JPH10242941A - Optical wavelength multiplex transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of a transmission characteristic owing to mutual phase modulation to be minimum by setting a pulse occultation rate at every wavelength to be the RZ(return to zero) intensity modulation signal of a specified value in the signal system of signal light generated in respective optical transmitters. SOLUTION: A light wavelength multiplex transmission terminal station 10 is provided with the two optical transmitters 11a and 11b generating the signal light of the mutually different wavelengths. The signal light beams of the respective wavelengths outputted from the optical transmitters 11a and 11b are multiplexed in a multiplexer 12 and are transmitted to a light transmission line 20. The signal light is the RZ intensity modulation signal whose pulse occupation rate γ is 0.6<γ<1.0. The optical transmission line 20 is constituted of a transmission line optical fiber 21 transmitting wavelength multiplex signal light, an optical amplifier 22 and a diffusive compensation medium 23. In a light wavelength multiplex reception terminal 30, transmitted wavelength multiplex signal light is multiplexed into the signal light beams of the respective wavelength in a multiplexed 31 and the multiplexed signal light is diffusively compensated for the respective wavelengths in a reception diffusive compensation medium 32. The signal light beams of the respective wavelengths which are diffusively compensated are received in optical receivers 33a and 33b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength division multiplex transmission apparatus for transmitting wavelength division multiplexed signal light. In particular, nonlinear effects of optical fibers (four-wave mixing,
The present invention relates to a technique for optimizing the suppression of transmission characteristic degradation due to cross-phase modulation and chromatic dispersion.

[0002]

2. Description of the Related Art In an optical wavelength division multiplexing transmission system, there is a problem of deterioration of transmission characteristics due to crosstalk between signal lights. The main cause of this crosstalk is nonlinear optical phenomena such as four-wave mixing and cross-phase modulation that occur in the transmission line optical fiber. These phenomena occur when a plurality of optical signals having different wavelengths propagate in the transmission line optical fiber, and interaction occurs between the optical signals. 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 of an optical signal occurs is cross-phase modulation.

In order to suppress four-wave mixing, a method of setting a large chromatic dispersion value of a transmission line optical fiber and arranging a dispersion compensator having a chromatic dispersion value opposite to that of the transmission line optical fiber at every fixed distance is used. It is known (“Study of 10 Gbit / s / ch WDM transmission system using distributed management”, IEICE Technical Report, OCS96-57). Further, in order to suppress the cross phase modulation, a method is known in which the signal format is an RZ intensity modulation signal. For example, a reference (“5 Gb / s 4-wave multiplex 4500 km transmission experiment using RZ code”, 1996 IEICE General Conference B-1139) uses an RZ intensity modulated signal having a pulse occupancy of 0.6 as a signal format. An example in which a transmission experiment was performed is shown.

[0004]

When the average signal light power is the same, the peak value of the signal light power increases as the pulse occupancy decreases, and the optical fiber nonlinear effect (self-phase modulation) for each wavelength. Becomes noticeable. Furthermore, since the influence of dispersion increases as the pulse occupancy decreases, it was unclear whether the pulse occupancy of the signal format described in the above document is actually optimal.

According to the present invention, in a configuration in which a dispersion compensator is arranged in a transmission line optical fiber having a large chromatic dispersion value to suppress four-wave mixing, deterioration of transmission characteristics due to cross-phase modulation can be minimized. An object of the present invention is to provide a wavelength division multiplex transmission device.

[0006]

SUMMARY OF THE INVENTION An optical wavelength division multiplex transmission apparatus comprises:
It comprises an optical transmitting means, an optical transmitting means, and an optical receiving means.
The optical transmitting unit includes a plurality of optical transmitters that generate signal lights having different wavelengths from each other, and a multiplexer that sends the wavelength multiplexed signal light obtained by multiplexing the signal lights output from the respective optical transmitters to the optical transmitting unit. including. The optical transmission unit includes a transmission line optical fiber and a dispersion compensating unit that compensates for chromatic dispersion of the transmission line optical fiber. The optical receiving means includes a demultiplexer that splits the wavelength multiplexed signal light input from the optical transmission means into signal lights of each wavelength, and a plurality of optical receivers that receive the signal lights of each wavelength.

[0007] The dispersion compensating means for compensating for the chromatic dispersion of the transmission line optical fiber is periodically inserted between the optical transmitting means and the optical receiving means. At this time, it may be inserted either before or after the transmission path optical fiber. In the above configuration, in the wavelength division multiplexing transmission apparatus of the present invention, the signal format of the signal light generated in each optical transmitter is such that the pulse occupancy r for each wavelength is 0.6 <r <1.
It is assumed that the RZ intensity modulation signal is 0.

When optical wavelength multiplex transmission is performed by an optical wavelength multiplex transmission apparatus using a transmission line optical fiber having a large chromatic dispersion value and a dispersion compensating means, the relative time difference between pulses caused by the group velocity difference between the channels becomes large. It decreases with each dispersion compensation, and the deterioration of transmission characteristics increases due to crosstalk between signal lights due to cross-phase modulation in the transmission line optical fiber. Therefore, an RZ intensity modulated signal in which the pulse occupation ratio r is optimized in the range of 0.6 <r <1.0 for each wavelength is used. As a result, it is possible to reduce the probability that each wavelength emits light at the same time, and to suppress deterioration in transmission characteristics due to crosstalk during optical wavelength multiplex transmission. Note that even when the number of optical wavelength multiplexes is changed,
There is an optimum value within the range of the pulse occupancy.

When a positive dispersion (abnormal dispersion) is used as the transmission line optical fiber, the spectrum spreads in the signal light to cause crosstalk, and the transmission characteristics deteriorate. Therefore, the chromatic dispersion value D of the transmission line optical fiber is
May be negative. Further, the chromatic dispersion value D is given by D ≦
By setting it to -1 ps / nm / km, it is possible to suppress deterioration of transmission characteristics due to four-wave mixing (claim 2).

An optical amplifier for amplifying the wavelength multiplexed signal light may be inserted in the optical transmission means. The optical receiver may include a dispersion compensator for dispersion-compensating the signal light of each wavelength demultiplexed by the demultiplexer.

[0011]

FIG. 1 shows an embodiment of an optical wavelength division multiplexing transmission apparatus according to the present invention. Here, a configuration example in the case of two-wavelength multiplexing is shown. The apparatus shown in FIG. 1 includes an optical wavelength multiplexing transmitting terminal station 10, an optical transmission line 20, and an optical wavelength multiplexing receiving terminal station 30.

The optical wavelength multiplexing transmitting terminal 10 has two optical transmitters 11a and 11b for generating signal lights having different wavelengths.
And a multiplexer 12 for multiplexing the signal lights of the respective wavelengths output from the optical transmitters 11a and 11b and transmitting the multiplexed signal light to the optical transmission line 20. This signal light has a pulse occupation ratio r of 0.6 <r <1.
0 RZ intensity modulated signal. The optical transmission line 20 includes a transmission line optical fiber 21 for transmitting the wavelength-division multiplexed signal light, an optical amplifier 22 for amplifying the wavelength-division multiplexed signal light transmitted to the transmission line optical fiber 21, and the optical transmission line 20. 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 is a demultiplexer 31 for demultiplexing the transmitted wavelength division multiplexed signal light into signal light of each wavelength.
A dispersion compensating medium 32 for dispersion-compensating the demultiplexed signal light for each wavelength, and optical receivers 33a and 33b for receiving the dispersion-compensated signal light of each wavelength. As the dispersion compensation medium 23 and the reception dispersion compensation medium 32, for example, a dispersion compensation optical fiber or an optical fiber grating is used.

FIGS. 2 and 3 show the results obtained by computer simulation of the relationship between the pulse occupancy of the optical transmitter and the eye opening deterioration (worst channel) of the received waveform in the optical receiver. The condition is that the optical amplifier repeat interval is 50k.
m, and the output of the optical amplifier is 9 dBm / ch. This output of the optical amplifier is an output of the optical amplifier in which transmission characteristic deterioration due to cross-phase modulation becomes remarkable.

FIG. 2 shows the result when dispersion compensation is not performed in the optical transmission line and the receiving end. Optical transmitters 11a and 11b
The bit rate of each is 10 Gbit / s (total bit rate
20 Gbit / s), the pulse occupancy was changed from 0.2 to 1.0, and the eye opening was deteriorated at transmission distances of 100 km and 200 km. From this result, it can be seen that, when the dispersion compensation is not performed, the eye opening deterioration becomes larger as the pulse occupancy is made smaller. This is because the influence of the self-phase modulation and the chromatic dispersion due to the decrease in the pulse occupancy is greater than the effect of the cross-phase modulation suppression.

FIG. 3 shows the result when dispersion compensation is performed in the optical transmission line and the receiving end. The dispersion compensation interval is 100km
And The bit rates of the optical transmitters 11a and 11b are each 10 Gbit / s (total bit rate 20 Gbit / s),
Change the pulse occupancy from 0.2 to 1.0 and set the transmission distance to 20
Eye opening deterioration at 0 km, 500 km, and 1000 km. From this result, it can be seen that when dispersion compensation is performed, the eye opening deterioration is reduced when the pulse occupation ratio r is 0.6 <r <1.0. In addition, it can be seen that the tendency becomes remarkable as the transmission distance increases.

[0017]

As described above, according to the present invention, in an optical wavelength division multiplexing transmission apparatus using dispersion compensation, the signal format of an optical transmitter is changed to an RZ intensity modulated signal having a pulse occupation ratio r of 0.6 <r <1.0. By doing so, it is possible to minimize the deterioration of transmission characteristics due to cross-phase modulation. Further, the chromatic dispersion value of the transmission line optical fiber is set to a negative dispersion (D ≦ −1 ps / nm /
km), it is possible to suppress the spread of signal light spectrum and deterioration of transmission characteristics due to four-wave mixing, and to realize an optical wavelength multiplex transmission apparatus capable of long-distance transmission.

[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 without dispersion compensation.

FIG. 3 is a diagram showing a simulation result with dispersion compensation;

[Explanation of symbols]

 Reference Signs List 10 optical wavelength multiplexing transmitting terminal 11 optical 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 31 demultiplexer 32 receiving dispersion compensating medium 33 light Receiver

 ──────────────────────────────────────────────────の Continued on the front page (72) Norio Okawa, Inventor, Nippon Telegraph and Telephone Corporation, 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (4)

[Claims] An optical transmission means including a transmission line optical fiber, a dispersion compensating means for compensating chromatic dispersion of the transmission line optical fiber, a plurality of optical transmitters for generating signal lights having mutually different wavelengths, An optical transmitting unit including a multiplexer for transmitting the wavelength multiplexed signal light obtained by multiplexing the signal light output from the optical transmitter to the optical transmission unit; and a wavelength multiplexed signal light input from the optical transmission unit. A wavelength division multiplexing transmission apparatus comprising: a demultiplexer for demultiplexing a signal light of a wavelength; and a plurality of optical receivers for receiving the signal light of each wavelength. An optical wavelength division multiplexing transmission apparatus characterized in that the signal format of the signal light is an RZ (return-to-zero) intensity modulation signal in which the pulse occupation ratio r for each wavelength is 0.6 <r <1.0. 2. The chromatic dispersion value D of the transmission line optical fiber is D
2. The optical wavelength division multiplex transmission apparatus according to claim 1, wherein ≤-1 ps / nm / km. 3. The optical wavelength multiplex transmission apparatus according to claim 1, wherein an optical amplifier for amplifying the wavelength multiplexed signal light is inserted in the optical transmission means. 4. The optical wavelength multiplex transmission according to claim 1, wherein the optical receiving means includes a dispersion compensating means for dispersion-compensating the signal lights of the respective wavelengths demultiplexed by the demultiplexer. apparatus.