JPH098773A - Wavelength monitoring method - Google Patents

Abstract

(57) [Abstract] [Purpose] A wavelength division multiplexing optical transmitter or a wavelength division multiplexing optical repeater monitors the wavelength and intensity of each optical signal without demultiplexing each optical signal. [Structure] A part of a wavelength-division multiplexed optical signal 2 is converted into a control electrical signal 4
To the variable wavelength bandpass filter 13 that selectively passes only the optical signal having the unique wavelength corresponding to the frequency of.
The output from the filter 13 is photoelectrically converted by the photodetector 14,
It is sent to the monitoring information generation circuit 15. The monitoring information generation circuit 15 observes the signal from the photodetector while sweeping the frequency of the control signal of the filter, and associates the frequency of the control signal at which this signal becomes maximum with one wavelength of the optical signal. At the same time, the maximum value and the light intensity are associated with each other. The monitoring light source 10-0 is modulated with these associated values, and the monitoring light signal 1-0 is transmitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitoring system in a wavelength division multiplexing optical communication system, and more particularly to a system for monitoring the wavelength and intensity of each optical signal without demultiplexing the wavelength division multiplexing signal.

[0002]

2. Description of the Related Art In a wavelength division multiplexing optical communication system, one or a plurality of optical repeaters are arranged in the middle of a transmission optical fiber, and a transmission distance is increased by collective optical amplification using an optical amplifier in the optical repeater. be able to. However, since the amplification factor of the current optical amplifier is not uniform with respect to the input optical signal wavelength, the intensity may change for each optical signal having a different wavelength when passing through a plurality of optical repeaters. Further, the intensity of an optical signal of a certain wavelength may change due to the characteristics of the optical component. Furthermore, there is a possibility that the wavelength of each optical signal may change due to changes over time in the light source in the wavelength division multiplexing optical transmitter or changes in the surrounding environment. In wavelength-division-multiplexed optical communication, the change of each optical signal wavelength and optical intensity from the design value leads to deterioration of transmission quality. Therefore, it is necessary to stabilize the wavelengths of the optical signals and to make the intensities of the optical signals uniform, and it becomes necessary to monitor that these are maintained. However, in the conventionally proposed wavelength division multiplexing optical communication system, the method of reducing the wavelength dependence of the amplification factor in the optical amplifier and the variation of the optical signal intensity when reaching the receiver are observed and the result is sent to the transmitter. Efforts have been focused on a method of returning and adjusting the output power of each light source, and the intensity and wavelength of each optical signal during fiber transmission have hardly been monitored.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength multiplexing optical communication system, which is a wavelength monitoring system for monitoring the wavelength and intensity of each optical signal without demultiplexing the wavelength multiplexed signal. .

[0004]

In order to achieve the above object, the present invention uses a wavelength tunable bandpass filter in which the wavelength that can be passed changes uniquely corresponding to the frequency of an electric signal given to a control input. Then, the wavelength of each optical signal and the frequency of the control electric signal are made to correspond to each other, and the optical signal strength passed through this variable wavelength bandpass filter is made to correspond to the electric signal strength.

[0005]

When the frequency of the control signal applied to the variable wavelength bandpass filter is swept, the wavelength of the optical signal passing through this variable wavelength bandpass filter also changes. Therefore, input the wavelength-multiplexed signal to the tunable bandpass filter that is sweeping,
When the photodetector photoelectrically converts the optical signal passing through the filter, the intensity of the electric signal output from the photodetector increases when the passing wavelength of the filter matches the wavelength of the optical signal. At this time, the frequency of the control signal and the value of the electric signal correspond to the wavelength and the light intensity of one of the optical multiplexed signals. Therefore, the monitoring signal can be generated by obtaining the values of the frequency and the electrical signal for all the optical signals.

[0006]

FIG. 1 shows an embodiment in which the present invention is applied to a wavelength division multiplexing transmitter. Further, FIG. 2 shows an explanatory diagram of the operation of this embodiment.

The wavelength division multiplex transmission apparatus 100 of FIG. 1 comprises a plurality of light sources (including a data modulation mechanism) 10-1 having different wavelengths,
The optical signals 1-1 and 1-2 output by 10-2 are combined by a multiplexer or optical coupler 11 to generate a wavelength division multiplexed signal 2, which is sent to the optical fiber 200. A part 3 of the wavelength-multiplexed signal 2 is input to the acousto-optic wavelength tunable bandpass filter 13 by the branching device 12. The optical signal that has passed through this acousto-optical wavelength tunable bandpass filter is converted into an electrical signal by the photodetector 14. The intensity of this electric signal is observed by the monitoring information generation circuit 15. The monitoring information generation circuit 15 sweeps the frequency of the acousto-optic wavelength tunable bandpass filter control signal 4 while observing the intensity of the electric signal from the photodetector.

This situation will be described with reference to FIG. Now, it is assumed that the wavelengths of the optical signals 1-1 and 1-2 are λ1 and λ2, respectively. The acousto-optic tunable bandpass filter has a wavelength λ1 when the control signal frequency is F1 and a control signal frequency of F1.
2 has a characteristic of passing the wavelength λ2 (see FIG. 2).
(B)). Here, when the control frequency is swept, the electric signal from the photodetector takes a maximum value when the pass wavelength of the filter matches the optical signal wavelength (FIG. 2 (c)).

In the monitoring information generating circuit 15 of FIG. 1, the frequency (F1 or F2) of the acousto-optical wavelength tunable bandpass filter control signal 5 when the electric signal exhibits a maximum value is set to the wavelength (λ1) of one optical signal. Or λ2). By this series of sweeping operations, the monitoring signal generation circuit associates the wavelengths of all the optical signals included in the wavelength division multiplexed signal with the frequencies of the acousto-optic wavelength tunable bandpass filter control signal. afterwards,
The monitoring information signal 5 is generated from the values of these frequencies, the monitoring light source 10-0 is modulated by this monitoring information signal 5, and the monitoring optical signal 1-0 is sent to the fiber 200. Note that the relationship between the passable wavelength of the acousto-optic wavelength tunable bandpass filter and the frequency of the acousto-optic wavelength tunable bandpass filter control signal does not need to be linear, and may be a unique relationship. However, if the relationship between the passable wavelength of the acousto-optic wavelength tunable bandpass filter and the frequency of the acousto-optic wavelength tunable bandpass filter control signal is not linear, measure the relationship beforehand and use the monitoring information generation circuit. It is necessary to calculate the signal from the measured correspondence.

Although FIGS. 1 and 2 show an example in which an acousto-optic type wavelength tunable bandpass filter is used as the wavelength tunable bandpass filter, it corresponds to the frequency of the electric signal applied to the control input uniquely. Any wavelength tunable bandpass filter having a variable passable wavelength can be used. 1 and 2, the number of light sources is two, that is, the number of wavelength multiplexing is two, but the present invention is applicable to any number of wavelength multiplexing of two or more.

FIG. 3 shows a second embodiment of the present invention. In this example, low frequency oscillators 30-1 and 30-2 are added to the light sources 1-1 and 1-2, respectively, as compared with FIG. The operation of transmitting the monitoring optical signal 1-0 in this embodiment is the same as in the case of FIG. However, the intensity of each light source is minutely modulated at different low frequencies. Therefore, the low frequency corresponding to the optical signal that matches the pass wavelength of the acousto-optic wavelength tunable bandpass filter is also superimposed on the electric signal photoelectrically converted by the photodetector 14. Therefore, by observing this low frequency by the control circuit 15, the optical signal passing through the acousto-optic wavelength tunable bandpass filter at that time can be easily identified. Further, although the embodiment of FIG. 3 shows the case where there are two light sources, that is, the number of wavelength multiplexing is two, the present invention is applicable to any number of wavelength multiplexing of two or more.

FIG. 4 shows a third embodiment of the present invention, and FIG. 5 shows an explanatory view of its operation. In this example, unlike the examples of FIGS. 1 and 3, the present invention is applied to an optical repeater. In FIG. 4, the wavelength division multiplexed signal 2 transmitted from the optical fiber 201 is input to the optical repeater 150. This wavelength-division-multiplexed signal is collectively amplified by the optical amplifier 20, passes through the optical branching device 21 and the optical multiplexer 26, and is sent to the optical fiber 202. A part of the wavelength division multiplexed signal 2 amplified by the optical amplifier is branched by the optical branching device and input to the acoustooptic wavelength tunable bandpass filter. After that, the light passing through this filter is converted into an electric signal by the photodetector 23. The acousto-optic wavelength tunable bandpass filter is swept by the acousto-optic wavelength tunable bandpass filter control signal 7 output from the monitoring information generation circuit 24. The monitoring light source 25 uses the monitoring information signal generated by this monitoring information generation circuit.
Is generated to generate the monitoring light 8 and is output to the optical fiber 202 via the multiplexer 26.

This operation will be described with reference to FIG. Optical signal 1-1
The process of obtaining information on the wavelengths of 1-2 and 1-2 is similar to that of FIG. Here, an example in which the optical intensities of the optical signals 1-1 and 1-2 are different from each other is shown. As shown in FIG. 5A, the intensity of the optical signal 1-1 is I1, and the intensity of the optical signal 1-2 is I2. In this case, the maximum value of the output of the photodetector is P1 or P2 as shown in FIG. That is, the intensity of the optical signal can also be quantitatively observed by the maximum value indicated by the output of this photodetector. From the frequencies F1 and F2 of these acousto-optical wavelength tunable bandpass filter control signals and the maximum values P1 and P2 of the photodetector output, it is possible to generate monitoring information regarding the wavelength and the light intensity of the optical signal. Further, in the embodiments of FIGS. 4 and 5, there are two light sources, that is, the number of wavelength division multiplexing is two.
In the present invention, the wavelength multiplexing number is 2 or more,
It is applicable in any number of cases.

[0014]

According to the present invention, it is possible to quantitatively monitor the wavelength and the light intensity of each optical signal transmitted in the wavelength division multiplexing optical communication, so that it is possible to detect a failure in the communication system at an early stage. Moreover, since the wavelength of each optical signal can be quantitatively transmitted to the receiver, adjustment of the demultiplexing wavelength of the demultiplexer, adjustment of the wavelength tunable filter for selecting the received optical signal, and the like become easy. Furthermore, since the wavelength and intensity of each optical signal can be quantitatively obtained, it is possible to control the wavelength of the light source, control the light output of the light source, adjust the amplification factor of the optical repeater, etc. from this information, and Optimal transmission conditions can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing that the wavelength of each signal light of wavelength division multiplexing optical communication can be observed by the present invention.

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

FIG. 4 is a block diagram showing a third embodiment of the present invention.

FIG. 5 is an explanatory view showing that the light intensity can be observed at the same time as the wavelength of each signal light of wavelength division multiplexing optical communication according to the present invention.

[Explanation of symbols]

1-0 ... Monitoring optical signal, 1-1 ... Optical signal, 1-2 ... Optical signal, 2 ... Wavelength multiplexed signal, 3 ... Wavelength multiplexed signal, 4 ... Filter control signal, 5 ... Monitoring information signal, 10-0 ... Monitoring light source, 10-1 ... Light source, 10-2 ... Light source, 11 ... Optical multiplexer or optical coupler, 12 ... Optical branching device, 13 ... Wavelength variable bandpass filter, 100 ... Wavelength multiplex optical transmitter, 200 ... Optical fiber.

Claims (6)

[Claims] 1. In a wavelength division multiplexing optical transmitter or wavelength division multiplexing optical repeater of a wavelength division multiplexing optical communication system, the wavelength of each optical signal of the wavelength division multiplexed signal is observed, and each observed wavelength is uniquely assigned to an electrical signal. Having a mechanism for associating with frequency, wavelength information of each optical signal quantified using the value of the frequency, the wavelength multiplexing optical repeater or wavelength of the downstream or upstream connected by an optical transmission line A wavelength monitoring system characterized by transmitting to a multiplex receiver and monitoring the wavelength of each optical signal by the wavelength multiplex optical repeater or the wavelength multiplex receiver. 2. A wavelength-division-multiplexing optical transmitter or a wavelength-division-multiplexing optical repeater of a wavelength-division-multiplexing optical communication system observes the wavelength and intensity of each optical signal of the wavelength-division-multiplexing signal, and makes each observed wavelength uniquely electric. Having a mechanism for associating with the frequency of the signal, the wavelength information of each optical signal quantified using the value of the frequency, downstream or upstream wavelength-multiplexed optical repeater connected by an optical transmission line, or While transmitting to the wavelength division multiplexing receiver, the information of the intensity of each observed optical signal is also transmitted to the wavelength division multiplexing optical repeater or the wavelength division multiplexing receiver, and the wavelength division multiplexing optical repeater or the wavelength division multiplexing receiver respectively The wavelength monitoring method is characterized in that the wavelength and intensity of the optical signal are monitored. 3. A part of the wavelength-division multiplexed signal is input to a wavelength tunable bandpass filter whose passable wavelength changes corresponding to a frequency of an electric signal supplied to a control input, and the wavelength tunable signal is tuned. The optical signal passed through the bandpass filter is converted into an electric signal by a photodetector, and the frequency at which the electric signal becomes maximum when the frequency is swept is the wavelength of one optical signal in the wavelength division multiplexed optical signal. By associating, the wavelength of each optical signal is quantified using the frequency of the electric signal to generate a monitoring information signal, and the monitoring optical signal is generated by modulating the monitoring optical light source with the monitoring information signal, The monitoring optical signal is transmitted to a downstream or upstream wavelength multiplex optical repeater or wavelength multiplex receiver connected by an optical transmission line, and the wavelength multiplex optical repeater or wavelength multiplex receiver is used. Wavelength monitoring system according to claim 1 for monitoring the wavelength of the people of the optical signal. 4. A part of the wavelength-division multiplexed signal is input to a wavelength tunable bandpass filter in which a wavelength that can be passed changes corresponding to a frequency of an electric signal supplied to a control input, and the wavelength tunable signal is tuned. The optical signal passed through the bandpass filter is converted into an electric signal by a photodetector, and the frequency at which the electric signal becomes maximum when the frequency is swept is the wavelength of one optical signal in the wavelength division multiplexed optical signal. With matching
By associating the maximum value of the electric signal with the intensity of the optical signal to generate a monitoring information signal by digitizing the wavelength and intensity of each optical signal, and by modulating the monitoring light source by the monitoring information signal. A monitoring optical signal is generated, and the monitoring optical signal is transmitted to a downstream or upstream wavelength-multiplexing optical repeater or wavelength-multiplexing receiving device connected by an optical transmission line, and the wavelength-multiplexing optical repeating device or wavelength-multiplexing receiving device respectively 2. The wavelength and intensity of the optical signal of the device are monitored.
Wavelength monitoring method described. 5. A wavelength monitoring method using an acousto-optic type wavelength tunable bandpass filter utilizing an acoustooptic effect as the wavelength tunable bandpass filter according to claim 3 or 4. 6. The monitoring information signal according to claim 3, 4 or 5, instead of modulating the monitoring light source with the monitoring information signal to generate a monitoring light signal, the monitoring information signal is supplied as an electrical signal to a downstream or upstream side. A wavelength monitoring system that transmits to a wavelength division multiplexing optical repeater or wavelength division multiplexing receiver, and monitors the wavelength and intensity of each optical signal at the wavelength division multiplexing optical repeater or wavelength division multiplexing receiver.