JP2014150210A - Short optical pulse generator and short optical pulse generator method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short optical pulse generator and a short optical pulse generation method which allow for emission of laser light of unimodal pulse stably at an arbitrary frequency, even when a drive current pulse of arbitrary waveform and frequency is inputted to a device.SOLUTION: A short optical pulse generator using a gain switching method for generating a short optical pulse by applying a pulse current to a semiconductor laser LD includes a waveform shaping circuit 2 performing waveform shaping of an externally inputted trigger signal train of arbitrary frequency into a pulse signal train of a predetermined pulse width, an amplitude adjustment circuit 3 for automatically adjusting the amplitude value of a pulse signal train outputted from the waveform shaping circuit 2 to a pulse signal train of a current value preset depending on the frequency of the trigger signal train, and a current application circuit 4 for applying the pulse signal train having an amplitude value adjusted automatically by the amplitude adjustment circuit 3, while adding a predetermined DC bias current value, to the semiconductor laser LD.

Description

  The present invention relates to a short light pulse generator and a short light pulse generation method.

  In a processing apparatus and a measuring apparatus using a semiconductor laser, it is necessary to generate a short optical pulse of nanosecond or less from the semiconductor laser in order to improve processing accuracy and measurement accuracy. For this reason, a gain switching method is used in which a short optical pulse is generated using relaxation oscillation in a semiconductor laser.

  Patent Document 1 discloses a control circuit using such a gain switching method. The control circuit includes a pulse generator that discretely generates a pulsed signal, and a driver that supplies a drive voltage pulse obtained by amplifying the pulse signal generated by the pulse generator with a predetermined amplification factor to the semiconductor laser. Yes. The voltage value of the drive voltage pulse is determined according to the signal level of the pulse signal generated by the pulse generator.

  The characteristics of a semiconductor laser that outputs a short optical pulse using the gain switching method is expressed by a rate equation as a transient response to a current pulse input. In a general semiconductor laser, the injection carrier density (which is described as a value corresponding to the laser driving voltage in Patent Document 1 but actually becomes an injection current (applied current) to the semiconductor laser) is increased. Thus, light emission is started slightly before the carrier density is saturated. As the injected carrier density increases, the photon density, that is, the emitted light intensity increases.

  The light emission start time calculated from the rate equation is inversely proportional to the injected carrier density. When the laser driving voltage is large, the amplitude of the injected carrier density appears as the first largest wave due to relaxation oscillation immediately after the start of light emission, and is gradually attenuated and stabilized as the second and third waves.

  In the control circuit, a driving voltage pulse having a voltage value necessary for the generation of relaxation oscillation is applied to the semiconductor laser, and the single-peak laser beam is composed of only the first wave due to relaxation oscillation and does not include the second and subsequent sub-pulses. (Hereinafter referred to as “single-peak pulse” in this specification) is emitted, and thereby the maximum value of the instantaneous emitted light intensity of the laser light is increased from the stable value. The pulse width of the drive voltage pulse is set to a time obtained by adding the light emission start time and the oscillation period of relaxation oscillation.

JP 2010-81884 A

  However, even if the pulse width and pulse amplitude of the applied current are adjusted so that a single peak pulse is emitted for an applied current pulse having a specific repetition frequency, if the applied current pulse frequency is different, The state of the carrier density, etc. of the laser beam changes, the laser light amplitude decreases significantly, or the second and subsequent sub-pulses are generated at the falling edge of the unimodal pulse, so that the unimodal pulse is stably generated from the semiconductor laser. There is a problem that it is difficult to emit light.

  For example, when such a semiconductor laser is used in a processing apparatus, if the unimodal pulse includes a second wave or a third wave sub-pulse, the effect is substantially the same as the pulse width is increased. As a result, there arises a problem that the processing accuracy and processing capability are lowered.

  In view of the above-described problems, the object of the present invention is a short optical pulse capable of stably emitting a single-peak pulse laser beam at that frequency even when a drive current pulse having an arbitrary frequency is input to the apparatus. It is in providing a generator and a method for generating short light pulses.

  In order to achieve the above object, the first characteristic configuration of the short optical pulse generator according to the present invention is to generate a short optical pulse by applying a pulse current to a semiconductor laser as described in claim 1 of the claims. A short optical pulse generator using a gain switching method, a waveform shaping circuit for shaping a trigger signal sequence of an arbitrary frequency input from the outside into a pulse signal sequence of a predetermined pulse width, and the waveform shaping circuit An amplitude adjustment circuit that automatically adjusts the amplitude value of the output pulse signal sequence to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence, and the amplitude value is automatically adjusted by the amplitude adjustment circuit. And a current application circuit for adding a predetermined direct current bias current value to the pulse signal train and applying it to the semiconductor laser.

  As a result of intensive research, the inventors of the present application have made a semiconductor laser to emit a unimodal pulse, that is, a unimodal laser beam consisting of only the first wave due to relaxation oscillation and not including the second and subsequent subpulses. It is found that the current value of the pulse current to be applied fluctuates with a certain correlation according to the frequency when the pulse width is fixed to a predetermined value, and the pulse applied to the semiconductor laser according to the frequency It was found that a single peak pulse having a desired frequency can be obtained by adjusting the current value of the current. However, in order to obtain a single-peak pulse with a desired frequency each time, a general user of a processing apparatus or a measuring apparatus using a semiconductor laser applies an application to the semiconductor laser while monitoring the emission waveform of the semiconductor laser with an optical oscilloscope. It is extremely difficult to adjust the current value.

  Accordingly, the inventors have conceived of a short light pulse generator that automatically adjusts the current value applied to the semiconductor laser and stably emits a single-peak pulse when a trigger signal train having a desired frequency is input from the outside. First, the waveform shaping circuit shapes the trigger signal train into a pulse signal train having the same frequency and a predetermined pulse width. When the waveform shaped pulse signal sequence is input to the amplitude adjustment circuit, it is automatically adjusted to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence, and the DC bias current value is set via the current application circuit. Is added to the semiconductor laser. As a result, a single peak pulse can be stably emitted.

  Therefore, a general user of a processing apparatus or a measuring apparatus using a semiconductor laser can input an arbitrary trigger signal sequence having a desired frequency to the short optical pulse generator without being conscious of the current value applied to the semiconductor laser. Thus, a single peak pulse can be obtained stably.

  In the second feature configuration, in addition to the first feature configuration described above, the amplitude adjustment circuit includes a frequency detection circuit that detects a frequency of the trigger signal sequence, and a short optical pulse. Based on the correlation stored in the storage circuit, the frequency detected by the frequency detection circuit, and the storage circuit for storing the intrinsic correlation between the frequency and the amplitude value of the current applied to the semiconductor laser And an amplification circuit that automatically adjusts the amplitude value of the pulse signal train.

  When the frequency of the trigger signal sequence is detected by the frequency detection circuit, a unique correlation between the frequency of the current applied to the semiconductor laser and the amplitude value in order to generate a unimodal pulse stored in advance in the storage circuit, that is, the correlation described above. From the relationship, the amplitude value, that is, the current value of the current to be applied to the semiconductor laser in order to generate a single peak pulse corresponding to the detected frequency is obtained. In the amplifier circuit, the amplitude value of the pulse signal train is automatically adjusted to obtain the current value.

  In the third feature configuration, in addition to the second feature configuration described above, the frequency detection circuit includes a frequency input circuit that numerically inputs a frequency of the trigger signal sequence, and the frequency A reading circuit is provided that reads a corresponding amplitude value from the memory circuit based on the frequency input to the input circuit and outputs the read amplitude value to the amplifier circuit.

  The frequency detection circuit is provided with a frequency input circuit for numerically inputting the frequency of the trigger signal sequence, and a readout circuit for reading out the corresponding amplitude value from the storage circuit based on the frequency input to the frequency input circuit and outputting it to the amplifier circuit It is preferable to provide. The frequency input circuit can be configured with a numeric input key, for example, and can also be configured with a receiving circuit that receives data transmitted from an external computer via a communication line.

  In the fourth feature configuration, as described in claim 4, in addition to the second feature configuration described above, the frequency detection circuit counts a rising edge or a falling edge of the trigger signal sequence and calculates a frequency. A frequency counter to be calculated and a reading circuit that reads a corresponding amplitude value from the storage circuit based on the frequency calculated by the frequency counter and outputs the read amplitude value to the amplifier circuit are provided.

  The frequency detection circuit has a frequency counter that calculates the frequency by counting the rising edge or falling edge of the trigger signal sequence, and reads and amplifies the corresponding amplitude value from the storage circuit based on the frequency calculated by the frequency counter It is preferable that a readout circuit for outputting to the circuit is provided. The frequency counter can be composed of, for example, a digital signal processing circuit, or can be composed of a computer that inputs a trigger signal string via an A / D converter and calculates a frequency from the value.

  In the fifth feature configuration, as described in claim 5, in addition to the second feature configuration described above, the frequency detection circuit receives a single pulse having a predetermined amplitude and pulse width from the trigger signal sequence. It is composed of a monostable multivibrator that repeatedly outputs a pulse signal sequence corresponding to the frequency, and the storage circuit is a logarithmic amplifier circuit that logarithmically converts the pulse signal sequence output from the monostable multivibrator, and the logarithm A signal corresponding to the amplitude value indicating the correlation when a pulse signal sequence having an arbitrary frequency is input from the monostable multivibrator. Correlation setting that adjusts the input offset of the logarithmic amplifier circuit, the input offset of the inverting amplifier circuit, and the amplification factor in advance so that In that it includes the road.

  Even if a trigger signal sequence having an arbitrary duty ratio is input from the outside to the device, a single pulse having a predetermined amplitude and pulse width is repeatedly output as a pulse signal sequence corresponding to the frequency by the monostable multivibrator. As a result, the average current of the signal sequence becomes a value corresponding to the frequency of the trigger signal sequence. That is, the monostable multivibrator functions as a frequency detection circuit. Then, the pulse signal sequence is input to the logarithmic amplifier circuit, and the logarithmically converted signal is inverted and amplified by the inverting amplifier circuit, and applied from the inverting amplifier circuit to the amplitude value indicating the correlation with the frequency of the trigger signal, that is, applied to the semiconductor laser. A signal corresponding to the current value is output. The characteristics of the logarithmic amplifier circuit and the inverting amplifier circuit are changed to the characteristics indicating the above-mentioned correlation by adjusting the correlation setting circuit in accordance with a pulse signal train of a plurality of frequencies which are inputted in advance from a monostable multivibrator. Adjusted. Specifically, the input offset of the logarithmic amplifier circuit, the input offset of the inverting amplifier circuit, and the amplification factor are adjusted. Therefore, the logarithmic amplifier circuit and the inverting amplifier circuit including the correlation setting circuit function as a memory circuit.

  In addition to the second feature configuration described above, the sixth feature configuration includes a monitor circuit that detects the output intensity of the semiconductor laser, and is detected by the monitor circuit in the amplifier circuit. An amplification factor adjustment circuit that adjusts the amplification factor based on the output intensity is provided.

  When the semiconductor laser is pulse-driven for a long time, the temperature rises and the light emission characteristics fluctuate. Therefore, the output intensity of the semiconductor laser is detected by the monitor circuit, and the amplification factor of the amplifier circuit is adjusted based on the detected value, so that the pulse shape is formed of only the first wave of the relaxation oscillation stably following the temperature fluctuation. The laser beam can be emitted.

  The first characteristic configuration of the short optical pulse generation method according to the present invention is the short optical pulse generation using the gain switching method in which the pulse current is applied to the semiconductor laser to generate the short optical pulse as described in claim 7. A waveform shaping step of shaping a trigger signal sequence of an arbitrary frequency input from the outside into a pulse signal sequence having a predetermined pulse width, and an amplitude value of the pulse signal sequence output from the waveform shaping step, An amplitude adjustment step for automatically adjusting to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence, and a predetermined bias current value for the pulse signal sequence whose amplitude value has been automatically adjusted in the amplitude adjustment step And a current application step of adding and applying to the semiconductor laser.

  In the second feature configuration, in addition to the first feature configuration described above, the amplitude adjustment step includes a frequency detection step for detecting the frequency of the trigger signal sequence, and a short optical pulse. A storage step for storing a specific correlation between the frequency of the current applied to the semiconductor laser and the amplitude value in advance in the storage circuit, and the frequency detected in the frequency detection step and the storage circuit stored in the storage circuit. And an amplification step for automatically adjusting the amplitude value of the pulse signal sequence based on the correlation.

  The third feature configuration includes a monitoring step for detecting the output intensity of the semiconductor laser in addition to the second feature configuration described above, and the amplification step is detected by the monitoring step. An amplification factor adjustment step for adjusting the amplification factor based on the output intensity is provided.

  As described above, according to the present invention, even when a drive current pulse having an arbitrary frequency is input to the apparatus, a short optical pulse generator capable of stably emitting a single-peak pulse laser beam at that frequency. In addition, a method for generating a short light pulse can be provided.

Functional block diagram of short optical pulse generator (A) to (c) are explanatory diagrams of the relationship between the injection current (applied current) to the semiconductor laser and the output light. (A), (b) is the correlation characteristic figure of the electric current value applied to the semiconductor laser which can generate a single peak pulse, and its pulse frequency (A) is an explanatory diagram of a general semiconductor laser drive signal and drive circuit, (b) is a waveform explanatory diagram. (A) is a waveform explanatory diagram of an externally input trigger signal sequence, (b) is a waveform explanatory diagram of a waveform-shaped pulse signal sequence, (c) is a waveform explanatory diagram of a current pulse sequence amplified by an amplifier circuit, d) Waveform explanatory diagram of the current applied to the semiconductor laser to which the bias current is added Functional block diagram of a short optical pulse generator showing another embodiment Explanatory drawing of the frequency detection circuit and memory circuit which show another embodiment Illustration of input offset characteristics of logarithmic amplifier circuit

  Hereinafter, embodiments of a short light pulse generator and a short light pulse generation method according to the present invention will be described. The short optical pulse generator is a pulse that does not include a sub-pulse after the second wave only by applying a pulse current to the semiconductor laser to form a single-peak pulse, that is, the first wave having the highest emission intensity immediately after the start of light emission by relaxation oscillation. It is an apparatus using a gain switching method for generating a laser beam.

  FIG. 1 shows a functional block configuration of the short optical pulse generator. The short optical pulse generator 1 includes an electronic circuit board including a waveform shaping circuit 2, an amplitude adjustment circuit 3, a current application circuit 4, a semiconductor laser LD, and an internal oscillator 5.

  The waveform shaping circuit 2 is a circuit that shapes a waveform of a trigger signal sequence having an arbitrary frequency input from the outside into a pulse signal sequence having a predetermined pulse width. Regardless of the value of the pulse width of the trigger signal sequence, the waveform is formed into a pulse signal sequence having a predetermined pulse width.

  The predetermined pulse width is a value that is appropriately set by experiment or the like for each short optical pulse generator, and is at least the time from when current is applied to the semiconductor laser until relaxation oscillation occurs, that is, the time that is longer than the light emission start time. Is a value that is set so as to be finally applied to the semiconductor laser, and is not limited to the time obtained by adding the light emission start time and the oscillation period of the relaxation oscillation. However, if the value of the predetermined pulse width is too long, sub-pulses after the second wave due to relaxation oscillation are included, and therefore, it is appropriately set within such a range that does not occur.

  In this embodiment, a compound semiconductor that outputs laser light with a near-infrared wavelength is used, and in addition to the type and individual difference of the semiconductor laser, the influence of the circuit and signal line impedance until actually applied to the semiconductor laser, etc. In consideration of the above, the predetermined pulse width is set in the range of 80 picoseconds to 1 nanosecond in full width at half maximum.

  The amplitude adjustment circuit 3 is a circuit that automatically adjusts the amplitude value of the pulse signal sequence output from the waveform shaping circuit 2 to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence. The amplitude adjustment circuit 3 adjusts the current value so that a single peak pulse is obtained.

  The current application circuit 4 is a circuit that adds a predetermined DC bias current value to the pulse signal train whose amplitude value has been automatically adjusted by the amplitude adjustment circuit 3 and applies the pulse current to the semiconductor laser LD. As shown in FIG. 4B, in order to obtain good and stable switching characteristics of the semiconductor laser, it is necessary to apply an injection current obtained by adding a DC bias current to the pulse current to the semiconductor laser.

  Therefore, as shown in FIG. 4 (a), an adder circuit for adding the pulse voltage generated by the pulse generator and the DC bias voltage generated by the DC bias generator circuit is generally provided and added by the adder circuit. A current pulse obtained by converting the obtained voltage by the voltage / current conversion circuit is applied to the semiconductor laser. The current application circuit 4 is a circuit that realizes the same function as this addition circuit.

  Returning to FIG. 1, the amplitude adjustment circuit 3 has a frequency detection circuit 31 for detecting the frequency of the input trigger signal sequence, and the frequency and amplitude values of the current applied to the semiconductor laser LD in order to generate a single peak pulse. And an amplifier circuit 33 that automatically adjusts the amplitude value of the pulse signal sequence based on the frequency detected by the frequency detection circuit 31 and the correlation stored in the storage circuit 32. Yes.

  A semiconductor memory is mainly used as the memory circuit 32, and a rewritable flash memory is preferably used. The amplifier circuit 33 is a circuit that performs voltage / current conversion on the pulse signal string output from the waveform shaping circuit 2 and amplifies the current.

  The specific circuit configuration of the amplifier circuit 33 is not particularly limited, and a voltage amplifier circuit that amplifies the voltage value of the pulse signal string output from the waveform shaping circuit 2 to a predetermined voltage value based on the above-described correlation. And a conversion circuit that performs voltage / current conversion on the output of the voltage amplification circuit.

  It is also possible to configure the current value of the pulse signal sequence output from the waveform shaping circuit 2 with a current amplification circuit that amplifies the current value to a predetermined current value based on the above-described correlation. That is, the amplitude adjustment circuit 3 has a function of automatically adjusting the amplitude value of the pulse signal sequence output from the waveform shaping circuit 2 to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence. Just do it.

  As shown in FIG. 2A, when the pulsed applied current value (indicated as “injection current” in the figure) to the semiconductor laser LD is low, the semiconductor laser LD has a sufficient intensity. If no light is emitted and the pulsed applied current value to the semiconductor laser LD is too large as shown in FIG. 2B, the first wave having the highest emission intensity immediately after the start of light emission, and then the second wave. Then, an optical pulse to which the third wave and the sub pulse are added is generated.

  However, as shown in FIG. 2C, when a current having an appropriate value is applied, a stable unimodal pulse can be obtained. When the pulse width is fixed to a predetermined value, the appropriate value of current varies depending on the frequency of the pulsed applied current, and is adjusted by the waveform shaping circuit 2 described above.

  FIG. 3A shows the correlation between the pulse frequency of the current applied to a semiconductor laser and the normalized optimum current value for obtaining a single peak pulse. While monitoring the emission waveform of the semiconductor laser with an optical oscilloscope, the operation of adjusting the value of the current applied to the semiconductor laser is performed from 100 Hz to about 250 MHz so that the single peak pulse shown by the solid line in FIG. It is the correlation obtained by repeating until.

  In this example, the optimum current value has a substantially flat characteristic in the frequency range from about 100 Hz to 100 kHz, but when it exceeds 100 kHz, it gradually decreases as the frequency increases. For example, when a pulse current of 80% (for example, 100 mA) is applied in a frequency range from about 100 Hz to 100 kHz, when a single peak pulse is obtained, the current value corresponding to 80% is obtained at 10 MHz (as described above). When a pulse current of about 78 mA is applied when the current is 100 mA, a unimodal pulse is obtained. However, when a pulse current of 80% (100 mA) is applied at 10 MHz, an optical pulse including the second wave and the third wave as shown in FIG. 2B is generated.

  Therefore, based on the correlation described with reference to FIG. 3A, a current value such that a single peak pulse is obtained with respect to a desired pulse frequency is obtained, and a pulse current of the current value is applied to the semiconductor laser LD. A single peak pulse can be obtained stably regardless of the frequency of the pulse current.

  When a stepped current is applied to the semiconductor laser under a specific condition, the light emission start time and the oscillation period of the relaxation oscillation can be obtained almost accurately based on the rate equation. It is also conceivable to control the pulse width of the current required to generate the peak pulse.

  However, in reality, when the current applied to the semiconductor laser, the temperature, etc. vary, the light emission start time also varies, and various factors such as the influence of the impedance of the drive circuit and wiring are involved. When this current is applied to the semiconductor laser, it is extremely difficult to finely control the pulse width of the current applied to the semiconductor laser because the change in carrier density is complicated and not uniform.

  According to the present invention, even if the current value is controlled by the amplitude adjustment circuit 3 based on the above-described correlation, the pulse width of the pulse signal sequence output from the waveform shaping circuit 2 is fixed to a predetermined value. A single peak pulse can be obtained stably.

  Specifically, the frequency detection circuit 31 reads a corresponding amplitude value from the storage circuit 32 based on the frequency input circuit to which the frequency of the trigger signal string is numerically input, and the frequency input to the frequency input circuit, and the amplification circuit 33. It is possible to provide a readout circuit that outputs to

  The frequency input circuit can be configured with, for example, a numerical value input key, and is a digital circuit that recognizes a value as a frequency when the numerical value is input by operating the numerical value input key. In addition, the frequency input circuit may include a reception circuit that receives frequency data transmitted from an external computer via a communication line, and may be configured by a digital circuit that recognizes data received by the reception circuit as a frequency. it can.

  The frequency detection circuit 31 counts the rising edge or falling edge of the trigger signal sequence to calculate the frequency, and reads the corresponding amplitude value from the storage circuit based on the frequency calculated by the frequency counter. A readout circuit that outputs to the amplifier circuit 33 can also be provided.

  The frequency counter can be constituted by, for example, a digital signal processing circuit including an edge detection circuit that detects a rising edge or a falling edge of a trigger signal string and a counter circuit that counts detected edges, and the trigger signal string. Can be input via an A / D converter, and a computer that calculates a frequency from the value can also be configured.

  The above-described waveform shaping circuit 2, frequency detection circuit 31, and storage circuit 32 can also be constituted by a microcomputer and its peripheral circuits.

  FIG. 5A shows a trigger signal sequence having an arbitrary amplitude value and pulse width at a desired frequency inputted externally, and FIG. 5B shows a predetermined pulse width with a predetermined amplitude shaped by the waveform shaping circuit. FIG. 5C shows a current pulse train amplified to a desired current value by the amplifier circuit 33, and FIG. 5D shows the application of a DC bias current by the current application circuit 4. The waveform of the current applied to the semiconductor laser LD is shown. By applying a pulse current of the current waveform to the semiconductor laser LD, a single peak pulse can be stably output.

  That is, in the short optical pulse generator described above, a waveform shaping step for shaping a trigger signal sequence of an arbitrary frequency input from the outside into a pulse signal sequence having a predetermined pulse width, and a pulse signal sequence output from the waveform shaping step An amplitude adjustment step for automatically adjusting the amplitude value of the signal to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence, and a predetermined direct current to the pulse signal sequence whose amplitude value has been automatically adjusted in the amplitude adjustment step A short light pulse generation method including a current application step of adding a bias current value and applying the bias current value to the semiconductor laser is executed.

  In the amplitude adjustment step, the frequency detection step for detecting the frequency of the trigger signal sequence, and the specific correlation between the frequency of the current applied to the semiconductor laser and the amplitude value to generate a single peak pulse are stored in the storage circuit in advance. And an amplification step of automatically adjusting the amplitude value of the pulse signal sequence based on the correlation detected in the frequency detection step and the correlation stored in the storage circuit.

  In FIG. 6, the short light pulse generator 1 is provided with a photodiode PD as a monitor circuit for detecting the output intensity of the semiconductor laser LD, and the amplifier circuit 33 has the output intensity of the laser light detected by the monitor circuit PD. An example is shown in which an amplification factor adjustment circuit 34 that adjusts the amplification factor is further provided.

  When the semiconductor laser LD is pulse-driven for a long time, the temperature rises and the light emission characteristics fluctuate. Even in such a case, the output intensity of the semiconductor laser LD is detected by the monitor circuit PD, and the amplification factor of the amplifier circuit 33 is adjusted based on the detected value. A pulse is emitted. In other words, the amplification factor adjustment circuit 34 feedback corrects the amplification factor for the current value read from the storage circuit 32 so that the output intensity of the semiconductor laser LD becomes a constant target intensity by the monitor circuit PD.

  The monitor step of detecting the output intensity of the semiconductor laser is executed by the monitor circuit PD described above, and the amplification factor adjustment step of adjusting the amplification factor based on the output intensity detected in the monitor step in the amplification step by the amplification factor adjustment circuit 34. Executed.

  The internal oscillator 5 is used when storing the inherent correlation between the current frequency and the amplitude value in the storage circuit 32. First, the switch for switching between the internal oscillator 5 and the external trigger signal is operated so that the output from the internal oscillator 5 is input to the waveform shaping circuit 2 and the frequency detection circuit 31.

  Next, the oscillation frequency of the internal oscillator 5 is set to 100 Hz, and the amplification factor of the amplifier circuit 33 is adjusted so that a single peak pulse is output while monitoring the output light of the semiconductor laser LD with an optical oscilloscope. Specifically, the gain of the amplifier circuit 33 can be adjusted by rewriting data in the memory circuit 32 via a computer connected externally as a jig.

  By switching the oscillation frequency of the internal oscillator 5 one digit at a time from 100 Hz to 100 MHz and repeating such adjustment work, the amplification factor or current value for the frequency at which the frequency is switched one digit at a time from 100 Hz to 100 MHz can be obtained. The obtained amplification factor or current value is a value normalized based on an arbitrarily set reference amplification factor or reference current value, and the value is written in the storage circuit 32.

  FIG. 3B shows the correlation obtained in this way. An intermediate value between the obtained optimum current values at each frequency can be determined by linear interpolation between the values. A value obtained by linear interpolation of the single-digit frequency range obtained by the adjustment at a predetermined frequency interval is stored in the storage circuit 32, and the optimum current value read from the storage circuit 32 corresponding to the frequency closest to the frequency of the trigger signal sequence is stored. The amplifier circuit 33 may be controlled by the above, or an optimum current value corresponding to the latest upper and lower frequencies including the frequency of the trigger signal sequence is read from the storage circuit 32, and a value obtained by linear interpolation between the optimum current values is used as the optimum current value. The amplifier circuit 33 may be controlled.

FIG. 7 shows a frequency detection circuit 31 and a storage circuit 32 of still another aspect.
The frequency detection circuit 31 includes a monostable multivibrator 310 that repeatedly outputs a single pulse having a predetermined amplitude and pulse width as a pulse signal sequence corresponding to the frequency from the trigger signal sequence.

  The memory circuit 32 includes a logarithmic amplifier circuit 320 that performs logarithmic conversion on the pulse signal sequence output from the monostable multivibrator 310, and an inverting amplifier circuit 325 that inverts and amplifies the output signal of the logarithmic amplifier circuit 320. .

  Further, when a pulse signal sequence having an arbitrary frequency is input from the monostable multivibrator 310, the input offset and inversion of the logarithmic amplifier circuit 320 are output so that a signal corresponding to the amplitude value indicating the above correlation is output. Correlation setting circuits 321, 326 and 327 for adjusting the input offset and amplification factor of the amplifier circuit 325 are provided.

  A trigger signal sequence having an arbitrary pulse width input to the terminal A is converted into a pulse signal having a pulse width Td (C1 × R1) and an amplitude Vh by a monostable multivibrator 310 including a flip-flop circuit, a resistor R1, and a capacitor C1. Waveform shaping into columns.

  When the time response characteristic of the logarithmic conversion transistor Tr1 in the next stage is sufficiently low, the current I1 flowing through the resistor R2 can be calculated as an average current of the pulse signal train. At this time, it can be expressed as I1 = Td × F × (Vh / R2). F is the frequency of the trigger signal train. That is, the average current of the pulse signal sequence becomes a value corresponding to the frequency of the trigger signal sequence, and functions as the frequency detection circuit 31.

  An addition current obtained by adding the constant current I2 input from the terminal B via the resistor R3 to the current I1 is input to the logarithmic amplifier circuit 320 including the transistor Tr1 and the operational amplifier OP1.

  As shown in the lower center graph of FIG. 7, the length of the horizontal portion of the output voltage V1 of the logarithmic amplifier circuit 320 is set by the constant current I2 (offset current) input through the resistor R3. . That is, the correlation setting circuit 321 is configured by the resistor R3 to which the constant current I2 is input.

  FIG. 8 shows the characteristics of the output voltage of the logarithmic amplifier circuit 320 and the frequency of the pulse signal sequence output from the monostable multivibrator 310 when the value of the constant current I2 is changed. By adjusting the value of the constant current I2, a flat region range in which the pulse frequency shown in FIG. 3A is 100 Hz to 100 kHz is set.

  The logarithmically converted voltage V1 is input to the inverting amplifier circuit 325 and output with the polarity inverted as shown in the lower right graph of FIG. At this time, the output is shifted to the plus side by the offset current flowing through the resistor R7.

The shift amount can be adjusted by adjusting the resistor R7. The adjustment amount is expressed by the following mathematical formula. Vs is the power supply voltage value of the negative power source of the inverting amplifier circuit 325.
Shift amount = (R6 / R7) × Vs

The amplification factor of the inverting amplifier circuit 325 can be adjusted by the resistor R6, and the slope of the drooping portion of the graph can be adjusted. At this time, the amplification factor is expressed by the following equation.
Amplification factor =-(R6 / R5)

  That is, after the resistance R7 is adjusted, the correlation setting circuit 326 that adjusts in advance the level of the flat region in which the pulse frequency of FIG. 3A is 100 Hz to 100 kHz is configured by the resistance R7 that adjusts the shift amount. The correlation setting circuit 327 that preliminarily adjusts the slope of the drooping portion when the pulse frequency of FIG. 3A is higher than 100 kHz is configured by the resistor R6 that adjusts the amplification factor.

  By adjusting the current I2 and the resistors R7 and R6 in order in advance, the pulse frequency of the current applied to the semiconductor laser and the normalized optimum current value for obtaining a unimodal pulse consisting only of the first wave by relaxation oscillation, Correlation is set. Therefore, the logarithmic amplifier circuit 320, the inverting amplifier circuit 325, and the correlation setting circuits 321, 326 and 327 for adjusting the input offset of the logarithmic amplifier circuit 320, the input offset of the inverting amplifier circuit 325, and the amplification factor are analog It functions as the memory circuit 32.

  It is also possible to incorporate the above-described amplification factor adjusting circuit 34 into the short optical pulse generator of such an aspect.

  The above-described correlation varies depending on the type of semiconductor laser used, and even the same type of semiconductor laser may vary depending on individual differences. Even in such a case, if the short light pulse generation device and the short light pulse generation method according to the present invention are employed, a correlation is first obtained for each semiconductor laser, and the correlation is stored in the storage circuit 32. There is no need for the user to make adjustments, and a single-peak pulse can be stably obtained simply by inputting a trigger signal sequence having a desired frequency to the short optical pulse generator.

  In the above-described embodiment, a compound semiconductor that outputs laser light having a near-infrared wavelength has been described as an example. However, the type and emission wavelength of the semiconductor laser used in the present invention are not particularly limited. It may be a wavelength region.

  The short light pulse generator according to the present invention can be suitably used for a processing device using a semiconductor laser, various measuring devices for measuring distances and shapes, and measuring fluorescence lifetime in the medical field and the like.

  The above-described embodiment is merely one embodiment of the present invention, and the scope of the present invention is not limited by the description. The specific numerical value of the correlation for generating the short light pulse (single peak pulse) is not a value common to all the semiconductor lasers, but is different for each semiconductor laser. In addition, the specific circuit configuration of each part constituting the short optical pulse generator can be appropriately changed and designed within the range where the effects of the present invention can be achieved.

1: Short optical pulse generator 2: Waveform shaping circuit 3: Amplitude adjustment circuit 31: Frequency detection circuit 32: Memory circuit 33: Amplifier circuit 4: Current application circuit 5: Internal oscillation circuit LD: Semiconductor laser

Claims (9)

A short optical pulse generator using a gain switching method for generating a short optical pulse by applying a pulse current to a semiconductor laser,
A waveform shaping circuit that shapes a trigger signal sequence of an arbitrary frequency input from the outside into a pulse signal sequence of a predetermined pulse width; and
An amplitude adjustment circuit that automatically adjusts the amplitude value of the pulse signal sequence output from the waveform shaping circuit to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence;
A current application circuit for adding a predetermined DC bias current value to the pulse signal train whose amplitude value is automatically adjusted by the amplitude adjustment circuit and applying the pulse current to the semiconductor laser;
A short light pulse generator.   The amplitude adjustment circuit includes a frequency detection circuit that detects a frequency of the trigger signal string, and a storage circuit that stores a unique correlation between a frequency and an amplitude value of a current applied to the semiconductor laser in order to generate a short optical pulse. 2. A short optical pulse according to claim 1, further comprising: an amplification circuit that automatically adjusts an amplitude value of the pulse signal sequence based on a frequency detected by the frequency detection circuit and a correlation stored in the storage circuit. Generator.   The frequency detection circuit is configured to input a numerical value of a frequency of the trigger signal sequence, and to read out a corresponding amplitude value from the storage circuit based on the frequency input to the frequency input circuit and to output to the amplification circuit The short optical pulse generator according to claim 2, further comprising a readout circuit.   The frequency detection circuit counts a rising edge or a falling edge of the trigger signal sequence to calculate a frequency, and reads a corresponding amplitude value from the storage circuit based on the frequency calculated by the frequency counter 3. A short optical pulse generator according to claim 2, further comprising a readout circuit for outputting to the amplifier circuit. The frequency detection circuit includes a monostable multivibrator that repeatedly outputs a single pulse having a predetermined amplitude and pulse width as a pulse signal sequence corresponding to the frequency from the trigger signal sequence,
The storage circuit includes a logarithmic amplifier circuit that logarithmically converts the pulse signal sequence output from the monostable multivibrator, and an inverting amplifier circuit that inverts and amplifies the output signal of the logarithmic amplifier circuit. An input offset of the logarithmic amplifier circuit and an input offset of the inverting amplifier circuit so that a signal corresponding to the amplitude value indicating the correlation is output when a pulse signal train of an arbitrary frequency is input from the multivibrator. And a correlation setting circuit for adjusting the amplification factor in advance.   3. The short light according to claim 2, further comprising a monitor circuit that detects an output intensity of the semiconductor laser, and an amplification factor adjustment circuit that adjusts the amplification factor based on the output intensity detected by the monitor circuit. Pulse generator. A short optical pulse generation method using a gain switching method for generating a short optical pulse by applying a pulse current to a semiconductor laser,
A waveform shaping step for shaping a trigger signal sequence of an arbitrary frequency input from the outside into a pulse signal sequence of a predetermined pulse width;
An amplitude adjustment step of automatically adjusting the amplitude value of the pulse signal sequence output from the waveform shaping step to a pulse signal sequence having a preset current value according to the frequency of the trigger signal sequence;
A current application step of adding a predetermined DC bias current value to the pulse signal train whose amplitude value is automatically adjusted in the amplitude adjustment step and applying the pulse current to the semiconductor laser;
A method for generating short light pulses.   In the amplitude adjustment step, a frequency detection step for detecting the frequency of the trigger signal sequence, and a specific correlation between the frequency and the amplitude value of the current applied to the semiconductor laser in order to generate a short optical pulse are stored in a storage circuit in advance. 8. A storage step for storing, and an amplification step for automatically adjusting the amplitude value of the pulse signal sequence based on the frequency detected in the frequency detection step and the correlation stored in the storage circuit. Method for generating short light pulses.   9. The short light according to claim 8, further comprising a monitoring step for detecting an output intensity of the semiconductor laser, and an amplification factor adjusting step for adjusting the amplification factor based on the output intensity detected in the monitoring step in the amplification step. Pulse generation method.

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