JP4643679B2 - Optical transmission system - Google Patents

Description

  The present invention relates to an optical transmission system, and more particularly to an optical transmission system that performs WDM (Wavelength Division Multiplex) optical transmission.

  Conventionally, in a long-distance optical transmission system, an optical regenerative repeater that converts an optical signal into an electrical signal and performs retiming (timing), reshaping (equalization amplification), and regenerating (identification regeneration) has been used. At present, linear optical amplifiers that amplify light as a fiber by using a fiber as an amplification medium are mainly used. By replacing the optical regenerative repeater with an optical amplifier, the number of parts in the repeater can be greatly reduced, so that reliability can be ensured and cost can be greatly reduced.

  In addition, as one of the methods for realizing a large capacity of an optical transmission system, a wavelength division multiplexing transmission system (WDM) that multiplexes and transmits optical signals having two or more different wavelengths on one transmission path has been developed. . By combining this WDM and an optical amplifier, it becomes possible to relay and amplify optical signals having two or more different wavelengths in a lump, and a large-capacity and long-distance transmission can be realized with an economical configuration.

  In such a system, as the optical signal power increases, the transmission distance becomes longer, and the number of optical signals increases, the chromatic dispersion and nonlinear action of the optical transmission line become extremely important transmission characteristics that cannot be ignored. Come. For this reason, in order to construct a high-speed and large-capacity optical transmission line, chromatic dispersion and nonlinear action are two important design factors.

  Here, chromatic dispersion refers to a phenomenon in which the waveform spreads along the time axis when light propagates through the fiber. Non-linearity refers to a phenomenon in which the physical properties of glass change according to the light intensity when light of relatively strong power is propagated through the glass. In order to transmit an optical signal for a long distance without distortion, it is essential that the chromatic dispersion and nonlinearity are sufficiently small.

  On the other hand, when the optical signal propagates through the fiber, the above-mentioned chromatic dispersion occurs. However, if a dispersion compensating fiber that compensates the dispersion value in the propagation direction is connected, the dispersion is equivalently made zero (cancel). be able to. Transmission path design that repeats this periodically is called dispersion management. It is known that a dispersion-compensated transmission line compensates for dispersion deterioration and relaxes nonlinear effects.

  Conventional dispersion compensation technology is a dispersion-shifted fiber (NZ-DSF: Non-zero Dispersion-Shifted Fiber) with a zero dispersion wavelength at 1585 nm and a chromatic dispersion of approximately -2 (ps / nm / km) in the signal light band. And a single mode fiber (SMF) having a zero dispersion wavelength at 1310 nm and a chromatic dispersion of about +18 (ps / nm / km) in the signal light band has been proposed. (For example, Non-Patent Document 1).

In addition, a positive dispersion fiber (+ D fiber) having positive dispersion in the signal light band and zero dispersion at 1.3 μm in the first half of one relay section, and chromatic dispersion of + D fiber in the second half of the section There is also a system in which dispersion compensation is performed using a mixed transmission line including a negative dispersion fiber (-D fiber) that can compensate for a chromatic dispersion slope (for example, Non-Patent Document 2).
NSBergano, “Wavelength Division Multiplexing in Long-Haul Transmission Systems, IEEE Journal of Lightwave Technology, vol. 14, no. 6, pp. 1299-1308, 1996” M. Murakami, “Long-haul 16x10 WDM transmission experiment using higher order fiber dispersion management technique”, M. Murakami et al, pp.313-314, ECOC'98, 1998.

  However, in the technique of Non-Patent Document 1 as described above (hereinafter, Conventional Technique 1), when the transmission band is expanded due to the influence of a chromatic dispersion slope (first derivative with respect to the wavelength of chromatic dispersion) indicating the slope of chromatic dispersion. There is a problem that it is impossible to compensate for dispersion for all the expanded signal light wavelengths.

  Further, in the technique of Non-Patent Document 2 (hereinafter, Conventional Technique 2), when the transmission band is expanded, dispersion compensation can be performed for the expanded signal light wavelength. Since the bit arrangement becomes the same position, waveform deterioration due to nonlinear phenomenon occurs, and transmission characteristics deteriorate.

  On the other hand, in recent years, optical amplifiers using Raman amplification have attracted attention. This utilizes a physical phenomenon in which light having a wavelength different from that of incident light is scattered by a vibration phenomenon in a substance, and makes strong excitation light incident on the entire optical fiber transmission line to perform optical amplification.

  The gain peak due to Raman scattering is at a position where the frequency is shifted by about 100 nm toward the long wavelength side. That is, since an optical signal on the long wavelength side of about 100 nm of the incident excitation light is excited, for example, in order to amplify an optical signal having a wavelength of 1.55 μm, excitation light having a wavelength near 1.45 μm is used. The light enters the optical fiber transmission line.

By applying such a Raman amplification method to a repeater and performing optical amplification, it is longer than an optical amplifier using an erbium (Er ³⁺ ) -doped fiber (EDF) as an amplification medium. The optical fiber cable can be laid and the relay interval can be increased. In addition, the Raman amplification has low noise, and a wide band can be realized by using a multi-wavelength excitation light source.

However, the Raman gain changes depending on the length of the fiber that is the optical amplifying medium. Therefore, the mixed transmission path (+ D fiber and -D fiber is composed of the upstream transmission path and the downstream transmission path across the repeater. In the state where the length ratio of the mixed transmission path is changed between upstream and downstream in order to change the dispersion characteristic, the Raman gain output in the upstream and downstream fibers is different. There was a problem that the reliability of optical amplification was lowered.

  The present invention has been made in view of these points, and an object of the present invention is to provide an optical transmission system that reduces the variation in characteristics of Raman amplification and improves the transmission quality and reliability of optical communication. .

In order to solve the above problems, an optical transmission system for transmitting an optical signal is provided. The optical transmission system includes an optical transmission system that transmits optical signals, a first fiber having positive dispersion, and a second fiber having negative dispersion and a mode field diameter smaller than that of the first fiber. And an upstream line in which the optical signal propagates in an upward direction from the first fiber to the second fiber, the first fiber, and the second fiber, A downlink that constitutes a relay section, in which the optical signal sequentially propagates in the downlink direction from the first fiber to the second fiber, an uplink relay section that is the relay section on the uplink side, and the downlink An optical repeater including a pumping unit that emits pumping light having the same power in opposite directions is provided in the downstream relaying section that is the relay section on the side.

Here, in the dispersion compensation section including a plurality of relay sections, the second fiber has a length different from the length of the first fiber, and a section in which the average dispersion of the relay section is positive is a positive relay section. When the average dispersion of the relay section is a negative relay section, the upstream relay section that emits pumping light is a positive relay section, and the downstream relay section that emits pumping light is a negative relay section. A first pumping unit (pumping LDd, e, and f in FIG. 39 corresponds to the pumping unit in the first optical repeater to be arranged) and an upstream relay section that emits pumping light are negative relay sections. , A second pumping unit (pumping LDa, b, and c in FIG. 39 corresponds to the pumping unit in the second optical repeater arranged at the relay point where the downlink relaying section that emits pumping light is the forward relaying section) When the first pumping unit increases its own pumping light power The second pumping unit lowers its own pumping light power, and when the first pumping unit lowers its own pumping light power, the second pumping unit increases its own pumping light power and falls within the dispersion compensation interval. The upstream / downstream power balance of the optical signal flowing through the upstream and downstream channels is adjusted.

  In the optical transmission system, a relay section is configured by a first fiber having positive dispersion and a second fiber having negative dispersion and a mode field diameter smaller than that of the first fiber. The power balance of upstream / downstream optical signals in units of dispersion compensation intervals with respect to a plurality of relay sections having different lengths of the second fiber with respect to the optical transmission line propagating in order from the first fiber to the second fiber The power supply control of the excitation light is performed so as to adjust the power. Thereby, the characteristic variation of the Raman gain can be reduced, so that the optical transmission quality and reliability can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The contents of the inventions according to claims 1 and 2 will be described in FIG.
FIG. 1 is a principle diagram of an optical transmission system. The optical transmission system 1 is provided with a transmission device 10, a reception device 20, and a plurality of optical repeaters 40-1 to 40-n (collectively referred to as an optical repeater 40). The optical transmission path 3 has a high-speed, large-capacity, long-distance optical transmission. Actually, the transmitter 10 and the receiver 20 are provided in one station, and optical communication is performed bi-directionally between the stations on the upstream / downstream optical transmission path 3. Only the direction is shown.

  The transmission apparatus 10 performs wavelength division multiplexing of WDM on optical signals from SONET, SDH, ATM, and the like, and transmits the wavelength multiplexed optical signal from the optical transmission line 3. The receiving device 20 receives an optical signal that is wavelength-multiplexed through the optical transmission path 3, and separates and processes it for each wavelength. The optical transmission line 3 is provided with optical repeaters 40-1 to 40-n, and dispersion compensation is performed so that the accumulated chromatic dispersion does not become zero or the number of times that the accumulated chromatic dispersion becomes zero with respect to the dispersion compensation interval. To do.

  Here, the difference in dispersion management between the conventional and the optical transmission system 1 will be described with reference to the dispersion map shown in the figure (a diagram showing transition of cumulative dispersion with respect to distance). The dispersion map m0 indicating the conventional dispersion management is the same with the accumulated chromatic dispersion being zero at each dispersion compensation interval. For this reason, a non-linear phenomenon has occurred, causing deterioration in transmission quality.

  On the other hand, the dispersion map M0 indicating the dispersion management of the optical transmission system 1 compensates so that the accumulated chromatic dispersion does not become zero at each dispersion compensation interval, thereby suppressing nonlinear effects and enabling high-quality transmission. (Chromatic dispersion should be zero for the entire optical transmission line. Accordingly, in the optical transmission system 1, the accumulated chromatic dispersion for each dispersion compensation interval is removed from zero so that it becomes zero for the entire optical transmission line). Details of specific distributed management will be described later with reference to FIG.

  Next, problems to be solved will be described in detail. FIG. 2 is a diagram showing a configuration of distributed management. The figure shows distributed management in the case of the prior art 1 described above. EDF amplifiers 301 to 319 are installed on the optical transmission path connecting the transmitting station 100 and the receiving station 200.

  Also, for 9 spans of relay sections LA1 to LA9 (1 span = 50 km), NZ-DSF (having zero dispersion wavelength at 1585 nm and chromatic dispersion of about -2 ps / nm / km in the signal light band) The dispersion compensation interval LA is configured using SMF (having zero dispersion wavelength at 1310 nm and chromatic dispersion of about +18 ps / nm / km in the signal light band) in one span of LA10. In the illustrated system, another transmission path having a dispersion compensation interval LA is connected between the transmitting station 100 and the receiving station 200 so that the transmission distance is about 1000 km.

  In the prior art 1, dispersion management is performed using the dispersion compensation interval LA that compensates the accumulated dispersion caused by the NZ-DSF with one SMF, so that the chromatic dispersion value is zero (((−2 ) × 50 km) × 9 span + 18 × 50 km = 0).

  However, in the prior art 1, when the transmission band is expanded, it is impossible to perform dispersion compensation for the expanded signal light wavelength. FIG. 3 is a diagram showing chromatic dispersion compensation. The slope of wavelength dispersion (wavelength dispersion slope) of NZ-DSF and SMF of prior art 1 is shown, the vertical axis is wavelength dispersion D (ps / nm / km), and the horizontal axis is wavelength λ (nm).

  The zero dispersion wavelengths of NZ-DSF and SMF are 1585 nm and 1310 nm, and the respective chromatic dispersions are -2 ps / nm / km and +18 ps / nm / km, and the length of NZ-DSF and SMF is 9: 1. When used in ratio, the mean zero dispersion is 1558 nm.

  Then, the chromatic dispersion obtained by averaging the linear lines of NZ-DSF and SMF has a slope as a linear line K1 (this linear line K1 represents the chromatic dispersion of the dispersion compensation interval LA). Is).

  In this case, in order to expand the capacity at the time of WDM transmission, if an attempt is made to expand the transmission band in the system of the prior art 1, the chromatic dispersion does not become zero at the dispersion compensation interval LA. For example, if the band is expanded to the wavelength λa, the dispersion value becomes Da and the chromatic dispersion does not become zero. Therefore, in the system of the prior art 1 using the dispersion compensation interval LA, there is a problem that when the transmission band is expanded, it becomes impossible to compensate the chromatic dispersion of the entire optical transmission line.

  Next, a conventional system using a mixed transmission line combining + D fiber and -D fiber will be described. FIG. 4 is a diagram showing a configuration of distributed management. The figure shows the distributed management in the case of the above-described prior art 2. EDF amplifiers 401 to 419 are installed on a transmission path connecting the transmitting station 101 and the receiving station 201.

  In addition, for each of the 9 spans of the relay sections LB1 to LB9 (1 span = 50 km), a mixed transmission path composed of + D fiber and −D fiber (average chromatic dispersion of 1 section is −2 ps / nm / km) The dispersion compensation interval LB is configured by using + D fiber (wavelength dispersion is about +18 ps / nm / km) for one span of the LB 10. In the system shown in the figure, another transmission path with a dispersion compensation interval LB is connected between the transmitting station 101 and the receiving station 201 so that the transmission distance is about 1000 km.

  In the prior art 2, by performing dispersion management using the dispersion compensation interval LB that compensates the accumulated dispersion generated in the mixed transmission line composed of + D fiber and −D fiber with + D fiber of one section, the entire optical transmission line is The chromatic dispersion value is zero (((−2) × 50 km) × 9 span + 18 × 50 km = 0).

  Further, in the related art 2, when the transmission band is expanded, it is possible to compensate for the chromatic dispersion to be zero even for the expanded signal light wavelength. FIG. 5 is a diagram showing chromatic dispersion compensation. The slope of chromatic dispersion (wavelength dispersion slope) of + D fiber and -D fiber of prior art 2 is shown, the vertical axis is chromatic dispersion D (ps / nm / km), and the horizontal axis is wavelength λ (nm).

  The + D fiber having zero dispersion at 1300 nm is almost a linear line (having no curvature and having a curvature when it becomes a wide band), and the −D fiber takes the shape of a curve. The chromatic dispersion obtained by averaging + D fiber and -D fiber is a curve K2 indicated by a dotted line in the figure (this curve K2 represents the chromatic dispersion of the dispersion compensation interval LB).

  In this case, in order to expand the capacity during WDM transmission, even if the transmission band is expanded in the system of the conventional technique 2, the chromatic dispersion can be made substantially zero at the dispersion compensation interval LB. For example, the chromatic dispersion value is almost 0 even when the band is widened to the wavelength λb. Therefore, in the prior art 2 system using the dispersion compensation interval LB, the WDM transmission band can be expanded.

  FIG. 6 is a diagram showing a dispersion map. The dispersion map m1 shows the chromatic dispersion transition state of the system of the prior art 2 having four dispersion compensation intervals LB, where the vertical axis represents dispersion (ps / nm) and the horizontal axis represents distance (km).

  Since the mixed transmission line of + D fiber and −D fiber has a dispersion value of −2 (ps / nm) per km, it is −100 (ps / nm) in one relay section of 50 km, and this is −900 in 9 spans. (Ps / nm). When + D fiber with a dispersion value of +18 (ps / nm) per 1 km is used for one relay section of 50 km, it is +900 (ps / nm), so the average dispersion value of the dispersion compensation interval LB becomes zero, and this is repeated. Is represented in the figure.

  In the prior art 2, dispersion compensation can be performed over the entire signal band to be used. However, since the accumulated chromatic dispersion is zero for each dispersion compensation interval LB, it is susceptible to nonlinear effects in this region, and transmission characteristics are degraded. There was a problem (this has the same problem with the prior art 1).

  Here, transmission degradation caused by the nonlinear effect will be described. Non-linear phenomena in optical fibers include four wave mixing (FWM), self phase modulation (SPM), cross phase modulation (XPM), and the like.

  FWM is a phenomenon in which when two waves of ω1 and ω2 are incident on an optical fiber, new interference light of ω3 and ω4 is generated through third-order nonlinear polarization (when the phase difference becomes almost zero, FWM is generated). Happens).

  XPM is a phenomenon in which when light of two different wavelengths is incident on an optical fiber, the phase of the other signal changes due to a change in refractive index caused by a change in the intensity of one light. SPM is a phenomenon in which its own phase changes due to a change in refractive index induced by its own light pulse.

  7 and 8 are diagrams showing the correlation between wavelengths. The vertical axis represents wavelength, and the horizontal axis represents time. FIG. 7 shows the correlation of each wavelength when the accumulated dispersion per dispersion compensation interval is zero dispersion. FIG. 8 shows the correlation at each wavelength per dispersion compensation interval when the dispersion has an arbitrary dispersion value. Show.

  In the region where the cumulative dispersion is zero as shown in FIG. 7, since the pulse trains of the wavelengths λ1 to λ4 have the same arrangement (because the bit arrangement between the wavelengths is the same), the nonlinear effect between the wavelengths is emphasized. (Note that non-linear effects are strongly affected even when the optical signal power and optical density in the fiber are high. Therefore, in the region where the cumulative dispersion is zero, and near the output of the optical amplifier and small parts of the core system Most susceptible to non-linear effects). Then, phase matching between optical pulses is likely to occur, and phase change is likely to occur due to the intensity of light of another wavelength, so that FWM and XPM are likely to occur.

On the other hand, when the accumulated dispersion in the dispersion compensation interval in FIG. 8 has an arbitrary value, the arrangement of the pulse trains of the wavelengths λ1 to λ4 is arbitrary, and thus the nonlinear effect between wavelengths is not emphasized.
In the prior art 2, since the average zero dispersion wavelength is within the signal light wavelength, the degradation of transmission characteristics due to SPM and chromatic dispersion can be reduced, but the dispersion compensation interval (dispersion compensation interval LB) at which the accumulated chromatic dispersion becomes zero is set. Since they are periodically arranged, the locations where the pulse trains between the wavelengths as shown in FIG. 7 are arranged in the same manner increase on the transmission path, and the nonlinear effect generated between the wavelengths increases, resulting in FWM and XPM. There is a problem that the waveform is distorted (note that this is not limited to the conventional techniques 1 and 2 but is also a problem of the conventional system generally configured by normal distributed management).

  Next, a conventional problem when Raman amplification is used for an optical repeater in an optical transmission line in which dispersion management is performed will be described. FIG. 9 is a diagram showing the configuration of the optical repeater. The optical repeater 320 includes a Raman pumping light source 321, an optical coupler 322, and multiplexers 323a and 323b. The excitation light from the Raman excitation light source 321 is branched into two by the optical coupler 322. Each of the multiplexers 323a and 323b emits pumping light in a direction opposite to the direction of the signal light and performs backward pumping to perform Raman amplification.

  Here, in the system shown in the figure, dispersion compensation is performed using a mixed transmission path of + D fiber and -D fiber in the relay section, and the dispersion characteristics are changed by changing the length of the fiber in the upstream and downstream. (For example, the relay section LC1 is positively distributed and the relay section LC2 is negatively distributed).

  In the figure, the downstream -D fiber f1 is shorter than the upstream -D fiber f2. When constant pumping light is output from the Raman pumping light source 321 in such a state, the Raman gain changes depending on the length of the optical fiber that is the optical amplifying medium. Therefore, the Raman gain using −D fiberf1 as the amplifying medium This is different from the Raman gain using -D fiber f2 as an amplification medium, and the variation of the Raman gain occurs between the uplink and the downlink, which causes a problem that the reliability of optical amplification is lowered.

  As described above, in the conventional dispersion management system, the degradation of transmission characteristics due to the nonlinear effect in the region where the accumulated chromatic dispersion at each dispersion compensation interval is zero, and the Raman amplification when the Raman amplification is used for optical repeater. There was a problem of fluctuation of characteristics. The present invention solves these problems and reduces the waveform distortion and Raman amplification characteristic fluctuation due to the nonlinear effect, thereby realizing the construction of a high-quality and highly reliable optical transmission system.

  Next, the specific contents of distributed management will be described. First, the first embodiment will be described. In the first embodiment of dispersion management, a relay section having negative dispersion is used as a main transmission path, and a dispersion compensation interval is generated by compensating for dispersion of the main transmission path in one relay section having positive dispersion. Randomize chromatic dispersion.

  FIG. 10 is a schematic diagram showing the configuration of distributed management. The optical transmission line 3 is connected to the transmission device 10. In addition, between the black circles in the figure represents one relay section (illustration of the receiving device 20 is omitted).

  The optical transmission line 3 has a relay section having negative dispersion (average dispersion) as a main transmission line, and the dispersion of the main transmission path is compensated by a compensating transmission line of one relay section having positive dispersion. The compensation interval is used (hereinafter, such a system configuration is referred to as a distributed management configuration A).

  Next, in the dispersion management configuration A, a configuration example when the lengths of the dispersion compensation intervals are all equal will be described. FIG. 11 is a diagram illustrating an example of a distributed management configuration. In the dispersion management configuration A-1, the optical transmission line 3-1 is connected to the transmission device 10. In the main transmission line 31-1, one relay section having negative dispersion has 9 spans, and the compensation transmission line 32-1 having positive dispersion has 1 span, and a plurality of 10 span dispersion compensation intervals 33-1 are connected. Thus, the optical transmission line 3-1 is configured (since the number of relay sections having negative dispersion is equal (= 9 spans), the lengths of the dispersion compensation intervals are all equal).

Next, in the dispersion management configuration A-1, a case will be described in which the absolute value of the average dispersion in the relay section is varied with respect to the dispersion compensation interval, and the accumulated chromatic dispersion is randomized.
FIG. 12 is a diagram showing a dispersion map. The dispersion map M1-1 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is multi-variable and the accumulated chromatic dispersion is all negative (the dispersion map shown later including FIG. 12). Then, the black circles representing the relay sections in the main transmission path are omitted).

  The main transmission line 31a-1 in the first half (0 to 1000 km) of the optical transmission line 3-1 includes, for example, the main transmission line 31a in -2.5 (ps / nm / km) and the second half (1000 km to 2000 km). -2 uses a fiber having a dispersion of -1.5 (ps / nm / km), and the compensating transmission line 32a uses a fiber having a dispersion of +18 (ps / nm / km) (one relay section ) Is 50 km, and the absolute value of the average variance of the relay section is various (125 (= 2.5 × 50), 75 (= 1.5 × 50), 900 (18 × 50))) .

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation interval 33a are all negative (because the accumulated chromatic dispersion does not become zero), so the nonlinear effect is suppressed. And degradation of transmission quality can be reduced.

  FIG. 13 is a diagram showing a dispersion map. The dispersion map M1-2 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is multi-variable and the accumulated chromatic dispersion is all positive.

  The main transmission line 31b-1 in the first half (0 to 1000 km) of the optical transmission line 3-1 includes, for example, a main transmission line 31b in the latter half (1000 km to 2000 km) and -1.5 (ps / nm / km). A fiber having a dispersion of -2.5 (ps / nm / km) is used for -2, and a fiber having a dispersion of +18 (ps / nm / km) is used for the compensating transmission line 32b (in the relay section). The absolute value of the average variance is various as in the case of FIG.

  In the case of such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation interval 33b are all positive, nonlinear effects can be suppressed, and deterioration of transmission quality can be reduced. it can.

  FIG. 14 is a diagram showing a dispersion map. The dispersion map M1-3 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is made various and the cumulative chromatic dispersion is mixed with negative and positive.

  The main transmission lines 31c-1 to 31c-4 of the optical transmission line 3-1 have, for example, dispersions of -1.5, -3, -1, and -2.5 (ps / nm / km) in order. A fiber is used, and a fiber having a dispersion of +18 (ps / nm / km) is used for the compensation transmission line 32c (one relay section is 50 km, and the absolute value of the average dispersion in the relay section is 75 (= 1) .5 × 50), 150 (= 3 × 50), 50 (= 1 × 50), 125 (= 2.5 × 50), and 900 (= 18 × 50)).

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation interval 33c are positive, negative, and positive, respectively, so that nonlinear effects can be suppressed and transmission quality is deteriorated. Can be reduced.

  Next, in the dispersion management configuration A, a configuration example when the lengths of the dispersion compensation intervals are different from each other will be described. FIG. 15 is a diagram illustrating an example of a distributed management configuration. In the dispersion management configuration A-2, the optical transmission path 3-2 is connected to the transmission device 10. The dispersion compensation interval is composed of a plurality of relay section main transmission lines having negative dispersion and a one relay section compensation transmission line having positive dispersion. In the dispersion management configuration A-2, since the number of relay sections having negative dispersion is arbitrary, the length of the dispersion compensation interval is also different.

  For example, a dispersion compensation interval 33-2a is configured by a main transmission line 31-2a having a negative dispersion of 4 spans and a compensation transmission line 32-2 of one relay section having a positive dispersion. A dispersion compensation interval 33-2b is configured by a main transmission line 31-2b having a span of 8 spans and a compensation transmission line 32-2 having one relay section having a positive dispersion. The optical transmission line 3-2 is configured with different dispersion compensation intervals.

  Next, randomization of cumulative chromatic dispersion in the dispersion management configuration A-2 will be described. FIG. 16 is a diagram showing a dispersion map. The dispersion map M2-1 shows dispersion management in the case where the number of relay sections is varied to change the length of the dispersion compensation interval and the accumulated chromatic dispersion is all negative. For the optical transmission line 3-2, all of the main transmission lines 31d-1 to 31d-4 having negative dispersion use, for example, a fiber having a dispersion of -2 (ps / nm / km). The spans of the paths 31d-1 to 31d-4 are 12, 10, 7, and 7, respectively. Further, a fiber having dispersion of +18 (ps / nm / km) is used for the compensation transmission path 32d.

  In such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation intervals 33d-1 to 33d-3 are all negative, the nonlinear effect can be suppressed, and the transmission quality can be reduced. Deterioration can be reduced.

  FIG. 17 is a diagram showing a dispersion map. The dispersion map M2-2 shows dispersion management when the number of relay sections is varied and the length of the dispersion compensation interval is changed so that the accumulated chromatic dispersion is all positive. For the optical transmission line 3-2, all of the main transmission lines 31e-1 to 31e-5 having negative dispersion use, for example, a fiber having dispersion of −2 (ps / nm / km). The spans of the paths 31e-1 to 31e-5 are 3, 4, 7, 10, and 12, respectively. Further, a fiber having dispersion of +18 (ps / nm / km) is used for the compensation transmission path 32e.

  In the case of such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d4 with respect to the dispersion compensation intervals 33e-1 to 33e-4 are all positive, the nonlinear effect can be suppressed, and the transmission quality can be reduced. Deterioration can be reduced.

  FIG. 18 is a diagram showing a dispersion map. The dispersion map M2-3 shows dispersion management in a case where the cumulative chromatic dispersion is mixed in a negative and positive manner by changing the length of the dispersion compensation interval by changing the number of relay sections and changing the length of the dispersion compensation interval. For the optical transmission line 3-2, all of the main transmission lines 31f-1 to 31f-4 having negative dispersion use, for example, a fiber having dispersion of -2 (ps / nm / km). The spans of the paths 31f-1 to 31f-4 are 3, 17, 3, and 13, respectively. Further, a fiber having dispersion of +18 (ps / nm / km) is used for the compensation transmission path 32f.

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation intervals 33f-1 to 33f-3 are positive, negative, and positive, respectively, so that the nonlinear effect can be suppressed. And degradation of transmission quality can be reduced.

  Next, in the distributed management configuration A, a configuration example in the case where multiple types of relay section distances are described will be described. FIG. 19 is a diagram illustrating an example of a distributed management configuration. In the dispersion management configuration A-3, the optical transmission path 3-3 is connected to the transmission device 10.

  In the above-described distributed management configurations A-1 and A-2, one relay section is all equal to 50 km, but in the distributed management configuration A-3, the length of one relay section is variable.

  For example, the dispersion compensation interval between the main transmission line 31-3a having 9 spans and the compensating transmission line 32-3 having one relay section having a positive dispersion is equal to each other (for example, 50 km). 3-3a, the relay section length having negative dispersion is different from that of the main transmission path 31-3a (for example, 25 km), and the 9-span main transmission path 31-3b has a positive dispersion. A dispersion compensation interval 33-3b is configured with the compensation transmission path 32-3 of one relay section, and an optical transmission path 3-3 is configured by combining such dispersion compensation intervals.

  Next, randomization of cumulative chromatic dispersion in the dispersion management configuration A-3 will be described. FIG. 20 is a diagram showing a dispersion map. The dispersion map M3-1 shows dispersion management in the case where the relay section distances per dispersion compensation interval are made various, and the accumulated chromatic dispersion is all negative.

  For the optical transmission line 3-3, all of the main transmission lines 31g-1 to 31g-4 having negative dispersion use, for example, a fiber having dispersion of -2 (ps / nm / km). One relay section of 31g-1 and 31g-2 is 50 km, and one relay section of the main transmission lines 31g-3 and 31g-4 is 25 km. A fiber having dispersion of +18 (ps / nm / km) is used for the compensation transmission line 32g, and the compensation transmission line 32g is 50 km.

  In such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation intervals 33g-1 to 33g-3 are all negative, the nonlinear effect can be suppressed, and the transmission quality can be suppressed. Deterioration can be reduced. In addition, about dispersion management structure A-3, when all the accumulated chromatic dispersion is positive, and dispersion management in the case where negative and positive are mixed, since it can be configured in the same way, description is omitted.

  Next, a second embodiment of distributed management will be described. In the second embodiment, a dispersion compensation interval including a negative dispersion transmission path including a relay section having negative dispersion and a positive dispersion transmission path including a relay section having positive dispersion with respect to the optical transmission path. In order to randomize the accumulated chromatic dispersion (that is, in the first embodiment, the main transmission path having negative dispersion is compensated for in one relay section having positive dispersion, In this embodiment, the main transmission line having negative dispersion is compensated in a plurality of relay sections having positive dispersion).

  FIG. 21 is a schematic diagram showing the configuration of distributed management. The optical transmission line 3 is connected to the transmission device 10. The optical transmission path 3 includes a negative dispersion transmission path composed of a relay section having negative dispersion and a positive dispersion transmission path composed of a relay section having positive dispersion to form one dispersion compensation interval (hereinafter, this Such a system configuration is called a distributed management configuration B). Note that the order relationship between the negative dispersion transmission path and the positive dispersion transmission path may be switched.

  Next, in the dispersion management configuration B, a configuration example when the lengths of the dispersion compensation intervals are all equal will be described. FIG. 22 is a diagram illustrating an example of a distributed management configuration. In the dispersion management configuration B-1, the optical transmission path 3-4 is connected to the transmission device 10. The negative dispersion transmission path 34-4 has 5 spans in one relay section having negative dispersion, and the positive dispersion transmission path 35-4 has 5 spans in one relay section having positive dispersion. A dispersion compensation interval of 10 spans. An optical transmission path 3-4 is configured by connecting a plurality of 36-4 (the lengths of the dispersion compensation intervals are all equal).

  Next, in the dispersion management configuration B-1, a case will be described in which the absolute value of the average dispersion in the relay section is varied with respect to the dispersion compensation interval, and the accumulated chromatic dispersion is randomized. FIG. 23 is a diagram showing a dispersion map. The dispersion map M4-1 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is varied and the cumulative chromatic dispersion is negative.

  For the negative dispersion transmission lines 34a-1 and 34a-2 of the optical transmission line 3-4, for example, fibers having dispersions of −3 and −2 (ps / nm / km) are used in order, and the positive dispersion transmission line 35a is used. -1 and 35a-2 use fibers having dispersions of +1.5 and +3.5 (ps / nm / km) (one relay section is 50 km, and the absolute value of the average dispersion in the relay section is 150). (= 3 × 50), 100 (= 2 × 50), 75 (= 1.5 × 50), 175 (= 3.5 × 50).

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 with respect to the dispersion compensation interval 36a is negative, so that the nonlinear effect can be suppressed and the deterioration of transmission quality can be reduced. In addition, regarding the dispersion management configuration B-1, the description of the dispersion management when the cumulative chromatic dispersion is positive and when negative and positive are mixed is omitted.

  Next, dispersion management in the case where the accumulated chromatic dispersion is set to zero at one point in the entire transmission line will be described. In the explanation so far, the cumulative chromatic dispersion is not zero, but even if the cumulative chromatic dispersion becomes zero at one point in the entire transmission line, it is much more nonlinear than the conventional dispersion management. Since transmission degradation due to the effect can be reduced, the fact that such a pattern can also be configured will be described with reference to FIG.

  FIG. 24 is a diagram showing a dispersion map. The dispersion map M4-2 shows dispersion management when the accumulated chromatic dispersion is zero at only one point in the transmission path. For the negative dispersion transmission lines 34b-1 and 34b-2 of the optical transmission line 3-4, for example, a fiber having a dispersion of -2 (ps / nm / km) is used, and the positive dispersion transmission lines 35b-1 and 35b are used. For -2, a fiber having dispersion of +2 (ps / nm / km) is used. Each of the positive dispersion transmission line and the negative dispersion transmission line has 10 spans.

  In the case of such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 of the dispersion compensation interval 36b is zero for one point in the entire transmission path. In this case, as compared with the conventional dispersion management, the portion where the accumulated chromatic dispersion becomes zero can be reduced, so that the nonlinear effect can be suppressed and the deterioration of the transmission quality can be reduced.

  Next, in the dispersion management configuration B, a configuration example when the lengths of the dispersion compensation intervals are different will be described. FIG. 25 is a diagram showing a distributed management configuration example. In the dispersion management configuration B-2, the optical transmission path 3-5 is connected to the transmission device 10. The dispersion compensation interval is composed of a negative dispersion transmission line and a positive dispersion transmission line. In the dispersion management configuration B-2, since the number of relay sections of the negative dispersion transmission path and the number of relay sections of the positive dispersion transmission path are arbitrary, the length of the dispersion compensation interval is also different.

  For example, the dispersion compensation interval 36-5a includes a negative dispersion transmission line 34-5a having 3 spans of negative dispersion and a positive dispersion transmission line 35-5a having 2 spans of positive dispersion. The dispersion compensation interval 36 is composed of a negative dispersion transmission line 34-5b having 9 spans having negative dispersion and a positive dispersion transmission line 35-5b having 6 spans having positive dispersion. -5b is configured, and the optical transmission line 3-5 is configured with such dispersion compensation intervals having different lengths.

  Next, randomization of cumulative chromatic dispersion in the dispersion management configuration B-2 will be described. FIG. 26 is a diagram showing a dispersion map. The dispersion map M5-1 shows dispersion management in the case where the cumulative chromatic dispersion is negative by changing the length of the dispersion compensation interval by changing the number of relay sections to various types.

  For the optical transmission line 3-5, for example, the negative dispersion transmission lines 34c-1 and 34c-2 all use fibers having dispersion of -2 (ps / nm / km), and the negative dispersion transmission line 34c- The span of 1 and 34c-2 is assumed to be 10. In addition, fibers having dispersion of +2 (ps / nm / km) are used for the positive dispersion transmission lines 35c-1 and 35c-2, and the spans of the positive dispersion transmission lines 35c-1 and 35c-2 are set to 8, 12

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 with respect to the dispersion compensation interval 36c-1 is negative, so that the nonlinear effect can be suppressed and transmission quality deterioration can be reduced. .

  FIG. 27 is a diagram showing a dispersion map. The dispersion map M5-2 shows dispersion management in the case where the number of relay sections is varied to change the length of the dispersion compensation interval and the cumulative chromatic dispersion is positive. For the optical transmission line 3-5, all of the negative dispersion transmission lines 34d-1 and 34d-2 use, for example, a fiber having a dispersion of -2 (ps / nm / km), and the negative dispersion transmission line 34d- The spans 1 and 34d-2 are 7 and 13, respectively. Further, fibers having dispersion of +2 (ps / nm / km) are used for the positive dispersion transmission lines 35d-1 and 35d-2, and the spans of the positive dispersion transmission lines 35d-1 and 35d-2 are set to 11, 13

  In the case of such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 with respect to the dispersion compensation interval 36d-1 is positive, so that the nonlinear effect can be suppressed and the deterioration of the transmission quality can be reduced. . In addition, regarding the dispersion management configuration B-2, description of dispersion management when cumulative chromatic dispersion is a mixture of negative and positive is omitted.

  Next, a third embodiment of distributed management will be described. In the third embodiment, a dispersion compensation interval including a mixed transmission line including a positive dispersion fiber having positive dispersion and a negative dispersion fiber having negative dispersion is generated for one relay section, and cumulative chromatic dispersion is achieved. (That is, in the first and second embodiments, the fiber in one relay section uses either a positive dispersion fiber or a negative dispersion fiber. In the third embodiment, both the positive dispersion fiber (+ D fiber) and the negative dispersion fiber (−D fiber) are used in one relay section).

  FIG. 28 shows a mixed transmission path. The mixed transmission line LM includes + D fiber and −D fiber. Two types of fibers are applied in one relay section, the ratio of the fiber length in one relay section is changed, and the average dispersion in one relay section is varied.

  The order of connection of + D fiber and -D fiber may be any first, and in the figure, one + D fiber and one -D fiber are used in one relay section, but a plurality of each may be used (for example, , 3 relays + D fiber, 2 relays -D fiber, etc.)

  Next, in the optical transmission line that constitutes the dispersion compensation interval in which the main transmission line is compensated with the compensation transmission line using the mixed transmission line, the dispersion compensation intervals are all equal, and the absolute value of the average dispersion in the repeater section is varied. A case where the accumulated chromatic dispersion is randomized will be described.

  FIG. 29 is a diagram showing a dispersion map. The dispersion map M6-1 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is made various, and the cumulative chromatic dispersion is all negative. For the main transmission lines La-1 and La-2 of the optical transmission line, one relay section is a mixed transmission line in the order of + D fiber and -D fiber, and + D fiber is +20 (ps / nm / km) and 30. 8 km, -D fiber is -40 (ps / nm / km) and 19.2 km. In the main transmission lines La-3 and La-4, one relay section is a mixed transmission line in the order of -D fiber and + D fiber, and -D fiber is -40 (ps / nm / km) and 17.5 km. + D fiber is 32.5 km at +20 (ps / nm / km). The compensation transmission line Lk1 uses + D fiber and is 40 km of +20 (ps / nm / km).

  In the case of such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation interval Ls1 are all negative, it is possible to suppress nonlinear effects and reduce deterioration in transmission quality. it can.

  Next, using the mixed transmission line, in the optical transmission line that forms the dispersion compensation interval in which the main transmission line is compensated with the compensation transmission line, the number of relay sections is varied, the dispersion compensation interval is changed, and the accumulated chromatic dispersion is changed. A case of randomization will be described.

  FIG. 30 shows a dispersion map. The dispersion map M7-1 shows dispersion management in the case where the number of relay sections is varied and the accumulated chromatic dispersion is all negative. For the main transmission lines Lb-1 to Lb-4 of the optical transmission line, one relay section is a mixed transmission line in the order of + D fiber and -D fiber, and + D fiber is +20 (ps / nm / km) and 30. 8 km, −D fiber is −40 (ps / nm / km) and 19.2 km, and the spans of the main transmission lines Lb-1 to Lb-4 are 13, 10, 6, 3, respectively. The compensation transmission line Lk2 uses + D fiber and is 60.5 km of +20 (ps / nm / km).

  In the case of such a configuration, as can be seen from the figure, since the accumulated chromatic dispersions d1 to d3 with respect to the dispersion compensation intervals Ls2a to Ls2c are all negative, the nonlinear effect can be suppressed and the deterioration of transmission quality can be reduced. be able to.

  Next, using a mixed transmission line, an optical transmission line composed of a dispersion compensation interval including a negative dispersion transmission line composed of a relay section having negative dispersion and a positive dispersion transmission line composed of a relay section having positive dispersion. The case where the dispersion compensation intervals are all equal, the absolute value of the average dispersion in the relay section is varied, and the accumulated chromatic dispersion is randomized will be described.

  FIG. 31 shows a dispersion map. The dispersion map M8-1 shows dispersion management in the case where the absolute value of the average dispersion in the relay section is made various, and the cumulative chromatic dispersion is all negative. For the negative dispersion transmission line Lc-1 of the optical transmission line, one relay section is a mixed transmission line in the order of + D fiber and -D fiber, and + D fiber is +20 (ps / nm / km) and is 30.8 km,- The D fiber is 19.2 km at -40 (ps / nm / km).

  The negative dispersion transmission line Lc-3 is a mixed transmission line in the order of + D fiber and -D fiber in one relay section, + D fiber is +20 (ps / nm / km), 32.5 km, and -D fiber is It is 17.5 km at -40 (ps / nm / km).

  Further, the positive dispersion transmission lines Lc-2 and Lc-4 are a mixed transmission line in the order of + D fiber and -D fiber in one relay section, and + D fiber is +20 (ps / nm / km) and is 35 km, -D The fiber is -40 (ps / nm / km) and 15 km.

  In such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 with respect to the dispersion compensation interval Ls3 becomes negative, so that the nonlinear effect can be suppressed and the deterioration of transmission quality can be reduced.

  Next, using a mixed transmission line, an optical transmission line composed of a dispersion compensation interval including a negative dispersion transmission line composed of a relay section having negative dispersion and a positive dispersion transmission line composed of a relay section having positive dispersion. The case where the number of relay sections is increased and the accumulated chromatic dispersion is randomized will be described.

  FIG. 32 shows a dispersion map. The dispersion map M9-1 shows dispersion management in the case where the number of relay sections is varied and the accumulated chromatic dispersion is all negative. For the negative dispersion transmission lines Ld-1 and Ld-3 of the optical transmission line, one relay section is a mixed transmission line in the order of + D fiber and -D fiber, and + D fiber is +20 (ps / nm / km) and 30 .8 km, -D fiber is -40 (ps / nm / km) and 19.2 km. The spans of the negative dispersion transmission lines Ld-1 and Ld-3 are 12 and 6, respectively.

  The positive dispersion transmission lines Ld-2 and Ld-4 are a mixed transmission line in the order of + D fiber and -D fiber in one relay section, and + D fiber is +20 (ps / nm / km) and 35.9 km. -D fiber is 14.1 km at -40 (ps / nm / km).

  In the case of such a configuration, as can be seen from the figure, the accumulated chromatic dispersion d1 with respect to the dispersion compensation interval Ls4a is negative, so that the nonlinear effect can be suppressed and the deterioration of the transmission quality can be reduced.

  Next, a case will be described in which the transmitter 10 is provided with a pre-compensation fiber, and the receiver 20 is provided with a post-compensation fiber to randomize accumulated chromatic dispersion. FIG. 33 is a diagram showing a distributed management configuration example. The transmission device 10 includes a pre-compensation fiber (pre-compensation DCF (Dispersion Compensating Fiber)) 11 and a post-compensation fiber (post-compensation DCF) 21, and a light is transmitted between the pre-compensation DCF 11 and the post-compensation DCF 21. Transmission line 3 is connected. The optical transmission line 3 is provided with the optical repeater 40 and is subjected to the dispersion management as described above.

  Here, although the chromatic dispersion is zero at the input terminal of the pre-compensation DCF 11 of the transmission apparatus 10, chromatic dispersion is given to the optical signal through the pre-compensation DCF 11 (chromatic dispersion value D) and transmitted from the output terminal. The optical signal is relayed on the optical transmission line 3 while being compensated so that the accumulated chromatic dispersion does not become zero.

  Thereafter, the receiving device 20 receives the optical signal, and compensates the chromatic dispersion value of the optical signal to zero through the post-compensation DCF 21 inside the receiving device 20. In this way, by using the pre-compensation DCF 11 and the post-compensation DCF 21 and randomizing so that the chromatic dispersion does not become zero at both ends of the optical transmission line 3, it is possible to further suppress the nonlinear effect. Deterioration of transmission quality can be reduced.

  FIG. 34 is a diagram showing a dispersion map. The dispersion map M10 shows dispersion management when the pre-compensation DCF 11 and the post-compensation DCF 21 are used. As can be seen from the figure, the dispersion value is 500 (ps / nm) at both ends of the optical transmission line, and the chromatic dispersion value is zero after passing through the post-compensation DCF 21.

  Next, the overall configuration of an optical transmission system to which dispersion management is applied will be described. FIG. 35 is a diagram showing the overall configuration of the optical transmission system 1. The optical transmission system 1 includes a transmission device 10, a reception device 20, and a plurality of optical repeaters 40-1 to 40-m, and includes an optical transmission path 3 having a plurality of relay sections (in the drawing, The optical transmission line 3 is shown only in one direction).

  The transmission device 10 includes a pre-compensation DCF 11, a wavelength multiplexing unit 12, a post-amplifier 13, and E / Os 14-1 to 14 -n, and the reception device 20 includes a post-compensation DCF 21, a wavelength separation unit 22, a preamplifier 23, It is composed of O / E 24-1 to 24-n. Note that the pre-compensation DCF 11 is disposed either between the E / Os 14-1 to 14-n and the wavelength multiplexing unit 12 or between the wavelength multiplexing unit 12 and the post amplifier 13. Further, the post-compensation DCF 21 is disposed either between the preamplifier 23 and the wavelength separation unit 22 or between the wavelength separation unit 22 and the O / E 24-1 to 24-n.

  Each of the E / Os 14-1 to 14-n performs electrical / optical conversion and outputs a plurality of optical signals having different wavelengths. The wavelength multiplexing unit 12 wavelength-multiplexes a plurality of optical signals. The postamplifier 13 amplifies the WDM signal light from the wavelength multiplexing unit 12 to a required level and outputs it to the optical transmission line 3.

  The preamplifier 23 amplifies the WDM signal light of each wavelength band transmitted through the optical transmission path 3 to a required level. The wavelength separation unit 22 separates the output light from the preamplifier 23 into a plurality of optical signals according to the wavelength. The O / E 24-1 to 24-n perform optical / electrical conversion and receive and process a plurality of optical signals, respectively.

  As described above, the optical transmission system 1 is configured so that the accumulated chromatic dispersion does not become zero with respect to the dispersion compensation interval or the number of times that the accumulated chromatic dispersion becomes zero is reduced. The configuration is such that WDM optical transmission is performed. As a result, waveform distortion due to a nonlinear effect can be reduced, and transmission quality and reliability of optical communication can be improved.

  Note that the above dispersion management described using the dispersion map is an example for realizing the embodiment, and the optical transmission system is not limited to the above example, and the dispersion compensation intervals described above are various. In combination, the optical transmission path can be flexibly constructed (an example is shown in FIG. 36).

  Next, a description will be given of an optical transmission system that aims to reduce the characteristic fluctuation of Raman amplification on the optical transmission line. FIG. 37 shows the principle of the optical transmission system. The optical transmission system 1a is a system that performs Raman optical amplification and performs optical signal relay control.

  The optical transmission line 3 includes a first fiber having positive dispersion (hereinafter, + D fiber) and a second fiber having negative dispersion and a mode field diameter smaller than that of + D fiber (hereinafter, -D fiber). A relay section is formed, and + D fiber and −D fiber are arranged so that the optical signal propagates in the order from + D fiber to −D fiber. Further, in order to change the dispersion value for the relay section, the lengths of + D fiber and -D fiber are made different (in the figure, -D fiberF1> -D fiberF2).

  The optical repeater 40 includes a monitor unit 41 and a pump unit 42-1. The excitation unit 42-1 includes an excitation control unit 42a, a duplexer 42b, and couplers c3 and c4. The monitor unit 41 receives the optical signal flowing through the uplink / downlink via the couplers c1 and c2, and monitors the power of the optical signal. The excitation control unit 42a variably outputs excitation light based on the monitor result. The demultiplexer 42b demultiplexes the excitation light into the uplink and the downlink in order to enter the -D fiber. The demultiplexed excitation light is incident in a direction opposite to the optical signal direction via the couplers c3 and c4 (backward excitation). In the figure, the number of excitation control units 42a that are excitation light sources is one. However, a plurality of excitation control units 42a may be provided to provide a redundant configuration (that is, a configuration having a plurality of excitation light sources may be used).

  Next, the control operation of the optical signal power of the optical transmission system 1a will be described in detail. FIG. 38 is a diagram illustrating a configuration example of the optical transmission system 1a. Stations 110 and 120 are connected by an upstream / downstream optical transmission line 3. The arrow shown in the figure indicates the Raman pumping light output from the optical repeater 40. The illustration of the optical repeater 40 is omitted.

  One relay section is a mixed transmission path of + D fiber (dispersion value is, for example, +20 (ps / nm / km)) and -D fiber (dispersion value is, for example, -40 (ps / nm / km)). Because the + D fiber and -D fiber are arranged so that the optical signal propagates in the order from + D fiber to -D fiber and the dispersion value is changed for the relay section, the length ratio of + D fiber and -D fiber Have to be different. “−” And “+” in the figure indicate the average variance of one relay section.

  First, in order to simplify the description, a sign is determined such that a section having a negative section average variance is −Dave and a section having a positive section average variance is + Dave. When the uplink is −Dave and the downlink is + Dave, the display is −Dave / + Dave.

Here, span NO. Consider that the optical signal power is adjusted at dispersion compensation intervals of 1 to 6 (three sections each having a negative section average dispersion and a positive section average dispersion).
There are four types of cables within the dispersion compensation interval: -Dave / + Dave, + Dave / -Dave, + Dave / + Dave, and -Dave / -Dave. The section where the excitation LD (Pump) excites is -Dave / + Dave. Is 3 sections, + Dave / -Dave is 3 sections. By adjusting the pump light power of these six sections, the signal light power balance between the uplink and the downlink is adjusted. 39 is a diagram showing the number of Pumps within the dispersion compensation interval, and FIG. 40 is a diagram showing the number of Cables within the dispersion compensation interval. FIG. 41 shows a table T1 indicating the number of Pumps and the number of Cables within the dispersion compensation interval for the system of FIG.

  FIG. 42 is a diagram showing an algorithm for adjusting the optical signal power balance. The algorithm AL1 shows how to adjust the pumping LD according to the state of the optical signal power in the uplink and downlink.

Looking at state 1, the power of the uplink is large (the power of the excitation LDa, b, and c in FIG. 39 located near the uplink transmission source is large), and the power of the downlink is small (downlink 39. Since the power of the excitation LDs d, e, and f in FIG. 39 located near the transmission source is small), the power of the excitation LD that excites -Dave / + Dave (the excitation LDa, b, and c in FIG. 39) is reduced. , + Dave / −Dave, the power of the excitation LD (excitation LDd, e, f in FIG. 39) is increased.

  By performing such control, it is possible to make the signal light power balance between the uplink and the downlink uniform while maintaining the average Raman gain constant. The same applies to states 2-4.

  Here, the result of quantitatively examining the adjustment of the optical signal power when the dispersion compensation interval in FIG. 38 is 6 will be described with reference to FIGS. 43 to 45. FIG. 43 is a diagram showing transition of optical signal power. FIG. 44 is a graph of the table of FIG. 43, and shows the transition when the optical signal power is monitored at point A on the uplink / downlink in FIG.

  FIG. 45 is a diagram showing pump light power and Raman gain. Assuming that the target optical signal power is -7 dBm, the optical signal power is first controlled using the algorithm AL1 of FIG. 42 when it is large at -6 dBm at point A in the upstream section and -8 dBm at point A in the downstream section. Shows the results.

  With these controls, by reducing the pumping light power in the -Dave / + Dave section and increasing the pumping light power in the + Dave / -Dave section, the difference in optical signal power between the upstream section and the downstream section at point A can be reduced. It is possible to approach the required optical signal power of -7 dBm.

  Next, optical signal power adjustment when a variable optical attenuator (VOA) is applied will be described. FIG. 46 is a diagram illustrating a configuration example of an optical transmission system. VOAs 51 and 52 for assisting the adjustment of the optical signal power for each fiber core line are inserted into the uplink / downlink connecting the stations 110 and 120 at a rate of every several relays.

  FIG. 47 is a diagram showing an algorithm for adjusting the optical signal power balance. As for state 1, when the uplink power is large and the downlink power is small, the power of the excitation LD that excites + Dave / −Dave is increased, and the power of the excitation LD that excites −Dave / + Dave is decreased. To do. In addition, the attenuation amount of the uplink VOA is increased and the attenuation amount of the downlink VOA is decreased.

  By performing such control, the average Raman gain remains constant, and the signal light power balance between the uplink and the downlink can be made uniform (VOA can adjust the power that could not be adjusted only by the pump LD). Tweak). The same applies to states 2-4.

  Next, optical signal power adjustment when a variable gain equalizer (VGE) is applied will be described. FIG. 48 is a diagram illustrating a configuration example of an optical transmission system. In addition to VOAs 51 and 52, VGEs 61 and 62 are inserted into the uplink / downlinks connecting the stations 110 and 120.

  When the increase in loss is compensated by adjusting the pumping power of the pumping LD, the Raman gain changes, so the gain deviation of the Raman amplification changes. In order to compensate for the Raman gain deviation, VGE is effective and can suppress characteristic deterioration.

  FIG. 49 is a diagram showing an optical transmission line including a gain equalization section. When gain equalization control is performed by the VGEs 61 and 62, it is desirable that the length of the −D fiber connected to both ends of the VGEs 61 and 62 is the same as the length of the + D fiber. In this case, since the absolute value of the dispersion of -D fiber is larger than that of + D fiber, the average dispersion of the gain equalization section is negative. In addition, by setting the fiber length of -D fiber to the same length as the section in which the section average dispersion is negative, it is possible to reduce the types of optical repeaters (there is no need to prepare optical repeaters having different pump LD powers). The insertion loss allowed for the gain equalizer can be increased.

  FIG. 50 is a diagram illustrating a configuration example of an optical transmission system. The gain equalization section is applied to a section where the section average variance is negative for both the uplink and the downlink, as described above. Further, since the lengths of + D fiber and −D fiber are substantially the same, a cumulative variance that is about three times the normal interval average variance is generated in one interval. Accordingly, the configuration of the dispersion compensation interval of 6 sections includes -Dave having 2 sections (1 section being a gain equalization section) and + Dave having 4 sections.

  In the dispersion compensation interval including the gain equalization section, as shown in Table T2, there are four types of cables: -Dave / + Dave, + Dave / -Dave, + Dave / + Dave, and -Dave / -Dave, and the excitation LD Excitation intervals are -Dave / + Dave is 2 intervals, + Dave / -Dave is 2 intervals, and + Dave / + Dave is 2 intervals. By adjusting the pump light power in the −Dave / + Dave 2 section and + Dave / −Dave 2 section among the six sections, the signal light power balance between the uplink and the downlink can be adjusted.

  Next, a modification of the optical repeater will be described. FIG. 51 is a diagram showing a modification of the optical repeater. The optical repeater 40a includes a monitor unit 41 and a pump unit 42-2. The excitation unit 42-2 includes an excitation control unit 42c, a branching ratio variable demultiplexer 42d, and couplers c3 and c4. The monitor unit 41 receives the optical signal flowing through the uplink / downlink via the couplers c1 and c2, and monitors the power of the optical signal. The excitation control unit 42c outputs constant excitation light. The branching ratio variable demultiplexer 42d sets the branching ratio to be variable based on the monitoring result, and demultiplexes the constant excitation light to enter the -D fiber based on the set branching ratio. The demultiplexed excitation light is incident in a direction opposite to the optical signal direction via the couplers c3 and c4 (backward excitation).

  Thus, in the optical repeater 40a, the pumping light power incident on the uplink and the downlink is adjusted by using the branching ratio variable demultiplexer 42d. The branching ratio variable demultiplexer 42d can be realized, for example, by applying a Mach-Zender type waveguide device (when applied to locations corresponding to −Dave / + Dave and + Dave / −Dave, it is more effective. Also, it is desirable to have one insertion point for several relays).

  Next, a plurality of patterns are shown for the configuration example of the optical transmission system, and the adjustment of the optical signal power will be described. FIG. 52 is a diagram showing a configuration example of the optical transmission system, and FIG. 53 is a diagram showing an algorithm for adjusting the optical signal power balance. For the optical transmission system 1a-1, there are four types of cables: -Dave / + Dave, + Dave / -Dave, + Dave / + Dave, and -Dave / -Dave. The section where the excitation LD is excited is + Dave / -Dave. Are two sections, -Dave / + Dave is two sections, + Dave / + Dave is one section, and -Dave / -Dave is two sections.

  In the algorithm AL3, the signal light power balance between the uplink and the downlink can be adjusted by adjusting the pumping light power in the −Dave / + Dave 1 interval and the + Dave / −Dave 1 interval among the 6 intervals. Further, by adjusting −Dave / −Dave and + Dave / + Dave, it is possible to change the average gain of both the uplink and the downlink.

FIG. 54 is a diagram illustrating a configuration example of an optical transmission system. Relative to the optical transmission system 1a-2, the type of cable - Dave / + Dave, a two + Dave / -Dave, interval excitation LD is excited, -Dave / + Dave are two sections, the + Dave / -Dave Two sections, -Dave / -Dave is one section, + Dave / + Dave is one section.

  The adjustment algorithm of the excitation LD is the same as that in FIG. By adjusting the pump light power in the −Dave / + Dave 2 section and + Dave / −Dave 2 section among the six sections, the signal light power balance between the uplink and the downlink can be adjusted. Further, by adjusting −Dave / −Dave and + Dave / + Dave, it is possible to change the average gain of both the uplink and the downlink.

  FIG. 55 is a diagram illustrating a configuration example of an optical transmission system. For the optical transmission system 1a-3, there are four types of cables: -Dave / + Dave, + Dave / -Dave, + Dave / + Dave, and -Dave / -Dave. Is one section, + Dave / −Dave is one section, −Dave / −Dave is two sections, and + Dave / + Dave is two sections.

  The adjustment algorithm of the excitation LD is the same as that in FIG. By adjusting the pumping light power in the −Dave / + Dave 1 section and the + Dave / −Dave 1 section among the six sections, the signal light power balance between the uplink and the downlink can be adjusted. Further, by adjusting −Dave / −Dave and + Dave / + Dave, it is possible to change the average gain of both the uplink and the downlink.

  FIG. 56 is a diagram illustrating a configuration example of an optical transmission system. For the optical transmission system 1a-4, there are two types of cables: + Dave / + Dave and -Dave / -Dave, and the excitation LD is excited by -Dave / + Dave is 1 and + Dave / -Dave is 1 Section, -Dave / -Dave is 2 sections, + Dave / + Dave is 2 sections.

  The adjustment algorithm of the excitation LD is the same as that in FIG. By adjusting the pumping light power in the −Dave / + Dave 1 section and the + Dave / −Dave 1 section among the six sections, the signal light power balance between the uplink and the downlink can be adjusted. Further, by adjusting −Dave / −Dave and + Dave / + Dave, it is possible to change the average gain of both the uplink and the downlink.

(Supplementary note 1) In an optical transmission system for transmitting optical signals,
A transmitter for transmitting an optical signal by performing wavelength division multiplexing of WDM;
A receiving device for receiving a wavelength-multiplexed optical signal;
An optical repeater is installed, and the dispersion compensation interval is such that the accumulated chromatic dispersion does not become zero or the number of times the accumulated chromatic dispersion becomes zero is reduced, and the dispersion compensated optical transmission line,
An optical transmission system comprising:

  (Supplementary Note 2) The optical transmission line is configured by the dispersion compensation interval in which the relay section having negative dispersion is used as a main transmission line, and the dispersion of the main transmission path is compensated by one relay section having positive dispersion, Randomization of accumulated chromatic dispersion is performed by at least one of multiple types of absolute values of average dispersion of relay sections, multiple types of relay sections, and various types of relay section distances with respect to dispersion compensation intervals. The optical transmission system according to supplementary note 1, wherein

  (Supplementary Note 3) The optical transmission path is configured with a dispersion compensation interval including a negative dispersion transmission path including a relay section having negative dispersion and a positive dispersion transmission path including a relay section having positive dispersion, Randomization of accumulated chromatic dispersion is performed by at least one of multiple types of absolute values of average dispersion of relay sections, multiple types of relay sections, and various types of relay section distances with respect to dispersion compensation intervals. The optical transmission system according to supplementary note 1, wherein

  (Additional remark 4) The said optical transmission path is comprised with the mixed transmission path which consists of a positive dispersion fiber with positive dispersion, and a negative dispersion fiber with negative dispersion with respect to 1 relay area. Transmission system.

  (Supplementary Note 5) The optical transmission line is configured with the dispersion compensation interval in which the relay section having negative dispersion is used as a main transmission line, and the dispersion of the main transmission path is compensated by one relay section having positive dispersion. APPENDIX 4 characterized by randomizing cumulative chromatic dispersion by performing at least one of multiple types of absolute values of average dispersion of sections, multiple types of relay sections, and various types of relay section distances The optical transmission system described.

  (Supplementary Note 6) The optical transmission path is configured with a dispersion compensation interval including a negative dispersion transmission path including a relay section having negative dispersion and a positive dispersion transmission path including a relay section having positive dispersion. APPENDIX 4 characterized by randomizing cumulative chromatic dispersion by performing at least one of multiple types of absolute values of average dispersion of sections, multiple types of relay sections, and various types of relay section distances The optical transmission system described.

  (Supplementary Note 7) The transmitter has a pre-compensation fiber, and transmits an optical signal with a non-zero chromatic dispersion value from an output end connected to the optical transmission line, and the receiver has a post-compensation fiber. The optical transmission system according to appendix 1, wherein a chromatic dispersion value of an optical signal is made zero through the post-compensation fiber.

(Supplementary Note 8) In a dispersion compensation method for performing dispersion compensation of an optical transmission line,
A relay section having negative dispersion is used as a main transmission path, and the dispersion of the main transmission path is configured by the dispersion compensation interval compensated by one relay section having positive dispersion.
For the dispersion compensation interval, perform at least one of multiple types of absolute values of average dispersion of relay sections, multiple types of relay sections, and multiple types of relay section distances,
A dispersion compensation method for compensating for dispersion in an optical transmission line so that the accumulated chromatic dispersion does not become zero or the number of times the accumulated chromatic dispersion becomes zero is reduced.

  (Supplementary note 9) The dispersion compensation according to supplementary note 8, wherein the optical transmission line is configured by a mixed transmission line composed of a positive dispersion fiber having positive dispersion and a negative dispersion fiber having negative dispersion for one relay section. Method.

  (Supplementary Note 10) A pre-compensation fiber is installed in the transmitting station, an optical signal is transmitted from the output end connected to the optical transmission line with a non-zero chromatic dispersion value, and a post-compensation fiber is installed in the receiving station. The dispersion compensation method according to appendix 8, wherein the chromatic dispersion value of the optical signal is made zero through the post-compensation fiber.

(Supplementary Note 11) In a dispersion compensation method for performing dispersion compensation of an optical transmission line,
A dispersion compensation interval including a negative dispersion transmission path composed of relay sections having negative dispersion and a positive dispersion transmission path composed of relay sections having positive dispersion is configured.
For the dispersion compensation interval, perform at least one of multiple types of absolute values of average dispersion of relay sections, multiple types of relay sections, and multiple types of relay section distances,
A dispersion compensation method for compensating for dispersion in an optical transmission line so that the accumulated chromatic dispersion does not become zero or the number of times the accumulated chromatic dispersion becomes zero is reduced.

  (Supplementary note 12) The dispersion compensation according to supplementary note 11, wherein the optical transmission line is constituted by a mixed transmission line composed of a positive dispersion fiber having positive dispersion and a negative dispersion fiber having negative dispersion for one relay section. Method.

  (Supplementary note 13) A pre-compensation fiber is installed in the transmitting station, an optical signal is transmitted from the output end connected to the optical transmission line with a non-zero chromatic dispersion value, and a post-compensation fiber is installed in the receiving station. The dispersion compensation method according to appendix 11, wherein the chromatic dispersion value of the optical signal is made zero through the post-compensation fiber.

(Additional remark 14) In the optical transmission system which transmits an optical signal,
A first fiber having positive dispersion and a second fiber having negative dispersion and having a mode field diameter smaller than that of the first fiber constitute a relay section, and an optical signal is transmitted from the first fiber. An optical transmission line propagating in order to the second fiber;
Based on the monitoring result and a monitoring result for monitoring the power of the optical signal, the power balance of the upstream / downstream optical signal in units of dispersion compensation intervals for the plurality of relay sections having different lengths of the second fiber. An optical repeater composed of a pumping unit that performs power supply control of pumping light so as to adjust,
An optical transmission system comprising:

  (Additional remark 15) The said excitation part is comprised from the excitation control part which variably outputs excitation light based on a monitoring result, and the splitter which demultiplexes in order to make the said excitation light inject into a said 2nd fiber. The optical transmission system according to appendix 14, wherein:

  (Additional remark 16) The said excitation part sets a branching ratio variably based on the excitation control part which outputs fixed pumping light, and a monitoring result, and based on the said branching ratio, constant pumping light is sent to said 2nd fiber 15. The optical transmission system according to appendix 14, characterized by comprising: a branching ratio variable demultiplexer for demultiplexing to enter.

  (Supplementary note 17) The supplementary note 14, wherein at least one of a variable optical attenuator for assisting optical signal power adjustment by the optical repeater and a variable gain equalizer for compensating for gain deviation is provided in the optical transmission line. Optical transmission system.

  (Supplementary note 18) The first fiber and the second fiber in the gain equalization section whose gain deviation should be compensated by the variable gain equalizer have the same length, and the dispersion includes the gain equalization section 18. The optical transmission system according to appendix 17, wherein the number of sections of section average dispersion is changed in the compensation interval.

(Supplementary note 19) In an optical repeater that performs optical amplification and performs optical signal relay control,
A first optical fiber having positive dispersion and a second fiber having negative dispersion and a mode field diameter smaller than that of the first fiber constitute a relay section, and an optical signal is transmitted from the first fiber. A monitor for monitoring the power of the optical signal on the optical transmission line that propagates in sequence to the second fiber;
Based on the monitoring result, supply of pumping light power so as to adjust the power balance of upstream / downstream optical signals in units of dispersion compensation intervals for the plurality of relay sections having different lengths of the second fiber An excitation unit for controlling,
An optical repeater characterized by comprising:

  (Additional remark 20) The said excitation part is comprised from the excitation control part which variably outputs excitation light based on a monitoring result, and the splitter which demultiplexes in order to make the said excitation light inject into a said 2nd fiber. Item 20. The optical repeater according to appendix 19, wherein

  (Additional remark 21) The said excitation part sets a branching ratio variably based on the excitation control part which outputs fixed pumping light, and a monitoring result, and based on the said branching ratio, constant pumping light is sent to said 2nd fiber The optical repeater according to appendix 19, characterized by comprising: a branching ratio variable demultiplexer for demultiplexing to enter.

(Supplementary note 22) In an optical relay method for performing optical amplification and performing optical signal relay control,
A first fiber having positive dispersion and a second fiber having negative dispersion and having a mode field diameter smaller than that of the first fiber constitute a relay section, and an optical signal is transmitted from the first fiber. For the optical transmission line that propagates in order to the second fiber,
Monitor the power of the optical signal,
Based on the monitoring result, supply of pumping light power so as to adjust the power balance of upstream / downstream optical signals in units of dispersion compensation intervals for the plurality of relay sections having different lengths of the second fiber An optical relay method that performs control.

  (Supplementary note 23) At least one of a variable optical attenuator for assisting optical signal power adjustment and a variable gain equalizer for compensating for gain deviation should be provided in the optical transmission line, and the gain deviation should be compensated by the variable gain equalizer. The lengths of the first fiber and the second fiber in the gain equalization section are the same, and the number of constituents of the section average dispersion is changed in the dispersion compensation interval including the gain equalization section. The optical relay method according to appendix 22.

1 is a principle diagram of an optical transmission system. It is a figure which shows the structure of distributed management. It is a figure which shows chromatic dispersion compensation. It is a figure which shows the structure of distributed management. It is a figure which shows chromatic dispersion compensation. It is a figure which shows a dispersion | distribution map. It is a figure which shows the correlation of a wavelength. It is a figure which shows the correlation of a wavelength. It is a figure which shows the structure of an optical repeater. It is the schematic which shows the structure of distributed management. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is the schematic which shows the structure of distributed management. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows a mixed transmission line. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows a dispersion | distribution map. It is a figure which shows the example of a distributed management structure. It is a figure which shows a dispersion | distribution map. It is a figure which shows the whole structure of an optical transmission system. It is a figure which shows a dispersion | distribution map. 1 is a principle diagram of an optical transmission system. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the number of Pumps in a dispersion compensation interval. It is a figure which shows the number of Cables in a dispersion compensation interval. It is a figure which shows the table which showed the number of Pumps in the dispersion compensation space | interval, and the number of Cables. It is a figure which shows the algorithm which adjusts an optical signal power balance. It is a figure which shows the transition of optical signal power. FIG. 44 is a graph of the table of FIG. 43. It is a figure which shows pumping light power and a Raman gain. It is a figure which shows the structural example of an optical transmission system. An algorithm for adjusting the optical signal power balance will be described. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the optical transmission line containing a gain equalization area. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the modification of an optical repeater. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the algorithm which adjusts an optical signal power balance. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the structural example of an optical transmission system. It is a figure which shows the structural example of an optical transmission system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical transmission system 10 Transmitting device 20 Receiving device 3 Optical transmission line 40-1 to 40-n Optical repeater m0 Dispersion map which shows conventional dispersion management M0 Dispersion map which shows dispersion management

Claims (2)

In an optical transmission system that transmits optical signals,
A first fiber having a positive dispersion, has a negative dispersion, said second fiber mode field diameter is small with respect to the first fiber, in a repeater section configured, the optical signal is the first fiber An uplink that sequentially propagates in the upstream direction from the second fiber to the second fiber;
The first fiber and the second fiber constitute the relay section, and the optical signal propagates in the downstream direction from the first fiber to the second fiber; and
An optical repeater including a pumping unit that emits pumping lights of the same power in opposite directions in an uplink relay section that is the relay section on the uplink side and a downlink relay section that is the relay section on the downlink side When,
With
In a dispersion compensation section including a plurality of the relay sections, the second fiber has a length different from the length of the first fiber,
When the average dispersion of the relay section is a positive relay section, and the average dispersion of the relay section is a negative relay section,
The upstream relay section that emits pumping light is the positive relay section, and the downstream relay section that emits pumping light is the negative relay section. A second light disposed at a relay point where a certain first pumping unit and the upstream relay section that emits pumping light are the negative relay section, and the downstream relay section that emits pumping light is the positive relay section For the second excitation unit that is the excitation unit in the relay device,
When the first excitation unit increases its own excitation light power, the second excitation unit decreases its own excitation light power, and when the first excitation unit decreases its own excitation light power, The second pumping unit increases its own pumping light power to adjust the upstream / downstream power balance of the optical signal flowing through the uplink and the downlink in the dispersion compensation section;
An optical transmission system characterized by that. A variable gain equalizer for compensating for a gain deviation generated when the pumping light power is adjusted;
The length of the first fiber is the same as the length of the second fiber, and the relay section having a negative average dispersion is defined as a gain equalization section.
Connection points between the first fiber and the second fiber on the uplink and connection points between the first fiber and the second fiber on the downlink within the gain equalization section. At least one of the variable gain equalizers is disposed;
The optical transmission system according to claim 1.

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