JP4666403B2 - Optical fiber amplifier control method and optical transmission system - Google Patents

Description

  The present invention relates to a control technique for an optical fiber amplifier used in an optical transmission system to which a wavelength division multiplexing (WDM) transmission technique is applied, and in particular, a pump light control method in a rare earth-doped optical fiber amplifier or a Raman amplifier, and And an optical transmission system to which the same is applied.

  In recent years, construction of an optical transmission system or a photonic network that realizes large-capacity optical communication by applying a WDM transmission technology has been put into practical use. In such an optical transmission system, for example, the WDM signal light is collectively amplified using an optical fiber amplifier such as a rare earth-doped optical fiber amplifier or a Raman amplifier, so that the WDM signal light is relayed over a long distance. It is possible to transmit.

  As for the optical transmission system using the optical fiber amplifier as described above, for example, a request for expanding the wavelength band of the WDM signal light to increase the transmission capacity, or the optical signal-to-noise ratio (Optical in each relay section). There is a common problem of improving signal-to-noise ratio (OSNR) to realize excellent transmission characteristics.

  As a conventional technique for extending the signal light band, for example, as shown in FIG. 15A, a WDM signal light having a wavelength band of 1530 nm to 1565 nm, which is generally called a C-band, is a rare earth doped light corresponding to the C-band. FIG. 15B shows a system in which transmission is performed on a transmission line fiber 3 from a transmission terminal station (Tx) 1 to a reception terminal station (Rx) 2 while being amplified by a plurality of repeaters 4 including fiber amplifiers. In this way, the rare earth doped optical fiber amplifier 4L corresponding to the wavelength band of 1565 nm to 1625 nm, generally called L-band, is provided in parallel with the rare earth doped optical fiber amplifier 4C for the C-band of each repeater 4 so that the signal light band is increased. Techniques for extending to C-band and L-band are known. Also, for example, for a system using a Raman amplifier, a technique for extending a signal light band by adding a Raman pumping light source and supplying a plurality of pumping lights having different wavelengths to an amplification medium is also known. (For example, refer to Patent Documents 1 to 4 and Non-Patent Document 1 below).

As a conventional technique for improving the OSNR in each relay section, for a system in which a plurality of repeaters using rare earth-doped optical fiber amplifiers are arranged on the transmission line fiber, the transmission line fiber in each relay section is used as an amplification medium. By applying a distributed Raman amplifier (DRA), for example, the power of the WDM signal light input from the transmission line fiber to the repeater is Raman-amplified as indicated by the level diagram (dotted line) in FIG. A technique for improving the OSNR by increasing the frequency is known. Regarding DRA applied to such a system, a backward pumping type configuration in which pumping light is given to a transmission line fiber in a direction opposite to the propagation direction of signal light is generally used. In order to further improve the OSNR in the system as described above, a system using a forward-pumped Raman amplifier that applies pumping light to the transmission line fiber in the same direction as the propagation direction of the signal light is also considered. ing. However, for forward-pumped Raman amplifiers, the relative intensity noise (RIN) of the pumping light has a problem of RIN transfer in which the signal light transitions as noise, and the Raman gain largely depends on the polarization state of the signal light. The problem of PDG (Polarization Dependent Gain) is known (for example, see Non-Patent Documents 2 and 3 below). Therefore, in order to alleviate the problems of the forward pumping Raman amplifier as described above, the use of a bidirectional pumping Raman amplifier to which both forward pumping and backward pumping are applied has been studied (for example, non-patent literature). 4).
Japanese Patent Laid-Open No. 10-73852 JP 2000-98433 A JP 2002-76482 A JP 2002-303896 A M. Takeda et al., “Active gain-tilt equalization by Preferentially 1.43μm-or 1.48 μm-Pumped Raman Amplification”, ThA3, OAA1999. CRSFludger et al., “Pump to Signal RIN Transfer in Raman Fiber Amplifier”, Journal of Lightwave Technology Vol.19, No.8, 2001. J. Zhang et al., “Dependence of Raman Polarization Dependent Gain on Pump Degree of Polarization at High Gain Levels”, OMB4, OAA 2001 J. Bromage et al., “Raman-enhanced pump-signal four-wave mixing in bidirectionally-pumped Raman amplifiers” OWA5, OAA 2002

However, the conventional technique for extending the signal light band as described above and the conventional technique for improving the OSNR in each relay section have the following problems.
That is, as shown in FIG. 15 described above, when a rare earth-doped optical fiber amplifier corresponding to a different band is added to expand a signal light band in a system using a rare earth-doped optical fiber amplifier, Since repeaters are added in parallel, there is a problem that, for example, when the demand for transmission capacity increases after system installation, the bandwidth expansion service becomes expensive. In addition, even when the extension of the signal light band is realized by adding a pumping light source in a system using a Raman amplifier, a high-power pumping light source is generally expensive, resulting in an increase in the cost of the band expansion service. In order to provide a bandwidth expansion service at a minimum cost, it is desirable to easily expand the amplification band of a rare earth-doped optical fiber amplifier used in many optical transmission systems.

  Further, as described above, when the OSNR is improved by using the bidirectional excitation type Raman amplifier, depending on the position of the loss lump (lamp loss) existing on the transmission line fiber serving as the amplification medium, There is a problem that the performance largely fluctuates. More specifically, the lamp loss is a relatively large loss that is intensively generated due to a connection failure of a connector or a fusion part for connecting a transmission line fiber, bending of the fiber, or the like.

  For example, in a 100 km transmission line fiber, when a 1 dB lamp loss is present at the input end of signal light and when it is present at the output end, the level diagram of signal light is larger in each case as shown in FIG. To be different. For this reason, when there is a lamp loss at the input end, the level diagram is lowered over the entire relay section, and the OSNR deteriorates. On the other hand, when there is a lamp loss at the output end, there is a possibility that various nonlinear phenomena occur due to an increase in the signal light power in the transmission line fiber and the signal waveform deteriorates.

  Taking into account the performance degradation of the Raman amplifier caused by the lamp loss as described above, taking a large margin for the lamp loss leads to an increase in the cost of the bidirectionally pumped Raman amplifier. For this reason, it is desired to suppress the fluctuation of the performance of the Raman amplifier due to the influence of the lamp loss as much as possible.

  The present invention has been made paying attention to the problems related to the control technology of the optical fiber amplifier as described above, and a control method of the rare earth-doped optical fiber amplifier for realizing the service for expanding the signal light band at low cost, and One object is to provide an optical transmission system. Another object of the present invention is to provide a bidirectional pumping Raman amplifier control method and an optical transmission system capable of obtaining stable performance regardless of lamp loss on the transmission line fiber.

In order to achieve the above object, one aspect of a method for controlling an optical fiber amplifier according to the present invention is to supply a forward pumping light and a backward pumping light to a transmission line fiber, and to propagate a signal propagating through the bidirectionally pumped transmission line fiber. A method for controlling an optical fiber amplifier for Raman amplification of light. First, signal light is input to the transmission line fiber and supplied to the transmission line fiber in a state where the supply of backward pumping light to the transmission line fiber is cut off. The power of the forward pumping light is changed within a preset range, and the output power of the signal light that is propagated through the forward-pumped transmission line fiber and Raman-amplified is measured according to the power of the forward pumping light. Next, based on the measurement result of the signal light output power, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the signal set in advance for the forward-pumped transmission line fiber according to the obtained ratio. The forward pumping light power necessary for realizing the target value of the optical output power is calculated. Then, according to the calculation result, the power of the forward pumping light supplied to the transmission line fiber during system operation is controlled , and the controlled forward pumping light and backward pumping light are supplied to the transmission line fiber to be bi-directionally pumped. The output power of the Raman-amplified signal light propagating through the transmission line fiber is measured, and the power of the backward pumping light is controlled based on the measurement result of the signal light output power .

One aspect of the optical transmission system according to the present invention is an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber, and Raman-amplifies signal light propagating through the bidirectionally pumped transmission line fiber. An optical transmission system configured to include the power of the forward pumping light supplied to the transmission line fiber while the signal light is input to the transmission line fiber and the supply of the backward pumping light to the transmission line fiber is cut off. A measurement unit that changes the output power of the signal light that has been Raman-amplified by propagating through the forward-pumped transmission line fiber in accordance with the power of the forward pumping light, and the measurement unit Based on the measurement result of the signal light output power at, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the transmission path pumped forward according to the obtained ratio A calculation unit that calculates the forward pumping light power necessary to realize a target value of the signal light output power set in advance for the fiber, and the forward pumping light supplied to the transmission line fiber during system operation according to the calculation result in the calculation unit After measuring the power of the power, the measurement unit measured the output power of the Raman-amplified signal light propagating through the transmission line fiber bidirectionally pumped by the supply of the controlled forward pumping light and backward pumping light And a control unit that controls the power of the backward pumping light.

According to such a control method and optical transmission system, the ratio of the change in the signal light output power to the change in the forward pumping light power is obtained in a state where the supply of the backward pumping light is cut off, and the forward pumping light power is calculated according to the ratio. Since optimization is performed, even when there is a lamp loss on the transmission line fiber, a level diagram substantially equivalent to that when there is no lamp loss is realized . Then, based on the measurement result of the output power of the signal light that has been Raman-amplified by propagating through the transmission path fiber that is bidirectionally pumped by supplying the optimized forward pump light and backward pump light, the power of the backward pump light is By being controlled, the power distribution of the forward pumping light and the backward pumping light is optimized .

  According to the present invention as described above, since a desired level diagram can be obtained regardless of the lamp loss on the transmission line fiber, the signal light can be stably amplified in the bidirectionally pumped transmission line fiber. It becomes possible.

  The best mode for carrying out the method for controlling an optical fiber amplifier according to the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.

FIG. 1 is a block diagram showing a main configuration of an embodiment of an optical transmission system to which an optical fiber amplifier control method related to the present invention is applied.
In FIG. 1, the optical transmission system of this embodiment includes, for example, an amplification fiber 11, pumping light sources 12A and 12B, additional pumping light sources 13A and 13B, multiplexers 14A and 14B, 15A and 15B, variable gain equalizers ( dynamic gain equalizer (DGEQ) 16, optical coupler 17, monitor 18, and optical amplification repeater 10 having control circuit 19. The overall configuration of the optical transmission system is the same as the conventional configuration shown in FIG. 15A, and the optical amplification repeater 10 corresponds to each repeater 4 on the transmission line fiber 3. In addition, a portion surrounded by a dotted line in the figure shows a portion similar to the configuration of a conventional rare earth-doped optical fiber amplifier.

Specifically, a known rare earth-doped optical fiber in which a rare earth element such as erbium is added to the core is used as the amplification fiber 11 constituting the optical amplification repeater 10.
The excitation light sources 12 </ b> A and 12 </ b> B generate excitation light in a required wavelength band that can excite the rare earth element in the amplification fiber 11. For example, when an erbium-doped optical fiber (EDF) is used as the amplification fiber 11, the wavelength bands of the excitation light sources 12A and 12B are set to the 980 nm band, the 1480 nm band, or the like.

  The additional pumping light sources 13A and 13B are pumping light sources that are added to expand the signal light band by extending the amplification band of the signal light in the amplification fiber 11 to the short wavelength side, as will be described later. Each additional pumping light source 13A, 13B generates pumping light having a slightly different wavelength from the pumping light sources 12A, 12B, or pumping light having the same wavelength as the pumping light sources 12A, 12B but having a different polarization state.

  The multiplexer 14A supplies the excitation light output from the excitation light source 12A to the amplification fiber 11 from the front (signal light input side). The multiplexer 14B supplies the pumping light output from the pumping light source 12B to the amplification fiber 11 from the rear (signal light output side). A general WDM coupler or the like can be used as the multiplexers 14A and 14B. Although a bidirectional pump type configuration will be described here, the present invention is not limited to this, and the present invention can also be applied to a rare earth doped optical fiber amplifier having a forward pump type or a rear pump type configuration.

  The multiplexers 15A and 15B combine the excitation light output from the excitation light sources 12A and 12B and the excitation light output from the additional excitation light sources 13A and 13B and provide them to the multiplexers 14A and 14B. Each of the multiplexers 15A and 15B can use a WDM coupler when the wavelengths of the excitation light sources 12A and 12B and the additional excitation light sources 13A and 13B are slightly different. When the wavelengths are the same and the polarization states are different. Can use a polarization synthesizer.

  The variable gain equalizer 16 receives the amplified WDM signal light propagating through the amplification fiber 11 supplied with pumping light, and transmits the input light controlled in accordance with a control signal from the control circuit 19. It is a known optical device capable of transmitting according to wavelength characteristics.

  The optical coupler 17 branches a part of the WDM signal light transmitted through the variable gain equalizer 16 and sends it to the monitor 18. The monitor 18 measures the spectrum of the branched light from the optical coupler 17 by a general method, and monitors the wavelength characteristic of the WDM signal light power output from the optical amplification repeater 10 based on the result.

  The control circuit 19 equalizes the power and variable gain of the pumping light supplied to the amplification fiber in accordance with the setting of the wavelength band of the WDM signal light input to the optical amplification repeater 10 and the monitoring result in the monitor 18. The transmission wavelength characteristics of the device 16 are controlled in relation to each other.

Next, the operation of the optical transmission system having the above configuration will be described.
In this optical transmission system, the WDM signal light transmitted from the transmission terminal station 1 (FIG. 15) to the transmission line fiber 3 is amplified by the optical amplification repeaters 10 arranged on the transmission line fiber 3 while being received by the reception terminal station. 2 is relayed. In each optical amplification repeater 10, the WDM signal light propagated through the transmission line fiber 3 is sent to the amplification fiber 11 via the multiplexer 14A. The pumping light source 12A and the pumping light source 13A are combined with the pumping light source 12A and the pumping light source 12B through the multiplexer 14A and then supplied as forward pumping light to the amplifying fiber 11 after being combined with the pumping light source 12B. The pumping light from the amplification pumping light source 13B is multiplexed by the multiplexer 15B and then supplied as backward pumping light through the multiplexer 14B. Then erbium) is excited.

  At this time, the power of the pumping light supplied from both directions to the amplification fiber 11 is adjusted by the pumping light sources 12A and 12B or the pumping light sources 13A and 13B according to the control signal output from the control circuit 19 as will be described later. As a result, the level is controlled according to the wavelength band of the WDM signal light. Details of the control of the excitation light power by the control circuit 19 will be described later.

  The WDM signal light propagating through the amplifying fiber 11 supplied with the pumping light is amplified by the stimulated emission action of erbium, and the amplified WDM signal light is given to the variable gain equalizer 16 via the multiplexer 14B. It is done. The variable gain equalizer 16 performs gain equalization on the WDM signal light in accordance with the transmission wavelength characteristic controlled by the control signal from the control circuit 19. The gain equalization means that the optical power corresponding to each wavelength of the WDM signal light is adjusted so as to match or approach a desired level. Then, the WDM signal light transmitted through the variable gain equalizer 6 is sent to the transmission line fiber 11 in the next relay section, and a part of the WDM signal light is branched by the optical coupler 17 and supplied to the monitor 18 to output power power. Wavelength characteristics are monitored.

Here, the control of the additional excitation light sources 13A and 13B and the variable gain equalizer 16 by the control circuit 19 will be described in detail with reference to the flowchart of FIG.
For example, assuming that the transmission capacity demand expands after the installation of this optical transmission system and the wavelength band of the signal light is required to be extended to the short wavelength side or the long wavelength side, the control circuit 19 is configured as shown in FIG. The pumping light power and variable gain equalizer supplied to the amplification fiber 11 according to the algorithm for extending the band toward the short wavelength illustrated in A) or the algorithm for extending the band toward the long wavelength illustrated in FIG. The 16 transmission wavelength characteristics are controlled in relation to each other.

  Specifically, when the wavelength band of the signal light is extended to the short wavelength side, first, the signal light is supplied to the amplification fiber 11 in step 10 of FIG. A control signal for increasing the pumping light power to be generated is generated by the control circuit 19 and output to the additional pumping light sources 13A and 13B.

  In step 11, the drive state of each additional pump light source 13A, 13B is controlled according to the control signal from the control circuit 19, and the power of the pump light output from each is adjusted to a required level. As a result, the gain wavelength characteristic of optical amplification generated in the amplification fiber 11 using EDF is the band extension example centering on the C-band in FIG. 3 and the band extension example centering on the L-band in FIG. As shown in the figure, the wavelength band in which the effective gain occurs is extended to the short wavelength side (thin line) as compared with the characteristic before the band extension (bold line) where the pumping light power is set to the same condition as in the prior art. Further, as the pump light power increases, the overall level of the gain wavelength characteristic increases and the shape of the gain wavelength characteristic also changes. The increase in the gain and the change in the wavelength shape due to the increase in the pumping light power are absorbed by optimizing the transmission wavelength characteristic of the variable gain equalizer 16 in the next step 12.

  Specifically, in step 12, a control signal for optimizing the transmission wavelength characteristic of the variable gain equalizer 16 corresponding to the increase in pumping light power is generated by the control circuit 19 and output to the variable gain equalizer 16. Is done. In the variable gain equalizer 16, the transmission wavelength characteristic is variably controlled in accordance with a control signal from the control circuit 19, and gain equalization and level adjustment of the WDM signal light output from the amplification fiber 11 are performed. Here, the wavelength characteristics of the WDM signal light gain-equalized by the variable gain equalizer 16 are monitored by the optical coupler 17 and the monitor 18, and the result is fed back to the control circuit 19 to be variable gain equalizer 16. This is reflected in the optimization control.

  On the other hand, when the wavelength band of the signal light is extended to the long wavelength side, a control signal for reducing the pumping light power supplied to the amplification fiber 11 is sent from the control circuit 19 in step 20 of FIG. And are output to the excitation light sources 12A and 12B, respectively.

  In step 21, the drive state of each of the pump light sources 12A and 12B is controlled according to the control signal from the control circuit 19, and the power of the pump light output from each is adjusted to a required level. As a result, the gain wavelength characteristic of the optical amplification generated in the amplification fiber 11 is the band extension in which the pumping light power is set to the same condition as in the prior art as shown in the band extension examples of FIGS. 3 and 4 described above. Compared to the previous characteristic (thick line), the wavelength band in which an effective gain occurs is a characteristic (dotted line) in which the wavelength band is extended to the long wavelength side. In addition, as the pumping light power decreases, the overall level of the gain wavelength characteristic decreases, and the shape of the gain wavelength characteristic also changes.

  In the next step 22, a control signal for optimizing the transmission wavelength characteristic of the variable gain equalizer 16 corresponding to the decrease in the pumping light power is generated by the control circuit 19, and the same as in the case of step 12 described above. Thus, feedback control of the variable gain equalizer 16 is executed according to the control signal from the control circuit 19.

  As described above, according to the optical transmission system of the present embodiment, the power of the pumping light supplied to the amplification fiber 11 is increased and decreased, and the variable gain is adjusted in accordance with the change in the gain wavelength characteristic caused by the increase and decrease of the pumping light power. By optimizing the transmission wavelength characteristics of the equalizer 16, the amplification band of the rare earth-doped optical fiber amplifier can be easily expanded to the short wavelength side or the long wavelength side. As a result, it becomes possible to expand the signal light band without adding in parallel optical fiber amplifiers of different bands as in the conventional example shown in FIG. The bandwidth expansion service can be provided at a minimum cost when the network expands. In addition, since the extension of the signal light band in the present embodiment can be performed during the existing wavelength operation (in-service), the convenience in terms of system operation is also excellent.

  In the above embodiment, an example is shown in which the variable gain equalizer 16 is disposed after the rare earth doped optical fiber amplifier. However, the positional relationship between the rare earth doped optical fiber amplifier and the variable gain equalizer in the present invention is as described above. It is not limited to an example. For example, the present invention can be applied to any configuration that can be assumed as an optical amplification repeater, such as a configuration in which a variable gain equalizer is disposed between stages of a two-stage rare earth-doped optical fiber amplifier.

  In addition, an erbium-doped optical fiber amplifier was cited as an example of a rare-earth doped optical fiber amplifier. However, an optical fiber amplifier doped with a rare earth other than erbium can also be used by increasing / decreasing pumping light power and optimizing a variable gain equalizer. Extension of the signal light band can be realized.

  Furthermore, the wavelength characteristics of the WDM signal light output from the variable gain equalizer is monitored and the variable gain equalizer is feedback-controlled. However, the optimum of the variable gain equalizer corresponding to the setting of the pump light power The conditions may be specified in advance and stored in a memory or the like, and when the signal light band needs to be expanded, the conditions to be matched may be determined by referring to the stored data. In this way, since the output monitor can be omitted, a lower cost system can be provided.

Next, another embodiment of an optical transmission system to which an optical fiber amplifier control method related to the present invention is applied will be described.
FIG. 5 is a block diagram showing a main configuration of an optical transmission system according to another embodiment.

  5, the optical transmission system of the present embodiment combines the distributed constant Raman amplifier 20 using the transmission line fiber 3 as an amplification medium with each optical amplification repeater 10 in the optical transmission system shown in FIG. The noise characteristics in each relay section are improved. Here, the Raman amplifier 20 includes, for example, a Raman amplification pumping light source 21, an additional Raman amplification pumping light source 22, and multiplexers 23 and 24.

  Specifically, the Raman amplification pumping light source 21 generates pumping light having a required wavelength and power capable of generating Raman amplification with respect to the WDM signal light propagating through the transmission line fiber 3. In the Raman amplification, for example, when a quartz optical fiber is used as the transmission line fiber 3 (amplification medium), a gain peak occurs at a frequency 13.2 THz lower than the frequency of the excitation light. For this reason, the wavelength of the Raman amplification excitation light source 21 is set, for example, to a band on the short wavelength side of about 100 nm with respect to the C-band signal light. The output light power of the Raman amplification pumping light source 21 is controlled to a required level in accordance with a control signal from the control circuit 19.

  The additional Raman amplification pumping light source 22 is a pumping light source that is added to expand the Raman amplification band in response to the expansion of the amplification band in the rare-earth doped optical fiber amplifier in the subsequent stage. The wavelength of the additional Raman amplification excitation light source 22 is set in accordance with the extended signal light band, and is basically set to a value different from the wavelength of the Raman amplification excitation light source 21. The output optical power of the additional Raman amplification excitation light source 22 is also controlled to a required level in accordance with a control signal from the control circuit 19.

  The multiplexer 23 supplies the pumping light output from the Raman amplification pumping light source 21 to the transmission line fiber 3 from behind (the signal light output side). The multiplexer 24 combines the pumping light output from the Raman amplification pumping light source 21 and the pumping light output from the additional Raman amplification pumping light source 22 and supplies the multiplexed light to the multiplexer 23. As a specific example of each of the multiplexers 23 and 24, a general WDM coupler or the like can be used.

  In the optical transmission system having the above-described configuration, the WDM signal light generated by the transmission terminal station 1 (FIG. 15) is transmitted to the transmission line fiber 3. The transmission line fiber 3 is supplied with pumping light from the Raman amplification pumping light source 21 and the additional Raman amplification pumping light source 22 controlled by the control circuit 19 through the multiplexers 23 and 24. Excitation light for Raman amplification propagates through the transmission line fiber 3 in the opposite direction to the signal light. As a result, the WDM signal light propagating through the transmission line fiber 3 is Raman amplified and reaches the optical amplification repeater 10.

  The WDM signal light Raman-amplified by the transmission line fiber 3 is sent to the amplification fiber 11 via the multiplexer 14A in the same manner as in the embodiment shown in FIG. The WDM signal light is amplified by the stimulated emission action of erbium or the like excited by the supply of the excitation light from the controlled excitation light sources 12A and 12B and the amplified excitation light sources 13A and 13B. The WDM signal light propagated through the amplification fiber 11 and amplified is given to the variable gain equalizer 16 whose transmission wavelength characteristics are controlled in accordance with the control signal from the control circuit 19, and the gain is equalized. Then, the WDM signal light that has passed through the variable gain equalizer 16 is sent to the transmission line fiber 11 in the next relay section, and a part of the WDM signal light is branched by the optical coupler 17 and supplied to the monitor 18 to obtain the output optical power. Wavelength characteristics are monitored.

Here, the control operation of the control circuit 19 in the present embodiment will be described in detail with reference to the flowchart of FIG.
Similar to the case where the operation is described with reference to FIG. 2 described above, for example, after the installation of the present optical transmission system, the transmission capacity demand expands and the wavelength band of the signal light is expanded to the short wavelength side or the long wavelength side. Is required, the control circuit 19 follows the algorithm for extending the band toward the short wavelength illustrated in FIG. 6A or the algorithm for extending the band toward the long wavelength illustrated in FIG. 6B. The Raman amplification pumping light power supplied to the transmission line fiber 3, the pumping light power supplied to the amplification fiber 11, and the transmission wavelength characteristic of the variable gain equalizer 16 are controlled in relation to each other.

  Specifically, when extending the wavelength band of the signal light to the short wavelength side, first, in step 30 of FIG. 6A, a control signal for increasing the pumping light power supplied to the amplification fiber 11 is provided. It is generated by the control circuit 19 and output to the additional excitation light sources 13A and 13B. In step 31, the drive states of the additional pump light sources 13A and 13B are controlled according to the control signal from the control circuit 19, and the power of the pump light output from each is adjusted to a required level. As a result, the gain wavelength characteristic of optical amplification in the amplification fiber 11 expands to the short wavelength side, and the gain level increases as a whole, and the wavelength shape also changes.

  Next, in step 32, the Raman supplied to the transmission line fiber 3 is expanded so that the wavelength band of Raman amplification in the transmission line fiber 3 is also expanded to the short wavelength side in response to the extension of the signal light band to the short wavelength side. The wavelength or power of the amplification excitation light is adjusted. Here, for example, by adding a Raman amplification pumping light source 22 having a wavelength shorter than that of the Raman amplification pumping light source 21, the wavelength band of Raman amplification is expanded to the short wavelength side. The output light powers of the Raman amplification pumping light source 21 and the additional Raman amplification pumping light source 22 are correlated with the control of the transmission wavelength characteristic of the variable gain equalizer 16 performed in the next step 33, and the WDM signal light is correlated. Is set to an optimum level so that the desired gain equalization is realized, and the OSNR for the optical signal of each wavelength included in the WDM signal light is flattened. Specifically, the optimization of the Raman amplification pumping light power and the transmission wavelength characteristic of the variable gain equalizer 16 is such that the Raman amplification pumping light power on the short wavelength side is relatively larger than that on the long wavelength side. It is preferable to optimize the transmission wavelength characteristic of the variable gain equalizer 16 so that the slope of the wavelength difference of the Raman gain generated according to the inclination is flattened by the variable gain equalizer 16.

  In this case, the Raman amplification pumping light source is added to cope with the extension of the signal light band to the short wavelength side. For example, a plurality of pumping light sources having different wavelengths are used as the Raman amplification pumping light source 21. In such a case, it is possible to expand the wavelength band of Raman amplification to the short wavelength side by increasing the output power of the pumping light source on the short wavelength side among them.

  On the other hand, when the wavelength band of the signal light is extended to the long wavelength side, a control signal for reducing the pumping light power supplied to the amplification fiber 11 is sent from the control circuit 19 in step 40 of FIG. And are output to the excitation light sources 12A and 12B, respectively. In step 41, in accordance with a control signal from the control circuit 19, the driving state of each of the pumping light sources 12A and 12B is controlled and the power of pumping light output from each is adjusted to a required level. As a result, the gain wavelength characteristic of optical amplification in the amplification fiber 11 is expanded to the long wavelength side, and the gain level is generally lowered and increased, resulting in a change in the wavelength shape.

  Next, in step 42, the Raman supplied to the transmission line fiber 3 is expanded so that the Raman amplification wavelength band in the transmission line fiber 3 is also extended to the long wavelength side in response to the extension of the signal light band to the long wavelength side. The wavelength or power of the amplification excitation light is adjusted. Here, for example, by adding a Raman amplification excitation light source 22 having a longer wavelength than the Raman amplification excitation light source 21, the wavelength band of Raman amplification is expanded to the longer wavelength side. The output light powers of the Raman amplification pumping light source 21 and the additional Raman amplification pumping light source 22 are correlated with the control of the transmission wavelength characteristic of the variable gain equalizer 16 performed in the next step 43, so as to correlate with the WDM signal light. Is set to an optimum level so that the desired gain equalization is realized, and the OSNR for the optical signal of each wavelength included in the WDM signal light is flattened. A preferred specific example for optimizing the Raman amplification pumping light power and the transmission wavelength characteristic of the variable gain equalizer 16 is the same as in the case of the extension to the short wavelength side described above.

  As described above, according to the optical transmission system of the present embodiment, the same effects as those of the embodiment shown in FIG. 1 can be obtained, and the Raman amplifier 20 using the transmission line fiber 3 as an amplification medium can be provided. By combining and controlling the pumping light for Raman amplification corresponding to the expansion of the signal light band, the level of the WDM signal light input to the amplification fiber 11 of each optical amplification repeater 10 is Raman amplified. Therefore, it is possible to improve the OSNR in each relay section. Further, the gain of the rare earth-doped optical fiber amplifier is increased or decreased by increasing or decreasing the pumping light power supplied to the amplification fiber 11 in order to extend the signal light band. Even if it exceeds the range that can be absorbed by the amplifier 16, the transmission wavelength characteristic of the variable gain equalizer 16 is controlled in cooperation with the control of the Raman gain in the transmission line fiber 3. Since the level diagram of the entire optical amplifying relay node including can be reset, the signal light band can be extended over a wider range.

Next, an optical transmission system to which an optical fiber amplifier control method according to the present invention is applied will be described.
FIG. 7 is a block diagram showing a main configuration of an embodiment of an optical transmission system to which an optical fiber amplifier control method according to the present invention is applied. FIG. 8 is a diagram showing a configuration of the entire optical transmission system.

  In the optical transmission system of the present embodiment, for example, as shown in FIG. 8, a plurality of repeaters 4 are arranged on a transmission line fiber 3 that connects between a transmission terminal station (Tx) 1 and a reception terminal station (Rx) 2. At the same time, a bidirectionally pumped Raman amplifying unit 30 that supplies pumping light bidirectionally using the transmission line fiber 3 between the repeaters 4 as an amplification medium and Raman-amplifies the WDM signal light propagating through the transmission line fiber 3. Is arranged for each relay section. As shown in FIG. 7, for example, the bidirectional pumping Raman unit 30 in each relay section includes Raman amplification pumping light sources (LD) 31A and 31B, multiplexers 32A and 32B, an optical coupler 33, a monitor 34, and an arithmetic circuit 35. And a control circuit 36. Each repeater 4 can be a general repeater applied to a known optical transmission system or an optical amplification repeater as shown in FIGS. 1 and 5 described above.

  Specifically, the Raman amplification pumping light sources 31A and 31B respectively generate pumping light having a required wavelength and power capable of generating Raman amplification with respect to the WDM signal light propagating through the transmission line fiber 3. It is. Here, it is assumed that the pumping light output from each of the Raman amplification pumping light sources 31A and 31B has a single wavelength.

  The multiplexer 32A supplies the pumping light output from the Raman amplification pumping light source 31A to the transmission line fiber 3 from the front (signal light input side). Further, the multiplexer 32B supplies the pumping light output from the Raman amplification pumping light source 31B to the transmission line fiber 3 from the rear (signal light output side). As a specific example of each multiplexer 32A, 32B, a general WDM coupler or the like can be used.

  The optical coupler 33 branches a part of the WDM signal light that propagates through the transmission line fiber 3 and is input to the repeater 4 and sends it to the monitor 34. The monitor 34 measures the power of the branched light from the optical coupler 33 and monitors the output power of the WDM signal light that has been propagated through the transmission line fiber 3 and Raman-amplified.

  Based on the monitor value of the signal light output power in the monitor 34, the arithmetic circuit 35 calculates the set value of the pumping light power considering the influence of the lamp loss existing on the transmission line fiber 3 as will be described later, and the result is calculated. The signal shown is output to the control circuit 36.

  The control circuit 36 generates a signal for controlling the driving state of the Raman amplification excitation light sources 31A and 31B according to the output signal from the arithmetic circuit 35, and outputs the control signal to each of the Raman amplification excitation light sources 31A and 31B. To do.

Next, the operation of the optical transmission system having the above configuration will be described.
In this optical transmission system, the power of the forward pumping light and the backward pumping light supplied to the transmission line fiber 3 in each relay section is set at the time of system startup, for example, according to an algorithm as shown in the flowchart of FIG. Thus, even when there is a lamp loss on the transmission line fiber 3, the signal light is transmitted according to a desired level diagram.

  Specifically, first, in step 100 of FIG. 9, signal light equivalent to the WDM signal light transmitted between the transmitting and receiving end stations during operation is sequentially input from the transmission side to the transmission line fiber 3 in each relay section. The In step 101, the power of the forward pumping light and the rear pumping light supplied to the transmission path fiber 3 is 0 mW in the relay section where the signal light is input to the transmission path fiber 3, that is, the transmission path. The operation of each of the Raman amplification excitation light sources 31A and 31B is controlled by the control circuit 36 so that the excitation light is not supplied to the fiber 3.

  In step 102, the signal light output power propagated through the transmission line fiber 3 and given to the repeater 4 is measured by the optical coupler 33 and the monitor 34. In step 103, the value of the signal light output power measured by the monitor 34 is stored in a memory (not shown) in the arithmetic circuit 35 in correspondence with the excitation light power at that time. When the storage of the measured value of the signal light output power is finished, it is determined in step 104 whether or not the forward pumping light power has reached the maximum value (output limit) of the pumping light source 31A. When the forward pumping light power does not reach the maximum value, the driving state of the Raman amplification pumping light source 31A is controlled by the control circuit 36 so that the forward pumping light power is increased by a required amount (for example, 5 mW) in step 105. After that, the process returns to step 102 to measure and store the signal light output power. The above-described series of processing is repeated until the forward pumping light power reaches the maximum value, and when the maximum value is reached, the next step 106 is performed.

  The signal light output power measured by the monitor 34 is a power obtained by adding the signal light component and the noise light (natural Raman scattered light) component. For example, Japanese Patent Application No. 2001- It is possible to estimate the natural Raman scattered light power based on the excitation light power by applying the technique described in Japanese Patent No. 553962, and subtract the natural Raman scattered light power from the measured value of the monitor 34 to obtain the signal light component. Only the output power can be obtained.

  In step 106, the calculation circuit 35 calculates the ratio of the increase in the signal light output power to the increase in the forward pumping light power using the data stored in the above step 103. The relationship between the forward pumping light power and the signal light output power is obtained by applying a known approximate expression based on the data of the measurement points plotted on the left side of FIG. FIG. 10 shows a flow of a series of processes at the time of starting the system, with time on the horizontal axis and signal light output power on the vertical axis.

  When the relationship between the forward pumping light power and the signal light output power is calculated, in the next step 107, the forward pumping light power for realizing the target value Pt1 (see FIG. 10) of the signal light output power is realized. The set value is calculated using the relationship obtained in step 106. The target value Pt1 of the signal light output power is a value designed in advance for the signal light output power at which a desired level diagram can be realized in a state where only the forward pumping light is supplied to the transmission line fiber 3. When the setting value of the forward pumping light power corresponding to the target value Pt1 of the signal light output power is obtained by the arithmetic circuit 35, a signal indicating the setting value is transmitted to the control circuit 36. The driving state of the Raman amplification excitation light source 31A is controlled by the control circuit 36 in accordance with the signal from the arithmetic circuit 35.

  When the forward pumping light power is optimized, in the next step 109, the rear pumping light power is gradually increased while the signal light output power is monitored by the monitor 34. In step 110, the signal light output power reaches the target value Pt2 (see FIG. 10) in the bidirectional excitation state and becomes substantially constant, thereby completing the control at the time of starting the system.

  By optimizing the forward pumping light power at the time of starting the system as described above, even if there is a lamp loss on the signal light input side on the transmission line fiber 3 as shown in FIG. A level diagram that is almost the same as when it does not exist can be realized. That is, when the forward pumping light power is set to a predetermined value regardless of the presence of the lamp loss as in the prior art, the transmission path has a lamp loss on the input side as shown in the level diagram C indicated by the broken line in FIG. At the same time as the input level of the signal light to the fiber 3 decreases, the forward pumping light power that can be supplied to the transmission line fiber 3 also decreases, so the Raman gain obtained by the forward pumping light decreases, and the insufficient gain is caused by the backward pumping light. It will be supplemented. As a result, the minimum level of the signal light on the transmission line fiber 3 is lowered, and the OSNR is deteriorated. On the other hand, in the case of this system, as shown in the level diagram A shown by the solid line in FIG. 11, the signal light output power (see level diagram A ′) when only the forward pumping light is supplied to the transmission line fiber 3 is obtained. Since the Raman gain is obtained by the backward pumping light, the minimum level of the signal light is improved and the influence of the lamp loss is suppressed to a small level because the Raman gain is obtained by the backward pumping light. Can do. Therefore, it is possible to stabilize the performance of the bidirectionally pumped Raman amplifier regardless of the lamp loss on the transmission line fiber.

  In the above embodiment, an example is shown in which the power of the backward pumping light is set so that the output power of the signal light propagated through the transmission line fiber 3 and Raman amplified is substantially constant at the target value Pt2. However, the present invention is not limited to this. For example, the power of the backward pumping light is set so that the on / off gain of the Raman-amplified signal light propagating through the transmission line fiber 3 becomes substantially constant at a preset value. You may make it do.

Next, another embodiment of an optical transmission system to which an optical fiber amplifier control method related to the present invention is applied will be described.
In the optical transmission system shown in FIG. 7, the output power of the Raman-amplified signal light propagating through the bidirectionally-pumped transmission line fiber 3 is measured by the monitor 34, and the result is used to forward and backward. The pump light power was optimized. In the present embodiment, a function as an optical spectrum analyzer is added to the monitor 34, the OSNR is calculated based on the measurement result of the monitor 34, and the forward and backward pumping lights are set so that the OSNR becomes a desired value. A modification in which power optimization is performed will be described. The configuration of the optical transmission system of this embodiment is the same as that shown in FIGS. For this reason, here, the control operation at the time of starting the system will be described in detail with reference to the flowchart of FIG.

  When the present optical transmission system is started up, first, in step 120 of FIG. 12, signal light equivalent to WDM signal light transmitted between the transmitting and receiving terminal stations during operation is sequentially transmitted from the transmission side to the transmission line fiber 3 in each relay section. Is input. In step 121, for each relay section in which the signal light is input to the transmission line fiber 3, each Raman amplification amplification is performed so that each power of the forward pumping light and the rear pumping light supplied to the transmission line fiber 3 is 0 mW. The operation of the excitation light sources 31A and 31B is controlled by the control circuit 36. In step 122, the output power of the signal light propagating through the transmission line fiber 3 and given to the repeater 4 is measured by the optical coupler 33 and the monitor 34. Then, in step 123, it is determined whether or not the backward pumping light power has reached the maximum output (power limit) of the Raman amplification pumping light source 31B. If YES, step 126 follows.

  In step 124, it is determined whether or not the value of the signal light output power measured in step 122 has reached the target value Pt2 (see FIG. 10) of the signal light output power at the time of bidirectional excitation set in advance. When the measured value is equal to or smaller than the target value Pt2, after the driving state of the Raman amplification pumping light source 31A is controlled by the control circuit 36 so that the backward pumping light power is increased by a required amount (for example, 10 mW) in step 125. Returning to step 122, the signal light output power is measured. On the other hand, when it is determined in step 124 that the measured value has reached the target value Pt2, the process proceeds to step 129 described later.

  In step 126, in response to the determination result that the backward pumping light power has reached the maximum value in step 123, the Raman amplification pumping light source 31B is driven so that the forward pumping light power increases by a required amount (for example, 10 mW). The state is controlled by the control circuit 36. In step 127, the output power of the signal light that is propagated through the transmission line fiber 3 that has been supplied with the forward and backward pumping light and is Raman-amplified is measured by the optical coupler 33 and the monitor 34. Then, in step 128, as in the case of step 124, it is determined whether or not the value of the signal light output power measured in step 127 has reached the target value Pt2, and the measured value is equal to or less than the target value Pt2. In this case, the process returns to step 126, the forward pumping light power is increased, and the signal light output power is measured again. On the other hand, when the measured value reaches the target value Pt2, the process proceeds to the next step 129.

  In step 129, the OSNR of the signal light propagated through the transmission line fiber 3 is calculated by the arithmetic circuit 35 using the optical spectrum measured by the monitor 34 in a state where the measured value of the signal light output power exceeds the target value Pt2. Desired. In step 130, it is determined whether the OSNR measurement value obtained in step 129 is larger than the OSNR value (design value) assumed based on the loss (span loss) in the relay section. If the measured value of OSNR is less than or equal to the design value, it is determined that optimization of the forward and backward pumping light power is necessary. First, in step 131, the forward pumping light power is increased by a required amount (for example, 10 mW). Subsequently, the backward pumping light power is lowered until the signal light output power measured by the monitor 34 in step 132 substantially matches the target value Pt2, and the process returns to step 129 again to calculate the OSNR. Then, when it is determined in step 130 that the measured value of OSNR is larger than the design value, the control at the time of starting the system is completed.

  As described above, the OSNR of the Raman-amplified signal light is measured at the time of starting the system, and the forward and backward pumping light power is optimized based on the measurement result. In addition, it is possible to stabilize the performance of the bidirectional excitation type Raman amplification unit.

  In the bidirectional excitation type Raman amplifying unit 30 shown in FIG. 7 described above, the forward pumping light and the backward pumping light are each configured with a single wavelength, but a plurality of forward pumping light or backward pumping light is used. The present invention can also be applied to a bidirectionally pumped Raman amplifying unit configured with a wavelength. For example, as shown in FIG. 13, front and rear Raman amplification pumping light sources 31A and 31B are respectively output from two pumping light sources 41 and 41 ′ having different wavelengths and the pumping light sources 41 and 41 ′. You may make it comprise from the WDM coupler 42 which combines excitation light. In this case, for the monitor 34, the signal light branched by the optical coupler 33 is further branched into two by the optical coupler 51, and two lights having a transmission band corresponding to the peak wavelength of the Raman gain due to the pumping light of each wavelength. As a configuration in which the light receiving elements 63 and 53 ′ receive light through the filters 62 and 52 ′, the signal light is individually monitored corresponding to each excitation light wavelength, and the excitation light having the corresponding wavelength based on each monitoring result. The power may be controlled. With such a configuration, it becomes possible to optimize the front and rear pumping light powers with higher accuracy. Note that, for a specific algorithm for controlling the excitation light power of a plurality of wavelengths as described above, for example, a technique described in Japanese Patent Application Laid-Open No. 2002-72262 can be applied.

  Further, with respect to the configuration of the optical transmission system shown in FIG. 7 described above, a control signal generated by the control circuit 36 arranged on the receiving side in one relay section is transmitted to the Raman amplification pumping light source 31A arranged on the transmitting side. As a specific means, for example, it is possible to use a supervisory control signal (OSC) transmitted on the opposite line as shown in FIG. In the configuration example of FIG. 14, the control signal for controlling the forward pumping light power of the uplink shown in the upper side in the figure is transmitted from the control circuit 36 to the OSC transmitter 71 on the downlink side in the same relay station. Then, the control signal on the uplink side is transmitted on the monitoring control signal propagating on the downlink, and the control signal received by the OSC receiver 72 is transmitted to the pump light source 31A for Raman amplification on the uplink side in the same relay station. It is done. 14 shows only the configuration for transmitting the control signal on the uplink side, the control signal can be transmitted on the downlink side with the same configuration as that on the uplink side.

  The main inventions disclosed in this specification are summarized as follows.

(Appendix 1) A control method for an optical fiber amplifier that supplies pumping light to a rare earth-doped optical fiber and amplifies signal light propagating through the rare earth-doped optical fiber,
Adjusting the power of pumping light supplied to the rare earth-doped optical fiber and amplifying signal light propagating through the rare earth-doped optical fiber in accordance with a change in gain wavelength characteristics generated by adjusting the power of the pumping light By expanding the transmission wavelength characteristics of the variable gain equalizer that equalizes the wavelength deviation of the output power generated in the optical fiber, the signal light band that can be amplified by the rare earth-doped optical fiber is expanded to the short wavelength side or the long wavelength side A method for controlling an optical fiber amplifier.

(Appendix 2) A method of controlling an optical fiber amplifier according to appendix 1,
When the rare earth doped optical fiber is an erbium doped optical fiber,
By reducing the power of the pumping light supplied to the erbium-doped optical fiber from a preset reference power, and controlling the transmission wavelength characteristic of the variable gain equalizer according to the amount of reduction of the pumping light power A method for controlling an optical fiber amplifier, wherein a signal light band that can be amplified by the erbium-doped optical fiber is expanded to a longer wavelength side.

(Additional remark 3) It is the control method of the optical fiber amplifier of Additional remark 1, Comprising:
When the rare earth doped optical fiber is an erbium doped optical fiber,
By increasing the power of pumping light supplied to the erbium-doped optical fiber from a preset reference power, and controlling the transmission wavelength characteristics of the variable gain equalizer according to the amount of increase of the pumping light power A method of controlling an optical fiber amplifier, wherein a signal light band that can be amplified by the erbium-doped optical fiber is expanded to the short wavelength side.

(Additional remark 4) It is a control method of the optical fiber amplifier of Additional remark 1, Comprising:
By supplying excitation light to the transmission line fiber connected to the signal light input side of the rare earth-doped optical fiber, Raman amplification of the signal light propagating through the transmission line fiber is performed,
A control method for an optical fiber amplifier, wherein the wavelength of pumping light supplied to the transmission line fiber is increased in accordance with the expansion of a signal light band that can be amplified by the rare earth-doped optical fiber.

(Additional remark 5) It is the control method of the optical fiber amplifier of Additional remark 4, Comprising:
A plurality of pumping lights having different wavelengths are supplied to the transmission line fiber to perform Raman amplification of the signal light,
Light that adjusts the power of at least one of a plurality of pump lights supplied to the transmission line fiber in accordance with the expansion of a signal light band that can be amplified by the rare earth-doped optical fiber. Fiber amplifier control method.

(Appendix 6) A method of controlling an optical fiber amplifier according to appendix 4,
Light that compensates for a decrease in gain generated by adjusting the power of pumping light supplied to the rare earth-doped optical fiber by increasing the power of pumping light for Raman amplification supplied to the transmission line fiber Fiber amplifier control method.

(Supplementary note 7) An optical transmission system including an optical fiber amplifier that supplies pumping light to a rare earth-doped optical fiber and amplifies signal light propagating through the rare earth-doped optical fiber,
A variable gain equalizer for equalizing the wavelength deviation of the output power generated in the amplified signal light propagating through the rare earth-doped optical fiber;
By adjusting the power of the pumping light supplied to the rare earth-doped optical fiber and controlling the transmission wavelength characteristic of the variable gain equalizer according to the change of the gain wavelength characteristic generated by the power adjustment of the pumping light And an optical transmission system comprising: a control circuit that expands a signal light band that can be amplified by the rare earth-doped optical fiber to a short wavelength side or a long wavelength side.

(Appendix 8) The optical transmission system according to appendix 7,
The rare earth-doped optical fiber is an erbium-doped optical fiber,
The control circuit reduces the power of pumping light supplied to the erbium-doped optical fiber from a preset reference power, and the transmission wavelength characteristics of the variable gain equalizer according to the amount of reduction of the pumping light power An optical transmission system characterized in that the signal light band that can be amplified by the erbium-doped optical fiber is expanded to the longer wavelength side by controlling the erbium-doped optical fiber.

(Supplementary note 9) The optical transmission system according to supplementary note 7,
The rare earth-doped optical fiber is an erbium-doped optical fiber,
The control circuit increases the power of pumping light supplied to the erbium-doped optical fiber from a preset reference power, and the transmission wavelength characteristics of the variable gain equalizer according to the amount of increase of the pumping light power An optical transmission system characterized in that the signal light band that can be amplified by the erbium-doped optical fiber is expanded to the short wavelength side by controlling

(Supplementary note 10) The optical transmission system according to supplementary note 7,
A transmission line fiber connected to the signal light input side of the rare earth-doped optical fiber;
A pumping light source for supplying pumping light to the transmission line fiber, and a Raman amplifier for Raman amplification of signal light propagating through the transmission line fiber,
The control circuit controls the pumping light source of the Raman amplifier in response to the expansion of the signal light band that can be amplified by the rare earth-doped optical fiber, and increases the wavelength of the pumping light supplied to the transmission line fiber. A characteristic optical transmission system.

(Supplementary note 11) The optical transmission system according to supplementary note 10,
The Raman amplifier has a plurality of pump light sources that supply a plurality of pump lights having different wavelengths to the transmission line fiber,
The control circuit controls at least one pumping light source of the plurality of pumping light sources corresponding to the expansion of a signal light band that can be amplified by the rare earth-doped optical fiber, and supplies the pumping light source from the pumping light source to the transmission line fiber. An optical transmission system characterized by adjusting the power of pumping light.

(Supplementary note 12) The optical transmission system according to supplementary note 10,
The control circuit compensates for the decrease in gain generated by adjusting the power of the pumping light supplied to the rare earth-doped optical fiber by increasing the power of the Raman amplification pumping light supplied to the transmission line fiber. An optical transmission system characterized by

(Supplementary note 13) A method of controlling an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber, and Raman-amplifies signal light propagating through the bidirectionally pumped transmission line fiber,
While the signal light is input to the transmission line fiber and the supply of the backward pumping light to the transmission line fiber is cut off, the power of the forward pumping light supplied to the transmission line fiber is changed within a preset range, Measure the output power of the Raman-amplified signal light propagating through the pumped transmission line fiber according to the power of the forward pumping light,
Based on the measurement result of the signal light output power, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the signal light output set in advance for the forward-pumped transmission line fiber according to the obtained ratio Calculate the forward pumping light power required to achieve the target power value,
In accordance with the calculation result, the power of the forward pumping light supplied to the transmission line fiber during system operation is controlled, and the power of the rear pumping light is controlled according to the power of the front pumping light. Control method.

(Supplementary note 14) The method for controlling an optical fiber amplifier according to supplementary note 13, comprising:
The power of the backward pumping light is controlled so that the output power of the signal light propagated through the bidirectionally pumped transmission line fiber and Raman-amplified becomes constant at a preset value. Amplifier control method.

(Supplementary note 15) The method for controlling an optical fiber amplifier according to supplementary note 13, comprising:
The power of the backward pumping light is controlled so that the on / off gain of the Raman-amplified signal light propagating through the bidirectionally pumped transmission line fiber is constant at a preset value. Amplifier control method.

(Supplementary Note 16) A method of controlling an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber, and Raman-amplifies and outputs signal light propagating through the bidirectionally pumped transmission line fiber,
The signal light is input to the transmission line fiber, and at least the backward pumping light is supplied to the transmission line fiber, and the output power of the Raman-amplified signal light propagating through the transmission line fiber is measured.
When the measured signal light output power reaches a preset target value of the signal light output power for the bidirectionally excited transmission line fiber, the optical signal-to-noise ratio of the signal light propagated through the transmission line fiber is obtained. ,
When the optical signal-to-noise ratio is less than a predetermined value, the power of the forward pumping light is increased while adjusting the power of the rear pumping light so that the output power of the signal light is substantially constant at the target value. Forward pumping light power and backward pumping light power at the time when the optical signal-to-noise ratio of the signal light propagated through the channel reaches a predetermined value, and forward pumping light supplied to the transmission line fiber during system operation according to the judgment result And a control method of the optical fiber amplifier, wherein each power of the backward pumping light is controlled.

(Supplementary Note 17) An optical transmission system including an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber and Raman-amplifies signal light propagating through the bidirectionally pumped transmission line fiber. And
While the signal light is input to the transmission line fiber and the supply of the backward pumping light to the transmission line fiber is cut off, the power of the forward pumping light supplied to the transmission line fiber is changed within a preset range, A measurement unit that measures the output power of the Raman-amplified signal light propagating through the pumped transmission line fiber and corresponding to the power of the forward pumping light; and
Based on the measurement result of the signal light output power in the measurement unit, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the transmission path fiber pumped forward is set in advance according to the obtained ratio. A calculation unit for calculating the forward pumping light power necessary to achieve the target value of the signal light output power;
A control unit for controlling the power of the forward pumping light supplied to the transmission line fiber during system operation according to the calculation result of the computing unit, and for controlling the power of the rear pumping light according to the power of the front pumping light. An optical transmission system characterized by being configured.

(Supplementary note 18) The optical transmission system according to supplementary note 17,
The control unit controls the power of the backward pumping light so that the output power of the Raman-amplified signal light propagating through the bidirectionally pumped transmission line fiber becomes constant at a preset value. Optical transmission system.

(Supplementary note 19) The optical transmission system according to supplementary note 17,
The control unit controls the power of the backward pumping light so that the on / off gain of the Raman-amplified signal light propagating through the bidirectionally pumped transmission line fiber becomes constant at a preset value. Optical transmission system.

(Supplementary Note 20) Optical transmission configured to include an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber and Raman-amplifies and outputs signal light propagating through the bidirectionally pumped transmission line fiber A system,
A measurement unit that inputs signal light to the transmission line fiber, supplies at least backward pumping light to the transmission line fiber, and propagates the transmission line fiber to measure the output power of the Raman-amplified signal light;
When the signal light output power measured in the measuring unit reaches a target value of the signal light output power set in advance for the bidirectionally excited transmission line fiber, the optical signal pair of the signal light propagated through the transmission line fiber An arithmetic unit for obtaining a noise ratio;
When the optical signal-to-noise ratio obtained by the calculation unit is less than a predetermined value, the power of the forward pumping light is adjusted while adjusting the power of the rear pumping light so that the signal light output power is substantially constant at the target value. The forward pumping light power and the rear pumping light power at the time when the optical signal-to-noise ratio of the signal light propagated through the transmission path fiber reaches a predetermined value are determined, and the transmission path fiber is determined during system operation according to the determination result. An optical transmission system comprising: a control unit that controls each power of the forward pumping light and the backward pumping light supplied to the light source.

It is a block diagram which shows the principal part structure of one Embodiment of the optical transmission system to which the control method of the optical fiber amplifier relevant to this invention is applied. 2 is a flowchart for explaining the operation of the optical transmission system in FIG. 1. FIG. 2 is a characteristic diagram illustrating a band extension example centered on a C-band in the optical transmission system of FIG. 1. FIG. 2 is a characteristic diagram illustrating a band extension example centered on an L-band in the optical transmission system of FIG. 1. It is a block diagram which shows the principal part structure of other embodiment of the optical transmission system to which the control method of the optical fiber amplifier relevant to this invention is applied. 6 is a flowchart for explaining the operation of the optical transmission system of FIG. 5. It is a block diagram which shows the principal part structure of one Embodiment of the optical transmission system to which the control method of the optical fiber amplifier by this invention is applied. It is a figure which shows the structure of the whole optical transmission system of FIG. It is a flowchart explaining the control operation at the time of starting in the optical transmission system of FIG. FIG. 8 is a diagram illustrating a flow of a series of processing at startup in the optical transmission system of FIG. 7 with time on the horizontal axis and signal light output power on the vertical axis. It is the figure which illustrated the level diagram of the signal light of one relay area in the optical transmission system of FIG. It is a flowchart explaining the control operation at the time of starting about other embodiment of the optical transmission system to which the control method of the optical fiber amplifier relevant to this invention is applied. FIG. 8 is a block diagram illustrating an application example in which Raman amplification pumping light is configured with a plurality of wavelengths in association with the optical transmission system of FIG. 7. FIG. 8 is a block diagram illustrating an application example in which a control signal is transmitted using a monitoring control signal of a counter line in relation to the optical transmission system of FIG. 7. It is a figure explaining the technique for extending the conventional signal light band. It is a figure which shows an example of the level diagram in the conventional system which applied the Raman amplifier and aimed at the improvement of OSNR. It is a figure for demonstrating the influence by the lamp loss on a transmission line fiber about the conventional system which aimed at the improvement of OSNR using the bidirectional | two-way excitation type | mold Raman amplifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmission terminal station 2 ... Reception terminal station 3 ... Transmission line fiber 4 ... Repeater 10 ... Optical amplification repeater 11 ... Amplification fiber 12A, 12B ... Excitation light source 13A, 13B ... Additional excitation light source 14A, 14B, 15A, 15B DESCRIPTION OF SYMBOLS 16 ... Variable gain equalizer 17 ... Optical coupler 18 ... Monitor 19 ... Control circuit 20 ... Raman amplifier 21 ... Raman amplification pumping light source 22 ... Additional Raman amplification pumping light source 23, 24 ... Multiplexer 30 ... Bidirectionally pumped Raman amplifiers 31A, 31B ... Raman amplification pumping light sources 32A, 32B ... multiplexer 33 ... optical coupler 34 ... monitor 35 ... arithmetic circuit 36 ... control circuit

Claims (6)

A method for controlling an optical fiber amplifier that supplies forward pumping light and backward pumping light to a transmission line fiber, and Raman-amplifies signal light propagating through the bidirectionally pumped transmission line fiber,
While the signal light is input to the transmission line fiber and the supply of the backward pumping light to the transmission line fiber is cut off, the power of the forward pumping light supplied to the transmission line fiber is changed within a preset range, Measure the output power of the Raman-amplified signal light propagating through the pumped transmission line fiber according to the power of the forward pumping light,
Based on the measurement result of the signal light output power, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the signal light output set in advance for the forward-pumped transmission line fiber according to the obtained ratio Calculate the forward pumping light power required to achieve the target power value,
According to the calculation result, the power of the forward pumping light supplied to the transmission line fiber during system operation is controlled ,
Supplying the controlled forward pumping light and backward pumping light to the transmission line fiber, and propagating through the bidirectionally pumped transmission line fiber to measure the output power of the Raman-amplified signal light;
A control method of an optical fiber amplifier, wherein the power of backward pumping light is controlled based on the measurement result of the signal light output power . A method of controlling an optical fiber amplifier according to claim 1,
Power of the backward pumping light, the light, characterized in that the bi-directional pumping output power of propagating the transmission path fiber Raman amplified signal light is controlled to be constant at a preset value Fiber amplifier control method. A method of controlling an optical fiber amplifier according to claim 1,
Power of the backward pumping light, the light, characterized in that the on-off gain of the propagating bidirectional excited transmission line fiber Raman amplified signal light is controlled to be constant at a preset value Fiber amplifier control method. An optical transmission system comprising an optical fiber amplifier that supplies a forward pumping light and a backward pumping light to a transmission line fiber and Raman-amplifies signal light propagating through the bidirectionally pumped transmission line fiber,
While the signal light is input to the transmission line fiber and the supply of the backward pumping light to the transmission line fiber is cut off, the power of the forward pumping light supplied to the transmission line fiber is changed within a preset range, A measurement unit that measures the output power of the Raman-amplified signal light propagating through the pumped transmission line fiber and corresponding to the power of the forward pumping light; and
Based on the measurement result of the signal light output power in the measurement unit, the ratio of the change in the signal light output power with respect to the change in the forward pump light power is obtained, and the transmission path fiber pumped forward is set in advance according to the obtained ratio. A calculation unit that calculates the forward pumping light power necessary to achieve the target value of the signal light output power;
After controlling the power of the forward pumping light supplied to the transmission line fiber during system operation according to the calculation result in the calculation unit, the transmission line fiber bidirectionally pumped by the supply of the controlled forward pumping light and backward pumping light An optical transmission system comprising: a control unit configured to control the power of backward pumping light based on a result of measurement of the output power of the propagated and Raman-amplified signal light by the measurement unit . The optical transmission system according to claim 4,
Wherein the control unit, so that the bi-directional pumping output power of propagating the transmission path fiber Raman amplified signal light is constant at a preset value, characterized by controlling the power of the backward pumping light And optical transmission system. The optical transmission system according to claim 4,
Wherein the control unit, as on-off gain of the propagating bidirectional excited transmission line fiber Raman amplified signal light is constant at a preset value, characterized by controlling the power of the backward pumping light And optical transmission system.

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