Laser device and laser waveform control method

Abstract

To provide laser equipment which can be downsized and a laser waveform control method.SOLUTION: Laser equipment 1A comprises: a semiconductor laser element 5; a waveform calculation part 3 that calculates input waveform data Da; a driver circuit 4 that supplies a drive current Id having a time waveform according to the input waveform data Da to the semiconductor laser element 5; an optical amplifier 7 that amplifies laser beam La output from the semiconductor laser element 5; and an optical waveform detection part 10 that detects the waveform of the amplified laser beam Lb output from the optical amplifier 7. The waveform calculation part 3 compares the waveform of the amplified laser beam Lb detected by the optical waveform detection part 10 with a target waveform, and adjusts the time waveform of the input waveform data Da to bring the amplified laser beam Lb close to the target waveform.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laser device and a laser waveform control method. [Background technology]

[0002] Non-Patent Document 1 discloses a laser device that outputs optical pulses with a pulse width on the order of nanoseconds. This laser device includes a light source that outputs continuous wave (CW) laser light, an acousto-optic modulator (AOM) that temporally cuts the laser output from the light source to generate pulsed light, and an electro-optic modulator (EOM) that shapes the pulsed light output from the AOM into an arbitrary waveform. The light source is a fiber laser pumped by a laser diode (LD). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Saumyabrata Banerjee et al., “100 J-level nanosecond pulsed diodepumped solid state laser”, Optics Letters, Vol. 41, No. 9 (2016) Summary of the Invention [Problem to be solved by the invention]

[0004] Arbitrarily shaping the time waveform of ultrashort pulse light or short pulse light is extremely useful, for example, for laser processing and various measuring instruments (e.g., shape monitors, shock wave monitors). By selecting an appropriate pulse light waveform according to the processing object or measurement object, it is expected that the processing accuracy and measurement accuracy can be improved. However, even if a desired waveform is generated with high accuracy, there is a problem that when optical amplification is performed to obtain the required pulse light intensity, the amplified optical waveform is distorted due to the nonlinearity of the optical amplifier. Therefore, it is conceivable to input pulse light of a waveform into the optical amplifier that will give the amplified optical waveform a desired shape, taking into consideration the nonlinearity of the optical amplifier in advance.

[0005] In conventional pulsed light generating devices, as described in, for example, Non-Patent Document 1, continuous light output from a fiber laser or solid-state laser is shaped into an arbitrary waveform by an EOM. The dimensions of fiber lasers and solid-state lasers tend to be large, and EOMs have large fluctuations in characteristics due to temperature changes (temperature drift), so a separate configuration is required to compensate for the temperature drift of the EOM. These are factors that hinder the miniaturization of laser devices.

[0006] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a laser device and a laser waveform control method that enable the device dimensions to be reduced. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a laser device according to one aspect of the present invention includes a single semiconductor laser element, a waveform calculation unit that calculates input waveform data, a driver circuit electrically connected to the waveform calculation unit and the single semiconductor laser element and that generates a drive current having a time waveform corresponding to the input waveform data and supplies the drive current to the single semiconductor laser element, an optical amplifier optically coupled to the single semiconductor laser element and that amplifies light output from the single semiconductor laser element, and an optical waveform detection unit that detects the amplified optical waveform output from the optical amplifier. The single semiconductor laser element is a single laser diode.The amplified optical waveform detected by the optical waveform detector is the waveform of light output from a single semiconductor laser element and then amplified by an optical amplifier. The waveform calculator compares the amplified optical waveform detected by the optical waveform detector with a target waveform to calculate a waveform. Generate differential data , the time waveform of the input waveform data is Based on target waveform and difference data Adjust, By adjusting the optical waveform output from a single semiconductor laser element using only a drive current having a time waveform adjusted according to input waveform data, The amplified optical waveform is made closer to the target waveform. The waveform calculation unit adjusts the time waveform of the input waveform data so that the difference between the amplified optical waveform detected by the optical waveform detection unit and the target waveform approaches zero.

[0008] A laser waveform control method according to one aspect of the present invention includes a current supply step of generating a drive current having a time waveform corresponding to input waveform data and supplying the drive current to a single semiconductor laser element, an optical amplification step of amplifying light output from the single semiconductor laser element, an optical waveform detection step of detecting the amplified optical waveform, and comparing the amplified optical waveform detected in the optical waveform detection step with a target waveform. Generate differential data , the time waveform of the input waveform data is Based on target waveform and difference data Adjust, By adjusting the optical waveform output from a single semiconductor laser element using only a drive current having a time waveform adjusted according to input waveform data, and a waveform adjustment step of adjusting the amplified optical waveform to approximate a target waveform. The single semiconductor laser element is a single laser diode. The amplified optical waveform detected in the optical waveform detection step is the waveform of light that is output from a single semiconductor laser element and then amplified in the optical amplification step. In the waveform adjustment step, the time waveform of the input waveform data is adjusted so that the difference between the amplified optical waveform detected in the optical waveform detection step and the target waveform approaches zero.

[0009] In the above laser device and laser waveform control method, a semiconductor laser element is used as a light source, instead of a fiber laser or solid-state laser that outputs continuous light. The waveform of a drive signal for driving the semiconductor laser element is adjusted based on the amplified optical waveform detected by the optical waveform detection unit (optical waveform detection step). This allows the optical waveform output from the semiconductor laser element to be adjusted so that the amplified optical waveform approaches a target waveform. In addition, the size of electronic circuits such as the waveform calculation unit and the semiconductor laser element is significantly smaller than that of a fiber laser or solid-state laser, and an EOM. Furthermore, with regard to the temperature drift of the semiconductor laser element, it is sufficient to keep the temperature of the semiconductor laser element constant using a Peltier element or the like. As a result, the above laser device and laser waveform control method allow the device dimensions to be reduced compared to conventional devices and methods.

[0010] In the above laser device, the waveform calculation unit may adjust the time waveform of the input waveform data so that the difference between the amplified optical waveform detected by the optical waveform detection unit and the target waveform approaches 0. Similarly, in the waveform adjustment step of the above laser waveform control method, the time waveform of the input waveform data may be adjusted so that the difference between the amplified optical waveform detected in the optical intensity detection step and the target waveform approaches 0. This makes it possible to make the amplified optical waveform approach the target waveform with even greater accuracy. In this case, the waveform calculation unit may have a storage unit that pre-stores data indicating the target waveform.

[0011] In the above laser device, the driver circuit may have a D / A conversion unit that converts digital input waveform data into an analog drive signal and a current conversion unit that converts the drive signal into a drive current, and the D / A conversion unit may convert a plurality of continuous section waveform data obtained by dividing the time waveform of the input waveform data into drive signals sequentially with a time difference. Similarly, the current supply step of the above laser waveform control method may include a D / A conversion step that converts digital input waveform data into an analog drive signal and a current conversion step that converts the drive signal into a drive current, and in the D / A conversion step, a plurality of continuous section waveform data obtained by dividing the time waveform of the input waveform data may be converted into drive signals sequentially with a time difference. According to these devices and methods, the drive signal can be made faster to improve the time resolution of the optical waveform. In the above laser device, the optical waveform detection unit Single The laser device may have an optical branching section that branches the light output from the semiconductor laser element and then amplified by the optical amplifier into a part and a remainder, and an optical detection section that detects the optical waveform after amplification by generating an electrical signal according to the optical intensity of the part. The waveform calculation section may obtain the optical waveform after amplification based on the electrical signal. The remainder may be output to the outside of the laser device. Similarly, the optical waveform detection step of the above laser waveform control method includes: Single The method may include a step of splitting the light output from the semiconductor laser element and amplified in the optical amplification step into a part and a remainder, and a step of detecting the optical waveform after the amplification by generating an electrical signal according to the optical intensity of the part. In the waveform adjustment step, the optical waveform after the amplification may be obtained based on the electrical signal. The laser waveform control method may further include a step of outputting the remainder. In the above-mentioned laser device and laser waveform control method, the ratio (P1 / P2) of the intensity P1 of the portion to the intensity P2 of the remaining portion may be within a range of 0.005 to 0.01. Effect of the Invention

[0012] According to one aspect of the present invention, it is possible to provide a laser device and a laser waveform control method that enable the device dimensions to be reduced. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a configuration of a laser device 1A according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a block diagram showing a specific example of a laser device 1A. [Diagram 3] 2 is a block diagram showing a detailed configuration example of a driver circuit 4. FIG. [Figure 4] 4 is a diagram illustrating a schematic diagram of a function of a waveform timing adjustment section 43. FIG. [Diagram 5] 4 is a flowchart showing the operation of the laser device 1A. [Figure 6] 4(a) to 4(d) are diagrams showing schematic diagrams of optical pulse waveforms. [Figure 7] 1A shows the time waveform (square wave) of laser light La before amplification, and FIG. 1B shows the time waveform of laser light Lb after the laser light La having the time waveform shown in FIG. [Figure 8] 1A shows the time waveform (ramp wave) of laser light La before amplification, and FIG. 1B shows the time waveform of laser light Lb after the laser light La having the time waveform shown in FIG. [Figure 9] 5 is a graph showing an example of the time waveform of laser light La output from the semiconductor laser element 5. (a) shows a Gaussian waveform with a full width at half maximum of 4 nanoseconds, and (b) shows a Gaussian waveform with a full width at half maximum of 32 nanoseconds. [Figure 10] 5 is a graph showing an example of the time waveform of laser light La output from a semiconductor laser element 5. (a) shows a square wave with a full width at half maximum of 120 nanoseconds, and (b) shows a ramp waveform with a full width at half maximum of 4 nanoseconds. [Figure 11] FIG. 1 is a block diagram showing a configuration of a conventional laser device. [Figure 12] FIG. 12 is a block diagram showing a configuration in which a feedback circuit for adjusting a drive signal based on an output waveform is added to the laser device shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser device and a laser waveform control method according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals and duplicated description will be omitted.

[0015] Fig. 1 is a block diagram showing the configuration of a laser device 1A according to one embodiment of the present invention. As shown in Fig. 1, the laser device 1A of this embodiment includes a waveform calculation unit 3, a driver circuit 4, a semiconductor laser element 5, an optical isolator 6, an optical amplifier 7, an optical branching unit 8, and an optical detection unit 9.

[0016] The waveform calculation unit 3 is composed of electronic circuits and is electrically connected to the driver circuit 4. The waveform calculation unit 3 calculates and generates input waveform data Da for making the waveform of the optical pulse output from the optical amplifier 7 (hereinafter, referred to as output waveform) closer to a target waveform, and provides the input waveform data Da to the driver circuit 4. In one example, the waveform calculation unit 3 has a computer 31, a waveform adjustment unit 32, and a comparison unit 33. The computer 31 has a CPU and a memory, and operates according to a program stored in the memory. The memory of the computer 31 is a storage unit in this embodiment, and stores in advance data representing a desired (arbitrary) optical waveform, that is, a target waveform (hereinafter, referred to as target waveform data). This target waveform data is stored in advance in the memory by an operator through a data input terminal of the computer 31 before the operation of the laser device 1A. Alternatively, the computer 31 may design the target waveform by itself as a waveform design unit. In other words, the computer 31 may calculate a target waveform for realizing light irradiation conditions (processing conditions, observation conditions) given from the outside. Target waveform data representing the calculated target waveform is stored in the memory of the computer 31.

[0017] The comparison unit 33 is electrically connected to the light detection unit 9 described later, and obtains an output waveform based on a detection signal (light intensity signal Sc) obtained from the light detection unit 9. The comparison unit 33 is also electrically connected to the computer 31, and obtains target waveform data Db from the computer 31. The comparison unit 33 compares the output waveform with the target waveform, and sends difference data Dc indicating the difference therebetween to the waveform adjustment unit 32. The comparison unit 33 may be configured by a computer having a CPU and a memory. In that case, the comparison unit 33 may be separate from the computer 31, or may be realized in a computer common to the computer 31.

[0018] The waveform adjustment unit 32 is electrically connected to the computer 31 and acquires the target waveform data Db from the computer 31. The waveform adjustment unit 32 is also electrically connected to the comparison unit 33 and acquires the difference data Dc output from the comparison unit 33. The waveform adjustment unit 32 generates input waveform data Da based on these data Db and Dc so that the output waveform approaches the target waveform (i.e. so that the difference becomes small). The waveform adjustment unit 32 may also be configured by a computer having a CPU and a memory. In that case, the waveform adjustment unit 32 may be separate from the computer 31 and the comparison unit 33, or may be realized in a computer common to at least one of the computer 31 and the comparison unit 33.

[0019] An input end of the driver circuit 4 is electrically connected to the waveform adjustment unit 32 of the waveform calculation unit 3, and receives input waveform data Da from the waveform adjustment unit 32. The driver circuit 4 generates a drive current Id having a time waveform corresponding to the input waveform data Da. An output end of the driver circuit 4 is electrically connected to the semiconductor laser element 5, and supplies the generated drive current Id to the semiconductor laser element 5. Note that a bias current that does not change with time and has a constant magnitude may be superimposed on the drive current Id.

[0020] The semiconductor laser element 5 is a laser diode and is electrically connected to the driver circuit 4. The driver circuit 4 supplies a driving current Id to either the cathode or the anode of the semiconductor laser element 5. The semiconductor laser element 5 receives the driving current Id and generates a laser light La. This laser light La is a light before being amplified by the optical amplifier 7, and has a time waveform according to the input waveform data Da. In one example, the semiconductor laser element 5 is a distributed feedback (DFB) laser diode. Since the semiconductor laser element 5 is a DFB laser diode, it is easy to optimize the gain of the optical amplifier 7 according to the wavelength characteristics. Note that the waveform A in the figure shows a schematic representation of the time waveform of the laser light La output from the semiconductor laser element 5. The output power of the semiconductor laser element 5 is, for example, several nanojoules.

[0021] An optical input end of the optical isolator 6 is optically coupled to a laser light output end of the semiconductor laser element 5. In addition, an optical output end of the optical isolator 6 is optically coupled to an optical input end of the optical amplifier 7. In other words, the optical isolator 6 is located on the optical path between the semiconductor laser element 5 and the optical amplifier 7. The optical isolator 6 prevents the light amplified by the optical amplifier 7 from returning to the semiconductor laser element 5.

[0022] The optical input end of the optical amplifier 7 is optically coupled to the semiconductor laser element 5 via the optical isolator 6, and amplifies the laser light La output from the semiconductor laser element 5. The optical amplifier 7 does not convert the laser light into an electrical signal, but directly amplifies the light as it is. The optical amplifier 7 may be, for example, an optical fiber amplifier, a solid-state laser amplifier, or a combination thereof. The optical fiber amplifier has an optical fiber made of glass doped with impurities such as Er and Yb, and amplifies the laser light La by inputting pumping light together with the laser light La to the optical fiber. The solid-state laser amplifier may be made of glass or yttrium-aluminum-garnet (YAG) doped with impurities such as Nd. The solid-state laser amplifier amplifies the laser light La by inputting pumping light together with the laser light La. The gain of the optical amplifier 7 is, for example, within a range of 3 to 30 dB.

[0023] The optical branching unit 8 and the optical detection unit 9 constitute an optical waveform detection unit 10. The optical waveform detection unit 10 detects the amplified optical waveform output from the optical amplifier 7. The optical branching unit 8 is optically coupled to the optical output end of the optical amplifier 7. The optical branching unit 8 reflects (or transmits) a portion Lb1 of the amplified laser light Lb output from the optical amplifier 7 and transmits (or reflects) the remaining portion Lb2, thereby branching the portion Lb1 of the amplified laser light Lb. The optical branching unit 8 may be formed of, for example, a glass plate. The ratio (branching ratio) P1 / P2 of the intensity P1 of the portion Lb1 of the laser light Lb to the intensity P2 of the remaining portion Lb2 is, for example, within a range of 0.005 to 0.01. The optical detection unit 9 is optically coupled to the optical branching unit 8, and receives the portion Lb1 of the amplified laser light Lb. The remaining portion Lb2 of the laser light Lb is output to the outside of the laser device 1A and is used for laser processing, various measurements, and the like.

[0024] The light detection unit 9 generates a light intensity signal Sc, which is an electrical signal corresponding to the light intensity of a portion Lb1 of the laser light Lb, and provides this light intensity signal Sc to the comparison unit 33. In one example, the light detection unit 9 may be configured to include a photodiode and a circuit that converts a photocurrent flowing through the photodiode into a voltage signal. The light detection unit 9 may output the generated voltage signal as the light intensity signal Sc, or may convert the generated voltage signal into a digital signal and output the digital signal as the light intensity signal Sc. When the light intensity signal Sc is a voltage signal, it is converted into a digital signal in the comparison unit 33. The light detection unit 9 may include a phototube (e.g., a biplanar phototube) instead of a photodiode.

[0025] Fig. 2 is a block diagram showing a specific example of the laser device 1A. In the specific example shown in Fig. 2, the laser device 1A includes optical isolators 61, 62, 63, and 64 as the optical isolator 6 shown in Fig. 1, and an optical fiber amplifier 71 and solid-state laser amplifiers 72 and 73 as the optical amplifiers 7. Thus, in this specific example, the optical amplifiers 7 are configured in multiple stages. Furthermore, the laser device 1A includes a bandpass filter 12, an optical fiber connector 13, and a collimator lens 14.

[0026] The optical input end of the optical fiber amplifier 71 and the semiconductor laser element 5 are optically coupled via an optical fiber F1. An optical isolator 61 is interposed between the optical fiber amplifier 71 and the semiconductor laser element 5. The optical isolator 61 prevents light (laser light La and pumping light) from returning from the optical fiber amplifier 71 to the semiconductor laser element 5. This prevents damage to the semiconductor laser element 5. The optical output end of the optical fiber amplifier 71 and the bandpass filter 12 are optically coupled via an optical fiber F2. An optical isolator 62 is interposed between the optical fiber amplifier 71 and the bandpass filter 12. The optical isolator 62 prevents light from the stage after the bandpass filter 12 from returning to the optical fiber amplifier 71. The optical fiber amplifier 71 is a first-stage optical amplifier, and amplifies the laser light La output from the semiconductor laser element 5. The gain of the optical fiber amplifier 71 is, for example, within a range of 20 to 30 dB. The bandpass filter 12 blocks the wavelength component of fluorescence contained in the light output from the optical fiber amplifier 71. The bandpass filter 12 may be formed of, for example, a dielectric multilayer film.

[0027] The bandpass filter 12 is optically coupled to the optical fiber connector 13 via the optical fiber F3. The optical fiber connector 13 terminates the optical fiber F3. That is, the light that has passed through the bandpass filter 12 propagates through the optical fiber F3 to reach the optical fiber connector 13, and is then output into space. The collimator lens 14 is optically coupled to the optical fiber connector 13 via space, and collimates the light radially output from the optical fiber connector 13. Since the intensity of the light amplified by the solid-state laser amplifiers 72 and 73 described later is high, the light is propagated through space rather than through optical fibers in the stage subsequent to the optical fiber connector 13 in this manner in order to avoid damage to optical materials such as glass by the laser. In FIG. 2, the light propagating through space is indicated by dashed lines.

[0028] The solid-state laser amplifier 72 is optically coupled to the collimator lens 14 via an optical isolator 63. The optical isolator 63 prevents the light from the solid-state laser amplifier 72 from returning to a stage prior to the solid-state laser amplifier 72, thereby preventing damage to the optical fiber amplifier 71. The solid-state laser amplifier 72 is a second-stage optical amplifier, and further amplifies the amplified laser light output from the optical fiber amplifier 71. The gain of the solid-state laser amplifier 72 is within a range of, for example, 3 to 20 dB.

[0029] The solid-state laser amplifier 73 is optically coupled to the solid-state laser amplifier 73 via the optical isolator 64. That is, the optical fiber amplifier 71, the solid-state laser amplifiers 72 and 73 are coupled to each other in series. The optical isolator 64 prevents the light of the solid-state laser amplifier 73 from returning to a stage prior to the solid-state laser amplifier 73. This makes it possible to prevent damage to the solid-state laser amplifier 72. The solid-state laser amplifier 73 is a third-stage optical amplifier, and further amplifies the amplified laser light output from the solid-state laser amplifier 72. The gain of the solid-state laser amplifier 73 is, for example, within a range of 3 to 10 dB. The light amplified by the solid-state laser amplifier 72 is output as amplified laser light Lb.

[0030] Fig. 3 is a block diagram showing a detailed configuration example of the driver circuit 4. As shown in Fig. 3, the driver circuit 4 has a control board 41, a waveform data storage unit 42, a waveform timing adjustment unit 43, a waveform signal generation unit 44, and a current conversion unit 45. The control board 41 is also configured to include a CPU 41a and a high-speed DAC interface 41b. Among these, the high-speed DAC interface 41b, the waveform data storage unit 42, the waveform timing adjustment unit 43, and the waveform signal generation unit 44 configure a D / A conversion unit 46. The D / A conversion unit 46 is an electronic circuit that converts digital input waveform data Da into an analog drive signal Sd.

[0031] The control board 41 is a circuit board that serves as an interface with the waveform calculation unit 3. The CPU 41a is electrically connected to the waveform adjustment unit 32 (see FIG. 1) of the waveform calculation unit 3 via a communication line, and receives input waveform data Da from the waveform adjustment unit 32. The CPU 41a transmits this input waveform data Da to the high-speed DAC interface 41b at an appropriate timing. The high-speed DAC interface 41b temporarily stores the input waveform data Da in the waveform data storage unit 42. The waveform data storage unit 42 is electrically connected to the high-speed DAC interface 41b, and is composed of, for example, a volatile storage element. The waveform adjustment unit 32 of this embodiment outputs the input waveform data Da as a plurality of continuous section waveform data obtained by dividing the time waveform of the input waveform data Da (see FIG. 4). These section waveform data are output in parallel and simultaneously for each set of two or more section waveform data. The waveform data storage unit 42 stores the plurality of section waveform data, and outputs the plurality of section waveform data upon request.

[0032] The waveform timing adjustment unit 43 is electrically connected to the waveform data storage unit 42, and adjusts (controls) the timing at which the input waveform data Da is output from the waveform data storage unit 42. FIG. 4 is a diagram showing a schematic diagram of the function of the waveform timing adjustment unit 43. As shown in FIG. 4, the waveform timing adjustment unit 43 sequentially outputs a plurality of section waveform data DD1 to DD4 read from the waveform data storage unit 42 while giving an appropriate time difference. Here, the appropriate time difference is, for example, the time width of each section waveform data. This time width specifies the time resolution of the output waveform, and is 1 nanosecond in one embodiment. The waveform signal generation unit 44 sequentially inputs the plurality of section waveform data DD1 to DD4 output from the waveform timing adjustment unit 43, and sequentially converts these section waveform data DD1 to DD4 into a drive signal Sd, which is an analog signal (voltage signal). At this time, the time difference of the conversion timing of the section waveform data DD1 to DD4 is approximately equal to the time difference given by the waveform timing adjustment unit 43.

[0033] The current conversion unit 45 is electrically connected to the waveform timing adjustment unit 43, and converts the drive signal Sd into a drive current Id. That is, the current conversion unit 45 is configured by an analog circuit including a transistor, and converts the drive signal Sd, which is a voltage signal, into the drive current Id, which is a current signal. The time waveform of the drive current Id generated at this time is approximately the same as the time waveform of the drive signal Sd. The bias current control unit 11 is further connected to the current conversion unit 45. The bias current control unit 11 controls the magnitude of the bias component included in the drive current Id. The semiconductor laser element 5 is electrically connected to the current output terminal of the current conversion unit 45, and receives the drive current Id from the current conversion unit 45 and outputs the laser light La. The time waveform of the laser light La is approximately the same as the time waveform of the drive current Id.

[0034] FIG. 5 is a flowchart showing the operation of the laser device 1A. Also, (a) to (d) of FIG. 6 are diagrams showing optical pulse waveforms. In these diagrams, the optical pulse waveform is shown as a set of peak values ​​(optical intensity) of a plurality of consecutive unit sections. A delay time TA is set as necessary, and the starting point of the optical pulse waveform is delayed from the reference time by the delay time TA. In (a) to (d) of FIG. 6, the vertical axis represents optical intensity, and the horizontal axis represents time. The operation of the laser device 1A and the laser waveform control method according to this embodiment will be described with reference to FIG. 5 and FIG. 6.

[0035] First, the waveform adjustment unit 32 sets initial input waveform data Da (step ST1). This initial input waveform data Da is set based on target waveform data Db. In one example, the target waveform data Db is used as the initial input waveform data Da as is. Next, based on this initial input waveform data Da, the driver circuit 4 supplies a drive current Id to the semiconductor laser element 5, and the semiconductor laser element 5 outputs laser light La (current supply step ST2). FIG. 6(a) shows a schematic diagram of the time waveform of the laser light La generated based on the initial input waveform data Da. This laser light La is amplified by the optical amplifier 7 (optical amplification step ST3).

[0036] The current supply step ST2 includes a D / A conversion step ST21 and a current conversion step ST22. In the D / A conversion step ST21, the D / A conversion unit 46 converts the digital input waveform data Da into an analog drive signal Sd. At this time, as described above, a plurality of continuous section waveform data DD1-DD4 (see FIG. 4) obtained by dividing the time waveform of the input waveform data Da are sequentially converted into drive signals Sd with a time difference. In the current conversion step ST22, the current conversion unit 45 converts the drive signal Sd into a drive current Id.

[0037] Next, the time waveform (output waveform) of the amplified laser light Lb is detected through the light detection unit 9 (light waveform detection step ST4). FIG. 6(b) shows a schematic diagram of the detected output waveform. In many cases, the time waveform of the amplified laser light Lb differs from the time waveform of the laser light La before amplification. One reason for this is that the excitation state in the light amplifier 7 changes over time. That is, immediately after the laser light La is incident, the light amplifier 7 is strongly excited and amplifies the laser light La with a high gain. However, as time passes from the start of the incidence of the laser light La, the excitation intensity of the light amplifier 7 gradually decreases, and the amplification gain of the laser light La also decreases accordingly.

[0038] 7 and 8 are graphs showing the time waveforms of the laser light La before amplification and the laser light Lb after amplification, which were actually measured. FIG. 7(a) shows the time waveform (square wave) of the laser light La before amplification, and FIG. 7(b) shows the time waveform of the laser light Lb after the laser light La having the time waveform shown in FIG. 7(a) is amplified. FIG. 8(a) shows the time waveform (ramp wave) of the laser light La before amplification, and FIG. 8(b) shows the time waveform of the laser light Lb after the laser light La having the time waveform shown in FIG. 8(a) is amplified. The vertical axis represents light intensity (arbitrary units), and the horizontal axis represents time (unit: nanoseconds). As shown in these figures, the time waveform of the laser light Lb after amplification is significantly different from the time waveform of the laser light La before amplification.

[0039] Referring again to FIG. 5, in the waveform adjustment step ST5, first, the comparison unit 33 compares the detected output waveform with the target waveform shown in the target waveform data Db ((c) of FIG. 6), and outputs the difference (error) (step ST51). Next, the waveform adjustment unit 32 adjusts the time waveform of the input waveform data Da based on this difference. That is, the waveform adjustment unit 32 calculates new input waveform data Da so that this difference becomes smaller (i.e., closer to 0) (step ST52). Based on this new input waveform data Da, the driver circuit 4 supplies a drive current Id to the semiconductor laser element 5, and the semiconductor laser element 5 outputs the laser light La (current supply step ST2). (d) of FIG. 6 shows a schematic time waveform of the laser light La generated based on the new input waveform data Da. This laser light La is amplified by the optical amplifier 7 (optical amplification step ST3). By repeating the above steps ST2 to ST5, the time waveform of the amplified laser light Lb approaches the target waveform. The laser light Lb thus generated is output to the outside of the laser device 1A.

[0040] The effects obtained by the laser device 1A and the laser waveform control method of this embodiment having the above configuration will be described together with the problems of the conventional laser device and the control method. Fig. 11 is a block diagram showing the configuration of the conventional laser device. This laser device includes an optical isolator 6 and an optical amplifier 7. Furthermore, this laser device includes a semiconductor laser element 100, a driver circuit 101, an optical amplifier 102, an acousto-optical modulator (AOM) 103, an electro-optical modulator (EOM) 104, a computer 105, an arbitrary pulse generator 106, a timing control unit 107, and an RF amplifier 108.

[0041] The driver circuit 101 supplies a constant magnitude drive current Ib to the semiconductor laser element 100. The semiconductor laser element 100 outputs a continuous light Le1 with a constant light intensity as a seed light source. The optical amplifier 102 is, for example, an optical fiber amplifier or a solid-state laser amplifier, and amplifies the continuous light Le1. The optical intensity of the continuous light Le1 before amplification is, for example, 10 mW, and the optical intensity of the continuous light Le2 after amplification is, for example, 2 W. The AOM 103 generates a pulsed light Lp1 by defining the time width of the amplified continuous light Le2. The time width of the pulsed light Lp1 is, for example, 100 nanoseconds.

[0042] The computer 105 stores target waveform data in advance or generates target waveform data. The arbitrary pulse generator 106 receives the target waveform data from the computer 105 and generates a drive signal based on the target waveform data. The arbitrary pulse generator 106 provides the drive signal to the RF amplifier 108. The timing control unit 107 synchronizes the timing at which the arbitrary pulse generator 106 provides the drive signal to the RF amplifier 108 with the timing at which the AOM 103 generates the pulsed light Lp1. The RF amplifier 108 amplifies the drive signal and provides it to the EOM 104. The EOM 104 is driven by the drive signal, adjusts the time waveform of the pulsed light Lp1 to a waveform corresponding to the drive signal, and generates the pulsed light Lp2. The EOM 104 is, for example, a lithium niobate (LN) modulator. The pulsed light Lp2 is sent to the optical amplifier 7 through the optical isolator 6. The optical amplifier 7 amplifies the pulsed light Lp2. The amplified pulsed light Lp2 is output to the outside of the laser device.

[0043] FIG. 12 is a block diagram showing a configuration in which a feedback circuit for adjusting a drive signal based on an output waveform is added to the laser device shown in FIG. 11. The laser device shown in FIG. 12 further includes an optical branching unit 8, an optical detection unit 9, a comparison unit 109, and a waveform adjustment unit 110 in addition to the elements shown in FIG. 11. The optical branching unit 8 branches a part of the pulsed light Lp2 amplified by the optical amplifier 7. The optical detection unit 9 detects the optical intensity of the branched part of the pulsed light Lp2. The comparison unit 109 compares the target waveform data output from the computer 105 with the detected time waveform of the pulsed light Lp2, and outputs the difference. The waveform adjustment unit 110 adjusts the drive signal so that this difference approaches zero.

[0044] 11 and 12, continuous light Le2 output from a fiber laser or solid-state laser is shaped into an arbitrary waveform by an EOM 104. The dimensions of fiber lasers and solid-state lasers tend to be large, and the EOM 104 has a large variation in characteristics due to temperature changes (temperature drift), so a separate configuration is required to compensate for the temperature drift of the EOM 104. These are factors that hinder the miniaturization of the laser device.

[0045] In this embodiment, the semiconductor laser element 5 is used as the light source of the amplified light, instead of a fiber laser or solid-state laser that outputs continuous light. The time waveform of the drive signal Sd for driving the semiconductor laser element 5 is adjusted based on the time waveform of the amplified laser light Lb detected by the optical waveform detection unit 10 (optical waveform detection step ST4). This adjusts the time waveform of the laser light La output from the semiconductor laser element 5, so that the time waveform of the amplified laser light Lb can be made closer to the target waveform. In addition, the size of the electronic circuit such as the waveform calculation unit 3 and the semiconductor laser element 5 is significantly smaller than the size of the fiber laser or solid-state laser, and the EOM. Furthermore, with regard to the temperature drift of the semiconductor laser element 5, it is sufficient to keep the temperature of the semiconductor laser element 5 constant by a Peltier element or the like.

[0046] From the above, according to this embodiment, it is possible to reduce the size of the device compared to the conventional device and method. In an example of an experimental setup created by the present inventor, if the width and depth of the laser device 1A of this embodiment is approximately the same as that of the conventional device, the height of the conventional device is 1500 mm, whereas the height of the laser device 1A of this embodiment is 88 mm, which is significantly smaller than that of the conventional device.

[0047] In addition, in the conventional method of shaping the continuous light Le2 by the EOM 104, the output waveform is shaped by adjusting the light transmittance, but it is difficult to make the light transmittance strictly zero, and a small amount of light intensity remains even in a section where the light intensity is desired to be strictly zero. In contrast, in this embodiment, the output waveform is shaped by adjusting the time waveform of the drive signal Sd for driving the semiconductor laser element 5. Therefore, if the drive signal Sd is controlled so that the drive current Id is smaller than a threshold value, the laser light La is not output from the semiconductor laser element 5, and the light intensity can be easily made strictly zero.

[0048] Furthermore, compared to a method of shaping an optical pulse waveform using the EOM 104, the method of this embodiment of shaping the drive current Id to the semiconductor laser element 5 makes it possible to control the output waveform with a shorter time resolution.

[0049] Furthermore, in the EOM 104, the input voltage (drive signal) and the optical transmittance have a nonlinear relationship with each other. Therefore, in the waveform adjustment unit 110, in addition to the change in the time waveform occurring in the optical amplifier 7, calculations or calibration tables for compensating for distortion of the time waveform in the EOM 104 are required, which complicates the calculations. In contrast, in this embodiment, the optical output intensity of the semiconductor laser element 5 and the drive current Id have an approximately linear relationship with each other, so the calculations in the waveform adjustment unit 32 are relatively easy.

[0050] In addition, in the method of shaping the optical pulse waveform using the EOM 104, the time width of the outputtable pulsed light Lp1 is limited to a short time such as 100 nanoseconds. In contrast, in this embodiment, the semiconductor laser element 5 does not have such a time limit, and therefore it is possible to generate an optical pulse with a longer duration.

[0051] 9 and 10 are graphs showing examples of the time waveform of the laser light La output from the semiconductor laser element 5. The vertical axis represents light intensity (arbitrary unit), and the horizontal axis represents time (unit: nanoseconds). (a) of FIG. 9 shows a Gaussian waveform with a full width at half maximum of 4 nanoseconds. (b) of FIG. 9 shows a Gaussian waveform with a full width at half maximum of 32 nanoseconds. (a) of FIG. 10 shows a square wave with a full width at half maximum of 120 nanoseconds. (b) of FIG. 10 shows a ramp waveform with a full width at half maximum of 4 nanoseconds. As described above, the laser device 1A of this embodiment can generate various arbitrary time waveforms.

[0052] Also, as in this embodiment, the waveform calculation unit 3 may adjust the time waveform of the input waveform data Da (in the waveform adjustment step ST5) so that the difference between the time waveform of the amplified laser light Lb detected by the optical waveform detection unit 10 and the target waveform approaches 0. This allows the amplified time waveform to approach the target waveform with even greater accuracy. In this case, the waveform calculation unit 3 may have a storage unit (memory of the computer 31) that stores data indicating the target waveform in advance.

[0053] Also, as in this embodiment, the driver circuit 4 (current supply step ST2) may have a D / A conversion section 46 (D / A conversion step ST21) that converts the digital input waveform data Da into an analog drive signal Sd, and a current conversion section 45 (current conversion step ST22) that converts the drive signal Sd into a drive current Id. The D / A conversion section 46 (D / A conversion step ST21) may then convert a plurality of continuous section waveform data DD1 to DD4, which are obtained by dividing the time waveform of the input waveform data Da, into drive signals Sd in sequence, with a time difference. This makes it possible to speed up the drive signal Sd and improve the time resolution of the output waveform.

[0054] The laser device and the laser waveform control method according to the present invention are not limited to the above-mentioned embodiment, and various other modifications are possible. For example, in the above-mentioned embodiment, the target waveform data is stored in the waveform calculation unit 3, but the target waveform data may be input from outside the laser device 1A. Also, the optical isolator 6 may be omitted as necessary. [Explanation of symbols]

[0055] 1A...laser device, 3...waveform calculation unit, 4...driver circuit, 5...semiconductor laser element, 6...optical isolator, 7...optical amplifier, 8...optical branching unit, 9...optical detection unit, 10...optical waveform detection unit, 11...bias current control unit, 12...bandpass filter, 13...optical fiber connector, 14...collimator lens, 31...computer, 32...waveform adjustment unit, 33...comparison unit, 41...control board, 41a...CPU, 41b...high-speed DAC interface, 4 2...waveform data storage unit, 43...waveform timing adjustment unit, 44...waveform signal generation unit, 45...current conversion unit, 46...D / A conversion unit, 61, 62, 63, 64...optical isolator, 71...optical fiber amplifier, 72, 73...solid-state laser amplifier, Db...target waveform data, Dc...difference data, DD1 to DD4...section waveform data, F1 to F3...optical fiber, Id...driving current, La, Lb...laser light, Sc...light intensity signal, Sd...driving signal, TA...delay time.

Claims

1. A single semiconductor laser element; A waveform calculation unit that calculates input waveform data; a driver circuit electrically connected to the waveform calculation unit and the single semiconductor laser element, generating a drive current having a time waveform corresponding to the input waveform data, and supplying the drive current to the single semiconductor laser element; an optical amplifier optically coupled to the single semiconductor laser element and amplifying light output from the single semiconductor laser element; an optical waveform detector for detecting an amplified optical waveform output from the optical amplifier; Equipped with the single semiconductor laser element is a single laser diode, the amplified optical waveform detected by the optical waveform detection unit is a waveform of light output from the single semiconductor laser element and then amplified by the optical amplifier, the waveform calculation unit compares the amplified optical waveform detected by the optical waveform detection unit with a target waveform to generate differential data, adjusts a time waveform of the input waveform data based on the target waveform and the differential data, and adjusts an optical waveform output from the single semiconductor laser element only by the drive current having a time waveform adjusted in accordance with the input waveform data, thereby bringing the amplified optical waveform output from the optical amplifier closer to the target waveform; The waveform calculation unit adjusts the time waveform of the input waveform data so that a difference between the amplified optical waveform detected by the optical waveform detection unit and the target waveform approaches zero.

2. The laser device according to claim 1 , wherein the waveform calculation unit includes a storage unit that stores data indicating the target waveform in advance.

3. The driver circuit includes: A D / A conversion unit that converts the digital input waveform data into an analog drive signal; a current converter for converting the drive signal into the drive current; having 3. The laser device according to claim 1, wherein the D / A converter converts a plurality of continuous section waveform data obtained by dividing a time waveform of the input waveform data into the drive signal in sequence while providing a time difference therebetween.

4. The optical waveform detection unit an optical branching unit that branches the light output from the single semiconductor laser element and then amplified by the optical amplifier into a part and a remainder; a light detection unit that detects the waveform of the amplified light by generating an electrical signal corresponding to the light intensity of the part; having the waveform calculation unit obtains an amplified optical waveform based on the electrical signal; The laser device according to any one of claims 1 to 3, wherein the remainder is output to an outside of the laser device.

5. 5. The laser device according to claim 4, wherein a ratio (P1 / P2) of an intensity P1 of the portion to an intensity P2 of the remaining portion is within a range of 0.005 to 0.

01.

6. a current supply step of generating a drive current having a time waveform corresponding to input waveform data and supplying the drive current to a single semiconductor laser element; an optical amplifying step of amplifying the light output from the single semiconductor laser element; an optical waveform detection step of detecting an optical waveform after amplification; a waveform adjustment step of comparing the amplified optical waveform detected in the optical waveform detection step with a target waveform to generate differential data, adjusting a time waveform of the input waveform data based on the target waveform and the differential data, and adjusting an optical waveform output from the single semiconductor laser element only by the drive current having a time waveform adjusted in accordance with the input waveform data, thereby making the amplified optical waveform output in the optical amplification step closer to the target waveform; Including, the single semiconductor laser element is a single laser diode, the amplified optical waveform detected in the optical waveform detection step is a waveform of light output from the single semiconductor laser element and then amplified in the optical amplification step; A laser waveform control method, wherein the waveform adjustment step adjusts a time waveform of the input waveform data so that a difference between the amplified optical waveform detected in the optical waveform detection step and the target waveform approaches zero.

7. The current supplying step includes: A D / A conversion step of converting the digital input waveform data into an analog drive signal; a current conversion step of converting the drive signal into the drive current; Including, 7. The laser waveform control method according to claim 6, wherein in said D / A conversion step, a plurality of continuous section waveform data obtained by dividing a time waveform of said input waveform data are converted into said drive signal sequentially with a time difference.

8. The optical waveform detection step includes: a step of splitting the light output from the single semiconductor laser element and amplified in the optical amplification step into a part and a remainder; detecting the amplified optical waveform by generating an electrical signal corresponding to the optical intensity of the portion; Including, In the waveform adjustment step, an optical waveform after amplification is obtained based on the electrical signal, The laser waveform control method according to claim 6 or 7, further comprising the step of outputting the remainder.

9. 9. The laser waveform control method according to claim 8, wherein a ratio (P1 / P2) of an intensity P1 of the portion to an intensity P2 of the remaining portion is within a range of 0.005 to 0.01.

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