIG. 27C) of O ₂ .

[0251] Amplification ratio target value G ₅ of the optical amplifier 520 ₅ (FIG. 2
7 (g)) is a gain target value G ₂ (constant value in this case) of the optical amplifier 520 _{2 at} the preceding stage and a transmission loss α ₁₂ (FIG. 2).
7 (c)) and α ₂₅ (which can be regarded as a constant value). Incidentally, the amplification ratio target value G ₃ of the optical amplifier 520 ₃ also becomes the same as FIG. At this time, the period in which the value of the amplification factor target value G ₅ is updated, than the period in which the intensity of the pump light output from the pumping unit 522 in a feedback loop to maintain the gain of the optical amplifier 520 ₅ constant is updated long, and, it is preferable to sufficiently short to the extent that can follow the variation of the transmission optical fiber 810 _second transmission loss alpha _12.

In the optical amplifier 520 ₅ , the pumping light having the intensity corresponding to the amplification target value G ₅ determined in this way (FIG. 27 (g)) is transmitted from the pumping section 522 to the amplification optical fiber 521.
, The input multi-wavelength signal light is
The signals are collectively amplified by the amplification optical fiber 521 and output. At this time, the multi-wavelength signal lights (wavelengths λ _{1 to} λ _i ) appearing after time T ₁ are amplified with substantially the same amplification factor, and the output light power level (FIG. 27 (h)) is changed to time T 1. ₁ in front of 0, becomes substantially constant in time T ₁ or later.
Then, the signal light of such a wavelength lambda ₁ to [lambda] _i reaches the transceiver 700 through the optical amplifier 520 _6.

[0253] On the other hand, the input light power level of the optical amplifier 520 ₈ (FIG. 27 (i)) is the transceiver 70 to the time T _2, after
0 along with the signal light (wavelength λ _{j + 1} ~λ _k) is output from the time T _2, before those were 0, appeared suddenly in time T _2, and later also the transmission optical fiber 810 ₈ changes under the influence of the fluctuation of the transmission loss α ₇₈ (FIG. 27D).

[0254] Amplification ratio target value G ₈ of the optical amplifier 520 ₈ (FIG. 2
7 (j)) is a gain target value G ₃ of the optical amplifier 520 ₃ (similar to FIG. 27 (g)) and a transmission loss α ₇₈ (FIG. 2).
7 (d)) and α ₈₃ (which can be regarded as a constant value). At this time, the cycle at which the value of the gain target value G ₈ is updated is the same as the cycle at which the value of the gain target value G ₃ is updated, and the feedback loop for maintaining the gain of the optical amplifier 520 ₈ constant. Is longer than the cycle in which the intensity of the pumping light output from the pumping unit 522 is updated, and is sufficiently short so as to follow the fluctuation of the transmission loss α ₇₈ of the transmission optical fiber 810 ₈ .

In the optical amplifier 520 ₈ , the pumping light having the intensity corresponding to the amplification target value G ₈ determined in this way (FIG. 27 (j)) is transmitted from the pumping section 522 to the amplification optical fiber 521.
, The input multi-wavelength signal light is
The signals are collectively amplified by the amplification optical fiber 521 and output. At this time, the multi-wavelength signal lights (wavelengths λ _{j + 1 to} λ _k ) appearing after time T ₂ are amplified with substantially the same amplification factor. However, the output light power level (FIG. 27)
(K)), which appears in the time T ₂ or later, not necessarily constant.

The input optical power level of the optical amplifier 520 ₃ (FIG. 27 (l)) is determined by the wavelengths λ _{i + 1 to} λ _j output from the optical amplifier 520 ₂ and input through the optical demultiplexer 610 and the optical multiplexer 620. an input optical power level of the signal light, the sum of the signal light input optical power level of the wavelength λ _{j + 1} ~λ _k input through the optical multiplexer 620 is outputted from the optical amplifier 520 _8. That is, in the time T _2, before the input light power level of the optical amplifier 520 _3, the wavelength output from the optical amplifier 520 ₂ via the optical splitter 610 and optical multiplexer 620 inputs λ
_{i + 1} is only to [lambda] _j input optical power level of the signal light, changes under the influence of the variation of the transmission optical fiber 810 _second transmission loss alpha _12. Further, the time T _2, after an optical amplifier 5
20 ₃ of the input light power level, becomes that further apply an input optical power level of the signal light of the wavelength inputted through the optical multiplexer 620 is outputted from the optical amplifier _{520 8 λ j + 1 ~λ k} ,
The transmission optical fiber 810 ₈ is further affected by the fluctuation of the transmission loss α ₇₈ .

[0257] Amplification ratio target value G ₃ of the optical amplifier 520 _3, the previous amplifier 520 _{and second} amplifying ratio target value G ₂ (constant value in this case) as well as the transmission loss alpha ₁₂ (FIG. 27 (c)) and α
Is determined based on the ₂₃ (can be regarded as a constant value), and that changes in the same manner as the amplification ratio target value G ₅ of the optical amplifier 520 _5. At this time, the period in which the value of the amplification factor target value G ₃ is updated is the same as the period value of the amplification factor target value G ₂ is updated, the feedback loop for maintaining the gain of the optical amplifier 520 ₃ constant , The intensity of the pumping light output from the pumping unit 522 is longer than the cycle of updating, and the transmission loss α _{12 of} each of the transmission optical fibers 810 ₂ and 810 _{8 is}
And α ₇₈ are short enough to follow the respective variations.

In the optical amplifier 520 ₃ , the pump light having the intensity corresponding to the amplification factor target value G ₃ determined in this way is supplied from the pump section 522 to the amplification optical fiber 521, so that the input multi-wavelength Are collectively amplified by the amplification optical fiber 521 and output. At this time,
The multi-wavelength signal light (wavelengths λ _{i + 1 to} λ _j , λ _{j + 1 to} λ _k ) are amplified with substantially the same amplification factor, and the output light power level (FIG. 27 (m)) is will be due to the wave number of the light, it is substantially constant at the time T ₂ before, becomes substantially constant even time T ₂ or later. Then, the signal light of the wavelength output from the optical amplifier 520 ₃ λ _{i + 1} ~λ _j and λ _{j + 1} ~λ _k is the optical amplifier 5
20 ₄ through to reach the receiver 230.

In this embodiment, when it is detected that the input optical power level of each optical amplifier has become equal to or less than the predetermined threshold value, the gain target value of the optical amplifier is set to 0.
Then, it is preferable to shut down the optical amplifier. In particular, when it is detected that the input optical power level of the optical amplifier 520 ₂ on the input side in the optical ADM 600 has fallen below a predetermined threshold, the transmission optical fiber 810 is detected.
₂ is determined to be disconnected, the amplification factor target value G ₂ is set to 0, the optical amplifier 520 ₂ is shut down, and the input optical power level of the optical amplifier 520 ₈ also on the input side becomes lower than a predetermined threshold value. If it is detected that
Judging that the transmission optical fiber 810 ₈ is broken,
The target gain G ₈ is set to 0, and the optical amplifier 520 ₈ is shut down. However, even if only one of the optical amplifiers 520 ₂ and 520 ₈ on the input side is shut down, the gain target value G ₃ of the optical amplifier 520 ₃ on the output side is preferably maintained at the value immediately before the shutdown. is there. By doing so, the inflow of noise light and the like from the disconnected transmission path is prevented, and the signal light input through the non-disconnected transmission path is output in a predetermined direction through the optical ADM 600. obtain.

Also in the present embodiment, it is preferable that the amplification factor target value is set to a value larger than the transmission loss in the preceding section. However, in the present embodiment, the optical amplifiers including the optical amplifiers 520 ₂ to 520 ₅ are regarded as one optical amplifier, and the optical amplifiers including the optical amplifiers 520 ₂ to 520 ₃ are regarded as one optical amplifier. It is regarded as one optical amplifier including the optical amplifiers 520 ₈ to 520 ₃ . By doing so, the intensity of the signal light output from the optical amplifier increases in the later stages, so that the occurrence of self-phase modulation due to the nonlinear optical effect in the transmission optical fiber is suppressed, and the waveform distortion due to chromatic dispersion is suppressed. Is suppressed. That is, when the gain of the entire system is the same, it is advantageous in reducing the waveform distortion accompanying the self-phase modulation due to the nonlinear optical effect.

As described above, the optical amplifiers 520 _{1 to} 520-52
0 ₈ When each respective amplification ratio target value G ₁ ~G ₈ are determined, the optical amplifier 520 ₁ is out of the optical ADM600, 5
20 _4, 520 ₆ and 520 ₇ each amplification factor is controlled to be constant, and because the amplification factor when the light ADM600 regarded as one optical amplifier for each wavelength of each signal light is also controlled to be constant, the input Even if the signal light wavenumber suddenly changes,
The gain of each signal light in each optical amplifier is maintained substantially constant. In addition, since the amplification factor target value of the own-stage optical amplifier is determined according to the transmission loss in the transmission path from the preceding-stage optical amplifier to the own-stage optical amplifier, each optical amplifier is changed even if the transmission loss varies. The power level of each of the signal lights output from is maintained substantially constant. In addition, since the transmission loss in the transmission path is constantly monitored, a sudden disconnection in the transmission path is immediately detected, and the optical amplification operation is immediately shut down. If the cycle of updating the value of the gain target value G _i is made longer than the cycle of updating the intensity of the pump light output from the pump unit 522, the gain is kept constant and the output light power level of each signal light is maintained. It is preferable because both can be compatible with constant.

[0262]

As described above in detail, according to the multistage amplified optical transmission system and the optical amplifier of the present invention, each optical amplifier performs optical amplification based on the power level diagram of the propagating light in the overall system design. In this case, it is possible to suppress the waveform distortion due to the non-linear optical effect of the relay transmission line and secure the SN ratio, so that it is possible to realize a suitable optical transmission.

Also, based on the output light power level of the preceding-stage optical amplifier and the input light power level of the own-stage optical amplifier, the transmission loss in the transmission path from the preceding-stage optical amplifier to the own-stage optical amplifier is determined. Is determined, and the amplification factor of the optical amplifier in its own stage is determined based on the transmission loss, and the signal light is amplified at the determined amplification factor. Therefore, the power of each of the multi-wavelength signal light output from each optical amplifier is determined. The level is kept substantially constant, and suitable optical transmission can be realized.

[Brief description of the drawings]

FIG. 1 is a graph showing a general power spectrum at an output time of an optical amplifier.

FIG. 2 is an explanatory diagram of amplification and generation of noise light in an optical amplifier using an amplification optical fiber.

FIG. 3 is a configuration diagram of a multi-stage amplified optical transmission system according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram of the optical amplifier of FIG. 3;

FIG. 5 is a configuration diagram of a modified example of the optical amplifier of FIG. 4;

FIG. 6 is a configuration diagram of a multi-stage amplified optical transmission system according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a multi-stage amplified optical transmission system according to a third embodiment of the present invention.

FIG. 8 is a configuration diagram of the optical amplifier of FIG. 7;

FIG. 9 is a configuration diagram of a modified example of the optical amplifier of FIG. 8;

FIG. 10 is a configuration diagram of a multi-stage amplified optical transmission system according to a fourth embodiment of the present invention.

FIG. 11 is a configuration diagram of a multi-stage amplified optical transmission system according to a fifth embodiment of the present invention.

FIG. 12 is a diagram illustrating the dependence of the amplification factor on the wavelength.

FIG. 13 is a configuration diagram of a multi-stage amplified optical transmission system according to a sixth embodiment of the present invention.

FIG. 14 is a configuration diagram of the optical amplifier of FIG.

FIG. 15 is a configuration diagram of a modified example of the optical amplifier of FIG.

FIG. 16 is a configuration diagram of a multi-stage amplified optical transmission system according to a seventh embodiment of the present invention.

FIG. 17 is a configuration diagram of a multi-stage amplified optical transmission system according to an eighth embodiment of the present invention.

18 is a configuration diagram of the optical amplifier of FIG.

FIG. 19 is a configuration diagram of a modified example of the optical amplifier of FIG. 18;

FIG. 20 is a configuration diagram of a multi-stage amplified optical transmission system according to a ninth embodiment of the present invention.

FIG. 21 is a configuration diagram of a multistage amplified optical transmission system according to a tenth embodiment of the present invention.

FIG. 22 is a configuration diagram of the optical amplifier of FIG. 21;

FIG. 23 is an explanatory diagram of the operation of the optical amplifier in FIG. 21;

FIG. 24 is a configuration diagram of a multi-stage amplified optical transmission system according to an eleventh embodiment of the present invention.

FIG. 25 is a configuration diagram of the optical amplifier of FIG. 24;

FIG. 26 is a configuration diagram of a multi-stage amplified optical transmission system according to a twelfth embodiment of the present invention.

FIG. 27 is an explanatory diagram of the operation of the multi-stage amplified optical transmission system of FIG. 26;

[Explanation of symbols]

100, 110, 120 ... transmitter, 200, 210, 2
20 ... Receiver, 310, 320, 330, 340, 35
0, 360, 370, 380... Optical amplifiers, 311, 33
1,351,371 ... Amplification optical fiber, 312,33
2,352,372 ... Exciting part, 313,333,35
3,373 ... input light monitor section, 314,334,35
4,374... Amplification information input section, 315, 335, 35
5,375... Amplification rate adjusting section, 335, 355, 375.
Amplified information output unit, 316, 337, 357, 377: optical isolator, 321, 341, 361, 381: output light monitor unit, 322, 342, 362, 382: amplification factor fine adjustment unit, 383: optical demultiplexer, 384 ... optical multiplexer, 40
0: amplification management unit, 510, 520: optical amplifier, 511,
521: optical fiber for amplification, 512, 522: excitation unit,
513, 523: input light monitor, 514, 524: output light monitor, 515, 525: power level information input, 516, 526: power level information output, 51
7, 527: Amplification ratio adjustment unit, 518, 528: Optical isolator, 532: Optical demultiplexer, 532: Optical multiplexer, 600
... optical ADM, 610 ... optical demultiplexer, 520 ... optical multiplexer, 8
10,820 ... Transmission optical fiber.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/18

Claims (25)

[Claims] 1. A multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein each of the plurality of optical amplifiers has a pumping characteristic as an amplification characteristic. An amplification factor of the input light having a wavelength of the signal light corresponding to the light intensity and the input light intensity, and an optical amplification unit having a known relationship between the amplification factor value and the power level of the generated noise light, and the optical amplification unit is excited. A pumping unit that supplies light; an input light monitoring unit that monitors an input light power level; and an instruction based on amplification characteristics of the plurality of optical amplifiers and transmission loss in a relay transmission line between the plurality of optical amplifiers. Optical power level to be output and the input light power level detected by the input light monitor unit, determine an amplification factor, and determine the excitation light intensity supplied by the excitation unit according to the determined amplification factor. Amplification rate adjustment unit to adjust Multistage amplifier optical transmission system, characterized in that it comprises. 2. An optical power level to be initially output to each of the plurality of optical amplifiers, and information corresponding to an operating amplification factor is collected from each of the plurality of optical amplifiers, and the plurality of optical amplifiers are collected. Calculating an optical power level to be newly output to each of the plurality of optical amplifiers based on the operating amplification factors of the respective optical amplifiers, and instructing the calculated optical power level to each of the plurality of optical amplifiers; 2. The multi-stage amplified optical transmission system according to claim 1, further comprising an amplification management unit that performs the amplification. 3. The optical power level to be output by each of the optical amplifiers is the output optical power level of each of the optical amplifiers at which the power level of the signal light component output by each of the optical amplifiers becomes substantially constant. 2. The multi-stage amplified optical transmission system according to claim 1, wherein: 4. The output power of each of the optical amplifiers, wherein the optical power level to be output by each of the optical amplifiers increases as the power level of the signal light component output by each of the optical amplifiers increases. 2. The multi-stage amplified optical transmission system according to claim 1, wherein the level is a level. 5. The signal light has a plurality of transmission channels of different wavelengths, and the amplification characteristics of each of the plurality of optical amplifiers include amplification of wavelength dependence of an amplification factor in a wavelength range including the plurality of wavelengths. The amplification dependence is further known, and the amplification management unit is configured to determine the wavelength of the wavelength dependence of the amplification ratio and the operating amplification ratio of each of the plurality of optical amplifiers based on the amplification factor of the last stage. For the light of each wavelength component of the signal light in the output light of the amplifier, to reduce the dependence of the gain as a system, calculate the optical power level to be output of each of the plurality of optical amplifiers, The multi-stage amplified optical transmission system according to claim 2. 6. An optical amplifier used in a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, comprising: an excitation light intensity and an input light intensity. The amplification factor of the input light having the wavelength of the signal light corresponding to the optical amplification unit, and a known relationship between the amplification factor value and the noise light generation level, an excitation unit that supplies excitation light to the optical amplification unit, An input light monitoring unit for monitoring an input light power level; an information input unit for inputting level information relating to a specified light power level to be output; and an input light power level detected by the level information and the input light monitoring unit And an excitation light control unit that adjusts the intensity of the excitation light supplied by the excitation unit according to the determined amplification factor, and information that outputs amplification factor information related to the determined amplification factor. Output section and An optical amplifier, characterized in that to obtain. 7. An output light monitor for monitoring a level of an output light of the optical amplifier, a gain determined by the gain adjuster and a level of the output light detected by the output light monitor. 7. The optical amplifier according to claim 6, further comprising: a pump light fine-adjustment unit that finely adjusts the intensity of the pump light supplied by the pump unit. 8. A multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein the optical amplifier of a subsequent-stage amplifying unit other than the first-stage optical amplifier comprises: Amplification characteristics of the input light having a wavelength of the signal light corresponding to the excitation light intensity and the input light intensity, and a first optical amplification unit having a known relationship between the amplification factor value and the noise light generation level, A first pumping unit that supplies pumping light to the first optical amplifying unit and has a controllable pumping light intensity; a first input light monitoring unit that monitors a power level of input light; An amplification information input unit for receiving input level information relating to the power level of the signal light and the power level of the noise light at the time of output; the power level of the signal light to be output according to a preset level diagram; Detected by the monitor A first amplification factor adjustment unit that determines an amplification factor based on the power level of the input light obtained and the input level information, and instructs the excitation unit to supply excitation light according to the determined amplification factor. A multi-stage amplified optical transmission system, comprising: 9. The optical amplifier of the latter-stage optical amplifier other than the final-stage optical amplifier, based on the input level information and the determined amplification factor, outputs the power level of the signal light and the noise light at the time of output. 9. The multi-stage amplified optical transmission system according to claim 8, further comprising a first amplification information output unit that generates and outputs output level information related to a power level. 10. The first-stage optical amplifier, wherein amplification factors of a signal light wavelength corresponding to the pumping light intensity and a relationship between the amplification factor value and the noise light generation level are known as amplification characteristics. An optical amplifying unit, a second pumping unit that supplies pumping light to the second optical amplifying unit and has a controllable pumping light intensity, and a second input light monitoring unit that monitors a power level of the input light. Determining the amplification factor based on the power level of the signal light to be output according to the level diagram and the power level of the input light detected by the input light monitoring unit, and pumping light according to the determined amplification factor And a second amplification factor adjusting unit that instructs the pumping unit to supply the output signal, and output level information related to the power level of the signal light and the power level of the noise light at the time of output based on the determined amplification factor. Output the second amplified information Further comprising multistage amplifying optical transmission system according to claim 8, wherein the output unit. 11. A first transmission medium that mediates transmission of the signal light between the optical amplifiers, and a second transmission medium that mediates transmission of the signal carrying the level information between the optical amplifiers. The multi-stage amplified optical transmission system according to claim 8, further comprising: 12. The signal light has a wavelength in a first wavelength band, and the level information light carrying the level information has a wavelength in a second wavelength band that has no shared wavelength with the first wavelength band. 9. The multi-stage amplified optical transmission system according to claim 8, further comprising an optical fiber having transmission and transmitting both the signal light and the level information light between the optical amplifiers. 13. The multi-stage amplified optical transmission system according to claim 8, wherein the power level values of the signal light to be output set in each of the optical amplifiers are all the same. 14. The multi-stage amplifying optical transmission system according to claim 8, wherein the power level value of the signal light to be output, which is set for each of said optical amplifiers, increases in a later stage. 15. An optical amplifier used in a multi-stage amplified optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, comprising: an excitation light intensity and an input light intensity. The amplification factor of the light having the wavelength of the signal light according to the above, and the optical amplification unit having a known relationship between the amplification factor value and the noise light generation level, and the excitation light intensity for supplying the excitation light to the optical amplification unit. A controllable pumping unit, an input light monitoring unit that monitors the power level of the input light, and amplification information that receives input level information on the power level of the signal light and the power level of the noise light at the time of the output of the optical amplifier in the preceding stage. An input unit, a specified power level of the signal light to be output, and a power level of the input light detected by the input light monitoring unit;
An amplification factor is determined based on the input level information, an amplification factor adjustment unit that instructs the excitation unit to supply excitation light according to the determined amplification factor, and the input level information and the determined amplification factor And an amplification information output section for generating and outputting output level information on the power level of the signal light and the power level of the noise light at the time of output. 16. An output light monitoring unit for monitoring a power level of output light of the optical amplifier; an amplification factor determined by the amplification factor adjustment unit; and an output light level detected by the output light monitoring unit. 16. The optical amplifier according to claim 15, further comprising: an excitation light fine-adjustment unit that finely adjusts the intensity of the excitation light supplied by the excitation unit based on the information. 17. A multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein the plurality of optical amplifiers are other than the last-stage optical amplifier. Each of the optical amplifiers includes: an output light monitoring unit that monitors an output light power level; and a power level information output unit that outputs power level information indicating the output light power level to a subsequent optical amplifier. Each of the optical amplifiers other than the first-stage optical amplifier among the optical amplifiers includes an optical amplifier that amplifies the signal light at an amplification factor according to the intensity of the supplied pump light, and an optical amplifier that outputs the pump light and outputs the pump light. An input light monitoring unit that monitors an input optical power level; a power level information input unit that receives power level information output from a previous-stage optical amplifier; Based on the output light power level of the preceding optical amplifier and the input light power level represented by the power level information input by the level information input unit, from the preceding optical amplifier to the own stage optical amplifier. Determine the transmission loss in the transmission path of the transmission path, determine the amplification factor based on the transmission loss, an amplification factor adjustment unit that instructs the excitation unit to supply the excitation light having an intensity corresponding to the determined amplification factor, A multi-stage amplified optical transmission system, comprising: 18. A first transmission medium that mediates transmission of the signal light between the optical amplifiers, and a second transmission medium that mediates transmission of the signal carrying the power level information between the optical amplifiers. 18. The multi-stage amplified optical transmission system according to claim 17, further comprising: 19. The signal light has a wavelength in a first wavelength band, and the power level information is power level information having a wavelength in a second wavelength band that has no shared wavelength with the first wavelength band. The multi-stage amplifying optical transmission system according to claim 17, further comprising an optical fiber that is carried by light and mediates transmission of both the signal light and the power level information light between the optical amplifiers. . 20. The multi-stage amplified optical transmission system according to claim 17, wherein said amplification factor adjusting section determines said amplification factor to a value substantially equal to said transmission loss. 21. The multi-stage amplified optical transmission system according to claim 17, wherein said amplification factor adjusting section determines said amplification factor to a value larger than said transmission loss. 22. The amplification factor adjusting section compares the input light power level with a predetermined threshold value, and determines the amplification factor to be 0 when the input light power level is smaller than the predetermined threshold value. The multi-stage amplified optical transmission system according to claim 17, wherein: 23. The amplification factor adjusting unit updates the amplification factor with a period longer than a period for updating the intensity of the pumping light instructed to the pumping unit and a period that can follow the fluctuation of the transmission loss. 18. The multi-stage amplified optical transmission system according to claim 17, wherein the decision is made. 24. An optical amplifier used in a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein the output monitors an output optical power level. An optical amplifier, comprising: an optical monitor unit; and a power level information output unit that outputs power level information indicating the output optical power level to a subsequent optical amplifier. 25. An optical amplifier used in a multi-stage amplifying optical transmission system for transmitting signal light output from a transmitter to a receiver via a plurality of optical amplifiers sequentially, wherein the intensity of the supplied pump light is An optical amplifier for amplifying the signal light at a corresponding amplification factor; an excitation unit for outputting the excitation light and supplying the same to the optical amplifier; an input optical monitor for monitoring an input optical power level; A power level information input unit for inputting power level information output from the power level information output unit, and an output light power level and an input light power level of the upstream optical amplifier represented by the power level information input by the power level information input unit. , A transmission loss in a transmission path from the previous-stage optical amplifier to the own-stage optical amplifier is determined, and the amplification factor is determined based on the transmission loss. The supply of the excitation light intensity corresponding to the amplification factor and the amplification factor adjustment section instructs the excitation portion,
An optical amplifier comprising: