JPH0650786B2 - Oscillation frequency interval stabilization device for multiple laser devices - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oscillation frequency interval stabilizing device for a plurality of laser devices, which stabilizes the intervals between the oscillation frequencies 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 flow spectrum range of another Fabry-Perot resonator (Toba et al. Division National Convention Proceedings, Volume 2, 2-20
(See page 4), or stabilizes the frequency of one laser device, combines it with some other laser device output light, and then sweeps this light and frequency in a sawtooth shape with a constant period. By combining with the emitted light, the appearance time of each pulse forming a pulse train obtained as a beat signal is monitored by monitoring whether a constant time difference is maintained with respect to the appearance time of the pulse corresponding to the stabilized laser device. A method for stabilizing the transmission frequency interval of a laser device (I.O.C.E.C.
O-EC '85 (IOOC-ECOC'85) Technical Digest Vol. 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 provides a plurality of reference laser devices having different frequency sweep ranges in order to sweep the oscillation frequency range of the plurality of laser devices. Which are adjacent to each other when the plurality of reference laser devices are arranged in the order of the oscillating frequency sweep range, receiving the first output light of the optical multiplexer / demultiplexer that multiplexes the emitted light from A reference laser control device that outputs a control signal such that the sweep ranges overlap, and a reference laser drive device that changes an input signal to the plurality of reference laser devices according to a control signal from the reference laser control device, Optical combining means for combining the third output light of the optical branching device and the output light from the plurality of laser devices and outputting oscillation frequency interval signals of the plurality of laser devices, and branching by the optical branching device Was done An optical resonance unit that receives the second output light and outputs a frequency interval reference signal, an output of the optical resonance unit and an output of the optical multiplexing unit, and an oscillation frequency interval signal of the plurality of laser devices and the frequency interval. A control device that outputs a control signal for stabilizing an error from a reference signal to a constant value, and a laser device driving device that changes input signals to the plurality of laser devices according to a control signal from the control device. An oscillation frequency interval stabilizing device for a plurality of laser devices is provided.

(Operation) By adopting the configuration as described above in the present invention, 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 the pulse train and the generation time of the corresponding pulse of the reference pulse train as an error signal, the frequency intervals of an arbitrary number of laser devices are simultaneously stabilized, and the frequency intervals are also stabilized. Is strictly defined by the optical resonator used.

Moreover, since the oscillation frequency sweep range of the reference laser device is limited, the number of laser devices to be controlled that can stabilize the interval frequency is limited with only a single reference laser device, but the sweep range is limited. This limitation can be overcome by using a plurality of reference laser devices different from each other.

(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 wavelength tunable distributed Bragg reflection type semiconductor lasers 1 and 2 are constantly generated by the direct current injected into their active regions.
Also, according to the intermittent triangular wave applied to the phase control region by the reference laser control device 3 as shown in FIGS. 2 (a) and 2 (b), the emitted light frequency becomes a triangular wave with a cycle of 500 Hz. Is changing. The variable frequency width in one sweep cycle is 25
It is 0 GHz. The structure and characteristics of the wavelength tunable distributed Bragg reflection type semiconductor laser are described in detail, for example, in a paper by Murata et al., Electronic Letters, Vol. 23, No. 8, page 403. The light emitted from the 1.55 μm band tunable distributed Bragg reflection type semiconductor lasers 1 and 2 passes through the optical isolators 4 and 5, and is then combined by the first optical combiner 6 and then by the optical branching device 7. A power ratio of 1: 1: 1 is divided into first, second and third output lights. The first of these
The output light 8 of is converted into an electric signal by the first photodetector 9 and then input to the reference laser control device 3. In the reference laser control device 3, the oscillation frequencies of the 1.55 μm band wavelength tunable distributed Bragg reflection type semiconductor lasers 1 and 2 are matched only near both ends of the swept reference triangular wave, and the frequency sweep ranges of both are connected. It is in control. In particular,
The reference laser control device 3 selects only the low-frequency component of the input signal, and the low-frequency component appears within one cycle of the sweep of the 1.55 μm band wavelength tunable distributed Bragg reflection type semiconductor lasers 1 and 2 for zero. Instead, a control signal that is shorter than the time width corresponding to the interval frequency of 75 GHz set in this embodiment is output to the reference laser drive devices 10 and 11. The outputs of the reference laser driving devices 10 and 11 are 1.
It is applied to the active regions of the 55 μm band variable wavelength distributed Bragg reflection type semiconductor lasers 1 and 2. In the phase control region of the 1.55 μm wavelength tunable distributed Bragg reflection type semiconductor lasers 1 and 2, an intermittent triangular wave having a constant frequency of 500 Hz and a constant height (FIGS. 2 (a) and (b)) is used. Is stamped.

Next, the optical resonance means will be described. The optical resonance means includes the etalon plate B and the second photodetector 14. First, the second output light 12 of the optical branching device 7 has a refractive index of 1.5, a thickness of 2 mm, and a finesse of 30. The etalon plate 13 made of quartz glass has the reflectance, surface accuracy, and parallelism set on both sides. After being transmitted, the light is incident on the second photodetector 14. Pulsed light is input to the second photodetector 14 when the oscillation frequencies of the 1.55 μm band wavelength variable distributed Bragg reflection type semiconductor lasers 1 and 2 match the resonance frequency of the etalon plate 13. The number of pulses generated in one sweep period is determined by the ratio of the variable frequency width of 250 GHz in one sweep period and the free spectral range of the etalon plate of 75 GHz, and is three for each laser. The electrical signal from the second photodetector 14 is applied to the first input terminal 16 of the controller 15.

On the other hand, the optical multiplexing means comprises the second and third optical multiplexers 27 and 28 and the third optical multiplexer 28, and the operation is as follows. It is a target for stabilizing the frequency interval. 1.5
The light emitted from the 5 μm band distributed feedback lasers 17 to 21 passes through the optical isolators 22 to 26, respectively, and then is multiplexed by the second optical multiplexer 27. Secondly, the outgoing light from the optical multiplexer 27 is multiplexed by the third optical multiplexer 28 with the third output light 29 of the optical branching device 7. The output of the third optical multiplexer 28 is converted into an electric signal by the third photodetector 30 and then applied to the second input terminal 31 of the controller (details are shown in FIG. 3) 15. . The signal applied to the second input terminal 31 is first a low pass filter 32 with a cutoff frequency of 100 MHz.
Entered in. 1.55 μm from low pass filter
Pulsed when the difference between the oscillating frequency of either one of the band tunable distributed Bragg reflection type semiconductor lasers 1 and 2 and the oscillating frequency of the 1.55 μm band distributed feedback lasers 17 to 21 is within approximately ± 100 MHz. -Shaped electric signal is output. The number of pulses is 1.55 μm band tunable distributed Bragg reflection type semiconductor lasers 1, 2 and 1.55 within one sweep period.
The difference between the oscillation frequencies of the μm band distributed feedback lasers 17 to 21 is equal to the number of times of entering the range of ± 100 MHz, which is five. In the control device 15, the input to the first input terminal 16 of the control device 15 shown by the solid line in FIG.
The second input terminal 31 of the control device 15 shown by the dotted line in (c)
The difference between the pulse generation times of the inputs to is used as an error signal, and a control signal whose magnitude becomes zero is also output.

The pulse generation time difference measurement circuit in FIG. 3 (an example of the circuit is shown in FIG. 4) has a corresponding order when the pulses forming the two input pulse trains are arranged in the order of generation time. It has a width proportional to the time difference of occurrence of two pulses (a total of 5 sets), and the height outputs one square pulse.
However, which of the two series pulse trains to which the earlier pulse of the above two pulses belongs is
The output has the function of becoming a positive or negative square pulse, the details of which are shown in FIG. Further, the control device 5 is
The square pulses, which are the five outputs from the pulse generation time difference measurement circuit, are each integrated, and added together with an appropriate bias voltage and output.

The first to fifth control signals from the control device 15 are input to the laser device driving devices 32 to 36, respectively. A driving current corresponding to a control signal is injected from the laser device driving devices 32 to 36 into the 1.55 μm band feedback laser. In addition,
1.55 μm wavelength tunable distributed Bragg reflection type semiconductor lasers 1, 2 and 1.55 μm band distributed feedback lasers 17 to 21
Are temperature fluctuations ± by the temperature control devices 37 to 43, respectively.
The temperature is stabilized within 0.1 ° C.

In this embodiment, only five laser devices are stabilized in frequency interval, but the number of laser devices to be controlled can be increased by increasing the number of reference laser devices. Further, the type of the laser device is not limited to the semiconductor laser, and any laser device capable of changing the oscillation frequency by applying an external signal may be used.

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

Further, the number of simultaneously controllable laser devices is not limited to the variable frequency width of each reference laser device, and can be easily increased by increasing the number of reference laser devices.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG.
The sweep waveform applied to the 1.55 μm band wavelength tunable distributed Bragg reflection type semiconductor laser 1 in the figure, and FIG. 2 (b) is applied to the 1.55 μm band wavelength tunable distributed Bragg reflection type semiconductor laser 2 in FIG. Sweep waveform, FIG. 2 (c) shows the second and third photodetectors 1 input to the control device 15 in FIG.
It is a figure showing the electric signal from 4,30. FIG. 3 is a block diagram of the control device 15 in FIG. 1, and FIG.
The drawing is a circuit diagram of the pulse generation time difference measuring circuit in FIG. In FIGS. 1, 2 (c), and 3, 1, 2, ... 1.55 μm band wavelength variable distributed Bragg reflection type semiconductor laser, 3 ... Reference laser control device, 4, 5, 22, 23, 24, 25, 26 ... Optical isolator, 6, 27, 28 ... Optical multiplexer, 7 ... Optical splitter, 8, 1
2, 29 ... Output light from the optical branching device 7, 8, 14, 30 ... Photodetector, 10, 11 ... Reference laser driving device, 13 ... Etalon plate, 15 ... Control device, 16, 31 ... Control device 15 Input terminals, 17, 18, 19, 20, 21 ... 1.55μ
m-band distributed feedback laser, 32, 33, 34, 35, 36
... Laser device driving device, 37, 38, 39, 40, 4
1, 42, 43 ... Temperature control device, 50, 51, 52, 5
3, 54 ... Error signal, 55 ... Frequency sweep period

Claims (1)

[Claims] 1. A plurality of reference laser devices having different frequency sweep ranges are provided in order to sweep oscillation frequency ranges of the plurality of laser devices, and light emitted from the plurality of reference laser devices is multiplexed and re-branched. And a first output light of the optical multiplexer / demultiplexer, and outputs a control signal such that adjacent sweep ranges overlap when the plurality of reference laser devices are arranged in the order of the oscillation frequency sweep ranges. A reference laser control device, a reference laser drive device that changes input signals to the plurality of reference laser devices according to a control signal from the reference laser control device, and a third output light of the optical branching device. Optical combining means for combining output lights from the plurality of laser devices and outputting oscillation frequency interval signals of the plurality of laser devices, and second output light branched by the optical branching device,
An optical resonance unit that outputs a frequency interval reference signal, an output of the optical resonance unit and an output of the optical multiplexing unit, and a constant value of the error between the oscillation frequency interval signals of the plurality of laser devices and the frequency interval reference signal. A plurality of lasers, each comprising a control device for outputting a control signal for stabilizing the laser light and a laser device driving device for changing an input signal to the plurality of laser devices according to a control signal from the control device. Equipment for stabilizing the oscillation frequency interval.