Projectors for solid-state LIDAR systems

Abstract

The present disclosure relates to a projector for a solid-state LIDAR system for determining the distance to a scene. The projector is configured to illuminate the scene with a discrete spot pattern. The projector includes: a laser array, the laser array including a plurality of discrete solid-state laser sources for simultaneously emitting a first laser beam; a mixing chamber configured to receive and allow propagation of each first laser beam until at least a portion of the light of each first laser beam overlaps with at least a portion of the light of an adjacent first laser beam; a shaping optical system configured to receive the overlapping light of the first laser beam and generate a plurality of second laser beams, so that each second laser beam includes light from a plurality of first laser beams; and a projector lens system for projecting a discrete spot pattern formed by the second laser beam to the scene. The present disclosure also relates to a solid-state LIDAR system including such a projector and a light receiving device for detecting reflected laser light.

Description

Technical Field

[0001] The present disclosure relates to a LIDAR (Light Detection and Ranging) system for determining the distance to a scene by using a laser beam and a time-of-flight (TOF) based sensing system. More specifically, the present disclosure relates to a LIDAR projector for illuminating a scene with a discrete spot pattern. Background Art

[0002] LIDAR systems measure the distance to a scene by illuminating the scene with laser light and by detecting the reflected laser light in a detector, which is usually located near the laser source that emitted the laser light.

[0003] Generally speaking, a LIDAR system includes two main components: a projector configured to illuminate a scene with laser light and a detection system for detecting reflected laser light. Some LIDAR systems use a projector that illuminates a scene with a uniform planar laser light pattern (also called global illumination), and the detection system is correspondingly adapted to determine distance information based on the reflected light after the global illumination. However, the present disclosure relates to a LIDAR system in which a projector illuminates a scene with a discrete laser spot pattern, and in which the detection system is adapted to determine distance information based on the reflected laser light after the spot pattern illumination.

[0004] Most known LIDAR systems use a direct TOF (DToF) detection method. These systems include a powerful pulsed laser operating in the nanosecond pulse range, a mechanical scanning system to scan the pulsed laser beam, and a pulse detector. Systems of this type are currently available from vendors including Velodyne LIDAR of Morgan Hill, California. As an example of an existing system, the Velodyne HDL-64E uses 64 high-power lasers and 64 avalanche diode detectors in a mechanical rotating structure at a speed of 5 to 15 revolutions per second.

[0005] These DToF systems are known to be able to measure distances with high spatial accuracy. However, these systems also have some disadvantages. For example, these systems require lasers with excessively high power levels that cannot be obtained with currently available semiconductor lasers, which have power levels that are several orders of magnitude lower. In addition, the use of mechanical rotating elements for scanning purposes further limits the prospects for miniaturization, reliability and cost reduction of such systems.

[0006] The compactness of LIDAR systems is an important factor for applications in the automotive industry, where the LIDAR system will be coupled to the front windshield or front bumper of the car, for example. In fact, LIDAR systems are a key factor in the development of autonomous driving or driver assistance systems. In this context, LIDAR systems are used to detect obstacles, such as other vehicles or objects in the vehicle's environment.

[0007] In WO2017 / 068199, a solid-state LIDAR system is proposed, which allows a projector and a detection system based on solid-state technology to be placed in a compact housing. The system is based on range-gated detection technology, which is different from DToF technology. The system disclosed in WO2017 / 068199 includes a projector for illuminating a scene with a discrete spot pattern, wherein each spot includes a time sequence of laser pulses. The laser is provided by a solid-state laser forming a compact low-power laser system, and the solid-state laser array is a semiconductor-based laser, also known as a VCSEL. Each laser beam is a pulsed laser beam, including a time sequence of laser pulses. A CMOS-based range-gated detector is used to detect a spot of reflected laser light, which represents a discrete spot pattern reflected by the scene. The detector also includes a control device for accumulating the reflected laser light synchronously with the illumination of the scene. The processing device finally allows the distance to the scene to be calculated based on the accumulated reflected laser light.

[0008] As described in WO2017 / 068199, it is challenging to develop a solid-state projector for a LIDAR system based on discrete spot pattern illumination. In practice, due to the use of different individual laser sources, for example, there are variations in the characteristics of the individual laser sources, including but not limited to variations in intensity, beam divergence, angular irradiance, wavelength, pulse shape, and thermal behavior. This results in the projection of a non-uniform spot pattern in both time and space on the scene. All of these elements will have an impact on the overall performance of the LIDAR system, such as the precision and / or accuracy of distance measurement and the range of distance that can be covered.

[0009] Therefore, there is room for improvement in LIDAR projectors for generating discrete spot patterns. Summary of the invention

[0010] An object of the present disclosure is to provide a robust, reliable, compact and cost-effective projector for illuminating a scene using a discrete spot pattern, and wherein the projector is contemplated for use as part of a solid-state LIDAR system for determining distance with an acceptable spatial accuracy required for specific applications, such as, for example, automotive applications.

[0011] The present disclosure is defined in the appended independent claims. The dependent claims define advantageous embodiments.

[0012] According to one aspect of the present disclosure, a projector for illuminating a scene with a discrete spot pattern is provided.

[0013] Such a projector according to the present disclosure includes a laser array, such as a one-dimensional or two-dimensional laser array, a mixing chamber, a shaping optical system, and a projector lens system.

[0014] The laser array includes a plurality of discrete solid-state laser light sources operative to emit a divergent first laser beam.

[0015] The mixing chamber extends along the main optical axis Z of the projector and is configured to receive and allow each of the first laser beams to diverge until, for each first laser beam, at least a portion of its light overlaps with light of an adjacent first laser beam.

[0016] A mixing chamber is to be understood as a hollow body, wherein the circumferential sides of the mixing chamber form the three-dimensional hollow body. The circumferential sides are the walls of the mixing chamber.

[0017] The shaping optical system is configured to receive overlapping light from the first laser beams emerging from the mixing chamber, preferably refocus the overlapping light, and generate a plurality of discrete second laser beams, wherein each second laser beam includes light from the plurality of first laser beams.

[0018] The projector lens system is configured to receive the second laser beam and project the second laser beam toward the scene, and wherein the projected second laser beam forms a discrete spot pattern.

[0019] Utilizing a projector in accordance with the present disclosure, several of the shortcomings of prior art devices are simultaneously addressed and performance is improved, as will be discussed in greater detail below.

[0020] Advantageously, the mixing of the first laser beams will result in a uniform power field incident on the shaping optical system, which will further result in a more uniform spot pattern formed by the second laser beam, which for example improves the accuracy of a LIDAR system using the present projector to illuminate a scene.

[0021] Furthermore, this mixing will lead to an improved repeatability of the pulse shape and its optical properties projected onto the scene in both the temporal and spatial domains.

[0022] Advantageously, by mixing the laser light of the first laser beams, the quality constraints on solid-state laser light sources (e.g., VCSEL laser light source arrays) can be reduced. In fact, when multiple laser sources are mixed, a failed first laser beam (i.e., a single laser emitter) has little effect on the overall light intensity and light distribution of the second laser beam. It improves the yield, thereby reducing the cost of the VCSEL array, and it also improves the robustness of the LIDAR system.

[0023] Advantageously, small VCSEL chips can be arranged into a one-dimensional or two-dimensional array of VCSEL chips forming a laser array. Each VCSEL chip includes multiple laser emitters. In this way, by using smaller VCSEL chips, the productivity problem of manufacturing large chips is solved and the production cost is reduced.

[0024] Advantageously, by bundling the light intensities of multiple first laser beams to form a second laser beam, the intensity and brightness of the second laser beam can be increased by forming the second laser beam so that the number of the second laser beams is lower than the number of the initial first laser beams. This increases the detection responsibility and range of the system. The intensity and brightness of a laser beam are defined as the optical power per surface area of ​​the spot (e.g., expressed in watts) and the optical power per solid angle (i.e., irradiance), respectively.

[0025] Advantageously, the shaping optical system can be adjusted to tune the spot size of the second laser beam. For example, a large diameter spot size can be used in the forward direction to illuminate the road, while a small diameter spot can be used to illuminate the surrounding environment.

[0026] Advantageously, the projector according to the present disclosure may be part of a LIDAR system in which a range-gated detection technique for detecting reflected laser light is used while maintaining high spatial accuracy, such as that required for automotive applications. In fact, by providing a mixing chamber and a shaping optical system, the coherent light of the various first laser beams is mixed and the resulting second laser beam consists essentially of coherent laser light. As a result, the dominant speckle problem, which leads to spatial inaccuracies as observed by the inventors when using prior art LIDAR systems based on range gating, is greatly reduced.

[0027] In various embodiments, at least a portion of the inner wall of the mixing chamber is a reflective wall for reflecting laser light.

[0028] In various embodiments, the laser light generated by the discrete solid-state laser source laser has a wavelength between 800 nm and 1600 nm.

[0029] In various embodiments, the length H of the mixing chamber is determined so that after the first laser beams propagate through the mixing chamber, 20% or more, preferably 40% or more, more preferably 60% or more of the light of each first laser beam overlaps with the light of the adjacent first laser beam.

[0030] In some embodiments, after propagating through the mixing chamber, 100% of the light of each first laser beam overlaps with the light of an adjacent first laser beam.

[0031] In various embodiments, each laser source is configured to emit the first laser beam at a divergence angle equal to or less than 15°.

[0032] In various embodiments, the solid-state laser sources are grouped into tiles. The tiles then form, for example, a one-dimensional or two-dimensional array of tiles. Each tile consists of a plurality of solid-state laser sources (i.e., emitters). The patch can be interpreted as a subarray of solid-state light sources, such as a one-dimensional or two-dimensional subarray of solid-state light sources. In various embodiments, the length of the mixing chamber measured along the main optical axis is then further defined so that after the first laser beam propagates through the mixing chamber, for each patch, at least a portion of its light overlaps with the light of an adjacent patch. In various embodiments, the patch is a VCSEL chip containing a plurality of laser emitters, and each of the laser emitters will be interpreted as a solid-state laser source.

[0033] In various embodiments, 20% or more, preferably 40% or more, more preferably 60% or more of the light from each patch overlaps with the light from adjacent patches. In some other embodiments, 100% of the laser light from each patch overlaps with the light from adjacent patches.

[0034] Advantageously, cheaper commercial VCSEL chips can be used as the main laser source for generating the first laser beam.

[0035] Advantageously, when using VCSEL patches as the primary laser source, the patches can be connected in series, requiring lower drive current and therefore less heat dissipation. This also reduces system cost and improves system robustness and thermal management.

[0036] In various embodiments, at least a portion of the inner wall of the mixing chamber comprises a mirror. Advantageously, light emitted by the peripheral light sources of the laser array may hit the mirror and be reflected back in the mixing chamber. The mirror helps to obtain a uniform light distribution in a plane perpendicular to the main optical axis.

[0037] In various embodiments, the shaping optical system comprises a microlens array comprising a plurality of microlenses, wherein each microlens is configured to generate a second laser beam.

[0038] In various embodiments, the first microlens array is configured such that each microlens comprises a focus located on a plane or a curved surface, and wherein the plane or the curved surface is located between the first microlens array and the projector lens system.

[0039] In a further embodiment, each microlens of the first microlens array comprises a focus located on a curved surface, and wherein the curved surface corresponds to a curved focal plane of the projector lens system. Advantageously, the projector lens system does not require additional lenses to correct optical aberrations of the projector lens system, more precisely to correct Petzval field curvature.

[0040] In various embodiments, each microlens in the first microlens array comprises a back focus located on a curved surface, and wherein the curved surface corresponds to a curved front focal plane of the projector lens system.

[0041] In some embodiments, each microlens of the first microlens array comprises an optical axis parallel to a principal optical axis of the projector.

[0042] In a preferred embodiment, at least a portion of the microlenses of the first microlens array comprises an optical axis that is not parallel to the main optical axis of the projector. Advantageously, the size of the projector lens system can be reduced. For example, the diameter of the projector lens system can be reduced.

[0043] In various embodiments, each laser source of the laser array has an emission surface located in an emission plane XY, wherein the first laser beam propagates in a direction parallel to a main optical axis Z perpendicular to said emission plane XY.

[0044] In various embodiments, the projector according to the present disclosure further includes a second microlens array configured to reduce the divergence angle of the first laser beam emitted by the solid-state laser source. Preferably, the second microlens array is arranged between the laser array and the first microlens array.

[0045] In a preferred embodiment, the number of microlenses in the first microlens array is less than the number of solid-state laser sources of the laser array. Generally speaking, the number of microlenses of the first microlens array is selected according to the required number of spots provided for the discrete spot pattern.

[0046] In some embodiments, where the laser array is formed of a plurality of VCSEL chips, and where the projector includes a second microlens array, the number of microlenses in the second microlens array is equal to or less than the total number of emitters of the laser array. The total number of emitters of the laser array is the sum of all emitters in each VCSEL chip of the laser array.

[0047] In other embodiments, the projector also includes any one or any combination of a diffuser, a circulator, a Bragg volume grating, and a beam expander.

[0048] Advantageously, in particular for embodiments of the projector comprising a beam expander, it is possible to use a patch-based array without being adversely affected by the seams that inevitably exist between the patches. In practice, the beam expander is configured to increase the illumination in the inter-patch region so as to increase the uniformity of the light distribution incident on the first microlens array.

[0049] According to yet another aspect of the present disclosure, a solid-state LIDAR system for determining distances to one or more objects of a scene is provided.

[0050] In addition to the projector discussed above, such a solid-state LIDAR system also includes a light receiving device including a multi-pixel detector (e.g., a range-gated or direct time-of-flight type detector) configured to detect reflected laser light spots representing a discrete light spot pattern reflected by one or more objects of the scene, a controller for controlling the projector and the light receiving device so as to detect and accumulate reflected laser light in synchronization with illumination of the scene, and a processing device configured to calculate the distance to one or more objects of the scene based on the accumulated reflected laser light.

[0051] In some embodiments based on the range-gated detection technique, the solid-state LIDAR system is configured to detect reflected laser light during at least two consecutive detection time windows, and the processing device is configured to calculate the distance to the object based on the laser light detected during the two consecutive detection time windows.

[0052] In an embodiment based on the range gated detection technique, a controller of the solid-state LIDAR system is configured to control the laser array so that each of the plurality of discrete solid-state laser sources emits a first pulse at a pulse frequency such that F P ≤1 / (TOF max +PW), where F P is the pulse frequency, PW is the time pulse width, TOF max is the predetermined maximum distance D to the object to be determined max The maximum flight time of the LIDAR system can be interpreted as the maximum operating range of the LIDAR system. For example, the maximum operating range can be a value between 50 and 500 meters.

[0053] In some embodiments, the inter-patch spacing (Δ T ) is equal to or greater than 0.3 mm, and wherein for each patch, the spacing distance (Δ VCSEL ) is equal to or less than 0.1 mm.

[0054] In various embodiments, the processing device comprises a processor or a microprocessor.

[0055] In various embodiments, a projector lens system of a projector includes a projector lens, such as an objective lens.

[0056] In various embodiments, one or more optical laser reflecting elements are located in the mixing chamber for extending the travel path of the first laser beam. Advantageously, the length of the mixing chamber can be reduced while maintaining adequate mixing of the first laser beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] These and other aspects of the present disclosure will be explained in more detail by way of example and with reference to the accompanying drawings, in which:

[0058] Figure 1 Schematically illustrates a LIDAR system according to the present disclosure,

[0059] Figure 2 Schematically shows the discrete spot pattern projected on the scene,

[0060] Figure 3 Schematically shows the time sequence of pulses forming a pulsed laser beam,

[0061] Figure 4 schematically shows the repetition of multiple frames,

[0062] Figure 5 Schematically shows a cross-sectional view of a projector according to various embodiments of the present disclosure,

[0063] Figure 6 Schematic illustration of the VCSEL patch geometry,

[0064] Figure 7 schematically illustrates a concept for mixing first laser beams to form second laser beams according to the present disclosure,

[0065] Figure 8 A cross-sectional view of a projector according to various embodiments of the present disclosure is schematically shown, wherein the projector includes a VCSEL patch laser array,

[0066] Fig. 9 Schematically shows a cross-sectional view of a portion of a projector according to an embodiment of the present disclosure, the projector comprising a microlens array, wherein the focal points are located on a curved surface,

[0067] Fig.10 Schematically shows a cross-sectional view of a portion of a projector according to yet another embodiment of the present disclosure, the projector comprising a microlens array, wherein the focal points are located on a curved surface,

[0068] Fig.11 schematically shows a cross-sectional view of a projector comprising an array of microlenses, wherein each microlens has an optical axis parallel to the main optical axis of the projector,

[0069] Fig.12 schematically shows a portion of a projector including a front-emitting VCSEL laser array,

[0070] Fig.13 Schematic diagram of the back-end emitting VCSEL laser array,

[0071] Figure 14a to Figure 14h schematically shows a cross section of various embodiments of a projector according to the present disclosure,

[0072] Fig.15a and Fig.15b Schematically shows the Fig.14b The optical effect of the second microlens array is shown.

[0073] Fig.16a and Fig.16b Schematically shows Fig.14f A possible implementation of a beam expander is shown in,

[0074] Fig.17a and Fig.17b Two embodiments of a mixing chamber are schematically shown,

[0075] Fig.18 schematically shows an embodiment of a circulator,

[0076] Fig.19 The working principle of the diffuser is shown schematically.

[0077] The drawings of these figures are neither to scale nor to proportion. In general, in the drawings, like components are represented by like reference numerals. DETAILED DESCRIPTION

[0078] The present disclosure will be described according to specific embodiments, which are illustrative embodiments of the present disclosure and should not be construed as limiting. It will be understood by those skilled in the art that the present disclosure is not limited by the content specifically shown and / or described, and that alternative or modified embodiments can be developed based on the overall teaching of the present disclosure. The drawings described are only schematic and non-limiting.

[0079] Use of the verb "comprise" and its conjugations does not exclude the presence of elements other than the stated elements. Use of the article "a", "an" or "the" preceding an element does not exclude the presence of a plurality of such elements.

[0080] In addition, the terms first, second, etc. in the specification and in the claims are used to distinguish between similar elements and are not necessarily used to describe order in time, space, in ranking or in any other manner. It should be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the present disclosure described herein are capable of operation in sequences other than those described or illustrated herein.

[0081] Throughout this specification, references to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in one or more embodiments of the present disclosure. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. Furthermore, in one or more embodiments, as will be apparent to one of ordinary skill in the art from this disclosure, the particular features, structures, or characteristics may be combined in any suitable manner.

[0082] According to one aspect of the present disclosure, a projector for illuminating a scene with a discrete light spot pattern is provided. Such a projector can be used, for example, in a solid-state LIDAR system to determine the distance to the scene. Figure 5 , Figures 8 to 11 and Figure 14a to Figure 14h Cross-sectional views of various embodiments of a projector according to the present disclosure are shown. These various embodiments will be discussed further below.

[0083] When used in a LIDAR system, embodiments of the projector of the present disclosure provide advantages of improving the accuracy and precision of the LIDAR system. As used herein and with reference to the LIDAR system, the term "accuracy" refers to the difference between the mean of the distance measurement and the actual distance, wherein a higher accuracy corresponds to a smaller difference; the term "precision" refers to the spread of the distance measurement around the mean (expressed as a standard deviation or equivalent measure), and thus, a higher precision corresponds to a smaller spread.

[0084] Without loss of generality, the following will describe the projector of the present disclosure with reference to its application in a LIDAR system. The LIDAR system may, for example, operate based on the direct time of flight (DToF) principle or based on range gating or based on any other distance determination method. It will be appreciated by those skilled in the art that the projector system of the present disclosure may also be used in other metrology and telemetry systems, such as but not limited to a displacement-based ranging system. The projector system of the present disclosure may also be used in non-telemetry applications.

[0085] Solid-State LIDAR Systems, Overview

[0086] A LIDAR system must be interpreted as any system that measures the distance to one or more objects in a scene by illuminating the scene with a laser and measuring the reflected laser with a detector. However, the present disclosure relates to a specific class of LIDAR systems, namely so-called "solid-state" LIDAR systems that utilize semiconductor technology. A solid-state LIDAR system must be interpreted as a system that uses solid-state technology to generate the laser light and uses a detector to detect the reflected laser light. For example, in various embodiments, the laser light is generated by a VCSEL-type semiconductor laser and the detector is a CMOS-based semiconductor pixel detector.

[0087] A scene is interpreted as an area, such as the area viewed by a LIDAR device mounted on a car windshield or bumper. Depending on the field of view of the LIDAR device, the scene can cover a large area or a smaller area. The field of view for automotive applications is, for example, 30°x10°, 120°x20° or any other field of view. The scene may include, for example, various objects at different distances from the LIDAR device, or several objects or just one object. LIDAR systems are intended to perform distance mapping of the scene, thereby identifying different distances to objects or distances to parts of the scene.

[0088] The laser used by the LIDAR system can be continuous wave, pulsed wave, or amplitude modulated wave, depending on the type of LIDAR system.

[0089] Figure 1 An example of an embodiment of a solid-state LIDAR system 1 according to the present disclosure is schematically shown. Such a system 1 for determining the distance to a scene 99 comprises a projector 100 for illuminating the scene 99 with a discrete light spot pattern 150, and a light receiving device 300 comprising a multi-pixel detector (e.g., a range-gated multi-pixel detector or a direct time-of-flight-based multi-pixel detector), wherein each light spot comprises a temporal sequence of laser pulses, and the multi-pixel detector is configured to detect a reflected laser light spot representing a discrete light spot pattern reflected by a scene object. The reflected laser light forms a reflected discrete light spot pattern 350, and at Figure 1 The reflected discrete spot pattern 350 corresponds to the discrete spot pattern 150 reflected by an object of the scene and observed as a plurality of detection spots on the range-gated multi-pixel detector.

[0090] Please note that Figure 1 In the diagram, the projected spot pattern and the reflected spot pattern are schematically represented as interrupted lines for illustration purposes only, and therefore these interrupted lines do not represent the actual timing of the pulses. In fact, in practice, as described below, when a pulse of a pulse sequence is emitted, the next pulse of the sequence is usually emitted only after the previous pulse is detected in the detector (after possible reflection of the object).

[0091] Figure 2 An example of a discrete spot pattern 150 illuminating a scene 99 is further shown. Figure 2 The circles on the diagram schematically illustrate the spots of the discrete spot pattern 150. Discrete spots must be interpreted as spots that are separated from each other, such as Figure 2 As shown. The spot pattern can be a regular pattern or an irregular pattern. The number of spots of the spot pattern can vary from embodiment to embodiment and, for example, ranges between 10,000 and 100,000 spots. In some embodiments, the number of spots can also be much lower and as low as four spots. As described above, each spot includes a sequence of laser pulses, typically provided by a pulsed laser beam.

[0092] The wavelength of the laser light generated by the laser beam forming the discrete light spots of the LIDAR system according to the present disclosure is generally between 800 nm and 1600 nm.

[0093] In embodiments where a range-gated multi-pixel detector is used, such a range-gated multi-pixel detector must be interpreted as a detector comprising a plurality of pixels and wherein the detector is configured to detect and accumulate laser light in at least two consecutive detection time windows.

[0094] An example of a range-gated multi-pixel detector is described in WO2017 / 068199. Such a detector is based on a range-gated detection technique, which is different from a direct ToF technique. With the range-gated technique, reflected laser light is detected as a function of time in at least two subsequent time windows, and wherein the time window is substantially equal to the pulse width of the emitted laser pulse forming the discrete spot pattern. The first time window generally substantially overlaps the period corresponding to the pulse emission. Based on the intensity identified in the at least two time windows, the distance to the scene can be determined.

[0095] like Figure 1 As schematically shown, the solid-state LIDAR system 1 also includes a controller 200 for controlling the light receiving device 300 and the projector 100 to detect and accumulate reflected laser light in synchronization with the illumination of the scene. The LIDAR system 1 also includes a processing device 400, which is configured to calculate the distance to the object of the scene based on the accumulated reflected laser light. In various embodiments, the controller 200 includes a synchronization device, which may include a conventional clock circuit or oscillator. The processing device 400 typically includes a processor or a computer, which includes an algorithm known in the art for calculating the distance to the object based on the detected reflected laser light.

[0096] In other embodiments, the solid-state LIDAR system does not use time-of-flight technology to determine the distance to the scene, but uses displacement technology, such as disclosed in WO2015 / 004213. These types of displacement-based LIDAR systems include a multi-pixel detector and a processing device, which is configured to determine the characteristics of the object, such as the distance to the object, by determining the displacement of the detection spot detected by the multi-pixel detector relative to the predetermined spot position. As will be discussed in more detail below, the projector according to the present disclosure can be used for a time-of-flight-based LIDAR system or a displacement-based LIDAR system.

[0097] In various embodiments, the solid-state LIDAR system according to the present disclosure includes a housing surrounding at least the projector 100 and the light receiving device 300. In other embodiments, the solid-state LIDAR system according to the present disclosure includes a housing surrounding the projector 100, the light receiving device 300 and the controller 200, and preferably also includes a processing device 400.

[0098] In an embodiment, the light receiving device 300 comprises an objective lens for projecting the reflected laser pattern onto a range-gated multi-pixel detector. In a preferred embodiment, the light receiving device 300 further comprises a narrow bandpass filter, for example for filtering out sunlight.

[0099] As mentioned above, in order to determine the distance to an object, a plurality of frames are used to determine the average object distance. Therefore, the illumination of the scene with a discrete spot pattern is repeated several times in order to obtain a plurality of distances, i.e. single-frame distance measurements, thereby allowing the average of the plurality of single-frame measurements to be taken. The frames may be transmitted at a frame rate F F repetition, which is usually much lower than the pulse frequency F of the pulses in the projected laser beam P .exist Figure 4 , an example of the repetition of frame 60 is schematically shown, and the frame rate F F In one example, three frame repetitions are shown, but in practice the number of frame repetitions used to determine the average distance value is typically much greater. Figure 4 As shown, after each pulse train 50, a processing time 65 is required to read out the exposure value and process the acquired data. The achievable frame rate F F Typically in the Hz range, in embodiments the frame rate is for example between 5 Hz and 50 Hz. The frame rate is typically limited by the speed of the CMOS detector and is often also limited by eye safety regulations.

[0100] Projector for generating discrete spot patterns, overview

[0101] An embodiment of a projector 100 for a solid-state LIDAR system 1 according to the present disclosure is Fig.14a is schematically shown above and Figure 5The projector 100 comprises a laser array 110 , such as a one-dimensional or two-dimensional laser array 110 , a mixing chamber 140 , a shaping optical system 120 , and a projector lens system 130 .

[0102] The mixing chamber should be interpreted as a hollow three-dimensional body. Figure 5 In the embodiment of the invention, the dashed outline represents the mixing chamber 140, and the circumferential wall of the mixing chamber is indicated by reference numeral 140a. Fig.17a and Fig.17b shown and discussed further below. Figure 14b to Figure 14h Other embodiments of projectors according to the present disclosure including additional components are shown and are also discussed further below.

[0103] The laser array 110 includes a plurality of discrete solid-state laser sources 111. In various embodiments, the solid-state laser sources 111 are semiconductor lasers, such as, for example, VCSEL semiconductor lasers.

[0104] In such Figure 5 In the embodiment shown, the solid-state laser sources generally have an emission surface 111a located in the emission plane XY of the array. The laser array 110 is operable so that each laser source simultaneously emits a first laser beam 10 that diverges in a direction parallel to the main optical axis Z of the projector. Figure 5 In the exemplary embodiment shown, the main optical axis Z of the projector is perpendicular to the emission plane XY. In this way, a plurality of parallel first laser beams are obtained, which propagate in a direction parallel to the main optical axis.

[0105] In other embodiments, the emitting surface of each solid-state laser source is not necessarily perpendicular to the projector's main optical axis Z. In various embodiments, the laser array may be formed, for example, on a generally curved substrate surface, whereby the respective directions of the individual laser beams are not strictly parallel to each other, but deviate from the mean optical axis to varying degrees.

[0106] In various embodiments, the first laser beams are continuous wave laser beams. In other embodiments, the first laser beams are pulsed, and each pulsed first laser beam emitted by the solid-state laser source comprises a temporal sequence of first pulses having a temporal pulse width PW. The mixing chamber 140 extends along the main optical axis Z and is configured to receive and allow each first laser beam 10 to propagate in a direction parallel to the main optical axis Z until at least a portion of the light of each first laser beam overlaps with the light of an adjacent first laser beam. In practice, since the first laser beam emitted by the solid-state laser source is a divergent beam, for example, with a divergence angle between 5° and 15°, the first laser beams will begin to overlap after propagating a given distance in the mixing chamber. Overlapping should be interpreted as overlapping in space.

[0107] In various embodiments, the divergence angle of the first laser beams is equal to or less than 25°.

[0108] By using a mixing chamber as described above and allowing the light of the laser beam to overlap with the light from the adjacent laser beam, the coherent laser light of each individual laser source is mixed with the coherent laser light from a plurality of other laser sources. In this way, the mixing of the first laser beams will cause the coherence of the light incident on the shaping optical system 120 to decrease, and the coherence of the second laser beam forming the spot pattern emitted by the projector lens system 130 will decrease.

[0109] The mixing chamber has a length H measured along the main optical axis Z. The longer the length of the mixing chamber, the more the light of each laser beam will intermix with the light of the other laser beams.

[0110] In various embodiments, the length H of the mixing chamber is determined so that after the first laser beams propagate through the mixing chamber, 20% or more, preferably 40% or more, and more preferably 60% or more of the light of each first laser beam overlaps with the light of the adjacent first laser beam. In other embodiments, after propagating through the mixing chamber, 100% of the laser light of each first laser beam overlaps with the adjacent first laser beam.

[0111] A person skilled in the art will define the length H of the mixing chamber according to the amount of mixing required to create a uniform power field to create a uniform spot pattern. At the same time, in order to minimize the effect of speckle on spatial accuracy, the coherence of the laser is significantly reduced. When determining the length H, it should also be considered that the LIDAR system should remain compact. A person skilled in the art can, for example, follow an iterative process to determine the amount of overlapping laser light required by modifying the length H so as to achieve a sufficient amount of mixing. Other examples of how to determine the optimal length H of the mixing chamber will be discussed in further detail below.

[0112] The shaping optical system 120 is located between the mixing chamber 140 and the projector lens system 130. The shaping optical system is configured to receive the overlapping light of the first laser beam 10 emitted from the mixing chamber 140, and is used to refocus the overlapping light to form a plurality of discrete second laser beams 20. These second laser beams 20 form a discrete spot pattern 150. Discrete laser beams must be interpreted as spatially separated beams. In an embodiment in which the first laser beam is a pulsed laser beam, the second laser beam is also a pulsed laser beam, and each pulsed second laser beam includes a time sequence of second pulses with a temporal pulse width PW. In fact, the second laser beam still has the same temporal pulse width PW as the first pulsed laser beam, because neither the mixing chamber nor the shaping optical system changes the temporal pulse width of the laser beam. In addition, the frequency of the second pulsed laser beam is the same as the frequency of the first pulsed laser beam. In fact, the mixing chamber only allows the first laser beam to diverge along a given distance corresponding to the length of the mixing chamber.

[0113] However, in various embodiments, if the number of second laser beams formed by the shaping optical system is lower than the number of first laser beams, the shaping optical system 120 may change the intensity of the second beam (when compared to the intensity of the first beam).

[0114] In some other embodiments, the shaping optical system generates a second laser beam having a lower intensity than the first laser beam.

[0115] Figure 3 Embodiments are concerned with pulsed first and second laser beams. Figure 3 , an example of a time sequence of pulses 11 forming a pulsed second laser beam is schematically shown. Such a time sequence of pulses is also referred to as a pulse train 50. In this illustrative example, only 5 pulses are shown, but in practice, the number of pulses in a pulse train is typically much larger. For example, in some embodiments, the number of pulses in a pulse train is between 50 and 500 pulses. These pulses are typically block pulses. The temporal pulse width PW and the pulse period P of the pulse 11 are P With pulse frequency F P Inversely proportional, such as Figure 3 The number of pulses in a sequence may depend on various factors, such as, for example, the amplitude of each pulse may be limited for eye safety reasons, and / or the number of pulses may be defined to obtain a sufficient signal-to-noise ratio to detect reflected laser light.

[0116] In various embodiments, the controller 200 of the solid-state LIDAR system 1 is configured to control the laser array 110 so that each of the plurality of discrete solid-state laser sources emits a pulse at a frequency F P The first pulse is emitted so that F P ≤1 / (TOF max +PW), where PW is the time pulse width defined above, and TOF max is the predefined maximum distance D to be determined max The maximum flight time. This maximum distance D max It can be interpreted as the maximum operating range of a solid-state LIDAR system, which defines the maximum distance in the scene up to which an object can still be detected and the distance determined. max For example, it can be a value between 50 and 500 meters. P A maximum pulse frequency defined as equal to or lower than the above definition ensures that when a given pulse is emitted, the next pulse in the time series is emitted only at a pulse located at the maximum distance D max The previous pulse reflected by an object at a certain distance is not emitted until it is detected in the range-gated multi-pixel detector. This avoids a problem known as aliasing.

[0117] In various embodiments, Figure 3 As shown, the pulse frequency F of the pulse train 50 P Typically in the kHz range, for example between 10kHz and 500kHz.

[0118] As described above, projector 100 also includes projector lens system 130. Projector lens system 130 is an optical system including one or more optical lenses configured to receive the second laser beam forming a discrete spot pattern and project the illumination pattern 150 formed by the second laser beam onto scene 99.

[0119] In prior art systems, such as the LIDAR system described in WO2017 / 068199, the projector lens system is a complex, custom and expensive lens system. In fact, a simple projector lens cannot be used because a single lens usually does not have a flat focal plane, the well-known Petzval field curvature. As a result, when the projector lens system projects a spot pattern into the scene, not all spots of the spot pattern are focused at infinity. Therefore, correction for this non-planar focal plane is required.

[0120] When compared to the projector system of WO2017 / 068199, the projector lens system 130 of the projector according to the present disclosure is simplified because the shaping optical system 120 can be designed so that its focal plane is curved and coincides with the curved focal plane of the projector lens system 130. In this way, a simple projector lens can be used to project the light pattern. In fact, since the shaping optical system 120 provides a curved focal plane, no further correction lens is required. As a result, the length of the projector lens system 130 along the main optical axis Z is reduced. Therefore, this reduction can compensate or partially compensate for the increased projector length due to the addition of the mixing chamber. In various embodiments, the size of the projector lens in a plane perpendicular to the XY plane is also reduced, which will be further discussed below. How the projector lens system 130 according to the present disclosure is simplified when compared to the prior art projector lens system will be further discussed below.

[0121] In various embodiments, at least a portion of the inner wall of the mixing chamber is a reflective wall 170 for reflecting laser light, so that the laser light extending out of the perimeter of the mixing chamber is reflected back into the mixing chamber. Figure 5 and Figure 8 Schematically explained.

[0122] In practice, the light from the peripheral light sources of the array may hit the reflective wall and reflect back in the mixing chamber, depending on the divergence angle of the light source and the length H of the mixing chamber. The reflective wall further helps to obtain a uniform light distribution in a plane perpendicular to the main optical axis after mixing of the first laser beams, which will be discussed in further detail.

[0123] To form the reflective wall 170, those skilled in the art may select, for example, a smooth and reflective material to reflect the laser. In various embodiments, at least a portion of the inner wall of the mixing chamber 140 includes a mirror for reflecting the laser.

[0124] In some embodiments, the reflective walls of the mixing chamber are configured to be specularly reflective as opposed to diffusely reflective.

[0125] In a further embodiment according to the present disclosure, one or more optical laser reflecting elements are located in the mixing chamber for extending the travel path of the first laser beam. In this way, the length H of the mixing chamber can be reduced while maintaining sufficient mixing of the first laser beam.

[0126] Microlens array

[0127] In various embodiments, the shaping optical system 120 includes a first microlens array 121 including a plurality of microlenses ML[i]. Figure 14a to Figure 14h 121 is shown above. For example, Figure 7 A cross-sectional view illustrating three microlenses ML[1], ML[2], and ML[3] of the first microlens array 121 is shown in FIG. Each microlens has its own appropriate optical axis. Each of these multiple microlenses is configured to form an associated second laser beam. Therefore, the number of microlenses defines the number of second laser beams formed, and therefore defines the number of spots in the discrete spot pattern.

[0128] A microlens array (abbreviated MLA) is understood to be an array covering miniaturized individual optical elements (eg lenses), whereby the dimensions of the individual optical elements are typically in the order of magnitude of the micrometer to millimeter range.

[0129] As described above, the number of light spots in the discrete light spot pattern is generally between 10000 and 100000. In various embodiments, the number of discrete light spots is, for example, about 20000, and thus in these embodiments, the number of microlenses of the first microlens array is 20000.

[0130] In various embodiments, the individual element size of the microlens is approximately 79 microns, and the projected light spot formed by the microlens is approximately 15 microns.

[0131] In some embodiments, the number of microlenses of the first microlens array is equal to the number of laser sources, while in other embodiments, the number of microlenses of the first microlens array is lower than the number of laser sources, so that the pulse intensity of the second light beam is greater than the pulse intensity of the first light beam.

[0132] The embodiment in which the number of laser sources is greater than the number of microlenses of the first MLA has many advantages. In fact, not only the power of each beam projected onto the scene is increased, but also the negative impact of failure of an individual laser source is reduced.

[0133] In various embodiments, each microlens of the MLA has a hexagonal shape. Using this type of microlens configuration, an efficiency of about 95% can be achieved, ie only 5% of the laser light is lost when switching from the first laser beam to the second laser beam.

[0134] The microlens array can be formed on a substrate using photolithography processes known in the art. Such processes can produce a microlens array in which the diameter of the microlenses is in the micrometer range, for example, between 30 micrometers and 100 micrometers in diameter, and the focal point is in the range between 30 micrometers and 100 micrometers. In some embodiments, as Fig.11 As shown, the optical axis Z of the individual microlens ML[i] of the first microlens array 121 is i Parallel to the main optical axis Z. In other embodiments, for example Fig. 9 and Fig.10 As shown, the optical axis of the microlens ML[i] is not necessarily parallel to the main optical axis Z, which will be further discussed below.

[0135] In various embodiments, the microlens array is also adapted to correct the above-mentioned optical problem, namely that the focal plane of the optical lens is not flat but curved, a fact known as Petzval field curvature. In fact, if the projector lens system has a curved focal plane instead of a flat plane, the result is that the projected spots of the spot pattern are not all focused at infinity, but only part of the spots are focused. Therefore, not all spots have the maximum intensity per surface area. In general, the central spot is focused, while the outer spots are out of focus. In the prior art LIDAR system, in order to remedy this problem, the projector lens system includes one or more additional correction lenses in addition to the objective lens to correct these optical aberrations. This makes the projector more expensive, larger, and more complex.

[0136] In various embodiments, Figure 8 As schematically shown, the first microlens array 121 is configured such that each microlens ML[i] comprises a focus RFP[i], more precisely a back focus, located on a plane FP, and wherein the plane FP is located between the microlens array 121 and the projector lens system 130 .

[0137] In other embodiments according to the present disclosure, the microlens array is configured so that each microlens includes a microlens located on a curved surface CFP (rather than Figure 8 The focus on the plane shown in FIG. 1 is the back focus RFP[i]. The surface CFP is Figures 9 to 11As shown. This curved surface CFP corresponds to the virtual imaging surface of the projector. More specifically, the curved surface corresponds to the curved focal plane of the projector lens system, more precisely the curved front focal plane. In other words, the microlens array has a curved rear focal plane that coincides with the curved front focal plane of the projector lens system. In this way, by providing a microlens array with a curved focal plane, the projector lens system 130 of the projector 100 can be greatly simplified when compared to, for example, the projector lens system disclosed in WO2017 / 068199 (which requires various additional correction lenses to correct the Petzval curvature of the projector lens).

[0138] In various embodiments, the curved focal plane CFP corresponds to the curved focal plane of the projector lens system 130 .

[0139] exist Fig.11 In the embodiment shown, as described above, the optical axis Z of the individual microlenses ML[i] i Parallel to the main optical axis Z.

[0140] On the other hand, for Fig. 9 and Fig.10 In the embodiment shown, at least a portion of the microlens ML[i] has an optical axis Z which is not parallel to the main optical axis Z. i Advantageously, for these embodiments, when the optical axis Z of each microlens i The size of the projector lens system 130, ie the size in a plane perpendicular to the principal optical axis Z, can be reduced when compared to embodiments where the principal optical axis is parallel. For example, if the projector lens system 130 is formed by a standard projector lens, the diameter of the projector lens can be reduced.

[0141] Semiconductor laser source

[0142] In various embodiments, the laser array 110 is formed by one or more VCSEL (vertical cavity surface emitting laser) chips, each of which includes an array of laser emitters. Each of these laser emitters is interpreted as an individual solid-state light source. .VCSEL emitters are a type of semiconductor laser diode whose laser beam emission is perpendicular to the top surface of the VCSEL chip, which forms the emission surface 111a. The emission surface of the VCSEL emitter is typically circular and has a diameter in the micron range, for example, between 10 microns and 25 microns in diameter. When forming an array of VCSEL emitters, individual VCSEL emitters are separated by a VCSEL pitch, which is typically between 10 microns and 60 microns. By combining multiple (e.g., hundreds to thousands) of VCSEL emitters, a one-dimensional or two-dimensional laser array is formed.

[0143] The laser light emitted from the emitting surface of the VCSEL laser has a divergence angle θ defined as the half-opening angle VCSEL , which is usually between 3° and 15°, i.e. the open angle or full width of the laser beam is between 6° and 30°. In practice, the laser light emitted by the laser source should be as small as possible to maintain a discrete spot illuminating the scene. The divergence angle θ of the VCSEL emitter VCSEL exist Fig.12 is shown schematically and is shown as the half angle of divergence or half width of the laser beam. The value of the divergence angle or width of a laser beam is usually expressed as 1 / e 2 value.

[0144] In order to choose a suitable divergence angle θ VCSEL A compromise needs to be made. On the one hand, the divergence angle should be as low as possible to obtain a small beam spot, while on the other hand, the divergence angle should not be too small so that the length H of the mixing chamber does not become too long. In various embodiments, the VSCEL is selected so that the divergence angle θ VCSEL In the range between 3° and 15°. In various embodiments, the divergence angle θ VCSEL It is 10°.

[0145] In certain embodiments according to the present disclosure, solid-state laser sources are grouped in the form of tiles, for example to form a one-dimensional or two-dimensional tile array. A tile can be interpreted as a sub-array of solid-state laser sources. i Each subarray consists of patches T i The number of associated ST i solid-state laser sources, so that the total number ST of solid-state laser sources in the laser array is expressed as:

[0146]

[0147] where NT is the total number of patches in the laser array.

[0148] An example implementation of such a patch is a VCSEL chip comprising a plurality of laser emitters, each of which corresponds to a solid-state laser source. i Usually named as VCSEL patch. Each VCSEL patch may include, for example, 500 to 2000 VCSEL light sources.

[0149] In various embodiments, to form the laser array 110, a plurality of VCSEL patches may be arranged in rows and columns so as to form a two-dimensional array of patches. For example, a rectangular two-dimensional laser array 110 may be formed by N rows and M columns of VCSEL patches, where N and M ≥ 2. The size of the patches is typically in the millimeter range. The patches may have dimensions of, for example, 2 mm x 2 mm or 1 mm x 1 mm. These types of VCSEL patches are commercially available. Note that the patches of the two-dimensional array 110 do not necessarily need to have the same shape or have the same number of VCSEL sources.

[0150] The individual patches of the VCSEL array formed by the patches are separated from each other by an inter-patch spacing. The inter-patch spacing is in the millimeter range. In various embodiments, the inter-patch spacing is equal to or greater than 0.3 mm, preferably equal to or greater than 0.5 mm.

[0151] For each patch, the inter-VCSEL spacing is equal to or lower than 0.1 mm, preferably equal to or lower than 0.05 mm.

[0152] In various embodiments, the inter-VCSEL pitch is in a range between 10 microns and 30 microns.

[0153] The tiles of a VCSEL array comprising tiles may be arranged on a flat or curved surface.

[0154] In embodiments where the patches have a rectangular shape and the patches are arranged to form a regular VCSEL pattern, the distance between the patches is the same for the entire two-dimensional laser array 110. In various embodiments, the laser array 110 is a front-end VCSEL array, such as Fig.12 The front-end VCSEL array is an array in which the laser light emitted by the VCSEL laser source 111 does not pass through the substrate 70 .

[0155] Fig.12 A portion of an embodiment of a projector is shown, wherein a microlens array 121 is located downstream of the laser array 110. The microlens array 121 corresponds to the first microlens array 121 discussed above, which is configured to generate a second laser beam for forming a discrete spot pattern.

[0156] In other embodiments, the laser array 110 is a back-end VCSEL array, such as Fig.13 The back-end VCSEL array is an array in which the laser light emitted by the VCSEL laser source 111 passes through the substrate 70. In a preferred embodiment, the back-end VCSEL array includes a second microlens array 122, also referred to as a VCSEL microlens array, which includes a microlens array configured to reduce the divergence angle θ of each VCSEL. VCSEL Microlens ML VCSEL[i] Such a second microlens array is, for example, etched in the substrate 70 of the VCSEL array 110. In order to be able to use the back-end VCSEL array, the substrate 70 needs to be transparent to the laser. Currently available back-end VCSEL arrays are, for example, transparent to 940 nm lasers. Fig.13 As shown, in addition to the first microlens array 121 located downstream of the second microlens array 122, the microlenses ML VCSEL The second microlens array of [i] can be interpreted as the second microlens array 122 of the projector.

[0157] In a further embodiment, the VCSEL array is of a multi-stack type.

[0158] Mixing chamber

[0159] As described above, the mixing chamber 140 extends between the laser array 110 and the shaping optical system 120 and has a length H measured along the primary optical axis.

[0160] In Figures 17 and Fig.17b , two embodiment examples of a mixing chamber 140 are schematically shown. The mixing chamber 140 extending along the main optical axis Z must be interpreted as a three-dimensional hollow body. The mixing chamber 140 comprises an inlet face 160a for receiving unmixed laser light, an opposite outlet face 160b for emitting mixed laser light, and a circumferential side 140a for forming a hollow body. The circumferential side 140a of the mixing chamber should be interpreted as a wall of the mixing chamber.

[0161] In some embodiments, Fig.17a As shown, the mixing chamber 140 has a rectangular parallelepiped shape, wherein the four side walls of the rectangular parallelepiped form the circumferential side 140a of the mixing chamber. Fig.17b In FIG. 1 , an example of the mixing chamber 140 is shown as having a truncated cone shape, wherein the surface of the inlet face 160 a is smaller than the surface of the outlet face 160 b. Fig.17a and Fig.17b In FIG. 1 , the circumferential side 140a forming the mixing chamber is shown as a shaded surface.

[0162] Typically, the laser array 110 is located at the entrance face of the mixing chamber, while the shaping optical system (such as the first microlens array 121) is located at the exit face of the mixing chamber.

[0163] In various embodiments, the mixing chamber is configured to mechanically couple the laser array to the inlet face of the mixing chamber and / or to mechanically couple the shaping optical system to the outlet face of the mixing chamber. In this way, the mixing chamber also forms a support structure for the laser array and / or the shaping optical system. In various embodiments, the mixing chamber is configured to support other elements.

[0164] In other words, the mixing chamber 140 is formed in a region between the laser array generating the first laser beam and the shaping optical system. This region can be interpreted as a cavity in which the first laser beam is mixed.

[0165] As described above, in the embodiment of the projector according to the present disclosure, at least a portion of the inner wall of the mixing chamber 140 , ie, a portion of the inner side of the circumferential side 140 a of the mixing chamber 140 , includes one or more reflective walls 170 for reflecting laser light.

[0166] In various embodiments, the mixing chamber is made of, for example, a plastic material suitable for reflecting laser light.

[0167] In other embodiments, the inner portion of the circumferential side 140a is made of a first material, while the outer portion of the circumferential side is made of a second material different from the first material. The first material is then selected to be a laser reflective material so that the inner side of the circumferential side 140a forms a reflective wall 170 for reflecting laser light.

[0168] The reflective walls of the mixing chamber produce a uniform spot pattern, in other words, the spots at the periphery of the spot pattern have the same intensity as the spots located in the central part of the spot pattern.

[0169] In such Fig.14a In some of the embodiments shown, the mixing chamber 140 may be empty, i.e., may not contain any additional devices that interfere with the diverging first light beam. Figure 14b to Figure 14f In other embodiments shown, the mixing chamber 140 may include additional elements, such as, for example, a second microlens array 122, a diffuser 145, a circulator 146, a Bragg volume grating 147, and / or a beam expander 148. These additional elements are typically elements that can affect the mixing of the first light beam. These various embodiments including such additional elements will be discussed further below. In these embodiments including one or more of these additional elements, the mixing chamber is configured to support these additional elements and thus also forms a support structure for these additional elements.

[0170] The main advantage of forming a mirror cavity (i.e., a mixing chamber with internal reflective walls) is that the light is constrained and the irregularities that are usually present at the sides of the VCSEL patch or patch array are no longer present. Due to the presence of the mixing chamber, the spot pattern produced by the projection system is uniform, so that the spots at the periphery of the spot pattern have the same intensity as the spots in the center area of ​​the spot pattern. Another advantage of the mixing chamber is that the VCSEL array can be protected from contamination. In various embodiments, the mixing chamber is airtight so that turbulence, such as heat sources, is avoided in the projector.

[0171] Advantageously, in various embodiments, the mixing chamber may be filled with an inert gas to avoid aging or degradation of components located within the mixing chamber.

[0172] In some embodiments, the reflective wall 170 is not perpendicular to the plane of the VCSEL array 110, for example when the mixing chamber 170 has a Fig.17b As such, the reflective wall 170 of the mirror cavity can be oriented to reduce the divergence angle of the light beam, which, for example, increases the range and / or accuracy of a LIDAR system using the present projector to illuminate a scene. The mirror cavity can perform this function in addition to other components of the projector, and optionally, the mirror cavity can replace the use of the second MLA 122, as described below.

[0173] The mixing chamber needs to be long enough to allow the laser light of the first laser beam to be fully mixed. Generally speaking, the mixing plane P is parallel to the emission plane XY. M is defined as follows: wherein the rays of the first laser beam overlap to such an extent that the light becomes uniformly distributed. A uniform light distribution is to be interpreted as M The length H of the mixing chamber is usually defined such that the mixing plane P M Located at the end of the mixing chamber or at the entrance of the shaping optical system 120. If the shaping optical system includes a microlens array, the mixing plane can be located just in front of the microlens array.

[0174] On the other hand, the length H of the mixing chamber 140 should also be as short as possible to maintain a compact LIDAR device. Figure 6 In the mixing plane P M Shown at the end of the mixing chamber.

[0175] When using patches as light sources, the length H of the mixing chamber measured along the main optical axis Z is defined so that after the first laser beam propagates through the mixing chamber, for each patch, at least a portion of its light overlaps with the light of an adjacent patch. Overlapping should be interpreted as overlapping in space. In various embodiments, at least 20% or more, preferably 40% or more, and more preferably 60% or more of the laser light of each patch overlaps with the light of an adjacent patch. In other embodiments, 100% of the laser light of each patch overlaps with the light of an adjacent patch. The following is a method for determining the optimal distance for the length of the mixing chamber when using patches. As Figure 6 Schematically shown, the minimum length H of the mixing chamber 140 can be determined by the following formula:

[0176]

[0177] Where Δ is the distance between the centers of two adjacent patches, θ is the beam divergence angle of the VCSEL laser source, and L is the length of one side of the rectangular patch. For example, if Δ = 2.5 mm, L = 2 mm and θ = 10°, then H ≥ 8.5 mm. Figure 3Above, an embodiment of a patch is shown where the light source is a VCSEL array.

[0178] In other embodiments, if patches are not used but the light source is formed, for example, of a plurality of individual VCSELs forming a regular matrix, the above formula can be applied to determine the minimum distance H required for the mixing chamber 140. For these embodiments where patches are not used, the distance Δ is in this case the distance between the centers of two adjacent VCSEL laser sources, for example 50 microns, and L is the diameter of the circular emitting surface of the individual VCSELs, for example 15 microns. If patches are not used, the minimum distance H required for sufficient spatial overlap between the first laser beams is much shorter.

[0179] The second laser beam 20 including rays from the plurality of first laser beams is formed at Figure 7 Schematically illustrated above. In this illustrative example, microlens ML[2] receives a portion of light from first laser beams 10a, 10b, and 10c. Microlens ML[2] has a focal length f, and focuses light transmitted through microlens ML[2] in a focal plane FP to form a second laser beam 20 composed of light portions of first laser beams 10a, 10b, and 10c. On the focal plane FP of microlens ML[2], an image of a light spot is observed with a light spot width W and a divergence angle θ SPOT The composed second laser beam 20 corresponds to the Figure 7 As shown, the width W of the second laser beam 20 in the focal plane 20 can be found by the following formula: tan(θ VCSEL ) = W / (2 x f), where θ VCSEL is the divergence angle of the first laser beams 10a, 10b, 10c. The divergence angle θ of the second laser beam 20 SPOT It can be found by the following formula: tan(θ SPOT ) = ((W + P) / (2x f)), where P is the distance between the centers of two adjacent microlenses. Figure 7 In the figure, only a schematic diagram of the principle of forming the second laser beam based on multiple first laser beams is shown. In practice, the number of overlapping first laser beams used to form the second laser beam is usually larger.

[0180] exist Figure 8, a cross-sectional view of an embodiment of a projector 100 according to the present disclosure is shown, wherein the projector includes a laser array 110 formed by a plurality of VCSEL patches T[i], such as a two-dimensional laser array. Each VCSEL patch includes a plurality of VCSEL lasers that generate first laser beams 10. In this example, a plurality of first laser beams 10 from different patches T[i] are mixed as they propagate through a mixing chamber 140. The microlens array 121 ultimately forms a second laser beam by intercepting overlapping light rays and refocusing them onto a focal plane FP, which is a common focal plane of each microlens of the microlens array. The second laser beam is focused onto the focal plane FP at Figure 8 Shown schematically.

[0181] As described above, a preferred method for obtaining a sufficiently large VCSEL array is to combine multiple VCSEL patches into a larger array. Smaller VCSEL patches have a higher yield than larger patches, which leads to a more efficient manufacturing process and lower associated costs. After assembling such patches into a VCSEL array, the distance between patches is usually greater than the distance between VCSELs within a patch. These "seams" cause light bands with less illumination to appear in the field of view FOV of the projector. Obviously, the distance h between the VCSEL array and the first MLA can be selected so that the beams of adjacent patches mix, resulting in a more uniform power field incident on the first MLA 110 and a more uniform scene illumination. In this way, the cost of the projector can be reduced and / or its size can be increased without sacrificing the uniformity of the projected pattern.

[0182] Another effect of the possibility of using smaller tiles and larger inter-patch distances is that a larger power budget per tile and therefore per VCSEL can be obtained without running into thermal constraints. The increased power per VCSEL increases the power per beam projected into the scene compared to the beams produced by the individual VCSELs, which, for example, increases the amount of laser light (i.e., the number of photons) reflected back to the detector of the LIDAR system. Since the range and / or accuracy of a LIDAR system depends largely on the Poisson noise in the measurement, and since Poisson noise decreases as the number of photons reflected back increases, the parallax and the resulting increased power per beam, for example, increases the range and / or accuracy of a LIDAR system that uses the present projector to illuminate a scene.

[0183] Projector with two microlens arrays

[0184] In such Fig.14bIn the embodiment of the present disclosure shown, the projector includes a second microlens array 122 for reducing the divergence angle of the first laser beam emitted by the solid-state laser source (111). The second microlens array is generally arranged between the laser array 110 and the first microlens array 121. In various embodiments, the second microlens array is configured to limit the divergence angle of the first laser beam, for example, to a maximum divergence angle of 5°. On the other hand, since the purpose of the mixing chamber is to overlap the first laser beams, a compromise needs to be made between limiting the divergence angle to a given maximum value and the amount of mixing required to obtain a uniform light distribution on the second microlens array to generate second laser beams with uniform irradiance for all second laser beams.

[0185] The projector embodiment with two microlens arrays retains the Fig.14a The illustrated embodiment includes all the features of the above-described embodiments including only the first microlens array 121. The second microlens array 122 is located between the emission side of the laser array 110 and the first microlens array 121. Preferably, the second MLA 122 includes a number of microlenses equal to or less than the number of VCSELs (i.e., the total number of laser emitters) in the VCSEL array 110. Preferably, the second MLA 122 is designed to reduce the divergence of the light beams emitted by each individual laser in the VCSEL array 110. In some embodiments, the laser array includes a plurality of VCSEL chips, wherein each VCSEL chip includes a plurality of laser emitters. The laser emitters of the VCSEL chips will be explained as solid-state laser sources, and the VCSEL chips are implementation examples of the above-described VCSEL patches.

[0186] In embodiments where the laser array 110 includes a plurality of VCSEL chips, each of which includes a plurality of laser emitters, the number of microlenses in the second microlens array 122 is equal to or less than the total number of emitters of the laser array. The total number of emitters is the sum of all emitters in each VCSEL chip in the laser array.

[0187] In some embodiments where the microlenses of the second MLA are aligned with the optical axes of the corresponding VCSELs, which may be parallel in the case of a strictly flat VCSEL array, the second MLA 122 reduces the divergence of the light beam emitted by the VCSEL array without disrupting the light beam. Fig.15a 1. The resulting reduction in laser beam divergence increases the irradiance of the first beam incident on the first MLA 121, and thus the second beam received by the projector lens 130 also has an increased irradiance. As a result, the angular irradiance of the beam projected by the projector onto the scene is reduced, which, for example, increases the range and / or accuracy of a LIDAR system using the present projector to illuminate a scene.

[0188] In various embodiments, the distance between the second MLA 122 and the first MLA 121 may vary, and this distance variation will affect the amount of mixing that occurs between the laser beam before it reaches the first MLA 121 .

[0189] In an alternative embodiment where the microlenses of the second MLA are not perfectly aligned with the respective optical axes of the individual VCSELs, the second MLA 122 can reduce the divergence of the light beam emitted by the VCSEL array 110 while also breaking up the light beam. In other words, there is a diffuser effect, thereby increasing the angular mixing of the first light beam. This is Fig.15b 1. This diffuser effect increases the mixing of the beams and therefore improves the uniformity of the field incident on the first MLA 121. This can result in a more uniform spot pattern projected on the scene and / or make it possible to reduce the distance between the first MLA 121 and the VCSEL array 110 without negatively affecting the uniformity of the spot pattern. In the case of imperfect alignment, the presence of the second MLA 122 can, for example, improve the accuracy and precision / range of a LIDAR system using the present projector.

[0190] As described above, for embodiments where the laser array 110 is a back-end VCSEL array, Fig.13 As schematically shown, such a second microlens array 122 is, for example, etched in the substrate 70 of the VCSEL array 110 and is configured to reduce the divergence angle θ of each VCSEL. VCSEL .

[0191] In some embodiments, instead of using a second MLA to reduce the divergence angle of the laser beam, one or more prisms are used to reduce the divergence angle of the laser beam.

[0192] Projector with diffuser

[0193] Fig.14c Another example of a solid-state projector according to the present disclosure is schematically shown. For clarity and without loss of generality, this embodiment retains the Fig.14b All features of the illustrated embodiment and additionally include a separate diffuser 145 between the first MLA 121 and the second MLA 122. This should not be interpreted as excluding embodiments lacking the second MLA 120.

[0194] like Fig.14c As shown, the diffuser 145 is included within the mixing chamber 140 , and preferably in these embodiments, the mixing chamber 140 is configured to support the diffuser 145 .

[0195] In some embodiments including the second MLA 122, the diffuser 145 may be positioned closer to the second MLA 122, as in Fig.14c In other embodiments, which are schematically shown, the diffuser 145 may be positioned further away from the second MLA 122 .

[0196] In some embodiments, a diffuser is attached to the second MLA 122. In various embodiments, the diffuser or diffuser function becomes an integral part of the second MLA 122. The diffuser is an optical element that scatters light by diffraction and refraction in order to evenly distribute the light from the VCSEL light source. It homogenizes the light so that it has a radiance that is independent of angle and / or position, and thus the light incident on the first MLA has more uniform characteristics to create a uniform spot pattern after the first MLA.

[0197] The diffuser is typically made of a patterned surface between two materials with different optical refractive indices at the wavelength of interest. Preferably, a material with a high refractive index contrast and easy to manufacture is used, such as a moldable material. For example, the following non-limiting material combinations can be used: glass / air, plastic / air, AlGaAs / air, epoxy / air, molded cured liquid crystal, epoxy / epoxy, plastic / plastic. In various embodiments, a colloidal suspension is used, such as, for example, the combination: glass / liquid.

[0198] Its working principle is based on the refraction and diffraction properties at the edges of different optical materials to diffuse light. The interface is usually non-periodic to avoid a fixed pattern, and the diffusion is therefore semi-random, preferably polarization-independent and sufficient.

[0199] exist Fig.19 , an embodiment is shown in which the laser light emitted from the second MLA 122 passes through the diffuser 145, and mixing of the laser light resulting from passing through the diffuser is schematically shown.

[0200] The diffuser 145 increases the angular beam mixing, resulting in a more uniform field incident on the first MLA 121. Therefore, the diffuser can reduce the distance between the first MLA 121 and the second MLA 122 without negatively affecting the uniformity of the spot pattern projected by the projector. However, the increase in angular beam mixing will result in a decrease in the angular irradiance of the projector.

[0201] Since there are small variations in the wavelengths emitted by each individual VCSEL, diffuser 145 provides not only angular mixing of the beams, but also wavelength mixing. Wavelength mixing increases the wavelength spectrum of the projected spot pattern, thereby reducing its coherence. This reduction in coherence reduces the presence of speckle patterns in the projection, thereby, for example, improving the accuracy of a LIDAR system that uses the present projector to illuminate a scene. However, the wide wavelength spectrum has an adverse effect on the range and / or accuracy of such LIDAR instruments, due to the necessitated presence of narrow band filters on the detector side of the LIDAR.

[0202] Those skilled in the art will appreciate that the diffuser needs to be tuned based on the characteristics of the first MLA 121, the second MLA 122 (if present), and the VCSELs of the VCSEL array 110 to achieve a balance between the angular irradiance of the projected spot pattern, the uniformity of the projected spot pattern, and the wavelength spectrum of the projected spot pattern and the thickness of the optical stack.

[0203] Projector with circulator

[0204] Another embodiment of the projector according to the present disclosure is Fig.14d For clarity and without loss of generality, this embodiment retains the Fig.14c and additionally includes an optical circulator 146. This should not be interpreted as excluding embodiments lacking the second MLA 122 or the diffuser 145.

[0205] In some embodiments, mixing with diffuser 145 as described above is not sufficient, and another optical element, namely circulator 146, is preferably used in combination with the diffuser described above.

[0206] like Fig.14d As shown, the circulator 146 is included within the mixing chamber 140 , and preferably in embodiments including the circulator, the mixing chamber 140 is configured to support the circulator 146 .

[0207] The purpose of the circulator 146 is to provide spatial beam mixing. Preferably, the circulator is placed between the VCSEL array 110 and the diffuser 145, or for embodiments including the second MLA 122, between the second MLA 122 and the diffuser 145. In this position, the beam angle is typically smaller than it is between the diffuser 145 and the first MLA 121. This may result in more spatial mixing and enable the use of a thinner circulator to obtain the same efficiency. The spatial mixing provided results in a more uniform field incident on the first MLA 121, and therefore a more uniform spot pattern projected onto the scene, which, for example, increases the accuracy of a LIDAR system using the present projector to illuminate the scene. Due to the enhanced mixing using the diffuser and circulator, the resulting laser light is more incoherent, so that speckle noise is further reduced.

[0208] The circulator increases the spatial mixing of the VCSEL light by partially diffracting / bending (preferably 90°) and partially transmitting the incident VCSEL light, for example, through a semi-transparent / semi-reflective element. According to its working principle, the circulator causes the VCSEL light to partially propagate from the incident position to the next further position and partially exit the circulator at the further position. This further increases the spatial mixing of the VCSEL beam, thereby improving the uniformity of the light incident to the MLA1.

[0209] Circulators are usually made of, for example, plastic or glass and have a number of semi-reflective / semi-transparent mirror components included in the optical path. There is a fixed distribution between the transmitted and reflected light. The operating principle is based on partially reflecting the incident light and letting it partially pass. The type of reflection depends on the choice of material: for example, frustrated total internal reflection, partial reflection due to two optical media, metallic reflection, polarizing beam splitters. The ratio of transmission and reflection is determined by the transparency of the reflective components placed in the optical path of the light.

[0210] It is preferred and advantageous to apply an antireflection coating on the bottom and top layers for the wavelength spectrum used.

[0211] exist Fig.18 In FIG. 1 , an example of an embodiment of a circulator 146 is shown. The circulator 146 shown comprises a transparent mirror 146a, i.e. a mirror that is transparent to a certain extent. For example, between 20% and 80% transparent, for example, 50% transparent. Fig.18 In FIG. 1 , four transparent mirrors 146a are schematically shown and are shown with dashed oblique lines. The incoming laser light partially passes through the transparent mirrors and is partially reflected in a direction perpendicular to the incoming laser light. The laser light reflected by the first transparent mirror will be at least partially reflected again by the adjacent transparent mirror and thus be directed again as the original incoming laser light. In this way, the laser light is spatially mixed. Fig.18In FIG, the incoming laser light, the reflected laser light, and the transmitted laser light are schematically indicated by black arrows.

[0212] Projector with volume Bragg grating

[0213] Another embodiment of the projector according to the present disclosure is Fig.14e For clarity and without loss of generality, the illustrated embodiment retains the Fig.14d and additionally includes a Bragg volume grating 147. This should not be interpreted as excluding embodiments lacking the second MLA 122 and / or the diffuser 145 and / or the circulator 145.

[0214] The volume Bragg grating is a device configured to reduce the wavelength spread of the first laser beams.

[0215] Preferably, the volume Bragg grating 147 is placed between the VCSEL array 110 and the diffuser 145. The volume Bragg grating 150 is made of glass, for example.

[0216] The Bragg volume grating 147 diffracts a portion of the emitted light back to the VCSEL array 110, also known as self-imaging, thereby causing VCSEL wavelength locking through the phenomenon of optical injection locking. Typically, the spread of wavelengths emitted by individual VCSELs in a VCSEL array is 2-3nm. By adding the Bragg volume grating 147, this spread can typically be reduced by an order of magnitude to 0.2-0.3nm.

[0217] Preferably, the volume Bragg grating is designed so that no optical power loss occurs, and the full power of the VCSEL should be emitted in a smaller wavelength spectrum.

[0218] The reduction in wavelength spread enables, for example, the use of narrower band filters in the detector of a LIDAR system using the present projector to illuminate a scene, thereby increasing the signal-to-noise ratio of the detector and thus increasing the range and / or accuracy of the LIDAR system. A possible side effect of the narrower bandwidth of the emitted light beam is an increase in the speckle produced by the projector.

[0219] The volume Bragg grating 147 makes the wavelength of the light beam emitted by the individual VCSEL less dependent on the temperature of the VCSEL and the current flowing through the VCSEL. Therefore, the dynamic wavelength shift during the light beam pulse is reduced. This reduction enables, for example, the use of narrower band filters in the detector of a LIDAR system that uses the present projector to illuminate a scene, thereby increasing the range and / or accuracy of the LIDAR system.

[0220] Preferably, the design of the volume Bragg grating 147 is such that it can spatially scan the wavelength of the VCSEL array to match it with the wavelength blue shift of the narrow band filter on the detector side of the LIDAR system. Alternatively, the matching can be performed by ordering the VCSEL patches as a function of wavelength and placing them in the correct position in the VCSEL array to match the narrow band filter.

[0221] Preferably, the Bragg volume grating 147 reduces the divergence of the emitted light beam. This reduction in divergence increases the angular irradiance of the projector system, which, for example, increases the range and / or accuracy of a LIDAR system that uses the present projector to illuminate a scene. A possible side effect of this reduction in divergence is that the angular mixing between the light beams incident on the first MLA 121 is reduced, and the uniformity of the spot pattern projected by the projector is correspondingly reduced.

[0222] like Fig.14e As shown, the volume Bragg grating 147 is included within the mixing chamber 140, and preferably in these embodiments, the mixing chamber 140 is configured to support the volume Bragg grating 147.

[0223] Projector with beam expander

[0224] According to another embodiment of the projector of the present disclosure, Fig.14f , including a beam expander 148. The beam expander 148 is a device configured to improve the uniformity of the light distribution incident on the first microlens array. As described above, the use of the beam expander 148 is particularly useful when the laser array 110 is composed of patches forming a plurality of sub-arrays. Fig.16a and 16b A detailed embodiment of the beam expander 148 and further implementation details are shown in FIG.

[0225] For clarity and without loss of generality, Fig.14f The embodiment shown above retains the Fig.14e and additionally includes a beam expander 148. However, this should not be interpreted as excluding embodiments lacking the second MLA 122 and / or the diffuser 145 and / or the circulator 146 and / or the volume Bragg grating 147.

[0226] A beam expander is to be interpreted as an optical element that bends / diffracts laser light to different locations in space by placing semi-transparent components in the optical path, among others. These components partially transmit the incident laser light and partially bend it 90° to propagate it to another location where it leaves the optical component.

[0227] The goal of the beam expander is to create a more uniform light field incident on the first MLA 121, and more specifically to produce flattened radiation at the interconnects of the VCSEL patches, which typically exhibit lower radiation due to the distance between the two patches.

[0228] Beam expanders are typically made of, for example, plastic and / or glass, and act on semi-transparent, semi-reflective components placed in the optical path, or can be implemented by a cascade of positive / negative lenses.

[0229] Preferably, the beam expander 148 is placed between the VCSEL array 110 and the first MLA 121, or when a Bragg volume grating 147 is present, between the VCSEL array 110 and the Bragg volume grating 147. As described above, the purpose of the beam expander 148 is to increase the illumination in the inter-patch region, thereby causing a more uniform power field incident on the first MLA 121, and as a result, a more uniform illumination of the scene, which for example improves the accuracy of a LIDAR system using the present projector to illuminate the scene. In this way, without sacrificing the uniformity of the projected pattern, the size of the VCSEL patch can be reduced and thus the price of the projector can be reduced and / or the number of VCSEL patches can be increased and thus the size of the projector can be increased.

[0230] Without loss of generality, Fig.16a and 16b The operating principles of a beam expander are explained with reference to two patches 100a and 100b, respectively, where a beam expander 148 is used to fill in low intensity gaps that would otherwise occur due to the presence of seams between patches. Those skilled in the art will appreciate that these principles can be applied to any number of patches, including patches arranged in a two-dimensional array, in which case they are used to fill in low intensity areas formed by the resulting grid of seams.

[0231] In such Fig.16a In the embodiment shown, the beam expander 148 includes a plurality of angled mirrors 148a, 148b, 148c that are at 45° angles to the patch surface. When the laser light originating from the patches 100a, 100b reaches the mirrors indicated by reference numerals 148a and 148b, the laser light is reflected at an angle of 45° and thus propagates parallel to the patch until it reaches another mirror indicated by reference numeral 148c. This other mirror 148c will reflect the light again at an angle of 45° so that the laser light is again perpendicular to the patches 100a, 100b. Fig.16a The horizontal arrow on indicates the laser light after being reflected by the mirrors shown by reference numerals 148a and 148b. Since the mirror shown by reference numeral 148c is located in the area between the two patches, the laser light will also reach the area between the two patches, and thus no low-intensity gap will appear between the patches.

[0232] In other embodiments, the beam expander includes, for each patch, a pair of negative L- and positive L+ lenses parallel to the patch surface, such as Fig.16b As shown. In this way, the laser is first defocused by the negative lens and reaches the inter-patch area in this way. Thereafter, the laser is refocused by the positive lens so that the laser propagates along the main axis Z again.

[0233] like Fig.14f As shown, the beam expander 148 is included within the mixing chamber 140, and preferably in those embodiments including the beam expander 148, the mixing chamber 140 is configured to support the beam expander.

[0234] like Figure 14g and Figure 14h In FIG. 1 , a further embodiment of the projector 100 is shown, in which the mixing chamber comprises a reflective inner wall 170. In this way, a mirror cavity is formed. Figure 14g and Figure 14h In the example shown, the projector 100 includes Fig.14f Components of the projector shown in FIG. 1 , however, in other embodiments, the projector may include Figures 14a to 14f Components of any of the projectors shown or any combination thereof.

[0235] Mixing chamber with inspection hole

[0236] In various embodiments, mixing chamber 140, and more specifically peripheral side 140a, includes an inspection port for inspecting the operation of the projector. Figure 14h In FIG. 1 , an example of an embodiment is shown in which the circumferential side of the mixing chamber is constituted by a reflective wall 170 and in which inspection ports 180 are provided through the reflective wall 170. In this way, the operation of the projector can be monitored during use. Preferably, these inspection ports 180 are located at different heights, for example at the location of a specific optical component or between different optical components. Without loss of generality, Figure 14h Examples of three possible locations for such inspection ports 180 are shown.

[0237] When an inspection port is provided, some of the light in the mirror cavity will propagate toward the inspection port 180, and thus the light emitted by the projector system can be analyzed at different levels of the optical stack through the opening 180. For example, this analysis can be performed using an optical photodiode 190a located at the inspection port or using a camera 190b mounted on a PCB external to the optical cavity.

[0238] Inspection port 180 provides the advantage of allowing an operator to monitor the quality of the emitted light beam, where the information obtained can be used to evaluate the performance of individual components in the optical stack, diagnose faults, schedule maintenance or parts replacement, or provide feedback to the control system.

[0239] Range-Gating Detection Technology, Overview

[0240] As described above, in some embodiments of the LIDAR system, a multi-pixel detector for detecting reflected laser light is combined with a pulsed laser beam to apply a range-gated detection technique for determining the distance to an object of the scene. This is a technique different from the direct time-of-flight technique. The range-gated technique must be interpreted as a detection technique in which the reflected laser light is detected and accumulated as a function of time. Detection and accumulation are usually performed in a time window, and the range-gated technique uses at least two consecutive time windows. As described above, the processing device calculates the distance to one or more objects in the scene based on the accumulated reflected laser light obtained by the range-gated multi-pixel detector. When the DToF technique is applied in combination with a pulsed laser beam, a pulse width of a few nanoseconds is used, i.e., the pulse width is much shorter than the TOF to be measured. On the other hand, when the range-gated technique is applied, the pulse width used is much longer and is usually equal to the TOF to be measured or the order of magnitude of the TOF to be measured. For example, if an object is at a distance of 100 meters, it takes about 666 nanoseconds for the light to propagate back and forth. Using a wider pulse allows the detector to accumulate charge over a longer time interval. Although the power provided by a solid-state laser beam is less than that of a conventional laser beam, a sufficient signal-to-noise ratio can be obtained using a CMOS-based detector using a range gating technique when sufficient pulse repetition is applied. An example of a range gating technique is known from WO2017 / 068199. A multi-pixel detector for range gating technology includes a plurality of pixels, which are configured to generate an exposure value for each spot of the detected reflected laser by accumulating a first charge amount representing a first amount of light reflected by the scene during a first predetermined time window and a second charge amount representing a second amount of light reflected by the scene during a second predetermined time window for all pulses of a pulse time sequence of the laser beam. The second predetermined time window appears sequentially after the first predetermined time window. The distance to the object of the scene is calculated based on the first charge amount and the second charge amount. In various embodiments, the duration of the first predetermined time window and the second predetermined time window is substantially equal and equal to the pulse width PW of the pulse forming the illumination pattern.

[0241] However, the use of the projector according to the present disclosure is not limited to a specific distance gating technique, and is therefore not limited to the specific distance gating technique disclosed in WO2017 / 068199. In fact, other distance gating techniques using the principle of detecting and accumulating reflected laser light as a function of time may also be applied.

[0242] Distance gating detection technology, distance accuracy

[0243] In embodiments where the laser is pulsed, the illumination of the scene using a temporal sequence of pulses forming a spot pattern, the accumulation of reflected laser light, the readout of charge, and the distance calculation based on the accumulated charge are generally referred to as frames or frame measurements. The spatial accuracy achievable by a LIDAR system that applies range-gated detection techniques generally depends on the accuracy of a single frame measurement and the number of frames taken to determine the average target distance. In fact, when multiple frame measurements are performed, there is a spread in the measured distances from frame to frame. The error in a single frame measurement is generally referred to as the temporal error, i.e., the sigma value σ of the measurement distribution. Therefore, multiple frames are always taken and the average object distance is determined. In this way, the error in the average object distance value is reduced by a factor of σ compared to the error in a single frame measurement. To reduce, where N F is the number of frames. For a perfectly calibrated LIDAR device, the calculated average distance obtained from multiple frames is equal to the standard deviation The actual distance within the determined confidence interval.

[0244] The acceptable spatial accuracy for these systems (e.g. automotive applications) is a four-sigma confidence interval, or 4xσ avg , i.e. between 0.1% and 0.5% of the average distance value. When the average distance determined after a plurality of frame measurements is equal to, for example, 100 m, and if the obtained four-sigma confidence interval is equal to 0.2%, then the determined average target distance of 100 m is equal to the actual distance within an interval of + / - 20 cm with a probability of 99.99%.

[0245] The present disclosure is based at least in part on the inventors' observation that despite significant efforts to reduce or correct the detected signal from noise contributions (e.g., background noise from ambient light, pixel noise, or noise resulting from, for example, TOF response time), the spatial accuracy obtained using the LIDAR system described in WO2017 / 068199 is less than theoretically expected, i.e., the average determined distance is found to be equal to the actual distance within a 99.99% confidence interval, for example. Even after making a sufficient number of distance measurements to reduce Poisson noise, it is observed that the measured average distance still differs from the actual distance by an amount that is much greater than the expected spatial accuracy. Analysis of multiple tests performed by the inventors on the solid-state LIDAR system described in WO2017 / 068199 led the inventors to realize that, after calibration for known system noise elements, the main noise contribution remaining when using the LIDAR system to generate spatially separated coherent laser pulses and in combination with range-gated detection techniques is speckle-related noise.

[0246] Speckle noise is a semi-random noise caused by interference effects at intersections with objects reflecting laser light, and it propagates through the reflected laser light and further accumulates in the detector, thereby adding noise to the integrated charge in the range-gated detector. Speckle causes non-uniform reflection of the laser light and depends on the material structure of the object. The speckle pattern also varies with time, and therefore the speckle varies between pulses and within the pulse width of the pulsed laser beam. When applying a range-gated technique, in which the reflected laser light is accumulated in multiple detection time windows corresponding to the time sequence of projected pulses, it is observed that the effect of speckle can vary from detection time window to detection time window and is different between multiple pixels or charge wells that integrate charge during the detection time window. For example, as described in WO2017 / 068199, when applying a range-gated technique, the accumulated counts over a pulse sequence are typically detected in a first time window and a subsequent second time window. In order to determine the distance, the ratio between the accumulated counts detected in the first time window and the sum of the accumulated counts detected in the first time window and the accumulated counts detected in the second time window is determined. Therefore, when such count ratios are employed, and because the speckle varies from time window to time window, an uncalibrated deviation will occur between the actual distance and the measured distance. This, therefore, results in poor spatial accuracy.

[0247] The main speckle noise contribution is believed to be a result of the properties of the laser and the combination of illuminating the scene with a pattern of discrete laser spots combined with the use of a range-gated detector that integrates the charge during a time period of the order of TOF, where each spot is formed by a pulse train of coherent laser light. As a contrast, for DToF LIDAR systems, extremely short pulses in the nanosecond range are used and there is no charge integration as with range-gated techniques. Therefore, speckle noise has not been observed to be a major issue for such DToF systems. Given the compactness of solid-state LIDAR systems, solving the random speckle problem is challenging for such systems based on patterned illumination with discrete laser spots and based on range-gated techniques.

[0248] Advantageously, a novel projector according to the present disclosure is used in which a second laser beam is formed by mixing a first laser beam, the second laser beam emitting substantially incoherent light. As a result, a projector that projects a laser spot pattern formed by discrete pulsed laser beams can be used as part of a LIDAR system that includes a range-gated detection technique. In fact, since the projector mixes the laser beams before generating the discrete spot pattern, the above-mentioned speckle noise is eliminated, and the spatial accuracy obtained using the LIDAR system according to the present disclosure falls within theoretical expectations. In other words, when a plurality of frames are taken and an average object distance value is determined, then within the standard deviation σ avg equal In which N Fis the number of frames and σ is the standard deviation of single frame measurement. The average target distance value obtained is within the standard deviation σ avg Therefore, by capturing a sufficient number of frames, the determined average distance is equal to the actual distance with a probability of 99.99% within an interval around the average value (e.g., + / - 0.1% or + / - 0.5%, depending on the number of frames captured).

[0249] Other detection technologies

[0250] The projector according to the present disclosure is not limited to use with LIDAR systems based on range gating techniques. The projector according to the present disclosure can be used with any range detection technology suitable for range determination. Other examples besides range gating are direct time-of-flight detection technology or displacement technology, in which the displacement of the spot relative to a reference position is determined for deriving range information.

[0251] Independent of the detection technology, the technical effects and advantages of a LIDAR system using a projector according to the present disclosure are directly related to the characteristics of the underlying projection system. As described above, the projector has a mixing chamber that mixes the laser light so that the resulting light pattern generated by the projector lens system is uniform, i.e., all spots of the spot pattern (including spots at the periphery of the spot pattern) have the same light intensity. In addition, due to the mixing of the light sources, the projector is very robust, and if a single light source (such as the emitter of a VCSEL chip) does not work, the impact on the light intensity of the individual spots is negligible. In addition, the laser array can advantageously be composed of a plurality of VCSEL chips, i.e., a VCSEL patch, which facilitates the production process and cost of the laser array. Finally, the mixing results in a less coherent laser and thus reduces speckle noise;

[0252] The LIDAR system according to the present disclosure is suitable for integration into a vehicle. The LIDAR system integrated in the vehicle is arranged to operably cover at least a portion of the area surrounding the vehicle. The at least a portion of the area corresponds to a scene where a distance needs to be determined. The covered area depends on the field of view (FOV) of the LIDAR device, and in various embodiments, the FOV is, for example, 30°x10° or 120°x30° or 63°x21° or any other FOV suitable for the LIDAR system. The LIDAR system according to the present disclosure is not limited to LIDAR for automotive applications, and the system can also be applied to other fields where LIDAR is installed, for example, on an aircraft or satellite.

[0253] Reference numerals

[0254]

[0255]

Claims

1. A projector for illuminating a scene with a discrete spot pattern, the projector comprising: a laser array comprising a plurality of discrete solid-state laser sources operable to emit a divergent first laser beam, a mixing chamber extending along the main optical axis Z and configured to receive and allow each of the first laser beams to diverge until, for each first laser beam, at least a portion of its rays overlaps with rays of an adjacent first laser beam, wherein at least a portion of the inner wall of the mixing chamber is a reflective wall for reflecting laser light, or wherein at least a portion of the inner wall of the mixing chamber comprises a mirror, A shaping optical system configured to: i) receiving overlapping rays of the first laser beam emitted from the mixing chamber, and ii) generating a plurality of discrete second laser beams, wherein each second laser beam comprises light originating from the plurality of first laser beams, And wherein the shaping optical system comprises a first microlens array, the first microlens array comprises a plurality of microlenses ML[i], and wherein each microlens ML[i] is configured to generate one of the plurality of second laser beams, a projector lens system, the projector lens system is configured to receive the second laser beam and project the second laser beam onto a scene, and wherein the projected second laser beam forms the discrete spot pattern.

2. The projector according to claim 1, characterized in that The mixing chamber includes an inspection port configured to inspect operation of the projector when in use.

3. The projector according to claim 1, characterized in that: The shaping optical system is configured such that the number of second laser beams formed by the shaping optical system is lower than the number of first laser beams emitted by the laser array.

4. The projector according to claim 1, characterized in that: The plurality of discrete solid-state laser sources are grouped into a plurality of patches T i , and the patches are arranged to form a one-dimensional or two-dimensional patch array, and each patch T i The plurality of discrete solid-state laser sources are connected to the patch T i Multiple STs associated i Discrete solid-state laser sources.

5. The projector according to claim 4, characterized in that: The patch T i Each of forms a one-dimensional or two-dimensional sub-array of solid-state laser sources.

6. The projector according to claim 4 or 5, characterized in that: The length H of the mixing chamber measured along the main optical axis Z is defined such that after the first laser beam propagates through the mixing chamber, for each patch at least a portion of its light overlaps with the light of an adjacent patch.

7. The projector according to claim 6, characterized in that: The patches have a rectangular shape, and wherein the patches are arranged to form a regular pattern such that the inter-patch distance is the same for the entire laser array.

8. The projector according to claim 7, characterized in that: The length of the mixing chamber is selected such that: Where H is the length of the mixing chamber, Δ is the distance between the centers of two adjacent patches, θ is the beam divergence angle of the solid-state laser source, and L is the length of one side of a rectangular patch.

9. The projector according to claim 4, characterized in that: The projector also includes a beam expander configured to increase illumination in inter-patch regions, thereby increasing uniformity of light distribution incident on the first microlens array.

10. The projector according to claim 1, characterized in that The first microlens array is configured such that each microlens ML[i] of the first microlens array comprises a focus RFP[i] located on a plane FP or a curved surface CFP, and wherein the plane FP or the curved surface CFP is located between the first microlens array ML[i] and the projector lens system.

11. The projector according to claim 1, characterized in that: The first microlens array is configured such that each microlens ML[i] comprises a focus RFP[i] located on a curved surface CFP, and wherein the curved surface CFP corresponds to a curved focal plane of the projector lens system.

12. The projector according to claim 10 or 11, characterized in that: Each of the microlenses ML[i] includes an optical axis Z parallel to the main optical axis Z. i .

13. The projector according to claim 10 or 11, characterized in that: At least a portion of the microlenses ML[i] include an optical axis Z that is not parallel to the main optical axis Z. i .

14. The projector according to claim 1, characterized in that The first microlens array is arranged such that each microlens of the first microlens array is located in an optical path of a plurality of solid-state laser sources of the laser array.

15. The projector according to claim 1, characterized in that The first microlens array includes a first number of microlenses, and wherein the laser array includes a second number of discrete solid-state laser sources, and wherein the first number is equal to or less than the second number.

16. The projector according to claim 1, characterized in that The projector also includes a second microlens array configured to reduce a divergence angle of a first laser beam emitted by the solid-state laser source.

17. The projector according to claim 16, characterized in that: The second microlens array is arranged between the laser array and the first microlens array.

18. The projector according to claim 1, characterized in that The projector also includes a diffuser and / or a circulator configured to increase overlap of the first laser beam within the mixing chamber.

19. The projector according to claim 16, characterized in that Also included is a diffuser configured to increase overlap of the first laser beam within the mixing chamber, and wherein the diffuser is disposed between the second microlens array and the first microlens array.

20. The projector according to claim 16, characterized in that A diffuser and a circulator are also included, and wherein the circulator is arranged between the second microlens array and the diffuser.

21. The projector according to claim 16, characterized in that The laser array is composed of a plurality of VCSEL chips, wherein each VCSEL chip includes a plurality of laser emitters, and wherein each laser emitter corresponds to one of the discrete solid-state laser sources.

22. The projector according to claim 21, characterized in that The number of microlenses in the second microlens array is equal to or less than the total number of laser emitters of the laser array.

23. The projector according to claim 1, characterized in that Also included is a Bragg volume grating configured to reduce a wavelength spread of the first laser beam.

24. The projector according to claim 1, characterized in that Each laser source of the laser array has an emission surface located in an emission plane XY, and wherein the first laser beam propagates in a direction parallel to a main optical axis Z perpendicular to the emission plane XY.

25. The projector according to claim 1, characterized in that The mixing chamber comprises a circumferential side forming a three-dimensional hollow body.

26. The projector according to claim 1, characterized in that The laser array is a one-dimensional or two-dimensional laser array.

27. The projector according to claim 1, characterized in that Each of the solid-state laser sources of the laser array is a semiconductor laser.

28. The projector according to claim 27, characterized in that Each of the solid-state laser sources of the laser array is a vertical cavity surface emitting laser.

29. The projector according to claim 1, characterized in that The laser array is a front-end VCSEL array.

30. The projector according to claim 1, characterized in that The laser array is a back-end VCSEL array including a plurality of vertical cavity surface emitting lasers configured to emit laser light through a substrate of the back-end VCSEL array.

31. The projector according to claim 16, characterized in that The laser array is a back-end VCSEL array including the second microlens array, and wherein the second microlens array includes a lens configured to reduce the divergence angle θ of each vertical cavity surface emitting laser of the VCSEL array. VCSEL Microlens ML VCSEL [i].

32. The projector according to claim 31, characterized in that The second microlens array is etched in a substrate of the back-end VCSEL array.

33. The projector according to claim 1, characterized in that The shaping optical system is further configured to refocus the overlapping light rays.

34. The projector according to claim 1, characterized in that The plurality of discrete solid-state laser sources are operable to simultaneously emit divergent and pulsed first laser beams, and wherein each of the pulsed first laser beams comprises a temporal sequence of first pulses having a temporal pulse width PW, and wherein the shaping optical system is configured to i) receive overlapping light of the pulsed first laser beam emitted from the mixing chamber, and ii) generate a plurality of discrete pulsed second laser beams, wherein each second laser beam comprises light originating from the plurality of first laser beams, and wherein each pulsed second laser beam comprises a temporal sequence of second pulses having the temporal pulse width PW, And wherein the projector lens system is configured to receive the pulsed second laser beam and project the pulsed second laser beam toward the scene, and wherein the projected pulsed second laser beam forms the discrete spot pattern.

35. A solid-state LIDAR system (1) for determining the distance to one or more objects in a scene, comprising: A projector as claimed in any preceding claim, adapted to illuminate the scene with a discrete spot pattern, a light receiving device including a multi-pixel detector configured to detect reflected laser light spots representing a pattern of discrete light spots reflected by one or more objects of the scene, a controller for controlling the projector and the light receiving device so as to detect and accumulate the reflected laser light in synchronization with illumination of the scene, and A processing device is configured to calculate a distance to one or more objects of the scene based on the accumulated reflected laser light.

36. The solid-state LIDAR system of claim 35, wherein: The multi-pixel detector is a direct time-of-flight multi-pixel detector and the processing means are configured to calculate the distance to the object by means of a direct time-of-flight scheme.

37. A solid-state LIDAR system for determining distances to one or more objects of a scene, comprising: The projector of claim 34, configured to illuminate the scene with a discrete spot pattern, a light receiving device comprising a multi-pixel detector configured to detect reflected laser light spots representing a discrete light spot pattern reflected by one or more objects of the scene, and wherein the multi-pixel detector is a range-gated multi-pixel detector configured to detect reflected laser light during consecutive detection time windows, a controller for controlling the projector and the light receiving device so as to detect and accumulate the reflected laser light in synchronization with illumination of the scene, and A processing device is configured to calculate a distance to one or more objects of the scene based on the accumulated reflected laser light.

38. The solid-state LIDAR system of claim 37, wherein: The range-gated multi-pixel detector is configured to detect reflected laser light during at least two consecutive detection time windows, and wherein the processing device is configured to calculate the distance to the object based on the laser light detected during the two consecutive detection time windows.

39. A solid-state LIDAR system according to any one of claims 37 to 38, characterized in that The controller is configured to control the laser array so that each of the plurality of discrete solid-state laser sources emits a pulse at a frequency F P The first pulse is emitted so that F P ≤1 / (TOF max +PW), Among them, F P is the pulse frequency, PW is the time pulse width, and TOF max is the predefined maximum distance D to be determined max Maximum flight time.

40. A vehicle comprising a solid-state LIDAR system according to any one of claims 35 to 39, the vehicle having a field of view covering at least a portion of an area surrounding the vehicle, and wherein the at least a portion of the area corresponds to the scene.

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