JP4101155B2 - Optical amplifier - Google Patents

Description

  In the present invention, a plurality of optical amplifiers are connected in multiple stages, and an optical signal is amplified and output while maintaining the total gain of the optical signal output from the final optical amplifier with respect to the optical signal input to the first optical amplifier. The present invention relates to an optical amplification device.

  Conventionally, control methods for rare earth doped optical fiber amplifiers (hereinafter referred to as EDFAs or simply optical amplifiers) include control methods based on ACC (auto current control constant excitation current control) and control based on ALC (auto level control constant light output control). A control method using a method, AGC (Auto Gain Control) is known. In the ACC method, feedback control is performed so that the drive currents of the excitation light sources of the optical amplifier always have the same value. In the ALC method, the output signal light power of the optical amplifier is detected by adjusting the drive current of the pump light source or the output power of the pump light source so that the detected value is always constant. The food back is controlled. Furthermore, the AGC method detects the input signal light power and the output signal light power of the optical fiber amplifier, and the drive current of the pump light source or the pump light source so that the ratio of the output signal light power to the input signal light power is always constant. The gain of the optical amplifier is food-back controlled by adjusting the output power.

  In an optical signal transmission device using an optical fiber amplifier, in order to realize high speed and large capacity in recent years, high-density wavelength multiplex transmission in which different wavelengths are multiplexed and transmitted through one optical transmission line is used. Here, the optical amplifier has a wide signal amplification band capable of collectively amplifying wavelength multiplexed signals of several tens of wavelengths. The characteristics in this signal amplification include wavelength dependency of input signal light and power dependency of input signal light. Here, when wavelength multiplexed signals are collectively amplified, there is a gain difference between signals having different wavelengths. In order to eliminate such wavelength dependence, a gain correction filter is inserted in the optical fiber amplifier, the gain spectrum is flattened, and the output signal light power is adjusted according to the input signal light power, thereby providing an optical amplifier. In general, an AGC system that maintains a constant gain and realizes a flat gain spectrum is used.

  FIG. 5 is a block diagram showing a configuration of an optical amplifying apparatus having an optical amplifier using the AGC method. The optical amplifying apparatus 120 mainly includes a first stage optical amplifier 120a and a second stage optical amplifier 120b, and the optical variable attenuator 8 and dispersion compensation are provided between the first stage optical amplifier 120a and the second stage optical amplifier 120b. A container 9. In the first stage optical amplifier 120a, a part of the input signal light input from the input optical connector 1a is extracted by the optical coupler 2a, and its optical power is measured by the photodiode (PD) 3a. On the other hand, the input signal light that has passed through the optical coupler 2a is input to the optical fiber amplifier 7a that is a rare earth-doped optical fiber that is excited by the pumping light source 6a via the optical isolator 4a, and is optically amplified by stimulated emission. . A part of the optically amplified signal light is extracted by the optical coupler 2b through the optical isolator 4b, and the optical power is measured by the PD 3b. The AGC circuit 10a adjusts the output of the excitation light source 6a so that the ratio of the input signal light from the PD 3a and the output signal light from the PD 3b is constant.

  On the other hand, the signal light that has passed through the optical coupler 2b is output to the optical variable attenuator 8 as output signal light. The optical variable attenuator 8 is adjusted in attenuation amount according to the fluctuation of the input signal light power, and keeps the gain inside the optical amplifier constant. For this reason, the wavelength dependency of the signal light gain with respect to the fluctuation of the input signal light power is improved, and output to the dispersion compensator 9. The dispersion compensator 9 corrects the chromatic dispersion of the signal light and outputs the corrected signal to the second stage optical amplifier 120b. The second-stage optical amplifier 120b has the same configuration as the first-stage optical amplifier 120a. The signal light input from the dispersion compensator 9 is used as input signal light, and the output signal light amplified by the optical fiber amplifier 7b is output light. While outputting from the connector 1b, the AGC circuit 10b adjusts the output of the excitation light source 6b so that the ratio of the input signal light from the PD 3c and the output signal light from the PD 3d is constant. As a result, even if the optical power of the input signal light input from the input optical connector 1a changes, the first-stage optical amplifier 120a and the second-stage optical amplifier 120b each keep the signal optical gain constant. The signal light gain of the amplification device 120 is also kept constant.

Japanese Patent Laid-Open No. 10-00557 Japanese Patent Laid-Open No. 08-248455 Japanese Patent Laid-Open No. 09-214034 Japanese Patent Laid-Open No. 11-275021 JP 2000-031572 A JP 2000-1515155 A Japanese Patent No. 3306712 Japanese Patent No. 3306713

  However, in the above-described conventional AGC optical amplifying apparatus, when the optical power of the input signal light to the first stage optical amplifier 120a is small, the output power of the pumping light source 6a of the first stage optical amplifier 1 is insufficient. The signal light-to-noise ratio in the amplifying apparatus 120 is degraded, the noise figure (NF) is increased (area E100 in FIG. 6), and the optical power of the input signal light to the first stage optical amplifier 120a is large. In some cases, the optical power of the output signal light from the first stage optical amplifier 120a becomes excessive, and is affected by the nonlinear effect in the dispersion compensator 9 (region E110 in FIG. 6).

  Further, in the optical amplifying apparatus in the ACC method, when the optical power of the input signal light to the first stage optical amplifier 120a increases, the optical power of the output signal light increases, and the influence of the nonlinear effect in the dispersion compensator 9 is reduced. (Region E110 in FIG. 7) and the ACC method does not detect the optical power of the output signal light, so whether or not the optical power of the output signal light reaches the region E110 affected by the nonlinear effect. However, there is a problem that good optical amplification cannot always be performed.

  Further, in the optical amplifying apparatus based on the ALC method, the signal light gain cannot be kept constant with respect to the change of the input signal light, so that the wavelength dependency of the signal light cannot be controlled, and the optical power of the input signal light is When it is small, there is a problem that the output power from the excitation light source becomes insufficient.

  The present invention has been made in view of the above, and is an optical amplifying device that can suppress deterioration of the signal light-to-noise ratio with a simple configuration and can suppress waveform deformation of signal light due to a nonlinear effect. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, an optical amplifying device according to the present invention includes a plurality of optical amplifiers connected in multiple stages, and outputs from the final-stage optical amplifier for an optical signal input to the first-stage optical amplifier. In an optical amplifying apparatus that amplifies and outputs an optical signal while keeping the total gain of the optical signal to be constant, when the input power input to the first optical amplifier is small, the gain of the first optical amplifier is largely distributed. And gain distribution means for distributing the gain of the first-stage optical amplifier small when the input power is large.

  In the optical amplifying device according to the present invention as set forth in the invention described above, the gain distribution means distributes the remaining gain distributed to the first-stage optical amplifier to the optical amplifiers other than the first-stage, The total gain of the optical signal output from the optical amplifier is made constant.

  The optical amplifying device according to the present invention includes an input power detecting means for detecting an input power of an optical signal input to the optical amplifier, and an output power detection for detecting an output power of the optical signal amplified and output from the optical amplifier. And gain control means for performing control to increase the gain of the optical amplifier when the input power input to the optical amplifier is low and to decrease the gain of the optical amplifier when the input power is high. It is characterized by that.

  Further, in the optical amplifying device according to the present invention, in the above invention, the optical amplifier is a first-stage optical amplifier among a plurality of optical amplifiers connected in multiple stages, and a final-stage optical amplifier is the final-stage optical amplifier. And a final output power detecting means for detecting the final output power of the optical signal amplified and output from the optical amplifier, and a power control means for controlling the final output power to be constant.

  Also, in the optical amplifying device according to the present invention, in the above invention, the gain distribution means or the gain control means may adjust the gain so that a noise figure is less than a first predetermined value when the input power is small. When the input power is large, the gain is reduced so as to be less than a second predetermined value at which a nonlinear effect occurs.

  In the optical amplifying device according to the present invention as set forth in the invention described above, the gain distribution means or the gain control means includes a relationship table between input power and gain, and performs gain control based on the relationship table. It is characterized by.

  In the optical amplifying device according to the present invention as set forth in the invention described above, the gain distribution means or the gain control means calculates a gain corresponding to input power based on a function indicating a relationship of gain to input power. The gain control is performed based on the calculation result.

  In the optical amplifying device according to the present invention as set forth in the invention described above, each optical amplifier is a rare earth-doped optical fiber amplifier.

  The optical amplifying device according to the present invention is characterized in that, in the above invention, an optical variable attenuator is provided between the stages of each optical amplifier.

  The optical amplifying device according to the present invention is characterized in that, in the above invention, a dispersion compensation circuit is provided between the stages of each optical amplifier.

  According to the present invention, when the input power input to the first-stage optical amplifier is small, the gain of the first-stage optical amplifier is largely allocated, and when the input power is large, the gain of the first-stage optical amplifier is allocated small. Therefore, it is possible to suppress the deterioration of the signal light-to-noise ratio with a simple configuration and to suppress the waveform deformation of the signal light due to the nonlinear effect.

  Embodiments of an optical amplifying device according to the present invention will be described below with reference to the drawings.

(Embodiment 1)
1 is a block diagram showing a configuration of an optical amplifying apparatus according to Embodiment 1 of the present invention. In FIG. 1, the optical amplifying apparatus 20 has a configuration in which a gain distribution control circuit 11 is added to the optical amplifying apparatus 120 shown in FIG. As shown in FIG. 2, the gain distribution control circuit 11 has a ratio of the optical power of the output signal light output from the first stage optical amplifier 20a to the optical power of the input signal light (for the first stage optical amplifier 20a ( (Gain) is not constant, the ratio is increased when the input signal light is small, so as not to enter the NF excessive region E1, and the ratio is decreased when the input signal light is large, and the nonlinear region E2 is entered. It is made not to enter, and it is made not to receive the influence of the nonlinear effect by the dispersion compensator 9. FIG. Examples of the nonlinear effect include a cross phase modulation effect (XPM), a self phase modulation effect (SPM), a stimulated Brillouin scattering (SBS), and the like. Occurs when the signal threshold value is exceeded, and the signal light waveform is distorted.

  This ratio corresponds to the gain, and as shown in FIG. 3, the gain distribution control circuit 11 does not control the first stage optical amplifier 20a to a constant gain with respect to the optical power of the input signal light, and the above-described ratio. As described above, the gain curve L1 is controlled so as to increase the gain when the input signal light is small and decrease the gain when the input signal light is large.

  Then, the second stage optical amplifier 20b is set so that the total gain of the first stage optical amplifier 20a and the second stage optical amplifier 20b is constant with respect to the optical power of the input signal light to the first stage optical amplifier 20a. To control the gain. That is, the gain distribution control circuit 11 performs the gain control shown in FIG. 3 to the first stage optical amplifier 20a to perform the output control as shown in FIG. 1, and also the first stage optical amplifier 20a and the second stage optical amplifier. The gain of the second stage optical amplifier 20b is controlled so that the total gain with the amplifier 20b is constant.

  Specifically, the gain distribution control circuit 11 has gain distribution tables 11a and 11b corresponding to the first-stage optical amplifier 20a and the second-stage optical amplifier 20b, respectively, and gain distribution for the first-stage optical amplifier 20a. Gain control is performed using the table 11a, and gain control is performed using the gain distribution table 11b for the second stage optical amplifier 20b. FIG. 3 shows the contents of the gain control table 11a for the first stage optical amplifier 20a as described above, and the gain control table 11b has a gain curve that cancels out the change in the gain curve L1. The above-described gain curve L1 is merely an example, and as shown in FIG. 2, it is sufficient that the ratio does not enter each of the NF excessive region E1 and the nonlinear region E2, and the shape of the curve is arbitrary. is there. Also, input signal light becomes larger or smaller due to wavelength multiplexing transmission. For this reason, the total optical power increases as the number of wavelengths increases, and the total optical power decreases as the number of wavelengths decreases. Results from doing.

  Here, the overall operation of the optical amplifying device 20 will be described. In this optical amplifying apparatus 20 using the AGC method, first, in the first stage optical amplifier 20a, a part of the input signal light input from the input optical connector 1a is taken out by the optical coupler 2a, and its optical power is increased by the PD 3a. The measurement result is output to the AGC circuit 10a and the gain distribution control circuit 11. On the other hand, the input signal light that has passed through the optical coupler 2a is input to the optical fiber amplifier 7a that is a rare earth-doped optical fiber that is excited by the pumping light source 6a via the optical isolator 4a, and is optically amplified by stimulated emission. . A part of the optically amplified signal light is extracted by the optical coupler 2b through the optical isolator 4b, the optical power is measured by the PD 3b, and the measurement result is output to the AGC circuit 10a. The gain distribution control circuit 11 outputs a gain value to be controlled with reference to the gain distribution table 11a from the measurement result of the optical power input from the PD 3a to the AGC circuit 10a. The AGC circuit 10a obtains the ratio of the input signal light from the PD 3a and the output signal light from the PD 3b, and adjusts the output of the excitation light source 6a so that the gain value input from the gain distribution control circuit 11 is obtained.

  On the other hand, the signal light that has passed through the optical coupler 2b is output to the optical variable attenuator 8 as the output signal light of the first stage optical amplifier 20a. The optical variable attenuator 8 improves the wavelength dependence of the input signal light gain, and outputs it to the dispersion compensator 9. The dispersion compensator 9 corrects the chromatic dispersion of the signal light and outputs the corrected signal to the second stage optical amplifier 20b. The second stage optical amplifier 20b has the same configuration as the first stage optical amplifier 120a, but the configuration of the AGC circuit 10b is different.

  Using the signal light input from the dispersion compensator 9 as input signal light, a part is taken out by the optical coupler 2c, its optical power is measured by the PD 3c, and the measurement result is output to the AGC circuit 10b. On the other hand, the input signal light that has passed through the optical coupler 2c is input to the optical fiber amplifier 7b that is a rare earth-doped optical fiber that is excited by the pumping light source 6b via the optical isolator 4c, and is optically amplified by stimulated emission. . A part of the optically amplified signal light is extracted by the optical coupler 2d via the optical isolator 4d, the optical power is measured by the PD 3d, and the measurement result is output to the AGC circuit 10b. The gain distribution control circuit 11 outputs a gain value to be controlled with reference to the gain distribution table 11b from the measurement result of the optical power input from the PD 3a to the AGC circuit 10b. The AGC circuit 10b calculates the ratio of the input signal light from the PD 3c and the output signal light from the PD 3d, and adjusts the output of the excitation light source 6b so that the gain value input from the gain distribution control circuit 11 is obtained.

  As a result, the optical power output from the optical output connector 1b is output with a certain gain with respect to the optical power input from the optical input connector 1a. In this case, the input signal light can be amplified without being affected by noise in the first stage optical amplifier 10a and without being affected by the nonlinear effect. Even if the second stage optical amplifier 10b performs the same operation as the first stage optical amplifier 10a, the output signal light from the first stage optical amplifier 10a is affected by high noise or non-linear effects. Since these noises are also amplified and amplified while being influenced by the nonlinear effect, it is preferable to perform the gain control shown in FIG. 2 or FIG. 3 in the first stage optical amplifier 10a. Of course, when multiple stages of optical amplifiers are connected in multiple stages, it is desirable to perform the same gain control as that of the first stage optical amplifier 10a for all of the optical amplifiers, but at least in the preceding stage, particularly the first stage optical amplifier. In addition, the same gain control as that of the first stage optical amplifier 10a is performed.

  Further, the gain distribution control circuit 11 is provided with the gain distribution tables 11a and 11b corresponding to the first stage optical amplifier 10a and the second stage optical amplifier 10b, respectively. It may be realized or may be calculated each time. This calculation can be performed using, for example, a function corresponding to the gain curve L1. Furthermore, when a plurality of stages of optical amplifiers are connected in multiple stages, the gain distribution control circuit 11 may provide a gain distribution table corresponding to each optical amplifier.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the first embodiment described above, the gain distribution control circuit 11 controls the first-stage optical amplifier 10a and the second-stage optical amplifier 10b in an integrated manner, but in this second embodiment, the first-stage optical amplifier 10b is controlled. The above-described gain control shown in FIGS. 2 and 3 is performed independently in the amplifier.

  FIG. 4 is a block diagram showing a configuration of an optical amplifying apparatus according to Embodiment 2 of the present invention. This optical amplifying device 30 mainly includes a first stage optical amplifier 30a and a second stage optical amplifier 30b, and between the first stage optical amplifier 30a and the second stage optical amplifier 30b, an optical variable attenuator 8 and A dispersion compensator 9 is provided. The first-stage optical amplifier 30a is the same as the first-stage optical amplifier 20a, and a gain setting unit 13 that newly performs control only on the first-stage optical amplifier 20a side of the gain distribution control circuit 11 is newly provided. On the other hand, unlike the second-stage optical amplifier 20b, the second-stage optical amplifier 30b performs output control by the ALC system instead of the control by the AGC system. Therefore, an ALC circuit 12 is provided instead of the AGC circuit 10b.

  Here, the operation of the optical amplification device 30 will be described. First, in the first stage optical amplifier 30a, a part of the input signal light input from the input optical connector 1a is taken out by the optical coupler 2a, the optical power is measured by the PD 3a, and the measurement result is the AGC circuit 10a and the gain setting. Is output to the unit 13. On the other hand, the input signal light that has passed through the optical coupler 2a is input to the optical fiber amplifier 7a that is a rare earth-doped optical fiber that is excited by the pumping light source 6a via the optical isolator 4a, and is optically amplified by stimulated emission. . A part of the optically amplified signal light is extracted by the optical coupler 2b through the optical isolator 4b, the optical power is measured by the PD 3b, and the measurement result is output to the AGC circuit 10a. The gain setting unit 13 outputs a gain value to be controlled with reference to the gain distribution table 11a from the measurement result of the optical power input from the PD 3a to the AGC circuit 10a. The AGC circuit 10a obtains the ratio of the input signal light from the PD 3a and the output signal light from the PD 3b, and adjusts the output of the excitation light source 6a so that the gain value input from the gain setting unit 13 is obtained. Here, the gain setting unit 13 may provide a gain table corresponding to the gain distribution table 11a, or may calculate a gain value using a function corresponding to the gain curve L1.

  On the other hand, the signal light that has passed through the optical coupler 2b is output to the optical variable attenuator 8 as the output signal light of the first stage optical amplifier 30a. The optical variable attenuator 8 improves the wavelength dependence of the input signal light gain, and outputs it to the dispersion compensator 9. The dispersion compensator 9 corrects the chromatic dispersion of the signal light and outputs the corrected signal to the second stage optical amplifier 30b.

  The input signal light which is the signal light input from the dispersion compensator 9 is input to the optical fiber amplifier 7b which is a rare earth-doped optical fiber which is excited by the pumping light source 6b via the optical isolator 4c, and is induced by stimulated emission. Optically amplified. A part of the optically amplified signal light is extracted by the optical coupler 2c through the optical isolator 4d, the optical power is measured by the PD 3c, and the measurement result is output to the ALC circuit 12. The ALC circuit 12 adjusts the output of the excitation light source 6b so that the level of the optical power of the input signal light from the PD 3c is constant.

  Thereby, the optical power output from the optical output connector 1b is output as a constant value by the control of the ALC system of the second stage optical amplifier 30b. In this case, it is possible to amplify the input signal light without being affected by noise in the first stage optical amplifier 30a and without being affected by the nonlinear effect.

1 is a block diagram showing a configuration of an optical amplifying device that is Embodiment 1 of the present invention. FIG. It is a figure which shows the relationship of the ratio of the optical power of the output signal light with respect to the optical power of the input signal light in a 1st step | paragraph optical amplifier. It is a figure which shows the gain curve for obtaining the ratio shown in FIG. It is a block diagram which shows the structure of the optical amplifier which is Embodiment 2 of this invention. It is a block diagram which shows the structure of the conventional optical amplifier. FIG. 6 is a diagram showing the relationship of the ratio of the optical power of the output signal light to the optical power of the input signal light in the first stage optical amplifier of the optical amplifying apparatus based on the AGC method shown in FIG. It is a figure which shows the relationship of the ratio of the optical power of output signal light with respect to the optical power of input signal light in the 1st step | paragraph optical amplifier of the optical amplifier which performs control by an ACC system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Optical input connector 1b Optical output connector 2a-2d Optical coupler 3a-3d Photodiode (PD)
4a to 4d Optical isolators 6a and 6b Excitation light sources 7a and 7b Optical fiber amplifiers (EDF)
8 Optical variable attenuator 9 Dispersion compensator 10a, 10b AGC circuit 11 Gain distribution control circuit 11a, 11b Gain distribution table 12 ALC circuit 13 Gain setting unit 20, 30 Optical amplifier 20a, 30a First stage optical amplifier 20b, 30b Second Stage optical amplifier L1 Gain curve E1 NF excessive region E2 Non-linear region

Claims (5)

In an optical amplifying apparatus in which a plurality of optical amplifiers are connected in multiple stages, and an optical signal is amplified and output while maintaining the total gain of the optical signal output from the final stage optical amplifier with respect to the optical signal input to the first stage optical amplifier. ,
A dispersion compensator provided between the first stage optical amplifier and the next stage optical amplifier of the first stage optical amplifier;
When the input power input to the first-stage optical amplifier is smaller than a predetermined value on the low power side, the gain of the first-stage optical amplifier is largely distributed so that the noise figure is less than the first predetermined value. When the input power is larger than a predetermined value on the high power side, the output power of the first-stage optical amplifier is less than a second predetermined value that causes a nonlinear effect in the dispersion compensator. Gain distribution means for distributing the gain of the first-stage optical amplifier smallly ;
An optical amplifying device comprising:   2. The optical amplifying apparatus according to claim 1, wherein the gain distribution unit includes a relationship table between input power and gain, and performs gain control based on the relationship table.   2. The gain distribution unit according to claim 1, wherein the gain distribution unit calculates a gain corresponding to the input power based on a function indicating a relationship of gain to the input power, and performs gain control based on the calculation result. The optical amplifying device described.   The optical amplifier according to claim 1, wherein each optical amplifier is a rare earth-doped optical fiber amplifier.   The optical amplifying apparatus according to claim 1, wherein an optical variable attenuator is provided between the stages of the optical amplifiers.

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