Optical distributed amplifier and optical distributed amplification system

Abstract

One aspect of the present invention relates to an optical distributed amplifier comprising: an excitation light generation unit (20) that generates excitation light for optically exciting an optical transmission path; and a multiplexing unit (30) that multiplexes n kinds (n is a positive integer) of light to be amplified (λs) and the excitation light outputted from the excitation light generation unit and outputs the multiplexed light to the optical transmission path. When the central wavelengths of the n kinds of light to be amplified are λS1-λSn, and the zero-dispersion wavelength of the optical transmission path is λ0, the intensities at n kinds of wavelengths from 2×λ0-λS1 to 2×λ0-λSn of the excitation light generated by the excitation light generation unit are lowered compared with the intensities at the other wavelengths of excitation light generated by the excitation light generation unit.

Description

[Technical field]

[0001] The present invention relates to the technology of distributed optical amplifiers, distributed optical amplification systems, and distributed optical amplification methods. [Background technology]

[0002] In designing high-speed, large-capacity optical transmission systems, it is important to reduce the degradation of the signal-to-noise ratio (SN) of the received signal due to transmission line losses. For this reason, various configurations have been devised to compensate for transmission line losses by optically amplifying the optical transmission line itself. Among these, distributed Raman amplification has the great advantage of being able to use existing optical fibers as the gain medium, and is therefore expected to be applied to next-generation high-speed, large-capacity optical communications.

[0003] The configuration of an optical transmission system using distributed Raman amplification is shown in Figure 10. Since bidirectional pumping is assumed here, the optical transmission line is forward pumped by pump light output from a forward pumping pumping light source, and backward pumped by another pump light output from a backward pumping pumping light source.

[0004] The signal light is sent from an optical transmitter. In the case of Raman amplification, the wavelength of the pump light is about 100 nm shorter than the wavelength of the signal light. Because Raman amplification in optical fiber has a wide gain band, this 100 nm wavelength difference is not so strict, and it is possible to obtain gain even with a slightly different wavelength difference.

[0005] Normally, pumping light propagates through the core of the optical transmission line in the same way as the signal light, so in forward pumping, it is necessary to multiplex the pumping light traveling in the same direction as the signal light onto the signal light. On the other hand, in backward pumping, it is necessary to send out pumping light traveling in the opposite direction to the signal light, and separate only the signal light to send it to the optical receiver. This multiplexing and separation can be achieved by a wavelength division multiplexing coupler or a circulator. Figure 10 shows an example of bidirectional pumping, but the pumping direction can be forward only or backward only.

[0006] Since Raman amplification is an optical effect that has polarization dependence, the pumping light output from the forward pumping pumping light source and the backward pumping pumping light source must be depolarized. A specific method for depolarizing the light may be, for example, the method described in Non-Patent Document 1. Although depolarization is essential, a detailed description will be omitted. The following description of this background art is based on the assumption that the forward pumping pumping light source and the backward pumping pumping light source have been depolarized.

[0007] When the noise in the pump light cannot be ignored, this noise is transferred to the signal light to be amplified. It is known that noise transfer is more pronounced in forward pumping because the pump light and signal light propagate in the same direction.

[0008] Here, the group velocity of the signal light in the optical transmission line is v s and the group velocity of the pump light ν p Consider the following. Figures 11 and 12 show these group velocities diagrammatically. The group velocity of light depends on the wavelength, and is fastest for a zero-dispersion wave. The zero-dispersion wavelength varies depending on the fiber structure, and is often designed to be in the vicinity of 1.3 μm or 1.55 μm, but other wavelengths may also be designed to have zero dispersion. In many cases, the group velocity is symmetrical with respect to the wavelength, sandwiching the zero-dispersion wave. As mentioned above, the wavelength of the pump light is about 100 nm shorter than the wavelength of the signal light, so the group velocity ν s and the group velocity of the pump light ν p are generally not the same.

[0009] FIG. 11 shows a schematic example in which the signal light and pump light are both longer than the zero dispersion wave. Since the pump light has a shorter wavelength than the signal light, v p >ν s In this case, even if the intensity noise of the pump light source cannot be ignored, the high frequency components of the noise are suppressed from propagating to the signal light.

[0010] This is because even if the intensity of the pump light fluctuates periodically at high speed, the signal light with different group velocities receives Raman gain from both strong and weak pump light, and ultimately receives an averaged Raman gain. However, since the time during which the signal light can receive Raman gain while propagating through the optical transmission line is finite, if the period of the fluctuation in the intensity of the pump light is long, the above-mentioned averaging is not performed completely, and the Raman gain also fluctuates over time. In other words, even if the group velocities of the signal light and the pump light are different, the low-frequency components of the noise of the pump light are propagated to the signal light, causing a certain degree of signal quality degradation. For details, see, for example, Non-Patent Document 2. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Hiroto Kawakami, Shoichiro Kuwahara, Yoshiaki Kisaka, Gain Instability in Forward-Pumped Raman Amplifier and Its Suppression Utilizing a Dual-Arm Depolarizer for Pump Light, ECOC2020 Tu1A-5 [Non-Patent Document 2] CRS Fludger, V. Handerek, Member, IEEE, and RJ Mears, Associate Member, IEEE, Pump to Signal RIN Transfer in Raman Fiber Amplifiers, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 19, NO. 8, AUGUST 2001 Summary of the Invention [Problem to be solved by the invention]

[0012] However, as shown in FIG. 12, care must be taken when the zero dispersion occurs at the midpoint between the wavelengths of the pump light and the signal light. In this case, v p and ν s Since the values ​​of are close to each other, the pump light and the signal light propagate through the optical transmission line at the same speed. Therefore, if the intensity noise of the pump light cannot be ignored, the signal light will receive Raman gain only from the strong pump light or only from the weak pump light. In other words, not only the low-frequency components but also the high-frequency components of the pump light noise are propagated to the signal light. Thus, the conventional technology has a problem in that the quality of the transmission signal can deteriorate significantly.

[0013] In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing deterioration in quality of a transmission signal caused by amplification of distributed light. [Means for solving the problem]

[0014] One aspect of the present invention is a method for generating an optical amplifier having a central wavelength of the n types of amplified light, the central wavelength being set to λ, the central wavelength being set to λ, the optical amplifier having a ... S1 ~λ S n When the zero dispersion wavelength of the optical transmission line is λ0, the pump light generated by the pump light generating unit is of light, 2×λ0-λ S1 From 2×λ0-λ Sn The intensity at n wavelengths ranging from 1 to 10 is suppressed compared to the intensity at other wavelengths of the pumping light generated in the pumping light generating section.

[0015] One aspect of the present invention is an optical distributed amplification system including an optical transmitter that transmits n types (n is a positive integer) of signal light, an optical distributed amplifier that amplifies the signal light transmitted by the optical transmitter as amplified light in an optical transmission line, and an optical receiver that receives the signal light amplified by the optical distributed amplifier, the optical distributed amplifier having a pumping light generating unit that generates pumping light that optically pumps the optical transmission line, and a multiplexing unit that multiplexes the n types of amplified light and the pumping light output from the pumping light generating unit and outputs the multiplexed light to the optical transmission line, and the central wavelength of the n types of amplified light is set to λ S1 ~λ Sn When the zero dispersion wavelength of the optical transmission line is λ0, the pumping light generated by the pumping light generating unit is 2×λ0-λ S1 From 2×λ0-λ Sn The intensities at n wavelengths ranging from 1 to 10 are suppressed compared to the intensities at other wavelengths of the pumping light generated by the pumping light generating unit.

[0016] One aspect of the present invention is an optical distributed amplification system including an optical transmitter that transmits n types (n is a positive integer) of signal light, an optical distributed amplifier that amplifies the signal light transmitted by the optical transmitter as amplified light in an optical transmission path, and an optical receiver that receives the signal light amplified by the optical distributed amplifier, the optical distributed amplifier having a pumping light generating unit that generates pumping light that optically pumps the optical transmission path, and a multiplexing unit that multiplexes the n types of amplified light and the pumping light output from the pumping light generating unit and outputs the multiplexed light to the optical transmission path, the optical transmission path from the optical distributed amplifier to the optical receiver being configured by connecting multiple optical waveguides having different chromatic dispersions in series, and the central wavelengths of the n types of amplified light being λ S1 ~λ Sn The zero dispersion wavelength of the optical waveguide in which the intensity of the propagating pump light is the highest among the plurality of optical waveguides is defined as λ 0in Then, 2×λ of the excitation light 0in -λ S1 From 2×λ 0in -λ Sn The intensities at n wavelengths ranging from 1 to 10 are suppressed compared to the intensities at other wavelengths of the pumping light generated by the pumping light generating unit.

[0017] One aspect of the present invention includes a pumping light generating step of generating pumping light for optically pumping an optical transmission line, and a multiplexing step of multiplexing n types (n is a positive integer) of amplified light and the pumping light output in the pumping light generating step and outputting the multiplexed light to the optical transmission line, and the central wavelength of the n types of amplified light is set to λ S1 ~λ Sn When the zero dispersion wavelength of the optical transmission line is λ0, the pump 2×λ0-λ of the excitation light generated in the light generation step S1 From 2×λ0-λ Sn The method for amplifying a light distribution is such that the intensity at n kinds of wavelengths up to is suppressed compared to the intensity at other wavelengths of the pumping light generated in the pumping light generating step. Effect of the Invention

[0018] According to the present invention, it is possible to provide a technique capable of suppressing deterioration in quality of a transmission signal caused by amplification of distributed light. [Brief description of the drawings]

[0019] [Figure 1] 1 is a block diagram showing a configuration of an optical distribution amplification system in a first configuration example. [Diagram 2] FIG. 1 is a schematic diagram showing an optical spectrum of excitation light, a part of which is blocked; [Diagram 3] FIG. 11 is a block diagram showing a configuration of an optical distribution amplification system in a second configuration example. [Figure 4] FIG. 2 is a diagram showing a schematic optical spectrum of excitation light, a part of which is blocked. [Diagram 5] FIG. 13 is a block diagram showing a configuration of an optical distribution amplification system in a second configuration example (variation example). [Figure 6] FIG. 2 is a diagram showing a schematic optical spectrum of excitation light, a part of which is blocked. [Figure 7] FIG. 11 is a block diagram showing a configuration of an optical distribution amplification system in configuration example 3. [Figure 8] FIG. 2 is a diagram illustrating an optical spectrum of excitation light. [Figure 9] FIG. 13 is a diagram showing the configuration of a light distribution amplification system in configuration example 4. [Figure 10] 1 shows the configuration of an optical transmission system using distributed Raman amplification. [Figure 11] FIG. 2 is a diagram illustrating a group velocity. [Figure 12] FIG. 2 is a diagram illustrating a group velocity. [Figure 13] 1 is a graph showing a transfer function of noise from pump light to signal light. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, a number of configuration examples of the light distribution amplification system will be described. Prior to this, however, content common to each configuration example will be described.

[0021] In the optical distributed amplification system of this embodiment, the amplification action by Raman amplification is generated in the optical transmission line. In many cases, the group velocity of the optical transmission line is symmetric with respect to the zero dispersion wavelength. p and ν s Since the wavelengths of the signal light and the pump light are close to each other, the pump light and the signal light propagate through the optical transmission line at the same speed. S , the zero dispersion wavelength of the optical transmission line is λ0, and the wavelength of the pump light is λ p Then, λ S -λ0=λ0-λ p This occurs with the following wavelength arrangement.

[0022] λ S -λ0=λ0-λ p Transforming this gives us λ p =2×λ0-λ S ...(1) is obtained. Therefore, it is necessary to prohibit pump light that satisfies this formula (1), or, if the pump light has a broad optical spectrum, to select the wavelength λ that satisfies formula (1). p The wavelength range including the above may be blocked by a filter.

[0023] Next, the extent of the wavelength region to be blocked will be described. The question of what extent of the wavelength region to be blocked should be determined based on the group velocity v s and the group velocity of the pump light ν p The question comes down to how different the two should be.

[0024] However, the degree of noise in the pump light before it propagates to the signal light varies greatly depending on the design of the pump light source, and the degree of penalty caused by the noise propagated to the signal light depends on the baud rate and signal format of the signal. p and ν s It is difficult to say how much difference between these two is acceptable for a transmission system.

[0025] First, in order to establish an acceptable guideline, the results of calculations on what percentage of the noise components of the pump light propagates to the signal light are shown. Fig. 13 is a graph showing the transfer function of noise from pump light to signal light. In this graph, the horizontal axis indicates frequency (GHz) and the vertical axis indicates noise (dB). The transfer function shown in the graph is calculated based on the model described in Non-Patent Document 2 on what percentage of the noise components of the pump light propagates to the signal light at the frequency shown on the horizontal axis. Note that forward pumping with an on-off gain of 7 dB is assumed, and the length of the optical transmission path (gain medium) is assumed to be 80 km.

[0026] The graph shows three curves, A, B, and C. Curve A is |1-ν s / ν p Curve B shows the transfer function when |1-ν s / ν p Curve C shows the transfer function when |1-ν s / ν p The transfer function for |=0.001 is shown.

[0027] As shown in these curves A, B, and C, |1-ν s / νp It can be seen that the noise propagation decreases rapidly when | is greater than 0.0001. Therefore, |1-ν s / ν p |>0.00001 can be used as a design guideline.

[0028] Taking the above into consideration, each configuration example will be described below. (Configuration example 1) 1 is a block diagram showing the configuration of an optical distributed amplifier system 100 according to a first configuration example of an embodiment. The optical distributed amplifier system 100 includes an optical distributed amplifier 10, an optical transmitter 40, an optical transmission line 50, and an optical receiver 60.

[0029] The optical transmitter 40 outputs a signal light to the optical receiver 60. The carrier wavelength of this signal light is λ S The optical distributed amplifier 10 amplifies the signal light output by the optical transmitter 40 and outputs the amplified signal light to the optical transmission line 50. The optical receiver 60 receives the signal light from the optical transmission line 50.

[0030] The optical distributed amplifier 10 is composed of a pumping light generating section 20 and a multiplexing section 30. The pumping light generating section 20 generates pumping light for optically pumping the optical transmission line. The pumping light generating section 20 is composed of a forward pumping pumping light source 21 and a band-stop optical filter 22. The forward pumping pumping light source 21 outputs pumping light having a wide spectral width. This wide spectrum can be generated from white noise. Note that a multimode laser that oscillates in a large number of longitudinal modes in a wide wavelength range may be used as the forward pumping pumping light source 21 as a pumping light source.

[0031] The pumping light output from the pumping light source 21 for forward pumping has a part of its spectrum blocked by the band-blocking optical filter 22. The multiplexing unit 30 multiplexes the pumping light output from the pumping light generating unit 20 and outputs the multiplexed light to the optical transmission line 50. That is, the optical output of the band-blocking optical filter 22 is multiplexed with the signal light by the multiplexing unit 30 and input to the optical transmission line 50.

[0032] 2 is a diagram showing a schematic diagram of an optical spectrum of pump light, a part of which is blocked by the band-stop optical filter 22. The horizontal axis of the graph shown in FIG. 2 indicates wavelength, and the vertical axis indicates pump light intensity. λ0 indicates the zero dispersion wavelength of the optical transmission line 50 as described above. Also, λ S As described above, denotes the wavelength of the signal light.

[0033] The band-stop optical filter 22 has a wavelength of 2×λ0-λ S That is, the pump light generated by the pump light generating unit 20 is blocked from the light having a wavelength in the wavelength range including 2×λ0-λ. S The intensity of the pump light of this wavelength is suppressed compared to the intensity of the pump light of other wavelengths generated by the pump light generating unit 20. p and ν s Since the worst-case condition that the wavelengths of the pump light and the pump light coincide with each other can be avoided, deterioration of the quality of the transmission signal can be suppressed. Since the gain band of Raman amplification is wide, Raman amplification is possible even if part of the pump light is blocked. Here, the wavelength range to be blocked is, as mentioned above, |1-ν s / ν p It is desirable to use a value that satisfies |>0.00001.

[0034] (Configuration example 2) 3 is a block diagram showing a configuration of an optical distributed amplification system 100 in configuration example 2 of the embodiment. The optical distributed amplification system 100 includes an optical distributed amplifier 10, a first optical transmitter 40-1, a second optical transmitter 40-2, a signal light multiplexing unit 70, an optical transmission line 50, and an optical receiver 60.

[0035] The first optical transmitter 40-1 outputs a signal light. The carrier wavelength of this signal light is λ S1 The second optical transmitter 40-2 outputs a signal light. The carrier wavelength of this signal light is λ S2 The signal light multiplexing unit 70 multiplexes the signal light output from the first optical transmitter 40-1 and the signal light output from the second optical transmitter 40-2. The optical distributed amplifier 10 amplifies the signal light output from the signal light multiplexing unit 70 and outputs it to the optical transmission line 50. The optical receiver 60 receives the signal light from the optical transmission line 50.

[0036] The optical distributed amplifier 10 is composed of a pumping light generating section 20 and a multiplexing section 30. The pumping light generating section 20 generates pumping light that optically pumps the optical transmission line. The pumping light generating section 20 is composed of a forward pumping pumping light source 21, a first band blocking optical filter 22-1, and a second band blocking optical filter 22-2. The forward pumping pumping light source 21 outputs pumping light having a wide spectral width. As described above, this wide spectrum can be generated from white noise. Note that a multimode laser that oscillates multiple longitudinal modes in a wide wavelength range may be used as the forward pumping pumping light source 21 as a pumping light source.

[0037] The pumping light output from the forward pumping pumping light source 21 has a part of its spectrum blocked by the first band blocking optical filter 22-1 and the second band blocking optical filter 22-2. The multiplexer 30 multiplexes the amplified light and the pumping light output from the pumping light generator 20, and outputs the multiplexed light to the optical transmission line 50. That is, the optical output of the band blocking optical filter 22 is multiplexed with the signal light by the multiplexer 30, and is input to the optical transmission line 50.

[0038] Thus, the difference between configuration example 1 and configuration example 2 is that two optical transmitters, a first optical transmitter 40-1 and a second optical transmitter 40-2, are used, and the signal light of different wavelengths output from these optical transmitters is multiplexed by a signal light multiplexing unit 70 and then combined with the pump light by an optical distributed amplifier 10.

[0039] Furthermore, the difference between the configuration example 1 and the configuration example 2 is that two filters, a first band-stopping optical filter 22-1 and a second band-stopping optical filter 22-2, are provided. The first band-stopping optical filter 22-1 has a wavelength of 2×λ0−λ S1 The second band-stop optical filter 22-2 blocks light having a wavelength in a wavelength range including 2×λ0-λ S2 As described above, λ0 indicates the zero dispersion wavelength of the optical transmission line 50. S As described above, denotes the wavelength of the signal light.

[0040] 4 is a diagram showing a schematic diagram of an optical spectrum of the excitation light, a part of which is blocked by the first band-blocking optical filter 22-1 and the second band-blocking optical filter 22-2. The horizontal axis of the graph shown in FIG. 4 represents the wavelength, and the vertical axis represents the excitation light intensity.

[0041] FIG. 4 shows the above-mentioned 2×λ0-λ S1 and light with a wavelength in the wavelength range including 2×λ0-λ S2 It is shown that the light having a wavelength in the wavelength range including 2×λ0-λ is blocked. S1 From 2×λ0-λ S2 is suppressed compared to the intensity of other wavelengths of the pump light generated by the pump light generating unit 20. This makes it possible to avoid the worst-case condition in which the group velocity of the signal light output from the first optical transmitter 40-1 and the second optical transmitter 40-2 matches the group velocity of the pump light, thereby suppressing quality degradation of the transmission signal.

[0042] The pump light generating unit 20 in the configuration example 2 is configured with the pump light source 21 for forward pumping and two band blocking optical filters (the first band blocking optical filter 22-1 and the second band blocking optical filter 22-2) as described above. The light output from the pump light source 21 for forward pumping has a wavelength of 2×λ0−λ S 1 to 2 × λ0-λ S2 The two band-stop optical filters are arranged to filter out the light output from the forward pumping pumping light source 21 from 2×λ0-λ S1 From 2×λ0-λ S It blocks two wavelengths of light ranging from 0.2 to 1.2.

[0043] That is, in the configuration example 2, "the pump light generating unit is composed of a light source and n or less band-stop optical filters, and the spectrum of the light output from the light source is 2×λ0-λ S1 From 2×λ0-λ Sn The band-stop optical filters include one or more of n kinds of wavelengths ranging from 2×λ0-λ S1 From 2×λ0-λ SnThis is a configuration example in which n=2 in the "all n wavelengths ranging from 0 to 100 that are included in the spectrum of the light output from the light source are blocked" and the number of band-blocking optical filters is two.

[0044] (Modification of Configuration Example 2) In the configuration example 2, a configuration using two optical transmitters has been described. However, the number of optical transmitters in an actual wavelength multiplexing transmission system is much greater than two, and many signal lights from these optical transmitters are often transmitted in a dense wavelength arrangement. Therefore, a configuration using n (n is a positive integer) optical transmitters will be described as a modified example of the configuration example 2.

[0045] 5 is a block diagram showing a configuration of an optical distributed amplification system 100 in a modified example of configuration example 2 in the embodiment. The optical distributed amplification system 100 includes an optical distributed amplifier 10, a first optical transmitter 40-1, a second optical transmitter 40-2, ..., an n-th optical transmitter 40-n, a signal light multiplexing unit 70, an optical transmission line 50, and an optical receiver 60.

[0046] The k-th optical transmitter 40-k (k=1 to n) outputs a signal light. The carrier wavelength of this signal light is λ Sk The signal light multiplexing unit 70 multiplexes the signal light output from the first optical transmitter 40-1, the signal light output from the second optical transmitter 40-2, ..., the signal light output from the n-th optical transmitter 40-n. The optical distributed amplifier 10 amplifies the signal light output from the signal light multiplexing unit 70 and outputs it to the optical transmission line 50. The optical receiver 60 receives the signal light from the optical transmission line 50.

[0047] The optical distributed amplifier 10 is composed of a pumping light generating section 20 and a multiplexing section 30. The pumping light generating section 20 generates pumping light that optically pumps the optical transmission line. The pumping light generating section 20 is composed of a pumping light source 21 for forward pumping and a band-stop optical filter 22. That is, the pumping light generating section 20 is composed of the pumping light source 21 for forward pumping and a number (one) of band-stop optical filters 22 that is less than n. The pumping light source 21 for forward pumping outputs pumping light having a wide spectral width. As described above, this wide spectrum can be generated from white noise. Note that a multimode laser that oscillates a large number of longitudinal modes in a wide wavelength range may be used as the pumping light source for the pumping light source 21 for forward pumping.

[0048] The pumping light output from the pumping light source 21 for forward pumping has a part of its spectrum blocked by the band-blocking optical filter 22. The optical output of the band-blocking optical filter 22 is multiplexed with the signal light by the multiplexing unit 30 and input to the optical transmission line 50. The pumping light generating unit 20 in the modified example is composed of the pumping light source 21 for forward pumping and one band-blocking optical filter 22, the number of which is less than n.

[0049] Thus, the optical distributed amplification system 100 includes an optical distributed amplifier 10 that amplifies n types of amplified light in an optical transmission line. The multiplexing unit 30 multiplexes the n types of amplified light with pumping light output from the pumping light generating unit 20, and outputs the multiplexed light to the optical transmission line. The n types of amplified light are used as pumping light for amplifying light of other wavelengths.

[0050] In the second configuration example, a band-stop optical filter is provided for each optical transmitter, but in the modified example, a single band-stop optical filter 22 is provided. Sk A band-stop optical filter may be provided for each k=1 to n. In a modified example, Sk An optical band-blocking filter 22 is used that blocks light having a wavelength in a single wavelength range including any of (k=1 to n).

[0051] FIG. 6 shows that the band-stop optical filter 22 is used to SkFIG. 6 is a diagram showing a schematic optical spectrum of pump light in which light of wavelengths (k=1 to n) is blocked all at once. The horizontal axis of the graph shown in FIG. 6 indicates wavelength, and the vertical axis indicates pump light intensity. In FIG. 6, 2×λ0-λ Sk It is shown that the light of wavelengths (k=1~n) is blocked at once. That is, 2×λ0-λ S1 From 2×λ0-λ Sn is suppressed compared to the intensities of the other wavelengths of the pump light generated by the pump light generating unit 20. This makes it possible to avoid the worst-case condition in which the group velocity of the signal light output from the k-th optical transmitter 40-k (k=1 to n) and the group velocity of the pump light match, thereby suppressing quality degradation of the transmission signal.

[0052] It should be noted that in a configuration in which all wavelengths are blocked at once, the wavelength range that is blocked is not necessarily in the center of the optical spectrum of the pump light. S -λ P = 100 nm, but this relation has no direct relation to λ0. Therefore, in order to obtain the maximum Raman gain, the cutoff wavelength region shown in FIG. 6 may be shifted toward the long wavelength side or short wavelength side of the optical spectrum of the pump light.

[0053] In addition, the wavelength arrangement that obtains the maximum Raman gain is selected, and the result is 2×λ0-λ, where m is a positive integer less than or equal to n. Sm Longer wavelength than 2×λ0-λ Sm In such a case, it is possible to narrow the blocking region of the band-stop filter so that the blocking region does not include the region where the excitation light does not exist.

[0054] The pump light generating unit 20 may be configured with fewer than n (n≧3) blocking light filters. For example, two filters are provided, and one blocking light filter has a filter width of 2×λ0−λ Sk The other blocking filter blocks r types of wavelengths, k=1 to r, out of (k=1 to n). The other blocking filter blocks 2×λ0-λ SkIn this way, at least one of the band-stop optical filters has a wavelength of 2×λ0-λ, where k=r+1 to n, and nr wavelengths are blocked. S1 From 2×λ0-λ Sn It is also possible to configure the system so that two or more of the n types of wavelengths ranging from 1 to 10 are blocked simultaneously.

[0055] (Configuration example 3) 7 is a block diagram showing the configuration of an optical distribution amplification system 100 in a configuration example 3 in an embodiment. All of the above-mentioned configuration examples 1 and 2 and the modified example of configuration example 2 are configurations using a band-stop optical filter. In contrast, configuration example 3 is a configuration in which pumping light with different center wavelengths output from a plurality of forward pumping pumping light sources is multiplexed without using a band-stop optical filter. Normally, high-output pumping light is required for Raman amplification, but it is difficult to meet this requirement with a single pumping light source, so multiplexing pumping light with slightly different wavelengths is widely used.

[0056] As shown in FIG. 7, the optical distributed amplifier system 100 includes an optical distributed amplifier 10, an optical transmitter 40, an optical transmission line 50, and an optical receiver 60.

[0057] The optical transmitter 40 outputs a signal light. The carrier wavelength of this signal light is λ S The optical distributed amplifier 10 amplifies the signal light output by the optical transmitter 40 and outputs the amplified signal light to the optical transmission line 50. The optical receiver 60 receives the signal light from the optical transmission line 50.

[0058] The optical distributed amplifier 10 is composed of a pumping light generating section 20 and a multiplexing section 30. The pumping light generating section 20 is composed of a first forward pumping pumping light source 21-1, a second forward pumping pumping light source 21-2, and a pumping light multiplexing section .

[0059] The first forward pumping pumping light source 21-1 outputs pumping light to the pumping light multiplexer 24. The central wavelength of this pumping light is λ p1 The second forward pumping pumping light source 21-2 outputs pumping light to the pumping light multiplexer 24. The central wavelength of this pumping light is λ p2In the configuration example 3, 2×λ0-λ S In order to prevent light of wavelengths in the wavelength range including p1 , λ p2 is λ p2 <2×λ0-λ S <λ p1 As described above, λ0 indicates the zero dispersion wavelength of the optical transmission line 50. S As described above, denotes the wavelength of the signal light.

[0060] The pumping light multiplexing unit 24 multiplexes the pumping light output from the first forward pumping pumping light source 21-1 and the pumping light output from the second forward pumping pumping light source 21-2, and outputs the multiplexed light to the multiplexing unit 30. The multiplexing unit 30 multiplexes the pumping light and the signal light output from the pumping light multiplexing unit 24, and outputs the multiplexed light to the optical transmission path 50.

[0061] FIG. 8 is a diagram showing a schematic diagram of an optical spectrum of pump light. The horizontal axis of the graph shown in FIG. 8 indicates wavelength, and the vertical axis indicates pump light intensity. As shown in FIG. 8, in the same manner as the above-mentioned configuration example, 2×λ0-λ S There is no pump light having a wavelength in the wavelength range including the wavelengths. Therefore, the same effect as in the above-mentioned configuration example can be achieved without using a band-stop optical filter. This makes it possible to avoid the worst condition in which the group velocity of the signal light and the group velocity of the pump light match, thereby suppressing deterioration in the quality of the transmission signal. Note that, although the forward pumping pumping light sources with two wavelengths are used in the configuration example 3, forward pumping pumping light sources with more wavelengths may be used. In this way, in the configuration example 3, the pumping light generating unit 20 is composed of a plurality of light sources (the first pumping light source 21-1 for forward pumping and the second pumping light source 21-2 for forward pumping), and the light output from the plurality of light sources has a wavelength of 2×λ0−λ S Furthermore, as shown in FIG. 8, the longest and shortest wavelengths of the light output from the multiple light sources are 2×λ0-λ S The wavelengths of the two wavelengths are not included in the range of the two wavelengths.

[0062] (Configuration Example 4) 9 is a block diagram showing the configuration of an optical distribution amplification system 100 in configuration example 4. Configuration example 4 is a configuration in which two optical transmission lines having different zero dispersion wavelengths are arranged in tandem.

[0063] As shown in FIG. 9, the optical distributed amplifier system 100 includes an optical distributed amplifier 10, an optical transmitter 40, a first optical waveguide 50-1, a second optical waveguide 50-2, and an optical receiver 60. The optical distributed amplifier 10 includes a first optical waveguide 50-1, a second optical waveguide 50-2, and an optical receiver 60.

[0064] The optical transmitter 40 outputs an optical signal. The optical distributed amplifier 10 amplifies the optical signal output by the optical transmitter 40 and outputs it to a first optical waveguide 50-1. A second optical waveguide 50-2 is connected to the rear of the first optical waveguide 50-1, and the second optical waveguide 50-2 is connected to an optical receiver 60. In this manner, the optical transmission line is formed by connecting a plurality of optical waveguides in tandem.

[0065] The optical receiver 60 receives the signal light from the second optical waveguide 50-2. The optical distributed amplifier 10 is composed of a pumping light generating section 20 and a multiplexing section 30. The pumping light generating section 20 is composed of a pumping light source 21 for forward pumping.

[0066] Since the first optical waveguide 50-1 is closer to the multiplexing section 30 than the second optical waveguide 50-2, the excitation light having a higher intensity propagates through the first optical waveguide 50-1 than through the second optical waveguide 50-2. p and ν s In order to satisfy this condition, the zero dispersion wavelength in the first optical waveguide 50-1 is set to λ 0in Then, the pump light is 2×λ 0in -λ S More generally, as described above, the central wavelength of the amplified light is set to λ S1 ~λ Sn Then, the pump light is 2×λ 0in -λ S 1 to 2×λ 0in -λ Sn It is also possible to exclude n types of wavelengths up to 100 .mu.m.

[0067] The intensity of the pump light attenuates during the propagation through the transmission line, and the Raman gain also decreases locally. p and ν s Even if the values ​​of and are close to each other, the propagation of noise from the pump light to the signal light can be suppressed, so that deterioration of the quality of the transmission signal can be suppressed.

[0068] In each of the above-mentioned embodiments, the configuration in which the pump light amplifies the signal light has been described. However, in a system performing high-order Raman amplification, a multi-stage configuration may be adopted in which the first pump light amplifies the second pump light, and the second pump light amplifies the signal light, using first and second pump lights with wavelengths separated by 100 nm. In such a configuration, the group velocity of the second pump light is set to v s , the wavelength of the second excitation light is λ S In this case, the first pumping light, the second pumping light, and the signal light may all propagate in the same direction, or only one of the three may propagate in the opposite direction to the other two by using backward pumping.

[0069] In addition, in each embodiment, optical amplification using Raman amplification has been described, but the amplification is not limited to Raman amplification and may be achieved using other nonlinear optical effects as long as the distributed optical amplifier amplifies light of other wavelengths using pump light within the optical transmission line.

[0070] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Industrial Applicability]

[0071] The present invention is applicable to an optical distributed amplification system that performs transmission through an optical fiber transmission line. [Explanation of symbols]

[0072] 10...optical distributed amplifier, 20...pumping light generating section, 21...pumping light source for forward pumping, 21-1...first pumping light source for forward pumping, 21-2...second pumping light source for forward pumping, 22...band-blocking optical filter, 24...pumping light multiplexing section, 30...multiplexing section, 40...optical transmitter, 40-1...first optical transmitter, 40-2...second optical transmitter, 40-n...optical transmitter, 50...optical transmission path, 50-1...first optical waveguide, 50-2...second optical waveguide, 60...optical receiver, 70...signal light multiplexing section, 100...optical distributed amplification system

Claims

1. an excitation light generating unit that generates excitation light for optically exciting the optical transmission line; a multiplexing unit that multiplexes n types (n is a positive integer) of amplified light and the pumping light output from the pumping light generating unit and outputs the multiplexed light to an optical transmission line; having The central wavelength of the n kinds of amplified light is λ Ｓ１ ~λ Ｓｎ The zero dispersion wavelength of the optical transmission line is λ 0 Then, 2×λ of the pump light generated by the pump light generating unit ０ -λ Ｓ１ From 2 × λ ０ -λ Ｓｎ The intensity at the n kinds of wavelengths up to is suppressed as compared with the intensity of other wavelengths of the excitation light generated by the excitation light generating unit, the pump light generating unit is composed of a light source and n or less band-stop optical filters that suppress a part of the optical spectrum of the pump light and do not suppress the other part; the spectrum of light output from the light source includes one or more of n kinds of wavelengths ranging from 2×λ 0 −λ S1 to 2×λ 0 −λ Sn ; The n or less band-stop optical filters block all of n kinds of wavelengths ranging from 2×λ 0 -λ S1 to 2×λ 0 -λ Sn that are included in the spectrum of the light output from the light source.

2. The group velocity of any one of the n types of amplified light in the optical transmission line is defined as v ｓ and the group velocity of light of an arbitrary wavelength contained in the pumping light output from the pumping light generating unit in the optical transmission line is v ｐ Then, |1-ν ｓ / ν ｐ The optical distributed amplifier according to claim 1 , wherein |>0.0001 is satisfied.

3. 2. The optical distributed amplifier according to claim 1, wherein the n types of amplified light are used as pump light for amplifying light of other wavelengths.

4. An optical distributed amplification system including an optical transmitter that transmits n types (n is a positive integer) of signal light, an optical distributed amplifier that amplifies the signal light transmitted by the optical transmitter as amplified light in an optical transmission line, and an optical receiver that receives the signal light amplified by the optical distributed amplifier, The optical distributed amplifier comprises: an excitation light generating unit that generates excitation light for optically exciting the optical transmission line; a multiplexing unit that multiplexes the n types of amplified light and pumping light output from the pumping light generating unit and outputs the multiplexed light to an optical transmission line; having The central wavelength of the n kinds of amplified light is λ Ｓ１ ~λ Ｓｎ The zero dispersion wavelength of the optical transmission line is λ ０ Then, 2×λ of the pump light generated by the pump light generating unit ０ -λ Ｓ１ From 2 × λ ０ -λ Ｓｎ The intensity at the n kinds of wavelengths up to is suppressed as compared with the intensity of other wavelengths of the excitation light generated by the excitation light generating unit, the pump light generating unit is composed of a light source and n or less band-stop optical filters that suppress a part of the optical spectrum of the pump light and do not suppress the other part; the spectrum of light output from the light source includes one or more of n kinds of wavelengths ranging from 2×λ 0 −λ S1 to 2×λ 0 −λ Sn ; The n or less band-stop optical filters block all of n wavelengths ranging from 2×λ 0 -λ S1 to 2×λ 0 -λ Sn that are included in the spectrum of light output from the light source.

5. An optical distributed amplification system including an optical transmitter that transmits n types (n is a positive integer) of signal light, an optical distributed amplifier that amplifies the signal light transmitted by the optical transmitter as amplified light in an optical transmission line, and an optical receiver that receives the signal light amplified by the optical distributed amplifier, The optical distributed amplifier comprises: an excitation light generating unit that generates excitation light for optically exciting the optical transmission line; a multiplexing unit that multiplexes the n types of amplified light and pumping light output from the pumping light generating unit and outputs the multiplexed light to an optical transmission line; having an optical transmission path from the optical distributed amplifier to the optical receiver is configured by connecting in series a plurality of optical waveguides having different chromatic dispersions; The central wavelength of the n kinds of amplified light is λ Ｓ１ ~λ Ｓｎ The zero dispersion wavelength of the optical waveguide in which the intensity of the propagating pump light is the highest among the plurality of optical waveguides is defined as λ ０ｉｎ Then, 2×λ of the excitation light ０ｉｎ -λ Ｓ１ From 2 × λ ０ｉｎ -λ Ｓｎ The intensity at the n kinds of wavelengths up to is suppressed as compared with the intensity of other wavelengths of the excitation light generated by the excitation light generating unit, the pump light generating unit is composed of a light source and n or less band-stop optical filters that suppress a part of the optical spectrum of the pump light and do not suppress the other part; the spectrum of light output from the light source includes one or more of n kinds of wavelengths ranging from 2×λ 0 −λ S1 to 2×λ 0 −λ Sn ; The n or less band-stop optical filters block all of n wavelengths ranging from 2×λ 0 -λ S1 to 2×λ 0 -λ Sn that are included in the spectrum of light output from the light source.

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