JP3090197B2 - WDM optical communication equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical communication device, and more particularly, to a wavelength division multiplexing optical system which automatically reduces deterioration of transmission characteristics due to four-wave mixing (FWM), which is one of the nonlinear effects of optical fibers. Related to a communication device.

[0002]

2. Description of the Related Art As an effective technique for expanding the capacity of an optical communication system, a plurality of signal lights having different wavelengths are wavelength-multiplexed, and a wavelength transmitted as a wavelength-multiplexed signal light through one optical fiber is used. A multiplex (WDM) optical transmission system is known. However, while being recognized as such an effective technique, in the WDM optical transmission system, the case where WDM transmission is performed using a dispersion-shifted optical fiber (DSF) having zero dispersion in a 1.5 μm band is used. In addition, four-wave mixing (FWM), one of the nonlinear effects of optical fibers,
It is also known that there is a drawback that the transmission characteristics are degraded. Since this FWM is more likely to occur as the variance is closer to zero, the above-mentioned DSF causes strong FWM, and the transmission characteristics are greatly deteriorated. In particular, FWM occurs most efficiently when the wavelength of one channel coincides with the zero-dispersion wavelength, or when the zero-dispersion wavelength is in the middle of the wavelengths of the two channels. Inoue, "Four-Wave Mixing in an Optical
Fiber in the Zero-DispersionWavelength Region ", Jo
urnal of Lightwave Technology, Vol.10, No.11, pp.1
553-1561, 1992).

In order to suppress the FWM, it is effective to separate the wavelength of the signal light from the zero dispersion wavelength of the optical fiber sufficiently and arrange the wavelengths so that the signal light has a finite chromatic dispersion. Conventionally, based on such a principle, FW
Japanese Patent Application Laid-Open No. 7-1 has proposed a method for suppressing M.
Japanese Unexamined Patent Publication No. 07069 (hereinafter, referred to as a conventional example) is exemplified. In the conventional WDM optical transmission system, as shown in FIG. 4, a guard band for FWM suppression of a predetermined bandwidth including a zero-dispersion wavelength is set, and signal lights of a plurality of channels to be multiplexed are transmitted to the guard band. FWM is suppressed by adopting a wavelength arrangement that is arranged on one of the outer short wavelength side and the longer wavelength side.

[0004]

However, in order to suppress the FWM by the technique disclosed in the above-mentioned conventional example, it is necessary to measure all the dispersion values of the wavelength in the optical fiber before laying the optical communication device. However, there is a problem that labor costs are required for measuring the dispersion and adjusting the wavelength, thereby increasing the cost of the entire apparatus.

Accordingly, the present invention provides a wavelength-division multiplexing optical communication apparatus for automatically reducing deterioration of transmission characteristics due to a nonlinear effect of an optical fiber typified by four-wave mixing (FWM) while suppressing an increase in the number of parts as much as possible. The purpose is to provide.

[0006]

In order to solve the above-mentioned problems, the present invention uses WDM signal light transmitted through an optical fiber also for dispersion measurement and suppresses an increase in the number of parts. Further, the present invention switches the channel having the wavelength closest to the zero dispersion wavelength obtained from the measured dispersion characteristics to a spare channel having a different wavelength and transmits the same.
It was decided to suppress the occurrence of WM.

More specifically, the present invention provides the following wavelength division multiplexing optical communication device as means for solving the above-mentioned problems.

That is, according to the present invention, as the first wavelength division multiplexing optical communication device, there is provided a wavelength dispersion measuring means for measuring the wavelength dispersion of the transmission line using the wavelength division multiplexed signal light transmitted through the transmission line. A wavelength division multiplexing optical communication device characterized by comprising:

According to the present invention, as a second wavelength division multiplexing optical communication device, the first wavelength division multiplexing optical communication device may include at least one set of optical transceivers, and An optical transceiver having a wavelength different from that of the wavelength multiplexed signal light to be transmitted according to the chromatic dispersion measured using the wavelength multiplexed signal light to be transmitted by the chromatic dispersion measuring means. Among them, the signal light of the channel using the wavelength closest to the zero dispersion wavelength of the transmission line is made unusable, and the data signal scheduled to be transmitted using the channel determined by the unusable signal light is used as the spare. A wavelength-division multiplexing optical communication device characterized by switching to a channel for transmission is obtained.

Further, according to the present invention, as a third wavelength division multiplexing optical communication device, in the second wavelength division multiplexing optical communication device, as a result of the measurement of the chromatic dispersion by the chromatic dispersion measuring means, the vicinity of the zero dispersion wavelength is obtained. In the case where there are two or more channels, the wavelength multiplexing optical communication apparatus is characterized in that the channel on the abnormal dispersion side is preferentially disabled from the channel on the normal dispersion side and the channel is switched to the spare channel.

Here, as a method of measuring the dispersion characteristics, for example, the WDM signal light is intensity-modulated with the same signal, transmitted through an optical fiber, and the phase difference between the intensity-modulated signals of the respective channels is measured at the receiver side. Calculate the variance by doing
A so-called phase difference method can be applied. Also, WDM
The signal light is phase-modulated (or frequency-modulated) by the same signal and transmitted, and the intensity of the AM component is measured on the receiver side by using the effect of phase-intensity (PM-AM) conversion by chromatic dispersion. A so-called PM-AM method for measuring dispersion may be applied. The method of measuring the dispersion characteristics is not limited to these, and other methods can be applied.

In the wavelength division multiplexing optical communication apparatus according to the present invention, the function of the conventional wavelength division multiplexing measurement apparatus is realized by also using the parts of the wavelength division multiplexing optical communication apparatus, and the increase in the number of parts can be suppressed. Further, the zero-dispersion wavelength can be determined from the dispersion characteristics thus measured.

Further, according to the present invention, when configuring an n-channel (where n is an integer of 2 or more) WDM optical communication apparatus, signal lights of different wavelengths of n + m (where m is an integer of 1 or more) are used in advance. Have it ready. Then, the zero-dispersion wavelength measured by the above method is changed from channel 1 to channel n.
If the signal light is within the optical band occupied by the signal light, the signal light of the channel having the wavelength closest to the zero dispersion wavelength is turned off, the data signal of the channel is switched to the channel (n + 1), and the signal of a different wavelength is output. Transmit using light. As a result, there is no signal light that matches or approaches the zero-dispersion wavelength, so that the generation efficiency of FWM can be significantly reduced. As a result, transmission characteristics by FWM can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a wavelength division multiplexing optical communication apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a configuration example of a wavelength division multiplexing optical communication apparatus according to a first embodiment of the present invention.
In the first embodiment, the concept of the present invention is applied to an 8-channel WDM optical communication device with 10 Gb / s per channel. In the present embodiment, one spare channel is prepared, and a set of optical transceivers is prepared accordingly. A total of nine optical transceivers constitute one system. The input data signals 101 to 108 to be transmitted are
The signal is passed through an 8-input / 9-output selector 1 which is switched by an external control signal 6, and then transmitted to nine optical transmitters 201 to 209.
Drive eight of the optical transmitters. 9 optical transmitters 20
1 to 209 are 3 from 1530 nm to 1562 nm.
Signal light having different wavelengths (λ1 to λ9) is output at equal frequency intervals of 500 GHz (corresponding to a wavelength interval of about 4 nm) in a 2 nm optical band. Each of the optical transmitters 201 to 209 is configured by employing an intensity modulation method, and uses a lithium niobate (LiNbO 3, hereinafter referred to as LN) Mach-Zehnder (MN) by using an input data signal.
Z) By driving the light intensity modulator, the signal light output from the semiconductor laser is intensity-modulated and output as signal light. These optical transmitters 201 to 209 can turn on / off the intensity modulation or turn on / off the signal light itself according to the control signal 7. The signal light output from the optical transmitters 201 to 209 is
Are wavelength multiplexed (WDM). In the present embodiment, this wavelength-multiplexed WDM signal light is input to a common polarization-independent optical intensity modulator 3 and then transmitted through an optical amplifier 9 and a dispersion-shifted optical fiber (DSF) 10 having a span of 100 km. Transmission is performed using the configured optical amplification relay transmission line. On the receiving side, the WDM signal light after transmission is separated by the optical demultiplexer 11 into signal light of each wavelength. The polarization independence of the light intensity modulator 3 can be realized by connecting two light intensity modulators in multiple stages so that the optical axes are orthogonal to each other in the case of an LN modulator. Further, in the semiconductor electro-absorption (EA) type optical intensity modulator, it is relatively easy to make the polarization independent. The optical wavelength-separated signal lights are split by the optical splitting coupler 12, respectively.
One is to the dispersion measuring circuit 14, and the other is to the optical receivers 301 to 303.
09 respectively. The data signals demodulated by the optical receivers 301 to 309 are supplied to a 9-input 8-output selector 13.
After that, the data is output as output data signals 401 to 408. In the present embodiment, a programmable one-chip microcomputer is used for both the controller 5 on the transmitting side and the controller 19 on the receiving side. However, the controller 5 may be configured only by hardware using an electric circuit.

Next, the procedure of dispersion measurement and channel setting will be described. In the present embodiment, the controller 5 on the transmission side transmits the optical transmitter 2 when the WDM optical communication apparatus starts up.
Control is performed using the control signal 7 so that all of 01 to 209 are turned on to output signal light. Also, the controller 5
The control signal 7 is output so that all the signal lights of the first to ninth channels output unmodulated continuous (CW) light.
Is used to control the optical transmitters 201 to 209. next,
The controller 5 turns on the signal generator 4 using the control signal 8.
To generate a 1 GHz sine wave signal. The signal generator 4 drives the light intensity modulator 3 with the sine wave signal.
The light intensity modulator 3 collectively modulates the intensity of the WDM signal. On the receiving side, the signal light after wavelength separation input from the optical branching coupler 12 is received by the photodetector array 15, and a sine wave signal component for each wavelength is obtained. The signal regenerator 18 regenerates a sine wave signal from the ninth channel signal and outputs the signal to the phase detector 17. Phase detector 17
Receives the signal of each channel from the selector 16 switched by the control signal 21 from the controller 19 on the receiving side,
The phase difference of the sine wave signal for each wavelength with respect to the sine wave signal reproduced by the signal regenerator 18 is measured in order. FIG.
An example of measuring this phase difference will be described. The controller 19 calculates the propagation delay time difference from the frequency and phase difference of the sine wave, and further calculates the dispersion characteristics by differentiating the propagation delay time difference with the wavelength. Here, the wavelength at which the dispersion becomes zero is the zero dispersion wavelength. In the present embodiment, the number of data is limited by the number of wavelengths.
We decided to supplement the data. In the measurement example shown in FIG.
In this case, the fourth channel is switched to the spare channel because the wavelength of the fourth channel is closest to the measured zero dispersion wavelength. For this purpose, the controller 19 notifies the controller 5 on the transmission side of the zero-dispersion wavelength using the uplink monitoring control signal line 23. The controller 5 compares the measured zero-dispersion wavelength with the wavelength of each channel stored in the controller 5 in advance, finds the channel having the wavelength closest to the zero-dispersion wavelength, and controls the signal light of the channel. Off at signal 7
At the same time, the selector 1 switches the input data signal to be transmitted on that channel to the ninth channel which is a spare channel. Other input data signals are directly input to the respective channels. A schematic diagram of this wavelength switching is also shown in FIG. Further, the controller 5 turns off the output of the signal generator 4 with the control signal 8 and turns off the intensity modulation by the sine wave signal. Subsequently, the controller 5 uses the control signal 7 to turn on the modulation of the optical transmitters other than the channel close to the zero-dispersion wavelength that has been turned off, and modulates the signal light. The controller 5 sets the switched channel number to
The controller 19 is notified using the downlink monitoring control signal line 22. The controller 19 controls the selector 13 with the control signal 20 and switches the output port of the channel number turned off by transmission so that the reception signal from the ninth channel is output.

In the present embodiment, by performing the above-described dispersion measurement and a series of operations of channel arrangement, the influence of FWM is automatically suppressed, and stable reception is performed on all channels. Was completed.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention. In the second embodiment, the PM-AM method is used as the dispersion measurement method. For wavelength, bit rate, number of channels, number of spare channels, and transmission path,
This is the same as the first embodiment described above. Optical transmitter 201
209 are wavelength-division multiplexed while maintaining all polarization states in an optical multiplexer 2 composed of a polarization preserving coupler, input to a common LN phase modulator 24, and input to a 1 GHz sine wave signal. Is phase modulated. Dispersion measuring circuit 14 on the receiving side
Then, the signal light of each wavelength is received by the photodetector array 15, the intensity component of the PM-AM converted sine wave signal is detected by the intensity detector 25 for each wavelength, and the variance is controlled by the controller 19. Measure. If the variance is zero, no PM-AM conversion is performed, and the wavelength at which the intensity component of the sine wave signal is minimum corresponds to the zero-dispersion wavelength. In the present embodiment, the wavelength of one of the two channels close to the zero-dispersion wavelength determined in this way is ± 1 nm from the zero-dispersion wavelength.
If it is within the range, the channel is switched off. In addition, both channels are ± 1 from the zero dispersion wavelength.
When the distance is at least nm, the channel on the abnormal dispersion side is preferentially turned off over the channel on the normal dispersion side.

In this embodiment for performing this control,
Since the channel on the normal dispersion side is less likely to generate FWM than the channel on the extraordinary dispersion side with respect to the zero-dispersion wavelength, the deterioration due to the FWM can be minimized. In addition, there was no difference in the dispersion measurement result between the PM-AM method and the phase difference method.

Although the embodiments of the present invention have been described above, the present invention is not limited to these configurations, and various modifications are possible.

In the embodiment of the present invention, the wavelength is 1.5 μm
Although the band semiconductor laser is used, the wavelength is not limited to this, and a semiconductor laser of any wavelength may be used. Further, the laser is not limited to a semiconductor laser, but may be any laser such as a gas laser, a solid laser, and an organic laser.

In the embodiment of the present invention, the wavelength interval has been described as being equal to 4 nm. However, the present invention is not limited to this. The wavelength interval may be wider or narrower, or may be unequal. The value of ± 1 nm as the switching range set in the second embodiment has better characteristics when it is changed according to the wavelength interval. The wavelength of the spare channel may be on the long wavelength side or the short wavelength side of the optical band of the WDM signal light, or may be in the optical band of the WDM signal light as long as it is away from the zero dispersion wavelength.

In the embodiment of the present invention, an optical fiber having a zero dispersion in the 1.5 μm band has been described, but the optical fiber is limited to a 1.5 μm zero dispersion optical fiber. However, the present invention is effective for optical fibers of any kind and dispersion.

In the embodiment of the present invention, the wavelength division multiplexing optical communication apparatus has been described as being applied to an optical amplifying repeater transmission system. However, the present invention can be applied to a repeaterless transmission system.

In the present embodiment, the result of the bit rate of 10 Gb / s has been described, but the present invention is not limited to this, and may be faster or slower.
Similarly, the number of channels is not limited to eight, but may be more or less.

In this embodiment, an example in which LN is used as a light intensity modulator has been described. However, any material may be used as long as the light intensity can be modulated with respect to an input signal. Not only MZ type and electroabsorption (EA) type, but also acousto-optic effect type, electro-optic effect type, polarization rotation type,
Any type of light intensity modulator, such as those utilizing nonlinear effects, can be used. The input signal does not necessarily need to be electric, but may be a light intensity modulator controlled by light. The same applies to the optical phase modulator, which does not specify the material, the configuration, the effect used, etc., and any type of optical phase modulator that changes the phase with respect to the input signal can be used. It is possible. Further, the drive current of the semiconductor laser may be modulated to perform frequency modulation. Also, WD
The M signal light was modulated as a sinusoidal wave, but each optical transmitter may be equipped with an intensity modulator or a phase modulator, or may be modulated using the optical modulator originally built for data modulation. May be.

In the embodiment of the present invention, the intensity modulation / direct detection reception system is used as the modulation / demodulation system. However, the present invention is not limited to this, and the modulation systems include frequency modulation, phase modulation, polarization modulation, and duo modulation. Any modulation method such as binary modulation can be applied. The same applies to the demodulation method, and any demodulation method such as a combination of an optical interferometer and direct detection detection or coherent detection can be applied.

Although an example has been described in which the optical transmitters 201 to 209 employ an external modulation method using an external modulator, a direct modulation method is also possible.

As the optical multiplexer 2 and the optical demultiplexer 11, those composed of optical fiber couplers, those using diffraction gratings (gratings), arrayed waveguide gratings (AWG), fiber Bragg gratings, MZ interference Any type of optical multiplexer / demultiplexer, such as a meter, can be used.

In the embodiment of the present invention, two examples of the phase difference method and the PM-AM method have been described as methods of dispersion measurement. However, the present invention is not limited to this, and measurement is performed while changing the wavelength. Any measurement method may be used as long as the method is used. Further, the modulation for measuring the dispersion characteristic is not limited to a sine wave signal, but may be any form such as a rectangular wave, a triangular wave, or a sawtooth wave as long as a change in phase difference or intensity can be measured. Further, the frequency of the signal is not limited to 1 GHz, but may be set to an optimum frequency according to the value of chromatic dispersion and the required resolution. It is also possible to modulate with a clock signal corresponding to the data signal.
Further, in the first embodiment, the phase difference is measured based on the sine wave signal detected from the channel 9 serving as the spare channel, but the reference may be any channel. Also, all WD
The M signal light may or may not be used for dispersion measurement.

In the embodiment of the present invention, the case where there is one spare channel has been described. However, if the cost permits, two or more spare channels are prepared and two or more channels are switched to the spare channel. This can further suppress the influence of FWM. Also,
The number of channels to be switched is not limited to the number of spare channels, and all input data signals and channels to be used may be switched so that the relationship between channels and wavelengths can be easily controlled.

In the embodiment of the present invention, the channels are switched by the electric selectors 1, 13, and 16, but may be switched by an optical switch. Further, this selector may be a combination of switches for simply switching two paths, or a switch capable of complete cross-connection. Further, the wavelength may be converted and switched to the spare channel. Further, the wavelength conversion may be entirely performed in the optical region, or a method of modulating the signal light having the wavelength of the spare channel after performing the electric reproduction may be used.

In the embodiment of the present invention, the photodetector array 15 used for dispersion measurement does not need to be an array, and a plurality of single photodetectors may be used. In addition, if switching is performed using an optical switch, only one photodetector may be used.

The transmission-side controller 5 and the reception-side controller 19
The monitoring control signal lines 22 and 23 used for communication with the wireless communication device may be any communication means, not limited to wired or wireless communication, and may also include electric signals, optical signals, SDH header signals, wavelength multiplexing, and optical signals on different paths. Any means such as fiber, telephone, and the Internet may be used.

[0035]

As described above, according to the present invention,
It is possible to provide a wavelength division multiplexing optical communication device that automatically reduces deterioration due to nonlinear effects (particularly, four-wave mixing, FWM) of an optical fiber while suppressing an increase in the number of parts as much as possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a measurement example of a phase difference and switching of a zero-dispersion wavelength and a channel in the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a diagram showing an example of a channel arrangement with respect to a zero dispersion wavelength in a conventional example.

[Explanation of symbols]

 Reference Signs List 1 selector 2 optical multiplexer 3 optical intensity modulator 4 signal generator 5 controller 6 switching signal 7 control signal 8 control signal 9 optical amplifier 10 optical fiber 11 optical demultiplexer 12 optical branch coupler 13 selector 14 dispersion measuring circuit 15 light Detector array 16 selector 17 phase detector 18 signal regenerator 19 controller 20 switching signal 21 switching signal 22 supervisory control signal line 23 supervisory control signal line 24 optical phase modulator 25 intensity detector 101-108 input data signal 201 -209 Optical transmitter (Tx1-Tx9) 301-309 Optical receiver (Rx1-Rx9) 401-408 Output data signal

Claims (7)

(57) [Claims] 1. A wavelength-division multiplexing optical communication device comprising a chromatic dispersion measuring means for measuring chromatic dispersion of a transmission line, wherein the chromatic dispersion measuring means also uses multiplexed signal light for chromatic dispersion measurement. A wavelength division multiplexing optical communication device characterized by the above-mentioned. 2. The wavelength multiplexing optical communication device according to claim 1, wherein at least one set of optical transceivers having an wavelength different from the wavelength multiplexed signal light to be transmitted is used as a spare channel in advance. According to the chromatic dispersion measured by using the wavelength-division multiplexed signal light to be transmitted by the wavelength-dispersion measuring means, of the wavelength-division multiplexed signal light to be transmitted, the wavelength closest to the zero-dispersion wavelength of the transmission line is set. Disable the signal light of the channel to be used,
A wavelength-division multiplexing optical communication device, wherein a data signal to be transmitted using a channel determined by the unusable signal light is transmitted by switching to the spare channel. 3. The wavelength division multiplexing optical communication device according to claim 2, wherein as a result of the chromatic dispersion measurement by the chromatic dispersion measuring means, if two or more channels exist near the zero dispersion wavelength, the normal dispersion side. A wavelength-division multiplexing optical communication apparatus characterized in that a channel on the anomalous dispersion side is preferentially disabled over a channel and is switched to the spare channel. 4. The wavelength-division multiplexing optical communication device according to claim 1, wherein the chromatic dispersion measuring unit is configured to perform a predetermined operation when the wavelength-division multiplexing optical communication device functions as a transmitter. The wavelength-division multiplexed signal light is used for collectively performing intensity modulation on the wavelength-division multiplexed signal light and outputting the new wavelength-division multiplexed signal light to the optical fiber. When functioning as a wavelength, the wavelength is characterized by receiving the new wavelength multiplexed signal light and measuring the dispersion by measuring the phase difference of the intensity modulation signal in each channel. Multiplexed optical communication device. 5. The wavelength-division multiplex optical communication device according to claim 1, wherein the chromatic dispersion measuring device is configured to perform a predetermined operation when the wavelength-division multiplex optical communication device functions as a transmitter. The wavelength-division multiplexed optical communication apparatus performs phase modulation on the wavelength-division multiplexed signal light at a time using a signal, and outputs the resultant to the optical fiber as a new wavelength-division multiplexed signal light. When functioning as, receiving the new wavelength multiplexed signal light, by measuring the intensity component in each channel, using the effect of phase-intensity conversion due to chromatic dispersion, to measure the dispersion Wavelength multiplexing optical communication device. 6. Using wavelength multiplexed signal light transmitted through a transmission line
To measure the chromatic dispersion of the transmission line
Having chromatic dispersion measuring means for detecting the wavelength.
Characteristic wavelength multiplexing optical communication device. 7. A wavelength multiplexed signal light transmitted through a transmission line is used.
To measure the chromatic dispersion of the transmission line
Wavelength dispersion measuring means for detecting wavelength and the zero-dispersion wave
Disable the signal of the wavelength closest to the length and separate this signal.
Means for switching to longer wavelengths.
Heavy light communication device.