JP3595119B2 - Optical WDM transmission equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to optical wavelength division multiplexing transmission. In particular, waveform degradation due to the combined effect of nonlinear effects (four-wave mixing, cross-phase modulation) and chromatic dispersion of optical fibers unique to optical wavelength division multiplexing transmission, and self-phase modulation, which is a nonlinear effect in optical single-wavelength communication, The present invention relates to a technique for optimizing suppression of waveform deterioration due to a combined effect with chromatic dispersion.
[0002]
[Prior art]
In the optical wavelength division multiplexing transmission method, there is a problem of deterioration of transmission characteristics due to crosstalk between signal lights. The main cause of the crosstalk is due to phenomena such as four-wave mixing and cross-phase modulation occurring in the transmission line optical fiber. These phenomena are caused by the interaction between optical signals when a plurality of optical signals having different wavelengths propagate in the transmission line optical fiber. The phenomenon that an optical signal component corresponding to each wavelength difference is generated by this interaction is four-wave mixing, and the phenomenon that phase modulation occurs in an optical signal is cross-phase modulation.
[0003]
Conventionally, as a means for suppressing four-wave mixing and cross-phase modulation, dispersion management is performed by setting the dispersion value of the transmission line optical fiber to a large value and arranging a dispersion compensator with dispersion opposite to that of the transmission line optical fiber at regular intervals. It has been known. For example,
Literature: "WDM Transmission Experiments over 2640 km of Eight NRZ, 10-Gb / s Data channels", OAA'96, ThB2
Shows an example in which dispersion compensation is performed at an interval of 600 km in a transmission line optical fiber having a dispersion value of -0.7 ps / nm / km.
[0004]
[Problems to be solved by the invention]
Conventionally, it has been common practice to perform dispersion compensation at intervals of several hundred km. However, it is unclear whether the dispersion compensation interval is optimal or not. There was a possibility that the cable was inserted into the transmission path optical fiber.
[0005]
An object of the present invention is to solve such a problem and to provide an optical wavelength division multiplexing communication apparatus in which transmission characteristic degradation due to crosstalk between signal lights is optimized.
[0006]
[Means for Solving the Problems]
An optical wavelength division multiplexing transmission device according to the present invention includes a transmission line optical fiber for transmitting wavelength-multiplexed signal light, and dispersion compensation means inserted into the transmission line optical fiber and compensating for chromatic dispersion of the transmission line optical fiber. In the wavelength division multiplexing transmission device, the chromatic dispersion of the transmission line optical fiber is negative dispersion, and the dispersion compensating means uses the super Gaussian waveform exp ｛-(1/2) · (T / T ₀₎ ^2m} (m is transmitted and _{T 0} of the super index Gaussian), and the center wavelength λ [nm], the speed of light c [km / s] in the transmission path optical the fiber, at the center wavelength λ [nm] Length L _d = T ₀ ² / | λ ² D / 2πc | expressed by the dispersion value D [ps / nm / km] of the optical fiber.
Against
0.1 <L _comp / L _d <0.4
_Are arranged at intervals L _comp [km] (hereinafter referred to as “dispersion compensation intervals”).
[0007]
As pulses transmitted by the transmission line optical fiber, high public secant waveform sech _(T / T ₀₎ or Lorentz type waveform ^{_{(1+ (T / T 0)}} 2) can be used as the ^-1/2.
[0008]
The super Gaussian and high public secant waveforms are described in detail, for example, in "NONLINEAR FIBER OPTICS" issued by Academic Press. When the index of super Gaussian m = 1, it is a normal Gaussian waveform. The Lorentz waveform is described in detail in "Basics of Optoelectronics" issued by Maruzen Co., Ltd.
[0009]
When a positive dispersion (abnormal dispersion) is used as the transmission line optical fiber, the spectrum spreads in the signal light, causing crosstalk and causing waveform deterioration. For this reason, the transmission distance is more restricted than the negative dispersion transmission line. Therefore, in the present invention, a negative dispersion optical fiber is used as the transmission line optical fiber. In addition, by optimizing the dispersion compensation interval L _comp , it is possible to optimize transmission characteristic degradation due to crosstalk between signal lights. As the dispersion compensating means, a dispersion compensating optical fiber or an optical fiber grating can be used.
[0010]
According to the present invention, although the conversion formula to T ₀ varies depending on the code format of the transmission signal, if the conversion is performed, it is not necessary to consider the code format of the transmission signal and its bit rate at the time of design, and system design is easy. become. Also, it is not necessary to consider the number of wavelength multiplexes.
[0011]
The dispersion value D of the transmission line optical fiber is preferably -1 to -2 ps / nm / km. With a value in this range, the dispersion compensation interval L _comp for optimizing the deterioration of transmission characteristics due to crosstalk between signal lights can be increased, which is advantageous in system design.
[0012]
An optical amplifier for amplifying the signal light can be inserted into the transmission line optical fiber. The optical transmission unit further includes an optical transmission unit that transmits the wavelength-division multiplexed light to the transmission line optical fiber and an optical reception unit that receives the wavelength-division multiplexed light from the transmission line optical fiber, wherein the optical transmission unit generates signal lights having different wavelengths from each other. A plurality of optical transmitters; and a multiplexer for multiplexing the signal lights from the plurality of optical transmitters, wherein the optical receiving means separates the transmitted wavelength-division multiplexed light into signal light of each wavelength. The optical receiver includes a wave receiver and a receiver that receives the demultiplexed signal light, and the optical receiving unit may further include a dispersion medium that dispersion-compensates the signal light demultiplexed by the demultiplexer for each wavelength. . As the dispersion medium, a dispersion compensating optical fiber or an optical fiber grating can be used as in the case of the dispersion compensating means inserted into the transmission line optical fiber.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram showing an embodiment of the present invention, and shows a configuration example of an optical wavelength division multiplexing transmission apparatus. Here, a case of four-wavelength multiplexing will be described as an example. The apparatus shown in FIG. 1 includes an optical wavelength division multiplexing transmitting terminal 10, an optical transmission line 20, and an optical wavelength division multiplexing receiving terminal 30. The optical wavelength division multiplexing transmission terminal 10 includes four transmitters 11a to 11d that generate signal lights having different wavelengths from each other, and a multiplexer 12 that multiplexes the signal lights from these optical transmitters 11a to 11d. Prepare. The optical transmission line 20 includes a transmission line optical fiber 21 for transmitting the wavelength-multiplexed signal light, an optical amplifier 22 for amplifying the signal light transmitted to the transmission line optical fiber 21, and an optical amplifier 22 inserted into the transmission line optical fiber 21. And a dispersion compensating medium 23 for compensating the chromatic dispersion of the transmission line optical fiber 21. The optical wavelength division multiplexing receiving terminal 30 includes a demultiplexer 31 for demultiplexing the transmitted wavelength multiplexed light into signal light of each wavelength, and a receiving dispersion medium 32 for dispersion-compensating the divided signal light for each wavelength. And receivers 33a to 33d that receive the split and dispersion-compensated signal light.
[0014]
As the dispersion compensating medium 23 and the receiving dispersion medium 32, a dispersion compensating optical fiber or an optical fiber grating is used. Dispersion compensation medium 23, Super Gaussian waveform exp of pulses transmitted by the optical transmission line _{20 {- (1/2) · (} T / T 0) 2m} (m is super index Gaussian) using _{T 0} of Dispersion length L _d = T ₀ ² / | λ ² D / 2πc |
However,
λ: center wavelength [nm]
c: speed of light c [km / s] in the transmission line optical fiber 21
D: Dispersion value D [ps / nm / km] of the transmission line optical fiber 21 at the center wavelength [nm].
Against
0.1 <L _comp / L _d <0.4
_Are arranged at every dispersion compensation interval L _comp [km] represented by
[0015]
Figures 2-4 show the results obtained by computer simulation the relationship between _L comp / _{L d} and transmission distance _{L e.}
[0016]
2, each bit rate of the transmitter 11a~11d and 10 Gbit / s (total bit rate 40 Gbit / s), the average signal light power (the optical amplifier output _{power) P av} the -3dBm / ch, 0dBm / ch, 3dBm / for the case where ch and varied are those sought distance opening penalty of the eye pattern at the worst channel is 1dB as transmission distance L _e. The dispersion value of the transmission line optical fiber was -1.0, -2.0, -10.0 ps / nm / km. As a result, when the dispersion compensation interval L _comp is L _comp / L _d ≦ 0.1, the waveform is caused by the combined effect of the nonlinear effect (four-wave mixing, cross-phase modulation) and the chromatic dispersion of the optical fiber specific to the optical wavelength division multiplexing transmission. When L _comp / L _d ≧ 0.4, waveform degradation occurs due to the combined effect of self-phase modulation and chromatic dispersion, which is a nonlinear effect in optical single-wavelength communication. On the other hand, when the dispersion compensation interval L _comp is 0.1 <L _comp / L _d <0.4, the transmission distance Le reaches a peak, and it can be seen that this is the optimal compensation interval. Since four-wave mixing and cross-phase modulation depend on the walk-off between channels (the relative time difference between pulses caused by chromatic dispersion between channels), the dispersion compensation interval is large, or the dispersion value of the transmission line optical fiber. Is larger, the waveform deterioration is less likely to occur, but there is a compensation interval where the waveform deterioration is minimized due to the limitation of the waveform deterioration due to the combined effect of self-phase modulation and chromatic dispersion.
[0017]
FIG. 3 shows that the bit rates of the transmitters 11a to 11d are 10 Gbit / s (total bit rate 40 Gbit / s), the average signal light power _Pav is 0 dBm / ch, and the dispersion value of the transmission line optical fiber is -0.5. , -1.0, -2.0, -4.0, for the case where the -10.0ps / nm / km, in which determined the transmission distance _{L e} as in FIG 2. From this result, when the dispersion value of the transmission line optical fiber was -0.5ps / nm / km _is, L comp _/ L d <0.2 in transmission distance _{L e} it is seen to deteriorate rapidly. Therefore, from the viewpoint of system design, it is desirable that the dispersion value of the transmission line optical fiber is in the range of -1.0 to -2.0 ps / nm / km.
[0018]
FIG. 4 shows a pulse transmitted to the transmission line optical fiber as a high public secant waveform or a Lorentzian waveform, the bit rates of the transmitters 11a to 11d are respectively 10 Gbit / s (total bit rate 40 Gbit / s), and the average signal light power. the P _av and 0dBm / ch, the case where the dispersion value of the transmission line optical fiber was -1.0ps / nm / km, in which determined the transmission distance _{L e.} From this result, the dispersion compensation interval L _comp is 0.1 <L _comp / L _d <0.4 for both the high public secant waveform and the Lorentzian waveform.
At the time, the transmission distance _Le reaches a peak, and it is understood that the optimum compensation interval is set.
[0019]
【The invention's effect】
As described above, in the present invention, the chromatic dispersion of the transmission line optical fiber is set to negative dispersion (normal dispersion) to suppress the spectrum spread of the signal light, and the dispersion compensation interval L _comp to the dispersion length L _d . By setting it optimally, it is possible to optimize transmission characteristic degradation due to crosstalk between signal lights. Since the dispersion compensation interval L _comp can be optimized, it is not necessary to insert an excessive number of dispersion compensators into the transmission line optical fiber.
[0020]
Further, by setting the dispersion value of the transmission line optical fiber to −1 to −2 ps / nm / km, the dispersion compensation interval L _comp for optimizing the deterioration of transmission characteristics due to crosstalk between signal lights can be increased. This is advantageous in system design.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing a simulation result.
FIG. 3 is a diagram showing a simulation result.
FIG. 4 is a diagram showing a simulation result.
[Explanation of symbols]
Reference Signs List 10 optical wavelength multiplexing transmitting terminal stations 11a to 11d transmitter 12 multiplexer 20 optical transmission line 21 transmission line optical fiber 22 optical amplifier 23 dispersion compensating medium 30 optical wavelength multiplexing receiving terminal station 31 demultiplexer 32 receiving dispersion medium 33a to 33d receiver

Claims (6)

A transmission line optical fiber for transmitting wavelength-multiplexed signal light;
A wavelength-division multiplexing transmission device having a dispersion compensating unit inserted into the transmission line optical fiber and compensating for chromatic dispersion of the transmission line optical fiber;
The chromatic dispersion of the transmission line optical fiber is negative dispersion,
Said dispersion compensating means, wherein the transmission line optical supergaussian waveforms of the pulses transmitted by the fiber exp - a _{{(1/2) · (T /} T 0) 2m} T 0 of the (m exponent of the super-Gaussian), The center wavelength λ [nm], the speed of light c [km / s] in the transmission line optical fiber, and the dispersion value D [ps / nm / km] of the transmission line optical fiber at the center wavelength λ [nm]. Dispersion length L _d = T ₀ ² / | λ ² D / 2πc |
Against
0.1 <L _comp / L _d <0.4
An optical wavelength division multiplexing transmission device arranged at intervals of _Lcomp [km] represented by: The pulses transmitted by the transmission line optical fiber is an optical wavelength multiplex transmission apparatus according to claim 1, wherein the waveform is a high public secant waveform sech (T / T _0). The pulses transmitted by the transmission line optical fiber is the waveform Lorentz type waveform ^{_{(1+ (T / T 0)}} 2) ^-1/2 is claim 1 the optical wavelength multiplex transmission apparatus according. 4. The optical wavelength division multiplex transmission apparatus according to claim 1, wherein a dispersion value D of the transmission line optical fiber is -1 to -2 ps / nm / km. 5. The optical wavelength division multiplexing transmission apparatus according to claim 1, wherein an optical amplifier for amplifying signal light is inserted in said transmission line optical fiber. Optical transmission means for transmitting wavelength-division multiplexed light to the transmission path optical fiber, and optical reception means for receiving wavelength-division multiplexed light from the transmission path optical fiber,
The optical transmission means includes a plurality of optical transmitters that generate signal lights having different wavelengths from each other, and a multiplexer that multiplexes the signal lights from the plurality of optical transmitters,
The optical receiving means includes a splitter that splits the transmitted wavelength multiplexed light into signal light of each wavelength, and a receiver that receives the split signal light,
6. The optical wavelength division multiplexing transmission apparatus according to claim 1, wherein said optical receiving means further includes a dispersion medium for dispersion-compensating the signal light demultiplexed by said demultiplexer for each wavelength.

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