Laser device and laser waveform control method

Abstract

The present invention provides a laser device (1A), which comprises: a semiconductor laser element (5); a waveform operation unit (3) that operates input waveform data (Da); a drive circuit (4) that supplies a drive current (Id) having a time waveform corresponding to the input waveform data (Da) to the semiconductor laser element (5); an optical amplifier (7) that amplifies the laser light (La) output from the semiconductor laser element (5); and an optical waveform detection unit (10) that detects the waveform of the amplified laser light (Lb) output from the optical amplifier (7). The waveform operation unit (3) compares the waveform of the amplified laser light (Lb) detected by the optical waveform detection unit (10) with a target waveform, and adjusts the time waveform of the input waveform data (Da) so that the waveform of the amplified laser light (Lb) approaches the target waveform. Thus, a laser device and a laser waveform control method that can reduce the size of the device can be realized.

Description

Technical Field

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

[0002] Non-patent document 1 discloses a laser device that outputs light pulses with a pulse width of nanoseconds. The laser device includes a light source that outputs laser light as continuous (CW) light, an acousto-optic modulator (AOM) that temporally cuts the laser light output from the light source into pulse light, and an electro-optic modulator (EOM) that shapes the pulse light output from the AOM into an arbitrary waveform. The light source is a fiber laser excited by a laser diode (LD).

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: Saumyabrata Banerjee et al., "100 J-level nanosecond pulsed diode pumped solid state laser", Optics Letters, Vol. 41 No. 9, pp. 2089-2092 (2016) Summary of the invention

[0006] Problem that the invention aims to solve

[0007] Arbitrarily shaping the temporal waveform of ultrashort pulse light or short pulse light is very useful for laser processing and various measuring instruments (such as shape monitors, shock wave monitors). This is because it is expected to improve the processing accuracy or measurement accuracy by selecting an appropriate pulse light waveform according to the processing object or the measurement object. However, even if the desired waveform is generated with high accuracy, when light amplification is performed to obtain the required pulse light intensity, there is a problem of distortion of the amplified light waveform caused by the nonlinearity of the optical amplifier. Therefore, considering the nonlinearity of the optical amplifier in advance, it is conceivable to input the pulse light whose amplified light waveform becomes a waveform of the desired shape into the optical amplifier.

[0008] For example, as disclosed in Non-Patent Document 1, the conventional pulse light generating device shapes the continuous light output from the fiber laser or solid laser into an arbitrary waveform through the EOM. Since the size of the fiber laser and the solid laser is easy to increase, and since the change (temperature drift) of the characteristics caused by the temperature change in the EOM is large, a structure for compensating the temperature drift of the EOM is also required. These are factors that hinder the miniaturization of the laser device.

[0009] An object of the present invention is to provide a laser device and a laser waveform control method capable of miniaturizing the device size.

[0010] Means of solving the problem

[0011] One embodiment of the present invention is a laser device. The laser device includes: a semiconductor laser element; a waveform operation unit that operates input waveform data; a drive circuit that is electrically connected to the waveform operation unit and the semiconductor laser element, generates a drive current having a time waveform corresponding to the input waveform data, and supplies the drive current to the semiconductor laser element; an optical amplifier that is optically coupled to the semiconductor laser element and amplifies light output from the semiconductor laser element; and an optical waveform detection unit that detects an amplified optical waveform output from the optical amplifier, wherein the waveform operation unit compares the amplified optical waveform detected by the optical waveform detection unit with a target waveform, and adjusts the time waveform of the input waveform data so that the amplified optical waveform approaches the target waveform.

[0012] One embodiment of the present invention is a laser waveform control method. The laser waveform control method includes: a current supply step, which generates a driving current having a time waveform corresponding to input waveform data, and supplies the driving current to a semiconductor laser element; a light amplification step, which amplifies light output from the semiconductor laser element; a light waveform detection step, which detects the amplified light waveform; and a waveform adjustment step, which compares the amplified light waveform detected by the light waveform detection step with a target waveform, and adjusts the time waveform of the input waveform data so that the amplified light waveform is close to the target waveform.

[0013] In the above-mentioned laser device and laser waveform control method, a semiconductor laser element is used as a light source instead of a fiber laser or a solid laser that outputs continuous light. Then, the waveform of a drive signal for driving the semiconductor laser element is adjusted based on the amplified light waveform detected by the light waveform detection unit (light waveform detection step). Thus, the light waveform output from the semiconductor laser element can be adjusted so that the amplified light waveform approaches the target waveform.

[0014] In addition, the size of the electronic circuit such as the waveform operation unit and the semiconductor laser element is much smaller than that of the fiber laser, the solid laser and the EOM. In addition, regarding the temperature drift of the semiconductor laser element, it is sufficient to keep the temperature of the semiconductor laser element constant by using a Peltier element or the like. In summary, according to the above-mentioned laser device and laser waveform control method, the device size can be miniaturized compared with the existing device and method.

[0015] Effects of the Invention

[0016] According to the embodiments of the present invention, a laser device and a laser waveform control method capable of miniaturizing the device size can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a block diagram showing the structure of a laser device 1A according to one embodiment.

[0018] Figure 2 1A is a block diagram showing a specific example of the laser device 1A.

[0019] Figure 3 2 is a block diagram showing a detailed configuration example of the drive circuit 4 .

[0020] Figure 4 This is a diagram schematically showing the function of the waveform timing adjustment unit 43 .

[0021] Figure 5 1 is a flowchart showing the operation of the laser device 1A.

[0022] Figure 6 (a) to (d) are diagrams schematically showing light pulse waveforms.

[0023] Figure 7 (a) is a graph showing a time waveform (rectangular wave) of laser light La before amplification, and (b) is a graph showing a time waveform of laser light Lb after amplifying the laser light La having the time waveform shown in (a).

[0024] Figure 8 (a) is a graph showing a time waveform (ramp-up wave) of laser light La before amplification, and (b) is a graph showing a time waveform of laser light Lb after amplifying the laser light La having the time waveform shown in (a).

[0025] Fig. 9 Graphs showing examples of the time waveform of the laser light La output from the semiconductor laser element 5 , (a) showing a Gaussian waveform with a full width at half maximum of 4 nanoseconds, and (b) showing a Gaussian waveform with a full width at half maximum of 32 nanoseconds.

[0026] Fig.10 1 and 12 are graphs showing examples of the time waveform of the laser light La output from the semiconductor laser element 5 , wherein (a) shows a rectangular wave with a full width at half maximum of 120 nanoseconds, and (b) shows a ramp wave with a full width at half maximum of 4 nanoseconds.

[0027] Fig.11 This is a block diagram showing the structure of a conventional laser device.

[0028] Fig.12 It means in Fig.11 The laser device shown is a block diagram showing a structure in which a feedback circuit for adjusting a drive signal based on an output waveform is added.

[0029] Explanation of symbols:

[0030] 1A...Laser device; 3...Waveform calculation unit; 4...Drive 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...Collimating lens; 31...Computer; 32...Waveform adjustment unit; 33...Comparison unit; 41...Control substrate; 41a...CPU; 41b...High-speed DAC interface; 42...Waveform data storage unit; 4 3……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; Da……input waveform data; Db……target waveform data; Dc……differential data; DD1~DD4……interval waveform data; F1~F3……optical fiber”; Id……driving current; La, Lb……laser; Sc……light intensity signal; Sd……driving signal; TA……delay time. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the laser device and the laser waveform control method are described in detail with reference to the accompanying drawings. In addition, in the description of the drawings, the same elements are represented by the same symbols, and repeated descriptions are omitted.

[0032] Figure 1 1 is a block diagram showing the structure of a laser device 1A according to one embodiment. Figure 1 As shown, the laser device 1A of the present embodiment includes a waveform calculation unit 3 , a drive circuit 4 , a semiconductor laser element 5 , an optical isolator 6 , an optical amplifier 7 , a light branching unit 8 , and a light detection unit 9 .

[0033] The waveform calculation unit 3 is composed of an electronic circuit and is electrically connected to the drive circuit 4. The waveform calculation unit 3 calculates and generates input waveform data Da for making the waveform of the light pulse output from the optical amplifier 7 (hereinafter referred to as the output waveform) close to the target waveform, and provides the input waveform data Da to the drive circuit 4. In one example, the waveform calculation unit 3 includes a computer 31, a waveform adjustment unit 32, and a comparison unit 33. The computer 31 includes a CPU and a memory, and operates according to the program stored in the memory.

[0034] The memory of the computer 31 is a storage unit in the present embodiment, which pre-stores the desired (arbitrary) light waveform, i.e., data representing the target waveform (hereinafter referred to as target waveform data). The target waveform data is pre-stored in the memory by the operator through the data input terminal of the computer 31 before the operation of the laser device 1A. Alternatively, the computer 31 can be used as a waveform design unit to design the target waveform by itself. That is, the computer 31 can calculate the target waveform for realizing the light irradiation conditions (processing conditions, observation conditions) given from the outside. The target waveform data representing the calculated target waveform is stored in the memory of the computer 31.

[0035] The comparison unit 33 is electrically connected to the light detection unit 9 described later, and obtains the output waveform based on the detection signal (light intensity signal Sc) obtained from the light detection unit 9. In addition, the comparison unit 33 is electrically connected to the computer 31, and obtains the target waveform data Db from the computer 31. The comparison unit 33 compares the output waveform with the target waveform, and sends the difference data Dc indicating the difference to the waveform adjustment unit 32.

[0036] In addition, the comparison unit 33 may be constituted by a computer having a CPU and a memory. In this case, the comparison unit 33 may be separate from the computer 31 or may be realized in a computer common to the computer 31 .

[0037] The waveform adjustment unit 32 is electrically connected to the computer 31, and obtains the target waveform data Db from the computer 31. In addition, the waveform adjustment unit 32 is electrically connected to the comparison unit 33, and obtains the difference data Dc output from the comparison unit 33. The waveform adjustment unit 32 generates the input waveform data Da based on these data Db and Dc so that the output waveform approaches the target waveform (that is, the difference becomes smaller).

[0038] In addition, the waveform adjustment unit 32 may be formed of a computer having a CPU and a memory. In this case, the waveform adjustment unit 32 may be separate from the computer 31 and the comparison unit 33, or may be implemented in a computer common to at least one of the computer 31 and the comparison unit 33.

[0039] The input end of the drive circuit 4 is electrically connected to the waveform adjustment unit 32 of the waveform calculation unit 3, and receives the input waveform data Da from the waveform adjustment unit 32. The drive circuit 4 generates a drive current Id having a time waveform corresponding to the input waveform data Da. The output end of the drive circuit 4 is electrically connected to the semiconductor laser element 5, and the generated drive current Id is supplied to the semiconductor laser element 5. In addition, a bias current of a constant magnitude that does not change with time is sometimes superimposed on the drive current Id.

[0040] The semiconductor laser element 5 is a laser diode and is electrically connected to the drive circuit 4. The drive circuit 4 supplies a drive current Id to either the cathode or the anode of the semiconductor laser element 5. The semiconductor laser element 5 receives the drive current Id to generate laser light La. The laser light La is light before being amplified by the optical amplifier 7 and has a time waveform corresponding to the input waveform data Da.

[0041] 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, the wavelength characteristics of the gain of the composite optical amplifier 7 can be easily optimized. In addition, the waveform A in the figure schematically shows 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.

[0042] The optical input end of the optical isolator 6 is optically coupled to the laser output end of the semiconductor laser element 5. In addition, the optical output end of the optical isolator 6 is optically coupled to the optical input end of the optical amplifier 7. That is, the optical isolator 6 is interposed in 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.

[0043] 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 itself. The optical amplifier 7 can be composed of, for example, an optical fiber amplifier, a solid laser amplifier, or a combination thereof.

[0044] The optical fiber amplifier has an optical fiber made of glass to which impurities such as Er and Yb are added, and the laser light La is amplified by inputting excitation light into the optical fiber together with the laser light La. In addition, the solid laser amplifier can be made of glass or yttrium aluminum garnet (YAG) to which impurities such as Nd are added. The solid laser amplifier amplifies the laser light La by inputting excitation light together with the laser light La. The gain of the optical amplifier 7 is, for example, in the range of 3 to 30 dB.

[0045] The optical branching section 8 and the optical detection section 9 constitute an optical waveform detection section 10. The optical waveform detection section 10 detects the amplified optical waveform output from the optical amplifier 7. The optical branching section 8 is optically coupled to the optical output end of the optical amplifier 7. The optical branching section 8 branches a part Lb1 of the amplified laser light Lb output from the optical amplifier 7 by reflecting (or transmitting) a part Lb1 of the amplified laser light Lb output from the optical amplifier 7 and transmitting (or reflecting) the remaining part Lb2. The optical branching section 8 can be composed of, for example, a glass plate.

[0046] The ratio (branching ratio) P1 / P2 of the intensity P1 of a portion Lb1 of the laser light Lb to the intensity P2 of the remaining portion Lb2 is, for example, in the range of 0.005 to 0.01. The light detection unit 9 is optically coupled to the light branching unit 8 to receive the amplified portion Lb1 of the laser light Lb. In addition, the remaining portion Lb2 of the laser light Lb is output to the outside of the laser device 1A and used for laser processing, various measurements, etc.

[0047] The light detection unit 9 generates a light intensity signal Sc which is an electrical signal corresponding to the light intensity of a part Lb1 of the laser light Lb, and provides the light intensity signal Sc to the comparison unit 33. In one example, the light detector 9 may 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. In the case where the light intensity signal Sc is a voltage signal, it is converted into a digital signal in the comparison unit 33. In addition, the light detection unit 9 may include a phototube (for example, a dual-plane phototube) instead of a photodiode.

[0048] Figure 2 1A is a block diagram showing a specific example of a laser device 1A. Figure 2 In the specific example shown, the laser device 1A has a Figure 1 The optical isolator 6 shown in FIG. 6 includes optical isolators 61, 62, 63, and 64, and optical amplifiers 71, 72, and 73 as optical amplifiers 7. As described above, in this specific example, the optical amplifier 7 is configured in multiple stages. In addition, the laser device 1A includes a bandpass filter 12, an optical fiber connector 13, and a collimating lens 14.

[0049] The optical input end of the optical fiber amplifier 71 and the semiconductor laser element 5 are optically coupled via the optical fiber F1. The 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 excitation light) from returning from the optical fiber amplifier 71 to the semiconductor laser element 5. Thus, damage to the semiconductor laser element 5 can be prevented.

[0050] The optical output end of the optical fiber amplifier 71 and the band pass filter 12 are optically coupled via the optical fiber F2. The optical isolator 62 is interposed between the optical fiber amplifier 71 and the band pass filter 12. The optical isolator 62 prevents light from the subsequent stage of the band pass filter 12 from returning to the optical fiber amplifier 71.

[0051] The optical fiber amplifier 71 is a first-stage optical amplifier that amplifies the laser light La output from the semiconductor laser element 5. The gain of the optical fiber amplifier 71 is, for example, in the range of 20 to 30 dB. The bandpass filter 12 blocks the wavelength component of the fluorescence contained in the light output from the optical fiber amplifier 71. The bandpass filter 12 can be composed of, for example, a dielectric multilayer film.

[0052] The bandpass filter 12 is optically coupled to the optical fiber connector 13 via the optical fiber F3. The terminal of the optical fiber F3 is connected to the optical fiber connector 13. That is, the light passing through the bandpass filter 12 propagates through the optical fiber F3 and reaches the optical fiber connector 13, and then is output to space.

[0053] The collimating 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 large, in order to avoid damage to optical materials such as glass by the laser, as described above, the light propagates in space rather than in the optical fiber in the later stages than the optical fiber connector 13. Figure 2 In FIG. 1 , light propagating in space is shown by dotted lines.

[0054] The solid laser amplifier 72 is optically coupled to the collimator lens 14 via the optical isolator 63. The optical isolator 63 prevents light from the solid laser amplifier 72 from returning to a stage preceding the solid laser amplifier 72. Thus, damage to the optical fiber amplifier 71 can be prevented.

[0055] The solid 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 laser amplifier 72 is, for example, in the range of 3 to 20 dB.

[0056] The solid laser amplifier 73 is optically coupled to the solid laser amplifier 72 via the optical isolator 64. That is, the optical fiber amplifier 71 and the solid laser amplifiers 72 and 73 are coupled in series with each other. The optical isolator 64 prevents the light of the solid laser amplifier 73 from returning to the stage preceding the solid laser amplifier 73. Thus, damage to the solid laser amplifier 72 can be prevented.

[0057] The solid laser amplifier 73 is a third-stage optical amplifier, and further amplifies the amplified laser light output from the solid laser amplifier 72. The gain of the solid laser amplifier 73 is, for example, in the range of 3 to 10 dB. The light amplified by the solid laser amplifier 73 is output as amplified laser light Lb.

[0058] Figure 3 4 is a block diagram showing a detailed configuration example of the drive circuit 4. Figure 3As shown, the drive circuit 4 includes a control substrate 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. In addition, the control substrate 41 includes a CPU 41a and a high-speed DAC interface 41b. Among them, 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 constitute a D / A conversion unit 46. The D / A conversion unit 46 is an electronic circuit that converts the digital input waveform data Da into an analog drive signal Sd.

[0059] The control board 41 is a circuit board used as an interface with the waveform calculation unit 3. The CPU 41a communicates with the waveform adjustment unit 32 (see Figure 1 ) is electrically connected to receive input waveform data Da from the waveform adjustment unit 32. The CPU 41a sends the 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.

[0060] The waveform adjustment unit 32 of this embodiment outputs the input waveform data Da as a plurality of continuous interval waveform data obtained by dividing the time waveform of the input waveform data Da (see Figure 4 ). These interval waveform data are outputted in parallel and simultaneously for each of two or more interval waveform data. Then, the waveform data storage unit 42 stores a plurality of interval waveform data, and outputs a plurality of interval waveform data as required.

[0061] The waveform timing adjustment section 43 is electrically connected to the waveform data storage section 42 , and adjusts (controls) the timing at which the input waveform data Da is output from the waveform data storage section 42 . Figure 4 4 is a diagram schematically showing the function of the waveform timing adjustment unit 43. Figure 4 As shown, the waveform timing adjustment unit 43 outputs the plurality of interval waveform data DD1 to DD4 read from the waveform data storage unit 42 in sequence while giving appropriate time differences. Here, the appropriate time difference is, for example, the time width of each interval waveform data. The time width specifies the time resolution of the output waveform, and in one embodiment is 1 nanosecond.

[0062] The waveform signal generating section 44 sequentially inputs a plurality of interval waveform data DD1 to DD4 output from the waveform timing adjusting section 43, and converts these interval 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 interval waveform data DD1 to DD4 is substantially consistent with the time difference given by the waveform timing adjusting section 43.

[0063] The current conversion unit 45 is electrically connected to the waveform signal generating unit 44, and converts the drive signal Sd into the drive current Id. That is, the current conversion unit 45 is composed of an analog circuit including a transistor, and converts the drive signal Sd as a voltage signal into the drive current Id as a current signal. The time waveform of the drive current Id generated at this time is substantially the same as the time waveform of the drive signal Sd.

[0064] At this time, the bias current control unit 11 is also 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, 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 substantially the same as the time waveform of the drive current Id.

[0065] Figure 5 1A is a flowchart showing the operation of the laser device 1A. Figure 6 (a) to (d) are diagrams schematically showing light pulse waveforms. In these diagrams, the light pulse waveform is represented as a collection of peak values ​​(light intensity) of multiple consecutive unit intervals. The delay time TA is set as needed, and the starting point of the light pulse waveform is delayed by the delay time TA from the reference time. Figure 6 In (a) to (d), the vertical axis represents light intensity and the horizontal axis represents time. Figure 5 and Figure 6 , the operation of the laser device 1A and the laser waveform control method involved in this embodiment are described.

[0066] First, the waveform adjustment unit 32 sets the initial input waveform data Da (step ST1). The initial input waveform data Da is set based on the target waveform data Db. In one example, the target waveform data Db is originally used as the initial input waveform data Da. Next, the drive circuit 4 supplies the drive current Id to the semiconductor laser element 5 based on the initial input waveform data Da, and the semiconductor laser element 5 outputs the laser La (current supply step ST2). Figure 6 (a) schematically shows the time waveform of the laser light La generated based on the initial input waveform data Da. The laser light La is amplified by the optical amplifier 7 (optical amplification step ST3).

[0067] In addition, 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, the continuous plurality of interval waveform data DD1 to DD4 (see Figure 4) is sequentially converted into the drive signal Sd while giving a time difference. In the current conversion step ST22, the current conversion unit 45 converts the drive signal Sd into the drive current Id.

[0068] Then, the time waveform (output waveform) of the amplified laser light Lb is detected by the light detection unit 9 (light waveform detection step ST4 ). Figure 6 (b) schematically shows the detected output waveform. In most cases, the time waveform of the laser light Lb after amplification is different from the time waveform of the laser light La before amplification. One of the reasons can be listed as the change of the excitation state in the optical amplifier 7 over time. That is, immediately after the incidence of the laser light La, the optical amplifier 7 is strongly excited and amplifies the laser light La with a high gain. However, as time passes from the incidence of the laser light La, the excitation intensity of the optical amplifier 7 gradually decreases, and the amplification gain of the laser light La also decreases accordingly.

[0069] Figure 7 and Figure 8 Graphs showing actually measured time waveforms of laser light La before amplification and laser light Lb after amplification. Figure 7 (a) shows the time waveform (rectangular wave) of the laser light La before amplification. Figure 7 (b) shows that Figure 7 The time waveform of the laser light La shown in (a) is the time waveform of the laser light Lb after the laser light La is enlarged. Figure 8 (a) shows the time waveform (ramp-up wave) of the laser light La before amplification. Figure 8 (b) shows that Figure 8 The time waveform of the laser La shown in (a) is the time waveform of the laser Lb after amplification. In addition, the vertical axis represents light intensity (arbitrary unit), and the horizontal axis represents time (unit: nanosecond). As shown in these figures, the time waveform of the laser Lb after amplification is greatly different from the time waveform of the laser La before amplification.

[0070] Refer again Figure 5 In the waveform adjustment step ST5, first, the comparison unit 33 compares the detected output waveform with the target waveform ( Figure 6 (c)) 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 the difference. That is, the waveform adjustment unit 32 calculates the new input waveform data Da so that the difference becomes smaller (that is, close to 0) (step ST52).

[0071] The driving circuit 4 supplies the driving current Id to the semiconductor laser element 5 based on the new input waveform data Da, and the semiconductor laser element 5 outputs the laser light La (current supply step ST2). Figure 6 (d) schematically shows the time waveform of the laser light La generated based on the new input waveform data Da. The 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 generated in this way is output to the outside of the laser device 1A.

[0072] Effects obtained by the laser device 1A and the laser waveform control method of the present embodiment having the above-described configuration will be described together with technical problems that the conventional laser device and control method have. Fig.11 1 is a block diagram showing the structure of a conventional laser device. The laser device includes an optical isolator 6 and an optical amplifier 7. In addition, the laser device includes a semiconductor laser element 100, a drive circuit 101, an optical amplifier 102, an acousto-optic modulator (AOM) 103, an electro-optic modulator (EOM) 104, a computer 105, an arbitrary pulse generator 106, a timing control unit 107, and an RF amplifier 108.

[0073] The driving circuit 101 provides a driving current Id of a constant magnitude 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 laser amplifier, and amplifies the continuous light Le1. The light intensity of the continuous light Le1 before amplification is, for example, 10 mW, and the light intensity of the continuous light Le2 after amplification is, for example, 2 W. The AOM 103 generates a pulse light Lp1 by specifying the time width of the amplified continuous light Le2. The time width of the pulse light Lp1 is, for example, 100 nanoseconds.

[0074] The computer 105 stores the target waveform data in advance or generates the 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 pulse light Lp1.

[0075] The RF amplifier 108 amplifies the driving signal and provides it to the EOM 104. The EOM 104 is driven by the driving signal, adjusts the time waveform of the pulse light Lp1 to a waveform corresponding to the driving signal, and generates the pulse light Lp2. The EOM 104 is, for example, a lithium niobate (LN) modulator. The pulse light Lp2 is sent to the optical amplifier 7 through the optical isolator 6. The optical amplifier 7 amplifies the pulse light Lp2. The amplified pulse light Lp2 is output to the outside of the laser device.

[0076] Fig.12 It means in Fig.11The laser device shown is a block diagram of a structure in which a feedback circuit for adjusting a drive signal based on an output waveform is added. Fig.11 In addition to the elements shown, Fig.12 The laser device shown in the figure further includes a light branching unit 8, a light detection unit 9, a comparison unit 109, and a waveform adjustment unit 110. The light branching unit 8 branches a part of the pulse light Lp2 amplified by the optical amplifier 7. The light detection unit 9 detects the light intensity of the branched part of the pulse light Lp2. The comparison unit 109 compares the target waveform data output from the computer 105 with the time waveform of the detected pulse light Lp2, and outputs the difference. The waveform adjustment unit 110 adjusts the drive signal in such a way that the difference is close to 0.

[0077] exist Fig.11 and Fig.12 In the laser device shown, the continuous light Le2 output from the fiber laser or the solid laser is shaped into an arbitrary waveform by the EOM 104. Since the size of the fiber laser and the solid laser is easy to increase, and since the change (temperature drift) of the characteristics caused by the temperature change in the EOM 104 is large, a structure for compensating the temperature drift of the EOM 104 is also required. These are factors that hinder the miniaturization of the laser device.

[0078] In this embodiment, the semiconductor laser element 5 is used as the light source of the amplified light instead of the fiber laser or solid laser that outputs continuous light. Then, based on the time waveform of the amplified laser light Lb detected by the light waveform detection unit 10 (light waveform detection step ST4), the time waveform of the drive signal Sd for driving the semiconductor laser element 5 is adjusted. Thus, the time waveform of the laser light La output from the semiconductor laser element 5 can be adjusted so that the time waveform of the amplified laser light Lb is closer to the target waveform.

[0079] In addition, the size of the electronic circuit such as the waveform calculation unit 3 and the semiconductor laser element 5 is much smaller than that of the fiber laser, solid laser and EOM. In addition, regarding the temperature drift of the semiconductor laser element 5, it is sufficient to keep the temperature of the semiconductor laser element 5 constant by using a Peltier element or the like.

[0080] In summary, according to the present embodiment, the size of the device can be miniaturized compared to the existing device and method. In the example of the experimental equipment made by the inventor, when the width and depth of the laser device 1A of the present embodiment are set to be substantially the same as those of the existing device, the height of the existing device is 1500 mm, while the height of the laser device 1A of the present embodiment is 88 mm, which is much smaller than the existing device.

[0081] 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 set the light transmittance strictly to 0, and a small amount of light intensity remains in the interval where the light intensity is expected to be strictly set to 0. On the other hand, in the present 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 in such a way that the drive current Id is less than the threshold value, the laser light La will not be output from the semiconductor laser element 5, so the light intensity can be easily set to 0 strictly.

[0082] Furthermore, according to the method of this embodiment in which the drive current Id of the semiconductor laser element 5 is shaped, the output waveform can be controlled with a shorter time resolution than the method in which the light pulse waveform is shaped using the EOM 104 .

[0083] In addition, in the EOM 104, the input voltage (drive signal) and the transmittance are in a nonlinear relationship with each other. Therefore, in the waveform adjustment unit 110, in addition to changing the time waveform generated in the optical amplifier 7, calculations or calibration tables for compensating for the distortion of the time waveform in the EOM 104 are required, and the calculations are complicated. In contrast, in the present embodiment, since the light output intensity of the semiconductor laser element 5 and the drive current Id are in a substantially linear relationship with each other, the calculations in the waveform adjustment unit 32 are relatively easy.

[0084] In the method of shaping the light pulse waveform using the EOM 104, the time width of the output pulse light Lp1 is limited to a short time such as 100 nanoseconds. In contrast, in the present embodiment, since the semiconductor laser element 5 has no such time limitation, a longer light pulse can be generated.

[0085] Fig. 9 and Fig.10 : is a graph showing an example 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: nanosecond). Fig. 9 (a) shows a Gaussian waveform with a full width at half maximum of 4 nanoseconds. Fig. 9 (b) shows a Gaussian waveform with a full width at half maximum of 32 nanoseconds. Fig.10 (a) shows a rectangular wave with a full width at half maximum of 120 nanoseconds. Fig.10 (b) shows a ramp wave with a full width at half maximum of 4 nanoseconds. As described above, according to the laser device 1A of this embodiment, it is possible to generate any various time waveforms.

[0086] In addition, as in the present embodiment, the time waveform of the input waveform data Da may be adjusted in the waveform calculation unit 3 (in the waveform adjustment step ST5) so that the difference between the time waveform of the amplified laser light Lb detected by the light waveform detection unit 10 and the target waveform approaches 0. Thus, the amplified time waveform can be made close to the target waveform with higher accuracy. In this case, the waveform calculation unit 3 may have a storage unit (a memory of the computer 31) that stores data representing the target waveform in advance.

[0087] In addition, as in the present embodiment, the drive circuit 4 (current supply step ST2) may include a D / A converter 46 (D / A conversion step ST21) that converts the digital input waveform data Da into an analog drive signal Sd, and a current converter 45 (current conversion step ST22) that converts the drive signal Sd into a drive current Id. Then, the D / A converter 46 (D / A conversion step ST21) may sequentially convert a plurality of continuous interval waveform data DD1 to DD4 obtained by dividing the time waveform of the input waveform data Da into the drive signal Sd while giving a time difference. Thus, the drive signal Sd can be made faster, thereby improving the time resolution of the output waveform.

[0088] The laser device and the laser waveform control method of the present invention are not limited to the above-mentioned embodiments and configuration examples, and various modifications are possible. For example, in the above-mentioned embodiments, the target waveform data is stored in the waveform operation unit 3, but the target waveform data can also be input from the outside of the laser device 1A. In addition, the optical isolator 6 can be omitted as needed.

[0089] The laser device of the above-mentioned embodiment is configured as follows: it comprises: a semiconductor laser element; a waveform operation unit that operates input waveform data; a drive circuit that is electrically connected to the waveform operation unit and the semiconductor laser element, generates a drive current having a time waveform corresponding to the input waveform data, and supplies the drive current to the semiconductor laser element; an optical amplifier that is optically coupled to the semiconductor laser element and amplifies the light output from the semiconductor laser element; and an optical waveform detection unit that detects the amplified optical waveform output from the optical amplifier, the waveform operation unit compares the amplified optical waveform detected by the optical waveform detection unit with the target waveform, and adjusts the time waveform of the input waveform data so that the amplified optical waveform approaches the target waveform.

[0090] The laser waveform control method of the above-mentioned embodiment is constructed as follows: it includes: a current supply step, which generates a driving current having a time waveform corresponding to the input waveform data, and supplies the driving current to the semiconductor laser element; a light amplification step, which amplifies the light output from the semiconductor laser element; a light waveform detection step, which detects the amplified light waveform; and a waveform adjustment step, which compares the amplified light waveform detected by the light waveform detection step with the target waveform, adjusts the time waveform of the input waveform data, and makes the amplified light waveform close to the target waveform.

[0091] In the laser device described above, the waveform calculation unit may adjust the time waveform of the input waveform data so that the difference between the amplified light waveform detected by the optical waveform detection unit and the target waveform approaches zero.

[0092] In the above-mentioned laser waveform control method, in the waveform adjustment step, the time waveform of the input waveform data may be adjusted so that the difference between the amplified light waveform detected in the light waveform detection step and the target waveform approaches zero.

[0093] According to such a configuration, the amplified light waveform can be made closer to the target waveform with higher accuracy. In this case, in the laser device, the waveform calculation unit may include a storage unit that stores data representing the target waveform in advance.

[0094] In the above-mentioned laser device, it can be: equipped with: a driving circuit; a D / A conversion unit, which converts digital input waveform data into an analog driving signal; and a current conversion unit, which converts the driving signal into a driving current, and the D / A conversion unit converts a plurality of continuous interval waveform data formed by dividing the time waveform of the input waveform data into driving signals in sequence while giving time differences.

[0095] In addition, in the above-mentioned laser waveform control method, it may be that: the current providing step includes: a D / A conversion step, which converts the digital input waveform data into an analog driving signal; and a current conversion step, which converts the driving signal into a driving current. In the D / A conversion step, a plurality of continuous interval waveform data formed by dividing the time waveform of the input waveform data are converted into driving signals in sequence while assigning time differences.

[0096] According to such a configuration, the driving signal can be accelerated, thereby improving the time resolution of the light waveform.

[0097] Industrial availability

[0098] The present invention can be used as a laser device and a laser waveform control method capable of miniaturizing the device size.

Claims

1. A laser device, characterized in that: have: A semiconductor laser element, which is a single laser diode; A waveform operation unit that operates input waveform data; a drive circuit electrically connected to the waveform calculation unit and the semiconductor laser element, generating a drive current having a time waveform corresponding to the input waveform data, and supplying the drive current to the laser diode of the semiconductor laser element; an optical amplifier optically coupled to the semiconductor laser element and amplifying light output from the semiconductor laser element; as well as an optical waveform detection unit that detects the amplified optical waveform output from the optical amplifier, The waveform operation unit compares the amplified light waveform detected by the light waveform detection unit with the target waveform to generate differential data, adjusts the time waveform of the input waveform data based on the target waveform and the differential data, and adjusts the light waveform output from the semiconductor laser element only by the drive current having the time waveform adjusted corresponding to the input waveform data, thereby making the amplified light waveform output from the optical amplifier close to the target waveform, and The waveform calculation unit adjusts the time waveform of the input waveform data so that the difference between the amplified light waveform detected by the light waveform detection unit and the target waveform approaches zero.

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

3. The laser device according to claim 1 or 2, characterized in that: The driving circuit comprises: A D / A converter that converts the digital input waveform data into an analog drive signal; and a current conversion unit that converts the drive signal into the drive current, The D / A converter sequentially converts a plurality of continuous interval waveform data obtained by dividing the time waveform of the input waveform data into the drive signal while giving a time difference.

4. A laser waveform control method, characterized in that: Include: a current supplying step of generating a driving current having a time waveform corresponding to input waveform data with respect to a semiconductor laser element as a single laser diode, and supplying the driving current to the laser diode of the semiconductor laser element; a light amplification step of amplifying light output from the semiconductor laser element by an optical amplifier; an optical waveform detection step of detecting the amplified optical waveform output by the optical amplifier; and a waveform adjustment step of comparing the amplified light waveform detected by the light waveform detection step with a target waveform to generate differential data, adjusting the time waveform of the input waveform data based on the target waveform and the differential data, adjusting the light waveform output from the semiconductor laser element only by the drive current having the time waveform adjusted corresponding to the input waveform data, so that the amplified light waveform output from the optical amplifier approaches the target waveform, In the waveform adjustment step, the time waveform of the input waveform data is adjusted so that the difference between the amplified light waveform detected in the light waveform detection step and the target waveform approaches zero.

5. The laser waveform control method according to claim 4, characterized in that: The current providing step comprises: A D / A conversion step of converting the digital input waveform data into an analog drive signal; and a current conversion step, which converts the drive signal into the drive current, In the D / A conversion step, a plurality of continuous interval waveform data obtained by dividing the time waveform of the input waveform data are sequentially converted into the drive signal while giving a time difference.

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