JPH04285830A - Measuring/controlling apparatus for deviation amount of optical frequency of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a compact and inexpensive measuring/controlling apparatus in a simple structure which measures/controls the amount of deviation of an optical frequency of a semiconductor laser which is frequency-modulated or phase-modulated based on an input modulating signal. CONSTITUTION:An operating point controlling circuit 42 stabilizes an operating point at the central value of the discriminating characteristics of the optical frequency of an interference device 20. At this time, the operating point is changed by a low frequency signal S from a low frequency oscillator 51. When the subtracting signals of electric signals EL1, EL2 from photodetectors 31, 36 are synchronously detected by the low frequency signal S in a synchronous detecting circuit 52, the deviation of the synchronously-detected output from zero represents the amount of deviation f of the optical frequency. Therefore, it becomes possible to measure the amount of deviation f of the optical frequency. A stabilizing circuit 53 can consequently control the amount of deviation f of the optical frequency.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is useful for measuring and controlling the amount of optical frequency deviation of a laser beam that is frequency- or phase-modulated based on an input modulation signal in communication, measurement, etc. that uses optical frequency modulation of a laser. This invention relates to a device for measuring and controlling the amount of optical frequency deviation of a semiconductor laser.

In recent years, communication, measurement, etc. have come to be performed by using direct optical frequency modulation for semiconductor lasers. For example, in communications, optical communication systems are being put into practical use that directly apply optical frequency modulation to laser light to generate optical data to be sent to a transmission path. One method is FSK (FSK) using coherent light.
An example of this is a coherent optical communication system based on a frequency shift keying method. In this FSK method, the data to be transmitted has two logical values (“1”
, "0"), data modulation (FM modulation) is performed to change the frequency of the output light from the semiconductor laser to a first optical frequency f1 and a second optical frequency f2.

In this case, the FM modulation efficiency (the amount of optical frequency variation per unit current of the semiconductor laser) changes due to aging of the bias of the semiconductor laser itself or aging of the optical module including the semiconductor laser. Then, even if the semiconductor laser is modulated with the same drive current, the modulation index, that is, the amount of frequency deviation of the first and second optical frequencies f1 and f2 with respect to the center frequency F0 will deviate from the initially set constant value. This deviation significantly deteriorates the receiving sensitivity in the receiving system of the optical communication system.

The present invention describes an apparatus for measuring and controlling the amount of optical frequency deviation of a semiconductor laser, which does not cause the above-mentioned deviation. Note that the present invention can also be applied to optical measurement systems using coherent light.

[0005]

[Prior Art] The technology of directly performing optical frequency modulation on a semiconductor laser has appeared very recently, and there is no concept of measuring or controlling the amount of optical frequency deviation, and no established conventional technology is known yet. Not yet.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a device for measuring and controlling the amount of optical frequency deviation of a semiconductor laser, which has a simple structure, can be miniaturized, and can be realized at low cost.

[0007]

[Means for Solving the Problems] FIG. 1 is a block diagram showing the basic configuration of the present invention. In the figure, 10 is a semiconductor laser, which changes the optical frequency to a first frequency f1 and a second frequency f2 in response to "1" and "0" of a high-speed modulation signal.
It outputs output light H0 changed to (FSK modulated).

The device for measuring and controlling the amount of optical frequency deviation of a semiconductor laser according to the present invention operates upon receiving FSK-modulated output light H0 from the semiconductor laser 10, and as shown in the figure, an optical interferometer 20 , a light receiver 30 , an operating point setting means 40 , and an optical frequency deviation detection means 50 .

Optical interferometer 20 receives output light H0 from semiconductor laser 10 and outputs interference light Hi in accordance with optical frequency discrimination characteristics. The light receiver 30 receives the interference light Hi and converts the light intensity into an electric signal EL.

The operating point setting means 40 receives the electric signal EL and sets the operating point of the optical interferometer 20 to match the optical frequency corresponding to the median value between the maximum value and the minimum value of the optical frequency discrimination characteristic. Set the operating point.

The optical frequency deviation detecting means 50 extracts a low frequency signal component of the average optical output intensity of the interference light Hi which has been low frequency modulated in advance at the operating point from the electrical signal EL by synchronous detection. and detect the amount of optical frequency deviation.

0012

[Operation] The operating principle of the device for measuring and controlling the amount of optical frequency deviation of a semiconductor laser according to the present invention is as follows: i) The optical frequency corresponding to the median value of the optical frequency discrimination characteristic in the optical interferometer 20 is ii) Under the stabilized operating point, a low frequency signal of the average optical output intensity of the interference light Hi which has been low frequency modulated in advance and is output from the optical interferometer 20; The process can be roughly divided into two parts: extracting the component from the electrical signal output from the optical receiver 30 by synchronously detecting it with a low frequency signal, and detecting the amount of optical frequency deviation from the obtained synchronously detected output signal. .

Each of the above operations i) and ii) is performed mainly by the operating point setting means 40 and the optical frequency deviation detection means 50.
perform each. I will discuss this in more detail below. First, setting of the operating point will be explained.

FIG. 2(a) is a graph showing the optical frequency discrimination characteristics of the optical interferometer 20. The horizontal axis of this graph indicates the optical frequency, that is, the operating frequency of the optical interferometer, and the vertical axis indicates the optical intensity P of the interference light Hi from the optical interferometer 20. It should be noted that there are two interference beams Hi, which are complementary interference beams Hi1 and Hi2 from the optical interferometer 20. In FIG. 2(a), the solid line is the optical frequency discrimination characteristic curve of the interference light Hi1, and the chain line is the optical frequency discrimination characteristic curve of the complementary interference light Hi2. As the optical interferometer 20, a Fabry-Perot interferometer, a Michelson interferometer, a Mach-Zehnder interferometer, etc. are well known, but any interferometer may be used in the present invention. This graph shows an example when a Mach-Zehnder interferometer is used, and this type of optical frequency discrimination characteristic is observed.

Generally, when a Mach-Zehnder interferometer is used, the optical frequency discrimination characteristic shows a light intensity that changes in a sinusoidal manner with respect to a change in optical frequency, and this graph shows a part of this. As shown in the figure, the light intensity takes a local maximum value MAX and a local minimum value MIN. The optical frequency that causes the maximum value MAX is fmax, and the optical frequency that causes the minimum value MIN is fmin. In the present invention, the operating point (first
The optical frequency f0 (intermediate between the optical frequency f1 and the second optical frequency f2) is the median value MED (frequency fm) between these extreme values.
ed).

Since the above two interference lights Hi1 and Hi2 are interference lights complementary to each other, when they are received respectively and their outputs are added, a flat output is obtained as shown by the dashed-dotted line in FIG. 2(a). This flat output value is proportional to the optical output of the semiconductor laser 10. In addition, the above two complementary interference lights H
When i1 and Hi2 are respectively received and their outputs are subtracted, the amplitude doubles and crosses the zero point at the median value MED, that is, the operating point. Therefore, by controlling the bias or temperature of the semiconductor laser 10 or the optical interferometer 20 so that the subtracted signal is always zero, the operating point can be made to coincide with the median value MED of the optical frequency discrimination characteristic.

Next, detection of the amount of optical frequency shift will be explained. Here, in order to simplify the explanation, it is assumed that the output light H0 from the semiconductor laser 10 is subjected to ideal FSK modulation with a mark rate of 1/2. The mark rate is the ratio of occurrences of "1" and "0" in a modulated signal, and if "1" and "0" occur with equal probability, the mark rate will be 1/2 and "1". If the ratio of "0" is 1:3, the mark ratio is 1/4. Ideal FSK modulation means that the transition time between optical frequencies f1 and f2 is infinitely small.

As described above, the operating point is stabilized at the median value MED of the optical frequency discrimination characteristic. This state is shown in Figure 3(a).
Shown below. For convenience, the amount of optical frequency deviation Δf is expressed as Δf=FSR/
It was set as 2. FSR is the optical frequency difference between adjacent maximum values (minimum values) of optical frequency discrimination characteristics in the free spectral range. Keep the operating point stable at the median value MED,
It is varied by a low frequency signal S. As shown in Fig. 3(b), if the operating point moves to the right, the optical frequencies f1 and f
2 Each also moves to the right, and the optical output P at optical frequency f1
1 increases, and the optical output P2 at the optical frequency f2 decreases. Furthermore, as shown in Fig. 3(c), if the operating point moves to the left, the optical frequencies f1 and f2 also move to the left, the optical output P1 at the optical frequency f1 increases, and the optical output P1 at the optical frequency f2 increases. The optical output P2 decreases. This optical output P1
, P2 is observed as a variation in the average optical output intensity from the optical interferometer 20. In this way, the phase and amplitude of the fluctuation in the intensity of the average optical output from the optical interferometer 20 change depending on the magnitude of the optical frequency deviation amount Δf, which is the difference (f1 − f2) between the two optical frequencies f1 and f2. happens. below,
Explain in detail.

FIG. 4A shows a case where the value of the optical frequency shift amount Δf is smaller than FSR/2 of the optical interferometer 20. In the figure, when the operating point is varied by the low frequency signal S,
As the operating point moves to the right, the optical frequencies f1 and f2 increase.
moves to the right, and as the operating point moves to the left, the optical output increases, and as the operating point moves to the left, the optical frequencies f1,
f2 moves to the left, and the light output decreases in accordance with the leftward movement. Therefore, the variation in the average light output intensity is as shown on the right side of the figure.

FIG. 4(b) shows that the value of the optical frequency shift amount Δf matches the FSR/2 of the optical interferometer 20, that is, Δf
=FSR/2. At this time, as shown in Fig. 2(b), the optical frequency f1, where the optical output is concentrated, is
Since f2 moves in a complementary manner to each other, the increase and decrease in the optical output output in response to the movement are equal, so even though the operating point is varied by the low frequency signal S,
As shown on the right side of b), there is no variation in the average light output intensity.

FIG. 4(c) shows the case where the value of the optical frequency shift amount Δf is larger than the FSR/2 of the optical interferometer 20. In the figure, when the operating point is varied by the low frequency signal S,
As the operating point moves to the right, the optical frequencies f1 and f2 increase.
moves to the right, and the output light output decreases in accordance with the movement. As the operating point moves to the left, the optical frequencies f1 and f2 move to the left, and the output optical power increases accordingly. Therefore, the variation in the average light output intensity is as shown on the right side of the figure. In the case of Δf>FSR/2 shown in FIG. 4(c), the phase is reversed from the case of Δf<FSR/2 shown in FIG. 4(a).

[0022] In this way, the phase and amplitude of fluctuations in the average optical output intensity change depending on the magnitude of the optical frequency shift amount Δf. Therefore, if the average optical output intensity from the optical interferometer 20 is converted into an electrical signal by the optical receiver 30, and this electrical signal is synchronously detected using the low frequency signal S, the magnitude of the optical frequency shift amount Δf can be determined.

The synchronous detection output signal of this average optical output intensity with respect to the optical frequency deviation amount Δf is generally as shown in FIG. Depending on whether the operating point is set to a positive or negative slope of the optical frequency discrimination characteristic curve or the phase of the reference signal of synchronous detection, either a solid line or a chain line signal is output. Here, the deviation of the synchronous detection output signal from zero represents the deviation of the optical frequency deviation amount Δf from FSR/2, and when the optical frequency deviation amount Δf matches FSR/2, the synchronous detection output signal is zero. becomes. Thereby, by measuring the synchronous detection output signal, the value of the optical frequency deviation amount Δf can be measured. Therefore, the value of the optical frequency deviation amount Δf can be measured, and the optical frequency deviation amount (modulation index) can also be controlled.

Thus, the operating point setting means 40 of FIG. 1 is provided with attention to the graph of FIG. 2, and the deviation amount detection means 50 of FIG. 1 is provided with attention paid to the graph of FIG. 5. A feature of the present invention is that the light intensity of the interference light Hi1 is used as a control variable, and only low frequency components of the light intensity are handled. Therefore, the device for measuring and controlling the amount of optical frequency deviation of the semiconductor laser according to the present invention is simple in structure and can be operated at an extremely low frequency.

[0025]

Embodiment FIG. 6 is a block diagram showing an embodiment based on the present invention. Note that similar components are designated with the same reference numbers or symbols throughout the drawings.

In the figure, for example, the forward light of the semiconductor laser 10 (a control signal may be taken from the forward light) is input to a transmission line (not shown) as optical data Dh. This optical data Dh is the data Din to be transmitted.
This data is optically modulated (f1, f2) or phase modulated according to the data D
Modulation by in is performed by the modulation circuit 11. Also,
Although not shown, the semiconductor laser 10 is provided with a well-known bias section so that this optical modulation is performed under optimal driving conditions.

The device according to the present invention operates upon receiving FSK-modulated output light H0, which is, for example, backward light from the semiconductor laser 10. The optical interferometer 20 receives the output light H0 from the semiconductor laser 10 and generates two mutually complementary interference lights Hi1 and Hi2 according to optical frequency discrimination characteristics.
Output.

FIG. 7 shows an example of an optical interferometer that outputs two complementary interference lights. In the figure, (a) is a diagram showing a Mach-Zehnder interferometer, M is a half mirror, and M is a diagram showing a Mach-Zehnder interferometer.
' is a mirror that causes two optical paths to interfere with each other with a predetermined difference in optical path length, and generates two complementary interference beams Hi1 and H.
Generate i2. These two complementary interference lights Hi1
The optical frequency discrimination characteristics of Hi2 and Hi2 are shown in Fig. 2(a).

In FIG. 7, (b) is a diagram showing a Fabry-Perot interferometer, in which one interference light Hi1 is normal transmitted light, while the other interference light Hi2 is reflected light. The reason why the Fabry-Perot interferometer FP is inclined with respect to the optical axis of the output light H0 is to prevent the reflected light Hi2 from returning to the semiconductor laser 10 side. Same figure (c)
FIG. 3B is a diagram showing the optical frequency discrimination characteristics of two interference lights in FIG. There are other ways to obtain two complementary interference lights, but they are not shown here.

Returning to FIG. 6, these two interference lights Hi1,
Two light receivers 31 and 36 are provided using photodiodes or the like to receive Hi2, and the optical intensities of the interference lights Hi1 and Hi2 are converted into electric signals EL1 and EL2, respectively. In addition, the electric signal E
Since voltage signals corresponding to L1 and EL2 are subtracted and added, voltage detection resistors 32 and 37 and instrumentation amplifiers 33 and 38 paired with these resistors, respectively, are provided.

The subtracter 41 outputs the difference component between the electric signals EL1 and EL2 from the two light receivers 31 and 36. The adder 43 outputs the added components of the electric signals EL1 and EL2 from the two light receivers 31 and 36.

In this embodiment, the operating point setting means 40 includes an operating point control circuit 42 and an APC control circuit 44. The operating point control circuit 42 receives each electrical signal EL1 from the subtracter 41.
, EL2, and use the difference component as an operating point detection signal, and set the operating point to the median value M of the optical frequency discrimination characteristic.
Always match the ED. This shift of the operating point can be carried out by controlling the oscillation frequency of the semiconductor laser 10 by feeding back to the bias or temperature of the semiconductor laser 10 via the control line L1, or by using an optical interferometer via the control line L1. There is a method of controlling the interference characteristics of the optical interferometer 20 by feeding back to the bias or temperature of 20. Also, both of these methods may be used. Note that a well-known Peltier element is used when controlling the temperature by returning it. 2 above
Since the two interference beams Hi1 and Hi2 are complementary interference beams, the difference between them crosses the zero point at the median value MED, as shown in FIG. 2(b). In other words, since the output obtained by subtracting the electrical signals EL1 and EL2 by the subtracter 41 crosses the zero point at the median value MED, the difference signal between the electrical signals EL1 and EL2 is used as the operating point detection signal, and this difference signal is always zero. Semiconductor laser 1 so that
By applying feedback to the bias or temperature of 0 or the bias or temperature of the optical interferometer 20, the operating point is stabilized at the optical frequency at which the difference signal is zero. At this time, when feedback is applied to the bias or temperature of the semiconductor laser 10, the control of the frequency of the operating point remains unchanged.
Since the oscillation frequency of the semiconductor laser 10 is also controlled, the operating point is stabilized and the automatic frequency control (A
FC) can also be performed.

The APC control circuit 44 uses the added components of the electric signals EL1 and EL2 from the adder 43 as an optical output detection signal, and includes, for example, a comparator, whose first input receives the optical output detection signal. receives a predetermined set voltage V1 at its second input, and this set voltage V1
The variation of the optical output detection signal relative to the output signal is detected and fed back to the bias of the semiconductor laser 10 via the control line L2 so that the error between these signals is always zero. Since the above two interference lights Hi1 and Hi2 are mutually relative interference lights, when they are added together, a flat output is obtained as shown by the dashed-dotted line in FIG. 2(a). This flat output is proportional to the optical output of the semiconductor laser 10. In other words, the output obtained by adding the electric signal EL1 and the electric signal EL2 in the previous period by the adder 43 becomes a flat signal, and the voltage V1 is set in correspondence with this flat signal, so that the level of the flat signal is always at a constant level. Automatic optical output control (APC) can be realized by applying feedback to the semiconductor laser 10 so as to achieve the following.

The optical frequency shift detection means 50 includes a low frequency oscillator 51, a synchronous detection circuit 52, an optical frequency shift stabilization circuit 53, and an amplifier 54. The low frequency oscillator 51 changes the oscillation frequency of the semiconductor laser 10 or the interference characteristic of the optical interferometer 20 at a low frequency via the control line L3 in order to change the oscillation frequency at the operating point in the optical frequency discrimination characteristic. Low frequency means a frequency lower than the frequency of data transmission speed, for example, 100Hz.
The operating point is varied by a low frequency signal S faster than the response speed of the circuit of the operating point setting means 40. The low frequency signal S is used as a synchronous detection signal in a synchronous detection circuit 52, which will be described later.
The oscillation frequency at the operating point is changed by superimposing the bias or temperature of the optical interferometer 20 or by superimposing the bias or temperature of the optical interferometer 20.

FIG. 8 is a waveform diagram for explaining the operation of the low frequency oscillator 51. However, an example will be explained in which the oscillation output of the low frequency oscillator 51 is superimposed on the drive current of the semiconductor laser 10. By changing the drive current into two values, the optical frequency of the output light H0 of the semiconductor laser 10 is changed to the first optical frequency f around the center frequency f0.
1 and the second optical frequency f2. In this state, when the oscillation output of the low frequency oscillator 51 is superimposed, the oscillation output has a frequency fs and undulates in a wave-like manner as shown in the figure. The electrical signal EL containing the low frequency component in this manner is synchronously detected by the synchronous detection circuit 52 using a low frequency oscillation output.

Furthermore, it is easy to change the bias of the optical interferometer 20, and basically it is sufficient to change the resonator length and delay time difference of the optical interferometer 20. Specifically, ■
The following methods are well known: ■ Change using photoelastic effect, ■ Change using electro-optic effect, ■ Change using external mechanical force, ■ Change using thermo-optic effect. It is being

Returning to FIG. 6, the synchronous detection circuit 52 inputs the difference component signal of each electric signal EL1, EL2 from the subtracter 41 and the modulation signal for synchronous detection from the low frequency oscillator 51, and generates the difference component signal. synchronous detection is performed on the synchronous detection modulation signal to extract a signal component synchronized with the synchronous detection modulation signal. The signal component extracted by this synchronous detection is an optical frequency deviation amount detection signal, and optical frequency deviation amount measurement is performed. The measurement of the optical frequency deviation amount Δf in the synchronous detection circuit 52 will be explained below.

As described above, the operating point of the FSK modulated optical signal is stabilized at the center MED of the optical frequency discrimination characteristic of the interferometer 20, and under that operating point, the low frequency signal S of the modulated signal for coherent detection is When the average optical output intensity is varied, the phase and amplitude of the variation in the average optical output intensity change depending on the magnitude of the optical frequency shift amount Δf, as shown in FIG. Therefore, if the average optical output intensity from the interferometer 20 is converted into an electrical signal by the optical receiver 30, and this electrical signal is synchronously detected with the low frequency signal S, the magnitude of the optical frequency shift amount Δf can be determined.

The synchronous detection output signal of the average optical output intensity with respect to the optical frequency deviation amount Δf is as shown in FIG. It represents a deviation from FSR/2, and when the optical frequency deviation amount Δf matches FSR/2, the synchronous detection output signal becomes zero. Thereby, by measuring the synchronous detection output signal, the value of the optical frequency deviation amount Δf can be measured.

The optical frequency deviation amount stabilizing circuit 53 includes, for example, a comparing section, and receives at its first input the detection signal of the optical frequency deviation amount Δf obtained by the synchronous detection circuit 52, and receives the detection signal of the optical frequency deviation amount Δf obtained by the synchronous detection circuit 52 at its first input. A predetermined setting voltage V2 is received and fed back to the modulation circuit 11 so that the error between them becomes 0, and the optical frequency deviation amount Δf (modulation index) is always kept constant. The optical frequency deviation amount Δf corresponding to the set voltage V2 is the optical frequency deviation amount Δf that should be kept at a constant value.
It becomes possible to control the stabilization of the amount of optical frequency deviation (modulation index).

As an input to the synchronous detection circuit 52, a difference signal between the electrical signals EL1 and EL2 is used. This difference signal is equivalent to adding the dotted line curve with polarity inverted to the solid line curve in FIG. 5. In other words, the amount of optical frequency shift can be controlled using a signal with a sharp slope characteristic. This results in a significant increase in the S/N ratio in controlling the amount of optical frequency deviation.

The amplifier 54 transmits the modulation signal for synchronous detection from the low frequency oscillator 51 to the semiconductor laser 1 via the control line L3.
When superimposing on a bias of 0, the optical frequency deviation amount detection signal is fed back from the optical frequency deviation amount stabilizing circuit 53 to the modulation amplitude of the modulation signal for synchronous detection, and the optical frequency of the optical FM modulation by the modulation signal is This is provided in order to keep the amount of deviation constant and to prevent the optical frequency deviation amount detection means 50 from being affected by the modulation efficiency of the light source portion of the semiconductor laser 10.

In other words, if the FM modulation efficiency (the amount of optical frequency variation per unit of bias current) decreases due to changes in the bias of the semiconductor laser 10 itself over time, in the worst case, the low frequency signal S may no longer be superimposed. be. Therefore, the operating point may no longer vary as set, and synchronous detection may become impossible. To resolve this,
When the FM modulation efficiency becomes small, the amplifier 54 increases the amplitude of the modulation signal for synchronous detection, and when the FM modulation efficiency becomes too large, the amplifier 54 decreases the amplitude of the modulation signal for synchronous detection. In other words, the low frequency signal S is always made to have the same amplitude. The magnitude of this FM modulation efficiency can be determined from the magnitude of the optical frequency deviation amount Δf.

The mark rate monitoring means 60 is comprised of an integrator provided within the modulation circuit 11, for example. Data that causes the modulation circuit 11 to change the frequency of the output light H0 of the semiconductor laser 10 to the first optical frequency f1 or the second optical frequency f2 corresponding to the two logical values "1" and "0" of the data to be transmitted. This means calculates the total probability of occurrence of logical values "1" and "0" when performing modulation, and controls the operating state of the optical frequency deviation detection means 50.

The graph shown in FIG. 2 shows that the mark rate is 1/2.
However, if the mark rate is, for example, 1/4, that is, if the ratio of "1" occurrences to "0" occurrences is 1:3, the average The optical output intensity moves to the upper right, and therefore the graph of the synchronous detection output signal against the optical frequency deviation amount Δf shown in FIG. 5 changes,
The value of Δf at which the synchronous detection output signal becomes zero changes depending on the mark rate. Therefore, it is necessary to change the set voltage V2 in the optical frequency deviation amount stabilizing circuit 53 according to the mark rate. The mark rate monitor means 60 calculates the mark rate of the modulated signal by the modulation circuit 11, changes the set voltage V2 based on the calculated value, and controls the operating state of the optical frequency deviation amount detecting means 50. That is, the mark rate monitor signal of the input modulated signal is fed back to the optical frequency deviation amount stabilizing circuit 53, so that it is not affected by the mark rate fluctuation.

[0046]

[Effects of the Invention] As explained in detail above, according to the present invention, it is possible to measure the amount of optical frequency deviation, which has been a problem in the past.
Control becomes possible. Furthermore, since it has a simple configuration that does not include a broadband photoreceiver or electronic circuit, the device can be made smaller and simpler, and can be constructed at lower cost. In addition, at the same time as measuring and controlling the amount of optical frequency deviation, the APC of the light source,
It becomes possible to perform AFC operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle configuration of the present invention.

FIG. 2 is a diagram showing the optical frequency discrimination characteristics of the Mach-Zehnder optical interferometer, (a) is a diagram showing the optical frequency discrimination characteristics of two interference lights, and (b) is a diagram showing the optical frequency discrimination characteristics of two interference lights in (a). It is a figure which shows the subtraction result intensity.

[Figure 3] Diagrams showing the optical frequency discrimination characteristics of the Mach-Zehnder optical interferometer; (a) is a schematic diagram when the operating point is stabilized at the median value, and (b) is a schematic diagram when the operating point is moved to the right. Figure 2(c) is a schematic diagram when the operating point is moved to the left.

FIG. 4 is a schematic diagram showing the variation in average optical output intensity when the operating point is varied; (a) is Δf<FSR/2, (
b) is Δf=FSR/2, (c) is Δf>FSR/
This is case 2.

FIG. 5 is a graph of a synchronous detection output signal with respect to the amount of optical frequency shift.

FIG. 6 is a diagram showing the configuration of an embodiment of the present invention.

FIG. 7 is a diagram showing an optical interferometer that outputs two complementary interference lights; (a) is a diagram showing a Mach-Zehnder interferometer, (b) is a diagram showing a Fabry-Perot interferometer, and (c is a diagram showing a Fabry-Perot interferometer.
) is a diagram showing the optical frequency discrimination characteristics of two interference lights in (b).

FIG. 8 is a waveform diagram for explaining the operation of a low frequency oscillator.

[Explanation of symbols]

10 Semiconductor laser 20 Optical interferometer 30, 31, 36 Light receiver

Claims (9)

[Claims] Claim 1: An optical frequency deviation of a semiconductor laser that measures the amount of optical frequency deviation of a laser light source that outputs frequency- or phase-modulated light based on an input modulation signal, or controls it to a predetermined constant value. In the quantity measurement and control device, the output light (H0
), the interference light (Hi) follows the optical frequency discrimination characteristic.
an optical interferometer (20) that outputs the interference light (Hi);
an optical receiver (30) that receives the signal and converts the optical intensity into an electrical signal (EL); operating point setting means (40) for setting the operating point to match the optical frequency corresponding to the median value of the minimum value and the minimum value, and the interference light (Hi
) from the electrical signal (EL) by synchronous detection to detect the amount of optical frequency deviation. A device for measuring and controlling the optical frequency deviation of a semiconductor laser. 2. The operating point setting means (40) transmits two complementary interference lights (Hi1, Hi2) output from the optical interferometer (20) to two light receivers (31, 36).
), and the difference component of the output signal of each light receiver (31, 36) is used as an operating point detection signal.
2. The apparatus for measuring and controlling the amount of optical frequency deviation of a semiconductor laser according to claim 1, wherein the added component of ) is used as an optical output detection signal of the semiconductor laser (10). 3. The operating point setting means (40) uses an added component of the output signals output from each light receiver (31, 36) as an optical output detection signal of the semiconductor laser (10),
2. The optical output of the semiconductor laser (10) is simultaneously stabilized by feeding back an error signal between the optical output detection signal and the set value to the bias or temperature of the semiconductor laser (10). A device for measuring and controlling the amount of optical frequency deviation of semiconductor lasers. 4. The operating point setting means (40) uses the difference component of the output signals output from each light receiver (31, 36) as an operating point detection signal, and uses the operating point detection signal to ), the optical frequency deviation amount of the semiconductor laser (10) is stabilized simultaneously by stabilizing the operating point and stabilizing the oscillation frequency of the semiconductor laser (10). Measurement and control equipment. 5. The operating point setting means (40) uses the difference component of the output signals output from each light receiver (31, 36) as an operating point detection signal, and transmits the operating point detection signal to an optical interferometer ( 3. The apparatus for measuring and controlling the optical frequency deviation of a semiconductor laser according to claim 2, wherein the operating point is stabilized by feedback to the bias or temperature of 20). 6. The optical frequency deviation detection means (50)
2. The apparatus for measuring and controlling the amount of optical frequency deviation of a semiconductor laser according to claim 1, wherein the modulation signal for synchronous detection is superimposed on the bias or temperature of the optical interferometer (20). 7. The optical frequency deviation amount detection means (50)
However, the modulation signal for synchronous detection is transmitted using a semiconductor laser (10
) measurement of the amount of optical frequency deviation of a semiconductor laser according to claim 1, characterized in that it is superimposed on the bias or temperature of
Control device. 8. The optical frequency deviation detection means (50)
However, the modulation signal for synchronous detection is transmitted by a semiconductor laser (10).
The light source of the semiconductor laser (10) 8. The apparatus for measuring and controlling the amount of optical frequency deviation of a semiconductor laser according to claim 7, wherein said optical frequency deviation amount detection means (50) is not affected by the variation efficiency of the portion. 9. A mark rate monitor signal is transmitted to the optical frequency deviation amount detection means (50) so that the mark rate fluctuation of the input modulation signal does not affect the optical frequency deviation amount detection means (50). 2. The apparatus for measuring and controlling the optical frequency deviation of a semiconductor laser according to claim 1, further comprising feedback mark rate monitoring means (60).