JP2005317815A - Optical fiber and multistage optical fiber amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the variation of a gain accompanying the propagation delay of signal light with a simplified constitution easily miniaturized. <P>SOLUTION: There are provided input light power detection means; output light power detection means; storage means for storing time series data of input light power; and gain control means for estimating an amplification gain on the basis of data of the input light power and output light power, and controlling a drive current of an excitation light source. It is assumed for a value of the input light power is Pin (t) at the time (t); a value of the output light power Pout (t); a value of the amplification gain G (t); and propagation time of the signal light between optical couplers provided on the input light power detection means and the output light power detection means is τb; the signal processing time defference of the input/output light power data in the gain control means is τe; and the time series data of Pin (t) is stored in the storage means at least from the time t-τf+τe to the time t, and further the amplification gain G (t) is estimated on the basis of Pout (t) and Pin (t-τf+τe). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber amplifier using an optical fiber as an amplification medium.

  In recent years, in a wavelength division multiplex transmission system, a part of multiplexed wavelength signals is separated into other transmission paths in units of signal channels, or conversely, they are joined to transmission paths in units of wavelength signal channels from other transmission paths. Thus, the number of wavelength signal channels in the transmission path increases or decreases. In addition, the number of wavelength signal channels propagating in the transmission path increases or decreases due to an increase in the number of wavelength signal channels on the transmission station side or a failure in the transmission path.

  Thus, constant gain control (AGC: Automatic Gain Control) is generally applied to an optical fiber amplifier used in a transmission system in which the number of wavelength signal channels increases or decreases. FIG. 11 shows a configuration of a general optical fiber amplifier. A part of the optical power of the signal light Sin input to the optical fiber amplifier 908 and a part of the optical power of the signal light Samp output from the optical fiber amplifying medium 1 are branched by the optical branching couplers 4a and 4b, respectively. The optical power of each branched signal light is input to the photodiodes 5a and 5b, and the excitation light source is set so that the current gain obtained based on the outputs from the photodiodes 5a and 5b becomes a desired target gain. 6 output is controlled.

  However, in the optical fiber amplifier 908 having the configuration shown in FIG. 11, since the optical fiber amplifying medium 1 exists between the optical branching couplers 4a and 4b, there is no signal between the change of the input optical power and the change of the output optical power. There is a delay associated with the propagation of light. As a result, when the input optical power changes abruptly, the gain greatly changes transiently. That is, for example, when the input optical power greatly increases due to an increase in the number of wavelength signal channels, the apparent gain is significantly reduced until the increase is detected as an increase in the output optical power.

  When a dispersion compensating fiber for shaping a signal waveform is inserted between the optical branching couplers 4a and 4b in addition to the optical fiber amplifying medium 1, an L band band such as 1565 to 1625 nm is amplified, or a concentrated type In the case of a Raman amplifier, the propagation delay time between the optical branching couplers 4a and 4b is increased, so that the time during which the above-described apparent gain fluctuation continues is also increased. When the optical fiber amplifier 908 is controlled by the constant gain control, the gain control operation is performed in response to the apparent gain fluctuation, and thus, for example, gain hunting occurs as shown by A in FIG. Therefore, the reliability of transmission will be significantly hindered.

JP2002-124725 JP 2002-261364 A

  In order to compensate for this, it is considered that a delay means, that is, a fiber coil 10 is provided in an optical propagation portion between the input side optical branching coupler 4a and the photodiode 5a as shown in FIG. 1).

  However, since the minimum bending radius of a general optical fiber is 30 mm, in order to obtain a delay time corresponding to the propagation delay time of the optical fiber amplifier described above, it is necessary to wind an optical fiber of several kilometers to several tens of kilometers. It becomes. As an example of a bobbin wound with an optical fiber, a bobbin having a body diameter of 60 mm, a heel diameter of 170 mm, and a thickness of about 10 mm is used. Since the optical fiber coil 10 is produced using the bobbin having such a size, a considerable installation space is required. In a situation where downsizing of optical fiber amplifiers is required in recent years, the installation of a part that requires a considerable space, such as an optical fiber coil 10 for delay compensation, is a great factor in realizing the downsizing requirement. It becomes an obstacle.

  Further, the length of the dispersion compensating fiber needs to be adjusted according to the characteristics of the transmission optical fiber to be subjected to dispersion compensation. Correspondingly, it is necessary to adjust the length of the optical fiber for delay compensation, which makes the adjustment at the time of installation complicated and increases the adjustment cost.

  In order to solve the above problems, an optical fiber amplifier according to claim 1 divides a part of signal light input to the optical fiber amplifier, detects optical power of the branched signal light, and An input optical power detection means for obtaining an input optical power of the optical fiber amplifier based on a detection result; a part of the signal light output from the optical fiber amplifying medium is branched; and the optical power of the branched signal light Output optical power detection means for detecting the output optical power of the optical fiber amplifier based on the detection result, storage means for storing time series data of the input optical power, and the input Gain control means is provided for obtaining an amplification gain based on data of the optical power and the output optical power, and controlling a drive current of the pumping light source based on a deviation between the amplification gain and a desired target gain. And the input optical power The value at time t is Pin (t), the value of the output optical power at time t is Pout (t), the value of the amplification gain at time t is G (t), and the input / output optical power detection means The propagation time of the signal light between the optical couplers provided is τf, and the difference between the signal processing time of the input optical power data and the signal processing time of the output optical power data in the gain control means is τe, The time series data of the input optical power Pin (t) is held in the storage means at least from time t-τf + τe to time t, and the amplification gain G (t) is set to Pout (t) and Pin (t− It is obtained based on (τf + τe).

  In the above optical fiber amplifier, propagation delay compensation can be realized without using an optical fiber coil.

  3. The optical fiber amplifier according to claim 2, wherein a part of the signal light input to the optical fiber amplifier is branched, optical power of the branched signal light is detected, and the optical fiber is detected based on the detection result. Input optical power detection means for obtaining the input optical power of the amplifier, a part of the signal light output from the optical fiber amplification medium is branched, the optical power of the branched signal light is detected, and the detection result Output optical power detection means for obtaining the output optical power of the optical fiber amplifier based on the above, storage means for storing time series data of the input optical power, the input optical power and the output optical power A gain control means for obtaining an amplification gain based on the-data and controlling a drive current of the excitation light source based on a deviation between the amplification gain and a desired target gain; Pin the value at time t t), the value of the output optical power at time t is Pout (t), the value of the amplification gain at time t is G (t), and the signal between the optical couplers provided in the input / output optical power detection means The propagation time of light is τf, the difference between the signal processing time of the input optical power data and the signal processing time of the output optical power data in the gain control means is τe, and the calculation in the gain control means The time required for the pumping light power to change based on the calculation is defined as a control delay time τc, and the time series data of the input light power Pin (t) is stored at least from time t−τf + τe + τc to time t. And the amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe + τc).

  In the above optical fiber amplifier, not only propagation delay compensation but also control delay compensation can be easily realized by changing the setting in the gain control means.

  The multistage optical fiber amplifier according to claim 3, wherein a part of the signal light input to at least two stages of optical fiber amplifiers adjacent to each other among the optical fiber amplifiers connected in a plurality of stages is obtained. An input optical power detecting means for detecting optical power of the branched signal light, and for obtaining input optical power of at least two stages of optical fiber amplifiers adjacent to each other based on the detection result; A part of the signal light output from the optical fiber amplifying medium of the optical fiber amplifying unit which is the final stage of the at least two optical fiber amplifying units adjacent to each other is branched, and the optical power of the branched signal light is split. Output optical power detection means for detecting the output optical power of the optical fiber amplifying unit at the final stage based on the detection result, and a memory for storing time-series data of the input optical power Means and said input An amplification gain is obtained based on the data of the optical power and the output optical power, and the pumping light source of the optical fiber amplifying unit as the final stage is driven based on a deviation between the amplification gain and a desired target gain. In addition to gain control means for controlling current, the input optical power at time t is Pin (t), the output optical power at time t is Pout (t), and amplification at time t determined by the gain control means The gain is G (t), the propagation time of the signal light between the optical couplers provided in the input / output optical power detection means is τf, and the input optical power data in the gain control means of the optical fiber amplifying unit at the final stage. The difference between the signal processing time of the data and the signal processing time of the output optical power data is τe, and the time series data of the input optical power Pin (t) is at least from time t−τf + τe to time t. While holding in the storage means, Amplification gain G at time t a (t) and obtains, based on the Pout (t) and Pin (t-τf + τe).

  In the above optical fiber amplifier, when a loss medium such as a dispersion compensation fiber is included between any of the optical fiber amplifiers of at least two optical fiber amplifiers adjacent to each other, the propagation delay due to the loss medium is reduced. In addition, it is possible to compensate for loss fluctuations of the loss medium due to temperature or the like.

  5. The multistage optical fiber amplifier according to claim 4, wherein a part of signal light inputted to at least two stages of optical fiber amplifiers adjacent to each other among the optical fiber amplifiers connected in a plurality of stages is branched. Input optical power detection means for detecting the optical power of the branched signal light and obtaining the input optical power of at least two stages of optical fiber amplifiers adjacent to each other based on the detection result; A part of the signal light outputted from the optical fiber amplifying medium of the optical fiber amplifying unit which is the final stage among at least two optical fiber amplifying units adjacent to each other is branched, and the optical power of the branched signal light is split. Output optical power detection means for detecting the output optical power of the optical fiber amplifier as the final stage based on the detection result, and storage means for storing time series data of the input optical power And the input An amplification gain is obtained based on the data of the power and the output optical power, and the drive current of the pumping light source of the optical fiber amplifying unit which is the final stage based on a deviation between the amplification gain and a desired target gain Gain control means for controlling the input optical power at time t is Pin (t), the output optical power at time t is Pout (t), and the amplification gain at time t determined by the gain control means G (t), the propagation time of the signal light between the optical couplers provided in the input / output optical power detection means τf, and the input optical power data in the gain control means of the optical fiber amplification unit at the final stage Τe is the difference between the signal processing time of the data and the signal processing time of the output optical power data, and the control delay is the time required for the pumping light power to change based on the calculation from the calculation in the gain control means The time τc The time series data of the word Pin (t) is held in the storage means at least from time t-τf + τe + τc to time t, and the amplification gain G (t) at time t is determined as Pout (t) and Pin (t− (τf + τe + τc).

  The optical fiber amplifier according to claim 5 is characterized in that the propagation time τf in claim 2 or 4 is at least twice as large as the sum of the signal processing time difference τe and the control delay time τc.

  The multi-stage optical fiber amplifier according to claim 6 divides a part of the signal light input to the first-stage optical fiber amplifier of the multi-stage optical fiber amplifier, detects the optical power of the branched signal light, and Input optical power detection means for obtaining the input optical power of the first-stage optical fiber amplifier based on the detection result is provided, and a part of the signal light output from the optical fiber amplification medium of the optical fiber amplifier is further branched Output optical power detection means for detecting the optical power of the branched signal light and obtaining the output optical power of each stage of the optical fiber amplifier based on the detection result; and at the time of the input optical power A storage means for storing sequence data; an amplification gain is obtained based on the data of the input optical power and the output optical power; and the excitation is based on a deviation between the amplification gain and a desired target gain. To control the drive current of the light source A control means is provided for each optical fiber amplifying unit, the input optical power at time t is Pin (t), and the output of the nth stage (1 ≦ n ≦ N) optical fiber amplifying unit at time t The optical power is Pnout (t), and the signal light between the optical coupler provided in the input optical power detection means and the optical coupler provided in the output optical power detection means of the n-th stage optical fiber amplifying unit. Is the signal processing time of the input optical power data in the gain control means of the n-th stage optical fiber amplifier and the output optical power data of the n-th stage optical fiber amplifier. Is the time series data of the input optical power at least from time t-τfn + τen to time t, and the n-th stage optical fiber amplifier at time t The amplification gain Gn (t) is changed to Pnout (t) And obtaining, based on the Pin (t-τfn + τen).

  In the above multi-stage optical fiber amplifier, in addition to realizing propagation delay compensation without using an optical fiber coil, the gain control of the optical fiber amplifying unit at each stage can be performed by providing one input optical power detection means. The multistage optical fiber amplifier can be further miniaturized.

  The multi-stage optical fiber amplifier according to claim 7, wherein a part of the signal light input to the first-stage optical fiber amplifier of the multi-stage optical fiber amplifier is branched, and the optical power of the branched signal light is detected. Input optical power detection means for obtaining the input optical power of the first-stage optical fiber amplifier based on the detection result is provided, and a part of the signal light output from the optical fiber amplification medium of the optical fiber amplifier is further branched Output optical power detection means for detecting the optical power of the branched signal light and obtaining the output optical power of each stage of the optical fiber amplifier based on the detection result; and at the time of the input optical power A storage means for storing sequence data; an amplification gain is obtained based on the data of the input optical power and the output optical power; and the excitation is based on a deviation between the amplification gain and a desired target gain. To control the drive current of the light source A control means is provided for each optical fiber amplifying unit, the input optical power at time t is Pin (t), and the output of the nth stage (1 ≦ n ≦ N) optical fiber amplifying unit at time t The optical power is Pnout (t), and the signal light between the optical coupler provided in the input optical power detection means and the optical coupler provided in the output optical power detection means of the n-th stage optical fiber amplifying unit. Is the signal processing time of the input optical power data in the gain control means of the n-th stage optical fiber amplifier and the output optical power data of the n-th stage optical fiber amplifier. The difference in signal processing time is τen, and the time required from the calculation in the gain control means of the n-th stage optical fiber amplifier to the change in pumping light power based on the calculation is the control delay time τcn. When the time series data of the input optical power is At least hold from time t-τfn + τen + τcn to time t, and obtain the amplification gain Gn (t) of the n-th stage optical fiber amplifier at time t based on Pnout (t) and Pin (t−τfn + τen + τcn). It is characterized by.

  The multistage optical fiber amplifier according to claim 8 is characterized in that in claim 7 the propagation time τfn is at least twice the sum of the signal processing time τen and the control delay time τcn.

The program for controlling the amplification gain of the optical fiber amplifier according to claim 9 includes: an input optical power detection procedure for obtaining an optical power of signal light input to the optical fiber amplifier; and a signal output from the optical fiber amplifier. Based on the output optical power detection procedure for obtaining the optical power of light, the procedure for storing the time series data of the input optical power, and the data of the input optical power and the output optical power An amplification gain calculation procedure for obtaining an amplification gain, a gain deviation calculation procedure for calculating a deviation between the amplification gain and a desired target gain, and a drive for calculating a correction amount of the drive current of the excitation light source based on the gain deviation A current correction amount calculation procedure, a procedure for calculating a new drive current setting value based on the correction amount, and a control output procedure for outputting the new drive current setting value and controlling the output of the excitation light source, The input light The input optical power value at time t obtained by the power detection procedure is Pin (t), the output optical power value at time t obtained by the output optical power detection procedure is Pout (t), The value of amplification gain at time t obtained by the gain control procedure is G (t), the propagation time of signal light in a predetermined section is τf, the signal processing time of the input optical power data, and the output optical power data A difference in signal processing time of data is τe, and time series data of the input optical power Pin (t) is held in the storing procedure from at least time t-τf + τe to time t,
In the amplification gain calculation procedure, the amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe).

  The program for controlling the amplification gain of the optical fiber amplifier according to claim 10 includes: an input optical power detection procedure for obtaining optical power of signal light input to the optical fiber amplifier; and a signal output from the optical fiber amplifier. Based on the output optical power detection procedure for obtaining the optical power of light, the procedure for storing the time series data of the input optical power, and the data of the input optical power and the output optical power An amplification gain calculation procedure for obtaining an amplification gain, a gain deviation calculation procedure for calculating a deviation between the amplification gain and a desired target gain, and a drive for calculating a correction amount of the drive current of the excitation light source based on the gain deviation Current correction amount calculation procedure, drive current set value calculation procedure for calculating a new drive current set value based on the correction amount, and control for controlling the output of the excitation light source by outputting the new drive current set value Output hand The input optical power value at time t obtained by the input optical power detection procedure is Pin (t), and the output optical power value at time t obtained by the output optical power detection procedure is Pout (t), amplification gain value at time t obtained by the gain control procedure, G (t), propagation time of signal light in a predetermined section τf, signal processing time of the input optical power data, The difference in signal processing time of the output optical power data is τe, the gain deviation calculation procedure from the calculation in the amplification gain calculation procedure, the drive current correction amount calculation procedure, the drive current set value calculation procedure, the control The time required until the pumping light power changes through the output procedure is defined as the control delay time τc, and the time series data of the input light power Pin (t) is stored at least from time t−τf + τe + τc to time t. And hold the amplification gain In calculation procedure and obtaining, based the amplification gain G a (t) and Pout (t) in the Pin (t-τf + τe + τc).

  The program for controlling the amplification gain of the optical fiber amplifier according to claim 11 is the optical branching coupler in which the propagation time τf is inserted for detecting the input optical power and the output optical power in claim 9 or 10. It is a time required for signal light to propagate between optical branching couplers inserted for detection.

  According to the present invention, the delay due to the propagation of the signal light through the optical fiber amplifying medium can be performed only by the processing of the control unit, the optical fiber coil for delay compensation becomes unnecessary, and the optical fiber amplifier can be easily downsized. .

  Further, the adjustment for delay compensation can be made only by changing the setting of the storage time of the time series data of the input optical power, and the adjustment work becomes easy.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The first embodiment, which is a basic configuration to which the present invention is applied, the second embodiment in which a dispersion compensating fiber is provided as a modification of the first embodiment, and the second embodiment that is applied to a plurality of continuous optical fiber amplifiers. A third embodiment and a fourth embodiment applied to the entire multistage optical fiber amplifier will be described.

  FIG. 1 is a configuration example of an optical fiber amplifier 901 according to the first embodiment of the present invention. The optical fiber amplifier 901 includes transmission optical fibers 3a and 3b used for input and output, an optical fiber amplification medium 1, a pumping light source 6, a driving circuit 7 for the pumping light source 6, and signal light and pumping light. In addition to the multiplexer 2 for multiplexing, an input composed of an optical coupler 4a for branching a part of the input signal light Sin and a photodiode 5a for detecting the optical power of the branched signal light. The optical power detection means includes an optical coupler 4b that branches a part of the signal light Samp output from the optical fiber amplifying medium 1, and a photodiode 5b that detects the optical power of the branched signal light. Output light power detection means, gain control means including a control unit 8 for controlling the drive current output from the drive circuit 7 to the excitation light source 6, and storage means including a memory 9 provided in the control unit 8 It consists of and.

  A part of the signal light Sin input from the transmission optical fiber 3a is branched by the optical branching coupler 4a, and the rest is combined with the pumping light from the pumping light source 6 by the optical multiplexer 2, and then the optical fiber. Input to the amplification medium 1. A part of the signal light Samp amplified by the optical fiber amplifying medium 1 is branched by the optical branching coupler 4b, and the rest is output as the output signal light Sout from the transmission optical fiber 3b. The signal lights branched by the optical branching couplers 4a and 4b are input to the photodiodes 5a and 5b, respectively. The optical powers Pin (t) and Pout (t) of the signal lights Sin and Sout are calculated using the outputs of the photodiodes 5a and 5b, and the changes are monitored. Since the optical branching couplers 4a and 4b are adjusted so as to obtain a substantially constant branching ratio in the wavelength range of the signal light, the signal light input to the optical fiber amplifier from the outputs of the photodiodes 5a and 5b is adjusted. It is possible to know the optical input power Pin (t) and the optical output power Pout (t) of the signal light output from the optical fiber amplifier. The time series data of the optical input power Pin (t) is stored in a memory 9 built in the control unit 8. The control unit 8 reads the value of Pin (t−τf + τe) from the memory 9, calculates the amplification gain G (t) from this and Pout (t), and supplies it to the excitation light source 6 so that this becomes a desired value. The drive current value is indicated and the excitation light power is controlled.

  In the calculation method of the gain G (t) described above, when Pout (t) and Pin (t−τf + τe) are logarithmic values expressed as dBm values, they are generally calculated by Equation 1. Further, in the case of a linear value expressed in units of mW, it is calculated by Equation 2.

          G (t) = Pout (t) −Pin (t−τf + τe) (1)

          G (t) = Pout (t) / Pin (t-τf + τe) (2)

  FIG. 2 shows changes in the optical power of each part when the present invention is applied, together with the case where the conventional control method is applied. The optical amplifier has the configuration shown in FIG. When Type A is not compensated for delay, Type B is compensated only for propagation delay, Type C is compensated for both propagation delay and control delay, and Type D is ideally operated without transient fluctuations. Shows the case.

  First, the case of Type A will be described. As the number of wavelength signal channels increases, the input light power -Pin of signal light starts increasing at time t0. This change is recognized by the control unit 8 as Pin1 through the optical branching coupler 4a and the photodiode 5a. There is a time delay τin ′ caused by AD conversion or the like between Pin and Pin1. The output light power Pout starts increasing at time t8 after propagation time τf after Pin starts increasing at time t0. This change in Pout is recognized by the control unit 8 as Pout1 delayed by τout. The control unit 8 obtains the current gain G based on Pin1 and Pout1. Therefore, in the case of Type A, the current gain G decreases as Pin1 increases from t1 to t7. The current gain G increases as Pout1 increases from time t9.

  In response to the change in the current gain G, the control unit 8 controls the drive current of the excitation light source 6 so as to keep the gain constant. As a result, the output Ppump of the excitation light source 6 starts to increase from time t5 delayed by the control delay time τc from time t1 corresponding to the decrease in the current gain G, and time increases corresponding to the increase in the current gain G. It starts to decrease from time t13, which is delayed from t9 by τc.

  The output light power changes as Pout ′ due to the change in the output Ppump of the excitation light source. First, Pout ′ increases in the same manner as Pout since the influence of Ppump does not appear from time t8 to time t13. From time t5 when τf has elapsed from time t5 when Ppump starts to increase, Pout ′ starts to increase further due to an increase in gain due to an increase in Ppump. Thereafter, Pout ′ starts decreasing from time t21 as Ppump decreases, and converges to a predetermined output value from time t23.

  Although the output optical power is considered to change as described above, the gain Gλs of the continuous signal light input before the increase in the number of wavelength signal channels is considered to change as follows. First, Gλs decreases as Pout increases from time t8. This is because the energy of the pumping light that contributes to the amplification of the continuous signal light is reduced because the output of the pumping light source 6 is in a state before the increase in the number of wavelength signal channels. During the time τf from time t5 to time t13, Gλs continues to decrease. From time t13, Gλs starts to increase as Ppump increases. Thereafter, from time t21, Gλs also decreases as Ppump decreases, and converges to the gain before the increase in the number of wavelength signal channels at time t27.

  Next, the case of Type B will be described. In the case of Type B that performs propagation delay compensation according to the present invention, the input optical power data is temporarily stored in the memory 9 after being AD converted and then read out to the arithmetic unit of the control unit 8. Therefore, the time delay between Pin and Pin1 in the case of Type B is larger than τin ′ in the case of Type A and becomes τin. Further, changes in Pout and Pout1 are the same as in the case of Type A.

  In Type B, propagation delay compensation is performed. Accordingly, the current gain G at time t9 is calculated based on Pout1 at time t9 and Pin1 at time t2. The time between time t2 and time t9 is τf−τe (τe = τin−τout). By this propagation delay compensation, the current gain G maintains the value before the increase in the number of wavelength signal channels until time t9. After the increase in the number of wavelength signal channels after time t9 appears in Pout1, the output Ppump of the excitation light source 6 has not changed, so the current gain G decreases.

  Corresponding to the decrease in the current gain G described above, Ppump starts to increase from time t13 delayed by the control delay time τc from time t9.

  As a result, the optical power Pout ′ of the entire output light changes as follows. Since the influence of Ppump does not appear from time t8 to time t21, it is the same change as Pout. From time t21 when the propagation time τf has elapsed from time t13, Pout ′ increases as Ppump increases and converges to a predetermined value at time t27.

  Further, the gain Gλs of the continuous signal light changes as follows. From time t8 to time t14, Gλs decreases as in the case of Type A, and once reaches a constant value after time t14. Gλs increases as Ppump increases from time t21, and converges to the gain before the increase in the number of wavelength signal channels at time t27.

  Next, the case of Type C will be described. Type C compensates for control delay in addition to Type B propagation delay compensation. Also in the case of Type C, the input optical power data is temporarily stored in the memory 9 after AD conversion, and then read out to the calculation unit of the control unit 8. Therefore, the time delay between Pin and Pin1 in the case of Type C is larger than τin ′ in the case of Type A and becomes τin. Further, changes in Pout and Pout1 are the same as in the case of Type A.

  In Type C, propagation delay compensation and control delay compensation are performed as described above. Accordingly, the current gain G at time t6 is calculated based on Pout1 at time t6 and Pin1 at time t2. The time between time t2 and time t5 is τf−τe−τc (τe = τin−τout). By this delay compensation, the current gain G maintains the value before the increase in the number of wavelength signal channels until time t5. From time t5 to time t9, the current gain G decreases because only Pin1 increases. From time t9 to time t11, an increase in Pin appears in Pout1, but since the output Ppump of the excitation light source 6 has not changed, the current gain G continues to decrease. The current gain G after time t11 slightly increases until time t15 because Pin1 used for calculation is constant after time t8.

  Corresponding to the decrease in the current gain G after time t5 described above, Ppump starts to increase from time t9 which is delayed by the control delay time τc from time t5.

  As a result, the optical power Pout ′ of the entire output light changes as follows. Since the influence of Ppump does not appear from time t8 to time t17, it is the same change as Pout. From time t17 when the propagation time τf has elapsed from time t9, Pout ′ increases as Ppump increases and converges to a predetermined value at time t27.

  Further, the gain Gλs of the continuous signal light changes as follows. From time t8 to time t14, Gλs decreases as in the case of Type A, and once reaches a constant value after time t14. Gλs increases as Ppump increases from time t17, further decreases as Ppump decreases from time t23, and converges to the gain before the increase in the number of wavelength signal channels at time t27.

  When the change in the gain Gλs of the continuous signal light in the above three cases is compared, since Type A shows a considerably large overshoot, several overshoots are observed in actual operation. -It is thought that it converges after passing through undershoot and undershoot. Therefore, Type A is expected to take time to converge. Also, since overshoot does not occur in Type B, it seems that it takes a relatively short time until it converges after returning to the original gain than Type A. It is expected that the state in which the deviation occurs will continue for a relatively long time. In Type C, the time until it returns to the initial gain is shorter than Type B, and the subsequent overshoot is also smaller than Type A. Therefore, the state where the gain deviation occurs is also relatively short. It is expected to be time and not require much time for convergence.

  Therefore, it can be said that Type B is more desirable control than Type A and Type C is more desirable control than Type B for dealing with gain fluctuations due to increase / decrease in the number of wavelength channels.

  Incidentally, since feedback control is performed in an actual optical fiber amplifier, the time series change of each parameter described above is slightly different from that in FIG.

  FIG. 3 shows an example of a flowchart of a control program for realizing the gain control operation of the present invention. FIG. 3 (a) is a part for storing time series data of input optical power in a memory. In step S101, various setting values necessary for the operation are read. Further, the propagation time τf and the signal processing time difference τe previously obtained are also read. Further, when the control delay time is also compensated, τc is also read in S101. Next, in step S102, the input optical power Pin (t) obtained from the output of the photodiode 5a is read as digital data, and the value is stored in the memory 9 in step S103. Here, the memory 9 needs at least WARD · (τf−τe) / Δt + 1 (Bite) (WARD: the number of words of AD conversion, Δt: sampling time). After the data is stored up to the memory full, the oldest data is deleted and the latest data is stored.

  FIG. 3B is a part for calculating the current gain from the input optical data and output optical power data stored in FIG. 3A and controlling the drive current of the pumping light source 6. In step S201, various setting values necessary for the operation are read. Similarly to S101, the propagation time τf and the signal processing time difference τe previously obtained here are also read, and when the control delay time is also compensated, τc is also read. In step S202, the data holding time τf-τe is calculated to determine how much previous Pin data from the present time is used for the amplification gain calculation. Next, in step S203, the value at time (t-τf + τe) is read out from the time series data of the input optical power stored in step S103, and in step S204, the optical output power data Pout is read out. (T) is AD-converted from the output of the photodiode 5b and read. The order of steps S203 and S204 need not be the same, and the optical output power data may be read first. In step S205, the current gain G (t) at time t is calculated from these values using the above-described equations 1 and 2, and the current gain G (t (t) calculated in step S205 is calculated in step S206. ) And the gain setting value Gset is calculated as a gain error. In step S207, the drive current correction value ΔI of the excitation light source is calculated from the gain error E based on a predetermined algorithm, for example, the equation shown in S207 of FIG. 3B, and in step S208, a new drive current value is calculated. The calculated value is output to the drive circuit 7 of the excitation light source 6 in step S209.

  When the control delay time is also compensated, the value read out from the time series data of the input optical power is the value of time (t-τf + τe + τc).

  Here, it is desirable that the sampling periods in the AD conversion of the input optical power and the output optical power are substantially the same period. Further, the delay time τf−τe is set in advance after being set to a value that is divisible by the value of the sampling period, so that the processing when it is not divisible can be omitted, and the control operation can be speeded up. Similarly, when compensating for the control delay time, it is desirable that τf−τe−τc be set to a value divisible by the value of the sampling period.

  FIG. 4 is a configuration example of the second embodiment of the present invention. The difference from the first embodiment is that a dispersion compensating fiber 10 is connected between the optical branching couplers 4a and 4b in addition to the optical fiber amplifying medium 1, so that the propagation time τf is larger than that in the case of FIG. growing.

  In the experimental system shown in FIG. 5, the operation of the actually configured embodiment of the present invention was confirmed. Light from the eight signal light sources 100 having the wavelengths λ1 to λ8 is multiplexed by the multiplexer 102 and input to the light SW 103. The output from the optical SW 103 and the output of the residual signal light source 101 having the wavelength λs are combined by the multiplexer 105, and the output is partially branched by the optical branching coupler 105 and then input to the measured optical fiber amplifier 106. To do. Of the output from the optical fiber amplifier 106 to be measured, only the signal light having the wavelength λs is extracted by the narrow-band optical filter 107 and input to the photodiode 108. Further, the signal light branched by the optical branching coupler 105 is input to the photodiode 109. Changes in the output of the photodiode 108 when the optical SW 103 is turned ON / OFF by inputting the outputs of the photodiodes 108 and 109 to the oscilloscope 110 and using the output of the photodiode 109 as a reference signal. That is, the level change of the residual signal light power of wavelength λS was observed.

As the optical fiber amplifier to be measured, the one in the second embodiment shown in FIG. 4 was used. The configuration conditions and operating conditions of the optical fiber amplifier to be measured are as follows.
・ Propagation delay time: 44μsec
・ Τe + τc = 600nsec
・ Amplification gain including loss in dispersion compensating fiber: 27dB
・ Sampling period in AD conversion of input / output optical power: 25nsec
・ Delay compensation: Propagation delay compensation and delay compensation are performed simultaneously.

  Among the above operating conditions, τe + τc is substantially equal to the time from when the input light power is input to the photodiode 5a until the corresponding excitation light is output.

  The following measurements were performed under the above operating conditions. By turning on the optical SW 103 (at the time of Add), the input optical power was increased by 15 dB from −22 dBm to −7 dBm. Conversely, by turning off the light SW 103 (Drop), the input light power was reduced from −7 dBm to −22 dBm. Further, the measurement was performed for the case where the wavelength of the residual signal light was 1538.98 nm and 1545.32 nm. The experimental results are shown in Table 1 and FIGS.

  In both cases of Add and Drop, transient fluctuations in the gain of the residual signal light could be suppressed.

  In the present invention, only time series data of the input optical power data is stored in the memory. Accordingly, the case where the time difference τf−τe> 0 or τf− (τe + τc)> 0 is applied. In the configuration of FIG. 1, when the optical fiber amplifying medium 1 is an EDF (Erbium Doped Fiber), the length of the EDF is about several meters to several hundred meters depending on use conditions. Accordingly, when the length of the EDF is short, the propagation time τf is short, and the time difference τf−τe ≦ 0 or τf− (τe + τc) ≦ 0 may occur. In that case, no delay compensation is performed.

  FIG. 8 shows the result of measuring the magnitude of the transient fluctuation due to the propagation delay. FIG. 8 shows the amount of transient gain variation during Add and Drop when the length of the dispersion compensation fiber 10 is changed and the propagation time is changed when the conventional control method is used in the configuration of FIG. Is. In this case, in the optical fiber amplifier 902, τe + τc was about 600 nsec.

  FIG. 8A shows the measurement result at 0.01 to 20 μsec, and FIG. 8B is an enlarged view of the portion of 5 μsec or less. The influence of the propagation delay time is larger at the time of Add than at the time of Drop. Although there is not much influence up to about 1.2 μsec, when the propagation delay time is longer than that, the gain fluctuation amount increases almost linearly especially at the time of Add. Further, although the influence of the propagation delay is not so great until about 1.2 μsec, the gain fluctuation amount is not so great even when the propagation delay is almost 0, that is, when τf− (τe + τc) is approximately − (τe + τc). not big. From this, − (τe + τc) ≦ τf− (τe + τc) ≦ τe + τc, that is, in the range of 0 ≦ τf ≦ 2 · (τe + τc), the transient fluctuation amount of the gain accompanying the propagation delay is not so large, but τf> 2. It can be seen that with τc, the amount of transient fluctuation in gain increases with an increase in propagation delay, and therefore the necessity for delay compensation according to the present invention increases.

  Next, a third embodiment of the present invention will be described. FIG. 9 shows the configuration of the third embodiment of the present invention. The signal light is input from the left transmission fiber 3a and output to the right transmission fiber 3b. The first-stage optical fiber amplifier 903a includes an optical fiber amplifying medium 1a, a pumping light / signal light multiplexer 2a, optical branching couplers 4a and 4b, photodiodes 5a and 5b, a pumping light source 6a, and a pumping light source. It comprises a drive circuit 7a and a control unit 8a. The second-stage optical fiber amplifying unit 903b includes an optical fiber amplifying medium 1b, an excitation light / signal light multiplexer 2b, an optical branching coupler 4c, a photodiode 5c, an excitation light source 6b, and an excitation light source drive circuit. 7b and a control unit 8b. A value obtained from the output of the photodiode 5a is used in common with the first stage for the input optical power used to calculate the amplification gain of the second-stage optical fiber amplifier 903b. The first stage and the second stage are connected by an optical fiber 31.

  In this embodiment, if the propagation time τfa between the optical branching couplers 4a and 4b and the difference in input / output optical power data processing time in the control unit 8a are τea, the memory 9a of the control unit 8a has at least τfa. The time series data of the input optical power for the time of τea is stored, and gain control is performed using the input optical power Pain (t−τfa + τea) and the optical output power Paout (t). Further, if the propagation time τfb between the optical branching couplers 4a and 4c and the difference in input / output optical power data processing time in the control unit 8b is τeb, the memory 9b of the control unit 8b has at least τfb−τeb. Time-series data of the input optical power for the time is stored, and gain control is performed using the input optical power Pain (t-τfb + τeb) and the optical output power Pbout (t). In the configuration of FIG. 9 also, when τfa−τea ≦ 0 and τfb−τeb ≦ 0, the gain control using the delay compensation of the present invention is not applied to the first stage, or the first stage and second stage gain control.

  In the conventional multistage optical fiber amplifier, for example, as shown in FIG. 13, the propagation delay of the dispersion compensating fiber or the like is increased in the portion of the optical fiber 31 between the first stage and the second stage, and the loss varies depending on the temperature or the like. When an optical element is inserted, it is conceivable that the gain of the entire optical fiber amplifying device varies due to the gain variation of the optical element. On the other hand, the configuration of the multi-stage optical fiber amplifying apparatus is the configuration shown in FIG. Even when an optical element such as a dispersion compensating fiber is inserted between the stages, the loss fluctuation of the optical element can be compensated while suppressing the transient fluctuation of the gain.

  In the above description of the third embodiment, the multistage optical fiber amplifier 903 configured with two stages of optical fiber amplifiers has been described. However, the multistage optical fiber amplifier configured with three or more stages of optical fiber amplifiers may also be used. Needless to say, this is applicable.

  In addition, the optical fiber amplifying unit to which the gain control of the present invention is applied is not necessarily limited to the final stage, and at least one optical fiber amplifying part at a stage subsequent to the position where the optical element whose loss varies is inserted. And apply.

  Furthermore, the optical input power data used to calculate the amplification gain of the optical fiber amplifier to which the gain control of the present invention is applied is the optical power upstream of the position where the optical element whose loss varies is inserted. I just need it. That is, in FIG. 9, the optical input power used for gain control of the optical fiber amplifier 903b is obtained from the output of the photodiode 5a, but it may be obtained from the output of the photodiode 5b, for example. Further, it may be obtained from the output of the photodiode of the optical fiber amplifying unit before 903a.

  Next, a fourth embodiment of the present invention will be described. FIG. 10 shows the configuration of the fourth embodiment of the present invention. The signal light is input from the left transmission fiber 3a and output to the right transmission fiber 3b. When N is an integer of 2 or more and n is an integer of 1 ≦ n ≦ N, the n-th stage optical fiber amplifying unit 904-n includes an optical fiber amplifying medium 1n, a pumping light / signal light multiplexer 2n, It comprises an optical branching coupler 4nb, a photodiode 52n, an excitation light source 6n, an excitation light source drive circuit 7n, and a control unit 8n. However, the first stage has an optical branching coupler 41a and a photodiode 51a in addition to the above configuration. The optical fiber amplifying units are connected by optical fibers 31 to 3N-1. The data obtained from the output of the photodiode 51a is used in common with the first stage for the input optical power data used for the calculation of the amplification gain of the optical fiber amplifiers in the second and subsequent stages.

  In this embodiment, if the propagation time τfn between the optical branching couplers 41a and 4nb and the difference between the input / output optical power data processing time in the control unit 8n are τen, the memory 9n of the control unit 8n has at least τfn. The time series data of input optical power for τen time is stored, and gain control is performed using the input optical power Pin (t−τfn + τen) and the nth optical output power Pnout (t) . Even in the configuration of FIG. 10, the gain control using the delay compensation of the present invention is not applied when τfn−τen ≦ 0.

  By configuring the multi-stage optical fiber amplifier 904 as shown in FIG. 10, the second-stage and subsequent input-side optical branching couplers and photodiodes can be omitted, and the structure can be simplified. Therefore, it is possible to reduce the cost as well as downsizing. Also, various setting value input means to the control unit of each optical fiber amplifying unit, communication I / F with the control unit of each optical fiber amplifying unit or communication I / F with other devices constituting the transmission system, etc. By providing the multi-stage optical fiber amplifier 904 with the central control unit 80 provided, operability can be improved or automated.

1 shows a first embodiment of the present invention. It is a figure explaining operation | movement of the Example shown in FIG. FIG. 2A is an example of a flow chart for performing the operation shown in FIG. 2. FIG. 2A is a flow chart for optical input data Pin (t) reading operation, and FIG. 2B is a flow chart for gain control operation. -G. 2 shows a second embodiment of the present invention. The experimental system in which the operation was confirmed is shown. The experimental result ((lambda) s = 1538.98nm) conducted in the experimental system of FIG. 5 is shown. The experimental result ((lambda) s = 1545.32nm) conducted in the experimental system of FIG. 5 is shown. In the second embodiment of the present invention, the magnitude of the effect of the present invention on the magnitude of τf is shown. (A) is the entire verification result, and (b) is an enlarged view of the portion of τf ≦ 5 μsec. 3 shows a third embodiment of the present invention. 4 shows a fourth embodiment of the present invention. A block diagram of a conventional optical fiber amplifier (without propagation delay compensation) is shown. The block diagram of the conventional optical fiber amplifier (with propagation delay compensation) is shown. The block diagram of the conventional multistage optical fiber amplifier is shown.

Explanation of symbols

901, 902, 908, 909 ... Optical fiber amplifiers 903, 904, 910 ... Multistage optical fiber amplifiers 903a, 903b, 910a, 910b ... Optical fiber amplifiers 904-1 to 904-N ... Optical fiber amplifiers 1, 1a, 1b ... Optical fiber amplification media 11 to 1N ... Optical fiber amplification media 2, 2a, 2b ... Optical multiplexers 21 to 2N ... ... Optical multiplexers 3a, 3b ......... Transmission optical fibers 31 to 3N-1 ... Optical fibers 4a, 4b ... Optical branching couplers 41a, 41b to 4Nb ... Optical branching couplers 5a, 5b, 5c, 5d: Photodiodes 51a, 51b to 5Nb ... Photodiodes 6, 6a, 6b ..... Excitation light sources 61 to 6N ........... Excitation light sources 7, 7a, 7b ..... Driving circuit 7 ~ 7N ............ Drive circuit 8, 8a, 8b ......... Control part 81-8N .......... Control part 80 ........................ Central control part 9, 9a, 9b ......... Memory 91-9N ……………… Memory

Claims (11)

In an optical fiber amplifier comprising an optical fiber amplification medium and at least one excitation light source,
A part of the signal light input to the optical fiber amplifier is branched, the optical power of the branched signal light is detected, and the input optical power for obtaining the input optical power of the optical fiber amplifier based on the detection result -Detection means;
Output light for branching part of the signal light output from the optical fiber amplifying medium, detecting the optical power of the branched signal light, and determining the output optical power of the optical fiber amplifier based on the detection result Power detection means;
Storage means for storing time-series data of the input optical power;
Gain control means for obtaining an amplification gain based on data of the input optical power and the output optical power, and controlling a drive current of the pumping light source based on a deviation between the amplification gain and a desired target gain With
The value of the input optical power at time t is Pin (t), the value of the output optical power at time t is Pout (t), the value of the amplification gain at time t is G (t), and the input / output light The propagation time of the signal light between the optical couplers provided in the power detection means is τf, and the difference between the signal processing time of the input optical power data and the signal processing time of the output optical power data in the gain control means Is τe,
The time series data of the input optical power Pin (t) is held in the storage means at least from time t-τf + τe to time t,
The amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe).
An optical fiber amplifier. In an optical fiber amplifier comprising an optical fiber amplification medium and at least one excitation light source,
A part of the signal light input to the optical fiber amplifier is branched, the optical power of the branched signal light is detected, and the input optical power for obtaining the input optical power of the optical fiber amplifier based on the detection result -Detection means;
Output light for branching part of the signal light output from the optical fiber amplifying medium, detecting the optical power of the branched signal light, and determining the output optical power of the optical fiber amplifier based on the detection result Power detection means;
Storage means for storing time-series data of the input optical power;
Gain control means for obtaining an amplification gain based on data of the input optical power and the output optical power, and controlling a drive current of the pumping light source based on a deviation between the amplification gain and a desired target gain With
The value of the input optical power at time t is Pin (t), the value of the output optical power at time t is Pout (t), the value of the amplification gain at time t is G (t), and the input / output light The propagation time of the signal light between the optical couplers provided in the power detection means is τf, and the difference between the signal processing time of the input optical power data and the signal processing time of the output optical power data in the gain control means Τe, the time required from the calculation in the gain control means until the pumping light power changes based on the calculation is the control delay time τc,
The time series data of the input optical power Pin (t) is held in the storage means at least from time t-τf + τe + τc to time t,
The amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe + τc).
An optical fiber amplifier. In a multi-stage optical fiber amplifier in which at least one optical fiber amplifying medium and at least one pumping light source are provided in one stage, and the optical fiber amplifying part is connected in a plurality of stages along the propagation direction of the signal light.
A part of the signal light inputted to at least two adjacent optical fiber amplifiers among the optical fiber amplifiers connected in a plurality of stages is branched, and the optical power of the branched signal light is split. Input optical power detection means for obtaining the input optical power of at least two stages of optical fiber amplifiers adjacent to each other based on the detection result;
A part of the signal light output from the optical fiber amplifying medium of the optical fiber amplifying unit which is the final stage of the at least two optical fiber amplifying units adjacent to each other is branched, and the optical power of the branched signal light is split. Output optical power detection means for detecting the output optical power of the optical fiber amplification unit as the final stage based on the detection result;
Storage means for storing time-series data of the input optical power;
An amplification gain is obtained based on the data of the input optical power and the output optical power, and a pumping light source of the optical fiber amplification unit which is the final stage based on a deviation between the amplification gain and a desired target gain And gain control means for controlling the drive current of
The input optical power at time t is Pin (t), the output optical power at time t is Pout (t), the amplification gain at time t obtained by the gain control means is G (t), and the input / output light The propagation time of the signal light between the optical couplers provided in the power detection means is τf, and the signal processing time of the input optical power data and the output optical power in the gain control means of the optical fiber amplifier as the final stage Let τe be the difference in signal processing time of data,
The time series data of the input optical power Pin (t) is held in the storage means at least from time t-τf + τe to time t,
An amplification gain G (t) at time t is obtained based on Pout (t) and Pin (t−τf + τe).
A multistage optical fiber amplifier. In a multi-stage optical fiber amplifier in which at least one optical fiber amplifying medium and at least one pumping light source are provided in one stage, and the optical fiber amplifying part is connected in a plurality of stages along the propagation direction of the signal light.
A part of the signal light inputted to at least two adjacent optical fiber amplifiers among the optical fiber amplifiers connected in a plurality of stages is branched, and the optical power of the branched signal light is split. Input optical power detection means for obtaining the input optical power of at least two stages of optical fiber amplifiers adjacent to each other based on the detection result;
A part of the signal light output from the optical fiber amplifying medium of the optical fiber amplifying unit which is the final stage of the at least two optical fiber amplifying units adjacent to each other is branched, and the optical power of the branched signal light is split. Output optical power detection means for detecting the output optical power of the optical fiber amplification unit as the final stage based on the detection result;
Storage means for storing time-series data of the input optical power;
An amplification gain is obtained based on the data of the input optical power and the output optical power, and a pumping light source of the optical fiber amplification unit which is the final stage based on a deviation between the amplification gain and a desired target gain And gain control means for controlling the drive current of
The input optical power at time t is Pin (t), the output optical power at time t is Pout (t), the amplification gain at time t obtained by the gain control means is G (t), and the input / output light The propagation time of the signal light between the optical couplers provided in the power detection means is τf, and the signal processing time of the input optical power data and the output optical power in the gain control means of the optical fiber amplifier as the final stage The difference in signal processing time of data is τe, and the time required from the calculation in the gain control means until the pumping light power changes based on the calculation is the control delay time τc,
The time series data of the input optical power Pin (t) is held in the storage means at least from time t-τf + τe + τc to time t,
An amplification gain G (t) at time t is obtained based on Pout (t) and Pin (t−τf + τe + τc).
A multistage optical fiber amplifier.   5. The optical fiber amplifier according to claim 2, wherein the propagation time τf is at least twice the sum of the signal processing time difference τe and the control delay time τc. In a multistage optical fiber amplifier in which N (N is an integer of 2 or more) stages of optical fiber amplifiers including at least one optical fiber amplification medium and at least one excitation light source are connected.
Branching part of the signal light input to the first-stage optical fiber amplifier of the multi-stage optical fiber amplifier, detecting the optical power of the branched signal light, and detecting the first-stage optical fiber amplifier based on the detection result Input light power detecting means for obtaining the input light power of
Further, a part of the signal light output from the optical fiber amplification medium of the optical fiber amplifier is branched, the optical power of the branched signal light is detected, and each of the optical fiber amplifiers is detected based on the detection result. Output light power detecting means for obtaining the output light power of the stage;
Storage means for storing time-series data of the input optical power;
Gain control means for obtaining an amplification gain based on data of the input optical power and the output optical power, and controlling a drive current of the pumping light source based on a deviation between the amplification gain and a desired target gain And
While preparing for each optical fiber amplifier,
The input optical power at time t is Pin (t), the output optical power of the n-th stage (1 ≦ n ≦ N) optical fiber amplifier at time t is Pnout (t), and the input optical power is detected. The propagation time of the signal light between the optical coupler provided in the means and the optical coupler provided in the output optical power detection means of the n-th stage optical fiber amplifier is τfn, and the n-th stage optical fiber amplifier. When the difference between the signal processing time of the input optical power data in the gain control means and the signal processing time of the output optical power data of the n-th stage optical fiber amplifier is τen,
Holding the time series data of the input optical power from at least time t-τfn + τen to time t;
An amplification gain Gn (t) of the n-th stage optical fiber amplifier at time t is obtained based on Pnout (t) and Pin (t−τfn + τen).
A multistage optical fiber amplifier. In a multistage optical fiber amplifier in which N (N is an integer of 2 or more) stages of optical fiber amplifiers including at least one optical fiber amplification medium and at least one excitation light source are connected.
Branching part of the signal light input to the first-stage optical fiber amplifier of the multi-stage optical fiber amplifier, detecting the optical power of the branched signal light, and detecting the optical power of the first-stage optical fiber amplifier based on the detection result Input light power detecting means for obtaining the input light power of
Further, a part of the signal light output from the optical fiber amplification medium of the optical fiber amplifier is branched, the optical power of the branched signal light is detected, and each of the optical fiber amplifiers is detected based on the detection result. Output light power detecting means for obtaining the output light power of the stage;
Storage means for storing time-series data of the input optical power;
Gain control means for obtaining an amplification gain based on data of the input optical power and the output optical power, and controlling a drive current of the pumping light source based on a deviation between the amplification gain and a desired target gain And
While preparing for each optical fiber amplifier,
The input optical power at time t is Pin (t), the output optical power of the n-th stage (1 ≦ n ≦ N) optical fiber amplifier at time t is Pnout (t), and the input optical power is detected. The propagation time of the signal light between the optical coupler provided in the means and the optical coupler provided in the output optical power detection means of the n-th stage optical fiber amplifier is τfn, and the n-th stage optical fiber amplifier. The difference between the signal processing time of the input optical power data in the gain control means and the signal processing time of the output optical power data of the n-th stage optical fiber amplifier is τen, and the n-th stage light When the time required from the calculation in the gain control means of the fiber amplifier to the change in pumping light power based on the calculation is defined as the control delay time τcn,
Holding time series data of the input optical power from at least time t-τfn + τen + τcn to time t;
An amplification gain Gn (t) of the n-th stage optical fiber amplifier at time t is obtained based on Pnout (t) and Pin (t−τfn + τen + τcn).
A multistage optical fiber amplifier.   8. The multistage optical fiber amplifier according to claim 7, wherein the propagation time τfn is at least twice as long as the sum of the signal processing time difference τen and the control delay time τcn. A program for controlling an amplification gain of an optical fiber amplifier including an optical fiber amplification medium and at least one excitation light source,
An input optical power detection procedure for obtaining optical power of signal light input to the optical fiber amplifier;
An output optical power detection procedure for determining the optical power of the signal light output from the optical fiber amplifier;
A procedure for storing time-series data of the input optical power;
An amplification gain calculation procedure for obtaining an amplification gain based on data of the input optical power and the output optical power;
A gain deviation calculation procedure for calculating a deviation between the amplification gain and a desired target gain;
A drive current correction amount calculation procedure for calculating a drive current correction amount of the excitation light source based on the gain deviation;
A procedure for calculating a new drive current set value based on the correction amount;
A control output procedure for outputting the new drive current set value and controlling the output of the excitation light source;
The input light power value at time t obtained by the input light power detection procedure is Pin (t), and the output light power value at time t obtained by the output light power detection procedure is Pout (t ), The gain value at time t obtained by the gain control procedure is G (t), the propagation time of signal light in a predetermined section is τf, the signal processing time of the input optical power data and the output light Let τe be the difference in signal processing time between power data,
Holding the time series data of the input optical power Pin (t) at least from time t-τf + τe to time t in the storing procedure;
In the amplification gain calculation procedure, the amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe).
A gain control program for an optical fiber amplifier. A program for controlling an amplification gain of an optical fiber amplifier including an optical fiber amplification medium and at least one excitation light source,
An input optical power detection procedure for obtaining optical power of signal light input to the optical fiber amplifier;
An output optical power detection procedure for determining the optical power of the signal light output from the optical fiber amplifier;
A procedure for storing time-series data of the input optical power;
An amplification gain calculation procedure for obtaining an amplification gain based on data of the input optical power and the output optical power;
A gain deviation calculation procedure for calculating a deviation between the amplification gain and a desired target gain;
A drive current correction amount calculation procedure for calculating a drive current correction amount of the excitation light source based on the gain deviation;
A drive current set value calculation procedure for calculating a new drive current set value based on the correction amount;
A control output procedure for outputting the new drive current set value and controlling the output of the excitation light source;
The value of input light power at time t obtained by the input light power detection procedure is Pin (t), and the value of output light power at time t obtained by the output light power detection procedure is Pout (t ), The gain value at time t obtained by the gain control procedure is G (t), the propagation time of signal light in a predetermined section is τf, the signal processing time of the input optical power data and the output light The difference in signal processing time of the power data is τe, and the gain deviation calculation procedure, the drive current correction amount calculation procedure, the drive current set value calculation procedure, and the control output procedure are calculated from the calculation in the amplification gain calculation procedure. Then, the time required for the pump light power to change is defined as the control delay time τc,
Holding the time series data of the input optical power Pin (t) at least from time t-τf + τe + τc to time t in the storing procedure;
In the amplification gain calculation procedure, the amplification gain G (t) is obtained based on Pout (t) and Pin (t−τf + τe + τc).
A gain control program for an optical fiber amplifier. The propagation time τf is the time required for the signal light to propagate between the optical branching coupler inserted for detecting the input optical power and the optical branching coupler inserted for detecting the output optical power. The gain control program for an optical fiber amplifier according to claim 9 or 10.

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