JP4336345B2 - Optical amplifier - Google Patents

Description

  The present invention relates to an optical amplification method and apparatus for adjusting the attenuation of an optical variable attenuator in order to make the gain and output of an optical signal constant regardless of wavelength.

  As a conventional optical amplifying apparatus, for example, as shown in Patent Document 1, there is an apparatus using an optical amplifying unit for wavelength multiplexing. In this optical amplifying device, as shown in FIG. 3, an optical variable attenuator 30 is connected between the optical amplifier 10 at the front stage and the optical amplifier 20 at the rear stage. The optical amplifying unit 10 is provided with an automatic gain control (hereinafter referred to as “AGC”) circuit 11, which is branched from the optical fiber transmission line 1 by optical branching couplers 12 and 13, and is a photodiode. The optical levels of the optical signals on the input side and output side detected by (PD) 14 and 15 are compared. The AGC circuit 11 controls the pumping light source 16 so that the comparison result is constant so that the gain wavelength characteristic of the optical amplifier 20 at the previous stage does not depend on the input power, and the optical amplifier at the previous stage. The gain wavelength characteristic of 10 is compensated to make the entire gain wavelength characteristic uniform and output to the optical amplifying unit 20 via the optical coupler 17. That is, the AGC circuit 11 performs gain control so that the gain of the entire optical amplifying unit 10 is constant without dependence on the wavelength.

  Similarly, the optical amplifying unit 20 is also provided with an AGC circuit 21. The AGC circuit 21 outputs optical signals on the input side and the output side detected by the photodiodes 24 and 25 via the optical branching couplers 22 and 23, respectively. The levels are compared, and the excitation light source 26 is controlled so that the comparison result is constant, so that the gain wavelength characteristic of the optical amplifier 20 at the latter stage is made independent of the input power, and the optical amplifier 20 at the latter stage is controlled. The gain wavelength characteristic is compensated to make the entire gain wavelength characteristic uniform and output to the optical fiber transmission line 1.

  Further, the output level of the optical amplifier 20 at the subsequent stage is branched from the optical fiber transmission line 1 by the optical branching coupler 31 and detected by the photodiode 32. An automatic optical output control (hereinafter referred to as “ALC”) circuit 33 controls the amount of attenuation of the optical variable attenuator 30 according to the detected output level of the optical amplifying unit 20, and the optical output of the optical amplifying unit 20. Was controlled to a certain level.

JP-A-8-248455 (pages 5-6, FIG. 1)

  However, in recent years, there has been an increasing demand for controlling the optical amplifying device with a constant gain using an AGC circuit, instead of controlling the output with a constant output using an ALC circuit as in the conventional example. In particular, the gain of the optical amplifying device is controlled by controlling the attenuation amount of the variable attenuator inside the optical amplifying device based on the gain of the optical amplifying device set by the user including the transmission loss of the transmission medium outside the optical amplifying device. There has been a growing demand for adjusting the gain to a constant gain set by the user. Here, the gain of the optical amplifying device set including the transmission loss of the transmission medium outside the optical amplifying device is the gain of the entire optical amplifying device desired by the user. For example, the optical amplifying device and the final gain outside this optical amplifying device are used. It compensates for transmission loss of an optical fiber transmission line connected between the output end.

  The present invention has been made in view of the above, and controls an optical amplifying device based on a preset gain, performs constant gain control according to needs, and performs highly versatile optical transmission. An object of the present invention is to provide an optical amplification method and apparatus capable of performing the same.

  In order to solve the above-described problems and achieve the object, an optical amplification method according to the present invention includes an optical amplification device in which at least two optical amplification units, at least one attenuator, and a dispersion-compensating optical transmission line are connected. A transmission medium connected between the optical amplification device and a final output terminal outside the optical amplification device in an optical amplification method in which the optical amplification unit amplifies an optical signal input via an optical transmission path And a control step of controlling the attenuation amount of the attenuator so that the gain at the wavelength of the final output terminal is equal to or greater than a predetermined gain and has flatness.

  According to the present invention, a user or the like sets a gain for compensating for transmission loss of a transmission medium outside the optical amplifying apparatus. For example, the gain of each optical amplifying unit is set to G1 and G2, and the total gain G1 + G2 of the optical amplifying unit is set. By controlling the attenuation amount of the attenuator in consideration of the attenuation amount of the dispersion compensation type optical transmission line so that the value approaches the target value C, the gain of the optical amplifying device can be controlled constantly according to the needs of the user and the like. Do.

The optical amplification method according to the present invention may further include a detection step of detecting a total optical input power of an optical signal to the downstream optical transmission line in the above-described invention, and the control step includes the detected total Attenuation correction value ΔL based on optical input power, a coefficient depending on the type of optical transmission line to which the total optical input power is input, and an effective length of the optical transmission line to which the total optical input power is input The attenuation amount of the attenuator is controlled so that the total gain of the optical amplification unit approaches the sum of the target value C and the correction value ΔL.

  According to the present invention, the correction value ΔL of the attenuation amount of the attenuator is further obtained, and the total gain G1 + G2 + G3 of the optical amplifying unit is the target value C and the correction value ΔL depending on the total optical input power of the optical signal to the optical transmission line. By controlling the attenuation amount of the attenuator in consideration of the attenuation amount of the dispersion-compensating optical transmission line so as to approach the sum of the above, the gradient of the gain generated by the SRS is reversed, and the final output terminal The gain dependence at each wavelength is eliminated, and the gain is made flat (constant).

The optical amplifying device according to the present invention includes at least two optical amplifying units, at least one attenuator connected to the optical amplifying unit, and a dispersion-compensating optical transmission line connected to the optical amplifying unit. An optical amplifier that amplifies an optical signal input via an optical transmission path by the optical amplifier and outputs the amplified optical signal to a transmission medium connected to an external final output terminal. Setting means including a gain for compensating for transmission loss of the transmission medium, and based on the set gain, the gain at the wavelength of the final output end is equal to or greater than a predetermined gain and has flatness As described above, control means for controlling the attenuation amount of the attenuator is provided.

  According to the present invention, when the gain value of the optical amplifying apparatus set by the user is input, the gain of the final output end is distributed so as to approach the target value C while being kept constant without dependence on the wavelength. By controlling the attenuation amount of the attenuator in consideration of the attenuation amount of the compensation type optical transmission line, the gain of the optical amplifying device is controlled to be constant.

The optical amplifying device according to the present invention is the optical amplifier according to the present invention, wherein the detecting means for detecting the optical input power of the optical signal to the downstream optical transmission line, the detected optical input power, and the optical input power Correction means for obtaining a correction value for the attenuation amount of the predetermined attenuator based on the coefficient depending on the type of the optical transmission line to which the optical input power is input and the effective length of the optical transmission path to which the optical input power is input; And the control means controls the attenuation amount of the attenuator based on the obtained correction value, the gain value of the entire optical amplifying device, and the attenuation amount of the dispersion compensating optical transmission line. And

  According to the present invention, the correction value ΔL of the attenuation amount of the attenuator based on the optical input power of the optical signal is further obtained, and the total gain of the optical amplifying unit depends on the total optical input power to the optical transmission line. The gain at the final output end is set in advance by controlling the attenuation amount of the attenuator in consideration of the attenuation amount of the dispersion-compensating optical transmission line so as to approach the sum of the value C and the correction value ΔL. The gain is kept constant.

  The optical amplification method and apparatus according to the present invention provide a gain at the wavelength of the final output terminal in consideration of the attenuation amount of the dispersion compensation type optical transmission line when the dispersion compensation type optical transmission line is connected between the stages. Since the attenuation of the attenuator is controlled by the control means while maintaining the flatness above the predetermined gain, the gain of the optical amplifying device is controlled constant according to the needs of the user, etc. There is an effect that it can be performed.

In order to prevent the influence of SRS, the optical amplification method and apparatus according to the present invention obtain a correction value for the attenuation amount of the attenuator so that the total gain of the optical amplification unit approaches the sum of the target value C and the correction value ΔL. In addition, since the attenuation of the attenuator is controlled by the control means so as to have a slope opposite to the slope of the gain generated by the SRS, the gain at each wavelength at the final output end can be flattened. .

  Embodiments of an optical amplification method and apparatus according to the present invention will be described below in detail with reference to the drawings of FIGS. The present invention is not limited to these embodiments, and various modifications can be made without departing from the scope of the present invention.

(Embodiment 1)
FIG. 1 is a configuration diagram showing a configuration of a first embodiment of an optical amplifying device according to the present invention. In the figure, the optical amplifying device 40 includes three optical fiber amplifying units 41, 42, and 50 and an optical variable attenuator 43 connected between the optical fiber amplifying units 41 and 42. The gains of the optical fiber amplifiers 41 and 42 are controlled by the AGC circuit 44, and the amount of attenuation of the optical variable attenuator 43 is controlled by the control circuit 45. The optical fiber amplifying unit 50 is controlled by the AGC circuit 51 and amplifies the multiplexed optical signals in a lump.

  In this optical amplifying apparatus 40, a dispersion compensation type optical transmission line (hereinafter referred to as “DCF”) 56 is connected between the optical fiber amplifying units 42 and 50. Further, in this optical amplifying apparatus 40, an optical branching coupler 52 and an optical power detection circuit (PD) 53 are connected to the input side of the optical fiber amplifier 50, and an optical branching coupler 54 and an optical power detection circuit 55 are connected to the output side. The optical input power P5 and the optical output power P6 of the optical signal are detected.

  The optical amplifying device 40 of the first embodiment is different from the conventional example shown in FIG. 3 in that the optical amplifying device 40 and a final output terminal outside the optical amplifying device 40 are, for example, from an external input means by a user. The gain G0 of the optical amplifying apparatus 40 can be arbitrarily inputted including the transmission loss of the transmission medium connected between the two and the gain G0 can be set in the control circuit 45. The gain G0 is the gain of the entire optical amplifying apparatus desired by the user, and compensates for transmission loss such as an optical fiber transmission line connected between the optical amplifying apparatus and the final output terminal outside the optical amplifying apparatus. It is gain. In addition to the optical output power P4 from the optical power detection circuit 49, the optical input power P5 from the optical power detection circuit 53 is input to the control circuit 45. The control circuit 45 receives these optical powers P4 and P5. The attenuation of the optical variable attenuator 43 is set so that the sum of the gain G1 of the optical fiber amplifier 41, the gain G2 of the optical fiber amplifier 42, and the gain G3 of the optical fiber amplifier 50 becomes C1 (constant). The amount A is controlled.

That is, the gains of the optical fiber amplifiers 41, 42, 50 are
G1 + G2 + G3 = C1 (1)
It becomes. Here, when the attenuation amount of the DCF 56 is D, the gain G0 set by the user is
G0 = G1 + G2 + G3-AD (2)
And substituting equation (1) into equation (2),
G0 = C1-AD (3)
It becomes. Therefore, the attenuation amount A of the optical variable attenuator 43 is
A = C1-D-G0 (4)
Here, since D = P4-P5, Equation (4) is
A = C1- (P4-P5) -G0 (5)
It becomes. Therefore, the value obtained by subtracting the optical power ratio P4-P5 and the set value G0 from the target value C1 is the attenuation amount A, and the control circuit 45 optically changes a control signal having a current value or a voltage value corresponding to the attenuation amount A, for example. It can output to the attenuator 43 and the attenuation amount of the optical variable attenuator 43 can be controlled.

By the way, C1 is a constant determined by the design of the optical amplifying device 40, and is determined based on system requirements such as the distance between relay stations and the total transmission distance. In addition, the parameter necessary to obtain this constant is
1. Maximum total gain G0 (max) of the optical amplifying apparatus 40
2. Maximum attenuation D (max) of the DCF 56 connected between the stages of the optical amplifying device 40
3. Minimum attenuation of optical variable attenuator A (min)
It consists of.

Here, for example, it is assumed that the respective parameters are set as G0 (max) = 22 [dB], D (max) = 10 [dB], and A (min) = 1 [dB] from a certain system request. Then, by substituting these numerical values into equation (3), C1 is obtained.
G0 = C1-AD
22 = C1-1-10
C1 = 33 [dB]
It becomes. In the design of this optical amplifying device, the optical design of each optical amplifying unit is determined so that a constant gain having no dependence on the wavelength is obtained at C = 33 [dB].

Next, an example of obtaining the attenuation amount A of the optical variable attenuator 43 from these design values will be described. Here, for example, assuming that the total gain G0 = 20 [dB] and D = 8 [dB], from the equation (4),
A = C1-D-G0
= 33-8-20
= 5 [dB]
Thus, it is possible to control the gain of the optical amplifying device according to the needs of the user.

  The total gain G0 is also input to the AGC circuits 44 and 51. The AGC circuits 44 and 51 control the optical fiber amplifiers 41, 42, and 50 using a new constant C2 (constant), The transmission loss of the optical fiber transmission line 1 is compensated by collectively amplifying the multiplexed optical signals.

  That is, the optical power detection circuit (PD) 47 detects the optical input power P1 of the optical signal through the optical branching coupler 46 connected to the optical fiber transmission line on the input side of the optical amplifying device 40, and The optical power detection circuit 49 detects the optical output power P4 of the optical signal via the optical branching coupler 48 connected to the optical fiber transmission line on the input side of the DCF 56. The detected optical powers P1 and P4 are taken into the AGC circuit 44, and the AGC circuit 44 controls the optical fiber amplifiers 41 and 42 as follows.

  In the AGC circuit 44, for example, the gains G1 and G2 are determined by controlling the current of the pump lasers of the optical fiber amplifiers 41 and 42 according to the size of P1, and the ratios of the gains G1 and G2 are determined in advance. Yes. Therefore, in the AGC circuit 44, when the optical power ratio P4-P1 is controlled to be constant at G0a, for example, the drive current value and the ratio of the pump laser are determined based on the voltage value of the optical power P1. The gain of the optical fiber amplifiers 41 and 42 is controlled to be G0a based on the determined drive current value and the ratio.

  The optical power detection circuit 53 detects the optical input power P5 of the optical signal via the optical branching coupler 52 connected to the optical fiber transmission line on the output side of the DCF 56, and the optical power detection circuit 55 The optical output power P6 of the optical signal is detected through the optical branching coupler 54 connected to the optical fiber transmission line on the output side of the optical amplifier 40. The detected optical powers P5 and P6 are taken into the AGC circuit 51, and the AGC circuit 51 controls the optical fiber amplifying unit 50 as follows.

  In the AGC circuit 51, for example, the gain G3 is determined by controlling the current of the pump laser of the optical fiber amplifying unit 50 according to the size of P5, and the ratio of the gain G3 is determined in advance. Therefore, in the AGC circuit 51, when the optical power ratio P6-P5 is controlled to be constant at G0b, for example, the drive current value and the ratio of the pump laser are determined based on the voltage value of the optical power P5. The gain of the optical fiber amplifying unit 50 is controlled to be G0b based on the determined drive current value and its ratio.

This C2 is the ratio of the total optical output power P4 of the front-stage optical amplifying unit and the total optical output power P6 of the rear-stage optical amplifying unit.
C2 = P6-P4 (6)
This C2 is a constant determined by the design of the optical amplifying device 40 as in C1.

Here, when the gain of the front-stage optical amplification unit is G0a and the gain of the rear-stage optical amplification unit is G0b, the gain G0 of the entire optical amplification device 40 is
G0 = G0a + G0b-D (7)
It becomes. Then, when obtaining the condition of the gain G0a of the first stage optical amplifying unit, from the equation (7),
G0a = G0−G0b + D (8)
It becomes. Further, the gain G0b of the latter-stage optical amplifying unit is shown in FIG.
G0b = P6-P5 (9)
It becomes. The attenuation amount D of the DCF 56 is
D = P4-P5 (10)
And when the formula is expanded by substituting the formula (9) and the formula (10) into the formula (8),
G0a = G0- (P6-P5)) + (P4-P5)
= G0- (P6-P4) (11)
This equation (11) is obtained from equation (6):
G0a = G0-C2 (12)
It becomes.

Next, when the condition of the gain G0b of the latter-stage optical amplifying unit is obtained, from the equation (7),
G0b = G0-G0a + D (13)
It becomes. Substituting equation (12) into equation (13) and expanding,
G0b = G0− (G0−C2) + D
= C2 + D (14)
It becomes.

By the way, as described above, C2 is a constant determined by the design of the optical amplifying apparatus 40 as described above, and is determined based on system requirements such as the distance between relay stations and the total transmission distance. In addition, the parameter necessary to obtain this constant is
1. Maximum total optical output power P4 (max) of the pre-stage optical amplifier
2. Maximum total optical output power P6 (max) of the latter stage optical amplifier
It consists of.

Here, for example, it is assumed that each parameter is set as P4 (max) = 15 [dBm] and P6 (max) = 21 [dBm] from a certain system request. Then, by substituting these numerical values into equation (6), C2 is obtained.
C2 = P6-P4
= 21-15
= 6 [dB]
It becomes.

  Next, an example of a method for setting the maximum total optical output powers P4 (max) and P6 (max) of the front-stage optical amplifier and the rear-stage optical amplifier will be described below. Here, each maximum total optical output power is limited by the threshold value of the nonlinear optical phenomenon of the optical fiber transmission line on which the optical signal is incident.

  Examples of this nonlinear optical phenomenon include cross phase modulation (XPM), four-wave mixing (FWM), stimulated Raman scattering (SRS), and stimulated Brillouin scattering (SBS). The optical output power of the pre-stage optical amplifying unit is the optical input power to the DCF connected between the stages of the optical amplifying device, and the power upper limit determined by this nonlinear effect is −2 [dBm]. The influence of SBS depends on the optical power of each wavelength regardless of the number of wavelength multiplexing and the wavelength multiplexing interval.

  That is, the threshold value of SBS in DCF is approximately −2 [dBm] when the number of wavelength multiplexing is one wave. For example, when the number of wavelength multiplexing is 80 waves, approximately 17 [dBm] = − 2 + 10 · log 80 It becomes.

  In actual device design, since a margin of 2 [dB] to 3 [dB] is taken into account, in the above-described device with the wavelength multiplexing number of 80 waves, the maximum total optical output power of the preceding optical amplification unit is 15 [dBm]. Set to Further, the optical output power of the latter-stage optical amplifying unit is also limited by the SBS threshold, as described above. However, the single-mode optical fiber (SMF) is generally used as the optical fiber transmission line connected to the output of the latter-stage optical amplification unit, and the threshold value of the SBS is approximately 6 [dB] larger than the DCF. . Therefore, the maximum total optical output power of the rear-stage optical amplifying unit in the apparatus with the wavelength multiplexing number of 80 waves is set to 21 [dBm].

  In this embodiment, based on the value set in this way, the AGC circuit 44 causes the optical fiber amplifying unit 41 so that the optical power ratio (P4−P1) is constant at G0a determined by the equation (12). 42, and the AGC circuit 51 controls the gain of the optical fiber amplifier 50 so that the optical power ratio (P6-P5) is constant at G0b determined by the equation (14).

  As described above, in this embodiment, even when the DCF is connected between the stages, the gain of the entire optical amplifying apparatus including the DCF is not dependent on the wavelength and is kept constant by the user or the like while maintaining a constant gain. Since the attenuation of the optical variable attenuator is controlled so as to approach the set gain, it becomes possible to perform constant gain control according to the user's needs, thereby obtaining a highly versatile optical amplifier. Can do.

In this embodiment, the gain of the optical variable attenuator is set so that the gain G0 is set including the transmission loss of the transmission medium connected between the optical amplifying device and the final output terminal outside the optical amplifying device. Since it is appropriately controlled according to the target values C1 and C2, the gain at the wavelength of the final output end is equal to or greater than a predetermined gain, and can have flatness.

  Further, in this embodiment, even when the DCF is connected between the stages, the total gain of the front-stage optical amplifying section becomes the optimum gain of the front-stage optical amplifying section in the system design, and the rear-stage optical amplifying section. Since the AGC control is performed so that the gain of the optical amplifier becomes the optimum gain of the post-stage optical amplifier in terms of system design, the gain of the optical amplifying device can be controlled constantly according to the needs of the user and the like.

  By the way, in the optical amplifying device of the above-described embodiment, the influence of SRS, which is one of nonlinear optical phenomena, is small. However, depending on the system configuration to be designed, the influence of SRS increases, so the difference in optical power between the short wavelength side and the long wavelength side increases, and the S / N of the optical signal on the short wavelength side deteriorates.

  Therefore, in the present invention, the configuration of the optical amplifying device when performing SRS correction will be described in the following embodiments.

(Embodiment 2)
FIG. 2 is a block diagram showing the configuration of the second embodiment of the optical amplifying device according to the present invention. In the figure, the difference from Embodiment 1 of FIG. 1 is that a correction circuit 60 in which the correction value of the attenuation amount of the optical variable attenuator 43 is set is provided to obtain the attenuation correction value ΔL, and the optical variable attenuation is obtained. This is a point for controlling the attenuation amount A of the device 43.

That is, in this embodiment, the attenuation amount A of the optical variable attenuator 43 is obtained as follows.
G1 + G2 + G3 = C + ΔL (15)
In addition, the gain G0 arbitrarily set by the user or the like is
G0 = G1 + G2 + G3-AD (16)
Are set in advance. Substituting this equation (15) into equation (16),
G0 = C + ΔL−A−D (17)
The attenuation amount A of the optical variable attenuator 43 is
A = C + ΔL−D−G0
= C + [Delta] L- (P4-P5) -G0 (18)
It becomes.

Next, ΔL is obtained. Here, the slope SRS (dG / dλ) of the gain wavelength characteristic generated by the influence of SRS is
SRS (dG / dλ) = 4.34 · (β · P0 · Leff) [dB / nm]
... (19)
Here, P0: Total optical power of the optical signal incident on the optical fiber transmission line 1
[W]
(Equivalent to P4 in FIG. 1)
β: Optical fiber transmission line 1 on which this total optical power is incident
Coefficient [1 / W · km · nm] depending on (type)
Leff: effective length [k of optical fiber transmission line into which this total optical power is incident [k]
m]
It becomes.

Incidentally, the expression ^{(19), ELECTRONICS LETTERS, 16 th April 1998} , Vol. 34, no. 8, M.M. It is described in the Zirngib literature.

Next, in order to cancel the slope of the gain wavelength characteristic generated by the influence of the SRS, the slope of the gain wavelength characteristic generated by the optical amplification unit OFA (dG / dλ) is the slope of the gain wavelength characteristic generated by the influence of the SRS. Since the slope is opposite to
OFA (dG / dλ) = − a · ΔL [dB / nm] (20)
Where, a: proportional coefficient [1 / nm] depending on the design of the optical amplifier
ΔL: Correction value [dB] of attenuation of the optical variable attenuator
It becomes.

When the sum of the equations (19) and (20) becomes zero, the gain of each wavelength after transmission through the optical fiber transmission line becomes uniform and the gain wavelength characteristic becomes flat. First, the sum of the equations (19) and (20) is
SRS (dG / dλ) + OFA (dG / dλ) = 4.34 · (β · P0 · Leff) −a · ΔL = 0 (21)
It becomes.

Next, ΔL is
ΔL = 4.34 · (β · P0 · Leff) / a (22)
It is obtained by That is, ΔL is the total optical power P0 of the optical signal incident on the optical fiber transmission line, the coefficient β depending on the type of the optical fiber transmission line on which the total optical power P0 is incident, and the total optical power incident. It is a value obtained from the effective length of the optical fiber transmission line.

In this embodiment, the correction value ΔL (actually, ΔL1 and ΔL2 are obtained and added) of the attenuation amount of the optical variable attenuator can be obtained based on the above-described equations (19) to (22). That is, the correction value ΔL1 of the attenuation amount of the optical variable attenuator for the optical fiber transmission line 1 connected to the optical amplifier of the next stage is
ΔL1 = 4.34 · (β1 · P6 · Leff1) / a
Here, P6: Total optical power [W] of the optical signal incident on the transmission path of the next stage
β1: Coefficient [1 / (W · km · nm)] depending on the optical fiber transmission line on which this total optical power is incident
Leff1: Effective length [km] of an optical transmission line on which this total optical power is incident
a: Proportional coefficient (unit: [1 / nm]) depending on the design of the optical amplification unit of the device itself
It becomes.

The correction value ΔL2 of the attenuation amount of the optical variable attenuator for the DCF 66 is
ΔL2 = 4.34 · (β2 · P4 · Leff2) / a
Here, P4: Total optical power [W] of the optical signal incident on the DCF
β2: coefficient [1 / (W · km · nm)] depending on the DCF to which this total optical power is incident
Leff2: The effective length [km] of the DCF on which this total optical power is incident. Therefore, the correction value ΔL of the attenuation of the optical variable attenuator in this embodiment is
ΔL = ΔL1 + ΔL2
= 4.34 · (β1 · P6 · Leff1) /a+4.34· (β2 · P4 · Leff2) / a
= 4.34 · {(β1 · P6 · Leff1) + (β2 · P4 · Leff2)} / a
It becomes.

  Note that the AGC control of the optical fiber amplifiers 41 and 42 by the AGC circuit 44 is controlled so that the optical power ratio (P4-P1) is constant at G0a determined by the equation (12), as in the second embodiment. In addition, the AGC control of the optical fiber amplifying unit 50 controls the optical power ratio (P6-P5) to be constant at G0b determined by the equation (14).

  As described above, in this embodiment, similarly to the first embodiment, it is possible to perform constant gain control according to the user's needs, and to correct the slope of the gain wavelength characteristic generated by the influence of SRS. In order to do so, the correction value of the attenuation amount of the optical variable attenuator is obtained from the detection result of the total optical output power, and the attenuation amount of the optical variable attenuator is controlled so as to cancel the slope of the gain wavelength characteristic. The gain wavelength characteristic at each wavelength is flattened at the input end (corresponding to the final output end of the first embodiment) of the next-stage optical amplifying device via the optical fiber transmission line, thereby improving the transmission efficiency. In addition, the influence of SRS in DCF can be prevented, and the transmission efficiency can be further improved.

  For this reason, in this embodiment, even if the optical power incident on the optical fiber transmission line fluctuates due to an increase or decrease in the number of channels, the slope of the gain of the wavelength multiplexed signal generated by the influence of the SRS is automatically corrected collectively. Thus, the deviation of the gain of the wavelength multiplexed signal can be minimized, so that the optical power at each wavelength becomes uniform, the S / N deterioration in the optical signal on the short wavelength side is prevented, and stable optical transmission is achieved. Can be done.

  The present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the structure of Embodiment 1 of the optical amplifier concerning this invention. Similarly, it is a block diagram which shows the structure of Embodiment 2 of an optical amplifier. It is a block diagram which shows an example of a structure of the conventional optical amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber transmission line 10,20 Optical amplification part 11,21,44,51 AGC circuit 12,13,22,23,31,46,48,52,54 Optical branch coupler 14,15,24,25,32, 47, 49, 53, 55 Optical power detection circuit (PD)
16, 26 Excitation light source 17 Optical coupler 30, 43 Optical variable attenuator 33 ALC circuit 40 Optical amplifier 41, 42, 50 Optical fiber amplifier 45 Control circuit 60 Correction circuit

Claims (1)

At least a front optical amplification block composed of two optical fiber amplifying unit, and the back optical amplification block, and at least one attenuator interposed between the two fiber amplifier of the front stage optical amplifying unit, front stage A dispersion-compensating optical transmission path interposed between the optical amplification section and the rear-stage optical amplification section, and an optical signal input via the optical transmission path is transmitted by the optical fiber amplification section and the rear-stage optical amplification section. In the optical amplifying device that amplifies and outputs to the output end side optical transmission line connected between the external final output end,
Setting for setting a pre-SL dispersion compensating optical transmission line gain value of the entire optical amplifier including a gain to compensate for the transmission loss of the transmission loss and the output terminal side optical transmission line, the gain G0 set by the user Means,
Pre-stage control for controlling the optical power ratio (P4-P1) of the total optical output power P4 of the optical signal from the pre-stage optical amplifier to the total optical input power P1 of the optical signal to the pre-stage optical amplifier. Means,
Post-stage control for controlling the optical power ratio (P6-P5) of the total optical output power P6 of the optical signal from the post-stage optical amplifier to the total optical input power P5 of the optical signal to the post-stage optical amplifier. Means,
First detection means for detecting a first total optical input power of an optical signal to the output end side optical transmission line ;
Second detection means for detecting a second total optical input power of an optical signal to the dispersion-compensating optical transmission line;
The detected first and second total optical input power , a coefficient depending on the type of each optical transmission line to which the first and second total optical input power are input , and the first and second total optical input An effective length of each optical transmission line to which power is input, and a proportionality coefficient indicating a relationship between a change in the sum of gains of each of the optical fiber amplifying units and the subsequent optical amplifying unit and a slope of the gain wavelength characteristic caused by the change. Correction means for obtaining a correction value ΔL of the attenuation amount of the attenuator,
Accepting the input of the gain G0 from the setting means and the input of the correction value ΔL from the correction means, and the gain of each of the optical fiber amplifiers and the subsequent optical amplifiers when there is no dependence on the wavelength the sum is constant value is C, the attenuation of the dispersion compensating optical transmission line is D, along with the set to the sum of the gain of each optical fiber amplifying unit and the back optical amplifying part (C + ΔL), before Symbol Control means for controlling the attenuation amount of the attenuator to (C + ΔL−D−G0) ;
The provided optical amplifier and wherein the one holding constant the gain of the entire optical amplifier to said set gain G0.

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