JPH07162070A - Variable wavelength filter control method, variable wavelength filter control equipment, and optical communication system using the same - Google Patents

Abstract

PURPOSE:To eliminate synchronous wavelength fluctuation due to micromodulation, by pulling the center wavelength of a wavelength filter into the wavelength of an optical signal by feedback control, stabilizing the center wavelength, and controlling a variable wavelength filter into which optical signal for receiving is introduced by an error signal. CONSTITUTION:An optical signal from an optical divider passes an optical waveguide 104, and enters a variable wavelength filter 401. According to a control signal from a filter driving circuit 404, the filter 401 transmits an optical signal having an arbitrary wavelength. A photodetector 402 converts the transmitted light from the variable wavelength filter 401 into an electric signal. An adder 403 adds an offset control signal 113 from a receiving part to an error signal 114 from a wavelength switching circuit, and delivers the obtained signal to the filter driving circuit 404. The injection current to the variable wavelength filter 401 is outputted according to the control signal from the adder. Since the center wavelength lambdaC<1> of the variable wavelength filter 401 is not modulated, the intensity fluctuation due to modulation is not generated in the optical signal after filtering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control device for a wavelength tunable filter used in a receiver of a wavelength division multiplexing communication system, and an optical communication system using the same.

[0002]

2. Description of the Related Art In recent years, as information has become multimedia,
Support for high-speed, large-capacity communication is under consideration regardless of subscriber system or LAN. In wavelength division multiplexing, it is possible to have a large number of independent lines for each optical fiber that is a transmission line. As a result, it is possible to provide a communication system that has flexibility for communication in addition to the high speed inherent in optical communication.

A wavelength filter that selects one wavelength from the multiplexed light is one of the essential elements for this wavelength multiplexing communication. In a system in which the number of multiplexes is about several waves and the wavelength spacing is wide, a dielectric multilayer fixed filter can be used. However, in a system with a large number of multiplexes and a narrow wavelength interval, a wavelength filter having a variable wavelength and a narrow transmission wavelength width is required.

When using such a wavelength tunable filter, tracking control is required. That is, the center wavelength of the transmission spectrum of the tunable filter (hereinafter, simply referred to as the center wavelength) needs to be drawn into the wavelength of the optical signal to be received and stabilized. Hereinafter, a conventional example of this wavelength tunable filter control system will be described. An example of this is the publication Elect
tronics Letters Vol. 26, No. 25 (1
(December 990) pages 2122 to 2123.

FIG. 9 shows a block diagram. The optical signal transmitted through the wavelength tunable filter 901 enters the light receiving element 902. This optical signal is converted into an electric signal by the light receiving element 902 and amplified by the amplifier 903. This signal is further amplified by the narrowband amplifier 904 that amplifies only the frequency component near the frequency f, and only the modulation component is amplified.
Entered in. The synchronous detection circuit 905 synchronously detects this signal with a modulation signal. The output of the synchronous detection circuit 905 is amplified by the integrator 906 so that only low frequency components are amplified. The time constant of the integrator 906 is set to be sufficiently longer than the cycle of the modulation signal. The feedback control circuit 907 generates a control signal by using this low frequency component as an error signal. The filter drive circuit 908 uses the wavelength tunable filter 90 based on three input signals of an offset signal, a modulation signal, and a control signal.
A current is injected into 1 to control the center wavelength λc of the filter. The sine wave oscillator 909 generates a sine wave having a frequency f for modulation and outputs it to the filter drive circuit 908 and the delay circuit 910.

FIG. 10 is a schematic diagram showing the relationship between the transmission spectrum of the wavelength tunable filter and the wavelength of the optical signal to be received. In the figure, λc is the center wavelength of the transmission spectrum of the wavelength tunable filter, and λs is the wavelength of the received optical signal. By tracking, it is pulled in from left to right when λc <λs, and from right to left when λc> λs, and stabilized. It should be noted that the range in which pull-in is possible is a range from the bottom of the transmission spectrum to a certain extent from the peak. This range is determined by the characteristics of the control system. Hereinafter, this range is referred to as a pull-in area.

The central wavelength λc of the transmission spectrum of the wavelength tunable filter 901 is modulated by the sinusoidal modulation signal input to the filter control circuit 908. The modulation amplitude of this wavelength is converted into a change in the amount of light of the wavelength λs that passes through the wavelength tunable filter 901, and is further converted into an electric signal by the light receiving element 902. The phase of the sine wave of the frequency f included in this electric signal is opposite when λc <λs and when λc> λs.

The low-frequency component of the output of the synchronous detection circuit 905 (that is, the output of the integrator 906) is positive when the phases of the two inputs are the same and negative when the phases of the two inputs are opposite. When the above-mentioned electric signal and sine wave oscillator 909 are used as these two inputs, the positive / negative of the output of the integrator 906 is opposite between λc <λs and λc> λs. By performing feedback control using this signal as an error signal, λc can be pulled into λs and stabilized.

[0009]

In the above tracking method, there is a periodic fluctuation of the wavelength due to the modulation after the center wavelength of the wavelength tunable filter is pulled into the wavelength of the LD (hereinafter referred to as stable time). This wavelength fluctuation is converted into a fluctuation of the light intensity incident on the light receiving element due to the transmission spectrum of the wavelength tunable filter, which deteriorates the reception characteristic. If the modulation amplitude is reduced, fluctuations in light intensity can be suppressed,
In such a case, the error signal becomes small, the response characteristic of the pulling is deteriorated at the time of pulling, and the stability of the wavelength is lowered at the time of stable.

In other words, the conventional system has a trade-off relationship between the response characteristic of pull-in and the receiving characteristic with respect to the modulation amplitude, and both cannot be improved at the same time. Also,
When applied to a wavelength multiplexing system, in the conventional method, it is necessary to pull the center wavelength of the filter into the wavelength of the received optical signal every time when switching the received wavelength. For this reason,
There is a drawback that it is difficult to switch wavelengths quickly.

[0011]

According to the present invention, there is provided a wavelength tunable filter control method for tracking a wavelength of an optical signal, wherein an input optical signal is branched into two or more as a tracking optical signal and a receiving optical signal. Then, at least one of the branched optical signals is guided as a tracking optical signal to a tracking wavelength tunable filter, and the center wavelength of the wavelength tunable filter is finely modulated to change the intensity of transmitted light of the wavelength tunable filter. An error signal is generated by comparing the phase of the minute modulation component included and the phase of the modulation signal used for the minute modulation, and the feedback control pulls the center wavelength of the wavelength filter into the wavelength of the optical signal to stabilize it, A wavelength tunable filter that controls a wavelength tunable filter to which an optical signal for reception different from the optical signal for tracking is guided by the error signal. To realize motor control method, a wavelength tunable filter can be eliminated periodic wavelength fluctuation stable time caused by micro-modulation. In addition, tracking is performed by a plurality of wavelength tunable filters, and switching is performed in response to a request, which enables quick wavelength switching.

[0012]

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of a variable wavelength filter control system to which the present invention is applied. As shown, the control system includes optical waveguides 101, 103, 104, an optical branching device 102, a wavelength tracking circuit 105, and an optical signal receiving circuit 10.
6, the sine wave oscillator 107 and the wavelength switching circuit 109 are main components.

The wavelength division multiplexed optical signal from the light source is sent to the optical waveguide 1.
The light enters the optical branching device 102 from 01 and is split into two.
One of the branched lights passes through the optical waveguide 103 and enters the wavelength tracking circuit 105, and the other passes through the optical waveguide 104 and enters the optical signal receiving circuit 106. The wavelength tracking circuit 105 outputs the modulated signal 108 from the sine wave oscillator 107 to the wavelength switching circuit 1
09, the bias signal 110 is obtained to track the optical signal of a specific wavelength, and the error signal 111 is output to the wavelength switching circuit 10.
Output to 9.

The optical signal receiving circuit 106 is the wavelength switching circuit 1
09, the bias signal 113 and the error signal 114 are obtained and tuned to the optical signal of the same wavelength as the wavelength tracking circuit 105, and the detected signal 115 is output to the receiving unit.

The sine wave oscillator 107 is a wavelength tracking circuit 10.
The modulated signal 108 is output to the No. 5. The modulation signal is for modulating the center wavelength of the wavelength tunable filter in the wavelength tracking circuit with a minute amplitude. The half-frequency of the modulation signal is
The upper limit is determined by the band of the transmitted signal, and the lower limit is determined by the response speed of tracking. Usually several hundred Hz to several kH
The frequency of z is used.

The wavelength switching circuit 109 obtains the wavelength allocation control signal 116 from the receiving unit and outputs one of several preset bias voltages to the signal lines 110 and 113. These bias voltages are wavelengths tracked by the wavelength tunable filter in the wavelength tracking circuit 105 and the optical signal receiving circuit 106, that is, each c of the wavelength multiplexed signal light.
It corresponds to the wavelength of h. In addition, the wavelength switching circuit 109 outputs the error signal 111 obtained from the wavelength tracking circuit 105 to the signal line 1
It outputs to 14. Further, a control signal indicating whether or not to perform tracking control of the wavelength tracking circuit 105 is sent to the signal line 11
Output to 2. As a result, the center wavelength of the wavelength tunable filter in the optical signal receiving circuit is matched with the wavelength tracked by the wavelength tracking circuit.

FIG. 2 shows a wavelength tracking circuit 1 according to this embodiment.
It is a block diagram of 05. The optical signal from the optical branching device enters the wavelength tunable filter 201 through the optical waveguide 103. This filter is a DFB filter, and the center wavelength can be controlled by changing the injection current near the oscillation threshold. Since the center wavelength is proportional to the injection current in a narrow range, the center wavelength can be modulated according to the modulation signal by superimposing a modulation signal having a small amplitude on the bias component of the injection current. In addition, DFB
Regarding the filter, publication: IEICE Transactions C-I J73-C-I No. 5 (May 1990) 34
It is described in detail on pages 7-353.

The light receiving element 202 is a wavelength tunable filter 201.
The optical signal transmitted through is converted into an electric signal. Amplifier 203
Amplifies the electrical signal.

The synchronous detection circuit 204 is a circuit for comparing the phase of the received electric signal and the phase of the modulated signal 108 from the sine wave oscillator, and is specifically a multiplier. A signal obtained by multiplying the received electric signal by the modulation signal 108 from the sine wave oscillator is output. The low frequency component of this signal is positive if the received electrical signal is in phase with the modulation signal and is negative if it is in antiphase. The LPF 205 is a filter that extracts a low frequency component from the output signal of the synchronous detection circuit 204, and its cutoff frequency is set so that the modulation signal 108 (frequency f) from the sine wave oscillator can be sufficiently attenuated.

The feedback control circuit 206 uses the signal from the LPF 205 as an error signal to generate a control signal. As a feedback control method, a well-known PID (Proportiona)
lIntegral Differential) control is preferably used. The output is the sum of the proportional component, integral component, and derivative component of the input signal, and the ratio is determined so that an appropriate response (short response time, small overshoot, etc.) can be obtained for the control system. It Also,
The feedback control circuit 2 is controlled by the control signal 112 from the receiver.
06 output ON / OFF, that is, tracking control O
Perform N / OFF.

The output from the feedback control circuit 206, the modulation signal 108 from the sine wave oscillator, and the offset control signal from the receiving section are added together by the adder 207 and output to the filter drive circuit 208.

The filter drive circuit 208 includes an adder 20.
The output of 7 is input. The output is the injection current to the wavelength tunable filter 201. The wavelength tunable filter 2
When a multi-electrode DFB filter is used as 01, there are as many outputs as the number of electrodes of the filter drive circuit 208, and the center wavelength can be changed by controlling the injection current of each electrode. Further, the modulation of the center wavelength for tracking is performed by superimposing a sinusoidal component on the injection current of one or more electrodes.

The operation of the wavelength tunable filter 201 will be described with reference to FIG. FIG. 3A shows the wavelength tracking circuit 10.
5 shows the relationship between the transmission spectrum of the wavelength tunable filter 201 in FIG. 5 and the wavelength of the wavelength-multiplexed signal light. The vertical axis represents transmitted light intensity, and the horizontal axis represents wavelength. Since the tracking control is performed, the center wavelength λc of the wavelength tunable filter 201 is drawn to the wavelength λi301 of a certain signal light. Reference numeral 302 denotes a transmission spectrum of the wavelength tunable filter 201, which is finely modulated.

FIG. 3B shows the wavelength tunable filter 201.
It represents the optical signal intensity after transmission. The vertical axis is the transmitted light intensity,
The horizontal axis is time. Since the wavelength tunable filter 201 modulates its center wavelength, the optical signal after passing through the filter has intensity fluctuation.

FIG. 4 is a block diagram of the optical signal receiving circuit 106 in this embodiment. The optical signal from the optical splitter is
The light enters the wavelength tunable filter 401 through the optical waveguide 104. This filter is also a DFB filter and transmits an optical signal of an arbitrary wavelength based on the control signal from the filter drive circuit 404. The light receiving element 402 is the tunable filter 4
The transmitted light of 01 is converted into an electric signal. The output is taken out to the receiver. The adder 403 adds the offset control signal 113 from the receiving unit and the error signal from the wavelength switching circuit 109, and outputs the signal to the filter drive circuit 404. The filter drive circuit 404 outputs the injection current to the wavelength tunable filter 401 based on the control signal from the adder. In addition, the wavelength tunable filters 201 and 40
The difference in the characteristics of 8 is absorbed by adjusting the drive circuit 404.

The operation of the wavelength tunable filter 401 in the optical signal receiving circuit 106 will be described with reference to FIG. Figure 5
(A) shows the relationship between the transmission spectrum of the wavelength tunable filter 401 in the optical signal receiving circuit 106 and the wavelength of the wavelength-multiplexed transmission light. Similarly, the vertical axis represents transmitted light intensity and the horizontal axis represents wavelength. Reference numeral 501 is an optical signal of wavelength λi, and 502 is a transmission spectrum of the wavelength tunable filter 401. In addition, the central wavelength λ of the wavelength tunable filter 401
c ′ coincides with the center wavelength λc of the wavelength tunable filter 201 due to the control signal from the wavelength switching circuit. on the other hand,
FIG. 5B shows the optical signal intensity after passing through the wavelength tunable filter 401. The central wavelength λc 'is not modulated. Therefore, the intensity variation due to the modulation does not occur in the optical signal after passing through the filter.

The operation of each section of this embodiment has been described above, but the summary is as follows. The wavelength-multiplexed signal light is divided into two by an optical branching device, one is made incident on the wavelength tracking circuit and the other is made incident on the optical signal receiving circuit. An optical signal of an arbitrary wavelength is selected and the wavelength tracking circuit is made to track it. The center wavelength of the wavelength tunable filter in the optical signal receiving circuit is matched with the center wavelength of the wavelength tunable filter in the wavelength tracking circuit. However, the modulation signal is not superimposed. The reception of the target optical signal is performed using the optical signal receiving circuit.

The intensity of the transmitted light from the tracked filter fluctuates as shown in FIG. 3 (b). Therefore, the center wavelength of the reception filter is matched with the center wavelength of the tracking filter for reception. Since the reception filter does not modulate the central wavelength, the target optical signal can be received without being affected by the intensity fluctuation caused by the modulation, as shown in FIG. 5B.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a block diagram of a second embodiment of a wavelength tunable filter control system to which the present invention is applied. As shown in the figure, the control system includes optical waveguides 101 and 103-k (k = 1 to 1).
n), 104, optical branching device 602, wavelength tracking circuit 105-
The main components are k (k = 1 to n), the optical signal receiving circuit 106, the sine wave oscillator 107, and the wavelength switching circuit 609.

The wavelength-multiplexed signal from the light source is sent to the optical waveguide 10.
It is incident on the optical branching device 602 from 1, and is branched into n + 1 lines. N of the branched lights are optical waveguides 103-k.
The light enters each wavelength tracking circuit 105-k through (k = 1 to n). The remaining light passes through the optical waveguide 104 and enters the optical signal receiving circuit 106.

The structure of the wavelength tracking circuit 105-k is similar to that of the first embodiment and is shown in FIG. There are a plurality (n) of wavelength tracking circuits, and each wavelength tracking circuit independently tracks the wavelength of an arbitrary optical signal. In the present embodiment, the wavelength tracking circuit 1 will be used thereafter.
The constituent elements in 05-k are expressed as 201-k and 202-k. The optical signal receiving circuit has the same structure and operation as those of the first embodiment, and its structure is shown in FIG.

The wavelength tunable filters 201-k, 40
The difference in the characteristics between 1 is that the filter drive circuits 208-k, 4
Each of 04 is adjusted and absorbed.

The wavelength switching circuit 609, based on the wavelength allocation control signal 116 from the receiving section, controls the center wavelength of the wavelength tunable filter in the wavelength tracking circuit, which is tracking to a desired wavelength, and the optical signal receiving circuit. Match the center wavelengths of the tunable filters. Specifically, the preset bias voltage is output to the signal lines 110-k and 113. Also,
The wavelength switching circuit 609 outputs the error signal 111-k obtained from each wavelength tracking circuit 105-k to the signal line 114. Further, a control signal indicating whether or not to perform tracking control of the wavelength tracking circuit 105-k is output to the signal line 112-k. These bias voltages are applied to each wavelength tracking circuit 105-
k and the wavelength tunable filter in the optical signal receiving circuit 106 corresponds to the wavelength for tracking.

The optical signal receiving circuit 106 receives the optical signal and outputs it to the receiving section as in the first embodiment.

FIG. 7 is a schematic diagram for explaining the operation of the wavelength tunable filter used in this embodiment.
It shows a state when the optical signal of i is received. FIG. 7A shows
The relationship between the transmission spectrum of each wavelength tunable filter in the wavelength tracking circuit 105-k and the wavelength of the wavelength-multiplexed signal light is shown. The vertical axis represents transmitted light intensity, and the horizontal axis represents wavelength. The wavelength tunable filter in each wavelength tracking circuit tracks the wavelength λk (k = 1 to n) of any signal light. For example, 702 represents the transmission spectrum of the wavelength tunable filter 201-i that is tracking the signal light 701 of wavelength λi. Its central wavelength is λc.

FIG. 7B shows the relationship between the transmission spectrum of the wavelength tunable filter 401 in the optical signal circuit 106 and the wavelength of the wavelength-multiplexed signal light. Similarly,
The vertical axis represents transmitted light intensity, and the horizontal axis represents wavelength. Reference numeral 704 represents the transmission spectrum of the wavelength tunable filter 401, whose center wavelength is λc ′.

The wavelength switching circuit 609 makes λc 'coincide with λc. Since λc ′ is not modulated, strength variation does not occur in the received signal as in the first embodiment. Further, when switching the wavelength of the signal to be received, the optical signal receiving circuit can obtain the error signal from the wavelength tracking circuit which has already tracked to the target wavelength through the wavelength switching circuit. Therefore, the pull-in time is shortened, and the wavelength can be switched quickly.

(Third Embodiment) FIG. 8 is a block diagram of a wavelength division multiplexing optical communication system according to a third embodiment of the present invention. This system is preferably used for video distribution. The number of channels is n, the number of receivers is m, and the wavelength of each channel is λ1 and λ2.
~? N. The transmitter 801 modulates each of the n light sources with a digital video signal and sends it to the optical fiber 802. This optical signal is sent by the optical splitter 803 to the m optical fibers 8
04-1 to m are sent to the receiving devices 805-1 to m. Each of the receiving devices 805-1 to 805-m has a wavelength tunable filter to which the control method of the first or second embodiment is applied, and by this, only the wavelength to be received is selected from the wavelength division multiplexed signal and the video signal is received.

FIG. 5 and FIG. 7 show an example of the reception status in this embodiment. A receiving device 805-k (1 ≦ k ≦ having a wavelength tunable filter to which the control method of the first embodiment is applied.
m) receives and tracks an optical signal of wavelength λi, the received optical signal and the transmission spectrum of the wavelength tunable filter are expressed as shown in FIG.

By using the wavelength tunable filter control system of the present invention, the center wavelength of the wavelength tunable filter can be tracked to the wavelength to be received, and the fluctuation due to the modulation signal at the time of tracking can be suppressed to maintain a good reception state. can do.

(Other Embodiments) In the above embodiment, the number of the optical signal receiving circuit is one, but a configuration having a plurality of optical signal receiving circuits is also conceivable. In this case, the wavelength switching circuit determines, based on the wavelength allocation control signal from the receiving unit, which wavelength tracking circuit and which optical receiving circuit the central wavelengths should match.

Although the DFB filter is used as the wavelength tunable filter in the above embodiment, another wavelength tunable filter capable of controlling the center wavelength of the transmission spectrum may be used.

The wavelength tunable filter used in the wavelength tracking circuit and the wavelength tunable filter used in the optical signal receiving circuit need not be of the same type. For example, with respect to the full width at half maximum of the transmission spectrum, a narrow wavelength tunable filter used in the wavelength tracking circuit and a wide wavelength tunable filter used in the optical signal receiving circuit may be used.

Furthermore, it is not necessary to use the same type of filter for each optical signal receiving circuit. For example, a wide reception bandwidth can be realized by assigning a unique wavelength tracking range to each wavelength tracking circuit.

Although a sine wave is used as a modulation signal for obtaining an error signal in the above embodiment, another signal having phase information may be used. When the phase shift in the control system of the two input signals of the phase comparison circuit is so large that it cannot be ignored with respect to the period of the modulation signal, a phase shifter such as a delay circuit is required between the oscillator and the synchronous detector. .

In the above embodiment, the center wavelengths of the filters are the same, but they need not be exactly the same. However, the farther away the wavelength of the received light is from the central wavelength of the wavelength tunable filter that extracts the optical signal to the receiving unit, the lower the intensity of the optical signal that is extracted to the receiving unit.

[0049]

EFFECTS OF THE INVENTION Since there is no wavelength fluctuation at the time of stabilization due to modulation, the tracking characteristic is improved and good reception can be performed. Further, by performing tracking for a plurality of wavelengths in advance and obtaining an error signal, it is possible to switch wavelengths quickly.

[Brief description of drawings]

FIG. 1 is a block diagram of a wavelength tunable filter control system according to a first embodiment of the present invention.

FIG. 2 is a wavelength tracking circuit 10 according to the first embodiment of the present invention.
Block diagram of 5

FIG. 3 is an optical signal receiving circuit 1 according to the first embodiment of the present invention.
Block diagram of 06

FIG. 4 is a schematic diagram illustrating the operation of the wavelength tunable filter 201 according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating the operation of the wavelength tunable filter 301 according to the first embodiment of the present invention.

FIG. 6 is a block diagram of a wavelength tunable filter control system according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating the operation of the wavelength tunable filter according to the second embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical communication system that is a third embodiment of the present invention.

FIG. 9 is a block diagram of a wavelength tunable filter control method in a conventional example.

FIG. 10 is a schematic diagram showing the relationship between the transmission spectrum of a wavelength tunable filter and the wavelength of an optical signal in a conventional example.

[Explanation of symbols]

102, 602 Optical branching device 105, 105-1, 105-2, 105-n Wavelength tracking circuit 107 Sine wave oscillator 106 Optical signal receiving circuit 109, 609 Wavelength switching circuit 110, 110-1, 110-2, 110-n , 113
Offset control signals 111, 111-1, 111-2, 111-n, 114
Error signal 201, 401 Wavelength variable filter 202, 402 Light receiving element 204 Synchronous detection circuit 205 LPF 206 Feedback control circuit 207, 403 Adder 208, 404 Filter drive circuit 803 Optical branching device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04B 10/26 10/14 10/04 10/06

Claims (5)

[Claims] 1. A wavelength tunable filter control method for tracking a wavelength of an optical signal, wherein an input optical signal is branched into two or more as a tracking optical signal and a receiving optical signal, and the branched optical signal At least one of them is led to a wavelength tunable filter for tracking as an optical signal for tracking, and the center wavelength of the wavelength tunable filter is finely modulated,
An error signal is generated by comparing the phase of the minute modulation component included in the intensity change of the transmitted light of the wavelength tunable filter with the phase of the modulation signal used for the minute modulation, and the central wavelength of the wavelength filter is set by feedback control. A wavelength tunable filter control method comprising: controlling a wavelength tunable filter which is guided to a wavelength of an optical signal to be stabilized, and a receiving optical signal different from the tracking optical signal is guided by the error signal. 2. A first wavelength tunable filter, first filter driving means for controlling the first wavelength tunable filter to finely modulate a central transmission wavelength, and receiving light transmitted through the first wavelength tunable filter. Light receiving means, a comparison means for comparing the signal received by the light receiving means with a phase of a signal for minutely modulating the wavelength tunable filter, a high frequency component attenuating means for removing a modulation component from an output from the comparing means, Feedback control means for forming and outputting an error signal for feedback controlling the wavelength tunable filter based on the output from the high frequency component attenuating means, the error signal from the feedback control means, and an offset for determining the tracking wavelength. A wavelength tracking means composed of a first addition means for adding a control signal and the minute modulation signal for minute modulation and inputting to the first filter driving means; A wavelength tunable filter, a second filter driving means for controlling the second wavelength tunable filter, a light receiving means for receiving transmitted light of the second wavelength tunable filter, an offset control signal for determining a wavelength to be received, and An optical signal receiving unit including a second adding unit that adds the error signals and inputs the error signal to the second filter driving unit, and a wavelength that outputs an offset control signal to the first and second adding units. A switching means, an oscillator for supplying a minute modulation signal for minute modulation to the comparing means and the first adding means, and a light for branching and inputting an optical signal to the first and second wavelength tunable filters. A tunable filter control device comprising: a branching device. 3. A DFB (Di
3. The wavelength tunable filter control device according to claim 2, wherein a striated FeedBack filter is used. 4. A plurality of wavelength tracking means are provided, and a plurality of error signals output from the plurality of wavelength tracking means are selected by a wavelength switching means and output to the optical signal receiving means. 2. The wavelength tunable filter control device according to 2 or 3. 5. An optical communication system comprising a receiver using the wavelength tunable filter controller according to claim 2.