JPH05198887A - Measurement-control equipment of optical frequency deviation amount of laser - Google Patents

Abstract

PURPOSE:To establish measurement.control technique to stabilize the optical frequency deviation amount, by installing an operation point setting circuit for setting an operation point, so as to coincide with the average optical frequency of optical frequencies. CONSTITUTION:The title equipment is provided with an operation point setting circuit 8 for setting an operation point, in the manner in which the operation point of an optical interference apparatus 4 to a laser light source 2 coincides with the average optical frequency of the optical frequency giving a local maximum point in an optical frequency discriminator and the optical frequency giving a local minimum point adjuscent to the local maximum point. Either circuit selected out of an optical frequency deviation amount measuring circuit 10 and an optical frequency deviation amount stabilizing circuit is installed. The above measuring circuit 10 detects the optical frequency deviation amount from the mean value or the effective value of amplitudes of frequency components corresponding with the frequency of a modulation signal in an electric signal at the above set operation point. The above stabilizing circuit operates the error value between the mean value or the effective value of amplitudes of frequency components corresponding with the frequency of the modulation signal in the electric signal at the above set operation point, and feeds back the error value to the modulation factor of the laser light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser for measuring an optical frequency deviation amount of a laser which is frequency-modulated or phase-modulated based on input data, or for stabilizing it to a predetermined value. The present invention relates to an optical frequency shift amount measuring / controlling device.

In recent years, a system for performing optical communication or optical measurement by directly performing optical frequency modulation or phase modulation on laser light with high coherency output from a laser diode or the like has been put into practical use.

For example, as an optical communication system, there is an optical communication system of the FSK system (frequency shift keying system) using coherent light. In this FSK method, 2 of “0” or “1” of data to be transmitted
Depending on the value logic, frequency modulation is performed so that the optical frequency of the output from the laser diode is changed to the first frequency f ₁ or the second frequency f ₂ .

In this case, the modulation efficiency, that is, the frequency variable amount per unit bias current changes due to the aging of the laser diode itself, the aging of the light source module including the laser diode, the bias current of the laser diode, and the like. As a result, even if the laser diode is modulated with the same drive current, the modulation index, that is, the optical frequency shift amount between the first frequency f ₁ and the second frequency f ₂ described above centered on the central optical frequency f _0. Deviates from the default setting.

This shift significantly deteriorates the receiving sensitivity of the optical signal in the receiving system of the optical communication system. Therefore, a measurement technique of the optical frequency shift amount in the laser diode or the like or a control technique for stabilizing the optical frequency shift amount to a predetermined value is necessary.

[0006]

2. Description of the Related Art However, the technique of directly modulating the frequency or phase of laser light is a technique that has finally been put into practical use. For this reason, we have established established measurements for stabilizing the optical frequency shift amount in the laser.
The control technology is currently unknown.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for measuring / controlling the optical frequency shift amount of a laser.

[0008]

FIG. 1 is a diagram showing a basic configuration of an apparatus according to the present invention, which can be used for measuring an optical frequency shift amount of a laser.

This apparatus receives light from a laser light source 2 which is frequency-modulated or phase-modulated based on a modulation signal and outputs an interference light according to an optical frequency discrimination characteristic, which is an optical interferometer 4.
And a photodetector 6 that receives the interference light and converts the intensity of the light into an electric signal, and an operating point of the optical interferometer 4 that receives the electric signal with respect to the laser light source 2 is a maximum point in the optical frequency discrimination characteristic. And the operating point setting circuit 8 for setting the operating point so as to match the average optical frequency of the optical frequencies that give the local minimum point adjacent to the local maximum point, and the operating point setting circuit 8 based on the set operating point. An optical frequency deviation amount measuring circuit 10 for detecting the optical frequency deviation amount from the average value or the effective value of the amplitude of the frequency component corresponding to the frequency of the modulated signal in the electric signal.

Here, the light that enters the optical interferometer 4 from the laser light source 2 is, for example, backward light output from the laser diode. In this case, the forward light output from the laser diode is sent to the transmission line 12 as an optical signal.

FIG. 2 is a diagram showing another basic configuration of the apparatus of the present invention, which is used for controlling the optical frequency shift amount of the laser. This device receives light from a laser light source 2 that is frequency-modulated or phase-modulated based on a modulation signal, outputs an interference light according to an optical frequency discrimination characteristic, and the interference light, and receives the interference light. A light receiver 6 for converting light intensity into an electric signal, and the optical interferometer 4 for receiving the electric signal.
Operation for setting the operating point so that the operating point for the laser light source 2 coincides with the average optical frequency of the optical frequency giving the maximum point in the optical frequency discrimination characteristic and the optical frequency giving the minimum point adjacent to the maximum point. The point setting circuit 8 calculates the error value between the average value or the effective value of the amplitude of the frequency component corresponding to the frequency of the modulated signal in the electric signal and the predetermined value under the set operating point, An optical frequency shift amount stabilizing circuit 14 for returning an error value to the modulation factor of the laser light source 2 is provided.

In FIG. 2, a bias circuit 16 and a modulation circuit 18 are additionally shown in order to facilitate understanding of the operation of the laser light source 2 and the like. Bias circuit 16
Supplies to the laser light source 2 a bias sufficient for the laser light source 2 to oscillate. The modulation circuit 18 supplies a modulation signal to the laser light source 2 or superimposes the modulation signal on a bias based on input data which is generally a digital signal.

Here, the laser light source 2 has a light frequency of a predetermined center light based on the modulation signal output from the modulation circuit 18 in correspondence with the binary logic "0" or "1" of the input data. To match any frequency selected from the first frequency and the second frequency centering on the frequency,
It is frequency-modulated or phase-modulated. The difference between the first frequency and the second frequency is defined as the optical frequency shift amount.

[0014]

[Operation] Measurement of optical frequency shift amount of laser according to the present invention
The operating principle of the control device is as follows: (1) The operating point of the optical interferometer is the average light of the optical frequency that gives the maximum point in the optical frequency discrimination characteristics of the optical interferometer and the optical frequency that gives the minimum point adjacent to the maximum point. The frequency (hereinafter, simply referred to as "average optical frequency") may be set, and (2) the frequency corresponding to the frequency of the modulation signal in the electric signal from the photodetector under the set operating point. Detecting and measuring the average value or the effective value of the amplitude of the component, and modulating the laser light source so as to focus the average value or the effective value toward the set value when producing the predetermined optical frequency shift amount. It is roughly divided into two points, that is, returning feedback every time.

That is, according to the present invention, when the operating point of the optical interferometer coincides with the average optical frequency, the average value or the effective value of the amplitudes of the frequency components corresponding to the frequency of the modulation signal in the electric signal from the photodetector. The fact that the value and the optical frequency shift amount have a predetermined functional relationship is used.

The operating point setting circuit 8 is specifically an operating point detecting circuit for detecting the difference between the average optical frequency and the operating point based on the electric signal from the light receiver 6, and the difference is zero. And an operating point control circuit for controlling the oscillation frequency of the laser light source 2 or the interference characteristic of the optical interferometer 4.

In this case, when the feedback control operation by the operating point control circuit is performed on the oscillation frequency of the laser light source 2, the automatic frequency control (AFC) of the laser light source 2 is simultaneously realized. That is, in this case, the laser light source 2
As a result of performing the control so that the center optical frequency of the laser light always matches the average optical frequency, the center light frequency of the laser light source 2 is always stabilized to a constant value.

The device according to the present invention can be applied to an optical communication system using an optical frequency division multiplexing system (FDM system). In this case, in particular, the feedback control operation in setting the operating point is performed for the oscillation frequency of the laser light source, so that the operating point of the optical modulator for each laser light source is 1
Localized at each of a plurality of average optical frequencies on a single optical frequency discrimination characteristic in a single optical interferometer, automatic frequency control for each laser light source is simultaneously realized.

Here, the interval between the adjacent average optical frequencies on the optical frequency discrimination characteristic is exactly a constant value. Therefore, as a result of the automatic frequency control of each laser light source being simultaneously realized as described above, the oscillation frequencies of each laser light source in the FDM transmission system can be accurately arranged at equal intervals on the optical frequency axis.

[0020]

EXAMPLES Examples of the present invention will be described below. FIG. 3 shows the measurement of the optical frequency shift amount of the laser according to the first embodiment of the present invention.
It is a block diagram of a control device.

For example, forward light output from the laser diode 22 is incident on the transmission line L as an optical signal D _h .
This optical signal D _h is “0” of the data D _in to be transmitted.
Alternatively, the optical frequency is frequency-modulated (FSK-modulated) to the first frequency f ₁ or the second frequency f ₂ based on the modulation signal I _p output from the modulation circuit 24 corresponding to the binary logic of “1”. It The data modulation for the optical signal D _h may be phase modulation (PSK modulation: phase shift keying).
Further, not the front light from the laser diode 22 but the rear light may be incident on the transmission line L as D _h . In this case, from the laser diode 22 to the optical interferometer 26 described later.
The laser light output to is forward light. Here, a predetermined bias current is inputted from the bias circuit 28 to the laser diode 22 so that the optical modulation operation in the laser diode 22 is performed around a certain center optical frequency f ₀ .

The optical interferometer 26 receives the backward light H ₀ from the laser diode 22 and outputs two complementary interference lights H _i1 and H _i2 . FIG. 4 is a diagram showing a Mach-Zehnder interferometer that outputs two complementary interference lights H _i1 and H _i2 . In the figure, M is a half mirror and M'is a mirror, and two complementary interference lights H _i1 and H _i2 are generated by making a predetermined difference between the optical path lengths of the two optical paths. The optical frequency discrimination characteristics of these two complementary interference lights H _i1 and H _i2 are shown by the solid line and the broken line in FIG.

FIG. 6 shows two complementary interference lights H._i1And H_i2
It is a figure which shows the Fabry-Perot interferometer which outputs. same
In the figure, one interference light H_i1Is normal transmitted light
On the other hand, the other interference light H_i2Is reflected light. Where
Abbey-Perot interference element FP from the laser diode
Back light H₀The reflected light is tilted with respect to the optical axis of
Interference light H_i2Not return to the laser diode
In order to do the back light H ₀Interference light H without blocking_i2Take out
This is because

The optical frequency discrimination characteristics of the Fabry-Perot interferometer are determined according to factors such as the surface reflectance of the Fabry-Perot interferometer FP. Optical frequency discrimination characteristics similar to those shown can be obtained.

FIG. 7 shows two complementary interference lights H._i1And H_i2
It is a figure which shows the other optical interferometer which outputs. In the figure
Is the first polarizer PL on the input side of the birefringent crystal CR._iBut
The second polarizer PL is provided on the output side._oIs provided.
First polarizer PL_iOptical axis and second polarizer PL_oLight of
The angle formed by the academic axes is set to 45 °, for example. like this
The backward light H from the laser diode depends on the configuration.₀From 2
Two complementary interference lights H _i1And H_i2Is obtained.

Returning to the explanation of the apparatus shown in FIG. Optical interferometer 2
Two interference lights H _i1 and H _i2 from the first and second photodetectors 30, which are photodiodes connected in series,
It is incident on 32 respectively. First and second light receivers 30,
The photocurrents I ₁ and I ₂ generated in 32 are respectively detected as voltage values by the resistors 34 and 36 for voltage detection and the operational amplifiers 38 and 40, and these two voltage values are added by the adder 42. The addition result is input to the automatic light output control circuit (APC circuit) 44. The output signal of the adder 42 corresponds to the sum component of the photocurrents I ₁ and I ₂ generated in the first and second photodetectors 30 and 32. APC circuit 4
The operation of No. 4 will be described later.

In this embodiment, in order to provide the difference component between the photocurrents I ₁ and I ₂ for detecting the operating point and stabilizing the optical frequency shift amount, the first photodetector 30 and the second photodetector 32 are provided. The change in the potential at the connection point is captured by the optical frequency shift amount stabilization circuit 46 and the operating point detection circuit 48. Reference numeral 50 is an operating point control circuit that controls the oscillation frequency of the laser light source 22 or the interference characteristic of the optical interferometer 26 based on the detected operating point.

When the operating point control circuit 50 controls the oscillation frequency of the laser diode 22, the control line L ₁ from the operating point control circuit 50 is applied to the bias circuit 28 as shown by the solid line in FIG. The bias current that is connected and is input from the bias circuit 28 to the laser diode 22 is changed based on the control signal. Alternatively, although not shown, the output of the operating point control circuit 50 is set to the laser diode 22.
By superimposing it on the control input to the temperature control element of
The temperature of the laser diode 22 may be changed. As the temperature control element, for example, a known Peltier element is used.

On the other hand, the operating point control circuit 50 has the optical interferometer 26.
When controlling the interference characteristics in the optical interferometer 26, the control line L ₁ from the operating point control circuit 50 is indicated by a broken line.
And the physical quantities such as the resonator length and the delay time difference of the optical interferometer 26 are changed by the control signal. Specific methods for changing these physical quantities are: changing using the photoelastic effect, changing using the electro-optical effect, changing by applying a mechanical external force, and changing using the thermo-optical effect. Methods such as making them known are well known.

The specific operation of the first embodiment will be described below. FIG. 5 is a graph showing a part of the optical frequency discrimination characteristic of the Mach-Zehnder interferometer used as the optical interferometer 26. In this graph, the vertical axis represents the light intensity of the interference light from the optical interferometer 26,
The horizontal axis represents the optical frequency. The characteristics represented by the solid line and the broken line correspond to the optical frequency discrimination characteristics for each of the two complementary interference lights output from the optical interferometer 26.

When a Mach-Zehnder interferometer is used as the optical interferometer 26, its optical frequency discrimination characteristic exhibits a characteristic that the value of the light intensity changes sinusoidally with respect to the change of the optical frequency, and the maximum point MAX. And the minimum point MIN appear alternately.

In this embodiment, in order to stabilize the optical frequency shift amount in the laser diode 22 of FIG. 3, first, the laser diode 22 of the optical interferometer 26 of FIG.
Is the average optical frequency of the optical frequency that gives the maximum point MAX in FIG. 5 and the optical frequency that gives the minimum point MIN adjacent to this maximum point (corresponding to the inflection point P at which the differential coefficient becomes maximum in the operating characteristic curve). The control is performed so as to always match the optical frequency). In this example, this inflection point coincides with the intersection of the optical frequency discrimination curves for the two complementary interference lights.

FIG. 8 is a diagram for explaining the principle of operating point setting by the optical frequency discrimination characteristics of two complementary interference lights. As shown in FIG. 8A, when the center frequency f ₀ of the laser diode 22 matches the average optical frequency, the photocurrent I ₁ generated in the first photodetector 30 based on the modulation signal I _p. The average value (DC level) of the
This coincides with the average value (DC level) of the photocurrent I ₂ generated in No. ₂ .

On the other hand, as shown in FIG. 8B, when the operating point drifts to the low frequency side of the optical frequency and the center frequency f ₀ of the laser diode 22 becomes lower than the average optical frequency, The DC level of the photocurrent I ₁ generated in the first photodetector 30 based on the optical frequency discrimination characteristic of the one interference light H _{i1 is} the photocurrent generated in the second photodetector 32 based on the other interference light H _i2. It will be lower than the DC level of I ₂ .

On the other hand, as shown in FIG. 8C, when the operating point drifts to the high frequency side of the optical frequency and the center frequency f ₀ of the laser diode 22 becomes higher than the average optical frequency, Contrary to the case of FIG. 8B, the DC level of the photocurrent I ₁ generated in the first photodetector 30 is higher than the DC level of the photocurrent I ₂ generated in the second photodetector 32.

[0036] Thus, by performing the feedback control as the DC level of the photocurrent I ₁ of the DC level and the difference between the DC level of the photocurrent I ₂ or photocurrents I ₁ and I ₂ of the difference signal is focused to zero, The operating point of the optical interferometer 26 can be set to the average optical frequency.

When such setting of the operating point is realized, the center frequency f ₀ of the laser diode 22 coincides with the optical frequency that gives the intersection P of the optical frequency discrimination characteristics for the two complementary interference lights. When the optical interferometer 26 is a Mach-Zehnder interferometer and the frequency discrimination characteristic is sinusoidal, the intersection point P coincides with the inflection point of the frequency discrimination characteristic, but it depends on the type of the optical interferometer used. The intersection point P may not coincide with the inflection point. The fact that the intersection point P does not match the inflection point does not affect whether or not the operating point can be set.

When the center frequency f ₀ of the laser diode 22 coincides with the frequency that gives the intersection point P of the frequency discriminating characteristics, the differential coefficient of the optical frequency discriminating characteristics is always maintained at a constant value, so that the photocurrent I ₁ or The average value or effective value of the amplitude of the frequency component corresponding to the modulation frequency in I ₂ and the optical frequency shift amount have a fixed functional relationship.

Based on such an operating principle, the optical frequency deviation amount stabilizing circuit 46 calculates an error value between the above-mentioned average value or effective value and a predetermined value, and the error value is modulated by the modulation circuit 24.
Return to and adjust the modulation. As a result, the optical frequency shift amount in the laser diode 22 can be stabilized regardless of changes over time in the laser diode 22.

In this embodiment, the reason why the difference components of the photocurrents I ₁ and I ₂ generated in the first and second photodetectors 30 and 32 are taken into the optical frequency deviation amount stabilizing circuit 46 is as follows. On the street.

As is apparent from the description with reference to FIG. 8, the photocurrents I ₁ and I ₂ obtained based on the optical frequency discrimination characteristics of the two complementary interference lights are in opposite phases to each other. The optical frequency discrimination characteristic for one interference light has the same waveform obtained by moving the optical frequency discrimination characteristic for the other interference light in parallel on the optical frequency axis. Therefore, by obtaining the difference signal of the photocurrents I ₁ and I ₂ , the detection sensitivity of the amplitude of the photocurrents I ₁ or I ₂ is improved, and the S / N in the control of the optical frequency shift amount is significantly increased. Will be possible.

By the way, the superiority of this embodiment is also found in that APC can be easily realized by converting two complementary interference lights into electric signals by two light receivers. The APC circuit 44 performs automatic light output control of the laser diode 22. The operating principle will be described below.

Since the two interference lights H _i1 and H _i2 output from the optical interferometer 26 are complementary interference lights, when they are added, the addition output is the alternate long and short dash line in FIG. As shown by, the signal becomes flat. That is, the signal obtained by adding the voltage values corresponding to the photocurrents I ₁ and I ₂ generated in the first and second photodetectors 30 and 32 by the adder 42 is a signal having a flat amplitude and close to direct current. Becomes

Based on this fact, the APC circuit 44
Automatic light output control is realized by applying negative feedback to the bias circuit 28 so that the level of the addition output having a flat amplitude from the adder 42 is always a constant level.

Specifically, the APC circuit 44 detects the fluctuation component of the addition output from the adder 42 with respect to the preset voltage V _{R, and} outputs a signal whose polarity is inverted to the bias circuit 28. As a result, the bias circuit 28
The bias current generated by the laser diode 22 is controlled, and the optical output of the laser diode 22 is maintained at a constant level.

FIG. 9 is a block diagram of an optical frequency shift amount measuring / control device for a laser according to a second embodiment of the present invention.
This embodiment is different from the first embodiment in that the difference signal input to the optical frequency deviation amount stabilizing circuit 46 and the operating point detection circuit 48 is the connecting portion of the first and second photodetectors 30 and 32. A mark ratio monitor circuit 54 is additionally provided, in addition to the output voltage of the operational amplifier 38, the output voltage of the operational amplifier 40 is subtracted by the subtractor 52 to obtain an output. That is the point.

The mark ratio monitor circuit 54 is composed of, for example, an integrator provided in the modulation circuit 24, and the generation ratio of the logical values “1” and “0” of the transmission data D _in input to the modulation circuit 24, that is, the mark. The ratio is calculated, and feedback is applied to the operating point control circuit 50 and / or the optical frequency shift amount stabilizing circuit 46.

Now, when the mark ratio is, for example, 1/2, that is, when "1" and "0" occur at a ratio of 1: 1 and when the mark ratio is, for example, 1/4, that is, "1". In the case where "0" occurs at a ratio of 1: 3, the operating point detection circuit 4
The DC level of the difference signal from the subtractor 52 that is taken into 8 has different values.

Therefore, by feeding back a correction signal corresponding to the mark rate detected by the mark rate monitor circuit 54 to the operating point control circuit 50 and / or the optical frequency deviation amount stabilizing circuit 46, regardless of the mark rate. It becomes possible to always perform stable control.

FIG. 10 is a block diagram of an optical frequency shift amount measuring / control device for a laser according to a third embodiment of the present invention. The present embodiment is an optical frequency division multiplexing (FDM) transmission system, that is, an optical communication system in which a plurality of lines of information are multiplexed and sent by simultaneously using a plurality of central optical frequencies on one optical fiber. Applied.

The laser diode 56, the modulation circuit 58, the bias circuit 60, the optical interferometer 62, the light receiver 64 of FIG.
Operating point setting circuit 66, optical frequency deviation amount stabilizing circuit 68
Are substantially the same as those in the first embodiment of FIG.

The third embodiment of FIG. 10 is different from the first embodiment of FIG. 3 in that in the FDM transmission system, a plurality of center optical frequencies are required, so that the laser diode 56 and the modulation circuit are provided. 58, bias circuit 60, light receiver 64,
Operating point setting circuit 66 and optical frequency deviation amount stabilizing circuit 68
Each of the above is composed of a plurality of # 1 to #n.

With this configuration, a plurality of # 1 to #n
Transmission data D for line_inMultiplex transmission is realized. still,
In this embodiment, the optical interferometer 62 is a Fabry-Perot.
It is composed of an interferometer. Then, each of # 1 to #n
Each rear light H of # 1 to #n from the laser diode 56
₀Is space-divided by n optical fibers,
Of Fabry-Perot interferometer 62 of
Interference light H of # 1 to #n _iWith n optical fibers
It is space-divided and guided to n light receivers 64.

The stabilizing operation of the operating point and the optical frequency shift amount in each of the n sets of # 1 to #n in FIG.
This is substantially the same as in the first embodiment. However, in this embodiment, in particular, the output of each operating point setting circuit 66 is superposed on the bias current in each bias circuit 60 or the control input of the temperature control element of each laser diode 56, and is negatively fed back to generate an optical signal. Each operating point for each laser diode 56 of the interferometer 62 is localized at each of the n average optical frequencies on one optical frequency discrimination characteristic.

Here, the interval between adjacent average optical frequencies on one optical frequency discrimination characteristic is exactly a constant value.
Therefore, as described above, the automatic frequency control (AFC) of each laser diode 56 is realized at the same time, which results in the FDM.
It is possible to arrange n operating points for each of the laser diodes # 1 to #n in the transmission system at exactly equal intervals on the optical frequency axis.

Then, for each laser diode 56, the optical frequency shift amount can be stabilized to a predetermined value under the above AFC. Further, by making the operating points for the plurality of laser diodes 56 correspond to one average optical frequency in the optical frequency discrimination characteristic, it is possible to correspond to one transmitting to different transmission lines at a common optical frequency. it can.

FIG. 11 is a block diagram of an optical frequency shift amount measurement / control device for a laser according to a fourth embodiment of the present invention. In the figure, the parts with the same numbers as in the third embodiment of FIG. 10 have the same functions.

The difference between the fourth embodiment and the third embodiment is that the operating point setting circuit and the optical frequency deviation stabilizing circuit are provided with only one reference numeral 70 and one reference numeral 72, respectively, and each of them is time-shared. This is the point of operation.

The outputs from the photoreceivers 64 of # 1 to #n are stabilized by the operating point setting circuit 70 and the optical frequency shift amount via the switches 74 and 76 at the time division timings assigned to the outputs. It is input to the circuit 72. Then, the respective control results are held in the data holding circuits 82 and 84 via the switches 78 and 80. Each of the data holding circuits 82 and 84 has the latest # 1 to # at each control point.
Each control data of n is negatively fed back to each bias circuit 60 (or the temperature control terminal of the laser diode 56) and each modulation circuit 58 at the same time.

With the configuration as described above, the circuit scale can be reduced.

[0061]

As described above, according to the present invention,
It is possible to provide a measurement / control device for the optical frequency shift amount of a laser.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a device of the present invention.

FIG. 2 is a diagram showing another basic configuration of the device of the present invention.

FIG. 3 is a block diagram of an apparatus showing a first embodiment of the present invention.

FIG. 4 is a diagram showing a Mach-Zehnder interferometer that outputs two complementary interference lights.

5 is a diagram showing optical frequency discrimination characteristics of two interference lights in FIG.

FIG. 6 is a diagram showing a Fabry-Perot interferometer that outputs two complementary interference lights.

FIG. 7 is a diagram showing another optical interferometer that obtains two complementary interference lights.

FIG. 8 is a diagram illustrating the principle of operating point setting.

FIG. 9 is a block diagram of an apparatus showing a second embodiment of the present invention.

FIG. 10 is a block diagram of an apparatus showing a third embodiment of the present invention.

FIG. 11 is a block diagram of an apparatus showing a fourth embodiment of the present invention.

[Explanation of symbols]

 2 Laser light source 4,26,62 Optical interferometer 6,30,32,64 Light receiver 8,66,70 Operating point setting circuit 10 Optical frequency deviation amount measuring circuit 14,46,68,72 Optical frequency deviation amount stable Circuit

Claims (13)

[Claims] 1. An optical interferometer (4) which receives light from a laser light source (2) that is frequency-modulated or phase-modulated based on a modulation signal and outputs interference light according to an optical frequency discrimination characteristic, and the interference. A light receiver (6) for receiving light and converting the light intensity into an electric signal, and the laser light source of the optical interferometer (4) for receiving the electric signal
Set the operating point so that the operating point for (2) matches the average optical frequency of the optical frequency that gives the maximum point in the optical frequency discrimination characteristics and the optical frequency that gives the minimum point adjacent to the maximum point. A circuit (8) and an optical frequency deviation that detects the optical frequency deviation amount from the average value or the effective value of the amplitude of the frequency component corresponding to the frequency of the modulated signal in the electric signal under the set operating point. Quantity measuring circuit (10), and calculates the error value between the average value or the effective value of the amplitude of the frequency component corresponding to the frequency of the modulation signal in the electric signal and the predetermined value under the set operating point And an optical frequency deviation stabilizing circuit (14) for returning the error value to the degree of modulation of the laser light source (2), the optical frequency deviation of the laser being provided. Transfer rate measurement and control circuit. 2. The operating point setting circuit (8) includes an operating point detection circuit (48) for detecting a difference between the average optical frequency and the operating point based on an electric signal from the light receiver, and the difference. Operating point control circuit (50) for controlling the oscillation frequency of the laser light source or the interference characteristics of the optical interferometer so that
The measurement / control circuit for measuring the optical frequency deviation of a laser according to claim 1, further comprising: 3. The laser light source (2) is a laser diode, and the oscillation frequency of the laser light source (2) is controlled by changing the bias or temperature of the laser diode. The optical frequency shift amount measurement / control device according to claim 2, wherein automatic frequency control is performed. 4. The optical interferometer (4) is an optical interferometer that outputs two types of interference light having complementary optical frequency discrimination characteristics, and the photodetector (6) is one of the two types. The optical frequency shift amount measuring and controlling apparatus according to claim 1, wherein the measuring and controlling apparatus comprises first and second light receivers (30, 32) respectively receiving the interference light. 5. The difference component between the electric signals from the first and second photo detectors (30, 32) is the operating point setting circuit and the optical frequency deviation amount measuring circuit or the optical frequency deviation amount stable. The optical frequency shift amount measuring / control device according to claim 4, wherein the measuring / control device inputs the optical frequency shift amount of the laser. 6. The operating point setting circuit sets the operating point based on the DC level of the difference component between the electric signals from the first and second photodetectors (30, 32). The measurement / control device for the optical frequency shift amount of a laser according to claim 5. 7. A control for detecting the oscillation output of the laser light source based on the sum component of the respective electric signals from the first and second light receivers (30, 32), and controlling the oscillation output to be constant. 5. The measurement of the optical frequency shift amount of the laser according to claim 4, further comprising an automatic light output control circuit (44) for performing
Control device. 8. A mark ratio monitor circuit (54) for measuring a mark ratio in the modulated signal, wherein the mark ratio measured by the mark ratio monitor circuit is the operating point setting circuit and the optical frequency deviation amount. The measurement / control device for the optical frequency shift amount of a laser according to claim 1, wherein the measuring / control device is fed back to a measuring circuit or the optical frequency shift amount stabilizing circuit. 9. A plurality of the laser light sources are provided, and the optical interferometer receives the plurality of spatially divided lights from the respective laser light sources in parallel and outputs the interference light corresponding to each of them in parallel. The optical receiver, the operating point setting circuit, the optical frequency deviation amount measuring circuit, or the optical frequency deviation amount stabilizing circuit is provided in plural according to the number of the laser light sources. An apparatus for measuring and controlling an optical frequency shift amount of a laser according to claim 1. 10. A plurality of the laser light sources are provided, and the optical interferometer receives a plurality of spatially divided lights from the respective laser light sources in parallel and outputs interference light corresponding to each of them in parallel. A plurality of the light receivers are provided according to the number of the laser light sources, and the operating point setting circuit and the optical frequency deviation amount measuring circuit or the optical frequency deviation amount stabilizing circuit are provided from the plurality of light receivers. 2. The apparatus for measuring and controlling the optical frequency shift amount of a laser according to claim 1, wherein the measurement / control device operates in a time-division manner based on each of the electric signals. 11. The operating points are set so that the operating points of the optical interferometer with respect to the plurality of laser light sources respectively match the plurality of average optical frequencies in the optical frequency discrimination characteristic. The measurement / control device for the optical frequency shift amount of the laser according to claim 9 or 10. 12. The measurement / control apparatus for the optical frequency shift amount of a laser according to claim 11, wherein the respective operating points are set at equal intervals on the optical frequency axis. 13. The operating points are set such that the operating points of the optical interferometer with respect to the plurality of laser light sources respectively match the common average optical frequency in the optical frequency discrimination characteristics. The measurement / control device for the optical frequency shift amount of the laser according to claim 9 or 10.