Semiconductor laser driver device

Abstract

An initial setting circuit (11) maintains an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element (2). A differential amplifier (17) receives a measured optical power from a first optical detection element (3), where the measured optical power indicates an optical power generated by the semiconductor laser element (2), and outputs a differential signal indicating the difference between the measured optical power and the target optical power. A correction circuit (13) corrects the initial setting value based on the differential signal to generate a corrected setting value. A current generation circuit generates a drive current, the magnitude of which corresponds to the initial setting value or the corrected setting value, and supplies the drive current to the semiconductor laser element (2).The correction circuit (13) generates or updates the corrected setting value to reduce the difference between the measured optical power and the optical target power based on the differential signal during an operating period in which the semiconductor laser element (2) is driven, by continuously or intermittently supplying the semiconductor laser element (2) with the drive current corresponding to the initial setting value or the corrected setting value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a semiconductor laser driving device, a semiconductor laser driving method, and a distance measuring device. STATE OF THE ART

[0002] In general, the optical power of a semiconductor laser element increases or decreases depending on a change in the element's temperature. To compensate for the change in the optical power of the semiconductor laser element, the techniques of, for example, Patent Documents 1 and 2 are disclosed. Patent Document 1 discloses achieving constant optical power while taking into account the sag of a semiconductor laser element used in an imaging device such as a laser printer and a digital copier. Patent Document 2 discloses improving the accuracy of optical power correction by performing optical power correction in real time according to a change in the characteristics of a semiconductor laser element used in an image display device such as a laser scanning display. CITATION LISTPATENT DOCUMENTS PATENT DOCUMENT 1: Japanese Patent No. JP 5672845 B2 PATENT DOCUMENT 2: Japanese Patent No. JP 5125390 B2 SUMMARY OF THE INVENTION TECHNICAL TASK

[0003] The semiconductor laser element can be used not only in imaging and image display devices, but also in distance measuring devices, such as a time-of-flight (ToF) sensor. The ToF sensor measures the distance from the ToF sensor to an object based on the time of flight of light from its emission to the object until its return after being reflected by the object. The ToF sensor can process three-dimensional information, including not only distance information in the Z direction but also planar information in the XY direction.

[0004] A semiconductor laser element for a ToF sensor continuously generates short light pulses to accurately measure the light's time of flight. Furthermore, attenuation due to reflection from the object and attenuation during propagation affect the detection of an optical detection element, so it is necessary to generate a sufficiently high optical power of the semiconductor laser element. Generally, a semiconductor laser element for a ToF sensor must be driven at a higher current and higher speed, depending on the distance and accuracy, than a semiconductor laser element for an imaging device or image display device. However, when the semiconductor laser element is driven at a high current and high speed, a significant temperature increase occurs due to heating of the semiconductor laser element itself.Therefore, it is necessary to avoid a change in the optical power of the semiconductor laser element even if the temperature of the semiconductor laser element changes due to heating of the semiconductor laser element itself or due to other heat sources in the use environment of the semiconductor laser element.

[0005] An object of the present disclosure is to provide a semiconductor laser driving device and a semiconductor laser driving method each capable of preventing a change in the optical power of a semiconductor laser element even when the temperature of the semiconductor laser element changes due to heating of the semiconductor laser element itself or due to other heat sources. Another object of the present disclosure is to provide a distance measuring device having such a semiconductor laser driving device. SOLUTION TO THE TASK

[0006] According to a semiconductor laser driving device according to a first aspect of the present disclosure, the semiconductor laser driving device drives a semiconductor laser element. The semiconductor laser driving device is provided with: an initial setting circuit, a differential amplifier, a correction circuit, and a current generation circuit. The initial setting circuit is configured to hold an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element. The differential amplifier is configured to receive a measured optical power from a first optical detection element, the measured optical power indicative of an optical power generated by the semiconductor laser element, and output a difference signal indicative of a difference between the measured optical power and the target optical power.The correction circuit is configured to correct the initial setting value based on the difference signal to generate a corrected setting value. The current generation circuit is configured to generate a drive current whose magnitude corresponds to the initial setting value or the corrected setting value and supply the drive current to the semiconductor laser element. The correction circuit is further configured to generate or update the corrected setting value to reduce the difference between the measured optical power and the target optical power based on the difference signal during an operating period in which the semiconductor laser element is driven by continuously or intermittently supplying the drive current with the magnitude corresponding to the initial setting value or the corrected setting value to the semiconductor laser element. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0007] According to the semiconductor laser driving device of one aspect of the present disclosure, it is possible to avoid the change in the optical power of the semiconductor laser element even when the temperature of the semiconductor laser element changes due to the heating of the semiconductor laser element itself or due to other heat sources. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a configuration of a semiconductor laser driving device 1 according to a first embodiment. Fig. Fig. 2 is a diagram showing an example of the optical power and current characteristics of a semiconductor laser element 2 used by the semiconductor laser driving device 1 of the Fig. 1 is driven. Fig. Fig. 3 is a diagram showing an example of the temporal change of the optical power of the semiconductor laser element 2 driven by the semiconductor laser driving device 1 of the Fig. 1 is driven. Fig. 4 is a timing chart showing an exemplary operation of the semiconductor laser driving device 1 of the Fig. 1 shows. Fig. 5 is a timing chart showing another exemplary operation of the semiconductor laser driving device 1 of the Fig. 1 shows. Fig. 6 is a block diagram showing a configuration of a semiconductor laser driving device 1A according to a first comparative example. Fig. 7 is a block diagram showing a configuration of a semiconductor laser driving device 1B according to a second comparative example. Fig. Fig. 8 is a diagram showing an example of temporal changes in the optical power of a semiconductor laser element 2 driven by the semiconductor laser driving device 1A of the Fig. 6 or the semiconductor laser driving device 1B of the Fig. 7 is controlled. Fig. 9 is a block diagram showing a configuration of a semiconductor laser driving device 1C according to a modification of the first embodiment. Fig. 10 is a block diagram showing the configuration of a distance measuring device 20 according to a second embodiment. DESCRIPTION OF THE EMBODIMENTS

[0008] Embodiments of the present disclosure will be described below with reference to the drawings. Similar components are designated by the same reference numerals throughout the drawings. [FIRST EMBODIMENT](CONFIGURATION OF THE FIRST EMBODIMENT)

[0009] Fig. 1 is a block diagram showing a configuration of a semiconductor laser driving device 1 according to a first embodiment. The semiconductor laser driving device 1 supplies a semiconductor laser element 2 with a driving current Iop to drive the semiconductor laser element 2. The semiconductor laser driving device 1 receives a measured optical power from an optical detection element 3, the measured optical power indicating an optical power generated by the semiconductor laser element 2, and determines a magnitude of the driving current based on the measured optical power.

[0010] The semiconductor laser element 2 is, for example, a laser diode. The optical detection element 3 is, for example, a photodiode. The optical detection element 3 can be provided separately from the semiconductor laser element 2 or integrated into the semiconductor laser element 2.

[0011] The semiconductor laser driver device 1 is provided with an initial setting circuit 11, a digital-to-analog converter (DAC) 12, a correction circuit 13, a digital-to-analog converter (DAC) 14, a switch 15, a reference voltage source 16, and a differential amplifier 17. The components of the semiconductor laser driver device 1 operate according to an externally supplied clock signal Sclk.

[0012] The initial setting circuit 11 contains an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element 2. The initial setting value is a combination of a digital code value Sbi, which indicates the magnitude of a bias current Ibi, and a digital code value Smod0, which indicates the magnitude of a modulation current Imod. The bias current Ibi can be set, for example, to a minimum current at which the semiconductor laser element 2 begins to emit light, i.e., to a threshold current Ith. If the current flowing through the semiconductor laser element 2 is less than the threshold current Ith, the semiconductor laser element 2 emits little or no light.The bias current Ibi and the modulation current Imod are adjusted so that the optical power of the semiconductor laser element 2 becomes equal to the target optical power when the sum of the bias current Ibi and the modulation current Imod flows in the semiconductor laser element 2. The initial setting circuit 11 determines the digital code values ​​Sbi and Smod0 in advance by performing automatic power control (APC) based on a difference signal Sdiff (described later) output from the differential amplifier 17 in accordance with a control signal Sinit. The initial setting circuit 11 stores the digital code values ​​Sbi and Smod0 in an internal memory 11m.

[0013] The digital-to-analog converter 12 converts the digital code value Sbi into a bias current Ibi with a corresponding current value.

[0014] The correction circuit 13 corrects the digital code value Smod0 based on the difference signal Sdiff (described later) output from the differential amplifier 17 and generates a corrected digital code value Smod according to a control signal Srun. The correction circuit 13 stores the digital code values ​​Smod0 and Smod in an internal memory 13m.

[0015] In this specification, a combination of the digital code values ​​Sbi and Smod is also referred to as a "corrected adjustment value." In other words, the correction circuit 13 corrects the original adjustment value based on the difference signal Sdiff to generate the corrected adjustment value.

[0016] The digital-to-analog converter 14 converts the digital code value Smod into a modulation current Imod with a corresponding current value.

[0017] Switch 15 passes or blocks the modulation current Imod depending on a control signal Son. Therefore, when switch 15 is turned on, semiconductor laser element 2 is supplied with the sum of bias current Ibi and modulation current Imod as the drive current Iop. When switch 15 is turned off, semiconductor laser element 2 is supplied only with bias current Ibi.

[0018] The optical detection element 3 generates a measured voltage indicative of the measured optical power. The reference voltage source 16 generates a reference voltage indicative of the target optical power. The differential amplifier 17 receives the measured voltage from the optical detection element 3, receives the reference voltage from the reference voltage source 16, and outputs the difference signal Sdiff indicative of the difference between the measured optical power and the target optical power. The differential amplifier 17 is, for example, an operational amplifier. As described above, the initial adjustment circuit 11 determines the initial adjustment value in advance based on the difference signal Sdiff, and the correction circuit 13 corrects the initial adjustment value based on the difference signal Sdiff to generate the corrected adjustment value.

[0019] The semiconductor laser driving device 1 has at least two periods with different operating modes, i.e., an initial adjustment period and an operating period. During the initial adjustment period, the semiconductor laser driving device 1 determines an initial adjustment value corresponding to the target optical power by gradually increasing the drive current Iop from zero. During the operating period, the semiconductor laser driving device 1 drives the semiconductor laser element 2 by continuously or intermittently supplying the drive current Iop to the semiconductor laser element 2 with a magnitude corresponding to the initial adjustment value or the corrected adjustment value. During the operating period, the correction circuit 13 generates or updates the corrected adjustment value to reduce the difference between the measured optical power and the target optical power based on the difference signal Sdiff.In this way, it is possible to correct the magnitude of the drive current Iop during the operation period, and therefore it is possible to avoid a change in the optical power of the semiconductor laser element 2 even if the temperature of the semiconductor laser element 2 changes due to the heating of the semiconductor laser element 2 itself or due to other heat sources.

[0020] Digital-to-analog converter 12, digital-to-analog converter 14, and switch 15 are an example of a current generation circuit that generates the drive current Iop, whose magnitude corresponds to the initial setting value or the corrected setting value, and supplies the drive current Iop to the semiconductor laser element 2. Digital-to-analog converter 12 is an example of a first current source that generates the bias current Ibi. Digital-to-analog converter 14 and switch 15 are an example of a second current source that generates the modulation current Imod. (OPERATION OF THE FIRST EMBODIMENT)

[0021] Fig. Fig. 2 is a diagram showing an example of the optical power and current characteristics of the semiconductor laser element 2 used by the semiconductor laser driving device 1 of the Fig. 1. As described above, the semiconductor laser element 2 emits little or no light when the current flowing through the semiconductor laser element 2 is less than the threshold current Ith. When the current flowing through the semiconductor laser element 2 exceeds the threshold current Ith, the semiconductor laser element 2 begins to emit light, and thereafter, the optical power increases in proportion to the increase in current. The bias current Ibi and a modulation current Imod1 are set so that the optical power of the semiconductor laser element 2 becomes equal to the target optical power when the sum of the bias current Ibi and the modulation current Imod flows in the semiconductor laser element 2.

[0022] When the semiconductor laser element 2 is driven, the semiconductor laser element 2 itself generates heat, and the characteristics of the semiconductor laser element 2 (e.g., the magnitude of the threshold current and the gradient of the optical power-current characteristic curve) change. Since the optical power decreases with increasing temperature, the measured optical power becomes smaller than the target optical power even when the sum of the bias current Ibi and the modulation current Imod1 flows through the semiconductor laser element 2. Therefore, the semiconductor laser driving device 1 generates a modulation current Imod2 obtained by increasing the modulation current Imod1. The modulation current Imod2 is adjusted so that the optical power of the semiconductor laser element 2 becomes equal to the target optical power when the sum of the bias current Ibi and the modulation current Imod2 flows through the semiconductor laser element 2.

[0023] If the measured current is greater than the target current, a modulation current Imod3 is generated by reducing the modulation current Imod1. The modulation current Imod3 is adjusted so that the optical power of the semiconductor laser element 2 becomes equal to the target optical power when the sum of the bias current Ibi and the modulation current Imod3 flows through the semiconductor laser element 2.

[0024] Fig. Fig. 3 is a diagram showing an example of temporal changes in the optical power of the semiconductor laser element 2 driven by the semiconductor laser driving device 1 of the Fig. 1. For example, when the semiconductor laser element 2 is used in a ToF sensor, the semiconductor laser element 2 successively generates short light pulses by intermittently supplying the drive current Iop to the semiconductor laser element 2 at a cycle of several tens of MHz. However, as described above, the semiconductor laser element 2 itself may generate heat when driven, and the optical power may gradually decrease. According to the present embodiment, it is possible to prevent a change in the optical power of the semiconductor laser element 2 by correcting the magnitude of the drive current Iop during the operating period.

[0025] Fig. 4 is a timing chart showing an exemplary operation of the semiconductor laser driving device 1 of the Fig. 1 illustrated. Fig. Figure 4 shows the temporal changes of the control signals Sinit, Srun and Son, the clock signal Sclk, the digital code values ​​Snbi and Smod and the optical power.

[0026] Initially, the control signal Srun is low (L), and the correction circuit 13 does not correct the input digital code value Smod0 and simply outputs the digital code value Smod0 as the digital code value Smod. In addition, the control signal Son is initially low, and the switch 51 is off.

[0027] When the control signal Sinit changes from low to high (H), the initial adjustment period begins, and the initial adjustment circuit 11 executes APC. The initial adjustment circuit 11 gradually increases the digital code value Sbi while monitoring the difference signal Sdiff, and holds a digital code value bi1 when the optical power starts to increase at a rate higher than a predetermined change rate. Then, the control signal Son changes from low to high, and the switch 15 is turned on. The initial adjustment circuit 11 gradually increases the digital code value Smod0 while monitoring the difference signal Sdiff, and holds the digital code value mod1 when the measured optical power reaches the target optical power. The initial adjustment circuit 11 holds the digital code values ​​bi and mod1 as initial adjustment values ​​corresponding to the target optical power, that is, as the digital code values ​​Sbi and Smod0.After that, the control signals Sinit and Son transition from high to low, and the initial setting period ends.

[0028] Thereafter, the semiconductor laser driving device 1 starts the operating period, during which the semiconductor laser element 2 is turned on for a desired task. The operating period includes first time intervals in which only the bias current Ibi is supplied to the semiconductor laser element 2, and second time intervals in which the sum of the bias current Ibi and the modulation current Imod is supplied to the semiconductor laser element 2 as the driving current Iop. The first and second time intervals alternate.

[0029] In the first operating phase, the control signal Son is low, and switch 51 is off. In the second operating phase, however, the control signal Son is high, and switch 51 is on.

[0030] In the first operating section, the control signal Srun is set to a low value. In this case, the correction circuit 13 does not correct the digital code value Smod0 based on the difference signal Sdiff. If the digital code value Smod is identical to the digital code value Smod0 of the initial setting value (time intervals t3 to t4), the correction circuit 13 maintains the digital code value Smod unchanged. If the digital code value Smod is corrected to a value that differs from the digital code value Smod0 of the initial setting value (time intervals t5 to t6), the correction circuit 13 can change the corrected setting value so that it approaches the initial setting value every predetermined cycles of the clock signal Sclk. In the example of Fig. 4, the digital code value Smod is reduced to approach the digital code value mod1. This is because the temperature of the semiconductor laser element 2 decreases when the modulation current Imod is not supplied to the semiconductor laser element 2 for a predetermined time, so that the corrected digital code value Smod for the target optical power is likely to be excessively high. On the other hand, in the second operation section, the control signal Srun is set to a high value. In this case, the correction circuit 13 corrects the digital code value Smod0 to reduce the difference between the measured optical power and the target optical power based on the difference signal Sdiff, and generates the corrected digital code value Smod. In the example of Fig. 4 the digital code value Smod gradually increases.

[0031] If the correction circuit 13 does not correct the digital code value Smod0, there is a possibility that the optical power will gradually decrease, as shown by the dashed line (“WITHOUT CORRECTION”) of the lower diagram in Fig. 4. According to the present embodiment, it is possible to prevent a change in the optical power of the semiconductor laser element 2 by correcting the magnitude of the drive current Iop during the operating period.

[0032] The cycle and step size at which the initial setting circuit 11 and the correction circuit 13 change the digital code value can be set depending on the application and the use environment of the semiconductor laser element 2.

[0033] Fig. 5 is a timing chart showing another exemplary operation of the semiconductor laser driving device 1 of the Fig. 1. The correction circuit 13 holds the digital code value Smod immediately before the transition from the second time interval to the first time interval (time t5 in Fig. 5). In the example of Fig. 5, the correction circuit 13 holds the digital code value mod2 as the digital code value Smod. During the transition from the first time interval to the second time interval (time t6 in Fig. 5) The semiconductor laser driving device 1 generates a driving current Iop whose magnitude corresponds to the held digital code values ​​Sbi and Smod, and supplies the driving current Iop to the semiconductor laser element 2. For example, when the first and second time intervals alternate with short periods, it is possible to ignore a temperature change of the semiconductor laser element 2 during a period in which the modulation current Imod is not supplied to the semiconductor laser element 2. In this case, by holding the digital code value Smod when turning on the semiconductor laser element 2 in an immediately preceding period, a change in the optical power when the semiconductor laser element 2 is turned on next can be avoided. [COMPARISON EXAMPLES]

[0034] Fig. Fig. 6 is a block diagram showing a configuration of a semiconductor laser driving device 1A according to a first comparative example. The semiconductor laser driving device 1A has a configuration in which the correction circuit 13 is removed from the semiconductor laser driving device 1 of the Fig. 1 is removed. The configuration of the Fig. 6 is used, for example, to drive a semiconductor laser element for a typical imaging device or image display device. The imaging device and the image display device scan a frame containing an image area and a non-image area using raster scanning. The semiconductor laser driving device 1A can correct the optical power of the semiconductor laser element 2 depending on the ambient temperature by forcibly turning on the semiconductor laser element 2 and executing APC while scanning the non-image area. However, the semiconductor laser driving device 1A cannot correct the optical power of the semiconductor laser element 2 after executing APC, for example, when scanning the image area. Therefore, the optical power of the semiconductor laser element 2 can be adjusted in the case of the configuration of Fig. 6 increase or decrease according to a temperature change of the semiconductor laser element 2.

[0035] Fig. Fig. 7 is a block diagram showing a configuration of a semiconductor laser driving device 1B according to a second comparative example. The semiconductor laser driving device 1B is used instead of the correction circuit 13 of Fig. 1 is provided with a correction circuit 13B and a memory 18. The memory 18 stores a predetermined pattern for correcting the digital code value Smod0. The correction circuit 13B corrects the digital code value Smod0 based on the pattern read from the memory 18 and generates a corrected digital code value Smod. The configuration of the Fig. 7 assumes an application in which the environment of the semiconductor laser element does not change significantly, such as a laser printer and a digital copier, and assumes the ability to estimate the properties of the semiconductor laser element 2, whose optical power increases or decreases according to a change in the temperature of the semiconductor laser element 2. Therefore, the configuration of the Fig. 7 may not follow a change in the optical power of the semiconductor laser element 2 if the operating environment is not always constant and an unpredictable change in the environment occurs, as in the ToF sensor.

[0036] Fig. Fig. 8 is a diagram showing an example of temporal changes in the optical power of the semiconductor laser element 2 driven by the semiconductor laser driving device 1A of Fig. 6 or the semiconductor laser driving device 1B of Fig. 7. According to the configurations of the Fig. 6 and Fig. 7, the semiconductor laser element 2 itself generates heat when driven, and the optical power may gradually decrease.

[0037] On the other hand, according to the semiconductor laser driving device 1 of the present embodiment, it is possible to avoid a change in the optical power of the semiconductor laser element 2 by correcting the magnitude of the driving current Iop during the operating period, as described with reference to Fig. 3. Furthermore, the semiconductor laser driving device 1 of the present embodiment is not limited to the correction pattern stored in advance in the memory device as shown in Fig. 7, and it is possible to follow any change in optical power according to the application environment. Furthermore, with the semiconductor laser driving device 1 of the present embodiment, it is possible to respond immediately even to a sharp change in optical power. (MODIFICATION OF THE FIRST EMBODIMENT)

[0038] Fig. Fig. 9 is a block diagram showing a configuration of a semiconductor laser driving device 1C according to a modification of the first embodiment. The semiconductor laser driving device 1C is provided with an initial setting circuit 11C instead of the initial setting circuit 11 of the semiconductor laser driving device 1 of the Fig. 1. The initial setting circuit 11C does not execute the APC, but holds a predetermined initial setting value in the internal memory 11m. By not executing the APC, it is possible to reduce the costs compared to Fig. 1 to reduce. (SECOND EMBODIMENT)

[0039] Fig. Figure 10 is a block diagram showing a configuration of a distance measuring device 20 according to a second embodiment. The distance measuring device 20 is equipped with a semiconductor laser driving device 1, a semiconductor laser element 2, an optical detection element 3, an optical detection element 4, and a processing circuit 5. The semiconductor laser driving device 1, the semiconductor laser element 2, and the optical detection element 3 of the Fig. 10 are set up in a similar way to the corresponding components of the Fig. 1. The optical detection element 4 receives a reflected optical power indicating an optical power generated by the semiconductor laser element 2 and then reflected by an object 30. The processing circuit 5 calculates a distance between the distance measuring device 20 and the object 30 based on the reflected optical power. The processing circuit 5 generates the clock signal Sclk and the control signals Sinit, Srun and Son from the Fig. 1. The distance measuring device 20 is, for example, a ToF sensor that provides a three-dimensional image of the object 30 as seen by the distance measuring device 20. Since the distance measuring device 20 is equipped with the semiconductor laser driving device 1 according to the first embodiment, it is possible to prevent a change in the optical power of the semiconductor laser element 2 even when the temperature of the semiconductor laser element 2 changes due to heating of the semiconductor laser element 2 itself or due to other heat sources. Therefore, the distance measuring device 20 can accurately calculate the distance between the distance measuring device 20 and the object 30. [OTHER MODIFIED EMBODIMENTS]

[0040] Fig. 4 and Fig.5 shows the case where the digital code value Smod of the corrected adjustment value is generated to be larger than the digital code value Smod0 of the original adjustment value. However, the digital code value Smod can also be generated to be smaller than the digital code value Smod0, depending on the application environment of the semiconductor laser element 2.

[0041] If the threshold current Ith has changed significantly, the initial setting circuit 11 can execute the APC again. [SUMMARY OF THE EMBODIMENT]

[0042] According to a semiconductor laser driving device 1 of a first aspect of the present disclosure, the semiconductor laser driving device 1 drives a semiconductor laser element 2. The semiconductor laser driving device 1 is provided with an initial setting circuit 11, a differential amplifier 17, a correction circuit 13, and a current generator. The initial setting circuit 11 is configured to hold an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element 2. The differential amplifier 17 is configured to receive a measured optical power from a first optical detection element, the measured optical power indicating an optical power generated by the semiconductor laser element 2, and output a difference signal Sdiff indicating a difference between the measured optical power and the target optical power.The correction circuit 13 is configured to correct the initial setting value based on the difference signal Sdiff to generate a corrected setting value. The current generation circuit is configured to generate a drive current Iop whose magnitude corresponds to the initial setting value or the corrected setting value and supply the drive current Iop to the semiconductor laser element 2.The correction circuit 13 is further configured to generate or update the corrected adjustment value to reduce the difference between the measured optical power and the target optical power based on the difference signal Sdiff during an operating period in which the semiconductor laser element 2 is driven by continuously or intermittently supplying the drive current Iop having the magnitude corresponding to the initial adjustment value or the corrected adjustment value to the semiconductor laser element 2.

[0043] According to a semiconductor laser driving device 1 of a second aspect of the present disclosure, the semiconductor laser driving device 1 of the first aspect may be configured as follows. The current generation circuit is provided with a first current source configured to generate a bias current Ibi and a second current source configured to generate a modulation current Imod. The operating period includes alternating first time intervals and second time intervals. In the first time interval, the current generation circuit supplies the bias current Ibi to the semiconductor laser element 2. In the second time interval, the current generation circuit supplies a sum of the bias current Ibi and the modulation current Imod as the driving current Iop to the semiconductor laser element 2.

[0044] According to a semiconductor laser driving device 1 of a third aspect of the present disclosure, the semiconductor laser driving device 1 of the first or second aspect may be configured as follows. The correction circuit 13 changes the corrected adjustment value to approximate the initial adjustment value every predetermined cycle in the first time interval.

[0045] According to a semiconductor laser driving device 1 of a fourth aspect of the present disclosure, the semiconductor laser driving device 1 of the first or second aspect may be configured as follows. The correction circuit 13 is further configured to hold the corrected adjustment value immediately before the transition from the second time interval to the first time interval. The current generation circuit is further configured to generate a drive current Iop, the magnitude of which corresponds to the held corrected adjustment value, at the transition from the first time interval to the second time interval, and supply the drive current Iop to the semiconductor laser element 2.

[0046] According to a semiconductor laser driving device 1 of a fifth aspect of the present disclosure, the semiconductor laser driving device 1 of any one of the first to fourth aspects may be configured as follows. The initial setting circuit 11 determines the initial setting value in advance based on the difference signal Sdiff.

[0047] According to a semiconductor laser driving device 1C of a sixth aspect of the present disclosure, the semiconductor laser driving device 1 of any one of the first to fourth aspects may be configured as follows. An initial setting circuit 11C holds the predetermined initial setting value.

[0048] A distance measuring device (20) of a seventh aspect of the present disclosure is provided with: a semiconductor laser driving device (1) of any one of the first to seventh aspects; a semiconductor laser element (2); a first optical detection element (3) configured to obtain a measured optical power indicative of an optical power generated by the semiconductor laser element (2); a second optical detection element (4) configured to obtain a reflected optical power indicative of an optical power generated by the semiconductor laser element (2) and then reflected by an object; and a processing circuit (5) configured to calculate a distance to the object based on the reflected optical power.

[0049] According to a semiconductor laser driving method of an eighth aspect of the present disclosure, the method controls a semiconductor laser element 2 and includes the following steps. The method includes a step of holding an initial adjustment value corresponding to a predetermined target optical power of the semiconductor laser element 2. The method includes a step of obtaining a measured optical power from a first optical detection element, the measured optical power indicating an optical power generated by the semiconductor laser element 2, and outputting a difference signal Sdiff indicating a difference between the measured optical power and the target optical power. The method includes a step of correcting the initial adjustment value based on the difference signal Sdiff to generate a corrected adjustment value.The method includes a step of generating a drive current Iop having a magnitude corresponding to the initial setting value or the corrected setting value and supplying the drive current Iop to the semiconductor laser element 2. The step of generating the corrected setting value includes generating or updating the corrected setting value to reduce the difference between the measured optical power and the target optical power based on the difference signal Sdiff during an operation period in which the semiconductor laser element 2 is driven by continuously or intermittently supplying the drive current Iop having the magnitude corresponding to the initial setting value or the corrected setting value to the semiconductor laser element 2. LIST OF REFERENCE SYMBOLS 1, 1A to 1C Semiconductor laser driving device 2 semiconductor laser element 3 optical detection element 4 optical detection element 5 Processing circuit 11, 11C Initial setting circuit 11m storage 12 digital-to-analog converters (DAC) 13, 13B Correction circuit 13m storage n14 Digital-to-analog converter (DAC) 15 switches 16 Reference voltage source 17 differential amplifiers 18 storage 20 Distance measuring device 30 objects QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 5672845 B2

[0002] JP 5125390 B2

[0002]

Claims

[1] A semiconductor laser driving device for driving a semiconductor laser element, the semiconductor laser driving device comprising: an initial setting circuit configured to hold an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element; a differential amplifier configured to receive a measured optical power from a first optical detection element, the measured optical power indicative of an optical power generated by the semiconductor laser element, and output a difference signal indicative of a difference between the measured optical power and the target optical power; a correction circuit configured to correct the original setting value based on the difference signal to generate a corrected setting value; and a current generation circuit configured to generate a drive current whose magnitude corresponds to the initial setting value or the corrected setting value and to supply the drive current to the semiconductor laser element, wherein the correction circuit is further configured to generate or update the corrected adjustment value to reduce the difference between the measured optical power and the target optical power based on the difference signal during an operating period in which the semiconductor laser element is driven by continuously or intermittently supplying the driving current to the semiconductor laser element whose magnitude corresponds to the initial adjustment value or the corrected adjustment value. [2] The semiconductor laser driving device according to claim 1, wherein the current generation circuit comprises a first current source configured to generate a bias current and a second current source configured to generate a modulation current, wherein the operating period comprises first time intervals and second time intervals which alternate with each other, wherein in the first time interval, the current generating circuit supplies the bias current to the semiconductor laser element, and wherein the current generating circuit supplies a sum of the bias current and the modulation current as a drive current to the semiconductor laser element in the second time interval. [3] The semiconductor laser driving device according to claim 2, wherein the correction circuit changes the corrected adjustment value to approach the original adjustment value every predetermined cycle in the first time interval. [4] The semiconductor laser driving device according to claim 2, wherein the correction circuit is further configured to hold the corrected setting value immediately before the transition from the second time interval to the first time interval, and wherein the current generation circuit is further configured to generate a drive current having a magnitude corresponding to the held corrected adjustment value and supply the drive current to the semiconductor laser element when transitioning from the first time interval to the second time interval. [5] The semiconductor laser driving device according to any one of claims 1 to 4, wherein the initial setting circuit determines the initial setting value in advance based on the difference signal. [6] The semiconductor laser driving device according to any one of claims 1 to 4, wherein the initial setting circuit stores the predetermined initial setting value. [7] A distance measuring device comprising: a semiconductor laser driving device according to claim 1; a semiconductor laser element; a first optical detection element configured to obtain a measured optical power indicative of an optical power generated by the semiconductor laser element; a second optical detection element configured to obtain a reflected optical power indicative of an optical power generated by the semiconductor laser element and then reflected by an object; and a processing circuit configured to calculate a distance to the object based on the reflected optical power. [8] A semiconductor laser driving method for driving a semiconductor laser element, the semiconductor laser driving method comprising the following steps: Holding an initial setting value corresponding to a predetermined target optical power of the semiconductor laser element; Obtaining a measured optical power from a first optical detection element, the measured optical power indicating an optical power generated by the semiconductor laser element, and outputting a difference signal indicating a difference between the measured optical power and the target optical power; Correcting the initial setting value based on the difference signal to produce a corrected setting value; and Generating a drive current whose magnitude corresponds to the initial setting value or the corrected setting value, and supplying the drive current to the semiconductor laser element, wherein the step of generating the corrected adjustment value comprises generating or updating the corrected adjustment value to reduce the difference between the measured optical power and the target optical power based on the difference signal during an operating period in which the semiconductor laser element is driven by continuously or intermittently supplying the drive current having the magnitude corresponding to the initial adjustment value or the corrected adjustment value to the semiconductor laser element.

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