JP6013992B2 - Optical amplifier and optical amplification method - Google Patents

Description

  The present invention relates to an optical amplifier and an optical amplification method.

  Advanced functions of optical nodes such as C / D / C-less (Color-less / Direction-less / Contention-less) of ROADM (Reconfigurable Optical Add / Drop Multiplexer) to efficiently transmit rapidly increasing communication traffic Is required. When this ROADM is converted to C / D / C-less, loss within the node increases, so that an optical fiber amplifier for loss compensation is required. Since an intra-node loss compensation optical fiber amplifier is provided for each route, a large number of optical fiber amplifiers are required. Therefore, it is important that the configuration and control method are simple and can be realized at low cost. Further, in such ROADM or the like, it is necessary to follow a change in the number of wavelengths accompanying a change in signal wavelength arrangement in the ring or a high-speed change in signal light power due to a transmission line break in the optical fiber transmission line. For this reason, an optical fiber amplifier having a forward pumping configuration capable of high-speed automatic gain control (hereinafter referred to as AGC (Automatic Gain Control)) by high-speed feedforward control is used as an optical fiber amplifier for intra-node loss compensation as described above. It becomes effective.

  FIG. 20 shows an example of the configuration of a forward-pumped optical fiber amplifier 100 to which AGC by feedforward control is applied. The optical fiber amplifier 100 includes a pumping light source 94 only on the input side of the amplification optical fiber, and an erbium-doped optical fiber 97 (hereinafter referred to as EDF (Erbium Doped Fiber)) that is an amplification optical fiber via an optical coupler 96. ) Has a simple structure in which excitation light is incident. In the AGC method by feedforward control, the signal light incident on the optical fiber amplifier 100 is branched using a tap optical coupler 91 on the input side of the amplification optical fiber, and the power of the signal light is changed to PD (Photo). Monitor 92). By this monitor, the power of the pumping light necessary to make the signal gain constant is obtained, and the power of the pumping light is controlled in accordance with the signal input power, thereby enabling high-speed gain control.

  An erbium-doped fiber amplifier for L-band amplification (hereinafter referred to as EDFA (Erbium Doped Fiber Amplifier)) having a forward pumping configuration such as the optical fiber amplifier 100 is compared with an EDFA for C-band amplification having the same configuration. Excitation efficiency is low. The reason is due to the principle of operation when a signal is amplified. FIG. 21 is a diagram illustrating the operation of an EDFA for L-band amplification with forward excitation. In the EDFA for L-band amplification of forward excitation, when the excitation light is absorbed, a large amount of C-band ASE (Amplified Spontaneous Emission) light is generated on the first half in the longitudinal direction of the EDF 97, that is, on the input side. This ASE light is absorbed again in the second half in the longitudinal direction of the EDF 97, thereby contributing to amplification of the L-band signal light. On the other hand, part of the C-band ASE light generated in the first half in the longitudinal direction propagates in the opposite direction to the signal light. Since the ASE light propagating in the reverse direction becomes useless energy that does not contribute to L-band signal amplification, the L-band amplification EDFA has lower excitation efficiency than the C-band amplification EDFA.

  Further, the EDFA for L-band amplification by forward pumping has a problem that control is difficult because the pumping light power for obtaining the same signal gain differs depending on the wavelength of the signal light. FIG. 22 shows the dependence of the pumping light power necessary for realizing this signal gain on the signal light input power when the target signal gain is 16.58 dB in the L-band amplification EDFA having the configuration of FIG. It is the graph which showed sex. Here, the target signal gain is the signal gain of the center wavelength of the WDM signal under the condition that the signal gain of the WDM (Wavelength Division Multiplexing) signal is flat in the L-band amplification EDFA used for measurement. It is. The condition that the signal gain of the WDM signal is flat is a condition in which the gain of the short wavelength signal light and the gain of the long wavelength signal light are equal or nearly equal in the signal light at both ends of the WDM signal. That is. FIG. 23 is a graph showing the signal gain for each wavelength included in the WDM signal when the graph shown in FIG. 22 is obtained. Specifically, a 14-wave WDM signal with equal intervals in the wavelength range of 1573.71 nm to 1606.60 nm, which is the wavelength band of the L-band amplification EDFA, is generated, and the incident power after combining the generated WDM signal is − It is the result of measuring the signal gain of each WDM signal when signal amplification is performed with an EDFA for L-band amplification set to 5 dBm. In FIG. 23, the signal gain of the signal having a wavelength of 1573.71 nm which is the short wavelength end of the WDM signal is 15.14 dB, and the signal gain of the signal having a wavelength of 1606.60 nm which is the long wavelength end is 15.15 dB. . That is, the signal gains at the wavelengths at both ends are substantially equal, and the condition for flat signal gain is satisfied. In FIG. 23, the signal gain of the center wavelength 1588.73 nm of the WDM signal is about 16.5 dB, which is the above-described target signal gain.

  In FIG. 22, the signal light has three wavelengths of 1573.71 nm, 1588.73 nm, and 1604.03 nm as incident single-wave signal light, and ranges from 0.01 mW (−20 dBm) to 1 mW (0 dBm). In the range of the signal light power, the value of the pumping light power necessary for realizing the signal gain of 16.5 dB is measured. From the measurement results shown in FIG. 22, the difference in pumping light power between the signal wavelengths of 1573.71 nm and 1604.03 nm at a signal light input power of 0.5 mW (−3 dBm) is a very large value of 318.5 mW. That is, there is a wavelength dependence of the signal gain in which the relationship between the pumping light power and the signal light input power varies greatly depending on the wavelength. Therefore, when specifying the power of the pumping light set as the pumping light source in the L-band amplification EDFA, not only the power of the signal light incident on the EDFA but also the wavelength of the pumping light required for amplification must be monitored. The power cannot be specified. In general, the method of monitoring the signal light incident on the EDFA is complicated. In particular, when performing the above-described AGC, the L-band amplification EDFA is more difficult to control than the C-band amplification EDFA. There is a problem.

  To date, with respect to the problem of low excitation efficiency, a method has been proposed in which C-band light is incident on an L-band amplification EDFA to improve excitation efficiency (see, for example, Patent Document 1). . Also, a method for improving the wavelength dependence of signal gain in an EDFA for L-band amplification has been proposed (for example, see Non-Patent Document 1).

Japanese Patent No. 4960198

M. A. Mahdi and H. Ahmad, “Gain enhanced L-band Er3 + -doped fiber amplifier utilizing unwanted backward ASE,” IEEE Photonics Technology Letters, Vol. 13, No. 10, pp. 1067-1069, 2001.

However, although Patent Document 1 shows that the pumping efficiency is improved by the incidence of C-band light, in an actual system such as ROADM, all of the signal light input power that changes as the number of wavelengths increases or decreases. After solving the problem of the wavelength dependence of the signal gain in the range, conditions such as a specific value of the C-band optical power incident on the EDF are not clarified.
Non-Patent Document 1 shows that the wavelength dependence of the signal gain with respect to a specific signal light input power is improved, but the signal light input power that changes with an increase or decrease in the actual number of wavelengths. The specific C-band optical power conditions for improving the wavelength dependence of gain in all the ranges are not clarified.

  The present invention has been made to solve the above problems, and its object is to allow a change in the input power of the signal light accompanying a change in the number of wavelengths when the L-band signal light is amplified by the forward pumping configuration. And providing an optical amplifier and an optical amplification method capable of suppressing the wavelength dependence of signal gain.

In order to solve the above problems, an aspect of the present invention is an L-band optical amplifier having a forward pumping configuration, and has one or more L-band input signal light having a power in the range of −20 dBm to −5 dBm. Is combined with the signal input unit to which the light is incident, the excitation light source that emits the excitation light that becomes the signal gain when the gain of the L-band WDM signal becomes flat, the input signal light, and the excitation light. An output combining unit, an amplification medium connected to the combining unit, amplifying the L-band input signal light output from the combining unit based on the excitation light, and outputting the amplified signal, and the combining unit And C-band light having a power ratio of 1/1000 or more with respect to the power of C-band ASE light propagating back from the amplification medium through the multiplexing unit. and a C-band light entrance portion incident on the C-band light entrance portion, the combined A separation and multiplexing unit that separates the C-band ASE light that propagates back from the amplification medium through the multiplexing unit, and a mirror that reflects the C-band ASE light separated by the separation and multiplexing unit The separation / multiplexing unit includes the C-band light reflected by the mirror having a power ratio of 1/1000 or more to the power of the C-band ASE light, and the incident L An optical amplifier characterized in that it combines the input signal light of the band and outputs it to the multiplexing section .

  According to another aspect of the present invention, in the above-described invention, an L-band light detection unit that detects power of the L-band input signal light, a predetermined power of the L-band input signal light, and the excitation A feedforward control unit that selects a power value of the pumping light based on information indicating a relationship with light power and a power value detected by the L-band light detecting unit, and the pumping light source May emit the excitation light having a power value selected by the feedforward control unit.

  Further, according to one embodiment of the present invention, in the above-described invention, the reflectance of the mirror is such that a ratio of the power of the C-band light reflected by the mirror and the power of the ASE light in the C-band is 1000 minutes. Or an optical attenuator that is arranged between the separation and multiplexing unit and the mirror and through which the C-band light reflected by the mirror passes, An optical attenuator is provided that attenuates the power of the C-band light reflected by the mirror so that the ratio of the reflected C-band light power to the C-band ASE light power is 1/1000 or more. This may be a feature.

Another embodiment of the present invention is an optical amplification method using an L-band optical amplifier with a forward pumping configuration, in which a signal input unit has an L-band of one or more waves having a power in the range of −20 dBm to −5 dBm. A signal light incident step for entering the input signal light, a pumping light emitting step for emitting the pumping light that becomes a signal gain when the pumping light source has a flat gain of the L-band WDM signal, and a multiplexing unit are incident A combining step for combining the excitation light with the L-band input signal light having the power in the range and the excitation light, and the amplification medium based on the excitation light. An amplifying step for amplifying the input signal light, and a C-band light incident portion located between the multiplexing portion and the signal input portion, and the C-band ASE light propagating backward from the amplification medium through the multiplexing portion . The power ratio is more than 1/1000. And a C-band light incidence step of entering the C-band light over to the amplifying medium, and in the C-band light entrance step, the connected separating multiplexing portion multiplexing portion, the through the multiplexing section The C-band ASE light propagating backward from the amplification medium is separated, a mirror reflects the C-band ASE light separated by the separation / combining unit, and the separation / combining unit is coupled to the C-band ASE light. The C-band light reflected by the mirror having a power ratio of 1/1000 or more to the power of the light is combined with the input signal light of the L-band incident to the combining unit. The light amplification method is characterized by emitting light.

  According to the present invention, when the L-band signal light is amplified by the forward pumping configuration, the change in the input power of the signal light accompanying the change in the number of wavelengths is allowed, and the wavelength dependence of the signal gain is suppressed. Is possible.

1 is a block diagram showing a configuration of an optical fiber amplifier according to a first embodiment of the present invention. It is a block diagram which shows the structure of the optical fiber amplifier by 2nd Embodiment of this invention. It is a graph which shows the relationship between (DELTA) G in the 1-wave signal input of L band and signal light input power in the embodiment. It is a graph which shows the relationship between the power of C-band ASE light and signal light input power in the 1-wave signal input of L band in the embodiment. It is a graph which shows the definition of (DELTA) G in the same embodiment. It is a graph (the 1) which shows the relationship between (DELTA) G and the ASE reflectance in the 1-wave signal input of the L band in the embodiment. It is a graph (the 2) which shows the relationship between (DELTA) G and the ASE reflectance in the 1-wave signal input of L band in the same embodiment. 4 is a graph (No. 1) showing a wavelength arrangement of an L-band WDM signal input in the embodiment. 4 is a graph (No. 2) showing a wavelength arrangement of L-band WDM signal input in the embodiment. 4 is a graph (No. 3) showing a wavelength arrangement of an L-band WDM signal input in the embodiment. It is a graph which shows the relationship between (DELTA) G in the WDM signal input of L band and signal light input power in the embodiment. It is a block diagram which shows the structure of the optical fiber amplifier by 3rd Embodiment of this invention. It is a block diagram which shows the structure of the optical fiber amplifier by the modification of the embodiment. It is a block diagram which shows the structure of the optical fiber amplifier by 4th Embodiment of this invention. It is a block diagram which shows the structure of the optical fiber amplifier by 5th Embodiment of this invention. It is a graph which shows the relationship between the excitation light power and signal light input power in the embodiment. It is a block diagram which shows the structure of the optical fiber amplifier by 6th Embodiment of this invention. It is a block diagram which shows the structure of the optical fiber amplifier by the modification (the 1) of the embodiment. It is a block diagram which shows the structure of the optical fiber amplifier by the modification (the 2) of the embodiment. It is a block diagram which shows the structure of EDFA for L band amplification of the forward excitation which applied AGC. It is a figure which shows operation | movement of EDFA for L band amplification of forward excitation. It is a graph which shows the signal light input power dependence of excitation light power. It is a graph for demonstrating the conditions where the signal gain of the WDM signal of L band becomes flat in the EDFA for L band amplification.

(First embodiment)
Embodiments of the present invention will be described below with reference to the drawings. The optical amplifier and optical amplification method of the present invention uses an erbium-doped optical fiber (EDF) or a planar optical waveguide doped with erbium ions as an amplification medium. In the following embodiments, an example using an EDF will be described. To do. FIG. 1 is a block diagram showing a configuration of an optical fiber amplifier 1 according to the first embodiment of the present invention. The optical fiber amplifier 1 is an amplifier that amplifies L-band light having a forward pumping configuration, and includes a configuration in which C-band light is incident on the EDF 13. The L-band input signal light and pumping light are incident on the EDF 13, and the EDF 13 The L-band signal light amplified in step 1 is emitted. The optical fiber amplifier 1 is applied, for example, to an intra-node loss compensation optical amplifier shown in the following references. In the technique described in the reference, it is necessary to compensate for a loss within the node of about 20 dB at the maximum in consideration of the loss of the passive optical component inside the node and the loss imbalance due to the wavelength / port. Assuming that the output of the WDM reception amplifier is about 0 dBm / ch, it is assumed that the optical power input to the intra-node loss compensation amplifier is about −20 dBm to −15 dBm per wavelength. In addition, in the case of the node configuration described in the reference document, the intra-node loss compensation amplifier may have a WDM input of about 10 wavelengths, so that the input power of the intra-node loss compensation amplifier is −20 dBm. It is desirable that (for one wavelength) to −5 dBm (for 10 wavelengths) can be covered with the same characteristics. Therefore, the power of the L-band signal light incident on the optical fiber amplifier 1 is set to −20 dBm (1 wavelength) to −5 dBm (10 wavelengths).

  References: Y. Sakamaki, T. Kawai, M. Fukutoku, T. Kataoka and K. Suzuki, “Experimental demonstration of arrayed optical amplifiers with a shared pump laser for realizing colorless, directionless, contentionless ROADM,” Optics Express, Vol. 20, No. 26, pp. B131-B140, 2012.

  The optical fiber amplifier 1 includes an optical isolator 10, a C-band light incident unit 20, an optical coupler 11, an excitation light source 12, an EDF 13, and an optical isolator 14. The optical isolator 10 and the optical isolator 14 prevent oscillation due to fiber end reflection. The excitation light source 12 emits 0.98 μm or 1.48 μm excitation light. In the configuration of each embodiment described below, the same characteristics and effects can be obtained at any wavelength of 0.98 um or 1.48 um, but 0.98 um (that is, 980 nm) is obtained in the measurement. Excitation light is used. The EDF 13 is an L-band amplification erbium-doped optical fiber. For the sake of explanation, the side on which the L-band light to be amplified is incident is called the input side, and the amplified L-band signal light is emitted. The side is called the output side. The EDF 13 amplifies the L-band light incident from the input side based on the excitation light incident from the input side, and emits the light from the output side. The C-band light incident unit 20 is disposed on the input side of the EDF 13 and emits C-band light. The optical coupler 11 combines the incident L-band signal light to be amplified, the C-band light emitted from the C-band light incident unit 20, and the excitation light emitted from the excitation light source 12 and enters the EDF 13.

The operation of the optical fiber amplifier 1 will be described. As a premise, the power of the L-band signal light incident from a signal input unit (not shown) of the optical fiber amplifier 1 is in the range of −20 dBm to −5 dBm as described above. Further, the C-band light incident unit 20 is configured such that the ratio of the power of the C-band light incident on the EDF 13 and the power of the C-band ASE light that propagates backward from the input side of the EDF 13 is 1/1000 or more. The power of the C band light to be emitted is set.
First, signal light enters the optical fiber amplifier 1 and passes through the optical isolator 10. The C-band light incident unit 20 emits C-band light. The excitation light source 12 emits excitation light. The optical coupler 11 combines the signal light, the C-band light, and the excitation light and enters the EDF 13. The EDF 13 amplifies the signal light based on the incident excitation light. At this time, the C-band light incident on the EDF 13 is absorbed in the longitudinal direction of the EDF 13 and the C-band light in the same direction as the signal light is increased. The C-band light is used to amplify the L-band signal light. Used. The EDF 13 emits the amplified signal light, and the emitted signal light passes through the optical isolator 14 and is emitted to the outside from a signal output unit (not shown) of the optical fiber amplifier 1.
With the above configuration, when the power of the L-band input signal light is in the range of −20 dBm to −5 dBm, the power of the C-band light incident on the EDF 13 and the power of the C-band ASE light propagating backward from the input side of the EDF 13 The C-band light incident part 20 enters the EDF 13 with the C-band light having a power ratio of 1/1000 or more. As a result, the excitation efficiency of the L-band signal amplification is improved by making the C-band light incident on the EDF 13 as shown in the configurations of the second and third embodiments to be described later, which embody the configuration of the first embodiment. It becomes possible to allow a change in the input power of the signal light accompanying a change in the number of wavelengths and to suppress the wavelength dependence of the signal gain.

(Second Embodiment)
FIG. 2 is a block diagram showing a configuration of the optical fiber amplifier 2 according to the second embodiment of the present invention. The optical fiber amplifier 2 according to the second embodiment has a configuration in which a C-band light incident portion 20 described below is embodied instead of the C-band light incident portion 20 in the optical fiber amplifier 1 according to the first embodiment. The light incident part 20a is provided. In the optical fiber amplifier 2 of the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and different configurations will be described below. The C-band light incident unit 20 a includes a C / L separation coupler 21, an optical attenuator 22, and a mirror 23. The C / L separation coupler 21 is a coupler that separates C-band light and L-band light, separates C-band ASE light that propagates backward from the input side of the EDF 13, and emits it to the optical attenuator 22 side. Further, the C / L separation coupler 21 combines the C-band light reflected by the mirror 23 and emitted through the optical attenuator 22 with the L-band signal light and emits it to the EDF 13 side. The optical attenuator 22 attenuates the power of the C-band ASE light reflected by the mirror 23 and emits it. The optical attenuator 22 can attenuate the power of the reflected C-band ASE light to an arbitrary value in response to a user operation. The reason why the optical attenuator 22 is disposed between the CL separation coupler 21 and the mirror 23 is that the power of the L-band signal light incident on the EDF 13 is not attenuated when setting the power of the C-band ASE light. It is to do. The mirror 23 reflects and emits incident C-band ASE light. The broken line shown in FIG. 2 propagates backward from the input side of the EDF 13, is reflected and attenuated by the C-band light incident portion 20a, and is returned to the EDF 13 (hereinafter also referred to as feedback to the EDF 13). Indicates the path through which light passes.

The operation of the C-band light incident part 20a in the second embodiment will be described. Similar to the first embodiment, the power of the L-band signal light incident on the optical fiber amplifier 2 is in the range of −20 dBm to −5 dBm. The C / L separation coupler 21 separates the C-band ASE light that propagates backward from the input side of the EDF 13 along the path indicated by the broken line in FIG. 2 from the L-band light. The separated C-band ASE light passes through the optical attenuator 22 and is reflected by the mirror 23. The power of the C-band ASE light reflected by the mirror 23 is attenuated by the optical attenuator 22. The optical attenuator 22 is reflected by the mirror 23 with an attenuation amount in which the ratio of the power of the C-band ASE light returning to the EDF 13 and the power of the C-band ASE light propagating back from the EDF 13 is 1/1000 or more. The C-band ASE light is attenuated. The C / L separation coupler 21 combines the C-band ASE light attenuated by the optical attenuator 22 and the incident L-band signal light, and outputs the combined light to the input side of the EDF 13.
In this way, the C-band ASE light that does not contribute to amplification of the signal light that propagates backward from the input side of the EDF 13 is reflected and attenuated by the C-band light incident portion 20a and fed back to the EDF 13, so that the same direction as the signal light As a result, the C-band ASE light propagating to the light increases and the excitation efficiency of the L-band signal amplification can be increased equivalently to the case where the C-band light is directly incident and increased.

(When a single wavelength signal is amplified)
FIG. 3 shows gain flatness (hereinafter also referred to as ΔG) when an L-band amplification EDFA having the configuration of the optical fiber amplifier 2 is used and an L-band single-wave signal light is amplified with the ASE reflectance as a parameter. It is a graph which shows the result of having measured the signal light input power dependence of (). Here, the ASE reflectivity is a ratio defined by the ratio of the power of the C-band ASE light returning to the EDF 13 and the power of the C-band ASE light propagating back from the input side of the EDF 13. FIG. 4 shows a C-band that is fed back to the EDF 13 when an L-band amplification EDFA having the configuration of the optical fiber amplifier 2 is used and an L-band signal light is amplified with the ASE reflectance as a parameter. It is a graph which shows the result of having measured the signal light input power dependence of ASE optical power.
In the measurement of the signal gain performed when obtaining the results of FIGS. 3 and 4, the wavelengths of the signals to be measured are three wavelengths of 1573.71 nm, 1588.73 nm, and 1604.03 nm. Further, in the EDFA for L-band amplification having the configuration of the optical fiber amplifier 2 used for the measurement, the signal gain of the wavelength 1588.73 nm which is the center wavelength is obtained under the condition that the gain is flat as shown in FIG. It is about 16.5 dB. As shown in FIG. 5, as shown in FIG. 5, 1573.71 nm, 1588.73 nm, 1604. The signal gain of 3 wavelengths of 03 nm was measured and plotted on the graph.

In FIG. 5, the difference between the measured signal gains at both ends of 1573.71 nm and 1604.03 nm is defined as ΔG, and the wavelength dependency of the signal gain is evaluated using ΔG as an index of the wavelength dependency of the gain. ΔG takes a positive value when the signal gain of 1573.71 nm which is the wavelength on the short wavelength side is larger, and is negative when the signal gain of 1604.03 nm which is the wavelength on the long wavelength side is larger. I take the.
As can be seen from FIG. 3, when the ASE reflectance is −30.27 dB, the absolute value of ΔG is suppressed to 3 dB or less in the range of the signal light input power from −20 dBm to −5 dBm. In addition, when the ASE reflectance is -10.65 dB, it can be seen that the absolute value of ΔG is 1 dB or less and the gain flatness is achieved when the signal light input power is in the range of −20 dBm to −5 dBm. Further, it can be seen that ΔG becomes 0 dB when the ASE reflectance is −10.65 dB and the signal light input power is −15 dBm. Also, from FIG. 4, when the ASE reflectivity is -10.65 dB, the power of the C-band ASE light returning to the EDF 13 increases according to the signal light input power, from -7.26 dBm to -5.94 dBm. I understand that

  Here, with reference to FIG. 6 and FIG. 7, the value of the ASE reflectance necessary to achieve gain flatness will be described. As described above, in the EDFA for L-band amplification having the configuration of the optical fiber amplifier 2 used for the measurement, the signal gain with a wavelength of 1588.73 nm is obtained under the condition that the gain is flat as shown in FIG. It is about 16.5 dB. Therefore, in the excitation state in which the signal gain at the wavelength of 1588.73 nm is 16.5 dB, the ASE reflectance is changed and the same as in the above-described measurement of FIG. 5, 1573.71 nm, 1588.73 nm, and 1604.03 nm. The signal gain was measured for three wavelengths. Furthermore, ΔG, which is a difference in signal gain when one wavelength of signal light having wavelengths of 1573.71 nm and 1604.03 nm is incident, was measured. The power of the signal light incident on the EDFA for L-band amplification was measured with two powers of −20 dBm and −5 dBm. 6 and 7 are graphs showing the relationship between the gain flatness (ΔG) and the ASE reflectivity when an L-band single-wave signal light is incident. FIG. 6 shows that the signal light input power is −20 dBm. FIG. 7 shows a case where the signal light input power is −5 dBm. 6 and 7 that ΔG monotonously decreases as the ASE reflectance increases. Further, when the ASE reflectance is −30.27 dB, the absolute value of ΔG is suppressed to 3 dB or less regardless of whether the signal light input power is −20 dBm or −5 dBm. That is, the ratio of the power of the C-band ASE light returning to the EDF 13 and the power of the C-band ASE light propagating back from the input side of the EDF 13 is set to be 1/1000 or more, thereby obtaining a gain wavelength. It becomes possible to suppress the dependency within 3 dB. In addition, when the ASE reflectance is -10.65 dB, it is understood that the absolute value of ΔG is 1 dB or less and the gain flatness is achieved in any condition of the signal light input power of −20 dBm and −5 dBm. . When the number of wavelengths changes and the signal light input power to the optical amplifier changes, in a system such as ROADM, it is important that the gain is constant, and the results of these measurements are the configuration of this embodiment. Is suitable when applied to a system such as ROADM. In general, on the Drop side of a C / D / C-less ROADM, if the gain difference is within 3 dB, it falls within the dynamic range of the optical receiver, so the wavelength dependence of gain is kept within 3 dB. Thus, the optical fiber amplifier 2 can be applied as an optical amplifier of such a drop-side optical receiver.

  When the wavelength dependence of the gain is suppressed to within 3 dB, in the case of the optical fiber amplifier 2 shown in FIG. 2, the pumping light power is set to be equal to the signal gain when the gain of the L-band WDM signal becomes flat. . Also, an arbitrary ratio is selected in advance so that the ratio of the power of the C-band ASE light returning to the EDF 13 and the power of the C-band ASE light propagating back from the input side of the EDF 13 is 1/1000 or more. The optical attenuator 22 is set with an attenuation amount according to the selected arbitrary ratio.

(When amplifying a WDM signal)
Next, a case where a WDM signal having the wavelength arrangement shown in FIGS. 8 to 10 is incident on the optical fiber amplifier 2 which is an EDFA for L-band amplification in FIG. 2 will be described. In any of the wavelength arrangements shown in FIGS. 8 to 10, WDM signals have wavelength channels of 1573.71 nm and 1606.60 nm at both ends, 12 waves are arranged between them, and a total of 14 WDM signals are generated. FIG. 8 shows a case where 12 wavelength channels are evenly arranged in the wavelength band of the WDM signal. FIG. 9 shows a case where 12 wavelength channels are concentrated on the short wavelength side of the wavelength band of the WDM signal. FIG. 10 shows a case where 12 wavelength channels are concentrated on the long wavelength side of the wavelength band of the WDM signal. The EDFA for L-band amplification used for the measurement has the configuration of the optical fiber amplifier 2, and under the condition that the gain is flat as shown in FIG. 23, as described above, the signal having a wavelength of 1588.73 nm is obtained. The signal gain is about 16.5 dB. In an excitation state where the signal gain of the wavelength of 1588.73 nm is 16.5 dB, the signal light input power is changed from −20 dBm to −5 dBm, and the wavelength channels 1573.71 nm and 1606 at both ends of the wavelength band of the WDM signal. ΔG, which is a difference in signal gain of 60 nm, was measured.

FIG. 11 is a graph obtained by measuring the dependence of the gain flatness (ΔG) on the signal light input power. In this measurement, the ASE reflectance is set to −10.65 dB. From FIG. 11, regardless of the wavelength arrangement deviation of the WDM signal, the absolute value of ΔG is 1 dB or less and the gain flatness is achieved when the combined signal light input power is in the range of −20 dBm to −5 dBm. I understand.
In the case of the same signal light input power, since the power deviation in the signal wavelength band is smaller in the case of the WDM signal than in the case of one wavelength, ΔG in the WDM signal is smaller than ΔG in one wavelength. Therefore, from the value of ΔG when the ASE reflectance is −30.27 dB described in FIGS. 6 and 7, the power of the C-band ASE light returning to the EDF 13 and the reverse propagation from the input side of the EDF 13 By setting the attenuation amount of the optical attenuator 22 so that the ratio with the power of the C-band ASE light is 1/1000 or more, a WDM signal having a uniform wavelength arrangement and a WDM signal having a biased wavelength arrangement. In both cases, it is possible to improve the wavelength dependency of the gain.

  With the configuration of the optical fiber amplifier 2 of the second embodiment described above, in the range where the power of the incident L-band signal light is in the range of −20 dBm to −5 dBm, the LDF signal is supplied to the EDF 13 under the condition that the gain of the L-band is flat. The amount of attenuation in the optical attenuator 22 is set so that the ratio of the power of the C-band ASE light that returns to the power of the C-band ASE light that propagates back from the input side of the EDF 13 is 1/1000 or more. As a result, the excitation efficiency of L-band signal amplification is improved, and the number of wavelengths is changed in the case where one wavelength of signal light, a WDM signal with a uniform wavelength arrangement, and a WDM signal with a biased wavelength arrangement are incident. A change in the input power of the signal light can be allowed, and the wavelength dependence of the signal gain can be suppressed.

(Third embodiment)
FIG. 12 is a block diagram showing the configuration of the optical fiber amplifier 3 according to the third embodiment of the present invention. The optical fiber amplifier 3 according to the third embodiment has a configuration in which a C-band light incident portion 20 described below is embodied instead of the C-band light incident portion 20 in the optical fiber amplifier 1 according to the first embodiment. The light incident part 20b is provided. In the optical fiber amplifier 3 of the third embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals, and different configurations will be described below. As in the first embodiment, the power of the L-band signal light incident on the optical fiber amplifier 3 is in the range of −20 dBm to −5 dBm. The C-band light incident part 20 b includes a C / L separation coupler 21 and a C-band light source 24. The C-band light source 24 of the C-band light incident part 20b has a C-band LD (Laser Diode) light source provided therein, and generates C-band light emitted by the LD light source. The C-band light source 24 can change the power of the C-band light emitted by adjusting the output power of the internal LD light source in response to a user operation. An arbitrary ratio in which the ratio of the power of the C-band light incident on the EDF 13 to the power of the C-band ASE light propagating back from the input side of the EDF 13 is 1/1000 or more is selected in advance, and the C-band light source 24 The power of the C-band light is set according to the selected ratio. The C-band light source 24 emits C-band light having a set power. The C / L separation coupler 21 combines the C-band light emitted from the C-band light source 24 and the L-band signal light and enters the EDF 13.

  In the second embodiment, the C-band ASE light propagating back from the input side of the EDF 13 is used, and the C-band ASE light is reflected to generate the C-band ASE light incident on the EDF 13. . In contrast, in the third embodiment, the C-band light source 24 is used to generate C-band light and enter the EDF 13 to improve the excitation efficiency.

  FIG. 13 is a block diagram showing a configuration of an optical fiber amplifier 3a that is a modification of the optical fiber amplifier 3 of the third embodiment. The optical fiber amplifier 3a includes a C-band light incident portion 20c having a configuration embodying a C-band light incident portion 20 described below instead of the C-band light incident portion 20 in the optical fiber amplifier 1 according to the first embodiment. Prepare. In the optical fiber amplifier 3a, the same components as those of the optical fiber amplifier 3 are denoted by the same reference numerals, and different configurations will be described below. In the optical fiber amplifier 3 described above, the ratio of the power of the C band light incident on the EDF 13 and the power of the C band ASE light propagating back from the input side of the EDF 13 is set to be 1/1000 or more. For this, it is necessary to know in advance the power of the C-band ASE light that propagates backward from the input side of the EDF 13. Therefore, information indicating the relationship between the pumping light power and the power of the C-band ASE light propagating back from the input side of the EDF 13 is obtained in advance, and the information indicating the relationship and the pumping light power set in the pumping light source 12 are obtained. Based on the above, it is necessary to estimate the power of the C-band ASE light by estimation. Then, the power of the C-band light incident on the EDF 13 is set in advance so that the ratio with the calculated power of the C-band ASE light is 1/1000 or more. In contrast, the optical fiber amplifier 3a monitors the power of the C-band ASE light that propagates backward from the input side of the EDF 13, and sets the power of the C-band light based on the monitored power of the C-band ASE light. It has a configuration to do. The C-band light incident unit 20 c includes a C / L separation coupler 21, an optical coupler 25, a PD 26, a C-band light source control unit 27, and a C-band light source 28. The optical coupler 25 branches a part of the C-band light separated by the C / L separation coupler 21, that is, taps and emits it to the PD 26 side. The optical coupler 25 emits C-band light emitted from the C-band light source 28 to the C / L separation coupler 21 side. The optical detector or PD 26, which is a photodetector, measures the power of the C-band ASE light branched by the optical coupler 25. The C-band light source control unit 27 calculates and outputs the power value of the C-band light emitted from the C-band light source 28 based on the power of the C-band ASE light measured by the PD 26. The C-band light source 28 emits C-band light having a power value output from the C-band light source control unit 27.

  The operation of the C-band light incident part 20c will be described. Similar to the first embodiment, the power of the L-band signal light incident on the optical fiber amplifier 3a is in the range of −20 dBm to −5 dBm. Also, an arbitrary ratio is selected in advance so that the ratio of the power of the C-band light incident on the EDF 13 and the power of the C-band ASE light propagating back from the input side of the EDF 13 is 1/1000 or more. It is assumed that it is stored inside the control unit 27. First, C-band ASE light that propagates backward from the input side of the EDF 13 is separated by the C / L separation coupler 21, and the C-band ASE light reaches the optical coupler 25. The optical coupler 25 taps a part of the C-band ASE light and emits it to the PD 26 side. The PD 26 measures the power of the C-band ASE light and outputs the measurement result to the C-band light source control unit 27. The C-band light source control unit 27 enters the EDF 13 according to the ratio between the power of the C-band light incident on the predetermined EDF 13 stored therein and the power of the C-band ASE light measured by the PD 26. The power of the C-band light is calculated, and the calculated power value of the C-band light is output to the C-band light source 28. The C-band light source 28 generates and emits C-band light according to the power value of the C-band light output from the C-band light source control unit 27.

  Due to the configuration of the optical fiber amplifier 3 and the optical fiber amplifier 3a of the third embodiment, the power of the incident L-band signal light is in the range of −20 dBm to −5 dBm. The power of the C-band light emitted from the C-band light sources 24 and 28 is set so that the ratio of the power and the power of the C-band ASE light propagating back from the input side of the EDF 13 is 1/1000 or more. Thereby, the C-band light is incident on the EDF 13 from the C-band light sources 24 and 28, so that the excitation efficiency of the L-band signal amplification is improved, the change in the input power of the signal light with the change in the number of wavelengths is allowed, and It becomes possible to suppress the wavelength dependence of the signal gain.

  Since the optical fiber amplifier 2 of the second embodiment uses C-band ASE light that propagates back from the input side of the EDF 13, it is not necessary to include a C-band light source that emits C-band light by itself. Since the insertion loss of the separation coupler 21 and the optical attenuator 22 and the reflectivity of the mirror 23 are affected, the power of the C-band light incident on the EDF 13 is greater than the power of the C-band ASE light propagating backward from the input side of the EDF 13. And also depends on the state of the C-band ASE light that propagates backward from the input side of the EDF 13. On the other hand, in the optical fiber amplifiers 3 and 3a of the third embodiment, the C-band ASE light propagating backward from the input side of the EDF 13 because the C-band light is incident by itself using the C-band light sources 24 and 28. C-band light having a power higher than that of the light and having a stable power can be incident. Therefore, it is possible to set the power of the C-band light that is stably incident on the EDF 13 without depending on the magnitude or state of the power of the C-band ASE light that propagates backward from the input side of the EDF 13.

  In the optical fiber amplifier 3a of the third embodiment, the power of the C-band light emitted from the C-band light source 28 is controlled by monitoring the power of the C-band ASE light propagating back from the EDF 13 by the PD 26. Calculated by the unit 27. Therefore, the power of the C-band ASE light propagating backward from the EDF 13 is directly measured without obtaining in advance information indicating the relationship between the pump light power and the power of the C-band ASE light propagating backward from the input side of the EDF 13. , C-band light having a power ratio of 1/1000 or more to the measured power can be emitted. Therefore, it becomes possible to make the C-band light having a more accurate power value based on the power of the C-band ASE light propagating backward from the input side of the EDF 13 at that time, and to make the amplification more efficient. It becomes possible.

(Fourth embodiment)
FIG. 14 is a block diagram showing a configuration of the optical fiber amplifier 4 according to the fourth embodiment of the present invention. In addition to the configuration of the optical fiber amplifier 1 according to the first embodiment, the optical fiber amplifier 4 has the above-described AGC configuration that monitors the power of the input signal light in the L band and feed-forward controls the power of the pumping light. ing. In the optical fiber amplifier 4 of the fourth embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and different configurations will be described below. The optical coupler 30 taps a part of the L-band input signal light and emits it to the PD 31 side. The PD 31 measures the power of the L-band input signal light tapped by the optical coupler 30. A feedforward control unit (hereinafter referred to as an FF control unit) 32 is based on the power of the L-band input signal light measured by the PD 31 and determines the excitation light source from the relationship between the predetermined input power of the signal light and the excitation light power The power value of the excitation light emitted from 12a is obtained. The excitation light source 12a emits excitation light with the power value obtained by the FF control unit 32.

  The operation of the optical fiber amplifier 4 will be described. As in the first embodiment, when an L-band signal light having a power value in the range of −20 dBm to −5 dBm is incident, the optical coupler 30 taps a part of the incident signal light and emits it to the PD 31. To do. On the other hand, the remaining signal light reaches the EDF 13 through the optical isolator 10, the C-band light incident portion 20, and the optical coupler 11. The PD 31 measures the power of the L-band input signal light tapped by the optical coupler 30 and outputs the measured power value to the FF control unit 32. Based on the power of the L-band input signal light measured by the PD 31, the FF control unit 32 obtains the power value of the excitation light from the predetermined relationship between the input power of the signal light and the excitation light power, and the excitation light source To 12a. The excitation light source 12a emits excitation light with the power value obtained by the FF control unit 32. On the other hand, the C-band light incident unit 20 is configured so that the ratio of the power of the C-band light incident on the EDF 13 and the power of the C-band ASE light propagating back from the input side of the EDF 13 is 1/1000 or more. , C band light power is set and emitted. The optical coupler 11 combines the L-band signal light, the C-band light emitted from the C-band light incident unit 20, and the excitation light emitted from the excitation light source 12 a and enters the EDF 13. The EDF 13 amplifies and emits L-band signal light based on the excitation light. At this time, the C-band light incident on the EDF 13 is absorbed in the longitudinal direction of the EDF 13 and used for amplification of the L-band signal light. The amplified signal light passes through the optical isolator 14 and is emitted to the outside of the optical fiber amplifier 4.

  With the configuration of the fourth embodiment, the PD 31 measures the power of the L-band input signal light incident at a power in the range of −20 dBm to −5 dBm, and the FF control unit 32 measures the power of the L band measured by the PD 31. Based on the power of the input signal light, the power value of the pump light is selected and output to the pump light source 12a. The excitation light source 12a emits excitation light with the power value selected by the FF control unit 32. In addition, the C-band light incident unit 20 has a ratio of 1/1000 or more of the power of the C-band light incident on the EDF 13 and the power of the C-band ASE light that propagates backward from the input side of the EDF 13. , C band light power is set and emitted. As a result, the power of the input signal light in the L band can be monitored without monitoring the wavelength of the signal light in the L band, as shown in the configurations of the fifth and sixth embodiments to be described later that embody the configuration of the fourth embodiment. It is possible to perform feedforward control on the power value of the pumping light by detecting the fluctuation and changing the power of the pumping light according to the detected fluctuation of the L-band signal light. Further, the C-band light is incident on the EDF 13 from the C-band light incident unit 20 to improve the excitation efficiency of the L-band signal amplification, permitting a change in the input power of the signal light according to the change in the number of wavelengths, and the signal It becomes possible to suppress the wavelength dependence of the gain. In addition, the configuration of the fourth embodiment makes the signal gain constant following the change in the high-speed signal light power due to the fluctuation in the number of wavelengths accompanying the change in the arrangement of the signal wavelengths in the ring or the disconnection of the optical fiber transmission line. It becomes possible.

(Fifth embodiment)
FIG. 15 is a block diagram showing a configuration of the optical fiber amplifier 5 according to the fifth embodiment of the present invention. The optical fiber amplifier 5 has a configuration in which the configuration of the C-band light incident portion 20 in the optical fiber amplifier 4 of the fourth embodiment is replaced with the C-band light incident portion 20a included in the optical fiber amplifier 2 of the second embodiment. The same reference numerals as those in the second and fourth embodiments described above perform the same operations as described above. A broken line shown in FIG. 15 indicates a path through which the C-band ASE light that propagates backward from the input side of the EDF 13, is reflected by the C-band light incident unit 20 a, is attenuated, and is returned to the EDF 13.

  FIG. 16 is an example of a graph showing the dependency of the pumping light power required for realizing the target signal gain on the signal light input power in the configuration of the optical fiber amplifier 5 of FIG. As shown in FIG. 23 described above, the signal gain at 1588.73 nm under the condition that the signal gain is flat is about 16.5 dB. Therefore, even in the measurement shown in FIG. 5 dB. Further, the attenuation amount of the optical attenuator 22 of the C-band light incident portion 20a was set so that the ASE reflectance was −10.65 dB. In the input signal light of one wave incident, its wavelength is set to three wavelengths of 1573.71 nm, 1588.73 nm, and 1604.03 nm, and the signal gain is 16.5 dB with respect to the signal light power range from 0.01 mW to 1 mW. The value of pumping light power necessary to realize the above was measured. The measurement conditions are the same as those in FIG. The difference between FIG. 22 and FIG. 16 is the difference in configuration between the optical fiber amplifier 100 and the optical fiber amplifier 5, and whether there is a configuration that reflects and attenuates the ASE light propagating back and returns it to the EDF 13. That is. From this point of view, when the measurement results of FIGS. 22 and 16 are compared, the C-band light incident unit 20a feeds back the C-band ASE light propagating back from the EDF 13 to obtain the signal light input power as shown in FIG. It can be seen that the relationship between and the required pumping light power is linear. In addition, the difference in pumping light power at each signal wavelength when the signal light input power is 0.5 mW is 318.5 mW in FIG. 22 and 23.0 mW in FIG. I understand that Therefore, by making the C-band light incident on the EDF 13, the conditions of the pumping light for realizing the same signal gain are almost the same regardless of the wavelength of the input signal light. Actually, under the same pumping light conditions, as described in FIG. 3 above, when the ASE reflectance is -10.65 dB, the gain difference depending on the signal wavelength is 1 dB or less. There is no need to monitor the wavelength of light, and the difficulty of controlling the excitation light when performing AGC can be reduced.

The FF control unit 32 stores in advance a graph showing the relationship between the input power of the L-band light and the pumping light power under the constant gain condition shown in FIG. 16, and the L-band measured by the PD 31. The pumping light power to be set is selected based on the signal light input power.
In the above example, the ASE reflectance is set to 10.65 dB, but the ratio between the power of the C-band light that returns to the EDF 13 and the power of the C-band ASE light that propagates back from the input side of the EDF 13. Is arbitrarily selected from a range of 1/1000 or more, and the attenuation amount set in the optical attenuator 22 of the C-band light incident portion 20a is a value corresponding to the selected ratio.

  With the configuration of the fifth embodiment described above, the PD 31 measures the power of the L-band input signal light incident at a power in the range of −20 dBm to −5 dBm, and the FF control unit 32 measures the power of the L band measured by the PD 31. Based on the power of the input signal light, the power value of the pump light is selected and output to the pump light source 12a. The excitation light source 12a emits excitation light with the power value selected by the FF control unit 32. Further, the ratio of the power of the C-band light returning to the EDF 13 and the power of the C-band ASE light propagating backward from the input side of the EDF 13 is at least 1/1000, so that the C-band light incident portion 20a is The C-band ASE light propagating backward is reflected by the mirror 23 and attenuated by the optical attenuator 22 to set the power of the C-band light that returns to the EDF 13. Therefore, the feed-forward control for the power value of the pumping light is detected by detecting the power fluctuation of the L-band input signal light and changing the power of the pumping light according to the detected fluctuation of the signal light of the L-band. This can be performed without monitoring the wavelength of the signal light. Further, the C-band light is fed back from the C-band light incident portion 20a to the EDF 13 to improve the excitation efficiency of the L-band signal amplification, to allow the change in the input power of the signal light accompanying the change in the number of wavelengths, and to It becomes possible to suppress the wavelength dependence of the gain. Further, the configuration of the fifth embodiment makes the signal gain constant following the change in the number of wavelengths accompanying the change in the arrangement of signal wavelengths in the ring or the change in high-speed signal light power due to the transmission line disconnection of the optical fiber transmission line. It becomes possible.

(Sixth embodiment)
FIG. 17 is a block diagram showing a configuration of the optical fiber amplifier 6 according to the sixth embodiment of the present invention. The optical fiber amplifier 6 has a configuration in which the configuration of the C-band light incident portion 20 in the optical fiber amplifier 4 of the fourth embodiment is replaced with the C-band light incident portion 20b of the optical fiber amplifier 3 of the third embodiment. The same reference numerals as those in the third and fourth embodiments described above perform the same operations as described above.

  FIG. 18 is a block diagram showing a configuration of an optical fiber amplifier 6a which is a modification of the optical fiber amplifier 6 according to the sixth embodiment of the present invention. The optical fiber amplifier 6a has a configuration in which the configuration of the C-band light incident portion 20 in the optical fiber amplifier 4 of the fourth embodiment is replaced with the C-band light incident portion 20c of the optical fiber amplifier 3a which is a modification of the third embodiment. Thus, the same operations as those described above are performed for the same reference numerals as those of the modified example of the third embodiment and the fourth embodiment described above.

  As a modification of the optical fiber amplifier 6 according to the sixth embodiment, a configuration such as an optical fiber amplifier 6b may be used as shown in the block diagram of FIG. As described in the optical fiber amplifier 3 of the third embodiment, the power of the C band light set in advance in the C band light source 24 is the pump light power obtained in advance and the C band that propagates backward from the input side of the EDF 13. It is necessary to calculate from the relationship with the power of the ASE light. On the other hand, in the optical fiber amplifier 6b, for example, information indicating the relationship between the pumping light power obtained in advance and the power of the C-band ASE light propagating backward from the input side of the EDF 13 is stored in the FF control unit 32a. Remember. When the FF control unit 32a selects the power of the pumping light to be set in the pumping light source 12a, the selected pumping light power and the C-band ASE light that propagates backward from the input side of the EDF 13 stored therein. The power of the C-band ASE light that propagates backward from the input side of the EDF 13 corresponding to the power of the selected pumping light is detected from the information indicating the relationship with the power of the pumping light. The value of the ratio between the power incident from the C-band light source 24a and the power of the C-band ASE light propagating back from the input side of the EDF 13 is predetermined by a value of 1/1000 or more. Remember me inside. The FF control unit 32a controls the C-band light source 24a so that the ratio between the C-band light power set in the C-band light source 24a and the detected C-band ASE light power becomes the ratio stored in the inside. The power of the C-band light to be set is calculated, and the calculated power value of the C-band light is output to the C-band light source 24. The C-band light source 24a sets the power value output from the FF control unit 32 and emits C-band light of the power. If the power of the C-band light is sufficiently high in advance, it is not necessary to adjust the power of the C-band light in accordance with the fluctuation of the signal light input power. Therefore, the configuration for controlling the C-band light source 24a from the FF control unit 32a is as follows. Not required.

  In the sixth embodiment, the FF control unit 32 and the FF control unit 32a refer to information indicating the relationship between the pumping light power and the signal light input power as illustrated in FIG. 16 described in the fifth embodiment. Thus, the pump light power is selected. Therefore, also in the sixth embodiment, information indicating the relationship between the pumping light power and the signal light input power as shown in FIG. 16 is obtained in advance and stored in the FF control unit 32 and the FF control unit 32a. The C-band light incident portions 20b, 20c, and 20d all have a configuration in which the C-band light is incident on the EDF 13, and the relationship between the excitation light power and the signal light input power is the same as the graph shown in FIG. Is linear, and the conditions of the pumping light for realizing the same signal gain are almost the same regardless of the signal wavelength.

  With the configuration of the sixth embodiment, the PD 31 measures the power of the L-band input signal light incident at a power in the range of −20 dBm to −5 dBm, and the FF control unit 32 and the FF control unit 32 a Based on the measured power of the L-band input signal light, the power value of the excitation light is selected and output to the excitation light source 12a. The excitation light source 12a emits excitation light with the power value obtained by the FF control unit 32 and the FF control unit 32a. Further, the ratio of the C-band light power incident on the EDF 13 to the C-band ASE light propagating backward from the input side of the EDF 13 is 1/1000 of the C-band light incident portions 20b, 20c, and 20d. The C-band light having the above power is emitted. Therefore, the feed-forward control for the power value of the pumping light is detected by detecting the power fluctuation of the L-band input signal light and changing the power of the pumping light according to the detected fluctuation of the signal light of the L-band. This can be performed without monitoring the wavelength of the signal light. In addition, the C-band light incidence sections 20b, 20c, and 20d make the C-band light incident on the EDF 13 to improve the excitation efficiency of L-band signal amplification, and allow the change in the input power of the signal light as the number of wavelengths changes. In addition, the wavelength dependence of the signal gain can be suppressed. The configuration of the sixth embodiment makes the signal gain constant following the change in the number of wavelengths accompanying the change in the arrangement of signal wavelengths in the ring or the change in high-speed signal light power due to the transmission line disconnection of the optical fiber transmission line. It becomes possible.

  Since the optical fiber amplifier 5 of the fifth embodiment uses C-band ASE light that propagates back from the input side of the EDF 13, it is not necessary to include a C-band light source that emits C-band light by itself. Since the insertion loss of the separation coupler 21 and the optical attenuator 22 and the reflectivity of the mirror 23 are affected, the power of the C-band light incident on the EDF 13 is greater than the power of the C-band ASE light propagating backward from the input side of the EDF 13. And also depends on the state of the C-band ASE light that propagates backward from the input side of the EDF 13. On the other hand, in the optical fiber amplifiers 6 and 6a of the sixth embodiment, the C-band ASE light propagating backward from the input side of the EDF 13 because the C-band light is incident by itself using the C-band light sources 24 and 28. C-band light having a power higher than that of the light and having a stable power can be incident. Therefore, it is possible to set the power of the C-band light that stably enters the EDF 13 without depending on the power or state of the C-band ASE light that propagates backward from the input side of the EDF 13.

  Further, in the optical fiber amplifier 6a which is a modification of the sixth embodiment, the power of the C-band light emitted from the C-band light source 28 is further monitored by monitoring the power of the C-band ASE light propagating backward from the EDF 13 by the PD 26. Calculated by the C-band light source control unit 27. Therefore, the power of the C-band ASE light propagating backward from the EDF 13 is directly measured without obtaining in advance information indicating the relationship between the pump light power and the power of the C-band ASE light propagating backward from the input side of the EDF 13. , C-band light having a power ratio of 1/1000 or more to the measured power can be emitted. Therefore, it becomes possible to make the C-band light having a more accurate power value based on the power of the C-band ASE light propagating backward from the input side of the EDF 13 at that time, and to make the amplification more efficient. It becomes possible.

  Further, in the optical fiber amplifier 6b which is a modification of the sixth embodiment, similarly to the optical fiber amplifier 6, the power of the pumping light is set by the feedforward control with the incidence of the L-band signal light. Furthermore, it is possible to set the power of the C-band light emitted from the C-band light source 24a using the set power value of the excitation light. The power of the pumping light changes with the change of the signal light power. When the power of the pumping light changes, the power of the ASE light that propagates backward from the EDF 13 also changes. Accordingly, the configuration of the optical fiber amplifier 6b can change the power of the C-band light emitted from the C-band light source 24a following the change in the power of the ASE light propagating backward from the EDF 13, so that it is incident from the C-band light source 24a. The ratio between the power of the C-band light to be transmitted and the power of the ASE light that propagates backward from the EDF 13 can be maintained at 1/1000 or more.

  Further, when the configuration of each of the embodiments according to the present invention is compared with the configuration of the L-band EDFA described in Non-Patent Document 1, the L-band EDFA described in Non-Patent Document 1 is the input side of the EDFA. In addition, optical couplers must be arranged on both the output side and the circuit configuration is complicated, and C-band light may oscillate in the EDFA. On the other hand, in the configuration of each embodiment according to the present invention, since the C-band light is incident from the input side of the EDF, an optical coupler on the output side is not required, the circuit configuration is simple, and the C-band is also provided. Light does not oscillate.

In each of the above embodiments, the optical isolator 10 and the optical isolator 14 may be omitted if there is no unnecessary reflection due to the fiber end or the like.
Further, the optical coupler 11, the C / L separation coupler 21, the optical coupler 25, and the optical coupler 30 may be a functional unit for separation / combining that separates (or branches) and combines light according to each application. What is necessary is not limited to a coupler.

  In addition, the optical fiber amplifier 2 and the optical fiber amplifier 5 are configured not to include the optical attenuator 22, and the power of the C-band ASE light fed back to the EDF 13 and the C-band ASE light propagating backward from the input side of the EDF 13. The reflectance of the mirror 23 may be set so that the ratio with the power is 1/1000 or more.

  You may make it implement | achieve the FF control parts 32 and 32a in embodiment mentioned above with a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be a program for realizing a part of the above-described functions, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. You may implement | achieve using programmable logic devices, such as FPGA (Field Programmable Gate Array).

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.
As described above, each embodiment according to the present invention realizes improvement in controllability of the L-band amplification EDFA, and is useful for the operation of an optical communication system.

DESCRIPTION OF SYMBOLS 1 Optical fiber amplifier 10 Optical isolator 11 Optical coupler 12 Excitation light source 13 EDF
14 Optical isolator 20 C-band light incident part

Claims (4)

An L-band optical amplifier having a forward pumping configuration,
A signal input unit to which one or more L-band input signal lights having a power in the range of −20 dBm to −5 dBm are incident;
An excitation light source that emits excitation light having a signal gain when the gain of the L-band WDM signal becomes flat;
A multiplexing unit that multiplexes and emits the input signal light and the excitation light; and
An amplification medium connected to the multiplexing unit and amplifying and emitting the L-band input signal light emitted from the multiplexing unit based on the excitation light;
C-band light having a power that is located between the multiplexing unit and the signal input unit and has a ratio of 1/1000 or more to the power of C-band ASE light that propagates back from the amplification medium through the multiplexing unit. A C-band light incident portion that is incident on the amplification medium;
Equipped with a,
The C-band light incident part is:
A demultiplexing / multiplexing unit that connects to the multiplexing unit and separates the C-band ASE light propagating back from the amplification medium through the multiplexing unit;
A mirror that reflects the C-band ASE light separated by the separating and combining unit,
The separation and multiplexing unit is
The C-band light reflected by the mirror having a power ratio of 1/1000 or more to the power of the C-band ASE light is combined with the incident L-band input signal light. An optical amplifier that emits light to the multiplexing unit . An L-band light detector for detecting the power of the L-band input signal light;
Based on information indicating a predetermined relationship between the power of the L-band input signal light and the power of the pumping light, and the power value detected by the L-band light detecting unit, the power value of the pumping light A feedforward control unit for selecting
The optical amplifier according to claim 1, wherein the pumping light source emits the pumping light having a power value selected by the feedforward control unit. The reflectivity of the mirror is set such that the ratio of the power of the C-band light reflected by the mirror and the power of the ASE light of the C-band is 1/1000 or more, or
An optical attenuator that is disposed between the separation and multiplexing unit and the mirror and through which the C-band light reflected by the mirror passes, the power of the C-band light reflected by the mirror, according to claim 1 or claim 2 ratio of the power of the ASE light is characterized in that it comprises an optical attenuator for attenuating the power of the reflected C-band light by said mirror to be 1 or more 1/1000 Optical amplifier. An optical amplification method using an L-band optical amplifier having a forward pumping configuration,
A signal light incident step in which the signal input unit enters one or more L-band input signal lights having a power in the range of −20 dBm to −5 dBm;
A pumping light emitting step for emitting pumping light having a signal gain when the gain of the L-band WDM signal becomes flat;
Multiplexing unit, and the input signal light L band having a power of the range to be incident, a multiplexing step for emitting said excitation light multiplexed by the amplification medium,
An amplification step in which the amplification medium amplifies the L-band input signal light based on the excitation light;
The C-band light incident part located between the multiplexing part and the signal input part has a ratio of 1/1000 or more to the power of the C-band ASE light that propagates back from the amplification medium through the multiplexing part. A C-band light incident step for injecting the C-band light having a power to the amplification medium ;
Have
In the C-band light incident step,
A separating / combining unit connected to the combining unit separates the C-band ASE light propagating back from the amplification medium through the combining unit;
A mirror reflects the ASE light in the C band separated by the separation and multiplexing unit,
The demultiplexing / multiplexing unit is configured such that the C-band light reflected by the mirror having a power ratio of 1/1000 or more to the power of the C-band ASE light and the incident L-band input signal An optical amplification method comprising: combining light and emitting the light to the combining unit .

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