Semiconductor lasers, distance measuring devices and on-board devices

Abstract

The present invention reduces the impact of a tail of a laser pulse, for example.　A semiconductor laser has, formed on a semiconductor substrate, at least two or more gain regions and at least two or more absorption regions. The gain regions and the absorption regions include contiguous active layers, and the gain regions and the absorption regions are formed alternately with separation regions interposed therebetween. A first laser pulse having first polarization is emitted from a front-end face, whereupon a second laser pulse having second polarization is emitted. The first polarization and the second polarization are orthogonal to each other.

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser, a distance measuring device, and an in-vehicle device. [Background technology]

[0002] Semiconductor lasers that output laser pulses (see, for example, Non-Patent Document 1 below) are used as light sources in, for example, time-of-flight measurement (hereinafter referred to as ToF). ToF distance sensors are used in a wide range of applications, including topographical measurement, structure management, autonomous navigation, defect inspection on production lines, sports, entertainment, and art. The pulse width of a laser determines the measurable time resolution. Since the speed of light is constant, the pulse width of a laser contributes to the measured distance resolution. For example, if the speed of light is 3×10 8 If the time resolution is 1 nanosecond, the distance resolution is 15 cm, and if the time resolution is 1 picosecond, the distance resolution is 0.15 mm. [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] Brigitte Lanz, et.al., Optics Express 29780 (2013). Summary of the Invention [Problem to be solved by the invention]

[0004] In such fields, it is desirable to minimize the influence of the pulse tail (hereinafter also referred to as the tail, as appropriate) of the laser pulse emitted from the semiconductor laser.

[0005] An object of the present disclosure is to provide a semiconductor laser, a distance measuring device, and an on-board device that minimize the influence of the tail of a laser pulse. [Means for solving the problem]

[0006] The present disclosure provides, for example, at least two gain regions and at least two absorption regions formed on a semiconductor substrate; the gain region and the absorption region include a continuous active layer, and the gain region and the absorption region are alternately formed with an isolation region interposed therebetween; A first laser pulse having a first polarization is emitted from the front end face, followed by a second laser pulse having a second polarization, the first polarization and the second polarization being orthogonal to each other. It is a semiconductor laser.

[0007] The present disclosure also relates to, for example, the semiconductor laser described above; Light separation unit and Equipped with The first laser pulse and the second laser pulse are separated by the optical separation unit. It is a distance measuring device. The present disclosure may also be an in-vehicle device having such a distance measuring device. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a semiconductor laser according to an embodiment. [Figure 2] FIG. 2 is a diagram to be referred to when explaining an example of driving a semiconductor laser according to an embodiment. [Figure 3] FIG. 3A is a diagram schematically showing currents applied to a plurality of gain regions, and FIG. 3B is a diagram schematically showing an example of the time waveforms of the first and second laser pulses generated. [Figure 4] FIG. 4A is a diagram schematically showing currents applied to multiple gain regions, and FIG. 4B is a diagram schematically showing another example of the time waveforms of the first and second laser pulses generated. [Figure 5]FIG. 5A is a diagram schematically showing currents applied to multiple gain regions, and FIG. 5B is a diagram schematically showing another example of the time waveforms of the generated first and second laser pulses. [Figure 6] FIG. 6A is a diagram schematically showing currents applied to multiple gain regions, and FIG. 6B is a diagram schematically showing another example of the time waveforms of the generated first and second laser pulses. [Figure 7] FIG. 7A is a diagram showing a schematic diagram of the currents applied to the multiple gain regions, and FIG. 7B is a diagram showing a schematic diagram of the time waveform of the first laser pulse generated in response to the applied currents and after being separated by a polarizing beam splitter. [Figure 8] FIG. 8A is a diagram showing a schematic diagram of currents applied to multiple gain regions, and FIG. 8B is a diagram showing a schematic diagram of the time waveform of a first laser pulse generated in response to the applied currents and after being separated by a polarizing beam splitter. [Figure 9] FIG. 9A is a diagram showing a schematic diagram of the currents applied to the multiple gain regions, and FIG. 9B is a diagram showing a schematic diagram of the time waveform of the first laser pulse generated in response to the applied currents and after being separated by the polarizing beam splitter. [Figure 10] FIG. 10 is a diagram for explaining a general Q-switched laser. [Figure 11] FIG. 11A is a diagram showing a schematic diagram of the currents applied to multiple gain regions of a Q-switched laser having a typical configuration, and FIG. 11B is a diagram showing a schematic diagram of the time waveform of the laser pulses generated in response to the applied currents. [Figure 12] FIG. 12A is a diagram showing a schematic diagram of the currents applied to multiple gain regions of a Q-switched laser having a typical configuration, and FIG. 12B is a diagram showing a schematic diagram of the time waveform of the laser pulses generated in response to the applied currents. [Figure 13]FIG. 13A is a diagram showing a schematic diagram of the currents applied to multiple gain regions of a Q-switched laser having a typical configuration, and FIG. 13B is a diagram showing a schematic diagram of the time waveform of the laser pulses generated in response to the applied currents. [Figure 14] FIG. 14A is a diagram schematically showing the behavior inside a resonator before and after Q-switching in a typical semiconductor laser, and FIG. 14B is a diagram schematically showing the light intensity inside the resonator. [Figure 15] FIG. 15 is a diagram showing a schematic diagram of the behavior of a laser pulse inside a resonator in a typical semiconductor laser. [Figure 16] FIG. 16A is a diagram schematically illustrating behavior within a resonator before and after Q-switching in a semiconductor laser according to one embodiment, and FIG. 16B is a diagram schematically illustrating the light intensity within the resonator. [Figure 17] FIG. 17 is a diagram illustrating the relationship between the first laser pulse and the second laser pulse according to one embodiment. [Figure 18] 18A to 18D are diagrams for explaining a specific configuration example of a semiconductor laser according to an embodiment. [Figure 19] FIG. 19 is a diagram showing an example of a layer structure of a semiconductor laser according to an embodiment, together with a transverse mode in the vertical direction. [Figure 20] FIG. 20 is a diagram for explaining that the vertical optical confinement by the refractive index distribution of the semiconductor layer structure is designed taking into consideration the propagation from the gain region to the absorption region. [Figure 21] FIG. 21 is a diagram for explaining an example in which a grating structure is introduced only in the first guide layer according to an embodiment. [Figure 22] FIG. 22 is a diagram illustrating an example in which a grating structure is introduced into the first guide layer and the second guide layer according to an embodiment. [Figure 23] FIG. 23 is a block diagram showing a specific example of the configuration of a distance measuring system according to an embodiment. [Figure 24] FIG. 24 is a diagram for explaining an application example. [Figure 25] FIG. 25 is a diagram for explaining an application example. [Figure 26] FIG. 26 is a diagram for explaining an application example. [Figure 27] FIG. 27 is a diagram for explaining an application example. [Figure 28] FIG. 28 is a block diagram showing an example of a schematic configuration of a vehicle control system. [Figure 29] FIG. 29 is an explanatory diagram showing an example of the installation positions of the outside-of-vehicle information detection unit and the imaging unit. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The description will be made in the following order. <Background of the Disclosure> <One embodiment> <Modification> The embodiments and the like described below are preferred specific examples of the present disclosure, and the contents of the present disclosure are not limited to these embodiments and the like. Unless otherwise specified, color shading, hatching, and other patterns in the drawings do not have any specific meaning. Furthermore, for the sake of convenience of explanation, the illustrations may be simplified as appropriate, and reference symbols may be assigned to only some of the components.

[0010] <Background of the Disclosure> First, to facilitate understanding of the present disclosure, the background of the present disclosure will be described. As described above, for example, semiconductor lasers are used in ToF distance sensors. A semiconductor laser that outputs laser pulses of several nanoseconds has a uniform active layer in a resonator, and is obtained by applying a pulse current of several nanoseconds. This is due to the response speed of the semiconductor switch and the carrier lifetime in the active layer of the semiconductor laser, which is sub-nanosecond to several nanoseconds.

[0011] Semiconductor lasers that output laser pulses of around 100 picoseconds have a region in the cavity where the amount of absorption changes passively or actively. Before laser oscillation, the absorption in the cavity exceeds the gain, so laser oscillation does not occur, and the carrier density in the active layer is higher than in continuous wave (CW). When absorption decreases, laser oscillation occurs suddenly, and a higher gain than in CW is obtained instantaneously, resulting in a pulsed laser with a high peak value.

[0012] For example, the structure reported in the aforementioned Non-Patent Document 1 has a cavity length of 1.4 mm and a stripe width of 128 μm, with a 20 μm or 40 μm absorption region in front of the cavity. A pulse current with a full width at half maximum of 1.46 nanoseconds is applied, and a laser pulse is obtained just after the current peak. Thereafter, a tail of about 25% of the laser pulse appears as the pulse current gradually decays. Furthermore, lowering the current value delays the timing of the laser pulse oscillation, reducing the tail and causing the laser pulse oscillation to cease.

[0013] Conventional semiconductor lasers that generate laser pulses with such high peak values ​​have the problem of being prone to pulse tails. Furthermore, suppressing the pulse tail requires highly accurate control of the pulse current, which complicates the system. Taking these points into consideration, the present disclosure will be described in detail with reference to one embodiment.

[0014] <One embodiment> The semiconductor laser according to this embodiment will be outlined with reference to Fig. 1. The semiconductor laser according to this embodiment is, for example, a Q-switched semiconductor laser (hereinafter, appropriately abbreviated as semiconductor laser 100).

[0015] First, we will provide an overview of Q-switched semiconductor lasers (hereinafter referred to as Q-switched lasers). Q-switched lasers continue excitation while suppressing oscillation by increasing the optical loss of the laser resonator, and when the number of carriers in the excited state in the laser medium becomes sufficiently large, the optical loss of the resonator is suddenly reduced to cause laser oscillation. In other words, the Q value of the resonator is instantly increased, resulting in high-intensity pulsed light.

[0016] Q-switching methods include passive types that use saturable absorbers and active types that actively control the absorption rate. Passive Q-switched lasers have the advantage of being relatively simple to fabricate, but they have the disadvantage that the pulsed light tends to self-oscillate and the timing of the pulsed light generation cannot be actively controlled, resulting in insufficient intensity. In contrast, active Q-switched lasers can actively control the timing of the pulsed light generation, which can compensate for the drawbacks of passive Q-switched lasers. However, the device configuration, including the drive circuit, is complex, which presents disadvantages in terms of controllability, size, and cost. Therefore, it is desirable to design the circuit configuration appropriately, taking these points into consideration.

[0017] In a Q-switched laser, an optical absorption region is placed inside a cavity formed by opposing end faces formed by cleavage or other methods. When a forward voltage is applied to the PN junction of a Q-switched laser, a forward current flows and spontaneous emission is obtained. Because the refractive index of the active layer is higher than that of the cladding layer, light is confined vertically to the active layer and its vicinity, and horizontally to the lower ridge and its vicinity due to the ridge structure. This confined optical propagation mode travels back and forth within the cavity, with both end faces of the ridge structure serving as mirrors. During this travel, the light induces radiative transitions of other electrons in an excited state, causing stimulated emission. The number of photons is amplified as they travel back and forth within the cavity, and when this gain exceeds the loss, laser oscillation occurs.

[0018] When a reverse voltage is applied to the PN junction of a Q-switched laser, the light absorption in the active layer increases. At this time, a photovoltaic voltage is generated in the PN junction, and a photovoltaic current flows in the reverse direction. In Q-switched lasers, the property of light absorption that occurs when a reverse bias is applied is used as a Q switch.

[0019] The optical absorption characteristics of the optical absorption region under reverse bias are affected by various factors. Optical absorption increases due to factors such as a decrease in the band gap of the active layer (e.g., quantum well) and an increase in the probability of tunneling from the quantum well to adjacent layers. On the other hand, because the carrier density in the p-layer and n-layer increases due to photoexcitation, if the anode and cathode are not connected, the potential difference across the PN junction due to photocarriers decreases, resulting in decreased absorption. Therefore, connecting the anode and cathode together can suppress the decrease in absorption. Furthermore, inserting a resistor in the closed circuit between the anode and cathode reduces the potential difference across the PN junction due to the voltage drop. Furthermore, increasing the time constant of the closed circuit can suppress photovoltaic current. A structure in which the optical absorption characteristics of the optical absorption region change transiently due to light generated in the gain region is generally called a passive type. On the other hand, in an active type, the optical absorption characteristics of the optical absorption region are directly modulated by the drive circuit. This concludes our general explanation of Q-switched lasers.

[0020] [Example of semiconductor laser configuration] As shown in FIG. 1, a semiconductor laser 100 has a waveguide (optical waveguide) 101. The waveguide 101 is formed by a layer structure (semiconductor layer) epitaxially grown on a semiconductor substrate and a ridge structure formed on the surface side of the semiconductor layer. The waveguide 101 includes at least two (plural) gain regions 102 and at least two (plural) absorption regions 103, which are formed on the semiconductor substrate and alternately arranged with separation regions interposed therebetween, as described below. When the layer structure and driving conditions, as described below, are satisfied, a first laser pulse 105, followed by a second laser pulse 106, which is the pulse tail, is emitted from a front end face 110 of the semiconductor laser 100 along an optical axis 104. The polarization of the first laser pulse 105 (an example of a first polarization) is in a transverse magnetic (TM) mode perpendicular to the semiconductor layer structure, and the polarization of the second laser pulse 106 (an example of a second polarization) is in a transverse electric (TE) mode parallel to the semiconductor layer structure. That is, the first polarized light and the second polarized light are orthogonal to each other.

[0021] The laser emitted from semiconductor laser 100 passes through a collimating lens or the like (not shown), and then is separated into a first laser pulse 105 and a second laser pulse 106 by a polarizing beam splitter 107, which is an example of a light separation section, and becomes first laser pulse 105 on optical axis 108 and second laser pulse 106 on optical axis 109, respectively.

[0022] [Driving example of semiconductor laser 100] Next, an example of driving the semiconductor laser 100 will be described with reference to Fig. 2. As shown in Fig. 2, the anode electrodes 120 (shown in black in Fig. 2) of the multiple gain regions 102 are connected to each other, and each anode electrode 120 is connected to a constant voltage source 121. The anode electrodes 122 of the multiple absorption regions 103 are connected to each other and to a Q switch circuit 123. The Q switch circuit 123 is a circuit that controls the Q switch operation, and a known circuit configuration can be applied.

[0023] A cathode electrode 124 provided on a semiconductor substrate 128 of the semiconductor laser 100 is connected to ground 126 via a switching element 125 such as an NMOS (Negative-channel Metal Oxide Semiconductor). The cathode voltage Vcathode while the switching element 125 is off (while the NMOS is closed) is a value obtained by subtracting a voltage Vbg corresponding to the bandgap energy of the PN junction of the semiconductor laser 100 from the voltage Vgain of the constant voltage source 121. When the switching element 125 is turned on (by opening the NMOS), the cathode voltage drops suddenly and a pulse current is applied to each of the multiple gain regions 102.

[0024] Here, while the NMOS is closed, the voltage Vqsw of the anode electrodes 122 of the multiple absorption regions 103 is lower than the voltage Vcathode, and therefore a reverse bias is applied to the PN junctions of the multiple absorption regions 103. The active layers of the multiple absorption regions 103 partially or completely overlap the depletion layer formed in the PN junction, increasing the absorption coefficient. There is capacitance and parasitic capacitance due to the PN junction between the anode electrodes 122 and the cathode electrodes 124, and this capacitance can also be intentionally added. When the NMOS is opened, the cathode voltage Vcathode drops sharply, and the voltage Vqsw of the anode electrodes 122 also drops sharply through this capacitance. Then, the voltage Vqsw is suddenly increased, eliminating the reverse bias of the multiple absorption regions 103 and causing a sudden drop in the absorption coefficient. This fluctuation in the voltage Vqsw of the anode electrodes 122 may be achieved by a self-generated method that utilizes the voltage drop linked to the voltage change of the cathode electrode 124, or by an active method linked to the switching timing of the NMOS.

[0025] Fig. 3A shows currents applied to multiple gain regions 102, and Fig. 3B is a simplified diagram showing the time waveforms of first laser pulse 105 and second laser pulse 106 generated in response to the currents. The horizontal axis in Fig. 3A indicates time, and the vertical axis indicates the magnitude of the injected current. The horizontal axis in Fig. 3B indicates time, and the vertical axis indicates the magnitude of the optical output. The same applies to the contents shown in Figs. 4 to 6.

[0026] The pulse current CA is longer than the carrier density saturation time of the active layer in the gain region 102, and has a pulse width of approximately 2 to 4 nanoseconds. Carrier density saturation in the active layer in a Q-switched laser is rate-determined by ASE (amplification of spontaneous emission). By alternately arranging multiple gain regions 102 and absorption regions 103 as in this embodiment, spontaneous emission generated in the gain region 102 is quickly absorbed by the adjacent absorption region 103. As a result, carrier density saturation due to stimulated emission using the spontaneous emission as a seed is suppressed. In other words, the carrier density saturation time is lengthened.

[0027] As shown in Figures 3A and 3B, when the Q-switching timing is delayed to the very last possible moment, the second laser pulse 106 is generated slightly after the first laser pulse 105. Due to the influence of the electrical time constant, the injection current begins to decrease at this timing. As shown in Figures 4A and 4B, when the Q-switching timing is advanced, the peak value of the first laser pulse 105 increases and the optical output of the second laser pulse 106 also increases. As shown in Figures 5A and 5B, when the Q-switching timing is further advanced, the peak value of the first laser pulse 105 increases slightly, but the optical output of the second laser pulse 106 increases significantly. As shown in Figures 6A and 6B, when the Q-switching timing is further advanced, the current injection time becomes sufficiently shorter than the carrier density saturation time of the gain region 102, and the optical output of the first laser pulse 105 decreases.

[0028] 7A shows a pulse current CA applied to multiple gain regions 102, and FIG. 7B shows a simplified time waveform of first laser pulse 105 generated when pulse current CA is applied and after being split by polarizing beam splitter 107. The same applies to FIGS. 8A and 8B, and 9A and 9B.

[0029] As shown in Figures 7A and 7B (and similarly for Figures 8A and 8B, and Figures 9A and 9B), if the timing of the Q-switching is appropriate, a first laser pulse 105 is generated that has no pulse tail over a wide time range and a high peak value.

[0030] <Advantages of this embodiment> The advantages of the semiconductor laser 100 of this embodiment will be explained in comparison with a Q-switched laser having a general configuration.

[0031] 10 shows an outline of a Q-switched laser (hereinafter referred to as semiconductor laser 200) having a general configuration. Semiconductor laser 200 has a gain region 202 formed in a waveguide 201, with an absorption region 203 provided on the front surface. A laser pulse 205 is emitted from front end face 207 along optical axis 204. Laser pulse 205 is accompanied by a tail 206, and both laser pulse 205 and tail 206 have the same polarization. In the example shown, the mode is TE.

[0032] 11A and 11B are simplified diagrams showing the pulse current CA applied to the gain region 202 and the time waveforms of the laser pulse 205 and tail 206. As shown in FIG. 11A, when the Q-switching timing is delayed to the maximum extent possible, the laser pulse 205 is generated with a slight tail 206, as shown in FIG. 11B. Due to the influence of the electrical time constant, the injection current begins to decrease at this timing. As shown in FIGS. 12A and 12B, when the Q-switching timing is advanced, the peak value of the laser pulse 205 becomes higher and the tail 206 also becomes stronger. As shown in FIGS. 13A and 13B, when the Q-switching timing is further advanced, the peak value of the laser pulse 205 becomes slightly higher, while the optical output of the tail 206 becomes significantly stronger.

[0033] Fig. 14A is a diagram schematically showing the behavior inside the resonator before and after Q-switching in the semiconductor laser 200. Fig. 14B is a diagram schematically showing the light intensity inside the resonator.

[0034] A resonator is formed in waveguide 201 of semiconductor laser 200 by rear end facet 208 and front end facet 207. Waveguide 201 is provided with gain region 202 and absorption region 203. Absorption region 203 is provided on the front facet. When a high-reflection film is formed on rear end facet 208, a backward wave generated by injecting current into gain region 202 is reflected (arrow 227) by rear end facet 208 and becomes a forward wave. On the other hand, reflection of the forward wave (arrow 228) at front end facet 207 is suppressed by absorption region 203. In gain region 202 with a significant length, for example, approximately 100 μm or more, ASE causes light intensity 230 in the resonator to be maximized in gain region 202 near absorption region 203 (see FIG. 14B).

[0035] As shown in Figure 15, when the absorption coefficient of the absorption region 203 decreases, it resonates due to reflection from the front facet 207 (arrow 240), resulting in laser oscillation. A tail 206 is generated because part of the laser pulse is coupled to the resonator by reflection, the carriers injected into the active layer are not completely depleted during laser pulse oscillation, and a pulse current is injected even after laser pulse oscillation. Therefore, it is believed that temporal coherence remains between the laser pulse 205 and the tail 206.

[0036] FIG. 16A is a diagram schematically showing the behavior inside the resonator before and after Q-switching in a semiconductor laser 100 according to one embodiment, and FIG. 16B is a diagram schematically showing the light intensity inside the resonator.

[0037] The waveguide 101 of the semiconductor laser 100 has a resonator formed by the rear end facet 111 and the front end facet 110. The waveguide 101 is also provided with multiple gain regions 102 and multiple absorption regions 103. The waveguide 101 further comprises an amplification region 307, in which each gain region and absorption region is short, and a seed region 308, which is long and consists of a single gain region and a single absorption region. A high-reflection coating is formed on the rear end facet 111, and a low-reflection coating is formed on the front end facet 110. The length of each gain region 102 in the amplification region 307 (the horizontal length in FIG. 16 , the length on the light propagation axis) is 100 μm or less, minimizing ASE. In other words, most of the spontaneously emitted light generated in each gain region 102 is absorbed by the adjacent absorption region 103 without causing stimulated emission due to ASE. The length ratio of the gain region 102 to the absorption region 103 is preferably between 1:1 and 1:0.2. When the ratio of the lengths of the gain region 102 and the absorption region 103 is 1:1, the length of each absorption region 103 in the amplification region 307 (the horizontal length in FIG. 16, the length on the optical propagation axis) is 100 μm or less. The shorter the gain region 102, the more effectively it can suppress the effects of ASE, but the proportion of the N-type isolation region 113 that electrically insulates the gain region 102 from the absorption region 103 becomes relatively large, and the electrode width of each region becomes narrow, which may result in step disconnection. The length of each region is determined appropriately taking these points into consideration.

[0038] On the other hand, the length of the gain region 102 in the seed region 308 may be longer than the length of the gain region 102 in the amplification region 307, and may be 100 μm or more. That is, the gain region 112 closest to the rear facet 111 may be longer in the cavity direction (on the optical propagation axis) than the other gain regions 112. Due to reflection by the rear facet 111, the light intensity 330 before Q-switching is maximized in the gain region 102 near the absorption region 103 due to ASE in the seed region 308 (see FIG. 16B). The seed region 308 is significantly shorter than the cavity of the semiconductor laser 200, and the saturation level of the carrier density before Q-switching is high. In the amplification region 307, ASE is suppressed as much as possible, so the saturation level of the carrier density before Q-switching is significantly high. When the absorption in the absorption region 103 decreases due to Q-switching, the light intensity 330 becomes seed light, and the carriers accumulated in the amplification region 307 generate a first laser pulse 105 with a high peak value. Thereafter, recovery of the absorption in the absorbing region 103 requires subnanoseconds to several nanoseconds due to the influence of various time constants, and therefore the pulse current CA that is continuously applied generates a second laser pulse 106, which is a pulse tail.

[0039] FIG. 17 is a diagram showing the relationship between the first laser pulse 105 and the second laser pulse 106 in this embodiment. The peak wavelength of the first laser pulse 105 is longer than that of the second laser pulse 106, and as the timing of inducing the Q-switching operation is delayed (the time difference is increased), the wavelength increases as shown by the solid line from the dashed line. The peak wavelength of the first laser pulse 105 has a peak wavelength jump (spacing) of at least 1 nm or more compared to the peak wavelength of the second laser pulse 106. In the case of the longest wavelength, the peak wavelength of the first laser pulse 105 may be 5 nm or more longer than the peak wavelength of the second laser pulse 106. In other words, with the semiconductor laser 100 according to this embodiment, the emitted first laser pulse 105 and second laser pulse 106 can be separated by appropriately controlling the timing of the Q-switching.

[0040] Furthermore, the increase in the peak wavelength of the first laser pulse 105 is not continuous, but may involve discontinuous jumps. Such an extreme red shift is thought to be renormalization due to many-body effects, and the band structure contributing to laser oscillation changes before and after Q-switching. As a result, the coherence between the laser pulse and the pulse tail is thought to decrease dramatically, or an incoherent state occurs. Note that in the semiconductor laser reported in the aforementioned Patent Document 1, the peak wavelength of the laser pulse is shorter than the pulse tail, which is thought to be due to band filling.

[0041] Experimental results showed that, for example, in a semiconductor laser 100 using AlGaAs (aluminum / gallium / arsenic) for the active layer and emitting at a wavelength of approximately 830 nm, when the single active layer is 80 nm, the first laser pulse 105 and the second laser pulse 106 are both in TE mode, and the central wavelength of the laser pulse is approximately 5 nm longer than the pulse tail. Therefore, this wavelength difference is advantageous for separating the laser pulse and the pulse tail with a wavelength filter. When the single active layer is 120 nm, the first laser pulse 105 is in TM mode, and the second laser pulse 106 is in TE mode, and the central wavelength of the first laser pulse 105 is longer than the second laser pulse 106. Therefore, the first laser pulse 105 and the second laser pulse 106 can be separated using a polarizing beam splitter.

[0042] When the single active layer was 240 nm, both the first laser pulse 105 and the second laser pulse 106 were in TM mode. The thickness of each active layer was longer than the Bohr radius, and although the quantum effect in the stacking direction of the semiconductor layers was weak, there was a slight contribution to the laser oscillation mode. Therefore, the Q-switched semiconductor laser of this embodiment, in which the laser pulse and the pulse tail have different polarizations, has a completely different operating mechanism and structure from conventional Q-switched semiconductor lasers. Furthermore, its operating mechanism and structure are completely different from those of the mixed TE-polarized and TM-polarized light and the phase-stable state that have been reported to occur with low current injection.

[0043] [Specific example of semiconductor laser structure] 18A to 18D, specific structural examples of the semiconductor laser 100 according to this embodiment will be described. Fig. 18A is a cross-sectional view showing a structural example of the gain region 102, Fig. 18B is a cross-sectional view showing a structural example of the absorption region 103, Fig. 18C is a cross-sectional view showing a cross-sectional view of the separation region, and Fig. 18D is a cross-sectional view showing a cross-sectional view of the ridge side.

[0044] The semiconductor layers formed on an n-type GaAs semiconductor substrate 401 (hereinafter also referred to as semiconductor substrate 401) by a semiconductor growth method such as MOCVD (Metal Organic Chemical Vapor Deposition) are stacked as follows: an n-type AlGaAs buffer layer 402, an n-type AlGaAs first cladding layer 403, an n-type AlGaAs first guide layer 404, and an AlGaAs active layer 405, which is an example of a continuous active layer. The upper part of the active layer 405 has at least three types of regions and a ridge structure. The three types of regions are a gain region 102, an absorption region 103, and an isolation region 113.

[0045] The gain region 102 is formed by laminating an n-type AlGaAs second guide layer 406, a p-type AlGaAs second cladding layer 407, and a p-type GaAs contact layer 408. The absorption region 103 is formed by laminating an AlGaAs second cladding layer 416 containing a PN junction, a p-type AlGaAs second cladding layer 417, and a p-type GaAs contact layer 418. The isolation region 113 is formed by laminating an n-type AlGaAs second guide layer 426, an n-type AlGaAs second cladding layer 427, and a dielectric film 428. These semiconductor layers are grown simultaneously, so the heterointerfaces of each region coincide.

[0046] On the other hand, the positions of the PN junctions are different in each region, and the distance from the PN junction in the absorption region 103 to the active layer 405 is closer than in the gain region 102. Also, no intentionally formed PN junction exists in the separation region 113. Such a structure in which the position of the p-type semiconductor layer differs for each region can be formed by, for example, impurity diffusion. However, it is not limited to the impurity diffusion method, and may also be formed by, for example, selective growth method or ion implantation method.

[0047] The gain region 102 and the absorption region 103 are separated by a separation region 113, and a PNP structure is formed between the anode electrode 409 of the gain region 102 and the anode electrode 419 of the absorption region 103, providing excellent electrical insulation. Therefore, sufficient insulation is possible even with a very narrow separation width, reducing optical propagation loss and improving the occupancy rate of the gain region 102 and the absorption region 103. The surface of the separation region 113 is protected by a dielectric film 428, preventing the formation of unintended PN junctions due to surface states, etc. The gain region 102 and the absorption region 103 are arranged as shown in FIG. 2. A cathode electrode 400 common to the entire region is provided on the back surface of the n-type GaAs semiconductor substrate 401. A common anode electrode may also be used. The second cladding layers 407, 417, 427, and 437 may each have an etching stop layer with a refractive index higher than that of the second cladding layer. The etching stop layer may be a single layer or multiple layers. These layers are used to control the dry or wet etching when forming the ridge waveguide.

[0048] The active layer 405 is a weak n-type with an adjusted doping concentration. The active layer 405 preferably has an SQW (single quantum well) structure. This is because, in the absorption region 103, photoexcited electron-hole pairs are easily separated under reverse bias and can quickly move to the cathode and anode electrodes. During Q-switching, the electron-hole distribution quickly overlaps, facilitating absorption saturation. For AlGaAs with an oscillation wavelength of approximately 830 nm, the active layer 405 is preferably a single layer with a thickness in the range of 100 nm to 250 nm. As described above, this range facilitates oscillation in which the first laser pulse 105 is in TM mode and the second laser pulse 106 is in TE mode. If the thickness is less than 100 nm, the first laser pulse 105 and the second laser pulse 106 are in TE mode, whereas if the thickness is greater than 250 nm, the first laser pulse 105 and the second laser pulse 106 are in TM mode.

[0049] The waveguide 101 is formed by a refractive index distribution and a ridge structure of semiconductor layers. The ridge width is preferably 8 μm to 12 μm, and a single fundamental transverse mode is obtained in both the horizontal and vertical directions. The dimensions are, for example, a cavity length of 4 mm, a separation width of 4 μm, a gain region length of 33 μm in the amplification region 307, a gain region length of 33 μm in the amplification region 307, a gain region length of 100 μm in the seed region 308, and a absorption region length of 200 μm in the seed region 308. In this example, the ratio of the gain region 102 to the absorption region 103 is 1:1. The ratio can be adjusted within a range of 0.2:1 to 1:1, but a gain region 102 exceeding 100 μm is undesirable because carrier density saturation occurs due to ASE. Therefore, if the absorption region 103 ratio is small, the length of each absorption region 103 becomes short, increasing the difficulty of processing. The front facet 110 and the rear facet 111 are formed by cleavage or dry etching. The front end facet 110 is coated with an AR (Anti Reflection) coating having a reflectance of a few percent or less, and the rear end facet 111 is coated with an HR (High Reflection) coating having a reflectance of 90% or more.

[0050] 19 is a diagram showing an example of the layer structure and vertical transverse modes of a semiconductor laser 100. As shown in the figure, an asymmetric waveguide in which the refractive index of the first cladding layer is significantly higher than that of the second cladding layer can narrow the vertical radiation pattern of the laser pulse.

[0051] The vertical light confinement due to the refractive index distribution of the semiconductor layer structure is designed taking into consideration propagation from the gain region 102 to the absorption region 103. This point will be explained with reference to FIG. 20. The active layer 451 is a refractive index waveguide sandwiched between guide layers 452, 453 and cladding layers 454, 455, and a fundamental transverse mode 456 exists. When part of the active layer 451 is the absorption region 103, if absorption becomes very large, the propagating light is not coupled and tends to scatter to the cladding layers 454 and 455 as indicated by arrow 458. As a result, the spontaneous emission light generated in the gain region 102 cannot be efficiently absorbed by the absorption region 103, and stray light in the laminated semiconductor layers causes ASE.

[0052] 21 shows an example in which a grating structure is introduced only in the first guide layer 404 (the guide layer closer to the semiconductor substrate 401 than the active layer 405). With the first guide layer 404 having a thickness of at least 1 μm or more, most of the transverse modes in the vertical direction on the semiconductor substrate 401 side are accommodated in the first guide layer 404. Even in the absorption region 103 before Q-switching, scattering of propagating light into the cladding layer is suppressed, and the spontaneous emission light generated in the gain region 102 can be efficiently absorbed in the absorption region 103.

[0053] FIG. 22 shows an example in which a grating structure is introduced into the first guide layer 404 and the second guide layer 406 (the guide layers on the semiconductor substrate 401 side and the surface side sandwiching the active layer 405). Because of the large difference in refractive index between the guide layers and the cladding layers, most of the transverse modes in the vertical direction are contained within the first guide layer 404, the active layer 405, and the second guide layer 406. Therefore, even in the absorption region 103 before Q-switching, scattering of propagating light into the cladding layer is suppressed, and spontaneous emission light generated in the gain region 102 can be efficiently absorbed by the absorption region 103. Because this structure tends to increase the beam divergence angle in the vertical direction, it is preferable that the first guide layer 404 and the second guide layer 406 each have a thickness of 300 nm or more. This narrows the beam divergence angle and improves the coupling efficiency with the collimating lens. The PN junction in the gain region 102 is located away from the active layer 405 and approximately 400 nm closer to the surface than the PN junction in the absorption region 103. This is because the PN junction in the absorption region 103 must ensure spatial overlap between the depletion layer and the active layer when reverse bias is applied, while the PN junction in the gain region 102 must suppress carrier overflow when a high current is injected. The distance between these PN junctions is preferably at least 100 nm. Incidentally, if the PN junction in the gain region 102 is far from the active layer 405, delay in laser oscillation may become a problem when a low current is injected, but this is not a problem when a high current is injected, as in a Q-switched laser.

[0054] [Range measurement system to which semiconductor lasers can be applied] The semiconductor laser 100 described in one embodiment can be applied to a distance measuring device. A specific example of a distance measuring method is the ToF method. ToF methods are classified into several categories. In particular, the direct time-of-flight (d-ToF) method, which uses a pulsed laser, is further subdivided into linear mode (LM), Geiger mode (GM), and single photon (SP) (hereinafter referred to as the LM method, GM method, and SP method, respectively). The LM method uses a linear light-receiving element such as an avalanche photodiode (APD) to ensure a high S / N ratio; that is, the number of measurable photons N is approximately 100 to 1,000. The GM method often performs photon counting using a single photon avalanche diode (SPAD), and the expected number of received photons in a single shot may be less than 1. Histogram processing is performed using the number of received photons N accumulated over multiple shots. The SP method uses a silicon photomultiplier (SiPM) or the like to perform single-shot measurement. The number of measurable photons is one or more.

[0055] [Example of a specific configuration for a distance measurement system] FIG. 23 is a diagram showing a specific example of the configuration of a distance measuring system (distance measuring system 501) when the semiconductor laser 100 described above is applied to the distance measuring system. In FIG. 23, solid arrows indicate control signals, thick arrows indicate optical paths, dashed arrows indicate signal lines, and dashed arrows indicate data lines. The distance measuring system 501 includes a distance measuring device 501A and a distance measuring object 1000. The distance measuring device 501A includes an interface 502, a control unit 503, a light source unit 504 to which the semiconductor laser 100 is applied, an optical path branching unit 505, an optical scanning unit 509, a first optical receiving unit 512, a first signal shaping unit 513, a time difference measuring unit 514, a second optical receiving unit 515, a second signal shaping unit 516, a light source monitoring unit 517, and a calculation unit 522.

[0056] The interface 502 is an interface through which the distance measuring device 501A and an external device exchange data and commands. The control unit 503 performs overall control of the entire distance measuring device 501A. The control unit 503 controls the operation of each unit of the distance measuring device 501A.

[0057] A control unit 503 receives control parameters from the outside via an interface 502 and sends control signals to a plurality of devices and circuits, which will be described later. The light source unit 504 includes a Q-switched semiconductor light-emitting element and a drive circuit, and emits high-quality pulsed light beams with a pulse width of sub-nanoseconds, preferably 20 picoseconds or less, and pulse energy of several hundred picojoules to several nanojoules.

[0058] In the optical path branching unit 505, light from the light source unit 504 is branched via a beam splitter or the like into measurement light 506 that is irradiated onto the object 1000 to be measured, reference light 507 for obtaining a start signal for time measurement, and control light 508 for controlling the light source. The measurement light 506 is sent to an optical scanning unit 509, and is sequentially irradiated within a designed FOV (Field of View). The measurement light 506 irradiated onto the object 1000 to be measured, such as a person, is scattered. Part of the scattered light passes through the optical scanning unit 509 and becomes detection light 511.

[0059] The reference light 507 is sent to a first optical receiving unit 512, where it is converted into a reference electrical signal 518 by a light receiving element such as a photodiode, an avalanche photodiode, or a SiPM. The reference electrical signal 518 is sent to a time difference measuring unit 514 via a first signal shaping unit 513. The detection light 511 is sent to a second optical receiving unit 515, where it is converted into a detection electrical signal 520 by a light receiving element such as a SiPM. The detection electrical signal 520 is sent to the time difference measuring unit 514 via a second signal shaping unit 516. As will be described later, the second signal shaping unit 516 amplifies the very weak detection electrical signal 520 generated by single photon detection with a high S / N ratio and low jitter.

[0060] The first signal shaping unit 513 amplifies the reference electrical signal 518, which is an analog waveform output from the light receiving element, and generates a reference square wave 519 based on a detection threshold that can be set arbitrarily. The second signal shaping unit 516 amplifies the detection electrical signal 520, which is an analog waveform output from the light receiving element, and generates a detection square wave 521 based on a detection threshold that can be set arbitrarily. The control light 508 is sent to the light source monitoring unit 517, which measures the pulse energy and pulse width and returns the information to the control unit 503. The square waves sent to the time difference measurement unit 514 may be one or more, and these may be different square waves obtained at two or more detection thresholds. The time difference measurement unit 514 measures the relative time of the input square waves using a TDC. This may be the time difference between the reference square wave 519 and the detection square wave 521, or the time difference between a separately prepared clock and the reference square wave, or the time difference between the clock and the detection square wave. This varies depending on the type of TDC. The TDC may use a counter alone, a counter combined with an inverter ring delay line to perform multiple measurements and calculate the average value, or a combination of a counter and a highly accurate measurement method with picosecond resolution such as vernier buffering or pulse shrink buffering. The time difference measurement unit 514 may also be provided with a function to measure the rise time, peak value, or pulse integral value of the detection electrical signal 520 output from the second optical receiving unit 515. These measurements can be performed using a TDC or an ADC (Analog to Digital Converter).

[0061] The time difference measured by the time difference measurement unit 514 is sent to the calculation unit 522. The calculation unit 522 performs offset adjustment, time-walk error correction using the rising edge, peak value, pulse integral value, etc. of the detection electrical signal 520, and temperature correction. The calculation unit 522 then performs vector calculation using the scanning timing information 523 sent from the optical scanning unit 509 to obtain the distance to the object 1000 to be measured. Note that the distance data and scanning angle data may be output from the interface 502 without performing vector calculation. Furthermore, appropriate processing such as noise removal, averaging with adjacent points, or interpolation may be performed on this data, or advanced algorithms such as recognition processing may be performed on the data.

[0062] <Modification> Although one embodiment of the present disclosure has been specifically described above, the content of the present disclosure is not limited to the above-described embodiment, and various modifications based on the technical concept of the present disclosure are possible. Modifications will be described below.

[0063] The matters described in each embodiment and modification can be combined as appropriate. Furthermore, the contents of the present disclosure should not be interpreted as being limited to the effects exemplified in this specification.

[0064] The present disclosure may also have the following configurations. (1) at least two gain regions and at least two absorption regions formed on a semiconductor substrate; the gain region and the absorption region include a continuous active layer, and the gain region and the absorption region are alternately formed with a separation region interposed therebetween; A first laser pulse having a first polarization is emitted from the front end face, followed by a second laser pulse having a second polarization, the first polarization and the second polarization being orthogonal to each other. Semiconductor laser. (2) At least two or more gain regions each having a length of 100 μm or less on the optical propagation axis are formed. The semiconductor laser according to (1). (3) At least two of the absorption regions are formed, each having a length on the light propagation axis of 100 μm or less. A semiconductor laser according to (1) or (2). (4) The gain region closest to the rear end face is longer in the cavity direction than the other gain regions. A semiconductor laser according to any one of (1) to (3). (5) The active layer is a single layer with a thickness in the range of 100 nm to 250 nm. A semiconductor laser according to any one of (1) to (4). (6) The guide layer closer to the semiconductor substrate than the active layer has a grated structure and a thickness of at least 1 μm. A semiconductor laser according to any one of (1) to (5). (7) The guide layers on the semiconductor substrate side and the surface side sandwiching the active layer have a grated structure and a thickness of at least 300 nm or more. A semiconductor laser according to any one of (1) to (5). (8) the guide layers on the semiconductor substrate side and the surface side sandwiching the active layer have a grated structure; The PN junction of the gain region is at least 100 nm farther from the active layer than the PN junction of the absorption region. A semiconductor laser according to any one of (1) to (5). (9) The peak wavelength of the first laser pulse is longer than the peak wavelength of the second laser pulse. A semiconductor laser according to any one of (1) to (8). (10) At the timing at which the Q-switching operation is induced in the absorption region, which is delayed from the timing at which the pulse current is applied to the gain region, as the time difference increases, the peak wavelength of the first laser pulse gradually becomes longer, and there is a jump in the peak wavelength of at least 1 nm or more. A semiconductor laser according to any one of (1) to (9). (11) The semiconductor laser according to (1), Light separation unit and Equipped with The first laser pulse and the second laser pulse are separated by the light separating unit. Ranging device. (12) The first laser pulse is a laser pulse that is irradiated toward an object to be measured. A distance measuring device according to (11). (13) A silicon photomultiplier is provided to receive scattered light from the object to be measured. (12) A distance measuring device according to (12). (14) An in-vehicle device having the distance measuring device according to any one of (11) to (13).

[0065] <Application example> Next, application examples of the present disclosure will be described, but the present disclosure is not limited to the application examples described below. The SP method using the semiconductor laser 100 described in one embodiment is capable of highly efficient distance measurement in a range of a dozen centimeters to several tens of meters, and is capable of outputting distance data with a latency of one millisecond or less. Taking advantage of the distance accuracy of millimeters to several millimeters, and the low power consumption and compact size, the following applications are possible.

[0066] For example, placing a distance measuring device 501A using the semiconductor laser 100 of the present disclosure in a corner of a room, as shown in Figure 24, can measure the entire room, allowing it to detect even the slightest movements, such as rapid movement in the room or a finger movement while watching TV on the sofa. This can be used to operate electronic devices such as home appliances, provide interactive gaming experiences, and for security purposes. Furthermore, because scanning SP has very little mutual interference between devices, real-time 3D modeling is possible by measuring distances from two or more directions using multiple distance sensor systems, providing a more realistic interactive experience. Because the SP method can be used even under sunlight, it can also provide an experience of expanding the space shown in Figure 24 into a larger space.

[0067] Figure 25 is a schematic diagram illustrating an application scenario envisioned as a human-centered urban usage scenario. The SP installed in a car CR performs highly accurate distance measurements in real time, making it possible to grasp even the slightest movements, even in narrow places such as intersections and alleys where people are close by. This not only ensures the safety of people H but also supports the smooth operation of the autonomous car CR. SPs grounded on utility poles or street corners can grasp the slightest movements of people passing by without interfering with the flow of people H. The acquired point cloud data allows for privacy-conscious operation. For example, it could function as an information service that predicts people H's movements, detects crimes in advance, or functions as an interface when people intentionally operate public objects. Such movements require the capture of finger movements.

[0068] FIG. 26 is a schematic diagram showing an application example related to photography technology. Even with a lens with a very shallow focal depth, such as that of a large camera, distance measuring device 501A can accurately capture position information of a subject (e.g., person H) to calculate the focal length and focal depth and automatically adjust the lens. This is not limited to this example and can be used in various devices that automatically control distance. For example, the present disclosure can also be applied to machine connections, train couplings, aircraft mid-air refueling, and satellite connections.

[0069] Furthermore, because the ranging device 501A is small and consumes low power, it can also be used for obstacle avoidance in unmanned aircraft such as drones. Drones often face difficult flight conditions, such as forests and underground passages, and the SP, which can output point cloud data in real time, enables fast and safe flight. The SP is also excellent for asset management of structures using drones, as it can acquire point clouds of more than megapoints per second in real time, and its low power consumption makes it possible to inspect many structures in a single flight.

[0070] Real-time SP is well suited to sports. Point clouds of more than megapoints per second can capture minute movements in sports judging and coaching, and real-time interactive experiences can digitize sports movements that were previously sensory. For example, wearing a wearable device that people can experience, such as a piezoelectric element, and communicating information obtained through SP to others in real time can improve understanding. Figure 27 shows an example of a sports image obtained in this way (e.g., golf). Multiple distance sensors enable real-time 3D modeling from all directions, 360 degrees, which can be used in golf, for example, for swing analysis and teaching, as well as injury prevention. Because it can cover distances of several tens of meters, it can be used not only for golf but also for a variety of sports, such as baseball, basketball, tennis, and gymnastics.

[0071] Furthermore, the technology according to the present disclosure is not limited to the above-described application examples and can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, a robot, construction machinery, or agricultural machinery (tractor).

[0072] 28 is a block diagram showing a schematic configuration example of a vehicle control system 7000, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied. The vehicle control system 7000 includes a plurality of electronic control units connected via a communication network 7010. In the example shown in FIG. 28, the vehicle control system 7000 includes a drive system control unit 7100, a body system control unit 7200, a battery control unit 7300, an outside-vehicle information detection unit 7400, an inside-vehicle information detection unit 7500, and an integrated control unit 7600. The communication network 7010 connecting these multiple control units may be an in-vehicle communication network conforming to any standard, such as a Controller Area Network (CAN), a Local Interconnect Network (LIN), a Local Area Network (LAN), or FlexRay (registered trademark).

[0073] Each control unit includes a microcomputer that performs arithmetic processing according to various programs, a memory unit that stores the programs executed by the microcomputer or parameters used in various calculations, and a drive circuit that drives various devices to be controlled. Each control unit includes a network I / F for communicating with other control units via a communication network 7010, and a communication I / F for communicating with devices or sensors inside and outside the vehicle via wired or wireless communication. FIG. 28 illustrates the functional configuration of the integrated control unit 7600, including a microcomputer 7610, a general-purpose communication I / F 7620, a dedicated communication I / F 7630, a positioning unit 7640, a beacon receiving unit 7650, an in-vehicle device I / F 7660, an audio / video output unit 7670, an in-vehicle network I / F 7680, and a memory unit 7690. Similarly, the other control units also include a microcomputer, a communication I / F, a memory unit, and the like.

[0074] The drivetrain control unit 7100 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 7100 functions as a control device for a driving force generating device for generating driving force for the vehicle, such as an internal combustion engine or a drive motor, a driving force transmission mechanism for transmitting driving force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating braking force for the vehicle. The drivetrain control unit 7100 may also function as a control device for an ABS (Antilock Brake System) or an ESC (Electronic Stability Control), etc.

[0075] A vehicle state detection unit 7110 is connected to the drivetrain control unit 7100. The vehicle state detection unit 7110 includes at least one of a gyro sensor that detects the angular velocity of the axial rotational motion of the vehicle body, an acceleration sensor that detects the acceleration of the vehicle, or a sensor that detects the amount of operation of the accelerator pedal, the amount of operation of the brake pedal, the steering angle of the steering wheel, the engine rotation speed, the rotation speed of the wheels, etc. The drivetrain control unit 7100 performs arithmetic processing using signals input from the vehicle state detection unit 7110, and controls the internal combustion engine, the drive motor, the electric power steering device, the brake device, etc.

[0076] Body system control unit 7200 controls the operation of various devices mounted on the vehicle body in accordance with various programs. For example, body system control unit 7200 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as head lamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches may be input to body system control unit 7200. Body system control unit 7200 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0077] The battery control unit 7300 controls the secondary battery 7310, which is the power supply source for the drive motor, in accordance with various programs. For example, information such as battery temperature, battery output voltage, or remaining battery capacity is input to the battery control unit 7300 from a battery device equipped with the secondary battery 7310. The battery control unit 7300 performs arithmetic processing using these signals, and controls the temperature regulation of the secondary battery 7310 or a cooling device or the like provided in the battery device.

[0078] The outside vehicle information detection unit 7400 detects information outside the vehicle equipped with the vehicle control system 7000. For example, at least one of an imaging unit 7410 and an outside vehicle information detection unit 7420 is connected to the outside vehicle information detection unit 7400. The imaging unit 7410 includes at least one of a ToF (Time Of Flight) camera, a stereo camera, a monocular camera, an infrared camera, and other cameras. The outside vehicle information detection unit 7420 includes at least one of an environmental sensor for detecting the current weather or climate, or a surrounding information detection sensor for detecting other vehicles, obstacles, pedestrians, etc. around the vehicle equipped with the vehicle control system 7000.

[0079] The environmental sensor may be, for example, at least one of a raindrop sensor that detects rain, a fog sensor that detects fog, a sunshine sensor that detects the intensity of sunlight, and a snow sensor that detects snowfall. The surrounding information detection sensor may be at least one of an ultrasonic sensor, a radar device, and a LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) device. The imaging unit 7410 and the outside vehicle information detection unit 7420 may each be provided as an independent sensor or device, or may be provided as a device in which multiple sensors or devices are integrated.

[0080] 29 shows an example of the installation positions of the imaging unit 7410 and the vehicle exterior information detection unit 7420. The imaging units 7910, 7912, 7914, 7916, and 7918 are provided, for example, at least one of the front nose, side mirrors, rear bumper, back door, and upper part of the windshield inside the vehicle cabin of the vehicle 7900. The imaging unit 7910 provided on the front nose and the imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 7900. The imaging units 7912 and 7914 provided on the side mirrors mainly acquire images of the sides of the vehicle 7900. The imaging unit 7916 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 7900. The imaging unit 7918 provided on the upper part of the windshield inside the vehicle cabin is mainly used to detect leading vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0081] 29 shows an example of the imaging ranges of the imaging units 7910, 7912, 7914, and 7916. Imaging range a indicates the imaging range of imaging unit 7910 provided on the front nose, imaging ranges b and c indicate the imaging ranges of imaging units 7912 and 7914 provided on the side mirrors, respectively, and imaging range d indicates the imaging range of imaging unit 7916 provided on the rear bumper or back door. For example, by overlaying the image data captured by imaging units 7910, 7912, 7914, and 7916, a bird's-eye view image of vehicle 7900 viewed from above can be obtained.

[0082] The vehicle exterior information detection units 7920, 7922, 7924, 7926, 7928, and 7930 provided on the front, rear, sides, and corners of the vehicle 7900 and above the windshield inside the vehicle cabin may be, for example, ultrasonic sensors or radar devices. The vehicle exterior information detection units 7920, 7926, and 7930 provided on the front nose, rear bumper, back door, and above the windshield inside the vehicle cabin of the vehicle 7900 may be, for example, LIDAR devices. These vehicle exterior information detection units 7920 to 7930 are mainly used to detect preceding vehicles, pedestrians, obstacles, etc.

[0083] Returning to FIG. 28 , the explanation will be continued. The outside-vehicle information detection unit 7400 causes the imaging unit 7410 to capture an image outside the vehicle and receives the captured image data. The outside-vehicle information detection unit 7400 also receives detection information from the connected outside-vehicle information detection unit 7420. If the outside-vehicle information detection unit 7420 is an ultrasonic sensor, a radar device, or a LIDAR device, the outside-vehicle information detection unit 7400 emits ultrasonic waves or electromagnetic waves and receives information on the received reflected waves. The outside-vehicle information detection unit 7400 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, text on the road, etc. based on the received information. The outside-vehicle information detection unit 7400 may also perform environment recognition processing for recognizing rainfall, fog, road conditions, etc. based on the received information. The outside-vehicle information detection unit 7400 may also calculate the distance to an object outside the vehicle based on the received information.

[0084] The outside vehicle information detection unit 7400 may also perform image recognition processing or distance detection processing to recognize people, vehicles, obstacles, signs, characters on the road, etc., based on the received image data. The outside vehicle information detection unit 7400 may perform processing such as distortion correction or alignment on the received image data, and may also generate an overhead image or a panoramic image by combining image data captured by different image capturing units 7410. The outside vehicle information detection unit 7400 may also perform viewpoint conversion processing using image data captured by different image capturing units 7410.

[0085] The interior information detection unit 7500 detects information inside the vehicle. A driver state detection unit 7510 that detects the state of the driver is connected to the interior information detection unit 7500, for example. The driver state detection unit 7510 may include a camera that captures an image of the driver, a biosensor that detects the driver's biometric information, or a microphone that collects audio from within the vehicle cabin. The biosensor is provided, for example, on the seat or steering wheel, and detects biometric information of a passenger sitting in the seat or the driver gripping the steering wheel. The interior information detection unit 7500 may calculate the driver's level of fatigue or concentration, or may determine whether the driver is dozing, based on the detection information input from the driver state detection unit 7510. The interior information detection unit 7500 may perform processing such as noise canceling on the collected audio signal.

[0086] The integrated control unit 7600 controls the overall operation of the vehicle control system 7000 in accordance with various programs. An input unit 7800 is connected to the integrated control unit 7600. The input unit 7800 may be implemented by a device that can be operated by a passenger, such as a touch panel, a button, a microphone, a switch, or a lever. Data obtained by voice recognition of a voice input through a microphone may be input to the integrated control unit 7600. The input unit 7800 may be, for example, a remote control device using infrared or other radio waves, or an externally connected device such as a mobile phone or a personal digital assistant (PDA) that can operate the vehicle control system 7000. The input unit 7800 may be, for example, a camera, in which case the passenger can input information by gestures. Alternatively, data obtained by detecting the movement of a wearable device worn by the passenger may be input. Furthermore, the input unit 7800 may include, for example, an input control circuit that generates an input signal based on information input by the passenger or the like using the input unit 7800 and outputs the input signal to the integrated control unit 7600. By operating this input unit 7800, passengers and the like input various data to the vehicle control system 7000 and instruct processing operations.

[0087] The storage unit 7690 may include a ROM (Read Only Memory) that stores various programs executed by the microcomputer, and a RAM (Random Access Memory) that stores various parameters, calculation results, sensor values, etc. The storage unit 7690 may also be realized by a magnetic storage device such as an HDD (Hard Disc Drive), a semiconductor storage device, an optical storage device, a magneto-optical storage device, or the like.

[0088] The general-purpose communication I / F 7620 is a general-purpose communication I / F that mediates communication between various devices present in the external environment 7750. The general-purpose communication I / F 7620 may implement a cellular communication protocol such as GSM (Global System of Mobile communications), WiMAX (registered trademark), LTE (Long Term Evolution), or LTE-Advanced (LTE-A), or other wireless communication protocols such as wireless LAN (also referred to as Wi-Fi (registered trademark)) or Bluetooth (registered trademark). The general-purpose communication I / F 7620 may connect to devices (e.g., application servers or control servers) present on an external network (e.g., the Internet, a cloud network, or an operator-specific network) via, for example, a base station or an access point. The general-purpose communication I / F 7620 may also connect to terminals present near the vehicle (e.g., terminals of drivers, pedestrians, or stores, or machine-type communication (MTC) terminals) using, for example, P2P (Peer to Peer) technology.

[0089] The dedicated communication I / F 7630 is a communication I / F that supports a communication protocol designed for use in vehicles. The dedicated communication I / F 7630 may implement a standard protocol such as WAVE (Wireless Access in Vehicle Environment), which is a combination of a lower layer IEEE802.11p and an upper layer IEEE1609, a dedicated short range communications (DSRC), or a cellular communication protocol. The dedicated communication I / F 7630 typically performs V2X communication, which is a concept including one or more of vehicle-to-vehicle communication, vehicle-to-infrastructure communication, vehicle-to-home communication, and vehicle-to-pedestrian communication.

[0090] The positioning unit 7640 performs positioning by receiving, for example, GNSS signals from GNSS (Global Navigation Satellite System) satellites (for example, GPS signals from GPS (Global Positioning System) satellites), and generates position information including the latitude, longitude, and altitude of the vehicle. Note that the positioning unit 7640 may identify the current position by exchanging signals with a wireless access point, or may obtain position information from a terminal such as a mobile phone, PHS, or smartphone that has a positioning function.

[0091] The beacon receiver 7650 receives, for example, radio waves or electromagnetic waves transmitted from radio stations or the like installed on the road, and acquires information such as the current location, congestion, road closures, required travel time, etc. The function of the beacon receiver 7650 may be included in the dedicated communication I / F 7630 described above.

[0092] The in-vehicle device I / F 7660 is a communication interface that mediates connections between the microcomputer 7610 and various in-vehicle devices 7760 present in the vehicle. The in-vehicle device I / F 7660 may establish wireless connections using wireless communication protocols such as wireless LAN, Bluetooth (registered trademark), NFC (Near Field Communication), or WUSB (Wireless USB). The in-vehicle device I / F 7660 may also establish a wired connection such as a Universal Serial Bus (USB), a High-Definition Multimedia Interface (HDMI (registered trademark), or a Mobile High-Definition Link (MHL)) via a connection terminal (and a cable, if necessary) not shown. The in-vehicle device 7760 may include, for example, at least one of a mobile device or a wearable device owned by a passenger, or an information device carried into or attached to the vehicle. The in-vehicle device 7760 may also include a navigation device that searches for a route to an arbitrary destination. The in-vehicle device I / F 7660 exchanges control signals or data signals with these in-vehicle devices 7760.

[0093] The in-vehicle network I / F 7680 is an interface that mediates communication between the microcomputer 7610 and the communication network 7010. The in-vehicle network I / F 7680 transmits and receives signals in accordance with a predetermined protocol supported by the communication network 7010.

[0094] The microcomputer 7610 of the integrated control unit 7600 controls the vehicle control system 7000 in accordance with various programs based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. For example, the microcomputer 7610 may calculate control target values ​​for the driving force generating device, the steering mechanism, or the braking device based on acquired information inside and outside the vehicle, and output control commands to the drivetrain control unit 7100. For example, the microcomputer 7610 may perform cooperative control aimed at realizing functions of an Advanced Driver Assistance System (ADAS), including vehicle collision avoidance or impact mitigation, following driving based on the following distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc. In addition, the microcomputer 7610 may perform cooperative control for the purpose of autonomous driving, in which the vehicle travels autonomously without relying on driver operation, by controlling a driving force generating device, a steering mechanism, a braking device, etc. based on information acquired about the vehicle's surroundings.

[0095] The microcomputer 7610 may generate three-dimensional distance information between the vehicle and objects such as surrounding structures and people, and create local map information including information about the vicinity of the vehicle's current location, based on information acquired via at least one of the general-purpose communication I / F 7620, the dedicated communication I / F 7630, the positioning unit 7640, the beacon receiving unit 7650, the in-vehicle device I / F 7660, and the in-vehicle network I / F 7680. Furthermore, the microcomputer 7610 may predict dangers, such as a vehicle collision, the approach of a pedestrian, or entry into a closed road, based on the acquired information, and generate a warning signal. The warning signal may be, for example, a signal for generating a warning sound or turning on a warning lamp.

[0096] The audio / video output unit 7670 transmits at least one of audio and image output signals to an output device capable of visually or audibly notifying vehicle occupants or the outside of the vehicle of information. In the example of FIG. 28 , an audio speaker 7710, a display unit 7720, and an instrument panel 7730 are illustrated as output devices. The display unit 7720 may include, for example, at least one of an on-board display and a head-up display. The display unit 7720 may have an AR (Augmented Reality) display function. The output device may be other devices besides these devices, such as headphones, a wearable device such as an eyeglass-type display worn by the occupant, a projector, or a lamp. When the output device is a display device, the display device visually displays results obtained by various processes performed by the microcomputer 7610 or information received from other control units in various formats, such as text, images, tables, and graphs. When the output device is an audio output device, the audio output device converts audio signals consisting of reproduced audio data or acoustic data into analog signals and audibly outputs the analog signals.

[0097] In the example shown in FIG. 28 , at least two control units connected via the communication network 7010 may be integrated into one control unit. Alternatively, each control unit may be composed of multiple control units. Furthermore, the vehicle control system 7000 may include another control unit not shown. In the above description, some or all of the functions performed by one control unit may be performed by another control unit. In other words, as long as information is transmitted and received via the communication network 7010, predetermined arithmetic processing may be performed by one of the control units. Similarly, a sensor or device connected to one control unit may be connected to another control unit, and multiple control units may transmit and receive detection information to and from each other via the communication network 7010.

[0098] In the vehicle control system 7000 described above, the semiconductor laser of the present disclosure can be applied to, for example, the outside-of-vehicle information detection unit. [Explanation of symbols]

[0099] 100... Semiconductor laser 102...gain area 103...Absorption region 105...First laser pulse 106...Second laser pulse 110...Front end surface 113...Separation area 401 Semiconductor substrate 405...Active layer

Claims

1. at least two gain regions and at least two absorption regions formed on a semiconductor substrate; the gain region and the absorption region include a continuous active layer, and the gain region and the absorption region are alternately formed with a separation region interposed therebetween; A first laser pulse having a first polarization is emitted from the front end face, followed by a second laser pulse having a second polarization, the first polarization and the second polarization being orthogonal to each other. Semiconductor laser.

2. At least two gain regions each having a length of 100 μm or less on the optical propagation axis are formed.

2. The semiconductor laser according to claim 1.

3. At least two of the absorption regions are formed, each having a length on the light propagation axis of 100 μm or less.

2. The semiconductor laser according to claim 1.

4. The gain region closest to the rear end face is longer in the cavity direction than the other gain regions.

2. The semiconductor laser according to claim 1.

5. The active layer is a single layer and has a thickness in the range of 100 nm to 250 nm.

2. The semiconductor laser according to claim 1.

6. The guide layer closer to the semiconductor substrate than the active layer has a grated structure and a thickness of at least 1 μm.

2. The semiconductor laser according to claim 1.

7. The guide layers on the semiconductor substrate side and the surface side sandwiching the active layer have a grated structure and a thickness of at least 300 nm or more.

2. The semiconductor laser according to claim 1.

8. the guide layers on the semiconductor substrate side and the surface side sandwiching the active layer have a grated structure; The PN junction of the gain region is at least 100 nm farther from the active layer than the PN junction of the absorption region.

2. The semiconductor laser according to claim 1.

9. The peak wavelength of the first laser pulse is longer than the peak wavelength of the second laser pulse.

2. The semiconductor laser according to claim 1.

10. At the timing at which the Q-switching operation is induced in the absorption region, which is delayed from the timing at which the pulse current is applied to the gain region, as the time difference increases, the peak wavelength of the first laser pulse gradually becomes longer, and there is a jump in the peak wavelength of at least 1 nm or more.

2. The semiconductor laser according to claim 1.

11. The semiconductor laser according to claim 1; Light separation unit and Equipped with The first laser pulse and the second laser pulse are separated by the light separating unit. Ranging device.

12. The first laser pulse is a laser pulse that is irradiated toward an object to be measured. The distance measuring device according to claim 11.

13. A silicon photomultiplier is provided to receive scattered light from the object to be measured.

13. A distance measuring device according to claim 12.

14. An in-vehicle device comprising the distance measuring device according to claim 11.

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