JPH0666506B2 - Laser device Oscillation frequency interval stabilization device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device oscillation frequency interval stabilizing device that stabilizes intervals between oscillation frequencies of a plurality of laser devices.

(Prior Art) Conventionally, as a method for stabilizing the frequency intervals of a plurality of laser devices, (1) the oscillation frequency of one laser device is stabilized with respect to the Fabry-Perot resonator, and the oscillation frequency of this laser device is On the other hand, a method of stabilizing the oscillation frequencies of other laser devices so that the frequency intervals of the other laser devices match the frequency interval reference given by the free spectral range of another Fabry-Perot resonator (Toba et al. Proceedings / Separate Volume 2, 2-
(Page 204), or (2) A reference laser that stabilizes the frequency of one laser device, combines it with the light emitted from several other laser devices, and sweeps this light and frequency in a sawtooth shape with a constant period. By monitoring whether the appearance time of each pulse forming the pulse train obtained as a beat signal by combining the emitted light from the device maintains a constant time difference with respect to the appearance time of the pulse corresponding to the stabilized laser device. A method for stabilizing the oscillation frequency interval of each laser device (I.O.O.C.-E.C.O.C. '85 (IOOC-ECOC'8 by Strebel et al.
5) Technical Digest Volume 3 (1985) 61
Page) is known.

In addition, (3) a method of phase-modulating the emitted light of a helium-neon laser and locking the oscillation frequency of each laser device to each of the sidebands generated at the modulation frequency intervals (Hankin et al., Electronics Letters No. 22). Volume (19
(86), 388), or (4) a method of independently stabilizing each laser device at each of the different resonant frequencies of the Fabry-Perot resonator (Glance et al., Electronics Letters, Volume 23 (1987)). , 750) are known.

(Problems of Prior Art) In the second and third methods of the above four methods,
Although not explicitly shown in the above-referenced document, by distributing the reference light as in the present invention, it is possible to generate several sets of laser devices having exactly the same combination of oscillation frequencies. However, in the second method, since the standard of the frequency interval is determined as the appearance time interval of each pulse with respect to the frequency change of the reference laser device, it is hard to say that the frequency interval of each laser device can be determined. Also, the third
In this method, the upper limit of the interval frequency that can be set is defined by the upper limit of the modulation frequency, and the number of laser devices that can be stabilized is limited to the number of sidebands with sufficient power that can be generated by phase modulation. There is a problem that is done.

On the other hand, since the first and fourth methods do not use the reference light for controlling the frequency interval stabilization, it is not possible to generate a plurality of sets of laser devices having the same combination of oscillation frequencies.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems, to make it possible to generate a plurality of sets of laser devices having the same combination of oscillation frequencies, and to strictly set the standard of the frequency interval to be set. , Removing the limitation of the number of controllable oscillation frequencies of the laser device and the settable frequency interval.

(Structure of the Invention) In order to achieve the above object, the present invention sweeps the oscillation frequency in a range including the oscillation frequencies of a plurality of laser devices, which are targets for stabilizing the oscillation frequency interval, according to an input signal from the outside. A reference laser device, a first optical branching device for branching emitted light from the reference laser device, and a frequency change of the first outgoing light from the first optical brancher into an amplitude change of transmitted light. An optical resonator to be converted, a plurality of local stations having a plurality of laser devices having mutually different oscillation frequencies, and a second branch for branching transmitted light of the optical resonator to the plurality of local stations
And a third optical branching device for branching the second emitted light of the first optical branching device to the plurality of local stations, the laser device oscillation frequency interval stabilizing device comprising: The local station includes a first optical multiplexer that combines at least a part of the emitted light of each of the plurality of laser devices, the emitted light of the first optical multiplexer, and the output of the third optical branching device. A second optical combiner for combining the emitted light, a first photodetector for converting the emitted light of the second optical combiner into an electric signal, and an emitted light of the second optical brancher for the electric signal And a second photodetector for converting into the reference laser device, and the reference laser device having oscillation frequency intervals of the plurality of laser devices detected by the emitted light of the second optical multiplexer when the oscillation frequency of the reference laser device is swept. Frequency set by using the emitted light corresponding to the resonance peak of the optical resonator when the oscillation frequency of A control device that outputs a control signal for stabilizing an error with respect to a number interval reference to a constant value, and a laser device drive device that changes input signals of the plurality of laser devices according to a control signal from the control device. A laser device oscillation frequency interval stabilization device is provided.

(Operation) In the present invention, the free spectral range of the optical resonator is adopted as the reference of the frequency interval to be set, so that the frequency interval is strictly defined, and the parameter of the optical resonator (for example, in Fabry-Perot etalon The frequency interval can be arbitrarily set by changing the thickness of the medium). Further, by expanding the frequency sweep range of the reference laser device, the number of oscillation frequencies of the controllable laser device can be increased. Further, one reference laser device is provided as a standard light source, and the emitted light and the emitted light passing through the optical resonator are branched, and the former is used as a reference for the absolute value of the frequency, and the latter is used as a reference for the frequency interval. It is possible to generate a plurality of sets of laser devices having the same combination of oscillation frequencies by distributing them to the laser device control system.

(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. In this embodiment, for the sake of simplicity, a case where the number of sets of laser devices is two and the number of laser devices included in each set is three will be described.

The 1.55 μm wavelength tunable distributed Bragg reflection type semiconductor laser (DBR) 1 used as a reference laser device has a frequency of emitted light which is changed with time in accordance with a sawtooth wave with a repetition frequency of 20 kHz applied by a sawtooth wave generator 2. In contrast, it changes in a sawtooth shape. The light emitted from the DBR 1 is transmitted through the first optical isolator 3 and then split by the first optical branching device 4 into the first and second emitted lights at a power ratio of 1: 1. Of these, the first output light is transmitted through the quartz glass etalon plate 5 whose reflectance, line accuracy, and parallelism are adjusted on both sides so that the finesse is 30 with a refractive index of 1.5 and a thickness of 1 cm. A power ratio of 1: 1 for the first and second outgoing lights by the branching device 6.
It is divided into The transmitted light of the etalon plate 5 is in the form of a pulse train generated when the frequency of DBR1 matches the resonance frequency of the etalon plate 5 during one cycle of the output signal (110 to 112 in FIG. 2) from the sawtooth wave generator 2. Although it is composed of light, 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. First
The second output light of the optical branching device 4 is divided into the first and second output lights by the third optical branching device 7 at a power ratio of 1: 1. The first and second emitted lights from the second optical branching device 6 are converted into electric signals by the second photodetectors 27 and 29, respectively.

On the other hand, the first to sixth objects that are targets for stabilizing the frequency interval
1.55 μm distributed feedback laser (DFB) 10, 1
The emitted lights from 1, 12, 13, 14 and 15 are first to sixth optical isolators 16, 17, 18, 19, respectively.
20 and 21 are transmitted. Then, the transmitted light from the first to third optical isolators 16, 17, and 18 is transmitted to the first optical multiplexer 22.
And the fourth to sixth optical isolators 1
The transmitted lights of 9, 20, and 21 are multiplexed by the first optical multiplexer 23. The output light of the first optical multiplexer 22 is combined with the first output light of the third optical branching device 7 by the second optical combiner 24, and then the electrical signal is output by the first photodetector 26. And is input to the first input 32 of the first controller 30. On the other hand, the output light of the first optical multiplexer 23 is combined with the second output light of the third optical branching device 7 by the second optical combiner 25, and then is output by the first photodetector 28. , Is converted into an electric signal, and is input to the first input 34 of the second control device 31. Further, the electric signals output from the second photodetectors 27 and 29 are supplied to the second input 3 of the first and second control devices 30 and 31.
3 and 35 are input.

The first and second control devices 30 and 31 use the same circuit. The structure is shown in FIG. The electrical signal applied to the first input 32 (or 34) has a cutoff frequency of 100.
It is input to the low pass filter 101 of MHz. From the low-pass filter 101, the difference between the output light frequency from the DBR 1 and the output light frequencies of the first to third DFBs 10, 11, 12 (or the fourth to sixth DFBs 13, 14, 15) is approximately ±. When it is within the range of 100 MHz, a pulsed electric signal is output. The number of pulses is the output signal 110, 111, 112 of the sawtooth wave generator 2 (see FIG. 2).
DBR1 and the first to third DFBs 10 and 11 in one cycle of
12 (or fourth to sixth DFBs 13, 14, 15)
Is equal to the number of times that the difference in the oscillation frequency of each of the two falls within the range of ± MHz, which is three. First and second control device 3
In 0 and 31, the first control device 30 shown in FIG.
(Or input to the second input 33 (or 35) of the second controller 31) and input to the first input 32 (or 34) shown in FIG. 2 (b) (or (c)) Pulse generation time difference 113, 114, 115 (or 11
6, 117, 118) as error signals, and a control signal is output so that the magnitudes of these error signals become zero.

The pulse generation time difference measurement circuit 102 in FIG. 3 (an example of the circuit is shown in FIG. 4) has a corresponding order when the pulses formed by the two input pulse trains are arranged in the order of generation time. It outputs a rectangular pulse having a width proportional to the time difference of occurrence of two pulses (3 sets in total) 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 of pulse trains to which the pulse generated earlier belongs is input. The first, second and third control signals from the first control device 30 are sent to the first, second and third laser device driving devices 36, 37 and 38, respectively, and from the second control device 31. The first, second and third control signals are respectively the first, second and third control signals.
Are input to the laser device driving devices 39, 40 and 41.
Laser device driving devices 36, 37, 38, 39, 40, 4
The drive currents corresponding to the control signals from 1 to 1st to 6th DF
B10, 11, 12, 13, 14, 15.

The first to sixth DFBs 10, 11, 12, 13, 1
4, 15 and DBR1 are temperature-stabilized within a temperature fluctuation range of 0.2 ° C. by the first to seventh temperature control devices 42, 43, 44, 45, 46, 47, 48, respectively.

In the present embodiment, three laser devices are set as one set, and two sets are simultaneously stabilized to generate two sets of laser devices having the same combination of oscillation frequencies. However, the number of laser devices per set and the number of sets are not limited to these values,
The former adjusts the frequency and peak voltage of the output signal from the sawtooth wave generator 2 to increase the number of pulses emitted from the etalon plate 5 per cycle, and the latter adjusts the second and third pulses. This can be increased by increasing the number of branches of the optical branching devices 6 and 7. The type of oscillation frequency of the laser device that is stabilized at each local station is the etalon plate 5
Can select any combination from the frequencies corresponding to the pulses emitted within one cycle of the output signal from the sawtooth wave generator 2. The number of combinations is given by 2 ^N -1 where N is the number of pulses in one cycle. The frequency interval can be freely set by changing the thickness of the etalon plate 5. Further, the laser device to be further stabilized is not limited to the semiconductor laser, and any laser device whose oscillation frequency changes according to a signal from the outside can be stabilized.

(Effects of the Invention) As has been described above, according to the present invention, the frequency interval of a combination of laser devices of an arbitrary number can be simultaneously set to an arbitrary number of groups.
Can be stabilized. The frequency interval to be set can be strictly defined by the optical resonator.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 (a) is an electric circuit for transmitting light transmitted through the etalon plate 5 which is input to the second inputs 33 and 35 of the control devices 30 and 31 of FIG. Converted signal, second
(B) and (c) are low pass filter output signals inside the control devices 30 and 31, respectively. FIG. 3 is a configuration diagram of the control devices 30 and 31, and FIG. 4 is a pulse generation time difference in FIG. It is a circuit diagram of a measurement circuit. 1 to 3, 1 ... 1.55 μm band wavelength tunable distributed Bragg reflection type semiconductor laser 2 ... Sawtooth wave generator 3, 16, 17, 18, 19, 20, 21, ... Optical isolator 4, 6, 7 ... Optical branching device 5 ... Etalon plate 10, 11, 12, 13, 14, 15 ... 1.55 μm
Band distributed feedback laser 22, 23, 24, 25 ... Optical multiplexer 26, 27, 28, 29 ... Photodetector 30, 31 ... Control device 32, 34 ... First input 33, 35 ... Second input 36, 37, 38, 39, 40, 41 ... Laser device driving device 42, 43, 44, 45, 46, 47, 48 ... Temperature control device 110, 111, 112 ... Sawtooth wave generation Output waveforms from the device 2 113, 114, 115 ... Error signal 116, 117, 118 obtained by the first controller 30 ... Error signal 101 obtained by the second controller 31 ... Low-pass filter 102 ...... Pulse generation time difference measuring circuit 103, 104, 105 ...... Integrator 106, 107, 108 ...... Differential amplifier

Claims (1)

[Claims] 1. A reference racer device for sweeping an oscillation frequency within 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, and the reference laser device. A first optical branching device for branching the outgoing light from the first optical branching device, and an optical resonator for converting a frequency change of the first outgoing light from the first optical branching device into an amplitude change of the transmitted light,
A plurality of local stations having a plurality of laser devices having mutually different oscillation frequencies; a second optical branching device for branching the transmitted light of the optical resonator to the plurality of local stations;
A laser device oscillating frequency interval stabilizing device comprising the optical branching device of FIG. 3 for branching the second outgoing light of the optical branching device of the plurality of local stations to the plurality of local stations. A first optical multiplexer for multiplexing at least a part of the emitted light of each device, and a second optical multiplexer for combining the emitted light of the first optical multiplexer and the emitted light of the third optical branching device. Optical multiplexer, first photodetector for converting emitted light of the second optical multiplexer into an electric signal, and second photodetector for converting emitted light of the second optical brancher into an electric signal And an optical system at the time of sweeping the oscillation frequency of the reference laser device at the oscillation frequency intervals of the plurality of laser devices detected by the light emitted from the second optical multiplexer at the time of sweeping the oscillation frequency of the reference laser device. For the frequency interval reference set using the emitted light corresponding to the resonance peak of the resonator A control device that outputs a control signal for stabilizing the difference to a constant value, and a laser device drive device that changes input signals of the plurality of laser devices in accordance with a control signal from the control device. Laser device oscillation frequency interval stabilization device.