JPS6364381A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain an optical output with no frequency variation resulting from modulation by alternately arranging a period when the driving currents of a semiconductor laser are modulated and controlled, and a period when modulation is stopped or weakened. CONSTITUTION:A modulation control circuit 46, a half mirror 35a, an optical switch 48, a sweep circuit 64 and a sweep control circuit 64a are added. The modulation control circuit 46 stops or weakens a vibration signal fed to a drive circuit 34 from a signal source 38 only for a desired period. The optical switch 48 synchronizes beams obtained by branching output beams from a laser diode 11 by a half mirror, etc. with stoppage and control by the modulation control circuit 46 and passes them, thus acquiring wavelength stabilizing output beams. Accordingly, an optical output with no frequency variation resulting from modulation is obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor laser device that can obtain a laser output with a controlled wavelength (frequency). The present invention relates to a semiconductor laser device including means for stabilizing wavelength using spectral lines.

[Conventional technology] In recent years, due to improvements in the performance of semiconductor lasers, frequency stabilization using semiconductor lasers has superior performance to frequency stabilization light sources using gas lasers (He Ne lasers, etc.) that have been commercialized in the past. Research on light sources is becoming more active. This type of research is based on the r
It has not yet been advanced in close connection with the gFJ initiative. The above optical communication system uses (1) a semiconductor laser with extremely high frequency stability;

(2) Improving the spectral purity of semiconductor lasers.

(3) Wideband, high efficiency modulation technology.

Due to the importance of hats, rapid progress is being made in research and development aimed at resolving these issues. These technologies are capable of measuring distances, lengths, displacements, etc. in coherent light applied measurements with high 7i! It is also important in measuring sevenths.

Among these technologies, the above-mentioned (1) and (2) in particular have undergone remarkable technological development due to improvements in semiconductor lasers themselves. For example, as a laser with a new structure, D B R
'(D 1tributed Bragg R
efIeCtQr) type (black reflective type) laser, D
FB (Distributed Feed Back)
) type (distributed feedback type) laser, etc. This is a V# laser that uses a diffraction grating to determine the wavelength, and is a so-called DSM (Dynamic Single Laser).
Mode) It is about to be put into practical use as a laser.

However, there are problems such as variations in the laser oscillation wavelength due to temperature and so-called wavelength chirping, in which the wavelength is slightly shifted when the semiconductor laser is subjected to velocity modulation.

By the way, servo control is essential for stabilizing the laser frequency. In this servo control,
It is necessary to discriminate the laser frequency with an optical frequency discriminator and control the oscillation so that an output corresponding to the frequency difference between the laser frequency to be stabilized and the frequency reference of the optical frequency discriminator is obtained at a constant level. There are two typical methods for optical frequency discrimination:

(1) A method using a Fabry-Bello interferometer (hereinafter referred to as FP interferometer).

(2) A method that uses absorption spectral lines of molecules or atoms.

FIG. 8 shows a semiconductor laser frequency (wavelength) stabilization device using a conventional FP interferometer, where (11) is a laser diode, (12) is a current pivot circuit for driving the laser diode, (13) is a PID (proportionalist integrator) circuit.

(14) is a differential amplifier, (25) is a laser diode (
The variable voltages, sources, ■ and V, for setting the optical output of 11) are the electrical output signals of the photodiodes (16) and (17), respectively, and are applied to the divider (15). (
18) is an FP interferometer, (19) is a mirror, (20) is a beam splitter 1 (2l) and (22) are spatial filters, for example, pinholes with a diameter of 5 to 10 μm.

(23) and (24) are lenses for focusing light similar to microscope objective lenses. Also, laser diode (11)
In order to record the error signal with respect to the oscillation frequency reference (in this case, the resonant frequency of the FP interferometer (18)) as frequency stability evaluation data, the signal input to the pig recorder (28) is filtered through a low-pass filter (26), Amplifier (27)
are getting through.

Next, an outline of the operation of the apparatus shown in FIG. 8 will be explained.

The optical output of the laser diode (11) is converted into a parallel beam by a lens (23), passes through a spatial filter (22), and is split into two beams by a beam splitter (20), as shown by the dotted line. One of the light beams continues straight and reaches the FP
Interferometer (18), lens (24) and spatial filter (21)
) and is incident on the foot diode (17). The other beam is reflected by the beam splitter (20), reflected again by the mirror (19), and then incident on the photodiode (16). Electrical output from the photodiode (17) to the diode (11), which contains information on the difference between the transmission frequency and the reference frequency. Since optical output fluctuation components other than the signal components are included, it is necessary to remove them. Therefore, an electric signal VA corresponding to the light that does not pass through the FP interferometer (18) is obtained by the photodiode (16), and V8/V is obtained by the divider (15). This results in
A signal can be obtained from which optical output fluctuation components other than the fluctuation component corresponding to the difference from the frequency reference of the optical frequency discriminator are removed. In this example, VB/V is obtained using the divider (15), but the same effect can be obtained by using a subtracter to obtain V and -V.

The output of the divider (15) is input to the differential amplifier (14),
It is compared with the reference voltage of a reference voltage source (25), and a signal corresponding to the difference in the re-input, that is, an error output, is given to the pivot circuit (12) via a PID (proportional + integral plus differential) circuit (13). As a result, the laser diode (11) is controlled by negative feedback so that the oscillation frequency of the laser diode (11) is constant, that is, the output of the divider (15) is constant.

By the way, the method shown in FIG. 8 has a drawback that the frequency discrimination characteristics of the FP interferometer (18) change due to temperature fluctuations. Temperature fluctuation of FP interferometer (18) is 10-2 to 1
It is extremely difficult to control the temperature to below 0-3° C., considering the size of the interferometer and the conditions in which it is installed. The following techniques have been proposed to solve the above drawbacks.

(1) The interferometer shall be hermetically sealed to protect it from atmospheric pressure, external temperature, water vapor, etc. (Special Publication No. 6 O-12 (2) The temperature change in the refractive index of two interferometers is set so that one becomes positive and the other becomes negative, so that the temperature characteristics of these two interferometers cancel each other out. (e-publication 60-1176
93>(3) The interferometer is arranged obliquely at a set angle θ with respect to the optical axis, and the set angle θ is changed in accordance with temperature fluctuations to keep the light transmittance of the interferometer constant. (Tokuko Showa 6O-11
7694) However, the methods shown in (1) to (3) above all require complicated and precise control, and have the drawback of being inferior in practicality and credibility. Therefore, it is actually difficult to obtain a stability of 10-9 or higher. Note that the square root σ(τ) of Allan variance will be used to express the stability.

Figure 9 shows a method using atomic or molecular absorption spectral lines to discriminate optical frequencies. A spectrometer (32) is disposed that separates the absorption spectrum of molecules such as H3 so as to eliminate the so-called Doppler effect, that is, the spectrum broadening caused by the Doppler effect. This spectrometer (32) includes an absorption cell, a half mirror, a polarizing beam splitter, an optical attenuator, etc., and includes a laser diode (1
1) Information on the difference between the oscillation frequency and the reference frequency, that is, absorption spectrum information without Doppler broadening corresponding to each absorption order of many absorption spectrum lines of atoms or molecules at the oscillation frequency of the laser diode (11). It is configured to transmit a spectral output (37), that is, a probe light output, which includes a spectral output (37), that is, a probe light output, and a spectral output (36), that is, a pump light output, that includes a detailed information of absorption spectral lines with Doppler spread of atoms or molecules. . (16) and (17) are photodiodes that detect the pump light output (36) and the probe light output (37), respectively. A divider (15) connected to the output lines of the photodiodes (16) and (17) is a circuit that calculates the division output v, /VA of the output signals VA, 2, of the photodiodes (16) and (17). The output line (39) of the divider (15) is connected to a lock-in amplifier (33). This lock-in amplifier (33) also connects the vibration signal source (38) to the line (45).
and is configured to respond to an input signal applied from line (39) and a reference signal applied to line (45), and to send an output corresponding to the phase difference between the two signals to line (40). There is. A vibration signal source (38) is connected to the pivot circuit (34) through a line (44), a lock-in amplifier (33) is connected through a line (40), and this output line (41) is connected to a laser diode (11). )It is connected to the.

(31) is a temperature control device, which detects the temperature of the laser diode (11) using a thermistor (not shown), and controls the temperature of the laser diode (11) to keep this temperature constant.
11), which controls, for example, a Beltier cord (not shown) attached to the belt. Note that the method shown in FIG. 9 is based on, for example, IEICE Technical Report V.

1.82. No. 267, pp. 61-66, in the paper "Frequency Stabilization of Semiconductor Laser Using Sum Absorption Spectroscopy".

FIG. 10 shows the principle of the lock-in amplifier (33), and shows the signal input terminal (71) to which the lines (3) in FIG. 9 are connected and the reference line (45) to which it is connected. It has a signal input terminal (72). Signal input terminal (71
) is a preamplifier (73) and a bandpass filter (74)
connected to PSD (phase sensitive detection) (75) via
The optical signal input terminal (72) is connected to a band pass filter (76).
), a phase shifter for phase adjustment (77), and a waveform shaping circuit (78)
) is connected to the PSD (75). P.S.D.
The output of (75) is connected to an output terminal (80) via a low-pass filter (79). Note that the output terminal (
80) is connected to the output line (40) in FIG. This lock-in amplifier (33) is connected to the signal source (38) shown in FIG.
) detects and amplifies a frequency component synchronized with the reference signal given from the output line (45) of the input signal, and sends out a DC output signal corresponding to the phase difference between the input signal and the reference signal.

Next, the operation of the method shown in FIG. 9 will be explained. The temperature of the laser diode (11) is stabilized by feedback control by the temperature controller i2 (31), and its fluctuation range is 10-2°.
The temperature will be around 10-4°C. Temperature fluctuation 10-3°C
If it is set below, a frequency stability of about 10-6 to 10-8 can be obtained by itself. The output light (35) of the laser diode (11) is input to a spectrometer (32), and a spectral output (37) containing absorption spectrum lines of cesium atoms, rubidium atoms, NH3 molecules, etc. is obtained. To obtain this absorption spectral line, an optical system for saturated absorption spectroscopy (not shown) is included. One photodiode (17) receives the spectral output (37), that is, the probe light output, which includes an absorption spectrum line without a broadening due to the Doppler effect, and the other photodiode (16) receives an absorption spectrum line with a broadening due to the Doppler effect. Spectral output including (
36) In other words, input the pump light output. A detection signal V containing a fluctuation component corresponding to the absorption spectrum line as an optical frequency discriminator is obtained from one of the photodiodes (17). It is desirable to remove this because it contains fluctuation components other than fluctuations in laser output other than fluctuation components corresponding to the difference between the frequency (for example, the central peak point of the absorption spectrum) and the oscillation frequency of the laser diode (11). . The divider (15) is provided for this purpose, and by calculating V8/V^, the laser diode (11) with respect to the frequency reference point of the absorption spectrum line is calculated.
) fluctuation components other than the oscillation frequency fluctuation are removed. Of course, this variation component may be removed by a subtracter.
In this way, the output line (39) of the divider (15) receives a signal containing information on absorption level fluctuations due to fluctuations in the oscillation frequency of the laser diode (11) to be stabilized, and this is transmitted to the lock-in amplifier (33). It becomes input. Divider (
The detection signal of the laser frequency fluctuation corresponding to the absorption level fluctuation near the frequency reference point of the absorption spectrum line in the output of 15) is at a minute level and is buried in noise, so it is amplified as is and used for feedback control. However, it is difficult to obtain good results.

Therefore, in the method shown in FIG. 9, wobbling control is performed. For example, a sine wave alternating current signal with a constant frequency of 1k (2) is transmitted from the vibration signal source (38) through the line (44).
3 (14), and a current (I) containing this vibration component as shown in FIG. 11 is caused to flow from the pivot circuit (34) to the laser diode (11). That is, the driving diagram f! The constant current supplied from @ (34) to the laser diode (11) is modulated at a level of about 1 μA and 1 kHz, for example. If the current (I) of the laser diode (11) oscillates minutely, the output frequency (light wavelength) of the laser diode (11) will be modulated, for example, by at least 108)12 to several tens of IHz, as shown in 1211U(a). be done. When the output frequency of the laser diode (11) is modulated in this way, a wobbling frequency component is included in the input signal of the input line (39) of the lock-in amplifier (33), which contains level fluctuation information of the absorption spectrum line. become. In the lock-in amplifier (33), the detection signal corresponding to the laser frequency fluctuation including the wobbling frequency component and the reference signal of the line (45) are compared in phase, and the line (40) is
An output corresponding to this phase difference is obtained. If the reference signal on the line (45) and the frequency component of the input signal on the line (39) synchronized therewith match, the error signal obtained on the output line (40) of the lock-in amplifier (33) will be zero, If the phase difference between both signals becomes negative, the output line (40
) error signal is output to the output line (40
) will have a negative error signal. This means, in other words,
This is equivalent to detecting the first-order differential signal of the absorption spectrum. Since the line (40) is connected to the pivot circuit (34), the current of the laser diode (11) is controlled by negative feedback using the error output, and a control state is obtained in which the error output becomes zero. The method shown in Fig. 9 is a combination of frequency stabilization based on the absorption spectrum line of atoms or molecules, adoption of a wobbling method (modulation method), and temperature control. 10-13, which is an improvement of 3 to 5 orders of magnitude compared to the FP interferometer system shown in FIG.

[Problems to be Solved by the Invention] Incidentally, there are cases where it is required to linearly change the frequency (wavelength) of the output light of a semiconductor laser over time, that is, to sweep it. This type of requirement arises, for example, in devices that use a variable frequency laser to analyze absorption spectra. Even in the case of wavelength sweeping, it is necessary to generate a wavelength swept output in a stable and reproducible state as light whose wavelength has been calibrated.In such cases, wavelength calibration has been performed using Fapley-Bello interference. Relative calibration was performed using a meter. However, there has not yet been a semiconductor laser device that has a relatively simple configuration and can obtain highly accurate wavelength-calibrated, single-wavelength stabilized output light. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor laser device that can easily obtain wavelength-calibrated, wavelength-swept stabilized output light.

"Means for Solving the Problems" The present invention for solving the above problems and achieving the above objects includes a semiconductor laser and a temperature control device that controls the temperature of the semiconductor laser to a predetermined value by feedback control. , an optical frequency discriminator that obtains a signal for detecting a frequency difference between the frequency of the output light of the semiconductor laser and a frequency serving as a frequency reference as an absorption level difference of the absorption spectrum, including an atomic or molecular absorption spectrum spectrometer; a vibration signal source that generates a vibration signal for micro-vibrating the driving current of the semiconductor laser; and a vibration signal source that is connected to the optical frequency discriminator and the vibration signal source, and a A phase difference compatible signal forming circuit that outputs a signal corresponding to the phase difference (error signal) is connected to the phase difference compatible signal forming circuit and the vibration signal source, and is modulated by the vibration signal and is modulated by the phase difference. In a semiconductor laser device having a pivot circuit that supplies a drive current that is negative feedback controlled by a corresponding signal to the semiconductor laser, the vibration signal that is supplied from the vibration signal source to the pivot circuit is stopped for a predetermined period of time or is extremely high. The present invention relates to a semiconductor laser device characterized in that it is provided with a control means for weakening the voltage and a means for sweeping the temperature/or the injection current of the semiconductor laser during the period in which v1 is stopped or extremely weakened.

[Operation] The control means according to the present invention controls the temperature of the semiconductor laser based on the temperature control device and the temperature control of the semiconductor laser based on the temperature control device, and the control of atoms or By combining the discrimination signal obtained using an optical frequency discriminator including an absorption spectrum spectrometer using molecules and the formation of a negative feedback control signal (error signal) using a vibration signal, a highly stable output can be achieved at extremely low temperatures. Frequency (wavelength) has been obtained. If the modulation of the drive current by the vibration signal is stopped or weakened in this state, the laser output frequency will no longer include frequency fluctuations based on the modulation, or will become minute. If the period of stopping or weakening is short, it is possible to obtain a stabilized wavelength (frequency) that substantially continues the effect of the control immediately before the period of stopping or weakening. Since the drive current is not substantially modulated during this stopping or weakening period, no variation in the output frequency occurs based on this. Further, at this time, the stability of the optical output frequency is determined in accordance with the temperature stability of the semiconductor laser.

On the other hand, when the temperature of the semiconductor laser or the injection current is subtracted during the stopping or weakening period, the frequency (wavelength) of the output light is also changed in response to the temperature or injection current change, resulting in a wavelength sweep. Since this wavelength sweep is performed while the temperature and drive current control loops are stable, a stable wavelength sweep output can be obtained. If this device is used to cancel the modulation stopping or weakening operation and the t-pulling operation, the modulation will always be controlled, and it can be used in the same way as the conventional system shown in FIG. Furthermore, if both output light based on modulation control and swept output light are required, re-output light can be obtained in a time-division manner. Furthermore, if the wavelength sweep period is made a part of the period during which modulation control is stopped or weakened, coherent light without frequency fluctuations due to modulation can be obtained in the remainder of the period during which modulation control is stopped or weakened.

[Example 2] Next, a semiconductor laser device according to an example of the present invention will be described.
This will be explained with reference to FIGS. However, parts in FIG. 1 that are common to those in FIG. 9 are designated by the same reference numerals and their explanations will be omitted. The semiconductor laser device shown in FIG. 1 includes a modulation M control circuit B (46), a half mirror (1B5a), an optical switch (48), a sweep circuit (64), and a sweep control circuit (64a) in addition to the device shown in FIG. It is constructed by adding.

The modulation control circuit (46) is provided as a control means for stopping or weakening the vibration signal supplied from the signal source (38) to the pivot circuit (34) for a desired period, and in this example, the vibration signal is is configured to stop the supply of

The optical switch (48) splits the output light of the laser diode (11) using a half mirror, etc., and sends it to a modulation control circuit (4).
The wavelength-stabilized output light is obtained by passing the light in synchronization with the stop control by the 6-channel.

Figure 2 shows the modulation control circuit (46) and signal source (3) in Figure 1.
8), the signal source (38) includes a Wien bridge oscillator, which oscillator is connected to an operational amplifier (50).
, capacitors (53), (54), resistors (51), (
52), (55), and (56) constitutes a positive period circuit with series-parallel circuits of R and C,
Oscillation is possible at a frequency where the phase change of this circuit becomes zero. Furthermore, the oscillation frequency is stabilized and the distortion of the output waveform is improved by the negative lIi feedback caused by Ri and Rf.

The modulation control circuit (46) includes a control pulse generation circuit IM (47) that intermittently generates pulses, a switch SW that responds to this output pulse, and an operational amplification Pr (
A resistor (49) is selectively connected in parallel to the feedback resistor (52) of the resistor (50).

The oscillation conditions of the Wien bridge oscillator are
If the voltage gain of 0) is determined as A, it will be as follows.

In order to cause oscillation, the voltage gain A must be positive, so the value Rr of the resistor (52) and the value Ri of the resistor (51) must be set to satisfy Rf>2Ri. In a circuit that satisfies the above oscillation conditions, the switch SW is turned on in response to the low level of the control pulse shown in FIG. 4 ("o") obtained from the control pulse generating circuit (47) shown in FIG. When a resistor (49) with a value Rf is connected, Rf in the above gain equation becomes 1/2, which no longer satisfies the Mt'! condition.Therefore, the switch S
By controlling W on and off, it becomes possible to intermittently generate an oscillation output, that is, a rolling signal.

Here, the signal source (38) is indirectly controlled by the switch SW of the modulation control circuit (46) so that undesirable waveforms such as noise are not generated in the output of the signal source (38). That is, the output of the signal source (38) is connected to the line (44).
) is applied to the pivot circuit (34), and the drive current is modulated. At this time, since the semiconductor laser diode is modulated by a minute current, the oscillator built in the signal source (38) is activated as described above to prevent noise from being superimposed on the drive current during on/off control of the switch SW. Controlling the oscillation conditions is extremely important.

By controlling the signal source (38) in the above manner, for example, the frequency of several tens of MHz to 1μ for a change in drive current is
Even in a stabilized state of a -shell semiconductor laser with an oscillation frequency variation of 100 NH, the oscillation frequency variation caused by switching the control method by the switch SW is completely eliminated. The waveform of the oscillator output Vt in FIG. 2 is not the same as the waveform output from the signal source (38) shown in FIG. 4(a). The output of the signal source (38) is formed by passing the oscillator output VL through a bandpass filter, attenuator, etc. for removing noise (not shown), and has the waveform shown in FIG. 4(a>). The 10 pull control circuit (64a) is the modulation control circuit (4
6) is connected to the control pulse generation circuit (47), which generates a constant time relationship (sweep gate signal) with the pulse shown in FIG. (48).

FIG. 3 shows the temperature control device (31) of FIG. 1 in detail.

Here, (60) is a Vertier element used to keep the temperature of the laser diode (11) constant, (61) and (62)
) is an operational amplifier, (63) is a pivot circuit, Rs is a thermistor used to detect the temperature of the laser diode (11), Rg and Rr are resistors, VC is a constant voltage source, and Vr is a variable voltage for temperature setting. It is the source. A sweep circuit (64) is connected between variable voltage source Vr and resistor Rr. The initial setting of this temperature control device (31) is performed as follows. When the wobbling control stabilizes the center of the absorption spectrum as a modulation type, the sweep circuit (
64) output level, that is, variable voltage source Vr and resistor R
Adjust so that the potential at the connection point is approximately zero volts.

At this time, by adjusting the variable voltage source (1) and adjusting the set temperature of the laser diode (11), the oscillation spectrum of the laser diode (11) is made to substantially match the absorption spectrum.

Next, the operation of the apparatuses shown in FIGS. 1 and 2 will be explained with reference to FIG. When the switch S'vV is turned off at time t1 in Fig. 4, the oscillation conditions are satisfied, and the output of the signal VfA (38), which is similar to a 1 kHz sine wave shown in Fig. 4(a), is on the line. 44), the pivot circuit (
34), and the drive current is modulated. Figure 4 (a
) The modulated current waveform of the laser diode used for wobbling control must be a minute level signal (for example, 1 μA peak-to-peak) with little waveform distortion and noise. t~1 in FIG. In the period 1 to t7, the drive current is modulated in the same way as in the case of FIG. 9, and a stabilized frequency can be obtained with the same operation. In this case, the control loop including the lock-in amplifier (33) immediately starts stabilizing operation and stabilizes at t2 after the T3 period,
A stable error signal is obtained from the lock-in amplifier (33) during the period t2 to t3. The stability of the output frequency during this period t2 to t3, that is, the stability of the optical frequency corresponding to the approximate center of the wobbling, is good, but as in the case of Fig. 9, the frequency changes periodically, so the coherent It is not possible to use this frequency output for devices that require light. When the switch SW shown in FIG. 2 is turned on at time t3 and the oscillation conditions of the oscillator shown in FIG. 2 are no longer satisfied, the amplitude of the output waveform of the signal source (38) changes as shown in FIG. 4 (a>). It gradually becomes smaller, and the supply of the vibration signal to the pivot circuit (34) is substantially stopped.Therefore, the control loop including the lock-in amplifier (33) is substantially cut off.At time t3 From then on, the state is controlled only by the temperature control device C (31), and this control is continued until t after the period T has elapsed.
Stabilizes by time point 4. In the period t5 to t5, the pulse shown in FIG. 4(d) is generated from the sweep control circuit (64a), and the sweep circuit (64) generates the sweep signal shown in FIG. 4(e) in response to this, and the laser The temperature of the diode (11) changes in response to the sweep signal, and the frequency (wavelength) of the output light also enters the sweep state. Since the control period T1 based on both modulation control and the temperature control period T4 are provided before the sweep periods t- and -t5, stability during the sweep operation is enhanced. Since the optical switch (48) is on during this sweep period, the wavelength-selected output light is extracted and sent out.

At time t5, the switch SW of the modulation control circuit (46) is turned off again, so that the vibration signal shown in FIG. 4(a) is generated again.

According to this method, T1 where the signal source (38) is operating
The period is controlled by both the temperature control loop and the control loop including the absorption spectrum spectrometer and lock-in amplifier (33) to provide a period of less than 20 kHz (approximately 1 second or less).
During the T2 period when the signal source (38) is not operating, the frequency is stabilized only by the temperature control loop, so it is possible to obtain period stability of 2 MHz or less. Remaining t4 of T period in T period
From ° to t5, a sweep output can be obtained. In addition, T
In one period, apart from the stability of the optical frequency corresponding to the approximate center of the wobbling below 20 kHz, based on the frequency modulation, the amplitude of the wobbling control is S/? 'Since J (signal-to-noise ratio) cannot be reduced, the minimum change in the laser oscillation frequency to obtain the effect of wobbling control! lJ range is 10MHz
~ several tens of MHz. 2 MHz during stop period T2
The following fluctuations are the above modulation fluctuations (10 MHz to several tens of Hz)
H2) It is much less than H2) and can be used for coherent optical application devices. This relationship is shown in FIG. 12 (a>(b)).

In this method, frequency outputs with different types of stability and control specifications can be obtained during period T, period T4 in period T2, and the remaining period (t4 to tS), so either one can be selected depending on the application. It can be extracted and used,
It is also possible to use both on a time-sharing basis. Furthermore, by operating the switch SW, the period T1 can be made slightly longer, and the modulated output can be generated continuously. Further, by making the period T2 an extremely long time and stopping the sweep, it is also possible to continuously generate an unmodulated output. Therefore, one semiconductor laser device can be used in various forms.

Modifications] The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(1) A control circuit (46a) may be provided on this output line to control the output of the signal source (38) as shown in FIG. The control circuit (46a) has an output line (44
) to the ground, and in response to the zero cross point of the vibration signal of the signal source (38),
Control pulse generation port that generates the switch control pulse of b)! It consists of @(47a). FIG. 6 shows the operation of a semiconductor laser device including the circuit shown in FIG. 5, and the vibration signal shown in FIG. 6 (a>) is generated only in the T1 period shown in FIG. 6 (b). If the waveform is generated in this way, undesirable waveform distortion near the time of switching between periods T and T2 will not occur.

(2) As shown in FIG. 7, the rise of the control pulse in (b) may be made to coincide with the zero cross of the vibration signal in (a), and the fall may be the same as in the case of FIG. 4.

(3) In the methods shown in Figs. 1 to 4, the S motion signal is stopped during period T2 except for the first part, but a vibration signal of extremely small amplitude is generated during the entire period T2. Good too.

(4) In FIG. 1, the optical switch (48) is turned on in synchronization with a period (T, ~t) other than period T4 of period T in FIG. It may also be possible to turn it on in some sections.

Further, the ratio between T2 and T2 may be changed arbitrarily within the range permitted by the desired performance.

(5) Period] Lock-in amplifier (33) at 2
A special circuit may be provided to bring the output line (40) to zero level or to hold the level of the output line (40) immediately before the period T2.

(6) For stable operation, it is desirable to reduce light reflection to the laser diode (11) as much as possible. For this reason, it is better to employ an optical isolator, apply anti-reflection coating to the end face of the optical element, and perform oblique polishing.

(7) If the laser diode (11) is replaced with a DSM laser diode that has a narrower oscillation frequency spectrum spread than a normal laser diode and can continuously tune the optical wavelength, such as the aforementioned DBR type laser or DFB type laser, great performance can be achieved. We can expect improvement.

(8) Furthermore, the photodiodes (16) and (17) may be replaced with avalanche photodiodes or photomultiplier tubes.

(9) The signal source (38) may be configured using a PLL.

(10) In order to use the period 'r and T in a time-sharing manner, or the period T2, the farmland period T, the period (t to t5) and other periods, a laser diode (11) is used.
Two output optical paths may be provided.

(11) The oscillator of the signal source (38) may be configured to oscillate in phase synchronization with Tarok.

(12) In Fig. 2, a so-called Terman oscillator is configured with Rr→ω and R1=0, and focusing on the S width condition A=3, the oscillation is controlled, for example, by controlling the power supply voltage of the operational amplifier (50). You may. This power supply voltage control is shown in Figure 4 (
This is done in synchronization with the control pulse of b).

(13) A subtracter may be provided in place of the divider (15) in FIG. 1 to obtain v - V.

^ (14) The oscillation frequency of the semiconductor laser may be swept by sweeping the injection current of the laser diode (11), or by a combination of the injection current sweep and temperature sweep, or by the temperature sweep and injection current sweep. If sweep is used in combination, it becomes possible to expand the sweep width of the optical frequency. In general, sweeping by injection current has the effect of quick response, so when the sweep range is limited and high-speed sweeping is desired, sweeping by injection current is effective. This can be easily realized, for example, by branching a part of the output signal of the sweep port 1 (64) and applying it to the pivot circuit (34).

[Effects of the Invention] As is clear from the above, in the present invention, periods in which the driving current of the semiconductor laser is modulated and controlled and periods in which the modulation is stopped or weakened are arranged alternately. Therefore, during the period when modulation is stopped or weakened, it is possible to obtain optical output without frequency fluctuations caused by modulation. Furthermore, it becomes possible to substantially continue the stabilized state during the modulation control period until the modulation is stopped or the number of volumes is increased, and the stability is improved even during this period. If the frequency (wavelength) of the output light is swept by temperature sweep during this period, the same effect can be expected because the effect when there is no modulation control is maintained. In other words, the stability of the sweep is also improved. Furthermore, if there is a device that can accept a modulated output or a device that requires a modulated output, the output light of the semiconductor laser during the modulation period can be used as a light source for this shade. That is, it becomes possible to use one semiconductor laser device as a plurality of types of light sources, expanding the range of applications. Furthermore, the light source whose wavelength is precisely calibrated to the absorption spectrum of atoms and molecules through modulation is swept using the calibrated wavelength as a reference, making it an extremely useful semiconductor in devices that use lasers to separate absorption spectra and determine wavelengths. A laser device is obtained.

[Brief explanation of the drawing]

1 is a block diagram showing a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the signal source and modulation control circuit of FIG. 1, and FIG. 3 is a circuit diagram showing the temperature control device of FIG. 1. 4 is a waveform diagram showing the state of each part in FIGS. 1 and 2, FIG. 5 is a block diagram showing a modified example of the signal source and modulation control circuit, and FIGS. 6 and 7 are FIG. 8 is a block diagram showing a conventional semiconductor laser device; FIG. 9 is a block diagram showing another conventional semiconductor laser device; FIG. 10 is a diagram similar to that of FIG. 9. FIG. 11 is a block diagram schematically showing the lock-in amplifier; FIG. 11 is a waveform diagram showing the driving current of the laser diode shown in FIG. 9; Figure 12 is a diagram showing the frequency fluctuation range when the frequency is stabilized, Figure 12 (a) shows the optical frequency fluctuation range due to wobbling, and Figure 12 (b) shows the optical frequency when wobbling is stopped. It is a figure showing a fluctuation range. (11)...Laser diode, (31)...Temperature control device, (33)...Lock-in amplifier, (34)
...Pivotal circuit, (38)...Signal source, 46)...
- Modulation control circuit, (48)... optical switch, (64a
)...Sweep control circuit.

Claims (3)

[Claims] (1) includes a semiconductor laser, a temperature control device that controls the temperature of the semiconductor laser to a predetermined value through feedback control, and an atomic or molecular absorption spectrum spectrometer, and the frequency of the output light of the semiconductor laser and the frequency reference; an optical frequency discriminator that obtains a discrimination signal for detecting a frequency difference with a frequency as an absorption level difference in the absorption spectrum; and a vibration signal source that generates a vibration signal for micro-vibrating the driving current of the semiconductor laser. , a phase difference compatible signal forming circuit connected to the optical frequency discriminator and the vibration signal source and outputting a signal (error signal) corresponding to the phase difference between the discrimination signal and the vibration signal; a pivot circuit connected to the signal forming circuit and the vibration signal source, respectively, and supplying the semiconductor laser with a drive current that is modulated by the vibration signal and controlled by negative feedback with a signal corresponding to the phase difference. In the semiconductor laser device, a control means for stopping or extremely weakening the vibration signal supplied from the vibration signal source to the drive circuit for a predetermined period of time, and controlling the temperature and/or the temperature of the semiconductor laser during the period of stopping or extremely weakening the vibration signal. 1. A semiconductor laser device comprising: means for sweeping an injected current. (2) The semiconductor laser device according to claim 1, wherein the vibration signal source includes an oscillator, and the control means is means for switching oscillation conditions of the oscillator. (3) The semiconductor laser device according to claim 1 or 2, wherein the phase difference signal forming circuit is a lock-in amplifier.