JP2000312047A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a flat gain characteristic about wavelength, even if the temperature changes. SOLUTION: A temperature sensor 4 in the optical amplifier detects the temperature in the periphery of an optical fiber 110, a reference voltage generation circuit 6 controls an AGC circuit 130 on the basis of an output signal of the sensor 4, in such a manner that the higher the temperature around the fiber 110 is, the higher an amplification factor in the fiber 110 is set. For an erbium-doped optical fiber, the higher the temperature is, the smaller the gain in its longer wavelength side will be. Furthermore, the gain characteristic of the fiber 110 is changed also by the strength of exciting light so that the stronger the exciting light is, the larger the gain in its longer wavelength side will be. Thus when the AGC circuit 130 is controlled, the higher the temperature is, the higher the amplification factor of the fiber 110 will be, the exciting light supplied to the fiber 110 becomes stronger at a higher temperature, which results in a change in the gain characteristic caused by the temperature change is canceled by a change in the gain characteristic caused by changing the intensity of the exciting light, thus the gain characteristic of the fiber 110 becomes flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier comprising an optical fiber for amplifying an optical signal.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an example of a conventional optical amplifier. The conventional optical amplifier 102 shown in FIG.
Includes first and second optical amplification units 104 and 106,
The optical signal amplified by the first optical amplifier 104 is applied to the optical attenuator 1
08, the signal is supplied to the second optical amplifier 106 and further amplified in the second optical amplifier 106, for example, forming an optical regenerative repeater of a wavelength division multiplexing transmission system.

[0003] First and second optical amplifiers 104 and 106
Has basically the same configuration, and the optical fiber 110
And peripheral elements for gain adjustment. The optical fiber 110 is an erbium-doped optical fiber and amplifies an optical signal with a gain according to the intensity of the pump light. In the first optical amplifier 104, an optical coupler 112 is inserted at the input of the optical fiber 110, while in the second optical amplifier 106, the optical coupler 112 is inserted at the output of the optical fiber 110. . And a light emitting means 1 using a laser light emitting diode.
Reference numeral 14 (LD) generates excitation light, and this excitation light is supplied to each optical coupler 112. These light emitting means 1
The optical coupler 14 and the optical coupler 112 constitute an amplification control means for controlling the amplification of the optical signal in each optical fiber 110.

[0004] In the first optical amplifying section 104, the optical coupler 11
Reference numeral 2 denotes an optical signal that is supplied from an input port 116 of the optical fiber 110 and propagates through the optical fiber 110, while passing the optical signal in the direction of the optical fiber body 118,
Is reflected and propagated in the direction of the optical fiber body 118. On the other hand, in the second optical amplifying unit 106, the optical coupler 112 allows the optical signal from the optical fiber main body 118 to pass through to the output port 120, and the light emitting unit 1
The excitation light from 14 is reflected and propagated in the direction of optical fiber body 118.

The first and second optical amplifiers 104,
At 106, optical splitters 122 and 124 are inserted into the input portion and the output portion of the optical fiber 110, respectively, and a part of the optical signal propagating through the optical fiber 110 is
The light is branched at 22 and 124, and the light detectors 126 and
128. The photodetectors 126 and 128 detect the optical signals from the splitters 1 and 2, respectively, convert the optical signals into electric signals, and output the electric signals to the AGC circuit 130 (AGC). AG
The C circuit 130 supplies a control voltage to the light emitting unit 114 so that the ratio of the magnitude of the electric signal from each of the photodetectors 126 and 128 becomes substantially constant.

Therefore, the first and second optical amplifiers 1
At 04 and 106, the optical signals input to the optical fiber 110 by the photodetectors 126 and 128 and the optical fiber 1
The AGC circuit 130 supplies a control voltage to the light emitting means 114 so that the ratio of the intensity of these optical signals becomes a preset substantially constant value. To adjust the emission intensity. As a result, the gains of the first and second optical amplifiers 106 are always set to a substantially constant value.

Specifically, for example, when the gain in the optical fiber 110 is small and the optical signal on the output side of the optical fiber 110 is not sufficiently large with respect to the optical signal on the input side, the AGC circuit 130 By outputting a high control voltage, the light emission intensity of the light emitting means 114 is increased.
As a result, stronger excitation light is supplied to the optical fiber 110, and the gain of the optical fiber 110 increases. Conversely, when the gain in the optical fiber 110 is large and the optical signal on the output side of the optical fiber 110 is too large with respect to the optical signal on the input side, the AGC circuit 130 outputs a low control voltage, The light emission intensity of the light emitting means 114 is reduced. As a result, weaker pump light is supplied to the optical fiber 110, and the gain of the optical fiber 110 is reduced.

As shown in FIG. 5, the first optical amplifier 10
The optical signal amplified in 4 is input from the optical splitter 124 to the optical splitter 122 of the second optical amplifier 106 via the optical attenuator 108 (ATT), and is input to the optical fiber 110 of the second optical amplifier 106. Supplied. And the optical attenuator 1
08 is controlled by the automatic level control circuit 132 (ALC). The optical attenuator 108 and the automatic level control circuit 132 are used to control the intensity of the optical signal at the output of the second optical amplifying unit 106 so as to be a predetermined substantially constant value. is there. In other words, at the output of the second optical amplifier 106, for example, when the optical signal is strong and the electric signal output from the photodetector 128 is large, the automatic level control circuit 132 sets the optical attenuator 1
The optical attenuator 108 is controlled so that the amount of attenuation of the optical signal at 08 becomes large. On the other hand, when the optical signal is weak at the output of the second optical amplifier 106 and the electric signal output from the photodetector 128 is small, the automatic level control circuit 132
Controls the optical attenuator 108 so that the amount of attenuation of the optical signal in the optical attenuator 108 is reduced. As a result, an optical signal of almost constant intensity is always output from the output port 120.

[0009]

By the way, in such an optical amplifying apparatus 102 used in a wavelength division multiplexing transmission system, if the difference in the intensity between the optical signals of each wavelength is large, especially when performing multistage relay, S / N is significantly deteriorated on the wavelength side where the signal strength is weak, and transmission errors are likely to occur. Therefore, it is desirable that the gain characteristic be as flat as possible within the wavelength band used.

However, in the 1580 nm band or the like, the temperature dependency of the optical amplifier is large, and the flatness of the gain characteristic may be significantly deteriorated due to a change in temperature. The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical amplifying device in which the flatness of gain characteristics with respect to wavelength does not deteriorate even when the temperature changes.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an optical fiber for amplifying a plurality of optical signals having different wavelengths, and pumping light having an intensity corresponding to a control voltage to the optical fiber. Amplification degree control means for controlling the degree of amplification of the optical signal in the optical fiber, and the intensity of the input optical signal and the intensity of the output optical signal of the optical fiber based on the input optical signal and the output optical signal of the optical fiber. An AGC circuit that generates the control voltage to stabilize the ratio of the optical fiber and supplies the control voltage to the amplification degree control means, and detects a temperature around the optical fiber to indicate a detection result. And a control voltage for controlling the AGC circuit based on an output signal of the temperature sensor to supply a stronger excitation light to the optical fiber as the temperature around the optical fiber is higher. Characterized by comprising an AGC control circuit for outputting to the circuit.

In the optical amplifying device according to the present invention, the temperature sensor comprises:
The temperature around the optical fiber is detected and a signal representing the detection result is output. The AGC control circuit controls the AGC circuit based on the output signal of the temperature sensor. The control voltage supplied to the fiber is output to the AGC circuit. For example, in an optical fiber doped with erbium, as the temperature increases, the gain decreases as the wavelength increases. The gain characteristics of this optical fiber are
It also changes depending on the intensity of the excitation light.
The gain increases on the longer wavelength side. Therefore, when the AGC circuit is controlled by the AGC control circuit so as to supply stronger pumping light to the optical fiber as the temperature increases, the gain characteristic changes due to the temperature change and the pumping light intensity changes. As a result, the change in the gain characteristic cancels out, and the gain characteristic of the optical fiber becomes flat. That is, in the optical amplifying device of the present invention, the flatness of the gain characteristic does not deteriorate even when the temperature changes.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of the optical amplifier according to the present invention. In the drawing, the same elements as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted here. Optical amplification device 2 shown in FIG.
However, the difference from the optical amplifier shown in FIG. 5 is that the optical amplifier includes a temperature sensor 4 and a reference voltage generating circuit 6 (an AGC control circuit according to the present invention) in relation to the second optical amplifier 106. It is. The temperature sensor 4 is arranged close to the optical fiber 110 constituting the second optical amplifier 106, detects the temperature around the optical fiber 110, and outputs a signal representing the detection result. The reference voltage generation circuit 6 controls the AGC circuit 130 based on the output signal of the temperature sensor 4, and increases the control voltage for supplying stronger excitation light to the optical fiber 110 as the temperature represented by the output signal of the temperature sensor 4 increases. 2 optical amplifiers 1
06 to the AGC circuit 130. Specifically, the reference voltage generation circuit 6 generates a higher reference voltage as the temperature indicated by the output signal of the temperature sensor 4 increases, and the second optical amplifier 10
The AGC circuit 130 of FIG. 6 outputs a control voltage for setting a higher gain than the original gain as the reference voltage is higher.
4 is output.

Next, the optical amplifying device 2 thus configured
Will be described. FIGS. 2A to 2F are graphs showing gain characteristics and the like in the second optical amplifier 106. In the figure, the horizontal axis represents the wavelength, and the vertical axis represents the wavelength.
(A) through (C) and (F) represent gain,
(D) and (E) show the output level. FIG.
(A) shows the gain characteristic of the second optical amplifying unit 106 at room temperature, and by setting the emission intensity of the light emitting means 114 appropriately, a substantially flat gain characteristic can be obtained in the entire wavelength band used. ing. Therefore, the output level of the optical signal of each wavelength is almost constant as shown in FIG. In FIG. 2D, each vertical line indicates an output level of each wavelength.

On the other hand, when the temperature of the optical fiber 110 rises together with the temperature around the optical fiber 110,
When the present invention is not implemented, as shown in FIG. 2B, the gain decreases on the longer wavelength side, and the flatness of the gain characteristic is lost. Therefore, as shown in FIG. 2E, the output level of the optical signal of each wavelength also becomes lower on the longer wavelength side.

As described above, in the optical fiber 110, as the temperature increases, the gain decreases as the wavelength becomes longer. However, the gain characteristic of the optical fiber 110 also changes depending on the intensity of the pump light. As shown in (2), when the pumping light is intensified, the gain increases on the longer wavelength side. In the figure, the solid line shows the gain characteristics when the pumping light is intensified, and the dotted line shows the gain characteristics when the temperature of the pumping light is increased with normal intensity.

In this embodiment, in the second optical amplifying unit 106, the reference voltage generating circuit 6 sets the degree of amplification of the optical fiber 110 higher as the temperature detected by the temperature sensor 4 is higher. The AGC circuit 130 is controlled, so that the higher the temperature, the stronger the pump light supplied to the optical fiber 110. As a result, the change in the gain characteristic due to the temperature change (FIG. 2B) and the change in the gain characteristic due to the change in the intensity of the pump light (FIG. 2C) cancel each other,
As shown in FIG. 2F, the gain characteristic of the optical fiber 110 becomes substantially flat over almost the entire wavelength band used. That is, in the optical amplifying device 2 of the present embodiment, even when the temperature changes, the flatness of the gain characteristic in the second amplifying unit 106 does not deteriorate. The change in the gain characteristic of the optical fiber as shown in FIG. 2 is described in “IEICE Technical Report: OQE92” (P.21) and “IEICE Technical Report: OQCS92” (P.58) issued by the Institute of Electronics, Information and Communication Engineers. ).

In the above embodiment, the second optical amplifier 10
6, the gain characteristic is flattened, but also in the first optical amplifying unit 104, the temperature sensor 4 and the reference voltage generating circuit 6 are provided to control the AGC circuit 130, and the gain characteristic is flattened to perform optical amplification. It is of course possible to further improve the performance of the entire device 2. Also, the second optical amplifier 106
, The AGC circuit 13
When controlling 0, it is also effective to perform compensation more strongly so as to cancel also the deterioration of the flattening of the gain characteristic in the first optical amplifier 104. In the present embodiment, the optical amplifying device 2 includes the first and second optical amplifying units 10.
4 and 106, but it is also possible to adopt a configuration using only the second optical amplifier 106 depending on the required performance level.

Next, a second embodiment of the present invention will be described. FIG. 3 is a block diagram showing an optical amplifying device according to the second embodiment. In the figure, the same elements as those in FIG. 1 are denoted by the same reference numerals, and a description thereof will be omitted here. The optical amplifying device 8 shown in FIG. 3 differs from the optical amplifying device 2 in connection with the automatic level control circuit 132 in that the optical splitter 10 and the wavelength separation photodetector 12 (AWG + P
D) and the signal detection means 14 (MAX / MIN D
ET). The optical splitter 10 includes an optical splitter 124 and a photodetector 1 in the second optical amplifying unit 106.
28, and the optical detector 1
A part of the optical signal supplied to the wavelength separation detector
Branch to The wavelength separation detector 12 detects the intensity of an optical signal for each optical signal having a different wavelength, and outputs a voltage (electric signal) representing the detection result. More specifically, the wavelength separation photodetector 12 converts a plurality of optical filters (not shown) for extracting optical signals of each wavelength into a voltage representing the strength of each of the extracted optical signals. It is configured to include a plurality of photodetectors (not shown).

The signal detecting means 14 detects the highest or lowest voltage among the voltages output from the wavelength separation photodetector 12, and detects the highest or lowest voltage.
32. Therefore, in this optical amplifying device 8,
The automatic level control circuit 132 does not control the optical attenuator 108 based on the overall intensity of the optical signal of each wavelength output from the optical fiber 110, as in the related art. The optical attenuator 108 is controlled based on the strength.

As a result, in the optical amplifier 8, for example, even when the number of channels is reduced and the number of wavelengths used is reduced, the voltage supplied to the automatic level control circuit 132 is reduced. In other words, the intensity of the optical signal output from the optical fiber 110 of the second optical amplifying unit 106 can be controlled to the same intensity as in the case of the original number of channels. Since the temperature sensor 4 and the reference voltage generating circuit 6 according to the present invention operate independently of the wavelength separation light detector 12 and the signal detecting means 14, the present embodiment also has the same configuration as the above embodiment. Similar effects can be obtained.

Next, a third embodiment of the present invention will be described. FIG. 4 is a block diagram showing an optical amplifying device according to the third embodiment. In the drawing, the same elements as those in FIGS. 1 and 3 are denoted by the same reference numerals, and description thereof will be omitted here. The optical amplifying device 16 shown in FIG. 4 differs from the optical amplifying device 8 in that a wavelength separation detector 13 is provided instead of the wavelength separation light detector 12, and this wavelength separation detector 13 An optical filter 18 (A) that scans the wavelength band and sequentially passes and extracts optical signals of each wavelength.
OTF) and a photodetector 20 that converts an optical signal extracted by the optical filter 18 into an electric signal.

The signal detecting means 14 is provided with the photodetector 2
0 detects the highest or lowest voltage among the voltages output for each wavelength (that is, for each channel) and supplies the detected voltage to the automatic level control circuit 132.
Therefore, also in the optical amplifying device 16, the automatic level control circuit 132 uses the optical attenuator 1 based on the strength of the entire optical signal of each wavelength output from the optical fiber 110 as in the related art.
08 instead of controlling the optical attenuator 108 based on the strength of the strongest or weakest optical signal.

As a result, for example, even when the number of channels is reduced and the number of wavelengths used is reduced,
As a result, the voltage supplied to the automatic level control circuit 132 does not decrease, and the intensity of the optical signal output from the optical fiber 110 of the second optical amplifying unit 106 is set to be equal to the case of the original number of channels. The same strength can be controlled. Since the temperature sensor 4 and the reference voltage generating circuit 6 according to the present invention operate independently of the wavelength separation light detector 12 and the signal detecting means 14, the present embodiment also has the same configuration as the above embodiment. Similar effects can be obtained.

[0025]

As described above, in the optical amplifying device of the present invention, the temperature sensor detects the temperature around the optical fiber and outputs a signal representing the detection result, and the AGC control circuit outputs the signal from the temperature sensor. The control circuit controls the AGC circuit based on the AGC circuit to output a control voltage for supplying stronger excitation light to the optical fiber as the temperature around the optical fiber is higher. For example, in an optical fiber doped with erbium, as the temperature increases, the gain decreases as the wavelength increases. In addition, the gain characteristics of this optical fiber change depending on the intensity of the pump light,
When the pump light is intensified, the gain increases as the wavelength becomes longer.
Therefore, when the AGC circuit is controlled by the AGC control circuit so as to supply stronger pumping light to the optical fiber as the temperature increases, the gain characteristic changes due to the temperature change and the pumping light intensity changes. As a result, the change in the gain characteristic cancels out, and the gain characteristic of the optical fiber becomes flat. That is, in the optical amplifying device of the present invention, the flatness of the gain characteristic does not deteriorate even when the temperature changes.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an optical amplifier according to the present invention.

FIGS. 2A to 2F are graphs showing gain characteristics and the like in a second optical amplifier.

FIG. 3 is a block diagram illustrating an optical amplifying device according to a second embodiment.

FIG. 4 is a block diagram illustrating an optical amplifying device according to a third embodiment.

FIG. 5 is a block diagram illustrating an example of a conventional optical amplifier.

[Explanation of symbols]

2 ... optical amplifying device, 4 ... temperature sensor, 6 ... reference voltage generating circuit, 8 ... optical amplifying device, 10 ... optical splitter, 12
…… Wavelength separation photodetector, 13 …… Wavelength separation photodetector, 1
4 ... signal detection means, 16 ... optical amplifier, 18 ... optical filter, 20 ... photodetector, 102 ... optical amplifier,
104: first optical amplifier, 106: second optical amplifier, 108: optical attenuator, 110: optical fiber, 11
2 ... optical coupler, 114 ... light emitting means, 116 ... input port, 118 ... optical fiber body, 120 ... output port, 122 ... optical splitter, 124 ... optical splitter, 12
6 photodetector, 128 photodetector, 130 AG
C circuit, 132 ... Automatic level control circuit.

Claims (9)

[Claims] 1. An optical fiber for amplifying a plurality of optical signals having different wavelengths, and an excitation light having an intensity corresponding to a control voltage is supplied to the optical fiber to control an amplification degree of the optical signal in the optical fiber. Amplification degree control means, based on an input optical signal and an output optical signal of the optical fiber, generating the control voltage to stabilize a ratio between the intensity of the input optical signal and the intensity of the output optical signal of the optical fiber. An optical amplifier comprising: an AGC circuit that supplies the amplification degree control unit; a temperature sensor that detects a temperature around the optical fiber and outputs a signal indicating a detection result; and an output signal of the temperature sensor. The AGC circuit is controlled on the basis of the AGC circuit, and the higher the temperature around the optical fiber, the higher the control voltage for supplying stronger excitation light to the optical fiber.
An optical amplifying device comprising: an AGC control circuit for outputting the signal to a circuit. 2. The amplification degree control means according to claim 1, wherein said amplification degree control means is inserted into an input portion or an output portion of said optical fiber, passes light propagating through said optical fiber, and introduces pump light supplied from outside into said optical fiber. An optical coupler that propagates light toward the optical fiber body, and a light emitting unit that generates light having an intensity corresponding to the magnitude of the control voltage and supplies the light to the optical coupler as the excitation light. The optical amplifying device according to claim 1. 3. A first optical splitter inserted into an input section of the optical fiber, a second optical splitter inserted into an output section of the optical fiber, and a branch by the first optical splitter. A first optical detector for detecting the optical signal and outputting an electric signal indicating the intensity of the optical signal; and detecting the optical signal branched by the second optical splitter to detect the optical signal. A second photodetector for outputting an electric signal representing the intensity;
The circuit generates the control voltage based on output signals of the first and second photodetectors to stabilize a ratio between an input optical signal intensity and an output optical signal intensity of the optical fiber. The optical amplifying device according to claim 1. 4. An optical attenuator inserted into an input section of the optical fiber, light detecting means for detecting an intensity of an output optical signal of the optical fiber and outputting an electric signal indicating a detection result, and An automatic level control circuit for controlling the optical attenuator by outputting an electric signal to keep the intensity of the output optical signal of the optical fiber substantially constant based on the output signal of the detection means. The optical amplifying device according to claim 1, wherein 5. A wavelength separation photodetector for detecting an intensity of an optical signal for each optical signal having a different wavelength and outputting an electric signal indicating a detection result, wherein the wavelength separation photodetector comprises: Signal detecting means for detecting an electric signal representing the intensity of the strongest or weakest optical signal among the electric signals to be output and supplying the electric signal to the automatic level control circuit. Item 5. The optical amplifying device according to Item 4. 6. The wavelength separation photodetector includes a plurality of optical filters for extracting optical signals of respective wavelengths, and a plurality of photodetectors for converting the optical signals extracted by each optical filter into electric signals. 6. The method according to claim 5, wherein
The optical amplifying device as described in the above. 7. A second optical filter that scans a wavelength band of an optical signal and sequentially passes and extracts optical signals of respective wavelengths, wherein the wavelength separation optical detector extracts the optical signal of each wavelength. And a third photodetector for converting the optical signal into an electric signal.
The optical amplifying device as described in the above. 8. The optical amplifier according to claim 1, wherein said optical fiber is an erbium-doped optical fiber. 9. The optical amplifying device according to claim 2, wherein said light emitting means comprises a laser light emitting diode.