FMCW LiDAR system with a laser light source

Abstract

FMCW LIDAR system (140) with: a laser light source (10), a beam splitter (141) configured to split laser radiation emitted by the laser light source (10) into a reference beam (154) and an object beam (144), and a detector (150) configured to detect a signal resulting from a superposition of the reference beam (154) with a reflected beam (145) resulting from a reflection of the object beam (144) on an object, wherein the laser light source (10) comprises an edge-emitting, first semiconductor laser (100) which is suitable for emitting pump radiation (110) of a single optical mode, an optical system (112) configured to cause beam expansion of the emitted pump radiation (110), and an array (120) of surface-emitting semiconductor lasers (125 1 , 125 2 , ...125 n ), a first voltage source, by means of which a voltage below a threshold voltage of the surface-emitting semiconductor lasers can be applied to the arrangement (120) of surface-emitting semiconductor lasers, wherein the arrangement (120) of surface-emitting semiconductor lasers is suitable for absorbing the pump radiation (110) and emitting laser radiation (130) with an emission wavelength via the injection-locking mechanism, wherein the wavelength of the pump radiation and the emission wavelength can be modulated by changing a current intensity impressed into the first semiconductor laser (100), and a second voltage source by means of which a variable voltage can be applied to the first semiconductor laser (100) so that the current intensity that can be impressed into the first semiconductor laser (100) can be varied.

Description

[0001] This patent application claims priority from German patent application DE 10 2019 133 797.6, the disclosure of which is hereby incorporated by reference.

[0002] LIDAR systems, particularly FMCW (Frequency Modulated Continuous Wave Light Detection and Ranging) LIDAR systems, are increasingly being used in vehicles, for example, for autonomous driving. They are used, for example, to measure distances or detect objects. To reliably detect objects at greater distances, laser light sources with correspondingly high power are required. For this reason, concepts are being developed that can increase the available laser power of so-called single-mode lasers, i.e., lasers that emit light at a single wavelength (single mode).

[0003] In the paper Yifat, Y;ua: “Dynamical trapping of light in coupled laser arrays: slow or fast?”; In: Proc. SPIE, Vol. 8273, Advances in Slow and Fast Light V, 827305 (8 February 2012) an experimental setup with coupled VCSELs is described.

[0004] Further light sources are known, for example, from the documents DE 10 2007 011 804 A1, US 2016 / 0 164 258 A1, US 2019 / 0 302 262 A1, DE 198 11 032 A1 and DE 199 48 353 A1.

[0005] The present invention is based on the object of providing an improved LIDAR system.

[0006] According to one embodiment, the object is achieved by the subject matter of the independent patent claims. Advantageous further developments are defined in the dependent patent claims.

[0007] A laser light source comprises a first semiconductor laser capable of emitting pump radiation and an array of surface-emitting semiconductor lasers capable of absorbing the pump radiation and emitting laser radiation at a frequency of the pump radiation.

[0008] The first semiconductor laser may be an edge-emitting laser capable of emitting pump radiation of a single optical mode.

[0009] For example, the laser light source may be capable of emitting laser radiation of a single optical mode. A frequency of the optical mode may be modulated.

[0010] For example, the array may contain more than 100 surface-emitting semiconductor lasers.

[0011] The laser light source may further include a polarization-rotating element disposed between the first semiconductor laser and a portion of the surface-emitting semiconductor lasers. For example, apertures of the surface-emitting semiconductor lasers may be formed in an elliptical shape. For example, the apertures formed in an elliptical shape may be oriented in different directions.

[0012] In the laser light source, the laser radiation may have a power greater than 100 mW.

[0013] Embodiments relate to a LIDAR system with the laser light source as defined above.

[0014] For example, in the LIDAR system, a beam splitter may be disposed between the first semiconductor laser and the arrangement of surface-emitting semiconductor lasers.

[0015] The accompanying drawings provide an understanding of embodiments of the invention. The drawings illustrate embodiments and, together with the description, serve to explain the same. Other embodiments and many of the intended advantages will become apparent from the following detailed description. The elements and structures shown in the drawings are not necessarily to scale. Like reference numerals refer to like or corresponding elements and structures. Fig. 1 schematically illustrates the structure of a laser light source. Fig. Figure 2A schematically illustrates the structure of another laser light source. Fig. Figure 2B schematically illustrates the structure of another laser light source. Fig. Figure 3A shows a schematic top view of a laser array. Fig. Figure 3B shows a schematic top view of another laser arrangement. Fig. 4 shows an example of an optical system using the described laser light source. Fig. 5A shows a schematic structure of a LIDAR system according to embodiments. Fig. 5B illustrates a portion of the LIDAR system according to embodiments.

[0016] In the following detailed description, reference is made to the accompanying drawings, which form a part of the disclosure, and in which, for purposes of illustration, specific embodiments are shown. In this context, directional terminology such as "top," "bottom," "front," "back," "over," "on," "in front of," "behind," "fore," "rear," etc., refers to the orientation of the figures just described. Because the components of the embodiments can be positioned in different orientations, the directional terminology is for the purpose of explanation only and is not limiting in any way.

[0017] The description of the embodiments is not limiting, as other embodiments exist and structural or logical changes may be made without departing from the scope defined by the claims. In particular, elements of embodiments described below may be combined with elements of other described embodiments, unless the context indicates otherwise.

[0018] The terms "wafer" or "semiconductor substrate" used in the following description may encompass any semiconductor-based structure having a semiconductor surface. Wafer and structure are understood to include doped and undoped semiconductors, epitaxial semiconductor layers, optionally supported by a base support, and other semiconductor structures. For example, a layer of a first semiconductor material may be grown on a growth substrate of a second semiconductor material, for example, a GaAs substrate, a GaN substrate, or a Si substrate, or of an insulating material, for example, a sapphire substrate.

[0019] Depending on the intended use, the semiconductor can be based on a direct or indirect semiconductor material. Examples of semiconductor materials particularly suitable for generating electromagnetic radiation include, in particular, nitride semiconductor compounds, which can generate ultraviolet, blue, or longer-wavelength light, such as GaN, InGaN, AlN, AlGaN, AlGaInN, AlGaInBN; phosphide semiconductor compounds, which can generate green or longer-wavelength light, such as GaAsP, AlGaInP, GaP, AlGaP; and other semiconductor materials such as GaAs, AlGaAs, InGaAs, AlInGaAs, SiC, ZnSe, ZnO, Ga 2 O 3, diamond, hexagonal BN, and combinations of the above materials. The stoichiometric ratio of the compound semiconductor materials can vary. Other examples of semiconductor materials may include silicon, silicon-germanium, and germanium. In the context of this description, the term "semiconductor" also includes organic semiconductor materials.

[0020] The term “substrate” generally includes insulating, conductive or semiconductor substrates.

[0021] The terms "lateral" and "horizontal," as used in this specification, are intended to describe an orientation or alignment that is substantially parallel to a first surface of a substrate or semiconductor body. This may, for example, be the surface of a wafer or a chip (die).

[0022] The horizontal direction can, for example, lie in a plane perpendicular to a growth direction when growing layers.

[0023] The term "vertical" as used in this description is intended to describe an orientation that is substantially perpendicular to the first surface of a substrate or semiconductor body. The vertical direction may, for example, correspond to a growth direction during layer growth.

[0024] Where the terms "have," "contain," "comprise," "have," and the like are used herein, these are open terms that indicate the presence of the elements or characteristics in question, but do not exclude the presence of other elements or characteristics. The indefinite and definite articles include both the plural and the singular, unless the context clearly indicates otherwise.

[0025] In the context of this description, the term "electrically connected" means a low-resistance electrical connection between the connected elements. The electrically connected elements do not necessarily have to be directly connected to each other. Additional elements may be arranged between the electrically connected elements.

[0026] The term “electrically connected” also includes tunnel contacts between the connected elements.

[0027] Fig. 1 shows a laser light source 10. The laser light source 10 comprises a first laser 100 capable of emitting pump radiation 110. The laser light source further comprises an array 120 of surface-emitting semiconductor lasers capable of absorbing the pump light 110 and emitting laser light 130. In this way, the array 120 of surface-emitting lasers can be coherently excited by the pump radiation 110 emitted by the first laser 100 and emit laser radiation 130 that is highly amplified compared to the originally emitted pump radiation 110. Accordingly, a semiconductor laser can be provided that is capable of emitting high laser power while still having a simple and cost-effective design.

[0028] The first laser 100 can be, for example, a semiconductor laser. The first semiconductor laser can, for example, have a first semiconductor layer 102, for example of a first conductivity type, for example p-type, and a second semiconductor layer of a second conductivity type, for example n-type. An active zone 130 can be arranged between the first semiconductor layer 102 and the second semiconductor layer 104. Laser radiation can be generated in the active zone 103.

[0029] The active zone 103 can, for example, have a pn junction, a double heterostructure, a single quantum well (SQW), or a multi-quantum well (MQW) structure for radiation generation. The term "quantum well structure" has no significance with regard to the dimensionality of the quantization. It thus includes, among other things, quantum wells, quantum wires, and quantum dots, as well as any combination of these layers.

[0030] The first semiconductor laser 100 can be a so-called edge emitter, in which generated laser radiation is emitted via a side surface 101 that is perpendicular, for example, to a growth direction of the individual semiconductor layers. By applying a suitable voltage between the first semiconductor layer 102 and the second semiconductor layer 104, pump radiation 110 can be generated, which is emitted via the side surface 101.

[0031] The array 120 of surface-emitting semiconductor lasers can, for example, be formed in a substrate 121 that is transparent to the pump radiation 101. A plurality of individual surface-emitting semiconductor lasers or VCSELs (“Vertical Cavity Surface Emitting Lasers”) 125 1 , 125 2 , ...,125 n is formed in a first main surface 124 of the substrate 121. The structure of surface-emitting semiconductor lasers is known and will therefore not be described in detail here. To manufacture the surface-emitting semiconductor lasers, layers for forming an optical resonator and the active zone are applied over a surface of the substrate 121 facing away from the second main surface 123. The active zone of the surface-emitting semiconductor laser 125 can be constructed similarly or identically to the active zone of the first semiconductor laser 110.

[0032] The pump radiation 110 can, for example, enter the array 120 of surface-emitting semiconductor lasers via the second main surface 123. As a result, laser light 130 is emitted. A voltage is applied to the array 120 of surface-emitting semiconductor lasers such that an operating current is below the threshold current of the array of surface-emitting semiconductor lasers. The voltage is set such that self-emission of the surface-emitting semiconductor lasers is prevented. In particular, it is set such that only induced emission occurs via the so-called injection-locking mechanism.

[0033] If the arrangement of surface-emitting semiconductor lasers is now excited by the pump radiation 110, the individual surface-emitting semiconductor lasers 125 emit 1 , 125 2 , ...,125 nLaser light with the same wavelength and polarization direction as the irradiated pump radiation 110. Due to the injection locking mechanism, the same wavelength can be achieved even if the active zone of the arrangement 120 of surface-emitting semiconductor lasers is not entirely identical to the active zone 103 of the first semiconductor laser 100.

[0034] For example, the arrangement 120 of surface-emitting semiconductor lasers has more than 10 x 10 individual emitters, each of which can emit approximately 10 mW, for example. The individual surface-emitting semiconductor lasers can each be identical in structure. The first semiconductor laser 100 can, for example, be a DFB ("Distributed Feedback") or DBR ("Distributed Brack Reflector") laser. This makes it possible for the first semiconductor laser 100 to emit a single laser mode. For example, an emission frequency of the first semiconductor laser 100 can be changed. For example, frequency modulation can be carried out by changing the operating current of the first semiconductor laser 100 in the µA range. Changing the impressed current strength results in a different refractive index and thus a different emission frequency.By controlling the voltage applied to the first semiconductor laser, frequency modulation in a wavelength range of, for example, 10 to 15 nm can be achieved. According to further examples, an external frequency modulator, for example a Mach-Zehnder modulator, can also be used. When the frequency of the pump radiation 110 changes, the frequency of the laser radiation 130 emitted by the arrangement 120 of surface-emitting semiconductor lasers changes due to the injection locking effect. Depending on the applied pump power, the operating current of the arrangement 120 of surface-emitting semiconductor lasers can be suitably adjusted to support the emission of the desired laser radiation.

[0035] Fig. 2A shows a schematic view of a laser light source 10 according to further examples. Deviating from the Fig. In the laser light source shown in Figure 1, the first semiconductor laser 100 is embodied as a DFB or DBR laser. This is indicated by the structuring 106 of the active zone 103.

[0036] Typically, the laser radiation emitted by a single-mode laser is linearly polarized. Generally, individual surface-emitting semiconductor lasers emit 125 1 , 125 2 , ..., 125 n , which are excited with the pump radiation 110, in the same polarization direction with which they are excited. On the other hand, objects can reflect polarization-selectively. Accordingly, irradiation with a single polarization direction can falsify a measurement result. For this reason, for example, a polarization-changing device, such as a λ / 2 plate 128, can be placed in the beam path, so that for some of the surface-emitting semiconductor lasers 125 1 , 125 2 ,...125n the polarization direction of linearly polarized light is changed by, for example, 90°, as in Fig. 2A is illustrated.

[0037] Fig. Figure 2B shows a further modification of the laser light source, in which an optical isolator 108 is arranged between the first semiconductor laser 100 and the array 120 of surface-emitting semiconductor lasers. The presence of the optical isolator 108 prevents laser radiation emitted by the array 120 in the direction of the first semiconductor laser 100 from re-entering the first semiconductor laser and thus influencing it.

[0038] Fig. 3A shows a plan view of a first main surface 124 of the arrangement 120 of surface-emitting semiconductor lasers 125 1 , 125 2 , ..., 125 nFor example, an aperture or opening 126 of the individual surface-emitting semiconductor lasers can be circular and thus isotropic.

[0039] As in Fig. 3B, the aperture 126 can also be elliptical. This allows the polarization direction of the emitted laser radiation relative to the pump radiation 110 to be changed. For example, some of the apertures 126 can have an orientation of the ellipses in the x-direction. Furthermore, another part of the surface-emitting semiconductor lasers can have an orientation of the aperture in the y-direction. In this way, the light emitted by the laser light source can have different polarization directions. According to further examples, the elliptical apertures can also be randomly aligned. In particular, they can be aligned in directions that are different from the x- or y-direction.

[0040] According to further examples, the Fig. 3B also in conjunction with a polarization-changing device 128 as shown in Fig. 2A. The polarization-changing device 128 can be positioned in the beam path in front of surface-emitting semiconductor lasers with a similar aperture orientation.

[0041] Fig. Figure 4 shows a schematic view of an optical system with the described laser light source 10. The laser light source again comprises the first semiconductor laser 100, as well as the arrangement 120 of surface-emitting semiconductor lasers. For example, a first optical system 112 can be arranged to, for example, cause a beam expansion of the emitted pump radiation 110. Furthermore, a mirror 116 can be provided which deflects the emitted pump radiation 110. In addition, the optical system can have a second optical system 114, which is suitable for further modifying the emitted laser radiation. For example, the second optical system 114 can comprise a collimator. The laser radiation thus generated can then be further used in a suitable manner and, for example, fed to a scanning mirror. As in Fig. As shown in Figure 4, the generated laser radiation can also be emitted via the second main surface 123 of the substrate 121 in which the arrangement 120 of surface-emitting lasers is formed. This means that the arrangement 120 is arranged such that the first main surface 124 faces the first semiconductor laser 100. In this case, the emitted laser radiation is emitted through the substrate 120. The substrate 120 can, for example, be a GaAs substrate and be transparent to the emitted laser radiation. For example, the pump radiation 110 emitted by the first semiconductor laser 100, and thus also the laser radiation emitted by the laser light source, can have a wavelength of 940 nm.

[0042] Fig. 5A shows an example of a LIDAR system, in particular an FMCW LIDAR system, in which the described laser light source 10 can be used. The laser radiation emitted by the laser light source 10 is split by a beam splitter 141 into a reference beam 154 and an object beam 144. The LIDAR system can, for example, have a frequency shifter 142 that can shift the emission frequency. As described, frequency modulation can also be achieved, for example, by changing a frequency emitted by the first semiconductor laser. The object beam is irradiated onto an object 156 and reflected by it. This creates the reflected beam 145. The reflected beam 145 is suitably shaped by receiving optics 143 and a collimator 147 and fed to a detector 150 via mirrors 146 and further optics 149.The reference beam 154 is fed directly to the detector 150 via mirror 146 and optics 149 without having been previously reflected by the object 156. When the reflected beam 145 is superimposed on the reference beam 154, which are coherent with each other, a signal is generated at the detector from which, for example, the distance and other information about the detected object can be evaluated. Because, as described above, a frequency of the emitted pump radiation and thus of the radiation emitted by the laser light source can be modulated, the frequency shifter 142 can be omitted.

[0043] When integrating the described laser light source 10 into the Fig. According to one embodiment, the LIDAR system shown in Figure 5A can have the beam splitter 141 arranged behind the array 120 of surface-emitting semiconductor lasers. However, according to further embodiments, the beam splitter 141 can also be arranged directly behind the first semiconductor laser 100 and in the radiation direction in front of the array 120 of surface-emitting semiconductor lasers. This is described in more detail in Fig. 5B, in which both positions of the beam splitter 141 are shown as examples.

[0044] As described above, it is possible to provide a laser light source capable of emitting a single mode at high output power. At the same time, the laser light source has a compact and cost-effective design. By changing the frequency of the emitted pump radiation, the frequency emitted by the laser light source can also be modulated. Due to injection locking, noise can be reduced.

[0045] Although specific embodiments have been illustrated and described herein, those skilled in the art will recognize that the specific embodiments shown and described may be replaced by a variety of alternative and / or equivalent configurations. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. LIST OF REFERENCE SYMBOLS 10 Laser light source 100 first semiconductor lasers 101 side surface 102 first semiconductor layer 103 active zone 104 second semiconductor layer 106 Structuring 108 optical isolator 110 Pump radiation 112 first optical system 114 second optical system 116 mirrors 120 VCSEL array 121 Substrat 123 second main surface 124 first main surface 125 1 , 125 2 ,...125 n surface-emitting semiconductor laser 126 aperture 128 1 / 2 tiles 130 laser radiation 140 FMCW system 141 beam splitters 142 frequency shifters 143 Receiving optics 144 Object beam 145 reflected beam 146 mirrors 147 Collimator 149 Optics 150 detector 154 Reference beam 156 Object

Claims

[1] FMCW LIDAR system (140) with: a laser light source (10), a beam splitter (141) configured to split laser radiation emitted by the laser light source (10) into a reference beam (154) and an object beam (144), and a detector (150) configured to detect a signal resulting from a superposition of the reference beam (154) with a reflected beam (145) resulting from a reflection of the object beam (144) on an object, wherein the laser light source (10) comprises an edge-emitting, first semiconductor laser (100) which is suitable for emitting pump radiation (110) of a single optical mode, an optical system (112) configured to cause beam expansion of the emitted pump radiation (110), and an arrangement (120) of surface-emitting semiconductor lasers (1251, 1252, ...125 n ), a first voltage source, by means of which a voltage below a threshold voltage of the surface-emitting semiconductor lasers can be applied to the arrangement (120) of surface-emitting semiconductor lasers, wherein the arrangement (120) of surface-emitting semiconductor lasers is suitable for absorbing the pump radiation (110) and emitting laser radiation (130) with an emission wavelength via the injection-locking mechanism, wherein the wavelength of the pump radiation and the emission wavelength can be modulated by changing a current intensity impressed into the first semiconductor laser (100), and a second voltage source by means of which a variable voltage can be applied to the first semiconductor laser (100) so that the current intensity that can be impressed into the first semiconductor laser (100) can be varied. [2] LIDAR system (140) according to claim 1, wherein the beam splitter (141) is arranged between the first semiconductor laser (100) and the array (120) of surface-emitting semiconductor lasers (1251, 1252, ...125 n ) is arranged. [3] LIDAR system (140) according to claim 1, wherein the beam splitter (141) is arranged on a side of the arrangement (120) of surface-emitting semiconductor lasers (1251, 1252, ...125 n ) is arranged.

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