JPH11122221A - Optical communication system, its optical transmitter and wavelength selector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To select the signal of a desired wavelength while crosstalk is suppressed to a minimum by previously overlapping identification signals having different frequencies with the light signals of respective channels on a transmission side and controlling a wavelength selector so that the amplitude of the identification signal becomes maximum on a reception side. SOLUTION: The identification signal of fk, which is overlapped with the light signal of the desired wavelength, and which corresponds to the light signal of wavelength λk, for example, is taken out from output of PD53 in BPF 61 in accordance with a control signal from the outside. The amplitude component of the identification signal of fk, which is taken out in a rectifier 66, is given to a phase shifter 62 with a low frequency signal fosc from a low frequency oscillator 65. The phases of both signals are compared and the result is given to an adder 64 through LPF 63. An adder 64 adds fosc of the low frequency oscillator 65 to the output of LPF 63 and the value is given to a variable wavelength light band pass filter OTF 51.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system realized as, for example, a wavelength multiplexing optical communication system, and an optical transmitter and a wavelength selector thereof.

[0002]

2. Description of the Related Art In recent years, technical development on a wavelength division multiplexing optical communication system has been actively pursued. Under these circumstances, various types of systems have been developed, and a system in which a wavelength selector is provided on the receiving side to select and receive an optical signal having a predetermined wavelength from wavelength multiplexed light has been developed. is there. FIG. 9 shows an example of such a wavelength multiplexing optical communication system.

The wavelength division multiplexing optical communication system shown in FIG. 9 comprises a plurality of distributed feedback lasers (DFB-LD) 1-1 to 1-n which oscillate and output optical signals λ1 to λn having different wavelengths.
Are respectively driven by data signals, and the intensity-modulated output light is wavelength-multiplexed by the optical coupler 2 and transmitted to the optical receiver 4 via the optical fiber 3. A wavelength selector 5 is provided on the input side of the optical receiver 4, and a control signal (not shown) from the outside is provided.
, An optical signal having a desired wavelength is selected from the wavelength multiplexed light and guided to the optical receiver 4.

The wavelength selector 5 includes a variable wavelength optical bandpass filter (OTF) 51 such as an acousto-optic filter, a Fabry-Perot filter, and a dielectric multilayer filter, an optical splitter 52, and a photodiode (PD) 53. , A control unit 54, the output light of the OTF 51 is partially branched by an optical splitter 52, photoelectrically converted by a photodiode 53, and a control signal is fed back from the control unit 54 to the OTF 51 based on the photoelectric conversion output. Has become.

By the way, the center wavelength of the OTF 51 and the wavelength of each channel may deviate from the set values due to the influence of ambient temperature change and aging. In order to avoid the deterioration of the reception characteristics due to this, the control unit 54 is provided with a so-called line lock function to stabilize the reception characteristics.

FIG. 10 shows the configuration of the control unit 54. The control unit 54 includes a phase comparator 541, a low-pass filter (LPF) 542, an adder 543, and a low-frequency oscillator 5
44. Then, the output of the PD 53 and the output of the low-frequency oscillator 544 are compared in phase by the phase comparator 541, and are guided to the adder 543 via the low-pass filter 542. The output of the low-frequency oscillator 544 and a control voltage from the outside are given to the adder 543, and the added value is fed back to the OTF 51.

[0007] According to the above configuration, it is possible to stabilize the reception characteristics irrespective of the change in the operating conditions, but on the other hand, it has the following disadvantages. That is, in the above configuration, since the intensity of the optical signal itself that has passed through the OTF 51 is observed, the intensity of the optical signal of each wavelength included in the wavelength-division multiplexed light and the central wavelength of the OTF 51 when the wavelength interval varies. Sometimes deviated from a desired value.

For example, as shown in FIG. 11, even if an attempt is made to match the characteristics of the OTF 51 to an optical signal having a wavelength of λ2, if the intensity of an optical signal having an adjacent wavelength of λ3 is too strong or the wavelength interval is too narrow, , The center wavelength of the OTF 51 may be shifted from the optical signal of λ3. This shift is caused by the optical receiver 4
In this case, crosstalk is caused, and the receiving characteristic is deteriorated.

[0009]

As described above, in the optical communication system using the conventional wavelength selector, the filter of the wavelength selector is monitored by monitoring the intensity itself of the optical signal passing through the variable wavelength optical bandpass filter. The characteristics were adjusted. For this reason, if the wavelength interval of the wavelength-multiplexed optical signal varies or the intensity differs, the center wavelength of the optical filter may deviate from the set value, causing crosstalk and causing the received signal to be degraded. There was a problem that it easily deteriorated.

[0010] The present invention has been made in view of the above circumstances,
An object of the present invention is to provide an optical communication system capable of selecting a signal of a desired wavelength while minimizing crosstalk even when wavelength intervals and optical power levels vary, an optical transmitter and a wavelength selector thereof. Is to provide.

[0011]

In order to achieve the above object, the present invention provides a wavelength multiplexing optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed on a transmitting side by a wavelength selector on a receiving side. In an optical communication system that selects and receives an optical signal of a wavelength, the transmitting side superimposes an identification signal having a different frequency on the optical signal of each channel in advance, and the receiving side superimposes the optical signal on the receiving channel. The wavelength selector is controlled so that the amplitude of the identification signal is maximized.

Further, according to the present invention, an optical signal having a predetermined wavelength is selected and received by a wavelength selector on a receiving side from a wavelength multiplexed optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed on a transmitting side. In the optical communication system, on the transmitting side, identification signals having different frequencies are superimposed on the optical signals of the respective channels in advance, and on the receiving side, the amplitude of the identification signals superimposed on the optical signals of the receiving channels and the amplitudes of signals other than the receiving channels are compared. The wavelength selector is controlled so that the ratio or difference between the sum of the amplitudes of the identification signals respectively superimposed on the optical signals becomes maximum.

In this way, even if the wavelength intervals of the wavelength-multiplexed optical signals vary or the intensity differs, the receiving side can reliably identify each channel based on the identification signal. become. Therefore, the absolute value of the identification signal level of the desired reception channel is maximized, or the ratio or difference between the identification signal level of the desired reception channel and the sum of the identification signals of the other channels is maximized. By doing so, the characteristics of the optical filter can always be optimally adjusted. This makes it possible to minimize the deterioration of the receiving characteristics due to the occurrence of crosstalk.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 shows a basic configuration of an optical communication system according to a first embodiment of the present invention. In addition,
The same parts as those in FIG. 9 are denoted by the same reference numerals, and redundant description will be omitted.

The optical communication system of the present embodiment has substantially the same configuration as that of the conventional optical communication system, except that data for driving each distributed feedback laser (DFB-LD) 1-1 to 1-n is used. An identification signal having a different frequency (frequency is f1 to fn) is superimposed on the signal, and the configuration of the control unit 54 is changed (reference numeral is 6).

FIG. 2 shows the configuration of the control unit 6 in the present embodiment. The control unit 6 includes a band pass filter (BPF) 61
, A phase comparator 62 and a low-pass filter (LPF) 6
3, an adder 64, a low frequency oscillator 65, and a rectifier 66
And Then, in response to an external control signal, the BPF 61 extracts an identification signal superimposed on an optical signal of a desired wavelength from the output of the photodiode (PD) 53. Here, it is assumed that an identification signal of fk corresponding to the optical signal of the wavelength λk is extracted.

The rectifier 66 extracts the amplitude component of the fk identification signal.
Together with the low frequency signal (fosc) output by the phase comparator 6
2 given. Here, the phases of both signals are compared, and the result is provided to the adder 64 via the LPF 63. In the adder 64, the fosc of the low frequency oscillator 65 and the LPF 6
3 are added to the output of the tunable optical band-pass filter (OTF) 51. For this reason, the filter characteristics of the OTF 51 move at a period of fosc around the output of the LPF 63.

FIG. 5 shows a state where the phase of the optical signal passing through the OTF 51 changes as the filter characteristics of the OTF 51 move. For example, when the filter characteristic of the OTF 51 moves around λ0, the wavelengths of λ1, λ2
Are output in opposite phases. On the other hand, λ
The 0 optical signal is output at twice the frequency of λ1 and λ2.

Thus, in the present embodiment, wavelength multiplexing is performed after the identification signals having different frequencies are superimposed on the optical signals of the respective channels in advance. From this wavelength multiplexed light, an optical signal of a desired wavelength is transmitted through a variable wavelength optical bandpass filter (OTF) 51. At this time, the OTF 51 is set so that the amplitude of the identification signal superimposed on the optical signal of the reception channel is maximized.
Is controlled. Thereby, even when the wavelength interval and the optical power level vary, the variable wavelength optical bandpass filter (OTF) 5 can be used.
This makes it possible to exactly match the center wavelength of one with the wavelength of a desired optical signal. FIG. 6A shows the filter characteristics according to the above configuration. Here, a case where control is performed so that the transmittance of an optical signal having a wavelength of λ2 is the best is shown.

(Second Embodiment) In the optical communication system of the present embodiment, the configuration of the control unit 6 in FIG. 1 is as follows (reference numeral 7). FIG.
FIG. 1 shows a configuration of the control unit 7 in the present embodiment. Control unit 7
Is a band pass filter (BPF) 71 and a subtractor 72
, A divider 73, a phase comparator 74, a low-pass filter (LPF) 75, an adder 76, a low-frequency oscillator 77
And a rectifier 78.

The output of the variable wavelength optical bandpass filter (OTF) 51 photoelectrically converted by the photodiode (PD) 53 is branched into two, and each of the output is divided into a BPF 71 and a subtractor 72.
And given to. The BPF 71 obtains an identification signal superimposed on an optical signal of a desired reception channel according to an external control signal. The output is branched into two and input to a subtractor 72 and a divider 73. The subtractor 72 outputs the sum of the identification signals of each channel other than the identification signal superimposed on the optical signal of the reception channel. Thus, the divider 73
Outputs the ratio of the identification signal superimposed on the optical signal of the reception channel to the sum of the other identification signals.

The output of the divider 73 is supplied to the phase comparator 74 via a rectifier 78, and the identification signal and the identification signal superimposed on the optical signal of the reception channel are input to the phase comparator 74 in the same manner as in the first embodiment. The filter characteristics of the OTF 51 are controlled so that the ratio with the sum of the other identification signals is maximized. By doing so, the center wavelength of the OTF 51 can be adjusted so that the signal / crosstalk ratio is maximized. FIG. 6B shows the filter characteristics of the OTF 51 according to the present embodiment.

(Third Embodiment) In the optical communication system of the present embodiment, the configuration of the control unit 6 in FIG. 1 is as follows (reference numeral is 8). FIG.
FIG. 2 shows a configuration of the control unit 8 in the present embodiment. Control unit 8
Are provided for each channel, and filters 81-1 to 81-n for extracting the components of the identification signal of each channel from the photoelectric conversion output of the photodiode (PD) 53
Rectifiers 82-1 to 82-n for extracting the amplitude of the identification signal from the outputs of the filters 81-1 to 81-n, an adder 83, a divider 84, a phase comparator 85, and a low-pass filter (LPF). ) 86, an adder 87, and a low-frequency oscillator 88.

The adder 87 includes rectifiers 82-1 to 82-2.
Among the outputs of −n, an identification signal of an optical signal other than a desired wavelength (for example, λ2) is provided. The output of the adder 87 and the identification signal of the optical signal of the desired wavelength (λ2) are input to the divider 84. Thus, the divider 84 outputs the ratio of the identification signal superimposed on the optical signal of the desired wavelength λ2 to the sum of the other identification signals. Thereafter, in the same manner as in the second embodiment, the variable wavelength optical bandpass filter (OTF) 51 is controlled so that the ratio of the identification signal superimposed on the optical signal of λ2 to the sum of the other identification signals is maximized. The filter characteristics are controlled. By doing so, the same effect as in the second embodiment can be obtained.

As described above, the configuration as shown in the first to third embodiments allows a signal of a desired wavelength to be minimized while minimizing crosstalk even when wavelength intervals and optical power levels vary. It is possible to provide an optical communication system capable of selecting the above, an optical transmitter thereof, and a wavelength selector.

The present invention is not limited to the above embodiments. For example, in the second embodiment, the divider 73 is provided, and the ratio between the identification signal superimposed on the optical signal of the reception channel and the sum of the other identification signals is obtained. The OTF 51 is set so that the ratio becomes maximum. Is controlled, but a subtractor is provided in place of the divider 73,
The difference between the identification signal superimposed on the optical signal of the reception channel and the sum of the other identification signals may be obtained by the subtracter, and the filter characteristic of the OTF 51 may be controlled so that the difference is maximized. . FIG. 7 shows the configuration of the control unit 7 that provides the above operation (the divider 73 in FIG. 3 is replaced with a subtractor 79). Even in this case, a similar effect can be obtained.

Similarly, in the third embodiment, a subtractor is provided in place of the divider 84. The subtractor subtracts the sum of the identification signal superimposed on the optical signal of the reception channel and the other identification signals. , And O is set so that this difference is maximized.
The filter characteristics of the TF 51 may be controlled.
FIG. 8 shows the configuration of the control unit 8 that provides the above-described operation (FIG. 4).
Is replaced by a subtractor 89). Even in this case, a similar effect can be obtained. In addition, various modifications can be made without departing from the gist of the present invention.

[0028]

As described above in detail, according to the present invention, a wavelength selector multiplexes optical signals of a plurality of channels having different wavelengths on the transmitting side from a wavelength multiplexed optical signal on the receiving side to obtain an optical signal of a predetermined wavelength by the wavelength selector. In an optical communication system that receives and selects a signal, an identification signal having a different frequency is superimposed on the optical signal of each channel in advance on the transmitting side, and the amplitude of the identification signal superimposed on the optical signal of the receiving channel is maximized on the receiving side. The wavelength selector is controlled so that Or
The amplitude of the identification signal superimposed on the optical signal of the receiving channel,
The wavelength selector is controlled such that the ratio with the sum of the amplitudes of the identification signals superimposed on the optical signals other than the reception channel is maximized.

Therefore, even if the wavelength intervals of the wavelength-multiplexed optical signals are varied or the intensities are different, the receiving side can surely identify each channel based on the identification signal. For this reason, the characteristics of the wavelength selector can always be adjusted optimally, and it is possible to minimize the deterioration of the reception characteristics due to the occurrence of crosstalk.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a basic configuration of an optical communication system according to an embodiment of the present invention.

FIG. 2 is a control unit 6 according to the first embodiment of the present invention.
FIG. 2 is a circuit block diagram showing the configuration of FIG.

FIG. 3 shows a control unit 7 according to a second embodiment of the present invention.
FIG. 2 is a circuit block diagram showing the configuration of FIG.

FIG. 4 shows a control unit 8 according to a third embodiment of the present invention.
FIG. 2 is a circuit block diagram showing the configuration of FIG.

FIG. 5 is a cross-sectional view of the first to third embodiments;
FIG. 9 is a diagram illustrating a state in which the phase of an optical signal that has passed through the OTF 51 changes as the filter characteristics of the TF 51 move.

FIG. 6 is a cross-sectional view of the first to third embodiments;
The figure which shows a mode that the filter characteristic of TF51 is controlled.

FIG. 7 is a control unit 7 according to the second embodiment of the present invention.
FIG. 4 is a circuit block diagram showing another example of the configuration of FIG.

FIG. 8 shows a control unit 8 according to the third embodiment of the present invention.
FIG. 4 is a circuit block diagram showing another example of the configuration of FIG.

FIG. 9 is a circuit block diagram showing a basic configuration of a conventional optical communication system.

FIG. 10 is a circuit block diagram showing a configuration of a control unit 54 of a conventional optical communication system.

FIG. 11 is a diagram used to show a problem of a conventional optical communication system.

[Explanation of symbols]

 1-1 to 1-n Distributed feedback laser (DFB-LD) λ1 to λn Optical signal 2 Optical coupler 3 Optical fiber 4 Optical receiver 5 Wavelength selector 51 Variable wavelength optical bandpass filter (OTF) 52 ... Optical splitter 53 ... Photodiode (PD) 54 ... Control unit 541 ... Phase comparator 542 ... Low pass filter (LPF) 543 ... Adder 544 ... Low frequency oscillator f1-fn ... Identification signal The frequency 6 ... Control unit of the first embodiment 61 ... Band pass filter (BPF) 62 ... Phase comparator 63 ... Low pass filter (LPF) 64 ... Adder 65 ... Low frequency oscillator 66 ... Rectifier 7 ... Second Control unit 71 of the embodiment: band pass filter (BPF) 72: subtractor 73: divider 74: phase comparator 75: low pass filter (LPF) 76: adder 77 Low frequency oscillator 78 Rectifier 79 Subtractor 8 Controller of the third embodiment 81-1 to 81-n Filters 82-1 to 82-n Rectifier 83 Adder 84 Divider 85 Phase Comparator 86 Low-pass filter (LPF) 87 Adder 88 Low-frequency oscillator 89 Subtractor

Claims (13)

[Claims] 1. An optical communication system for receiving and selecting an optical signal of a predetermined wavelength by a wavelength selector on a receiving side from a wavelength multiplexed optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed on a transmitting side. In the transmitting side, the identification signal having a different frequency is superimposed on the optical signal of each channel in advance, and the wavelength selection is performed on the receiving side such that the amplitude of the identification signal superimposed on the optical signal of the selected channel is maximized. An optical communication system characterized by controlling a device. 2. The variable wavelength optical bandpass filter for selectively outputting an optical signal of a predetermined wavelength from the wavelength multiplexed optical signal based on a given control signal, the variable wavelength optical bandpass filter. An optical splitter that splits and outputs a part of the output of the optical splitter; a photoelectric converter that photoelectrically converts the output of the optical splitter; and a control signal to the variable wavelength optical bandpass filter based on the output of the photoelectric converter. 2. The optical communication system according to claim 1, further comprising: a control unit for providing the information. 3. A variable narrow-band filter for extracting an identification signal superimposed on an optical signal of a receiving channel from an output of the photoelectric converter in accordance with a given control signal; A rectifier for extracting the amplitude of the output of the oscillator, an oscillator for outputting a predetermined low-frequency signal, a phase comparator for comparing the output of the rectifier with the low-frequency signal, and a low-frequency component of the output of the phase comparator. 3. A low-pass filter to be taken out, and an adder that adds an output of the low-pass filter to a low-frequency signal output by the oscillator and inputs the low-frequency signal as a control signal to the variable-wavelength optical band-pass filter. An optical communication system according to claim 1. 4. An optical communication system in which, on a receiving side, an optical signal of a predetermined wavelength is selected and received by a wavelength selector from a wavelength multiplexed optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed. In the transmitting side, identification signals having different frequencies are superimposed on the optical signals of the respective channels in advance, and on the receiving side, the amplitude of the identification signal superimposed on the optical signal of the selected channel and the optical signals other than the selected channel are compared. An optical communication system characterized in that the wavelength selector is controlled so that the ratio of the amplitude to the sum of the amplitudes of the identification signals superimposed on the wavelength selector is maximized. 5. A variable wavelength optical bandpass filter for selectively outputting an optical signal of a predetermined wavelength from the wavelength multiplexed optical signal based on a given control signal, the variable wavelength optical bandpass filter. An optical splitter that splits and outputs a part of the output of the optical splitter; a photoelectric converter that photoelectrically converts the output of the optical splitter; and a control signal to the variable wavelength optical bandpass filter based on the output of the photoelectric converter. 5. The optical communication system according to claim 4, further comprising: a control unit for providing the information. 6. A variable narrow band filter for extracting an identification signal superimposed on an optical signal of a selected channel from an output of the photoelectric converter in accordance with a given control signal, a predetermined low frequency signal. An oscillator that outputs the output of the photoelectric converter, a subtractor that subtracts the output of the variable narrow band filter from the output of the photoelectric converter, and a divider that obtains a ratio between the output of the subtractor and the output of the variable narrow band filter. A rectifier for extracting the amplitude of the output of the divider; a phase comparator for comparing the phase of the output of the rectifier with the low-frequency signal; a low-pass filter for extracting a low-frequency component of the output of the phase comparator; And an adder for adding the output of the low-pass filter to the low-frequency signal output by the adder and inputting the output to the tunable optical band-pass filter as a control signal. Optical communication system of claim 5, wherein. 7. The control means includes: a plurality of filters for extracting an identification signal component superimposed on each optical signal from an output of the photoelectric converter; and a plurality of filters provided for each of the plurality of filters. A plurality of rectifiers for extracting the amplitude of the identification signal component from the output; and for obtaining a sum of amplitudes of the respective identification signal components output from the plurality of rectifiers other than those corresponding to the optical signal of the selected channel. A divider for calculating a ratio of the output of the adder to the amplitude of the identification signal component corresponding to the optical signal of the selected channel; and a phase for comparing the phase of the output of the divider with the low-frequency signal. A comparator, a low-pass filter that extracts a low-frequency component of the output of the phase comparator, and an output of the low-pass filter to a low-frequency signal output by the oscillator, and a control signal. Optical communication system according to claim 5, characterized by comprising an adder to be input to the variable wavelength optical band pass filter Te. 8. An optical communication system in which a transmission side selects an optical signal of a predetermined wavelength by a wavelength selector from a wavelength multiplexed optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed, and receives the signal. An optical transmitter used in (1), characterized by comprising means for superimposing identification signals having different frequencies on optical signals of respective channels in advance. 9. An optical transmitter in which identification signals having different frequencies are superimposed on optical signals of a plurality of channels having different wavelengths in advance, and optical signals of a plurality of channels having different wavelengths are wavelength-multiplexed on the transmitting side. From wavelength multiplexed optical signals,
Used in an optical communication system including an optical receiver for selecting and receiving an optical signal of a predetermined wavelength on the receiving side, a wavelength selector for selecting an optical signal of any channel in the optical receiver, A variable wavelength optical bandpass filter for selectively outputting an optical signal of a predetermined wavelength from the wavelength multiplexed optical signal based on a given control signal; a part of an output of the variable wavelength optical bandpass filter is branched and output; An optical splitter; a photoelectric converter that photoelectrically converts an output of the optical splitter; and a control unit that supplies a control signal to the tunable wavelength bandpass filter based on an output of the photoelectric converter. Wavelength selector. 10. An optical communication system in which, on a receiving side, an optical signal of a predetermined wavelength is selected and received by a wavelength selector from a wavelength multiplexed optical signal in which optical signals of a plurality of channels having different wavelengths are multiplexed on a transmitting side. In the transmitting side, identification signals having different frequencies are superimposed on the optical signals of the respective channels in advance, and on the receiving side, the amplitude of the identification signal superimposed on the optical signal of the selected channel and the optical signals other than the selected channel are compared. An optical communication system characterized in that the wavelength selector is controlled so that the difference from the sum of the amplitudes of the identification signals superimposed on the wavelength selector is maximized. 11. A variable wavelength optical bandpass filter for selectively outputting an optical signal of a predetermined wavelength from said wavelength multiplexed optical signal based on a given control signal, said variable wavelength optical bandpass filter. An optical splitter that splits and outputs a part of the output of the optical splitter; a photoelectric converter that photoelectrically converts the output of the optical splitter; and a control signal to the variable wavelength optical bandpass filter based on the output of the photoelectric converter. The optical communication system according to claim 10, further comprising: a control unit for providing the information. 12. A variable narrow band filter for extracting an identification signal superimposed on an optical signal of a selected channel from an output of the photoelectric converter in accordance with a given control signal, a predetermined low frequency signal. An oscillator that outputs the output of the photoelectric converter, a subtractor that subtracts the output of the variable narrow band filter from the output of the photoelectric converter, and a subtractor that obtains a difference between the output of the subtractor and the output of the variable narrow band filter. A rectifier for extracting the amplitude of the output of the subtractor; a phase comparator for comparing the phase of the output of the rectifier with the low-frequency signal; a low-pass filter for extracting a low-frequency component of the output of the phase comparator; And an adder for adding an output of the low-pass filter to a low-frequency signal output by the adder and inputting the output to the variable-wavelength optical bandpass filter as a control signal. Motomeko 11 optical communication system described. 13. The control means includes: a plurality of filters for extracting an identification signal component superimposed on each optical signal from an output of the photoelectric converter; and a plurality of filters provided for each of the plurality of filters. A plurality of rectifiers for extracting the amplitude of the identification signal component from the output; and for obtaining a sum of amplitudes of the respective identification signal components output from the plurality of rectifiers other than those corresponding to the optical signal of the selected channel. An adder for calculating a difference between an output of the adder and an amplitude of an identification signal component corresponding to an optical signal of a selected channel; and a phase for comparing the output of the subtractor with the low-frequency signal. A comparator; a low-pass filter that extracts a low-frequency component of the output of the phase comparator; and a control signal that adds an output of the low-pass filter to a low-frequency signal output by the oscillator. Optical communication system according to claim 11, characterized by comprising an adder to be input to the variable wavelength optical band pass filter by.