JP2011170372A - Light amplifier using raman amplification and raman excitation light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for making Raman amplifier a wide band, and a method for controlling excitation light sources of three or more when excitation light sources are increased to plural in order to flat wavelength characteristics of output and gain, and when a result in which gain is obtained by the excitation light is monitored. <P>SOLUTION: An excitation light generating means is made a block state, a wavelength band of input/output monitor of a signal light is monitored classifying the number of block of the excitation light generating means or more and the number of signal channels or less. On the basis of the result, output power of the excitation light of each wavelength band is adjusted by using a control algorithm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention is a Raman amplifier that can be used for amplification of signal light in various optical communication systems, and is particularly suitable for amplification of wavelength division multiplexed light.

Most of the optical amplifiers used in current optical communication systems
This is a rare earth doped optical fiber amplifier. In particular, an optical fiber amplifier (abbreviated as EDFA) doped with Er is widely used. The wavelength division multiplexing (WDM) optical transmission system utilizing the wide gain band of EDFA is a transmission system capable of increasing communication capacity by transmitting optical signals of a plurality of wavelengths through one optical fiber.
This WDM optical transmission system has the advantages that the existing optical fiber can be used and the introduction cost is low, and the use of an optical amplifier or the like makes the transmission line bit-rate free and facilitates future upblade.
The band with a small loss (about 0.3 dB / km or less) of the optical fiber transmission line is 1450 nm to 1650 nm, but the practical amplification band of EDFA is 1530 nm to 1610 nm. EDFA is only applied to some of these. In this context, research and development of technologies that increase the transmission capacity with a single optical fiber are being actively pursued.
On the other hand, in a WDM optical communication system, in order to obtain a predetermined transmission characteristic, it is necessary to suppress variations in optical power between channels to 1 dB or less in each optical repeater stage.
This is because the upper limit of optical power is limited by the nonlinear effect, and the lower limit is limited by the received SNR.
Here, it is necessary to reduce loss wavelength characteristics of a transmission line, a dispersion compensating fiber, and the like constituting the WDM optical communication system. In an actual WDM optical communication system, wavelength characteristics occur in the optical transmission power between channels due to the following matters.
(1) Loss wavelength characteristics of transmission path due to Rayleigh scattering (2) Wavelength characteristics of dispersion compensator (3) Loss wavelength characteristics of transmission path due to stimulated Raman scattering (4) Wavelength characteristics of gain of optical amplifier (5) Transmission path, Specifically, the temperature characteristics of the dispersion compensator and the optical amplifier are as described above when, for example, a 1.3 μm zero-dispersion single mode fiber having a length of 100 km is used for the optical transmission line when the wavelength band of the signal is 1530 to 1610 nm. The deviation of the optical transmission power generated due to 1) and (3) is 7 dB.
The deviation due to the above (2) is about 0.5 dB when a general dispersion compensating fiber is used as a dispersion compensator, and the deviation due to the above (4) is when the general EDFA is used. 1 dB. Furthermore, the deviation due to the above (5) can be estimated to be about 0.3 dB when each optical device is used.
As described above, it is understood that the wavelength characteristic of the loss of the transmission line due to stimulated Raman scattering has the greatest influence on the wavelength characteristic of the signal.
The key component of the current wavelength division multiplexing transmission system is an EDFA that can amplify multi-wavelength signals at once. This EDFA transmits low noise, outputs a predetermined output, compensates for a predetermined gain, and outputs variations between channels. It had a characteristic that can be reduced.
In the future, in order to increase transmission capacity and enable ultra-long distance transmission, optical amplifiers having different characteristics while having these characteristics of EDFA are required. As an expansion of the band for increasing the transmission capacity, a Raman amplifier has attracted attention. The Raman amplifier can amplify at a frequency that is Stokes-shifted by the Raman shift amount of the amplification medium from the pumping light frequency. If a pumping light source having an arbitrary wavelength can be prepared, it can be amplified at an arbitrary wavelength.
For example, J. et al. Kani et al., Electronics Letter, vol. 34 pp. 1745 reports a gain of 1505-1522 nm outside the EDFA band using an excitation wavelength of 1420 nm.
In addition, M.M. Takeda et al., OSA TOPS vol. 30 pp. In 101-105 (1999) and Japanese Patent Laid-Open No. 2000-98433, a Raman amplifier is used as a correction for the output deviation of the EDFA, and the Raman amplifier is used as a transmission wavelength loss correction for the transmission line due to stimulated Raman scattering. Attention has been focused on Raman amplifiers for the reason that pump light can be introduced into the channel and the transmission channel can be used for output deterioration correction using a Raman amplification medium.
The following three applications can be considered as Raman amplifiers: (a) Use of EDFA outside the applicable wavelength band, (b) EDFA output deviation correction and optical SNR improvement, (c) Stimulated Raman scattering compensation of transmission line It is. In the wavelength division multiplexing transmission system, the characteristics first required for all of these applications are a wide band and a flat wavelength characteristic.

JP 2000-098433 A JP 09-211507 A

In order to widen the bandwidth of the Raman amplifier, it is considered to use a plurality of pumping lights having different wavelengths as disclosed in JP-A-2000-98433. JP 2000-98433 and M.K. Takeda et al. OSA TOPS vol. 30, pp. In 101-105 (1999), the Raman amplification output is monitored or the output after the inline amplifier is inserted after the Raman amplifier is used to secure the band of the Raman amplifier so that the gain deviation or the output deviation is reduced. The output of a plurality of excitation LDs is controlled.
However, the embodiment of Japanese Patent Application Laid-Open No. 2000-98433 only shows the case of controlling the excitation light sources divided into two groups. Takeda et al. Also shows a case where two excitation light sources are used. When there are three or more excitation light sources, algorithms for constant output power control, constant gain control, and wavelength characteristic flattening control become very complicated.
In other words, as the number of excitation wavelengths or the number of excitation light sources increases in order to broaden the bandwidth and flatten the wavelength characteristics, a complex control algorithm is required but there is no appropriate algorithm, and an optical system of a Raman amplifier using a multi-wavelength excitation light source. This is a factor that hinders the practical application of the system.

In the present invention, when performing Raman amplification, the output power is constantly controlled so as to widen the band using a plurality of pumping light wavelengths or pumping light sources, and to flatten the wavelength characteristics or to have characteristics having a specific inclination. A control algorithm for easily performing constant gain control and wavelength characteristic flattening control is provided.
The first means is to input a wavelength-multiplexed light in which a plurality of signal lights arranged in any of a plurality of channels are wavelength-multiplexed and to perform Raman amplification, and to output a plurality of pump lights having different wavelengths, respectively. A plurality of pumping light sources, pumping light supply means for outputting the plurality of pumping lights to the optical amplifying medium, and an output for monitoring the power of the wavelength multiplexed light output from the amplifying medium for each of a plurality of wavelength bands Excitation light control means for controlling the plurality of excitation light sources based on the monitoring means, the monitoring result of the output monitoring means, and the wavelength characteristics of the gain generated in the optical amplification medium by the excitation of each of the plurality of excitation lights The plurality of wavelength bands each include at least one of the channels, and are wavelength bands that are Raman-amplified in the optical amplification medium by any of the plurality of pump lights. And wherein the door.
The second means is to input a wavelength-multiplexed light in which a plurality of signal lights arranged in any of a plurality of channels are wavelength-multiplexed, an optical amplifying medium for performing Raman amplification, and a plurality of pumping lights having different wavelengths, respectively. A plurality of pumping light sources for outputting, a pumping light supplying means for outputting the plurality of pumping lights to the optical amplifying medium, and monitoring the power of the wavelength multiplexed light input to the optical amplifying medium for each of a plurality of wavelength bands; Input monitoring means, and output monitoring means for monitoring the power of each of the plurality of wavelength bands of the wavelength multiplexed light output from the optical amplification medium;
A monitoring result of the input monitoring means and the output monitoring means, and a pumping light control means for controlling the plurality of pumping light sources based on a wavelength characteristic of a gain generated in the optical amplifying medium by each pumping of the plurality of pumping lights. The plurality of wavelength bands each include at least one of the channels, and are wavelength bands that are Raman-amplified in the optical amplification medium by any of the plurality of pump lights. To do.
The third means is to input a wavelength-multiplexed light in which a plurality of signal lights arranged in any one of a plurality of channels are wavelength-multiplexed to perform Raman amplification, and to output a plurality of pumping lights having different wavelengths, respectively. A plurality of pumping light sources, pumping light supply means for outputting the plurality of pumping lights to the optical amplifying medium, and the wavelength multiplexed light output from the amplifying medium, the first wavelength band and the second wavelength band A band separation means for separating the first wavelength band, a first rare earth element doped fiber for amplifying the separated first wavelength band light, and a second rare earth element for amplifying the separated second wavelength band light. A doped fiber, a first monitor means for monitoring the output light of the first rare earth element doped fiber, a second monitor means for monitoring the output light of the second rare earth element doped fiber, the first monitor means, Of the second monitoring means And an excitation light control means for controlling each of the plurality of excitation light sources on the basis of the result of the detection and the wavelength characteristic of the gain generated in the optical amplification medium by the excitation of each of the plurality of excitation lights. The plurality of wavelength bands each include at least one of the channels, and are wavelength bands that are Raman-amplified in the optical amplification medium by any of the plurality of excitation lights.
A fourth means is a Raman pumping light source that pumps an optical amplifying medium that performs Raman amplification by inputting wavelength-multiplexed light in which signal light arranged in a plurality of channels is wavelength-multiplexed, and a plurality of pumps having different wavelengths. A plurality of pumping light sources that respectively output light, a pumping light supply unit that outputs the plurality of pumping lights to the optical amplification medium, and at least one channel of the wavelength-multiplexed light output from the amplification medium. Monitoring means for monitoring the power for each of a plurality of wavelength bands included, the monitoring result of the monitoring means, and the wavelength characteristics of the gain generated in the optical amplifying medium due to the excitation of each of the plurality of excitation lights. And pumping light control means for controlling the output power of each pumping light.

In order to increase the bandwidth of the Raman amplifier and to flatten the wavelength characteristics of the output and gain, when multiple pumping light sources are used and the result of gain generated by the pumping light is monitored, the number of pumping light sources is three or more. Regarding control.
In the present invention, a simple control algorithm is used by blocking the pumping light generating means and monitoring the wavelength band of the input / output monitor of the signal light by dividing it into the number of blocks of the pumping light generating means and the number of signal channels. Thus, it is possible to control the wavelength characteristic deviation of the output power and the gain, the constant output control, and the constant gain control.

Diagram showing the relationship between pump light and gain wavelength during Raman amplification Diagram showing band expansion of Raman amplification by wavelength multiplexing of excitation light source The figure which shows the 1st implementation structure The figure which shows the wavelength characteristic of the single excitation light source block The figure which shows the wavelength characteristic of the single excitation light source block The figure explaining the control to make the wavelength characteristic constant Control flow chart of excitation light control unit of first embodiment configuration Configuration diagram when the number of excitation light source blocks and the number of monitor blocks are arbitrary in the first embodiment configuration Diagram showing wavelength characteristics when the number of monitor blocks is arbitrary The figure which shows the specific structure of the excitation light source block of the structure of FIG.3 and FIG.8, and a wavelength multiplexing coupler The figure which shows the structure at the time of weighting in 1st implementation structure The figure which shows 2nd implementation structure Control flow chart of excitation light control unit of second embodiment The figure which shows the modification of 2nd implementation structure The figure which shows the 3rd implementation structure

The detailed description of the present invention will be described below. As shown in FIG. 1, the Raman amplification produces a gain at the signal wavelength shifted from the pumping light wavelength by the Raman shift amount of the amplification medium, and the Raman shift amount and the Raman band are given uniquely to the substance (amplification medium). Is.
HYPERLINK "JavaScript: void (0)" Figure 1 shows that when the excitation wavelength is shifted to the longer wavelength side, the center wavelength and gain band of the gain are shifted to the longer wavelength side by the same amount as the shift amount of the excitation wavelength. Has been. Therefore, Raman amplification is an optical amplification technique that can obtain a gain at an arbitrary wavelength as long as an excitation light source having an arbitrary wavelength is prepared. By making the excitation light sources having slightly different excitation wavelengths incident on the amplification medium at once, broadband optical amplification can be performed as shown in FIG.
A first embodiment of the present invention is shown in FIG. 0 is an input port, 1 is a Raman amplification medium, 2 is a multiplexing coupler, 3 is a branching coupler, 4 is a multiplexing coupler, 5 is a wavelength separation coupler, 6-1 to 6-3 are excitation light source blocks, 7-1 to 7-3 is a light receiving element, and 8 is an excitation light control unit.
Wavelength multiplexed light obtained by wavelength multiplexing a plurality of signal lights is incident on the Raman amplification medium 1 which is pumped backward from the input port of the Raman amplifier. The multiplexing coupler 4 is a wavelength multiplexing coupler that multiplexes pumping lights having average wavelengths λp1 to λp3 from pumping light source blocks 6-1 to 6-3 having different center wavelengths. The multiplexing coupler 2 is a wavelength multiplexing coupler that wavelength-multiplexes the pumping light of wavelengths λp1 to λp3 from the multiplexing coupler 4 and wavelength multiplexed light obtained by wavelength multiplexing a plurality of signal lights in the Raman amplification medium 1.
The branching coupler 3 is a beam splitter that branches the wavelength multiplexed light amplified by the Raman amplifying medium 1 on a one-to-one basis. The wavelength separation coupler 5 is a wavelength band branching coupler that divides the Raman gain wavelength band generated by the pumping light from the pumping light source blocks 6-1 to 6-3 into three wavelength band blocks (monitor blocks).
The light receiving elements 7-1 to 7-3 receive each of the three bands separated by the wavelength separation coupler 5 and perform optical / electrical conversion. The excitation light control circuit 8 controls the output power of the average wavelengths λp1 to λp3 of the excitation light source blocks 6-1 to 6-3 using the output from the light receiving element.
The control principle of the excitation light control circuit 8 will be described below.
The average excitation wavelength of the excitation light source block 6-1 is lp1, the output power of the excitation light source block 6-1 is Pp1, the average excitation wavelength of the excitation light source block 6-2 is lp2, and the output power of the excitation light source block 6-2 is Pp2. The average excitation wavelength of the excitation light source block 6-3 is lp3, and the output power of the excitation light source block 6-3 is Pp3.
The average output power of the wavelength band block (monitor block 1; average wavelength ls1) received by the light receiving element 7-1 is Ps1, and the average of the wavelength band block (monitor block 2; average wavelength ls2) received by the light receiving element 7-2. The output power is Ps2, and the average output power of the wavelength band block (monitor block 3; average wavelength ls3) received by the light receiving element 7-3 is Ps3.
FIG. 4A shows the output of the wavelength multiplexed light when only the pumping light source block 6-1 is operated and operated with the average pumping wavelength λp1 and the average pumping output power Pp1. The thin solid line indicates the output spectrum in the wavelength band block 1 (average wavelength ls1), and the thick solid line indicates the average output power Pp1 of the wavelength band block 1.
FIG. 4B shows the output of wavelength multiplexed light when only the pumping light source block 6-2 is operated and operated with the average pumping wavelength λp2 and the average pumping output power Pp2. The thin solid line indicates the output spectrum in the wavelength band block 2 (average wavelength ls2), and the thick solid line indicates the average output power Pp2 of the wavelength band block 2.
FIG. 4C shows the output of wavelength multiplexed light when only the pumping light source block 6-3 is operated and operated with the average pumping wavelength λp3 and the average pumping output power Pp3. The thin solid line indicates the output spectrum in the wavelength band block 3 (average wavelength ls3), and the thick solid line indicates the average output power Pp3 of the wavelength band block 3.
The signal light output monitor block to which the excitation light source block 6-1 contributes most is the block 1, the signal light output monitor block to which the excitation light source block 6-2 contributes most is the block 2, and the excitation light source block 6-3 is the most. It can be seen that the contributing signal light output monitor block is block 3.
At the same time, the excitation light source block 6-1 contributes to the signal light output monitor block ls2 and the signal light output monitor block ls3, and the excitation light source block 6-2 also contributes to the signal light output monitor block ls1 and the signal light output monitor block ls3. The excitation light source block 6-3 also contributes to the signal light output monitor block ls1 and the signal light output monitor block ls2.
Therefore, when using multiple wavelengths of pumping light to make a broadband optical amplifier, controlling the power of one pumping light source block results in a wide range of wavelength bands where gain is generated by the pumping light. It can be seen that multiple band blocks are affected.
In order to obtain a predetermined amplified signal power, it is sufficient to multiply the power of the excitation light source by a gain coefficient. Therefore, the average power fluctuation amount of the excitation light output of the excitation light source blocks 6-1 to 6-3 is ΔP, and the light receiving element 7-1. To 7-3, ΔPs is the amount of fluctuation in the average output power in the band where the gain is generated by the excitation light obtained from 7-3, and A is the average gain coefficient.

It becomes.
Therefore, in order to eliminate the wavelength characteristic deviation of the output power of each wavelength band block, if ΔPp is adjusted so that the power level of the wavelength multiplexed light in each wavelength band separated into three by the wavelength separation coupler 5 becomes the same. good.
ΔPp can be adjusted by changing the optical output power of the pumping light source, can be adjusted by changing the pumping wavelength and shifting the center-of-gravity wavelength, and can also be adjusted by changing the pumping light wavelength width. Here, an example of adjustment for varying the optical output power is shown.
As shown in FIG. 4, since the gain wavelength band generated by one excitation light source block is wide and has a gain across each monitor block, when one excitation light source block is changed, another monitor It is necessary to calculate Equation 1 in consideration of the influence on the wavelength of the block. In other words, it is necessary to control the output power of each pumping light block based on the wavelength characteristic of the gain generated in the optical amplifying medium for each pumping light source block.
Here, the average gain coefficient that the average output power fluctuation ΔPp1 of the average pumping wavelength lp1 of the pumping light block 6-1 has on the average output power fluctuation ΔPs1 of the block 1 of the monitoring block is A11, and the pumping light wavelength of the pumping light source block 6-1 The average output power fluctuation ΔPp1 of lp1 affects the average gain coefficient A12 on the average output power fluctuation ΔPs2 of the block 2 of the monitor block, and the average output power fluctuation ΔPp1 of the excitation wavelength lp1 of the pump light source block 6-1 is that of the block 3 of the monitor block. The average gain coefficient that affects the average output power fluctuation ΔPs3 is A13, and the average gain coefficient that the average output power fluctuation ΔPp2 of the excitation wavelength lp2 of the excitation light source block 6-2 has on the average output power fluctuation ΔPs1 of the monitor block block 1 is A21. The average output power fluctuation ΔPp2 of the excitation wavelength lp2 of the light source block 6-2 is equal to the level of the block 2 of the communication monitor block. The average gain coefficient that affects the output power fluctuation ΔPs2 is A22, the average gain coefficient that the average output power fluctuation ΔPp2 of the excitation wavelength lp2 of the excitation light source block 6-2 has on the average output power fluctuation ΔPs3 of the block 3 of the monitor block is A23, and the excitation light source The average gain coefficient that the average output power fluctuation ΔPp3 of the pump wavelength lp3 of the block 6-3 has on the average output power fluctuation ΔPs1 of the block 1 of the monitor block is A31, and the average output power fluctuation ΔPp2 of the pump light source block 6-3 of the pump wavelength lp3 A32 has an average gain coefficient affecting the average output power fluctuation ΔPs2 of the monitor block block 2, and the average output power fluctuation ΔPp3 of the pumping light source block 6-3 of the pumping light source block 6-3 has an influence on the average output power fluctuation ΔPs3 of the block 3 of the monitor block. The average gain coefficient is defined as A33.
FIG. 5A shows the average output power difference between the block 1 of the monitor block, the block 2 of the monitor block, and the block 3 of the monitor block with respect to the pump light output power difference when only the pump light source block 6-1 is operated. Show. The respective inclinations correspond to A11, A12, and A13.
In addition, when only the pumping light source block 6-2 is operated in FIG. 5B, the output monitor block block 1, the output monitor block block 2, and the output monitor block block 3 with respect to the pumping light output power difference. The average output power difference is shown. The respective inclinations correspond to A21, A22, and A23.
The average output of block 1 of the output monitor block, block 2 of the output monitor block, and block 3 of the output monitor block with respect to the pumping light output power difference when only the pumping light source block 6-3 is operated in FIG. The power difference is shown. The respective inclinations correspond to A31, A32, and A33.
An average gain coefficient matrix [A] having them as elements can be obtained.

As shown in FIG. 6 (a), the average output of the block 1, block 2 and block 3 of the output monitor block in the case of the signal light spectrum having a large wavelength characteristic of the signal light output is a thick solid line in the figure, and is in the entire wavelength band. The average output is indicated by a broken line as Pf.
As shown in FIG. 6B, the wavelength characteristic deviation of the wavelength multiplexed optical output is reduced by the Raman-amplified wavelength for the average outputs Ps1 to Ps3 of the block 1, block 2 and block 3 of the output monitor block. This means matching with the multiplexed light output Pf (average output of all wavelength bands).

In order to keep the output difference (tilt) small in the entire wavelength band where the Raman gain occurs in the Raman amplifying medium 1, the pumping light output Pp1 to Pp3 of the pumping light source blocks 6-1 to 6-3 is corrected so as to satisfy the above equation. The amounts may be calculated from the following equations as ΔPp1, ΔPp2, and ΔPp3.

That is, the HYPERLINK “JavaScript: void (0)” excitation light control unit 8 in FIG. 3 monitors the output power by dividing the wavelength multiplexed light in which a plurality of signal lights are wavelength-multiplexed into monitor blocks of a predetermined wavelength band, Averaging is performed by dividing the total output of the monitor block in each wavelength band by the number of channels, and the excitation wavelength of each excitation light source block required to reduce the output power difference in the entire wavelength band is the wavelength of each monitor block. The average output power difference of the pumping light is calculated by the above equation 5 to control the power of the pumping light output from each pumping light source block.
Then, feedback control is performed about 1 to 10 times until a predetermined wavelength characteristic deviation is obtained. By performing such control processing, the average power in the Raman gain wavelength band generated by the pump light can be set to a constant value of power Pf.
In the configuration of FIG. 3, the excitation light control unit 8 can be realized by being controlled by a processor such as a CPU according to the flow of FIG. 7.
As step 1: Control processing is started.
As Step 2: Average output powers Ps1 to Ps3 in the monitor block are obtained from outputs of the light receiving elements 7-1 to 7-3.
As Step 3, the average wavelength output powers Ps1 to Ps3 in the monitor block are compared with the target wavelength multiplexed light output value Pf to obtain ΔPs1 to ΔPs3.
As Step 4: When the difference between ΔPs1 to ΔPs3 and Pf is within the allowable range, the operation is stopped, and when it is within the allowable range, the process goes to Step 5.
As step 5, the control amounts ΔPp1 to ΔPp3 of the power levels Pp1 to Pp3 of λp1 to λp3 of the pump light source block are obtained from ΔPs1 to ΔPs3 using the inverse matrix of the average gain coefficients A11 to A33 that each pump light exerts on each monitor block. .
As Step 6, the control amounts ΔPp1 to ΔPp3 are added to the current Pp1 to Pp3 to control the output powers Pp1 to Pp3 of the excitation light source blocks 6-1 to 6-3.
Step 7: The control process is terminated.
In FIG. 3, as an example, there are three pump light source blocks, and the wavelength band monitor blocks that generate the gain generated by the pump light from the pump light source block are divided into three, but these numbers are arbitrary as required. Can be set to
A case where the number of excitation light source blocks and monitor blocks is set to an arbitrary number is shown in FIG. 8 for HYPERLINK “JavaScript: void (0)”. In the figure, it is assumed that the number of excitation source blocks is n (6-1 to 6-n) and m is a monitor block of wavelength multiplexed light.
The wavelength band of the Raman amplification gain generated by the pumping light here is shown in FIG. 9 and divided into m monitor blocks of the wavelength multiplexed light of the wavelength separation coupler 5. The fluctuation amount ΔPp of the pumping light power control is an n × 1 matrix, and the. The difference ΔPs between the average value of the wavelength multiplexed optical power and the target control value is an m × 1 matrix, and A is an n × m matrix.

In this case, ΔPpi is the fluctuation amount of the average output power of the block of the excitation source, and ΔPsj is the fluctuation amount of the average output power of the signal light monitor block. Since the fluctuation amount is used, it is not necessary to convert the monitor output power to the main signal output power. It can be seen that the inverse matrix [A] -1 of [A] may be obtained in order to obtain ΔPpi associated with ΔPsj. Therefore,

In order to reduce the deviation of the average output power between the blocks, the wavelength characteristic of the signal light output power is flattened.
In the first embodiment, the number of pumping light source blocks and the number of monitor blocks can be arbitrarily configured, but the number of monitor blocks should be less than or equal to the number of signal light channels multiplexed in the wavelength multiplexed light and more than the number of pumping light source blocks. desirable.
A specific configuration in the configuration of FIG. 3 is shown in FIG. 10 of HYPERLINK “JavaScript: void (0)”.
In the figure, 24 and 25 are WDM couplers, 61 to 63 are polarization combining couplers, 51 to 56 are fiber grating filters, and 81 to 86 are semiconductor lasers.
The excitation light source blocks 6-1 to 6-3 are respectively composed of combinations of two combinations 83 and 84 of semiconductor lasers 81 and 82 having slightly different wavelengths. (In this example, the wavelength interval of the semiconductor laser is about 4 nm)
Light from the semiconductor lasers 81 to 86 is transmitted through the fiber grating filters 51 to 56 at specific wavelengths (in this example, 1429.7 nm, 1433.7 nm, 1454.0 nm, 1480.0 nm, 1484.5 nm, and 1488.5 nm, respectively). Wavelength) to be reflected by the semiconductor lasers 81 to 86, respectively, and the semiconductor lasers 81 to 86 and the phi-hagrating filters 51 to 56 take a resonant structure and output excitation light of a specific wavelength.
The two pumping lights of each pumping light source block are respectively subjected to polarization synthesis by the polarization constituting couplers 61 to 63, and become the output of the pumping light source block. The reason for performing polarization synthesis is to eliminate the polarization dependence of Raman amplification. The multiplexing coupler 4 is composed of WDM couplers 24 and 25.
The WDM coupler 25 has a characteristic of reflecting light having a wavelength from the excitation light source block 6-2 and passing the wavelength from the excitation light source block 6-3. The WDM coupler 24 has a characteristic of reflecting light having a wavelength from the excitation light source block 6-1 and passing the wavelengths from the excitation light source block 6-2 and the excitation light source block 6-3.
In FIG. 10, the center of the semiconductor laser and the fiber grating in the excitation light source block outputs light having slightly different wavelengths, but light of the same wavelength may be used. In addition, the light of the excitation light source block is not necessarily constituted by a plurality of semiconductor lasers, and when a polarization-independent excitation light source or the like is used, it may be a single light source.
In the first embodiment, the target wavelength-multiplexed light output value is set to Pf, and the average power of all wavelength bands is controlled to be equal to Pf. Therefore, constant output control can be performed in all wavelength bands. . As a modified example of this constant output control, the constant output control can be performed individually for each wavelength block by defining Pf as Pf1, Pf2, and Pf3 for each wavelength band of the monitor block and comparing them.
In this case, Pf1, Pf2, and Pf3 are determined corresponding to each monitor block instead of Pf in step 4 of the flowchart of FIG. The excitation light control unit 8 can be controlled by subtracting the corresponding Ps1, Ps2, and Ps3 from Pf1, Pf2, and Pf3, respectively.
Further, as shown in FIG. 11 in which Pf is changed, variable or fixed attenuators 71 to 73 are provided in front of the light receiving elements 7-1 to 7-3 in FIG. 3 to arbitrarily weight each monitor block, Output constant control can be performed individually for each wavelength block.
In the first embodiment, as a Raman amplifying medium, not only a normal 1.3 zero micron fiber, but also a dispersion compensating fiber (DCF), a dispersion shifted fiber (DSF), a non-zero dispersion shift, which has a small effective area and a large nonlinearity. It is also possible to use a fiber (NZDSF). If these non-linear fibers are used, the fiber serving as the Raman amplifying medium for obtaining the necessary gain can be short, and concentrated amplification can be realized.
In the first embodiment, the monitor block is constituted by the wavelength demultiplexing couplers 5 and 10 and the light receiving elements 7-1 to 11-1, but these can be replaced by a spectrum analyzer.
A second implementation configuration is shown in FIG. In FIG. 12, the same components as those of FIG. In the figure, 9 is a branching coupler, 10 is a wavelength separation coupler, and 11-1 to 11-3 are light receiving elements. The branch coupler 9 is a beam splitter that is provided at the input port of the Raman amplifier and branches a plurality of wavelength-multiplexed light signals that are input to the input port at a branch ratio of 10: 1.
The wavelength demultiplexing coupler 10 generates wavelength-multiplexed light from the 1 / 10-side port of the branching coupler 9 by the Raman gain wavelength generated by the pumping light from the pumping light source blocks 6-1 to 6-3, like the wavelength demultiplexing coupler 5. This is a wavelength separation coupler that separates a band into three wavelength band blocks (monitor blocks). The light receiving elements 11-1 to 11-3 are provided corresponding to the three monitor blocks, respectively, and convert the optical power of each monitor block into an electrical signal.
The average wavelength of the monitor block 1 separated by the wavelength separation coupler 10 is ls1, the average output power is Pin_s1, the average wavelength of the monitor block 2 is ls2, the average output power is Pin_s2, the average wavelength of the monitor block 3 is s3, and the average output power is Pin_s3.
Thereafter, the signal light is incident on the Raman amplification medium 1 which is pumped backward. The excitation light source blocks 6-1 to 6-3 may be configured as shown in FIG. 10, and can be realized with various configurations similar to those in the first embodiment.
The signal amplified by the amplification medium 1 is then branched by a 10 to 1 branch coupler 3, and the signal light output from the 1/10 port is sent to the input port side by the wavelength separation coupler 5 as in FIG. It is divided into the same three wavelength band blocks as the provided wavelength separation coupler 10. The wavelength band block of the wavelength separation coupler 5 corresponds to the average wavelengths ls1, ls2, and ls3 of the monitor block of the wavelength separation coupler 10, respectively. The wavelength multiplexed optical output power is photoelectrically converted by the light receiving elements 7-1 to 7-3.
As in FIG. 3, the average output power of the monitor block average wavelength ls1 of the wavelength separation coupler 5 is Ps1, the average output power of the monitor block average wavelength ls2 is Ps2, and the average output power of the monitor block average wavelength ls3 is Ps3. . The excitation light controller 8 controls the gain to be a predetermined value by monitor inputs from the light receiving elements 7-1 to 7-3 and 11-1 to 11-3.
The specific operation of the control unit 8 in FIG. 12 will be described below. The average gains G1, G2, and G3 of each monitor block are input from Ps1, Ps2, and Ps3 obtained by the light receiving elements 7-1 to 7-3 after the wavelength multiplexed light amplified by the amplification medium 1 is separated by the wavelength separation coupler. It is obtained by subtracting Pin_s1, Pin_s2, and Pin_s3 obtained by the light receiving elements 11-1 to 11-3 after being separated by the port side wavelength separation coupler 10.

The pump light average output power of each monitor block and the wavelength light average gain of each monitor block can be linked by the average gain coefficient of each monitor block, the pump light average output power fluctuation amount is ΔPp, and the signal light average output power fluctuation amount Is ΔG and the average gain coefficient is A,

It becomes.
[A] used in Example 1 indicates the slope of the signal light average output power of the pumping light average output power, and the following relationship holds similarly for the gain A defined here.

The target gain level is the average gain Gf of all wavelength bands, the average gain of each monitor block is G1, G2, G3, the difference between Gf and G1 is ΔG1, the difference between Gf and G2 is ΔG2, and the difference between Gf and G3 Is ΔG3.

In order to suppress the gain wavelength deviation (tilt) to be small in the entire wavelength band, the average gain between the monitor blocks may be adjusted so as to match the average gain Gf of the entire wavelength band.
Here, by setting Gf to a predetermined value for making the gain constant, all wavelengths can be controlled to a constant gain.

Therefore, ΔPp1, ΔPp2, and ΔPp3 may be calculated from Expression 13 using Expression 11.

That is, in order to reduce the gain difference in the entire wavelength band, the pumping light control unit 8 obtains all the outputs of the wavelength multiplexed light monitor block and performs an averaging process by dividing the total output of the monitor block by the number of channels. In addition, in consideration of the influence of the gain of each pumping light source block on the wavelength of each monitor block, the average output difference of necessary pumping light is calculated, and the pumping light generating means of the monitor block is controlled. Until the wavelength characteristic deviation of the gain of each monitor block of the Raman optical amplifier is eliminated, food back control is performed about once to ten times.
FIG. 13 shows an example of an operation flowchart of the excitation light controller 8.
As Step 1: Control is started.
As Step 2, each monitor block is obtained by subtracting the power Pin_s1 to Pin_s3 of each monitor block of the wavelength separation coupler 5 provided on the input side from the power Ps1 to Ps3 of the monitor block of the wavelength separation coupler 5 provided on the output side of the optical amplification medium. Gains G1 to G3 are obtained.
As Step 3, the target gain Gf is compared with the gains G1 to G3f in the monitor block to obtain the differences ΔG1 to ΔG3.
As Step 4: When the difference between ΔG1 to ΔG3 and Gf is within the allowable range, the operation is stopped, and when it is within the allowable range, the process goes to Step 5.
As step 5, the control amounts ΔPp1 to ΔPp3 of the power levels p1 to Pp3 of λp1 to λp3 of the pumping light source block are obtained using the average gain coefficients A11 to A33 that each pumping light has on each monitor block from ΔG1 to ΔG3.
Step 6: Control amounts ΔPp1 to ΔPp3 are added to the current Pp1 to Pp3 to control the output powers Pp1 to Pp, 3 of the excitation light source blocks 6-1 to 6-3.
Step 6: The control process is terminated.
The excitation light control unit 8 controls the excitation light source block in the flow as described above.
Also in the second embodiment, as in the first embodiment, the number of excitation light source blocks and monitor blocks can be arbitrarily set. That is, when the number of excitation light source blocks is n and the number of monitor blocks is m, Expressions 10 to 13 can be rewritten as Expressions 14 to 18.

The excitation light controller 8 may be operated in correspondence with these equations.
In the second embodiment, the number of pumping light source blocks and the number of monitor blocks can be arbitrarily configured as in the first embodiment, but the number of monitor blocks is set to be equal to or less than the number of signal light channels multiplexed in wavelength multiplexed light. It is desirable to make it more than the number of blocks.
In the second embodiment, as in the first embodiment, the Raman amplification medium is not only a normal 1.3 zero micron fiber, but also a dispersion compensating fiber (DCF) and dispersion shifted fiber having a small effective area and a large nonlinearity. (DSF) and non-zero dispersion shifted fiber (NZDSF) can also be used. If these non-linear fibers are used, the fiber serving as the Raman amplification medium for obtaining the necessary gain can be short, and concentrated amplification can be performed.
In the case of a fiber having a small effective cross-section and a strong nonlinearity, the Raman amplification medium 1 can be made short. However, in the case of a normal 1.3 μm zero dispersion fiber, although it depends on the pumping power, it is about 40 km. Sometimes it is necessary. FIG. 14 shows an example in which the wavelength multiplexed optical input notification of the Raman amplifier shown in FIG. 12 is performed using an actual transmission line.
In FIG. 14, the power of each monitor block is detected by the monitoring control unit 12, and the result is converted into information and transmitted to the transmission path serving as the Raman amplification medium 1 via the multiplexing coupler 13 at the wavelength λOSC. The signal of wavelength λOSC is separated by the wavelength separation coupler 5, detected by the monitoring controller 14, and supplied to the excitation light controller 8. Although the wavelength λ OSC is separated by the wavelength separation coupler 5 in FIG. 14, a branch coupler may be separately provided from the transmission line, and the monitoring control signal may be separated and input to the monitoring control unit 14.
In the description of FIG. 13, by using the same value for Gf in all the monitor blocks, the Raman amplification medium is configured in such a configuration in the gain wavelength band generated in the amplification medium 1 by the excitation light from the excitation light source block. Even when 1 uses a transmission line, the gain can be controlled to be constant. Here, by setting a different gain for Gf for each monitor block, the gain is weighted for each wavelength band of each monitor book. Gain constant control can be performed.
Also in the second embodiment, as in the first embodiment, the above weighting process is made constant at Gf in all wavelength blocks, and the variable or fixed optical attenuator 71 is provided at the front stage of the light receiving element in units of monitor blocks. Alternatively, a process of weighting may be performed by providing.
In the second embodiment, the monitor block is composed of the wavelength separation couplers 5 and 10 and the light receiving elements 7-1 to 11-1, but these can be replaced by a spectrum analyzer.
As a third embodiment, a combination of the first and second embodiments with an optical amplifier using a rare earth element doped fiber (for example, an erboop doped fiber) will be described with reference to FIG. In the figure, 13-1 is a first rare earth element doped fiber amplifier, 13-2 is a second rare earth element doped fiber amplifier, 5-1 is a wavelength band separation coupler, 5-2 to 5-5 are branch couplers, Reference numeral 6 denotes a first wavelength band monitor, 5-7 denotes a second wavelength band monitor, 5-8 denotes a first spectrum analyzer, and 5-9 denotes a second spectrum analyzer. Blocks having the same functions as those having the same functions as those in FIGS. 3 and 12 are denoted by the same reference numerals.
The wavelength band separation coupler 5-1 divides the wavelength multiplexed light amplified by the Raman amplification medium 1 into a first wavelength band (C-band band 1530 nm to 1557 nm) and a second wavelength band (Lband band 1570 nm to 1610 nm). Output.
The first rare earth element doped fiber amplifier 13-1 is an optical amplifier composed of an erbium doped fiber (EDF) having a gain with respect to the first wavelength band. The second rare earth element doped fiber amplifier 13-2 is an optical amplifier composed of an erbium doped fiber (EDF) having a gain with respect to the second wavelength band. The light branched by the wavelength band separation coupler 5-1 is amplified by the first rare earth element doped fiber amplifier and the second rare earth element doped fiber amplifier.
The branch couplers 5-2 and 5-3 are branch couplers that branch the light in the first wavelength band about 10 to 1. Branch couplers 5-4 and 5-5 are branch couplers that branch the light in the second wavelength band about 10 to 1.
The first wavelength band monitor 5-6 monitors the power of the light in the first wavelength band branched by the branch coupler 5-2. The second wavelength band monitor 5-7 monitors the power of the light in the second wavelength band branched by the branch coupler 5-4.
The excitation light control circuit 8 calibrates the output power of the first spectral analyzer 5-8 and the second spectral analyzer 5-9 based on the outputs of the first and second wavelength monitors 5-6 and 5-7. Do.
The outputs of 5-8 and 5-9 are divided into three wavelength band blocks of 1528.773 to 1552.122 nm, 1552.524 to 1563.455 nm, 1570.416 to 1581.601 nm, and 1582.018 to 1607.035 nm. Then, the average output of each monitor block is obtained and the excitation lights 6-1 to 6-3 are controlled.
In the case of the combination with the second embodiment, the output from the wavelength demultiplexing coupler 10 of FIGS. 12 and 14 is used, and the signal before the Raman amplification from the monitoring control unit 14 is detected using the monitoring control wavelength signal OSC. Thus, a method for performing control can be used.
[Appendix 1] An optical amplifying medium for Raman-amplifying wavelength-multiplexed light obtained by wavelength-multiplexing a plurality of signal lights, a plurality of pumping light sources for generating pumping lights having different wavelengths, and a combination of the pumping lights First optical multiplexing means, second optical multiplexing means for multiplexing a plurality of signal lights and the excitation light, and detecting the power by dividing the wavelength multiplexed light amplified by the amplification medium into a plurality of wavelength bands And pumping light control means for controlling the output power of each pumping light based on the wavelength characteristics of the gain generated in the optical amplifying medium for each pumping light and the power of each wavelength band of the monitoring means An optical amplifier characterized by that.
[Appendix 2] The optical amplifier according to Appendix 1, wherein the pumping light control means controls the output of the pumping light so that the wavelength characteristic deviation of the power between the wavelength bands of the monitor is small.
[Supplementary note 3] The optical amplifier according to Supplementary note 1, wherein the pumping light control means controls the output of each pumping light so that the output power of each wavelength band becomes a specific value.
[Supplementary note 4] The optical amplifier according to Supplementary note 1, wherein the pumping light control means controls the output of each pumping light so that the output powers of the respective wavelength bands are all specified values.
[Supplementary Note 5] The optical amplifier according to Supplementary Note 1, wherein the pumping light control means controls the output of each pumping light so that the output power of each wavelength band becomes a specific value.
[Appendix 6] An optical amplifying medium for Raman-amplifying light obtained by wavelength-multiplexing a plurality of signal lights, a plurality of pumping light sources for generating pumping lights having different wavelengths, and a plurality of pumping lights for combining the pumping lights 1 optical multiplexing means, second optical multiplexing means for multiplexing a plurality of signal lights and the excitation light, input monitoring means for detecting power incident on the amplification medium, and detection of power amplified by the amplification medium An optical amplifier comprising: an output monitor means for controlling the output power of each pump light based on the input monitor means and the output monitor means.
[Supplementary Note 7] The input monitor means detects the power by dividing the wavelength multiplexed light incident on the amplification medium into a plurality of wavelength bands, and the output monitor means detects the wavelength multiplexed light amplified by the amplification medium. The optical amplifier according to appendix 6, wherein the power is detected by dividing it into a plurality of wavelength bands.
[Supplementary Note 8] The control means obtains the wavelength characteristic of the gain for each wavelength band obtained by comparing the powers of the same wavelength band of the input / output monitoring means and the gain generated in the optical amplifying medium for each pumping light. The optical amplifier according to appendix 7, which controls the output of each pumping light based on the above.
[Appendix 9] The optical amplifier according to appendix 8, wherein the pumping light control means controls the output of the pumping light so that the wavelength characteristic deviation of the gain between the wavelength bands of the monitor is reduced.
[Appendix 10] The optical amplifier according to appendix 8, wherein the pumping light control means controls the output power of each pumping light so that the gain of each wavelength band becomes a specific value.
[Supplementary note 11] The optical amplifier according to supplementary note 8, wherein the pumping light control means controls the output of the pumping light so that the gains of the wavelength bands are all set to specific values.

0: Input port
1: Raman amplification medium 2: multiplexing coupler,
3: Branch coupler,
4: multiplexing coupler,
5: Wavelength separation coupler,
6-1 to 6-3: excitation light source block,
7-1 to 7-3: light receiving elements,
8: Excitation light control unit

Claims (7)

A Raman pumping light source that pumps an optical amplifying medium that performs Raman amplification by inputting wavelength-multiplexed light in which signal lights arranged in a plurality of channels are wavelength-multiplexed,
At least three excitation light sources that respectively output excitation light of different wavelengths;
Excitation light supply means for outputting the excitation light to the optical amplification medium;
Monitoring means for monitoring the power of each of a plurality of wavelength bands including at least one channel of the wavelength multiplexed light output from the amplification medium;
Based on the output power for each of a plurality of wavelength bands obtained from the monitoring result of the monitoring means and the output power for each wavelength band when the excitation light source is individually operated, a plurality of wavelengths obtained from the monitoring result A Raman pumping light source comprising pumping light control means for controlling the output power of the plurality of pumping lights so that the output power in each of the bands becomes equal to the respective target output power.   2. The Raman excitation light source according to claim 1, wherein the number of the plurality of wavelength bands is larger than the number of the plurality of excitation light sources and smaller than the number of the channels.   2. The Raman pumping light source according to claim 1, wherein the plurality of pumping light sources respectively combine the outputs of the plurality of semiconductor lasers and output the plurality of pumping lights as the plurality of pumping lights. .   2. The Raman excitation light source according to claim 1, wherein each of the plurality of excitation light sources constitutes a resonance structure composed of a semiconductor laser and a fiber grating filter.   5. The Raman excitation light source according to claim 4, wherein the fiber grating filters of the plurality of excitation light sources have different reflection wavelengths.   2. The Raman excitation light source according to claim 1, wherein the excitation light supply unit includes a first optical multiplexing unit that combines the plurality of excitation lights, and the plurality of the optical components combined by the first optical multiplexing unit. A Raman excitation light source comprising: second optical multiplexing means for supplying excitation light to the optical amplification medium. 2. The optical amplifier according to claim 1, wherein the output monitor means branches the wavelength multiplexed light output from the amplification medium, and outputs light from the branch means to the plurality of wavelength bands. 3. A Raman excitation light source comprising a wavelength band separation coupler for separation.

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