JPH06338856A - Automatic controller for optical frequency - Google Patents

Abstract

PURPOSE:To accurately and speedily switch the optical frequency by reducing the delay while controlling the frequency by detecting the optical frequency and generating a reference signal to be used for the frequency control loop while taking the frequency detection output of an intermediate frequency signal into account. CONSTITUTION:Part of the output of a local oscillation light source 3 is divided and extracted by the beam splitter of a light distributor 5 and made incident on a opto- electric converter O/E 27 through an optical filter 25. The optic/electric conversion is performed by the O/E 27 and a comparator 23 compares the result signal with the reference signal corresponding to the required frequency and the oscillation frequency of the local oscillation light source 3 is controlled according to an error signal of the difference. An LPF 29 limits the control band, and the high speed performance and safety of the control are decided based on a gain relation between this signal and the entire control loop. The gain of a control signal amplifier 31 is a element which decides the gain of the entire loop and a control signal compensating filter 33 is inserted to allow the filter 33 to have the response characteristic and the characteristic to compensate the delay or the like of a semiconductor laser of the light source 3. Thus, more speeding up and stable control of switching the frequency can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency automatic control device, and more particularly to an optical frequency automatic control device for performing optical frequency switching in an optical frequency multiplexing system at high speed and with high accuracy.

[0002]

2. Description of the Related Art In optical communication, optical frequency multiplexing (hereinafter referred to as
The optical FDM (FDM: Frequency Division Multiple) technology is effective as a technology for providing a flexible and large-capacity optical transmission line. In the optical communication system using the optical FDM, the technique of switching the optical frequency on the transmitting side or the receiving side is important for improving flexibility. In particular, when it is used for a large capacity LAN, a high-speed cross connect device, an optical switching network that handles a lot of information, etc., the transmission delay time must be about 10 msec or less,
High-speed optical frequency switching is required.

As described above, in order to construct an optical FDM system capable of rapid optical frequency switching, the optical frequency of a semiconductor laser (hereinafter simply referred to as LD) as a light source can be directly controlled by its drive current, It is suitable to use coherent optical communication in which the reception frequency can be switched.

However, in coherent optical communication,
Since the signal light obtained by modulating the normal laser light according to the information signal is mixed with the local oscillation light (hereinafter, abbreviated as local light) and the beat of these two lights is detected as an electric signal, this beat signal is reliably generated. High-precision automatic optical frequency control (AF
C) is required.

On the other hand, in coherent optical communication, a method capable of frequency switching and performing highly accurate optical frequency control has been conventionally devised. For example, Japanese Patent Laid-Open No. 03-169129 by Oshima et al. There is a description. In this method, in order to reliably perform frequency switching in a wide range and to achieve highly accurate frequency stabilization, an optical frequency detection unit for coarse control and a frequency detection of an intermediate frequency signal for fine control are provided. Two frequency detections are used. However, since this optical frequency control includes many circuits such as a microwave circuit and a frequency discriminating circuit in the negative feedback circuit section that performs fine control, the delay of each section is limited and high-speed and highly accurate frequency switching is possible. Has become difficult to do.

Furthermore, in general, when the driving current of the LD is changed, the frequency is changed by the combination of the effect of changing the frequency due to the change of the carrier density of the active layer and the effect of changing the frequency due to the change of the temperature. . Since the time constant and the amount of frequency change of these two effects are different, high-speed frequency switching cannot be realized only by improving the delay.

Further, a method has been studied in which a transmitter or a receiver holding a plurality of light sources makes a standby light source stand by in advance to the next target frequency and frequency switching is realized by switching the light sources by a high-speed optical switch. (For example,
Shimosaka et al. "Study on optical network for packet transfer using wavelength address" IEICE technical report OCS92-79199
(February 3).

In this case, the frequency of each light source is stabilized by the AFC method using optical frequency detection. In this method, the frequency switching time is only limited by the switching time of the optical switch, and can be faster than the optical frequency switching time of the light source body. However, since a large number of expensive light sources are required and the switching time of the light sources themselves is not improved, there are problems that a large number of light sources are required when changing the optical frequency one after another in a short time as described above. Further, a periodic optical filter with high finesse is used to suppress an AFC control error due to optical frequency detection. As a result, it is difficult to perform frequency control at an arbitrary optical frequency, and it is impossible to correct the deviation of the optical filter.

[0009]

As described above, in the conventional optical frequency switching / stabilization control system, the large capacity optical LA is used.
When performing the high-speed optical frequency switching required for N etc., there was a problem in terms of high speed, accuracy, cost, and the like.

The present invention has been made in view of the above-mentioned problems, and the frequency is controlled by the optical frequency detection to essentially reduce the delay, and the reference signal used in the frequency control loop is used to detect the frequency of the intermediate frequency signal. An object of the present invention is to provide an automatic optical frequency control device capable of solving the above problems by taking the output into consideration and realizing high-speed and high-accuracy optical frequency switching and stabilization control.

[0011]

In order to achieve the above object, the first invention of the present application is to mix the local oscillation light outputted from the local oscillation light source with the signal light which is modulated in accordance with the information signal and is subjected to the optical frequency multiplexing. In the optical frequency automatic control device for automatically controlling the optical frequency when the information signal is demodulated from the intermediate frequency signal obtained as described above, first detecting means for detecting the optical frequency of the local oscillation light output from the local oscillation light source, Band limiting means for limiting the control band in the automatic control of the optical frequency, second detecting means for detecting the frequency of the intermediate frequency signal, and a target controlled according to the output of the second detecting means. Reference signal generating means for generating a reference signal corresponding to the optical frequency, comparing means for comparing the reference signal generated by the reference signal generating means with the signal relating to the first detecting means, and the comparing means. And summarized in that a control means for controlling the optical frequency of the local oscillation light source according to the output.

The second invention of the present application is summarized in that the band limiting means described in claim 1 is configured by connecting a plurality of band limiting means having different control bands in parallel.

The third invention of the present application is summarized in that the band limiting means described in claim 1 is provided between the first detecting means and the comparing means.

[0014]

In the automatic optical frequency control device of the first invention of the present application, the optical frequency of the local oscillation light is detected by the first detecting means, and the frequency of the intermediate frequency signal is detected by the second detecting means. Control is performed according to the frequency of the detected intermediate frequency signal, and a reference signal corresponding to the target optical frequency is generated and output by the reference signal generating means. The reference signal generated by the reference signal generation means and the signal relating to the optical frequency of the local oscillation light detected by the first detection means are compared by the comparison means, and the optical frequency of the local oscillation light source is determined according to the comparison output. Are controlled by the control means. At this time, the control band in the automatic control of the optical frequency is limited by the band limiting means.
As a result, the frequency control of the local oscillation light source is performed based on the optical frequency detection, the delay is essentially reduced, and the control error caused by the control based on the optical frequency detection is based on the frequency detection output of the intermediate frequency signal. Is controlled and reduced.

In the automatic optical frequency control device according to the second invention of the present application, the band limiting means according to claim 1 is constituted by connecting a plurality of band limiting means each having a different control band in parallel. To change the optical frequency greatly by changing the temperature on the one side, and perform high-speed switching by changing the carrier density on the other side, or to divide the high frequency and the low frequency for fast and stable optical frequency switching. Is possible. That is, by configuring the frequency control circuit with a plurality of circuits having different bands and responses, high-speed and high-accuracy optical frequency switching and stabilization control are realized for an LD having a complicated response generated by combining a plurality of effects. To be done. At this time, the control bands of the respective band limiting means may overlap.

An optical frequency automatic control device according to a third aspect of the present invention comprises the band limiting means according to claim 1 provided between the first detecting means and the comparing means, whereby the comparing means and the local oscillation are provided. It becomes possible to speed up between the light source,
Further, the optical frequency switching is speeded up.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a coherent optical receiver according to the automatic optical frequency control device of the present invention. First, the configuration of the present embodiment will be described with reference to FIG. The optical coupler 1 emits signal light that is incident via a transmission medium such as an optical cable from a local oscillation light source (hereinafter, abbreviated as local light source) 3 that is incident via an optical distributor 5 to generate local light and light. These are combined (mixed) and the mixed light is incident on the photoelectric converter 7. This photoelectric converter (hereinafter, simply O / E
7 also converts the mixed light into an electric signal, specifically an intermediate frequency signal (hereinafter abbreviated as IF signal), and an intermediate frequency amplifier (hereinafter, abbreviated as IF signal) to which the IF signal is connected.
(Also referred to as an IF amplifier) 9. The IF signal amplified by the intermediate frequency amplifier 9 is input to the frequency discriminator 13 via the band limiting filter 11. This frequency discriminator 13 demodulates the IF signal and extracts a data signal. This data signal is output via the low-pass filter 15 and the determiner 17 connected thereto, while the reference signal generator 1
9 is output.

The configuration and operation of the reference signal generator 19 will be briefly described with reference to FIGS. 2 and 3. The reference signal generation unit 19 includes a calculation unit 191, a memory 193, and D.
/ A and a monitoring unit 197 described later. The memory 193 includes each slot correction value storage unit 193a and each channel correction value storage unit 193b.
When the channel signal and the IF frequency detection signal are input, 1 outputs a reference signal with reference to the correction values stored in the slot correction value storage unit 193a and the channel correction value storage unit 193b.

That is, the channel correction value is read in step S11, the past slot correction value is read in step S13, and the new channel prediction reference signal is calculated and output based on these correction values in step S15.
Next, the monitoring unit monitors whether the IF frequency detection signal becomes valid (step S17), and at the same time, performs step S19.
Then, the "deviation" is read by the frequency discriminator 13 or the IF frequency detection signal from the intermediate frequency signal frequency detection unit 41 shown in FIG. 6, the process proceeds to step S21, the reference signal is recalculated, and the correction value is output. In step S23, the channel correction value and the past slot correction value are updated based on this correction value. Here, when the switching of the channel signal occurs, the process proceeds to step S27, after switching the channel signal, the process returns to step S11, and when there is no switching of the channel signal, the process returns to step S17 to repeat the same processing.

The reference signal generator 19 is also connected to a comparator 23 via a reference signal shaping filter 21 and receives a channel signal. The comparator 23 is connected to the optical filter 25 via the photoelectric converter 27 and also has a control band limiting filter (hereinafter, also simply referred to as LPF).
29, control signal amplifier 31, and control signal compensation filter 3
It is connected to the local light source 3 through 3. A predetermined bias current is applied to the local light source 3 by the bias circuit 35.

Next, the operation will be described with reference to FIG. First, the signal light is mixed with the local light emitted from the local light source 3 in the optical coupler 1, and then photoelectrically converted (heterodyne detection) in the photoelectric converter 7, and the obtained IF signal is a frequency discriminator. The data signal is demodulated at 13, the data signal is taken out, and further output through the low-pass filter 15 and the judging device 17.

On the other hand, automatic frequency control (AFC) is performed to control the frequency of local light so that a stable IF signal can be obtained. That is, a part of the output of the local light source 3 is split by the light distributor 5, specifically, for example, a beam splitter,
The light is taken out, is incident on the photoelectric converter 27 through the optical filter 25, and is photoelectrically converted.
3 is compared with a reference signal corresponding to a desired frequency, and the oscillation frequency of the local oscillation light source 3 is controlled according to the error signal which is the difference.

The optical filter 25 is capable of detecting an optical frequency, and the amount of transmitted light changes in a wide frequency range of several nm to 10 nm. Further, since the optical filter 25 serves as an optical frequency reference, its characteristics are temperature, humidity, pressure,
It should be composed of one that is as stable as possible for optical power and polarization.
The output of the optical filter 25 is converted into an electric signal by the photoelectric converter 27 and compared with a preset reference signal. The difference from this reference signal is added as an error signal to the drive current of the local light source 3 after being amplified by the control signal amplifier 31, and the frequency of the local light source 3 is controlled to the desired frequency indicated by the reference signal.

It is preferable that the current-frequency characteristics of the LD are stored in a straight line as shown by a dotted line in FIG. 5 for storing each slot correction value and each channel correction value, but in reality, a curve is shown as a solid line. This is because the temperature and the change with time may change appropriately (for example, change in the range indicated by the straight line arrow).

The control band limiting filter 29, the control signal amplifier 31, and the control signal compensation filter 33, which are circuits for controlling the local light source 3, play an important role in changing the frequency of the local light source 3 at high speed. Specifically, the LPF 29 limits the control band, and the high speed and stability of the control are determined by the relationship between this and the gain of the entire control loop.
The gain of the control signal amplifier 31 is one element that determines the gain of the entire loop. By inserting the control signal compensation filter 33 so as to have a characteristic for compensating for the response characteristics, response delay, etc. of the semiconductor laser of the local light source 3, it is possible to realize further speedup of frequency switching and stable control. In theory,
The filter having the inverse response characteristic of the LD becomes the optimum compensation filter, but it is difficult to realize this filter because the response characteristic of the LD is complicated.

However, if a circuit in which speed-up capacitors C are connected in parallel as shown in FIG. 4 is used,
Since a large amount of current flows at the rising of the LD drive current, the switching time can be shortened. Therefore, it is effective to insert a compensation filter for adjusting the control characteristics. Needless to say, a filter that also serves as the control band limiting filter 29 and the control signal compensating filter 33 can be used.

With this configuration, since the frequency control of the local light source 3 is performed by the negative feedback circuit using the optical frequency detection, a high-speed AFC with a small circuit delay can be realized. The high-speed AFC has an effect of quickly converging the frequency variation at the time of channel switching, and thus high-speed channel switching can be realized.

Further, in order to improve the accuracy of AFC, the center frequency of the IF signal is detected, and the reference signal corresponding to the above-mentioned desired frequency is finely adjusted so that this becomes a desired value. In FIG. 1, the center frequency is detected by the DC component of the output of the frequency discriminator 13. Further, as shown in FIG. 6, an intermediate frequency signal frequency detection unit 41 may be separately used. In the case shown in FIG. 6, the intermediate frequency signal frequency detecting section 41 is connected between the band limiting filter 11 and the reference signal generating section 19 shown in FIG.

In this way, the intermediate frequency signal frequency detecting section 41
In case of separately providing, the frequency discriminator 13 can be optimized for signal demodulation and the intermediate frequency signal frequency detector 41 can be optimized for AFC, so that the performance of the entire receiver can be improved.
By the frequency detection function of the intermediate frequency signal of the intermediate frequency signal frequency detection unit 41, it is possible to reduce the control error caused by frequency control by the optical frequency detection. In the feedback system that performs high-speed frequency control, there is a problem that the loop gain cannot be increased so much and a control error increases, but this problem can be solved by the function of finely adjusting the reference signal. Alternatively, this function can be used to detect and correct the frequency shift of the optical filter 25 by receiving the optical frequency reference light whose absolute frequency is controlled. As a result,
A highly accurate reference signal can be generated.

Information relating to the fine adjustment of the reference signal is stored in the reference signal generator 19. Based on the stored information on the fine adjustment, the reference signal generator 19 can cope with the secular change of the characteristics of the LD by utilizing it for the next reference signal setting, and can detect the deterioration of the LD. Therefore, even when the power is turned on, the local light source 3 is adjusted at the target optical frequency without adjustment
It becomes possible to oscillate the LD. The system for generating the reference signal operates the two systems at the same time by setting the response time to an order of magnitude longer than that of the frequency control system performed based on the frequency detection of the light, which is ten times or more. However, problems such as oscillation do not occur.

In order to further improve the accuracy of the reference signal, it is preferable to supply the error information of the data signal from the determiner 17 to the reference signal generator 19, as shown in FIG. From the preamble, scrambled data, error detection bit, etc. in the data, the decision unit 17 can detect the error occurrence state in the received data signal. By adjusting the reference signal based on this information, a better reception capability can be realized.

The switching of the reception frequency is performed by switching the channel signal to the reference signal generator 19. The reference signal generator 19 outputs a reference signal corresponding to the target frequency. This signal must have a rise time sufficiently faster than the AFC response speed.
Therefore, the reference signal shaping filter 21 of the reference signal may be inserted between the reference signal generation unit 19 and the comparator 23. Due to the change of the reference signal, the error signal output from the comparator 23 becomes large, and the frequency of the local light source 3 is largely changed. Then, when the intermediate frequency of the IF signal reaches a desired value, the frequency control is continued as it is.

If there is a deviation, the reference signal generator 1
Since the deviation can be detected from the DC component of the output of the frequency discriminator to 9, the reference signal generating unit 19 finely adjusts the reference signal according to the deviation. However, since this fine adjustment has a long response time, the reference signal generator 19 needs to generate a reference signal with an accuracy that enables coherent detection without performing fine adjustment in order to perform high-speed optical frequency switching. Also, the loop gain of the AFC loop itself is required.

In order to increase the accuracy of the reference signal generation, the reference signal generation unit 19 stores the fine adjustment data and uses it for generating the reference signal when switching to the next target frequency.

Therefore, the reference signal generator 19 is composed of a microcomputer having an arithmetic unit 191 and a memory 193 as shown in FIG. As a result, an accurate reference signal can be generated even when there is no frequency discriminator output. It is possible to start without adjustment when the power is turned on.

Further, in FIG. 1, the LPF 29 is provided between the comparator 23 and the local oscillation light source 3 as a function of defining the control band, but this is detected as shown in FIG. Photoelectric converter 27 and comparator 23 that output signals
It is also possible to insert the control band limiting filter 43 between and.

In this case, the control band does not change, but by designing the circuit from the output of the comparator 23 to the local oscillation light source 3 at high speed, when the output of the comparator greatly changes at the time of frequency switching, etc. A large change instantaneously affects the local light source 3. Therefore, frequency switching is performed more quickly. This limitation of the control band can be realized without using the LPF 43 obviously as shown in FIG. 8 and only by using a device having a desired band for photoelectric conversion.

Next, referring to FIG. 9, the second embodiment of the present invention will be described.
An example will be described. In this embodiment, as shown in FIG. 9, two systems for controlling the frequency of the local light source 3 are provided. This is to facilitate the control of the complicated response of the local light source 3.

Normally, the local light source 3 changes the injection amount of the drive current in order to change its frequency. This change in drive current causes a change in carrier density in the LD and a change in temperature. The optical frequency of the LD changes under the influence of these changes. However, the directions of increase and decrease in frequency with respect to increase and decrease in current do not always match in these two.
Although it depends on the operating point of the LD, etc., in the case of a distributed feedback laser (DFB-LD), which is often used in a coherent optical receiver because of its narrow line width, the direction of frequency increase / decrease does not usually match. Is. Further, the change of the carrier density is very fast with a time constant of several ps or less, whereas the change with temperature is slow as several μs to several hundreds of μs. Therefore, in order to constantly and largely change the frequency of the LD, it is generally advantageous to use the frequency change due to the temperature change. On the other hand, in order to perform high-speed switching, it is necessary to control the influence of frequency change due to carrier density change.

In order to ensure control of these two effects, in this embodiment, a part of the negative feedback circuit is divided into two branches and the response frequency regions of the two are divided to drive the local light source 3. It is a high-pass amplifier and a low-pass amplifier. This is 2
By utilizing the difference in the time constants of the two effects, the effect of changing the carrier density is mainly controlled by the high-frequency amplifier, and the effect of changing the temperature is mainly controlled by the low-frequency amplifier. However, since the output of each amplifier also affects the other effect, good frequency switching can be realized by dividing the frequency domain and setting the gain appropriately. Furthermore, a fine correction effect can be obtained by using three or more control circuits.

Next, referring to FIG.
An example of realizing high-speed frequency switching using one local light source will be described. Even if the number of local light sources is three or more, the same configuration as described below can be used. In FIG. 10, a frequency detector 45 and a switching control unit 47 are provided between the band limiting filter 11 and the comparator 23, respectively.

As described above, when it is desired to realize a frequency switching time shorter than the frequency switching time when the local light source 3 is used alone, or the frequency range to be switched is the variable frequency range of the semiconductor laser (LD) alone. If it is not possible to cover the above, a method of switching and using a plurality of LDs can be considered.

The case where the method of switching and using a plurality of LDs is applied to this embodiment will be described below.

As a result, the frequency switching time for each of the prepared local oscillator light sources is shortened, so that the conventional L
If two or more local light sources 3 are prepared because the frequency switching time of D is slow, the number of local light sources 3 can be reduced.
Further, when two or more local light sources 3 are prepared in order to widen the frequency range, the frequency switching time can be shortened.

The operation of FIG. 10 will be described. One of the outputs of the first local oscillation light source 3C and the second local oscillation light source 3D is selected by the optical switch 49, and after being mixed with the signal light, coherent detection is performed. Now, it is assumed that the first local light source 3C is selected and the first local light source 3C emits light in a certain channel. During this period, the LD switching control unit 47 reads the next channel signal.

FIG. 11 shows an example of the LD switching control section 47. In the following, referring to FIG. 11, the read channel signal is sent to the second reference signal generator 477 by the controller 471. At this time, the first reference signal generator 4
The first channel signal to 75 remains unchanged and switch 47
The IF frequency detection output selected in 3 also remains input to the first reference signal generator 475. The second reference signal generator 477 generates a new reference signal in response to the change in the second channel signal, and switches the frequency of the second local oscillation light source 3D. The manner of frequency switching is the same as in the above-described embodiment, and each effect can be obtained by providing a plurality of circuits for controlling the frequency or changing the location where the band is limited, as in the previous example.

When the frequency of the second local oscillation light source 3D stabilizes at the new frequency and the reception by the first local oscillation light source 3C is completed, a switching signal is input to the LD switching control unit 47 and the control unit 471 is turned on. The selection signal of the switch 49 and the switch 473 for switching the IF frequency detection is changed. Since the switching signal requires a high-speed response, it may be directly added to the two switches 49 and 47 without the control unit 471. By this switching, reception by the second local oscillation light source 3D is started this time. Then, the IF frequency detection information is used to control the second local oscillation light source 3D and correct the control. While receiving by the second local oscillation light source 3D, the next channel signal is taken in again and the first reference signal is controlled so that the first local oscillation light source 3C is provided in the next channel. When the reception using the second local light source 3D is completed, the local light is switched by the switching signal, and the first local light source 3C is used for reception. Further, the error signal is sent to the control unit 47.
Since it is possible to know whether or not the frequency switching of the local oscillation light has been completed by monitoring with 1, the functions such as stopping the switching of the local oscillation light source 3 and determining an error when the frequency switching is not completed within a predetermined time Can be provided in the control unit 471.

Further, a plurality of LDs having different frequency variable ranges
When the output light is switched by using, the control unit in the LD switching control unit 47 has a function of selecting the local light source 3 to be driven according to the channel input as the channel signal, that is, the reference signal generation unit. Hold. Local light source 3 that also uses an optical switch and a selection signal for switching the IF frequency detection output
Can be switched according to. Further, when the LD to be used is different for each channel switching, the effect of higher speed channel switching as described above can be obtained by this configuration. However, when the LD to be used is the same even if the channels are switched, this configuration is Only speeding up of frequency switching can be achieved by the effect of the present invention.

[0049]

As described above, in the present invention, frequency control is performed by optical frequency detection in the present invention, a plurality of circuits having different bands and responses are used for the frequency control circuit, and the reference signal used in the frequency control loop is used. By generating the intermediate frequency signal in consideration of the frequency detection output, it is possible to provide an optical frequency switching method that realizes high-speed and highly-accurate optical frequency switching and stabilization control.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a configuration of an embodiment according to the present invention.

FIG. 2 is a block diagram showing an outline of an internal configuration of a reference signal generation unit shown in FIG.

3 is a flowchart schematically showing the flow of processing in the reference signal generation unit shown in FIG.

FIG. 4 is a diagram showing an example of a configuration of a compensation filter shown in FIG.

FIG. 5 is a diagram showing an example of response characteristics of a semiconductor laser.

FIG. 6 is a block diagram showing an outline of a configuration having an independent intermediate frequency signal frequency detection unit according to another embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic configuration when an error information signal is used according to another embodiment of the present invention.

FIG. 8 is a block diagram showing an outline of a configuration for band limiting the optical frequency detection output according to another embodiment of the present invention.

FIG. 9 is a block diagram showing an outline of a configuration in the case of having two local oscillation light source control circuits according to another embodiment of the present invention.

FIG. 10 is a block diagram showing an outline of a configuration in the case of having two local oscillation light sources according to another embodiment of the present invention.

11 is a block diagram showing an internal configuration of an LD switching control unit shown in FIG.

FIG. 12 is a block diagram showing a schematic configuration of a conventional automatic optical frequency control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical coupler 3 Local light source 5 Optical distributor 7 Photoelectric converter 9 Intermediate frequency amplifier 11 Band limiting filter 13 Frequency discriminator 15 Low-pass filter 17 Judgmentor 19 Reference signal generating unit 21 Reference signal shaping filter 23 Comparator 25 Optical Filter 27 Photoelectric converter 29 Control band limiting filter 31 Control signal amplifier 33 Control signal compensating filter 35 Bias circuit 41 Intermediate frequency signal frequency detection unit 43 Control band limiting filter 45 Frequency detector 47 Switching control unit

Claims (3)

[Claims] 1. An optical frequency at the time of demodulating an information signal from an intermediate frequency signal obtained by mixing a local oscillation light output from a local oscillation light source with a signal light modulated in accordance with an information signal and subjected to optical frequency multiplexing In an automatic optical frequency control device for automatic control, first detection means for detecting an optical frequency of a local oscillation light output from the local oscillation light source, and band limitation for limiting a control band in the automatic control of the optical frequency. Means, second detecting means for detecting the frequency of the intermediate frequency signal, and reference signal generating means for generating a reference signal corresponding to a target optical frequency controlled in accordance with the output of the second detecting means. The reference signal generated by the reference signal generating means and the first signal
2. An automatic optical frequency control device, comprising: a comparing means for comparing the signal of the detecting means with the detecting means; and a controlling means for controlling the optical frequency of the local oscillation light source according to the output of the comparing means. 2. The optical frequency automatic control apparatus according to claim 1, wherein the band limiting unit is configured by connecting a plurality of band limiting units each having a different control band in parallel. 3. The optical frequency automatic control apparatus according to claim 1, wherein the band limiting means is provided between the first detecting means and the comparing means.