JP2009055058A - Optical amplifier, and optical amplification method and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system configuration for broadening the band of an optical amplifier for increasing a wavelength multiplex number and constituting a broad transmission signal band. <P>SOLUTION: The plurality of optical amplifiers of different optical amplification gain band widths are combined, and blocking is executed using a plurality of excitation light sources so as to configure a Raman amplifier covering the plurality of optical amplification gain bands. Thus, the band of the optical amplifier is broadened. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  Optical wavelength division multiplexing (WDM), which bundles optical signals of different wavelengths and transmits them through a single optical fiber, is a powerful means for realizing higher capacity and economy of communication systems and flexible optical networks. is there.

  In particular, due to the progress of amplifiers in recent years, it has been rapidly put into practical use as a backbone network backbone technology that supports Internet services.

In a WDM optical communication system, mainly long-distance transmission is possible while amplifying signal light at a relay stage using an optical amplification and relay technique.
Examples of the optical amplification means include a rare earth doped optical fiber amplifier (EDFA) and a Raman amplifier.

  The present invention is a Raman amplifier that can be used for amplification of signal light in various optical communication systems, and is particularly suitable for amplification of wavelength division multiplexed light.

  In a WDM system using an optical amplifier, the upper limit of the transmitted optical power is limited by optical waveform deterioration and crosstalk due to the nonlinear optical effect of the transmission path, and the lower limit is optical noise such as spontaneous emission generated from the optical amplifier. It is limited by the degradation of the optical SNR (signal-to-noise ratio) due to.

In a high-density WDM system that multiplexes several tens to several hundreds of waves, it is installed at intervals of about several tens of kilometers to compensate for transmission line loss in order to relax nonlinear optical effects and optical SNR restrictions. Technology that uses Raman amplifiers in combination with high-powered erbium-doped fiber amplifiers (EDFAs) is promising (1999 IEICE Communication Society Conference, Ohira et al. B-10-51 and Kawakami et al. B-10) -54 and Takeda et al. B-10-99).
Toshiki Ohira, 9 others "40Gb / s x 8 waves-80km x 5 repeat wavelength division multiplexing transmission experiment using distributed Raman amplification", IEICE Society Society, September 7, 1990, Proceedings 2 , B-10-51, p228 Hiroto Kawakami, two others "Zero-dispersion flat transmission line with suppressed nonlinear optical effect", IEICE Society Society, September 7, 1990, Proceedings 2, B-10-54, p231 Miki Takeda, 3 others "Examination of gain equalization method by Raman amplification", IEICE Society Society, September 7, 1990, Proceedings 2, B-10-99, p276

  In the above-described known technique, there is a description of combining a Raman amplifier and an EDFA, or a case where the number of multiplexed signal lights to be transmitted is increased has not been studied.

  The present invention relates to an optical amplifier that forms a wide transmission signal band by increasing the number of wavelength multiplexing.

  The first means is for increasing the bandwidth of the EDFA.

The optical amplifier is divided by a first optical amplifying unit that amplifies light using a plurality of pumping lights having different wavelengths, a band unit that divides the output of the first optical amplifying unit into a plurality of bands, and the band dividing unit. A plurality of second optical amplifying means having a gain with respect to each band.
The second means is a means for increasing the bandwidth of the EDFA.

The optical amplifier includes a first optical amplification unit that amplifies light in the first wavelength band, a second optical amplification unit that amplifies light in a second wavelength band different from the first wavelength band, and at least the first optical amplification unit. And a third optical amplifying means for pumping with a plurality of excitation lights so as to Raman-amplify light in both the second wavelength band, and the light amplified by the third amplifying means with the first wavelength band means and the first wavelength band means Wavelength separating means for separating the two wavelength band means, connecting the light of the first wavelength band of the separating means to be input to the first optical amplifier, and further, light of the second wavelength band of the separating means To be input to the second optical amplifier.
The third means is a means for controlling the gain wavelength characteristic of Raman amplification by a plurality of pump lights.

The optical amplifier includes an optical fiber, pumping light for generating a Raman gain in the optical fiber, and a gain equalizer for correcting the wavelength characteristics of the Raman gain generated in the optical fiber by the pumping light.
The fourth means is a means for preventing return light from the Raman amplification medium to the light excitation light source.

The optical amplifier includes an optical fiber, a plurality of pumping light sources that generate Raman gain in the optical fiber, a first combining unit that combines the plurality of pumping light sources, and pumping light from the combining unit that is input to the optical fiber. And an optical element for blocking the light output from the optical fiber from going to the excitation light source side between the first synthesizing unit and the second synthesizing unit.
The fifth means is a means for facilitating the addition of an optical amplifier whose wavelength band capable of performing optical amplification is determined.

The optical amplifier includes a first optical amplifier that Raman-amplifies input light with pumping light and a second optical amplifier that amplifies output light of the first optical amplifier. When the wavelength band of the amplified light increases, the first optical amplifier A third optical amplifier having a gain in a wavelength band different from that of the two optical amplifiers is provided in parallel with the second optical amplifier after the first optical amplifier, and the pumping light of the first optical amplifier is added to the third optical amplifier. The gain wavelength band is amplified.
The sixth means is a means for adjusting the dynamic range of an optical amplifier whose wavelength band capable of performing optical amplification is determined.

The optical amplifier includes a first optical amplifying unit that performs Raman amplification by a plurality of pumping light and a second optical amplifying unit that amplifies the output of the first optical amplifying unit. The power input to the second optical amplification means is controlled to be constant.
The seventh means is a Raman amplifier means for controlling the gain profile corresponding to the transmission line.

  The optical amplifier is an optical amplifying medium that also serves as a transmission path or connected to the transmission path, a plurality of pumping light sources for Raman amplification of light in the optical amplifying medium, and a plurality of pumping light source outputs to the optical amplifying medium. And a means for controlling the gain wavelength characteristic of the optical amplifying medium in accordance with the conditions of the transmission path.

  As in the present invention, a plurality of pumping light sources are provided corresponding to the amplification bands of the EDFA, and the output value of each pumping light source is controlled to widen the band of the EDFA and to compensate for the gain wavelength characteristics of Raman amplification by a plurality of pumping lights. , Preventing return light from the Raman amplification medium to the light pumping light source, facilitating the addition of optical amplifiers with a fixed wavelength band for optical amplification, and the dynamic range of optical amplifiers with a fixed wavelength band for optical amplification The gain profile can be controlled in accordance with systems (transmission path length, transmission path loss, input power, number of signals, etc.) with different adjustment and transmission conditions.

  FIG. 1 shows a first embodiment of the present invention.

The first embodiment is the most practical configuration.
In the figure, 1 is a transmission path, 2 is a control unit, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1Ap1B, 1C are optical connectors, 21, 22, 23, 24, 25, 26, 27, 28, 29, 2A, 2B are wavelength multiplexing / demultiplexing couplers, 31, 32, 33, 34, 35 are beam splitters, 41, 42, 43 are optical isolators, 51, 52, 53, 54, 55, 56 are Fiber grating filters 61, 62, 63 are polarization combining couplers, 71, 72, 73 are optical attenuators, 81, 82, 83, 84, 85, 86 are light sources, 91, 92, 93, 94, 95 are light receiving elements. , 101 and 102 are band-pass filters, 81, 82, 83, 84, 85 and 86 are excitation lasers, 601, 602 and 603 are excitation light source units, 121 and 122 are gain equalizers, and 400 is an optical element. Lock, 111 and 112 are optical amplifying unit, 200 is a wavelength characteristic monitor unit, 300 denotes a power monitor, 900 monitor unit, respectively.

  The transmission line 1 is connected to the wavelength multiplexing / demultiplexing coupler 21 via the optical connector 11 by the optical connector 1C.

  As the transmission line 1, a normal 1.3 μm zero dispersion fiber, a dispersion compensating fiber DCF having a large dispersion value, a dispersion shifted fiber DSF with a shifted zero dispersion value, or a non-zero dispersion shifted fiber NZ-DSF can be applied.

  Since DCF, NZ-DSF, and NZ-DSF have a small effective cross-sectional area, a non-linear effect appears greatly. Therefore, when used for a Raman amplification medium, it can be configured as a concentrated amplifier.

  The wavelength multiplexing / demultiplexing coupler 21 has a function of transmitting wavelength-multiplexed light (light obtained by multiplexing a plurality of signal lights) from the transmission path 1 and inputting excitation light to the transmission path 1.

  In the transmission line 1, when pumping light is input, a Raman amplification effect is generated and optical amplification of wavelength multiplexed light can be performed.

  The excitation light is composed of a plurality of excitation light source units 601 602 603.

  The excitation light source unit 601 includes two light sources 81 and 82, fiber grating filters 51 and 52, and a polarization combining coupler 61.

  The light source 81 feeds back the 1429.7 nm light by the fiber grating filter 51 so as to emit light centering on the 1429.7 nm light, performs external resonance, and inputs the light to the polarization combining coupler 61.

  The light source 82 feeds back 1433.7 nm light by the fiber grating filter 52 so as to emit light centering on 1433.7 nm light, performs external resonance, and inputs the light to the polarization combining coupler 61.

  The polarization combining coupler 61 combines the polarization so that the polarizations of the light beams that have passed through the fiber grating filters 51 and 52 are orthogonal to each other and outputs the combined light to the wavelength multiplexing / demultiplexing coupler 24.

  The excitation light source unit 602 includes two light sources 83 and 84, fiber grating filters 53 and 54, and a polarization combining coupler 62.

  The light source 83 feeds back 1454.0 nm light by the fiber grating filter 53 so as to emit light centering on 1454.0 nm light, performs external resonance, and inputs the light to the polarization combining coupler 62.

  The light source 84 feeds back 1458.0 nm light by the fiber grating filter 54 so as to emit light centering on 1458.0 nm light, performs external resonance, and inputs the light to the polarization combining coupler 62.

  The polarization combining coupler 62 combines the polarization so that the polarizations of the light beams that have passed through the fiber grating filters 53 and 54 are orthogonal to each other and outputs the combined light to the wavelength multiplexing / demultiplexing coupler 25.

  The excitation light source unit 603 includes two light sources 85 and 86, fiber grating filters 55 and 56, and a polarization combining coupler 63.

  The light source 85 feeds back the light of 1484.5 nm by the fiber grating filter 55 so as to emit light centering on the light of 1484.5 nm, performs external resonance, and inputs the light to the polarization combining coupler 63.

  The light source 86 feeds back the light of 1488.5 nm by the fiber grating filter 56 so as to emit light centering on the light of 1488.5 nm, performs external resonance, and inputs it to the polarization combining coupler 63.

  The polarization combining coupler 63 combines the polarization so that the polarizations of the light beams that have passed through the fiber grating filters 55 and 56 are orthogonal to each other, and outputs the combined light to the wavelength multiplexing / demultiplexing coupler 25.

  The excitation light source units 601, 602, and 603 have been described on the premise that laser diodes are used as the light sources 81, 82, 83, 84, 85, and 86. However, if the target gain wavelength characteristic is obtained in the transmission line 1, FIG. It is not limited to the configuration of

  The wavelength multiplexing / demultiplexing coupler 25 transmits the light from the excitation light source unit 603, reflects the light from the excitation light source unit 602, wavelength-multiplexes the light from the excitation light source units 603 and 602, and inputs the wavelength multiplexing / demultiplexing coupler 24. .

  The wavelength multiplexing / demultiplexing coupler 24 passes the optical wavelength multiplexed by the wavelength multiplexing / demultiplexing coupler 25 and reflects the light having the wavelength from the excitation light source unit 601, thereby combining the wavelength from the excitation light source unit 601 with the wavelength. Wavelength multiplexing of light from the demultiplexing coupler 25 is performed.

  The light wavelength-multiplexed by the wavelength multiplexing / demultiplexing coupler 24 is input to the optical element block 400.

  The optical element block 400 includes a beam splitter 31, an optical isolator 43, and a wavelength multiplexing / demultiplexing coupler 23.

  The beam splitter 31 branches a part of the wavelength multiplexed light from the excitation light source units 601, 602, and 603 and inputs it to the monitor block 900.

  The optical isolator 43 blocks the light reflected by the wavelength multiplexing / demultiplexing coupler 21 from the transmission path 1 (the return light of the excitation light corresponding to the crosstalk of the signal light) from being input to the excitation light source units 601 602 603. To do.

  The wavelength multiplexing / demultiplexing coupler 23 reflects the wavelength multiplexed light component and transmits the excitation light component to monitor the wavelength multiplexed light for the crosstalk reflected from the transmission line 1 by the wavelength multiplexing / demultiplexing coupler 21. Multiplexed light is output from the optical connector 12.

  The optical elements of the wavelength multiplexing / demultiplexing coupler 23 and the optical isolator 43 have an effect of preventing light from the transmission path 1 from being input to the excitation light source unit.

  The pumping light monitoring unit 900 includes wavelength multiplexing / demultiplexing couplers 26, 27, 28, 29, optical attenuators 71, 72, 73, and light receiving elements 91, 92, 93.

  The wavelength multiplexing / demultiplexing coupler 26 reflects the light corresponding to the wavelength of the excitation light source unit 601 out of the output of the excitation light branched by the beam splitter 31, and transmits the other light.

  The light corresponding to the excitation light source unit 601 reflected by the wavelength multiplexing / demultiplexing coupler 26 and further filtered through the wavelength multiplexing / demultiplexing coupler 27, attenuated by a predetermined amount by the optical attenuator 73, and then received by the light receiving element 93.

  Based on the output of the light receiving element 93, the output power of the excitation light source unit 601 is controlled by the control unit 2.

  The light transmitted through the wavelength multiplexing / demultiplexing coupler 26 is input to the wavelength multiplexing / demultiplexing coupler 28 and reflects the light corresponding to the wavelength of the excitation light source unit 602 and transmits the rest.

  The light corresponding to the excitation light source unit 602 reflected by the wavelength multiplexing / demultiplexing coupler 28 and further filtered through the wavelength multiplexing / demultiplexing coupler 29, attenuated by a predetermined amount by the optical attenuator 72, and then received by the light receiving element 92.

Based on the output of the light receiving element 92, the output power of the excitation light source unit 602 is controlled by the control unit 2.
The light transmitted through the wavelength multiplexing / demultiplexing coupler 28 is light corresponding to the wavelength of the excitation light source unit 601, and this light is attenuated by a predetermined amount by the optical attenuator 71 and then received by the light receiving element 91.

  Based on the output of the light receiving element 91, the output power of the excitation light source unit 603 is controlled by the control unit 2.

  Furthermore, the control unit 2 notifies the optical amplification units 111 and 112 of the information on the excitation light power obtained by the monitor block 900 so that the optical amplification units 111 and 112 can perform gain control together with the monitoring control information.

  The wavelength multiplexed light transmitted through the wavelength multiplexing / demultiplexing coupler 21 transmits light in the first wavelength band (for example, 1530 to 1560 nm), and reflects the light in the second wavelength band (for example, 1570 to 1600 nm). Input to the wave coupler 22.

  The first wavelength band corresponds to the amplification gain band of the subsequent optical amplification unit 111, and the second wavelength band corresponds to the amplification gain band of the subsequent optical amplification unit 111.

  The light in the first wavelength band separated by the wavelength multiplexing / demultiplexing coupler 22 is partially separated by the beam splitter 33, and the wavelength band in which the signal light in the band divided by the wavelength multiplexing / demultiplexing coupler 22 is selected by the bandpass filter 101 is selected. The selected power is detected by the light receiving element 95.

  The light in the second wavelength band separated by the wavelength multiplexing / demultiplexing coupler 22 is partly separated by the beam splitter 32, passes through the second wavelength band by the wavelength multiplexing / demultiplexing coupler 2 b, and then is combined by the bandpass filter 102. A wavelength band in which the signal light of the band divided by the wave coupler 22 is selected, and the selected power is detected by the light receiving element 94.

  The output of the beam splitter 33 is incident on the optical isolator 41.

  The optical isolator 41 prevents light from the optical amplification unit 111 provided in the subsequent stage from returning to the transmission path 1.

  The output of the beam splitter 32 is incident on the optical isolator 42.

  The optical isolator 42 prevents light from the optical amplification unit 112 provided in the subsequent stage from returning to the transmission path 1.

  The output of the optical isolator 41 is input to the gain equalizer 121.

  The gain equalizer 121 depends on the wavelength characteristic distortion of the Raman amplification gain in the first wavelength band generated in the transmission line 1 by the pumping light from the plurality of pumping light source units with a linear characteristic having a predetermined specific tilt, or on the wavelength. Gain equalization is performed so that there is no constant value.

  The output of the optical isolator 42 is input to the gain equalizer 122.

  The gain equalizer 122 depends on the wavelength characteristic distortion of the Raman amplification gain in the second wavelength band generated in the transmission line 1 by the pumping light from the plurality of pumping light source units with a linear characteristic having a predetermined specific tilt, or on the wavelength. Gain equalization is performed so that there is no constant value.

  The output of the gain equalizer 121 is input to the optical amplification unit 111 via the optical connectors 13 and 15.

  The optical amplifying unit 111 amplifies the light in the first wavelength band and inputs it to the wavelength multiplexing / demultiplexing coupler 2A via the optical connectors 17 and 19.

  The output of the gain equalizer 122 is input to the optical amplification unit 112 via the optical connectors 14 and 16.

  The optical amplifying unit 112 amplifies the light of the second wavelength band and inputs it to the wavelength multiplexing / demultiplexing coupler 2A via the optical connectors 18 and 1A.

  The wavelength multiplexing / demultiplexing coupler 2A reflects the light from the optical amplifying unit 111 and transmits the light from the optical amplifying unit 112, thereby wavelength-multiplexing the light from the optical amplifying unit 111 and the optical amplifying unit 112, and the optical connector 1B. Output more.

  Light from the optical amplification unit 111 and the optical amplification unit 112 is branched by the beam splitters 34 and 35 and input to the wavelength characteristic monitor 200.

The wavelength characteristic monitor 200 divides the inside of the band into predetermined bands so that the wavelength characteristics in each band can be understood, receives the light with the light receiving element, and notifies the control unit 2 of the result.
The control unit 2 controls the output power constant control and the wavelength characteristics of Raman amplification medium based on the information of the input monitor section 300 for the excitation light monitor unit 900 consisting of the light receiving elements 94 and 95.

  Further, the control unit 2 controls the Raman gain profile based on the information of the wavelength characteristic monitoring unit 200 to control the gain wavelength characteristic.

  These controls alone or in combination control the pumping light output level and wavelength of the pumping light source units 601, 602, and 603.

  In FIG. 1, two optical amplifying units are provided and an optical amplifier that amplifies two wavelength bands is described. However, the wavelength multiplexing / demultiplexing coupler 22 is divided into two or more bands. And hands are good.

  In other words, when branching into two or more, the configuration between the wavelength multiplexing / demultiplexing couplers 22 and 2A may be configured by the number corresponding to the number of separated wavelength bands.

  The optical amplification units 111 and 112 in FIG. 1 have different wavelength bands that can be optically amplified, but the system configuration can be configured in common as shown in FIG.

  In the figure, 111-1, 111-2 are erbium doped fibers (EDF), 111-8, 111-9, 111-10, 111-11, 111-12, 111-23 are beam splitters, 111-13, 111- 14 is a wavelength multiplexing coupler, 111-3 and 111-4 are automatic gain control circuits, 111-5 is an automatic output control circuit, 111-24 is a control circuit, 111-6 is a variable attenuator, and 111-7 is a dispersion compensator. 111-15, 111-17, 111-18, 111-20, 111-21, 111-22 are light receiving elements, 111-16, 111-19 are excitation light sources, and 15, 16, 17, 18 are optical connectors. Each is shown.

  The wavelength multiplexed light input from the optical connector 15 or 16 is branched by the beam splitter 111-23.

  The light branched by the beam splitter 111-23 detects the monitoring control signal light osc by the light receiving element 111-22, and outputs the detection result to the control circuit 111-24.

  One output of the beam splitter 111-23 is input to an erbium-doped fiber amplifier 1 (EDFA1).

  The input of the EDFA 1 is branched by the beam splitter 111-8.

  The light branched by the beam splitter 111-8 is input to the light receiving element 111-15.

  The light input to the light receiving element 111-15 is converted into an electrical signal and output to the automatic gain control circuit 111-3 as an input monitor or the like.

  One light of the beam splitter 111-8 is input to the erbium-doped fiber 111-1 via a wavelength multiplexing coupler 111-13 that multiplexes the excitation light.

  The output of the erbium-doped fiber 111-1 is branched by the beam splitter 111-9 and input to the light receiving element 111-17.

  The light receiving element 111-17 outputs an output monitor value to the automatic gain control circuit 111-3.

  The automatic gain control circuit 111-3 receives the input monitor value of the light receiving element 111-15, the output monitor value of the light receiving element 111-17, and predetermined gain information determined by the monitor control signal light osc from the control circuit 111-24. To control the level of the excitation light source 111-16.

  The output of the EDFA 1 is input to an erbium-doped fiber amplifier 2 (EDFA 2) via a variable attenuator 111-6 and a dispersion compensator 111-7.

  In EDFA2, the light input to EDFA2 is branched by beam splitter 111-10.

  The light branched by the beam splitter 111-10 is input to the light receiving element 111-15.

  The light input to the light receiving element 111-15 is converted into an electric signal and input to the automatic gain control circuit 111-4 as an input monitor value.

  One light of the beam splitter 111-10 is input to the erbium-doped fiber 111-2 through a wavelength multiplexing coupler 111-14 that wavelength-multiplexes the pump light.

  The output of the erbium-doped fiber 111-2 is branched by the beam splitter 111-11 and input to the light receiving element 111-20.

  The light receiving element 111-20 outputs an output monitor value to the automatic gain control circuit 111-4.

  The automatic gain control circuit 111-4 receives the input monitor value of the light receiving element 111-18, the output monitor value of the light receiving element 111-20, and predetermined gain information determined by the monitor control signal light OSC from the control circuit 111-24. To control the level of the excitation light source 111-19.

  The EDFA 1 and EDFA 2 in FIG. 2 perform forward excitation on the EDFs 111-1 and 111-2, but backward excitation or bidirectional excitation can also be applied.

  FIG. 3 shows the gain wavelength characteristics and the amplification unit gain wavelength characteristics in the transmission line 1 in the embodiment shown in FIG.

  FIG. 3A shows the Raman gain wavelength characteristics generated in the transmission line 1 by the pumping light of the pumping light source units 601, 602, and 603.

  A shows the Raman gain profile generated by the excitation light source unit 601, B shows the Raman gain profile generated by the excitation light source unit 602, C shows the Raman gain profile generated by the excitation light source unit 603, and F shows the excitation light source units 601 and 602. , 603, the gain characteristics in the transmission line 1 are shown.

  Each wavelength of the excitation light indicates a peak value of optical power when light having a plurality of wavelengths of the excitation light source in the excitation light source unit is synthesized.

  By overlapping the gain profiles generated by the respective light source units, a substantially uniform Raman gain can be obtained in a wide band as in the characteristic F.

  FIG. 3B shows gain wavelength characteristics generated in the optical amplification units 111 and 112.

  D indicates the gain wavelength characteristic generated in the optical amplification unit 111, and E indicates the gain wavelength characteristic generated in the optical amplification unit 112.

  The pumping light power is controlled so as to cover the gain band of the optical amplification unit 111 by the pumping light source units 601 and 602, and the pumping light power is controlled so as to cover the gain band of the light amplification unit 112 by the pumping light source units 602 and 603. Has been.

  FIG. 4 shows a second embodiment.

  4, the same members as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 4 is a modification of the embodiment of FIG. 1 in which two pumping light source blocks are provided so that the Raman gain band provided by each pumping light source unit corresponds to the amplification gain band of the individual light amplifying unit of each light amplification. is doing.

  In FIG. 4, the excitation light source unit 601 is the first excitation light source unit, the wavelength of the light source 81 is 1425 nm, the wavelength of the light source 82 is 1440 nm, the excitation light source unit 603 is the second excitation light source unit, and the wavelength of the light source 85 is 1465 nm. By setting the wavelength of the light source 82 to 1488 nm, the gains of the amplification gain bands of the optical amplification units 111 and 112 are obtained by the respective excitation light source units.

  A specific relationship between Raman gain wavelengths is shown in FIG.

  The light from the excitation light source 81 corresponds to λ1, the light from the excitation light source 82 corresponds to λ2, the light from the excitation light source 85 corresponds to λ3, and the light from the excitation light source 86 corresponds to λ4. Yes.

  A Raman amplification gain profile 1 is generated by λ1, a Raman amplification gain profile 2 is generated by λ2, a Raman amplification gain profile 3 is generated by λ3, and a Raman amplification gain profile 4 is generated by λ4.

  When the Raman amplification profiles 1 and 2 are combined, a combined gain profile as indicated by a broken line A can be obtained.

  When the Raman amplification profiles 3 and 4 are combined, a combined gain profile as shown by a broken line B can be obtained.

  Thereby, the Raman amplification gain corresponding to the gain wavelengths of the plurality of optical amplifier units can be obtained on the transmission line 1.

  That is, in FIG. 4, a broadband Raman amplifier can be realized by combining a plurality of light sources having different wavelengths.

  The configuration of FIG. 4 is configured with pumping wavelengths such that single-wavelength pumping light does not Raman-amplify the optical amplification wavelength bands of a plurality of optical amplification units at the same time for pumping light with a plurality of wavelengths of Raman amplification.

  The configuration as shown in FIG. 4 enables the following.

  By combining the Raman amplification gain bands of the individual pumping light source units and the amplification gain bands of the individual optical amplification units, the optical amplification units can be added or removed in accordance with the expansion or reduction of the signal light usage band.

  The expansion / reduction of the band for performing Raman amplification can be performed by adding or removing the excitation light source unit in accordance with the optical amplification unit.

  Thereby, the cost at the time of initial introduction of the system can be kept low, and can be added as necessary.

  In addition, even if the pumping light source unit in the light amplification wavelength band of one of the light amplification units fails, the failed pumping light source unit can be replaced without affecting the operation of the other light amplification unit.

  A specific example of band expansion using the configuration of FIG. 4 will be described below.

  Initially, the system is operated using the excitation light source unit 601 and the optical amplification unit 111.

  When the number of signal light wavelengths to be used is increased according to the user's request and the expansion of the amplification band is requested, the optical amplification unit 112 is added by a connector (not shown) provided between the wavelength multiplexing / demultiplexing couplers 22 and 2A. The excitation light source unit 603 is operated.

  Since the excitation light source units 601 and 603 correspond to the optical amplification units 111 and 112 independently, the bandwidth can be expanded even when the optical amplification unit 111 is in service.

  FIGS. 6 to 9 show an example of a Raman amplification pumping light source for generating pumping light, and Raman generating pumping light of the system configurations of FIGS. 1, 4 and 10 to 20, 22, and 24 is shown. It can be replaced with an amplifying excitation light source.

  The configuration of FIG. 6 uses two pumping LDs having the same wavelength in order to eliminate the power and polarization dependence of one pumping light wavelength.

  The polarization beam splitter (PBS) 1 multiplexes the outputs of two excitation light sources 81 that output light having a wavelength of λ1 with the planes of polarization orthogonal to each other.

  The two fiber grating filters 51 return light of the same wavelength to the two pumping light sources 81 to the pumping light source 81 made of LD, and are externally resonated between the rear end faces of the LD.

  The polarization beam splitter (PBS) 2 multiplexes the polarization planes of the outputs of the two excitation light sources 82 that output light having a wavelength of λ2 at right angles.

  The two fiber grating filters 52 return light of the same wavelength to the two pumping light sources 82 to the pumping light source 82 made of LD, and are externally resonated between the rear end faces of the LDs.

  The polarization beam splitter (PBS) 3 multiplexes the polarization planes of the outputs of the two excitation light sources 85 that output light having a wavelength of λ3 orthogonal to each other.

  The two fiber grating filters 55 return light of the same wavelength to the two pumping light sources 85 to the pumping light source 85 made of LD, and are externally resonated between the rear end faces of the LDs.

  The polarization beam splitter (PBS) 4 multiplexes the polarization planes of the outputs of the two excitation light sources 86 that output light having a wavelength of λ4 orthogonal to each other.

  The two fiber grating filters 56 return light of the same wavelength to the two pumping light sources 86 to the pumping light source 86 made of LD, and are externally resonating between the rear end faces of the LDs.

  The reason for external resonance using a fiber grating filter is that the oscillation wavelength and excitation spectrum of the semiconductor laser change depending on the driving state (driving current, ambient temperature, etc.), and the Raman gain spectrum also changes accordingly. End up.

  In order to prevent this, an external resonator (eg, fiber grating) is attached to the output side of the semiconductor laser to fix the oscillation wavelength and spectrum.

For example, when adjusting the gain of Raman amplification, the fluctuation of the center wavelength when the drive current of the semiconductor laser is changed is about 15 nm at the maximum, so that the wavelength characteristic of the gain of Raman amplification also changes greatly. End up.
Therefore, an external resonator for fixing the wavelength is required.

  Wavelength multiplexing is performed by combining light of the wavelengths of PBS 1 and PBS 2 by the multiplexer 5.

  Wavelength multiplexing is performed by combining the light of the wavelengths of PBS 3 and PBS 4 by the multiplexer 6.

  The wavelength multiplexing / demultiplexing coupler 24 wavelength-multiplexes the outputs of the multiplexers 5 and 6 to send the wavelength-multiplexed pumping light to the transmission line 1.

  The pumping light from the pumping light source unit 601 provides gain to the band of the optical amplification unit 111 in FIG. 1, and the pumping light from the pumping light source unit 603 provides gain to the band of the optical amplification unit 112 in FIG.

  As in the case of FIG. 1, the control unit 2 controls the output, wavelength, and barycentric wavelength of pumping light individually or in combination with information of the wavelength characteristic monitoring unit 200, pumping light monitoring unit 900, and input monitoring unit 300.

  FIG. 7 shows a modification of the excitation light source unit of FIG.

  In FIG. 7, the wavelength of the Raman gain profile generated in the pump light of one pump light source unit is increased by increasing the overlap of the Raman gain generated by the pump light by making the light wavelengths of the polarized light combined in each PBS slightly different. Make the characteristics uniform.

  The wavelength interval of light combined by each PBS is set to 6 nm or less, and is combined so that the gain profiles of Raman amplification are almost overlapped.

  As a result, the polarization dependence of the gain due to Raman amplification is eliminated, and at the same time, the excitation light power incident on the fiber is increased.

  The reason is that the gain in Raman amplification is obtained only with the component that matches the polarization of the pumping light. Therefore, when the pumping light is linearly polarized and the amplification fiber is not a polarization maintaining fiber, the signal light The gain fluctuates due to fluctuations in the relative polarization of the pumping light, but the fluctuation can be avoided by combining the linearly polarized pumping light sources so that the planes of polarization are orthogonal.

  The advantage of setting the pumping light wavelength interval to 6 nm or less is that the gain profile of each pumping light source is substantially overlapped to eliminate the polarization dependence.

  If the wavelength interval is widened within this range (if 6 nm is used), the dependency on the polarization wave is eliminated, and at the same time, the Raman amplification band is widened slightly, which is advantageous for gain wavelength flatness.

  Next, the output light of each PBS is wavelength-multiplexed by the multiplexer 6.

  In this case, in order to improve the multiplexing efficiency in consideration of the characteristics of the multiplexer, the wavelength interval is set to 6 nm or more.

  Other configurations and controls are the same as those in FIG.

  FIG. 8 shows an embodiment of an excitation light source unit.

8 differs from FIG. 7 in that a WDM coupler 8A that can wavelength-multiplex a plurality of light beams from the PBSs 1, 2, 3, and 4 of the excitation light source units 601 and 602 at once is used. The difference is in wavelength multiplexing.
Other configurations and controls are the same as those in FIG.

  FIG. 9 shows an embodiment of an excitation light source unit.

  9 is different from FIG. 7 in that wavelength multiplexing is performed using WDM couplers 7A and 7B capable of wavelength-multiplexing a plurality of lights at once in the pumping light source units 601 and 602 without using PBS. Is different.

  Other configurations and controls are the same as those in FIG.

  10 to 16 are diagrams for explaining the third embodiment.

  The third embodiment is an embodiment for correcting gain distortion caused when Raman amplification is performed by a plurality of pumping light sources as in the second embodiment. The principle of the gain equalizers 121 and 122 in FIG. It is description of a modification.

  FIG. 10 shows the principle for preventing gain distortion with respect to wavelengths that occurs when performing broadband Raman amplification by superimposing a plurality of Raman amplification gain profiles using excitation light having a plurality of wavelengths.

  The light having the characteristics as shown in FIG.

  In (a), the ratio of light on the long wavelength side is high due to the influence of Raman scattering in the transmission line 1.

  The light sources 81, 82, 85 and 86 combine the polarized lights orthogonally by the polarization combining couplers 61 and 63, multiplex the wavelengths by the wavelength multiplexing / demultiplexing coupler 24, and supply the excitation light to the transmission line 1 as shown in (b). A simple Raman gain profile is generated in the transmission line 1 and output to the wavelength multiplexing / demultiplexing coupler 21.

  A Raman amplification gain profile generated by one pumping light has one gain peak, and the gain peak wavelength differs depending on the wavelength of light output from the pumping light source.

  By superimposing a plurality of Raman gain profiles having different peak wavelengths, the total Raman gain profile generates an uneven gain characteristic with respect to the wavelength.

  In this figure, since four light sources having different wavelengths are used, there are four gain peaks.

  The light output from the wavelength multiplexing / demultiplexing coupler 21 is input to the optical filter 123.

  The gain equalizer 123 composed of an optical filter has the insertion loss characteristic of (c).

  The insertion loss characteristic has a characteristic for canceling the uneven characteristic of the Raman gain profile generated in the transmission line 1 and obtaining a linear characteristic with respect to the optical wavelength.

  Therefore, by passing through the gain equalizer 123, the Raman scattering characteristic generated in the transmission line 1 with respect to the wavelength and the gain unevenness generated by the plurality of excitation lights are obtained as a characteristic (d) linear with respect to the wavelength. I can do things.

  Although (d) shows a characteristic that is linear with respect to the wavelength and has the same gain, the filter may be configured to be linear and have a predetermined inclination.

  In this case, the characteristics of the gain equalizer 123 may be selected, and the output power and wavelength of the excitation light may be controlled based on the values detected by the power monitor unit 300 and the wavelength characteristic monitor unit 200.

  If the position of the beam splitter for splitting the light into the power monitor unit 300 and the wavelength characteristic monitor unit 200 is a position after the wavelength multiplexing / demultiplexing coupler 21, the wavelength multiplexing / demultiplexing coupler 21 is provided even before the wavelength multiplexing / demultiplexing coupler 22. Or between 2A.

  As the gain equalizer 123, a fiber grating filter, a dielectric multilayer filter, a Fabry-Perot etalon filter, or the like can be used.

  Each filter can be used singly or in combination.

  FIG. 11 shows a case where the principle described with reference to the configuration of FIG. 10 is used in a configuration in which a Raman amplifier based on the transmission line 1, an EDFA 1 of 1530 nm to 1560 nm, and an EDFA 21 of 1570 nm to 1600 nm are combined.

  1 and 4 in FIG. 10 are denoted by the same reference numerals, and detailed description of each part is omitted.

  In FIG. 11, a gain equalizer 123 is provided between the Raman amplification and the wavelength multiplexing / demultiplexing coupler 21.

  The beam splitters 32 and 33 are provided in front of the optical amplification units 111 and 112, and the power monitor unit 300 measures the optical power in the gain wavelength band of each optical amplification unit generated in the transmission path 1.

  The beam splitters 34 and 35 are provided at the subsequent stage of the optical amplification units 111 and 112, and the wavelength characteristic monitor unit 200 measures the wavelength characteristics of the gain wavelength band of each optical amplification unit.

  In FIG. 11, the beam splitters 34 and 35 are provided at the subsequent stage of the optical amplification units 111 and 112. However, the beam splitters 34 and 35 may be provided anywhere between the wavelength multiplexing / demultiplexing couplers 21 and 2A.

  The control circuit 2 uses the value of the monitored power monitor 300 and the value of the wavelength characteristic monitor 200 in accordance with each wavelength band of the optical amplifying units 111 and 112, and is linear with respect to the wavelength by the gain equalizer 123 formed of an optical filter. The control is performed so that a characteristic having the same gain or a linear and predetermined slope is generated.

It is desirable to provide an optical isolator 44 for preventing the return light generated by the gain equalizer 123 from going to the Raman amplifier (transmission path 1) side before the gain equalizer 123.

  The configuration of the optical isolator is essential when the gain equalizer 123 is a fiber grating filter manufactured by the chirp method, but is not necessary when the filter does not generate return light.

The optical isolator 44 has a characteristic of passing at least the wavelength band of the gain equalizer 123 (the gain band of the optical amplification units 111 and 112).
FIG. 12 corresponds to each of the optical amplification units 111 and 112 between the wavelength multiplexing / demultiplexing couplers 21 and 2A as in FIG.

  The case where the gain equalizer and the monitor are provided between the wavelength multiplexing / demultiplexing couplers 21 and 2A corresponding to the band of each optical amplification block is shown.

  The difference between FIG. 12 and FIG. 1 is that the number of pumping individual light sources is different and each pumping light source unit is provided corresponding to the gain wavelength band of each optical amplification unit.

  Other configurations are the same as those in FIG.

  FIG. 13 shows an example when the position of the gain equalizer is provided in the optical amplification unit.

  In FIG. 13, the same reference numerals as those in FIGS. 1, 2, and 4 denote the same members, and the descriptions thereof are omitted.

  In the figure, the optical amplification unit may be an optical amplification unit divided into a plurality of gain bands as shown by 111 and 112 in FIGS. 1 and 4, or if the optical amplification gain band is wide, the configuration shown in FIG. The optical amplification unit 113 may be used.

  The basic structure of these optical amplifying units is a structure having two EDFs as shown in FIG. 2. Between each EDFA, a variable attenuator 111-6, a dispersion compensator 111-7, and a transmission A gain equalizer 121, 122, or 123 for performing gain amplification equalization of Raman amplification in the path 1 is provided.

  The gain equalizers 121 and 122 have the same characteristics as the gain equalizer of FIG. 12, and cancel out the gain distortion of the Raman gain profile generated in the transmission line 1 in accordance with the gain band of the optical amplification units 111 and 112.

  The gain equalizer 123 has the same characteristic as the gain equalizer of FIG. 11 to cancel the gain distortion of the Raman gain profile generated in the transmission line 1.

  The gain equalizers 121, 122, and 123 not only cancel out the Raman gain profile distortion corresponding to the gain band of each amplification unit, but also compensate for the EDF gain wavelength characteristic in the optical amplification unit. It may also have.

  The gain equalizers 121, 122, and 123 may be provided anywhere between the EDFs in the optical amplification unit.

  If the gain equalizers 121, 122, and 123 are provided between the EDFs in the optical amplification unit, the light is amplified by the first-stage EDFA, so that a low-noise configuration is possible.

As shown in the figure, the lowest noise configuration is the lowest noise when it is provided after the optical variable attenuator 111-6 for adjusting the output of the optical amplification unit.
FIG. 14 shows an embodiment for enabling the gain control range to be expanded by variably controlling the gain equalization characteristic of the gain equalizer.

In FIG. 14, three gain equalizers 124 and 124′124 ″ for gain equalization are written so as to explain the system of FIGS. For the configuration, the gain equalizer 124 is applied. For the configuration of FIG. 12, the gain equalizer 124 ′ and 124 ″ for the configuration of FIG.

  Other configurations are the same as the configurations in the drawings.

  Normally, the gain and equalizer of the Raman gain generated by a plurality of pump light sources are gain equalized by a gain equalizer, but the wavelength characteristic monitor unit is a linear gain characteristic that is flat or has a predetermined tilt with respect to the wavelength. Based on the information of 200, the control unit 2 adjusts the output power and wavelength of the gain excitation light source.

  However, when the control range of the excitation light source is the maximum or minimum value, the target linear characteristic, flattening, and predetermined tilt cannot be realized.

In the embodiment shown in the figure, the equalization characteristics of the gain equalizers 124 and 124'124 '' can be changed and adjusted in these states.

  FIG. 15 is a modification of FIG. 10 and FIG.

  10 and 11, the gain equalizer 123 for controlling the Raman amplification characteristic is provided in the subsequent stage of the transmission line 1 serving as the Raman amplification medium. However, in the embodiment of FIG. 15, before the Raman gain is generated in the transmission line 1. By providing the gain equalizer 123 at the position of the transmission line or while the Raman gain is generated, the wavelength characteristic of the gain generated in the transmission line 1 by the Raman amplification light source 600 is pre-compensated.

  The wavelength-multiplexed optical signal transmitted by the transmitter 501 is input into the repeater and is amplified by the gain wavelength characteristic shown in FIG.

  The light amplified by the optical amplification block 530 is input to the gain equalizer 123 via the optical anisolator 47.

  The optical filter in the gain equalizer 123 has the loss characteristic (b).

  The loss characteristic of the gain equalizer 123 is a characteristic that obtains a flat characteristic when amplified to an irregularly distorted Raman amplification gain profile caused by a plurality of pump light wavelengths of the Raman amplification pump light source 600.

  The light that has passed through the gain equalizer 123 is output to the transmission line 1 via the optical isolator 47 'with the characteristic (c).

  The transmission line 1 has a transmission loss characteristic as shown in (d).

  When pumping light having a plurality of light wavelengths is input from the Raman amplification pumping light source 600 to the transmission line 1, a Raman gain profile as shown in (e) is generated.

  When the slope and amount of the loss characteristic of the Raman gain profile of (e) and the transmission line of (d) are the same, a flat gain characteristic as shown in (f) can be obtained.

  The Raman amplification light source 600 shown in FIG. 15 can be configured to generate excitation light below the wavelength multiplexing / demultiplexing coupler 21 shown in FIGS. 1, 4, 6, 7, 8, and 9.

  The embodiment of FIG. 16 is a repeater that performs Raman amplification and optical amplification by EDFA with respect to the uneven distortion of the Raman amplification gain profile generated by the pump light source for Raman amplification, and by shifting the pump light wavelength for performing Raman amplification, This is an example of obtaining a flat characteristic at the receiver end.

  In FIG. 16, the same reference numerals as those in FIG. 15 denote the same members, and a description thereof will be omitted.

  In FIGS. 16A-1 to 16A-3, the Raman amplification pumping light sources 600 of the repeaters 530-1 to 530-3 respectively transmit light of one wavelength to the transmission lines 1-1 to 1-. 3 shows the case of excitation.

  The Raman amplification pumping light source 600 in the repeater 530-1 can obtain the characteristic (a-1) by inputting the light of λ1 to the transmission line 1-1.

  The Raman amplification pumping light source 600 in the repeater 530-2 inputs light of λ2 different from the pumping wavelength of the repeater 530-1 to the transmission line 1-2.

  In the transmission line 1-2, the characteristic (a-2) can be obtained by the gain characteristic generated in the transmission line 1-1 and the total gain characteristic generated in the transmission line 1-2.

  The Raman amplification excitation light source 600 in the repeater 530-3 inputs light having a wavelength λ3 different from the excitation wavelengths of the repeaters 530-1 and 530-2 to the transmission line 1-3.

  In the transmission line 1-3, the characteristic (a-3) can be obtained by the sum of the gain characteristic generated in the transmission lines 1-1 and 1-2 and the gain characteristic generated in the transmission line 1-3.

  From the characteristic of (a-3), it is understood that the pumping light having different wavelengths is pumped to the transmission line from each repeater, and is averaged toward the receiver 502 side.

  16B-1 to FIG. 16B, the Raman amplification pumping light source 600 of each of the repeaters 530-1 to 530-3 has different wavelengths for each repeater. Thus, the case where excitation is performed on the transmission lines 1-1 to 1-3 is shown.

  The characteristic of (b-3) is seen. It can be seen that the characteristic is flatter than the characteristic of (a-3).

  The configuration of FIG. 16 can use the configuration of generating excitation light below the wavelength multiplexing / demultiplexing coupler 21 shown in FIGS. 1, 4, 6, 7, 8, and 9, and the filters of FIGS. Can be used in combination with an example in which the Raman gain characteristic is adjusted using.

  As a fourth embodiment, there is provided an optical element for preventing the return from the transmission path of pumping light when performing Raman amplification and the leakage of signal light from the wavelength multiplexing / demultiplexing coupler 21 from proceeding to the pumping light source side. An example of provision will be described with reference to FIGS.

  The configuration of FIG. 17 is the same as the configuration of the Raman amplification excitation light source below the wavelength multiplexing / demultiplexing coupler 21 of FIG. 7, but an optical member comprising an optical isolator 43 is provided between the wavelength multiplexing / demultiplexing coupler 21 and the wavelength multiplexing / demultiplexing coupler 24. It is an example.

  The optical isolator 43 transmits light from the wavelength multiplexing / demultiplexing couplers 24 to 21, but blocks light from the wavelength multiplexing / demultiplexing couplers 21 to 24.

  By this optical isolator 43, the pumping light input to the transmission line 1 returns to the pumping light source side due to scattering or the like, the return by reflection of each optical device, or the signal light due to the crosstalk of the wavelength multiplexing / demultiplexing coupler 21 is pumped. Prevents going to the light source side.

  By providing the optical isolator 43 in this manner, it is economical because it is not necessary to provide an optical isolator separately for the excitation light source.

  FIG. 18 shows an example in which the wavelength characteristic of the optical isolator 43 is further considered in the configuration of FIG.

  There is a wavelength difference of about 100 nm between the excitation light wavelength and the signal light wavelength.

  If there is no broadband optical isolator that covers such a wavelength difference, as shown in FIG. 18, the optical isolator 43 is an optical isolator that isolates the light of the excitation wavelength, and the wavelength multiplexing / demultiplexing coupler 24 By providing the optical isolator 49 for blocking the signal light wavelength on the port side where the wavelength of the signal light (long wavelength side light) returns due to the characteristics, the signal light due to the crosstalk of the wavelength multiplexing / demultiplexing coupler 21 advances to the pumping light source side. This can be prevented.

  In FIG. 19, the crosstalk of the signal light from the wavelength multiplexing / demultiplexing coupler 21 is taken out by the wavelength multiplexing / demultiplexing coupler 23 and used as a monitor, so that the signal light due to the crosstalk of the wavelength multiplexing / demultiplexing coupler 21 proceeds to the excitation light source side. This is an example of preventing this.

  The wavelength multiplexing / demultiplexing coupler 23 has a wavelength characteristic that reflects the wavelength band of the signal light and outputs it to the monitor port side.

  The monitor port is usually provided with a terminator 701 to terminate the signal light.

  When monitoring, a spectrum monitor 702 or an optical power meter 703 can be connected to measure the state of signal light.

  As shown in FIGS. 17 to 19, by using an optical element to block the light to the excitation light source, the return light due to Rayleigh scattering of the excitation light, leakage light of the signal light, or crosstalk of the wavelength multiplexing / demultiplexing coupler is used as the excitation light source. By not allowing the input to be input, the operation of the excitation light source is stabilized and deterioration is prevented.

  17 to 19 can be used as the excitation light source of FIGS. 1, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 20, 23, 24.

  Optical communication systems have different transmission line types (mode field diameter and insertion loss), signal light input power, transmission line length, and the like for each system.

  Therefore, the required gain characteristics required for optical amplifiers having Raman amplifiers differ depending on the optical communication system.

  Therefore, it is necessary to set an excitation wavelength and a wavelength interval for performing Raman amplification for each communication system.

Figure 20 shows an example of controlling a plurality of Raman amplification pumping light source, carried by the control of the light source 86 a specific example of a case of adjusting the Raman gain profile resulting in the transmission line 1.

  In FIG. 20, the operating temperature of the semiconductor laser, which is the light source 86, is changed by the output of the control unit 2 to make the oscillation wavelength variable.

  Generally, the change of the center wavelength due to the change of the operating temperature is about 0.45 nm / ° C. Therefore, for example, by changing the operating temperature by 10 ° C. and controlling the temperature, the center wavelength of the excitation light is changed to 4. The wavelength can be changed by 5 nm, whereby the gain wavelength characteristic of Raman amplification can be adjusted.

  Further, it is possible to make the oscillation wavelength variable by applying temperature control or stress to the fiber Bragg grating filter 56 for the external resonator added to the output side of the semiconductor laser.

  In the fiber Bragg grating filter 56, the change of the center wavelength due to the change of the operating temperature is about 0.01 nm / ° C.

  The light source 86 and the fiber Bragg grating filter 56 can perform wavelength control individually or in combination.

  In FIG. 20, the wavelength control is performed by the light source 86 and the fiber Bragg grating filter 56. However, the light source and the external resonator to be controlled may have any wavelength, and a plurality of light sources including all wavelengths and the external resonance. The wavelength of the vessel may be controlled.

  However, as shown in FIG. 20, when generating pump light of a Raman amplifier composed of pump light of a plurality of wavelengths, the oscillation wavelength is set for the pump light source whose center wavelength is longer than other pump light wavelengths. It is desirable to apply a variable configuration and control.

  The reason can be explained by the loss wavelength characteristic of the transmission line 1, the Raman scattering effect, and the shape of the Raman gain profile.

  FIG. 21 shows loss wavelength characteristics of three general transmission line fibers having different mode field diameters and chromatic dispersion values.

  The loss wavelength characteristic in FIG. 21 tends to increase the difference between the loss characteristics on the longest wavelength side.

  Further, the Raman scattering effect generated in the transmission path varies depending on the input conditions and the transmission path length, but this difference also tends to be larger on the longest wavelength side than the central wavelength band.

  The shape of the gain profile of Raman amplification tends to be steeper on the long wavelength side than on the short wavelength side from the gain peak, so the Raman gain profile on the longest wavelength side has less gain overlap caused by other excitation light There is a possibility that Raman amplification with a single wavelength is performed, and that the degree of freedom in adjusting gain wavelength characteristics with a plurality of wavelengths is reduced.

  As described above, by controlling the pumping light wavelength on the long wavelength side, the gain condition can be most effectively produced and an optical amplifier that can cope with different system conditions can be configured.

  By combining the adjustment of the pump light power of each pump light source and the wavelength adjustment of the pump light, it is possible to realize a Raman amplifier that can flexibly cope with changes in system conditions.

  Further, FIG. 22 shows an example in which the pumping light power in the pumping light source unit on the long wavelength side is adjusted using the pumping light source on the long wavelength side in the unit.

  By dividing the pumping wavelength into a plurality of pumping wavelengths narrower than other pumping light source wavelength intervals and changing the ratio of the pumping light power, the center of gravity wavelength of the oscillation wavelength can be further easily varied.

  In this case, the controllability can be improved by providing a fiber Bragg grating for the external resonator on the output side of the semiconductor laser and fixing the oscillation wavelength.

  Next, Raman amplification gain control in the case where Raman amplification is performed on the transmission line 1 by pump light and the result is optically amplified by an optical amplification unit made of EDFA will be described.

1, 4, 11, 12, 13, 14, and 16, in the configuration in which the Raman amplifier is provided on the input side of the EDFA, a part of the main signal system is branched and the output light is split between the power monitor 300 and the wavelength characteristic monitor 200. The following control is possible by monitoring and adjusting the pumping light powers of a plurality of wavelengths by the control circuit 2.
(1) The control unit 2 performs control so as to flatten the wavelength characteristic of the signal light due to the Raman scattering effect generated in the transmission line 1.

  In order to compensate for the Raman scattering effect generated in the transmission line 1, more pump light power on the short wavelength side can be provided for the pump wavelength of the pump light generating means.

For the pumping light source on the short wavelength side, a configuration in which the number of pumping light sources is increased or a light source capable of higher light output than the long wavelength side is applied, and Raman amplification is performed based on the results of the power monitor 300 and the wavelength characteristic monitor 200. In addition, by performing control corresponding to the gain value and gain wavelength characteristic of the optical amplifier, it is possible to provide input light with excellent wavelength flatness to the optical amplification unit.
(2) The control unit 1 controls the light input to the EDFAs of the optical amplifier units 111, 112, and 113 to be a constant value below the upper limit value of the input dynamic range of the EDFA.

  When the optical power of the optical amplifier units 111, 112, and 113 having the EDF is inputted with a large optical power exceeding the input dynamic range, the noise characteristics of the optical amplification deteriorate.

  Therefore, generating Raman amplification within a range that does not exceed the input dynamic range of the optical amplifier units 111, 112, and 113 is an element for maintaining good transmission characteristics of the optical communication system.

  In addition, when the optical amplification units 111, 112, and 113 perform constant gain control, the dynamic range is substantially expanded in a good SN state by making the input light constant at a predetermined level by Raman amplification.

  The EDFAs in the optical amplifier units 111, 112, and 113 are operated with constant gain control, constant output control, or both controls.

The transmission characteristics of the optical communication system can be improved in consideration of the noise characteristics generated by the optical amplifier.
(3) The control unit 2 adjusts the gain of Raman amplification generated in the transmission line 1 and performs control so that the input light to the optical amplification unit using the EDFA is always constant.

  FIG. 23 shows an example of the configuration when the optical amplification unit input light constant control is performed.

  In FIG. 23, the same members as those in FIGS.

  Since EDF has different wavelength characteristics depending on the magnitude of gain, constant gain control is performed.

  Normally, an EDFA that performs constant gain control prevents the EDFA output from changing when the input changes. Therefore, as shown in FIGS. 2 and 13, the optical amplifying units 111, 112,. Control is performed so that the output of 113 becomes constant output control.

  In FIG. 23, the input to the EDFA is made constant by Raman amplification of the transmission line 1 based on the monitoring results of the optical power monitor unit 300 and the wavelength monitor unit 200, so that the output of the EDFA is made constant only by the constant gain control of the EDFA. Therefore, an optical variable attenuator can be eliminated.

  FIG. 24 shows another configuration example when the input to the EDFA is constant.

  FIG. 24 shows a case where a dispersion compensator provided in the optical amplification unit is provided before the optical amplification unit in FIG.

  The transmission line 1 for performing the Raman amplification is arranged in front of the dispersion compensator 111-7, and the dispersion compensator 111-7 is arranged in front of the optical amplifier unit 111, 112 or 113.

  The Raman amplifier branches a part of the main signal system, monitors the output light, and controls so that the total power of the input light of the dispersion compensating fiber becomes a predetermined value.

  This is because if the input light level of the dispersion compensating fiber exceeds a predetermined value, the transmission characteristics of the signal light deteriorate due to non-linear effects.

  Generally, when the input of the dispersion compensating fiber is 0 dBm / ch or more, a nonlinear effect is produced.

  On the other hand, if the input light level of the dispersion compensating fiber is too low, the signal light is buried in noise light, the S / N is deteriorated, and the transmission characteristics are deteriorated.

  Therefore, control is performed so that the input power has an upper limit value that does not affect the nonlinear effect of the dispersion compensating fiber.

  At the same time, in order to flatten the wavelength characteristics of the signal light, the generation state (centroid wavelength and excitation light power) of the excitation light power of each excitation wavelength is adjusted and controlled.

  In this way, by controlling in consideration of nonlinear effects and S / N, the required characteristics (Raman amplification and gain values of optical amplifiers, gain wavelength characteristics, dispersion compensation values) that change depending on the system can be accommodated. The required characteristics can be maintained with a single type of Raman amplifier and optical amplifier, and the dynamic range of the EDFA can be expanded and adjusted, and the gain characteristics of the EDFA can be compensated.

    (Appendix 1)
  First optical amplification means for performing optical amplification with a plurality of pumping lights having different wavelengths;
Band dividing means for dividing the output of the first optical amplifying means into a plurality of bands;
An optical amplifier comprising a plurality of second optical amplifying means having a gain with respect to the band divided by the band dividing means.

    (Appendix 2)
  First optical amplification means for amplifying light in the first wavelength band;
Second optical amplification means for amplifying light in a second wavelength band different from the first wavelength band;
A third optical amplifying means for performing excitation with a plurality of excitation lights so as to Raman-amplify at least both the light in the first and second wavelength bands;
Providing a wavelength band separation means for separating the light amplified by the third amplification means into the first wavelength band means and the second wavelength band means;
The light of the first wavelength band of the wavelength band separating means is connected to be input to the first optical amplifier, and the light of the second wavelength band of the separating means is further input to the second optical amplifier. An optical amplifier characterized by being connected in such a manner.

    (Appendix 3)
  In the optical amplifier described in Appendix 2,
An optical amplifier characterized in that the third light amplifying means uses different excitation light sources for amplifying the light in the first wavelength band and the excitation light for amplifying the light in the second wavelength band. .

    (Appendix 4)
  In the optical amplifier described in Appendix 2,
The third light amplifying means comprises a plurality of pumping lights for amplifying the light in the first wavelength band and a plurality of pumping lights for amplifying the light in the second wavelength band. An optical amplifier characterized by comprising different light sources.

    (Appendix 5)
  In the optical amplifier described in Appendix 2,
An optical amplifier characterized in that the plurality of pumping lights of the third optical amplifying means combine the polarization of light from a plurality of light sources and supply them to an amplifying medium.

    (Appendix 6)
  In the optical amplifier described in Appendix 2,
An optical amplifier characterized in that the plurality of pumping lights of the third optical amplifying means wavelength-multiplex light from a plurality of light sources and supply them to an amplifying medium.

    (Appendix 7)
  In the optical amplifier described in Appendix 2,
The plurality of pumping lights of the third light amplifying means combine the light from a plurality of light sources with polarization,
A plurality of polarization-synthesized light having different wavelengths are provided,
An optical amplifier characterized in that the plurality of polarization-synthesized lights having different wavelengths are wavelength-multiplexed and supplied to an amplification medium.

    (Appendix 8)
  In the optical amplifier described in Appendix 2,
An optical amplifier comprising a gain equalizer provided between the wavelength band separation means and the first optical amplification means.

    (Appendix 9)
  In the optical amplifier described in Appendix 2,
An optical amplifier comprising a gain equalizer provided between the wavelength band separation means and the first optical amplification means and between the wavelength band separation means and the second optical amplification means.

    (Appendix 10)
  In the optical amplifier described in Appendix 2,
An optical amplifier characterized in that a gain equalizer is provided between the third optical amplification means and the wavelength band separation means.

    (Appendix 11)
  In Appendix 2,
An optical amplifier comprising a variable gain equalizer that variably equalizes the gain of the third optical amplifying means.

    (Appendix 12)
  The optical amplifier according to claim 2, wherein a gain equalizer for equalizing the gain of the third optical amplifying means is provided in the first optical amplifying means and the second optical amplifying means.

    (Appendix 13)
  In the optical amplifier described in Appendix 2,
The third optical amplifying means controls the power input to the first and second optical amplifying means to be constant.

    (Appendix 14)
  In the optical amplifier described in Appendix 2,
The third optical amplifying means changes the gain condition by changing the level of the plurality of pumping lights.

    (Appendix 15)
  In the optical amplifier described in Appendix 2,
An optical amplifier characterized in that the gain characteristic of the third optical amplifying means is changed by changing the temperature of the plurality of pumping light sources of the third optical amplifying means.

    (Appendix 16)
  In the optical amplifier described in Appendix 2,
An external resonator is provided for each of the plurality of pumping light sources of the third optical amplifying unit, and the temperature of the external resonator is varied or stress is varied to change the stress, thereby gain of the third optical amplifying unit. An optical amplifier characterized by changing characteristics.

    (Appendix 17)
  In the optical amplifier described in Appendix 2,
The gain characteristic of the third optical amplifying means is changed by controlling the wavelength interval of the plurality of pumping light sources for amplifying the first wavelength band of the third optical amplifying means. Optical amplifier.

    (Appendix 18)
  Optical fiber,
Excitation light for generating Raman gain in the optical fiber;
An optical amplifier comprising a gain equalizer for correcting wavelength characteristics of Raman gain generated in the optical fiber by the pumping light.

    (Appendix 19)
  Item 18. The optical amplifier according to item 18, wherein the excitation light is light having a plurality of wavelengths.

    (Appendix 20)
  Item 18. The optical amplifier according to item 18, wherein the gain equalizer equalizes the Raman gain generated in the optical fiber so as to be constant with respect to the wavelength.

    (Appendix 21)
  Item 18. The optical amplifier according to item 18, wherein the gain equalizer is provided at a subsequent stage of the optical fiber.

    (Appendix 22)
  Item 18. The optical amplifier according to item 18, wherein the gain equalizer equalizes light before a Raman gain is generated in the optical fiber.

    (Appendix 23)
  Item 18. The optical amplifier according to item 18, wherein the gain equalizer equalizes the light amplified by the optical fiber.

    (Appendix 24)
  The optical amplifier according to claim 18, wherein the gain equalizer is a variable gain equalizer.

    (Appendix 25)
  Optical fiber,
A plurality of pump light sources for generating Raman gain in the optical fiber;
First combining means for combining the plurality of excitation light sources;
Second combining means for inputting excitation light from the combining means to the optical fiber;
An optical amplifier characterized in that an optical element is provided between the first synthesizing unit and the second synthesizing unit to prevent the light output from the optical fiber from going to the pumping light source side.

    (Appendix 26)
  In the optical amplifier according to appendix 25,
The optical element is an optical isolator.

    (Appendix 27)
  In the optical amplifier according to appendix 25,
An optical amplifier, wherein the optical element is a wavelength separation element that extracts a wavelength in a band where Raman gain is generated by excitation.

    (Appendix 28)
  A first optical amplifier that Raman-amplifies input light with pumping light;
A second optical amplifier for amplifying the output light of the first optical amplifier;
When the wavelength band of light to be amplified increases, a third optical amplifier having a gain in a wavelength band different from that of the second optical amplifier is provided in parallel with the second optical amplifier after the first optical amplifier;
An optical amplification method characterized by adding the pumping light of the first optical amplifier to amplify the gain wavelength band of the third optical amplifier.

    (Appendix 29)
  First optical amplification means for performing Raman amplification with a plurality of excitation lights;
Second optical amplification means for amplifying the output of the first optical amplification means;
And the first optical amplifying means controls the power input to the second optical amplifying means to be constant.

    (Appendix 30)
  In Appendix 29,
The second optical amplification means includes a first amplification unit that amplifies the first wavelength band and a second amplification unit that amplifies the second wavelength band,
The first optical amplifying unit controls the gain so that the optical power input to the second optical amplifying unit is constant while the optical power input to the first amplifying unit is constant. Optical amplifier.

    (Appendix 31)
  An optical amplifying medium also serving as a transmission path or connected to the transmission path, and a plurality of excitation light sources for Raman amplification of light within the optical amplifying medium;
Means for coupling the plurality of excitation light source outputs to the optical amplification medium;
An optical amplifier comprising means for controlling a gain wavelength characteristic of the optical amplifying medium corresponding to the condition of the transmission path.

    (Appendix 32)
  In Appendix 31,
An optical amplifier characterized by changing the level of the plurality of pumping light powers.

    (Appendix 33)
  In Appendix 31,
An optical amplifier characterized in that gain characteristics of the optical amplifying medium are changed by changing temperatures of the plurality of pumping light sources.

    (Appendix 34)
  In Appendix 31,
An external resonator is provided for each of the plurality of excitation light sources,
An optical amplifier characterized by varying the temperature or stress of the external resonator to change the gain characteristic of the optical enhancement medium.

    (Appendix 35)
  In Appendix 31,
The gain characteristics of the optical amplifying medium are changed by setting the wavelengths of the plurality of pumping light sources so that the Raman amplification gain characteristics overlap with a specific wavelength band and controlling the wavelength interval between the pumping light sources. An optical amplifier.

    (Appendix 36)
  A transmission line that is divided into a plurality of transmission sections; an excitation light source provided for performing Raman amplification in each section in at least two transmission sections of the transmission path; and each excitation light source for each transmission section An optical amplification system characterized by having different wavelengths.

    (Appendix 37)
  In Appendix 36,
The optical amplification system, wherein the pumping light source provided in each transmission section includes a plurality of pumping light sources.

    (Appendix 38)
  In Appendix 36,
An optical amplification system characterized in that an optical amplifier comprising a rare earth element doped fiber is provided between each span.

Is a diagram showing an optical amplifier Fig. 2 is a diagram showing the configuration of an optical amplification unit Is a figure showing a Raman gain profile Figure shows a parallel configuration type optical amplifier and Raman amplifier Is a diagram showing the Raman gain profile of FIG. Is a diagram showing an excitation light source for Raman amplification Is a diagram showing an excitation light source for Raman amplification Is a diagram showing an excitation light source for Raman amplification Is a diagram showing an excitation light source for Raman amplification FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. FIG. 4 is a diagram showing the configuration of Raman amplification gain, etc. Is a diagram showing a structure for preventing return light Is a diagram showing a structure for preventing return light Is a diagram showing a structure for preventing return light Is a diagram showing the wavelength control configuration of the excitation light Is a diagram showing the characteristics of the transmission line Is a diagram showing the wavelength control configuration of the excitation light Is the Raman gain profile Is a diagram showing an optical amplifier

Explanation of symbols

1 is a transmission path 2 is a control unit 11, 12, 13, 14, 15, 16, 17, 18, 19, 1Ap1B, 1C is an optical connector 21, 22, 23, 24, 25, 26, 27, 28, 29, 2A and 2B are wavelength multiplexing / demultiplexing couplers 31, 32, 33, 34, and 35 are beam splitters 41, 42, and 43 are optical isolators 51, 52, 53, 54, 55, and 56 are fiber grating filters 61, 62, and 63, respectively. Polarization combining couplers 71, 72, 73 are optical attenuators 81, 82, 83, 84, 85, 86 are light sources 91, 92, 93, 94, 95 are light receiving elements 101, 102 are bandpass filters 81, 82, 83, 84, 85, 86 are pump lasers 601, 602, 603 are pump light source units 121, 122 are gain equalizer 400 are optical element blocks 111, 112 are optical amplifier units. 200 wavelength characteristic monitor 300 power monitor unit 900 monitors block 501 transmitter 502 receiver 530 relays 531 repeater optical amplifier block (EDFA)
600 is an excitation pumping light source 701 terminator 702 spectrum analyzer 703 power monitors 111-1 and 111-2 are erbium doped fibers 111-8, 111-9, 111-10, 111-11, 111-12, and 111-23 are beams Splitter,
111-13 and 111-14 are wavelength multiplexing couplers 111-3 and 111-4 are automatic gain control circuits 111-5 are automatic output control circuits 111-24 are control circuits 111-6 are variable attenuators 111-7 are dispersion compensations 111-11, 111-17, 111-18, 111-20, 111-21, 111-22 are light receiving elements 111-16, 111-19 are excitation light sources 15, 16, 17, 18 are optical connectors.

Claims (24)

First light amplifying means for amplifying light of 1530 nm to 1560 nm as a first wavelength band;
A second optical amplification means for amplifying light of 1570 nm to 1600 nm as a second wavelength band different from the first wavelength band;
A third optical amplifying means for performing backward pumping with pumping light having a plurality of different wavelengths so as to Raman-amplify at least light in both the first and second wavelength bands;
Providing a wavelength band separation means for separating the light amplified by the third amplification means into the first wavelength band means and the second wavelength band means;
The light of the first wavelength band of the wavelength band separating means is connected to be input to the first light amplifying means, and the light of the second wavelength band of the separating means is further connected to the second light amplifying means. An optical amplifier characterized by being connected so as to be inputted. The optical amplifier according to claim 1.
The third light amplification means is characterized in that the excitation light for amplifying the light in the first wavelength band and the excitation light for amplifying the light in the second wavelength band are different light sources. Optical amplifier. The optical amplifier according to claim 1.
The third optical amplifying means comprises pumping light for amplifying the light in the first wavelength band by a plurality of light sources having different wavelengths, and excitation for amplifying the light in the second wavelength band. An optical amplifier comprising a plurality of light sources having different wavelengths. The optical amplifier according to claim 1.
An optical amplifier characterized in that the plurality of pumping lights of the third optical amplifying means combine the polarization of light from a plurality of light sources and supply them to an amplifying medium. The optical amplifier according to claim 1.
An optical amplifier characterized in that the plurality of pumping lights of the third optical amplifying means wavelength-multiplex light from a plurality of light sources and supply them to an amplifying medium. The optical amplifier according to claim 1.
The plurality of pumping lights of the third light amplifying means combine the light from a plurality of light sources with polarization,
A plurality of polarization-synthesized light having different wavelengths are provided,
An optical amplifier characterized in that the plurality of polarization-synthesized lights having different wavelengths are wavelength-multiplexed and supplied to an amplification medium. The optical amplifier according to claim 1.
An optical amplifier comprising a gain equalizer provided between the wavelength band separation means and the first optical amplification means. The optical amplifier according to claim 1.
An optical amplifier comprising a gain equalizer provided between the wavelength band separation means and the first optical amplification means and between the wavelength band separation means and the second optical amplification means. The optical amplifier according to claim 1.
An optical amplifier characterized in that a gain equalizer is provided between the third optical amplification means and the wavelength band separation means. And have you to claim 1,
An optical amplifier comprising a variable gain equalizer that variably equalizes the gain of the third optical amplification means. And have you to claim 1, an optical amplifier and providing a gain equalizer for equalizing the gain of the optical amplification means of said 3 to the first optical amplifying means and said second optical amplifier in the unit . The optical amplifier according to claim 1.
The third optical amplifying means controls the power input to the first and second optical amplifying means to be constant. The optical amplifier according to claim 1.
The third optical amplifying means changes the gain condition by changing the level of the plurality of pump lights. The optical amplifier according to claim 1.
An optical amplifier characterized in that the gain characteristic of the third optical amplifying means is changed by changing the temperature of the plurality of pumping light sources of the third optical amplifying means. The optical amplifier according to claim 1.
An external resonator is provided for each of the plurality of pumping light sources of the third optical amplifying unit, and the temperature of the external resonator is varied or stress is varied to change the stress, thereby gain of the third optical amplifying unit. An optical amplifier characterized by changing characteristics. The optical amplifier according to claim 1.
The gain characteristic of the third optical amplifying means is changed by controlling the wavelength interval of the plurality of pumping light sources for amplifying the first wavelength band of the third optical amplifying means. Optical amplifier. The optical amplifier according to claim 1.
An optical amplifier, characterized in that at least the first occurring amplification medium is provided a gain equalizer for correcting the wavelength characteristic of the Raman gain in the second wavelength band by the pumping light. And have your optical amplifier of claim 17 wherein, the excitation light is an optical amplifier, characterized in that there in the light of multiple wavelengths. And have your optical amplifier of claim 17, wherein said gain equalizer is an optical amplifier, characterized in that the equalization to be constant with respect to wavelength Raman gain generated in the amplifying medium by the excitation light. And have your optical amplifier of claim 17, wherein said gain equalizer is an optical amplifier, characterized in that disposed downstream of the amplifying medium. And have your optical amplifier of claim 17, wherein said gain equalizer is an optical amplifier, characterized in that to equalize the light before Raman gain amplification medium by said pumping light is generated. And have your optical amplifier of claim 17, wherein said gain equalizer is an optical amplifier, characterized in that equalizing the light Raman amplified by the amplifying medium by the pumping light. And have your optical amplifier of claim 17, wherein the optical amplifier, wherein said gain equalizer is a variable gain equalizer. The optical amplifier according to claim 1.
An optical amplifier characterized in that the control unit performs constant output power control and wavelength characteristic control in the Raman amplification medium based on information of the pumping light monitoring unit and the input monitoring unit.

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