JPH0666505B2 - Method and apparatus for stabilizing oscillation frequency intervals of a plurality of laser devices - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for stabilizing an oscillation frequency interval of a plurality of laser devices, which stabilizes an interval of each oscillation frequency of the plurality of laser devices.

(Prior Art) Conventionally, as a method of stabilizing the frequency intervals of a plurality of laser devices, the oscillation frequency of one laser device is stabilized with respect to the Fabry-Perot resonator, and A method of stabilizing the oscillating frequencies of other laser devices so that their frequency intervals match the frequency interval criterion given by the free spectral range of another Fabry-Perot resonator (Toba et al. National Convention Proceedings, Volume 2,2-204), or stabilizing the frequency of one laser device,
A pulse train obtained as a beat signal is formed by combining the light emitted from some other laser devices, and combining the light emitted from the reference laser device whose frequency is swept in a sawtooth shape with a constant period. A method for stabilizing the oscillation frequency interval of each laser device by monitoring whether the appearance time of each pulse has a constant time difference with respect to the appearance time of the pulse corresponding to the above-mentioned stabilized laser device. I O O Sea E C O
The Sea '85 (IOOC-ECOC'85) Technical Digest Volume 3 (1985) p. 61) is known.

(Problems of the prior art) However, in the above-mentioned first method, it is necessary to sweep and use the mirror interval of the Fabry-Perot resonator that gives the reference of the frequency interval, and the device is more than the case where a simple etalon plate is used. Becomes larger. In the second method,
Since the frequency interval standard is calculated as the appearance time interval of each pulse with respect to the frequency change of the reference laser device that has been measured in advance, it is not enough that this interval standard changes significantly during actual control. It is hard to say that the frequency interval of each laser device is expected and fixed at the time of control.

(Object of the Invention) An object of the present invention is to solve the above problems. To solve the problems of the first method, the frequency axis is swept for searching the oscillation frequencies of a plurality of laser devices. Instead of sweeping the mirror spacing of the Fabry-Perot resonator, the frequency of the reference laser device is swept to enable the use of a simple etalon plate as the Fabry-Perot resonator. To downsize. Further, the problem of the second method is solved by using a Fabry-Perot resonator as a reference of the frequency interval to stably set the frequency interval.

(Structure of the Invention) In order to achieve the above object, the present invention is a reference in which the oscillation frequency is swept by a signal applied from the outside, and is swept within a range including each oscillation frequency of a plurality of laser devices whose oscillation frequency intervals are controlled. The emitted light of the laser device for use is split into at least two, and the first light is incident on the optical resonator to be converted into a reference optical pulse train generated at a time interval corresponding to the resonance frequency interval of the optical resonator, and After converting the beat light obtained by combining the second light with the light emitted from the plurality of laser devices into an electric signal, only the low-frequency component is extracted, and the electrical signals corresponding to each of the plurality of laser devices are extracted. A pulse train is generated, and an error signal obtained from the occurrence time of each pulse forming the pulse train and each pulse forming the reference light pulse train is used for control.

In order to achieve the above-mentioned object, the present invention provides a reference laser device that sweeps the oscillation frequency in a range including the oscillation frequencies of a plurality of laser devices that are targets for stabilizing the oscillation frequency interval according to an input signal from the outside. An optical splitter that splits the emitted light from the reference laser device, and an optical multiplexer that multiplexes one of the lights split by the optical splitter and the emitted light from the plurality of laser devices, An optical resonator for converting a frequency change of the other light branched by the optical branch device into an amplitude change, and the plurality of laser devices detected by the output of the optical multiplexer at the oscillation frequency sweep of the reference laser device. Control signal for stabilizing the error of the oscillating frequency interval with respect to the frequency interval reference set by using the optical output corresponding to the resonance peak of the optical resonator when the oscillating frequency of the reference laser device is swept to a constant value. A controller for outputting, characterized in that it is configured to include a laser device driving apparatus for changing the input signal to the plurality of laser devices according to a control signal from the control device.

(Operation) In the present invention, by adopting the above-mentioned configuration, the reference of the time difference corresponding to the frequency interval reference determined by the free spectral range of the optical resonator by the combination of the frequency-swept reference laser device and the optical resonator. Generate a pulse train. In addition, the light emitted from the reference laser device and the beat light of the emitted light from the plurality of laser devices to be controlled are received by a photodetector and then passed through a low-pass filter to correspond to the frequency intervals of the plurality of laser devices. A pulse train with a time difference is generated. By controlling the difference between the generation time of each pulse forming this pulse train and the generation time of the corresponding pulse of the reference pulse train as an error signal, the frequency intervals of any number of laser devices are stabilized at the same time The spacing is strictly defined by the optical resonator used.

(Examples) Hereinafter, the present invention will be described in detail with reference to Examples. FIG. 1 is a block diagram of an embodiment of the present invention.

The 1.55 μm band distributed reflection type laser with phase control area 1 has a sawtooth wave generator 2 which emits a sawtooth wave with respect to time according to the signals 27 and 28 with a repetition frequency of 20 kHz (see FIG. 2). Is changing. The light emitted from the distributed reflection laser 1 with a 1.55 μm band phase control region passes through the optical isolator 3 and is then split by the optical branching device 4 into a first and a second output light with a power ratio of 1: 1. this house,
The first output light is transmitted through a quartz glass etalon plate 5 having a refractive index of 1.5, a thickness of 1 cm, and a reflectance of both surfaces set to a finesse 30, and then enters a first photodetector 6. First
The photodetector 6 is pulsed when the frequency of the 1.55 μm band distributed control laser with phase control region 1 matches the resonance frequency of the etalon plate 5 during one cycle of the output signal from the sawtooth wave generator 2. The circular peak light is input, and the peak voltage of the output of the sawtooth wave generator 2 is adjusted so that the number of pulses in one cycle becomes three. The electric signal from the first photodetector 6 is applied to the first input terminal 71 of the controller 7.

On the other hand, the lights emitted from the 1.55 μm band distributed feedback lasers 8, 9 and 10 whose frequency intervals are to be stabilized pass through the optical isolators 11, 12 and 13, respectively, and then are combined by the first optical combiner 14. To be done. The light emitted from the first optical multiplexer 14 is combined with the second output light of the optical branching device 4 by the second optical multiplexer 15.
The output of the second multiplexer 15 is converted into an electric signal by the detector 16 and then input to a low-pass filter having a cutoff frequency of 100 MHz, which is not shown in the figure. From the low-pass filter, the frequency of the emitted light from the 1.55 μm band distributed reflection type laser with phase control region 1 and the 1.55 μm band distributed feedback laser 8, 9,
A pulsed electric signal is output when the difference in frequency of the emitted light of 10 is within a range of approximately ± 100 MHz. The number of pulses depends on the output signals 27, 28 of the sawtooth generator 2 (see FIG. 2).
The number of times that the difference between the oscillation frequencies of the distributed reflection type laser 1 with 1.55 μm band phase control region and the distributed feedback lasers 8, 9, 10 in the 1.55 μm band distributed feedback lasers 8, 9 and 10 is within ± 100 MHz in one cycle, which is 3
Is one. The electrical signal from the second photodetector 16 is applied to the second input terminal 72 of the controller (details shown in FIG. 3) 7. In the control device 7 shown in FIG. 3, the input to the first input terminal 71 of the control device 7 shown in FIG.
The pulse generation time difference 24, 25, 26 of the input to the second input terminal 72 of the control device 7 shown in (b) is used as an error signal, and a control signal that makes these magnitudes zero is output.

The pulse generation time difference measurement circuit 33 in FIG. 3 (an example of the circuit is shown in FIG. 4) is arranged as follows:
It outputs a square pulse having a width proportional to the time difference of occurrence of two pulses of a corresponding order (a total of three sets) and having a constant height. However, the output has a function of a positive or negative square pulse depending on which of the two series pulse trains to which the pulse generated earlier of the above two pulses is input, the details are as follows. It is shown in FIG. The first, second and third control signals from the control device 7 are input to the laser device driving devices 17, 18 and 19, respectively. Laser device driver 17,18,
A drive current corresponding to the control signal is injected from 19 into the 1.55 μm band distributed feedback lasers 8, 9 and 10. It should be noted that the 1.55 μm band distributed reflection type laser with phase control region 1 and the 1.55 μm band distributed feedback lasers 8, 9 and 10 are stabilized by temperature control devices 20, 21, 22 and 23, respectively, to stabilize the temperature within ± 0.1 ° C. Has been done.

In this embodiment, only three laser devices are stabilized in frequency intervals, but the frequency and peak voltage of the output signal from the sawtooth wave generator 2 are adjusted to adjust the etalon plate 5 per cycle.
By changing the number of pulses emitted from the laser, the frequency intervals of more laser devices can be stabilized at the same time. Further, the frequency interval can be freely set by changing the thickness of the etalon plate. Further, the laser device to be stabilized is not limited to the semiconductor laser, and can be stabilized if it is a laser device whose oscillation frequency changes according to a signal from the outside.

(Effects of the Invention) As described above, according to the present invention, the frequency intervals of an arbitrary number of laser devices can be stabilized at the same time, and the frequency intervals can be defined by the optical resonator used.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 (a) is a diagram showing an electric signal from a first photodetector 6 input to a control device 7 in FIG. FIG. 2 (b) is a diagram showing an electric signal from the second photodetector 16 input to the control device 7 in FIG. Further, FIG. 3 is a block diagram of the control device 7 in FIG.
The drawing is a circuit diagram of the pulse generation time difference measuring circuit of FIG. In FIGS. 1, 2 (a), 2 (b) and 3, 1 ... 1.55 μm band distributed reflection laser with phase control region, 2
...... Sawtooth wave generator, 3,11,12,13 …… Optical isolator,
4 ... Optical branching device, 5 ... Etalon plate, 6,16 ... Photodetector, 7 ... Control device, 8,9,10 ... 1.55 μm band distributed feedback laser, 14, 15 ... Optical multiplexing Device, 17,18,19 …… Laser device drive device, 20,21,22,23 …… Temperature control device 24,25,26…
... error signal, 27, 28 ... output waveform from the sawtooth wave generator 2.

Claims (2)

[Claims] 1. An emission light of a reference laser device which is swept within a range including each oscillation frequency of a plurality of laser devices whose oscillation frequency intervals are controlled by a signal applied from the outside. Then, by injecting the first light into the optical resonator, it is converted into a reference light pulse train generated at a time interval corresponding to the resonance frequency interval of the optical resonator, and the second light is converted into the plurality of laser devices. After converting the beat light obtained by combining the emitted light from the optical signal into an electric signal, only the low-frequency component is taken out, and an electric pulse train corresponding to each of the plurality of laser devices is generated to form this pulse train. A plurality of laser devices to be controlled so that the difference in the occurrence times becomes zero by using an error signal obtained from the difference in the occurrence times between the pulses forming each of the pulses and the pulse forming the reference optical pulse train. Oscillation frequency interval method for stabilizing a plurality of laser devices and controls the frequency. 2. A reference laser device for sweeping an oscillation frequency within a range including the oscillation frequencies of a plurality of laser devices for stabilizing the oscillation frequency interval according to an input signal from the outside, and the reference laser device. An optical splitter that splits the output light from the optical splitter, an optical multiplexer that multiplexes one of the lights split by the optical splitter and the output light from the plurality of laser devices, and the optical splitter splits the light. An optical resonator for converting a frequency change of the other light into an amplitude change, and an oscillation frequency interval of the plurality of laser devices detected by the output of the optical multiplexer at the time of the oscillation frequency sweep of the reference laser device, A control device for outputting a control signal for stabilizing an error with respect to a frequency interval reference set using an optical output corresponding to a resonance peak of the optical resonator at the time of sweeping an oscillation frequency of a reference laser device, It said plurality of oscillation frequency separation stabilizing device of the plurality of laser device according to claim comprise be configured and a laser device driving apparatus for changing the input signal to the laser device in accordance with a control signal from the control device.