LiDAR system and curved protective glass

Abstract

A LIDAR system (1) comprising a curved protective glass (2), characterized in that the LIDAR system (1) comprises a compensation element (11) configured to compensate for light refraction caused by the protective glass (2), wherein the compensation element (11) is surrounded by or embedded in the protective glass (2).

Description

[0001] The present invention relates to a LIDAR system and a curved protective glass, preferably for a LIDAR system. State of the art

[0002] The abbreviation LIDAR stands for Light Detection and Ranging. LIDAR uses a technology very similar to radar. LIDAR is a type of scanner that allows for the remote examination of objects. It is increasingly used in motor vehicles, for example, to monitor traffic in the vicinity. For instance, LIDAR can determine the distance to or speed of objects such as cars in the area. A LIDAR system typically includes at least one transmitting unit, which contains a light source, such as a laser source, and one receiving unit, namely a detector. The light source emits light beams, such as laser beams, towards an object, for example, a car, and the detector receives the light beam reflected by the object. This allows, for example, the determination of the object's position to help avoid collisions.Therefore, when installed in a motor vehicle, for example, the LIDAR system can effectively increase the driving safety of the vehicle.

[0003] LiDAR systems often feature a scanning and rotating LiDAR sensor. To protect against dirt and water, and for encapsulation, LiDAR sensors are frequently equipped with an exit window, also called protective glass or cover glass, that is transparent to the respective wavelength.

[0004] Due to a refractive index difference at the protective glass (n1=n Luft =1 and n2=n Glas =1.5) In some LIDAR systems, an unwanted beam deflection occurs at the curved protective glass. This is explained by the well-known Snell's law of refraction for the transition of light between two media: n1⋅sinα1=n2⋅sinα2

[0005] With a flat medium or a central or perpendicular beam passing through a non-curved protective glass, the beam angle relative to the normal of the interface remains the same both in front of and behind the protective glass, despite the light passing through the glass twice (air-glass-air). Therefore, with a non-curved protective glass, the beam continues behind the glass in exactly the same direction as it entered the glass. However, with a curved protective glass, the beam direction changes. In particular, if the transmitting and receiving units of the LiDAR sensor are positioned next to each other, a more pronounced beam change occurs at a curved interface, such as a curved protective glass, because the beam then passes through the protective glass not centrally, but laterally.

[0006] WO 2016 / 116733 A1 discloses a waveguide-based LIDAR, wherein the waveguides have holographic gratings for radiation deflection. In particular, both the transmitter waveguide and the receiver waveguide can include corresponding grating elements for targeted alignment to specific angular ranges.

[0007] CA 2 316 946 A1 discloses active and passive holographic components for curved surfaces. In particular, it is proposed to cover at least part of the inner or outer surface of a curved surface element, such as a light bulb, ornament, or light tube, with a diffraction grating, for example, a holographic diffraction grating or a mechanical diffraction grating. The diffraction grating is designed to deflect light in such a way as to produce a rainbow effect for an observer. However, in other applications, this rainbow effect may be an undesirable side effect. The diffraction grating can be in the form of a holographic optical element, also called a diffractive holographic optical pattern (HOP), which is attached to or imprinted on the curved surface.

[0008] From GB 2 444 138 A, a beam scanning device for aligning incident beams from a laser source to generate a scanning beam pattern is known. A window in the form of a spherical cap is provided to enable a wide field of view.

[0009] US 2018 / 0287336 A1 relates to a device, system and method for a laser projection module for a three-dimensional (3D) scanning device, which includes a simplified configuration with improved manufacturability.

[0010] US 2017 / 0328989 A1 relates to a system for outputting a patterned light beam, wherein the system comprises a light source; a positive optical element positioned to receive light from the light source and output converging light; and a negative optical element to receive the scanning beam from a reflective element, wherein the negative optical element is configured to output the scanning beam onto a viewing area. Disclosure of the invention

[0011] According to the invention, a LIDAR system having a curved protective glass is provided, wherein the LIDAR system has a compensation element designed to compensate for light refraction caused by the protective glass, wherein the compensation element is surrounded by or embedded in the protective glass.

[0012] In contrast to conventional optics, the LIDAR system according to the invention does not determine the beam deflection by refraction, but by diffraction at the compensation element. A light beam emanating from the LIDAR sensor thus essentially retains its original direction of travel after passing through the compensation element and the curved protective glass. For example, the laser beam is diffracted by the compensation element from an angle of incidence to an angle of emergence, so that the refraction of the laser beam caused by the curved protective glass is precisely compensated.

[0013] The LIDAR system according to the invention has the advantage that high diffraction efficiency can be achieved. Furthermore, the image quality of the LIDAR sensor can be improved. The compensation element can be inexpensive, thus enabling a cost-effective LIDAR system. Negative effects caused by the curved protective glass are compensated for.

[0014] In some embodiments, a compensation element is provided in transmission. In some embodiments, a compensation element is provided in reflection. Preferably, the compensation element consists of a holographic material and an optically transparent substrate on which the holographic material is applied. The substrate serves to support the holographic material. A preferred substrate is a plastic film, a glass block, or a plastic block. It is particularly preferred that the holographic material has a thickness of less than 5 mm. A thickness of less than 1 mm is particularly preferred, more preferably less than 500 µm, and more preferably less than 100 µm. It is preferred that the holographic material has a thickness of more than 1 µm. A thickness of more than 3 µm is particularly preferred, more preferably more than 5 µm, and more preferably more than 50 µm.

[0015] In a particular embodiment, the protective glass incorporates the compensation element. The compensation element is then attached to the protective glass or integrated into the protective glass assembly. This eliminates the need for a separate mounting for the compensation element. Furthermore, good stability for the compensation element is achieved.

[0016] Preferably, the compensation element is mounted on an inner surface of the protective glass. Some embodiments provide that a first interface on the protective glass is equipped with the compensation element in transmission to compensate for the angular misalignment. The compensation element is then arranged between the LIDAR sensor and the protective glass. This protects the compensation element from external environmental influences and tampering. Preferably, the substrate carrying the holographic material is applied to the protective glass. In particularly preferred embodiments, the holographic material is located between the protective glass and the substrate carrying the holographic material. The holographic material is then located on the side of the substrate facing the protective glass and is protected by the substrate, for example, the plastic film, during use.For example, the plastic film and the protective glass can protect the holographic element. In some embodiments, however, the compensation element is attached to an outer surface of the protective glass. In this case, the protective glass is positioned between the compensation element and the LiDAR sensor. This makes the compensation element easily accessible from the outside and, in some embodiments, allows for easy replacement if necessary. In other embodiments, a compensation element-protective glass assembly is provided, with the compensation element located in the center. In some embodiments, the compensation element then consists only of the holographic element and no longer has an additional support, such as a plastic carrier. The compensation element is then surrounded by the protective glass. For example, the compensation element can be embedded in the protective glass.This way, the compensation element is well protected against environmental influences and can be provided together with the protective glass as a single assembly.

[0017] Alternatively, the compensation element can be designed as a separate compensation plate from the protective glass. The compensation plate is preferably arranged between the protective glass and the LiDAR sensor. This allows, for example, an existing LiDAR system to be supplemented with the compensation element, and the existing protective glass to continue to be used unchanged. Preferably, the compensation plate is rotationally fixed with respect to the transmitting and receiving units, particularly preferably on a rotatably mounted carrier disk that also supports the transmitting and receiving units. As a further embodiment, it is also conceivable to place the compensation element for compensating the distortions caused by the curvature of the protective glass as an additional flat compensation element in the beam path between the LiDAR optics and the protective glass.The optical function of the compensation element, for example a holographic element, is locally adapted to the curvature of the protective glass in such a way that it can be compensated.

[0018] According to a preferred embodiment of the invention, the compensation element is a holographic optical element. Preferably, the holographic optical element consists of the holographic material and the optically transparent substrate on which the holographic material is applied. The holographic optical element is designed to precisely compensate for the refraction caused by the curved protective glass. Preferably, the holographic optical element is a volume hologram. This allows for high diffraction efficiency through volume diffraction. In contrast to conventional optics, in holographic optical elements implemented as volume holograms, the beam deflection is not determined by refraction, but by diffraction at the volume grating.The holographic optical elements can be manufactured in both transmission and reflection modes, and the free choice of incidence and diffraction angles enables new designs. The holographic diffraction grating is preferably exposed onto a thin film, particularly a thin layer applied to a thin substrate film, glass block, or plastic block. Volume diffraction allows the holographic optical elements to be further imparted with characteristic wavelength and angle selectivity, or even filter function. Depending on the exposure conditions (wavelength, angle), only light from defined directions and with defined wavelengths is diffracted by the structure. This results in a particularly high transparency of the holographic material applied to the film. Such film material can be inexpensive.Light is only diffracted by the structure from certain directions and wavelengths. For all other directions, the hologram remains transparent.

[0019] In some embodiments of the invention, the compensation element is assigned a characteristic wavelength selectivity and / or characteristic angular selectivity. Due to the curvature of the protective glass, an angular offset sometimes occurs between the incident and emitted waves of the laser beam. This angular offset is reduced by the optical function of the compensation element, preferably the holographic material or the holographic optical element. If the holographic optical element is assigned a characteristic angular selectivity, it can prevent light incident from the wrong direction and / or light of the wrong wavelength from being diffracted by the structure. An improved signal-to-noise ratio can thus be achieved.

[0020] Some embodiments of the invention provide for a filter function to be assigned to the compensation element. In these embodiments, the compensation element provides a filter function for ambient light when considering the reception path of the LiDAR system. Due to its characteristic angular and wavelength selectivity, only light from a specific direction and with a specific wavelength is diffracted by the structure. The remaining light also experiences an angular offset on the return path, i.e., from the scanned object back into the LiDAR system and to the receiver unit, and can thus be partially filtered. The strength of the filter function can be adjusted by the material parameters of the holographic material (thickness and refractive index modulation) and is system-dependent, representing a compromise between filter function and tolerances (for example, variations in laser source batches and temperature).An improved signal-to-noise ratio can also be achieved in this way.

[0021] Preferably, the holographic optical element has a pixel structure that is adapted to the curvature of the protective glass, depending on a calculated desired diffraction grating. The curvature of the cover glass, i.e., the protective glass, is preferably taken into account during hologram acquisition. Preferably, the unexposed holographic material is applied to the curved glass substrate, for example, the protective glass or the separate compensation plate. Two coherent light waves (first wave and second wave) are then made to interfere. An angle α1 corresponds to the angle of the light beam from the LIDAR system at the defined position. The angle of the second wave β is chosen such that the angle α2 results in the medium, and thus, upon exiting the curved structure, α1 = α3 is again obtained. Ideally, laser light with a wavelength corresponding to the subsequent target system is used for this purpose.Since lasers with very high coherence length are required for hologram recording, it is quite possible that these lasers will not be available. In this case, the grating can be recorded with adjusted angles even at wavelengths that deviate from the target wavelength by using a technique called angle and wavelength correction. The correction is calculated using the Bragg condition.

[0022] Furthermore, it is possible to print the compensation element pixel by pixel, preferably a holographic grating, or in some embodiments, a volume hologram. For this purpose, the desired diffraction grating is calculated and can thus be adapted pixel by pixel to the curvature. This allows the holograms to be exposed in the uncurved state and then later applied to the curved glass substrate, preferably by laminating.

[0023] One advantage of the invention is that it works better with increasing curvature of the protective glass, as this allows for a stronger separation of the first wave and the second wave during recording.

[0024] Some embodiments provide exactly one compensation element. This is particularly advantageous because all optical functions, such as angular and wavelength selectivity and filtering, can be combined in a single compensation element. Preferably, the compensation element is a film surrounding 360° of the inner surface of the protective glass. In other embodiments, however, different compensation elements are provided for different optical functions. For example, preferably at a first interface, a holographic optical element in transmission can be provided to compensate for the angular misalignment, while another holographic optical element is provided for filtering and / or characteristic wavelength selectivity.

[0025] According to the invention, a curved protective glass for a LIDAR system is also provided, wherein the protective glass has a compensation element which is designed to compensate for a refraction of light caused by the protective glass, wherein the compensation element is surrounded by or embedded in the protective glass.

[0026] In contrast to conventional optics, the protective glass according to the invention does not solely determine the beam deflection by light refraction at the protective glass, but additionally by diffraction at the compensation element to compensate for the offset caused by the light refraction at the curved protective glass.

[0027] The protective glass according to the invention has the advantage that high diffraction efficiency can be achieved. Furthermore, the image quality of the LiDAR sensor can be improved. The compensation element can be inexpensive, thus enabling a cost-effective LiDAR system. Negative effects caused by the curved protective glass are compensated for.

[0028] Preferred embodiments of the protective glass can be designed with respect to the compensation element as described above with regard to the LIDAR system with the aforementioned advantages.

[0029] Advantageous embodiments of the invention are specified in the dependent claims and described in the description. Drawings

[0030] Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. The drawings show: Fig. 1 a first embodiment of the present invention; Fig. 2 an enlarged section of the first embodiment of the present invention, which schematically illustrates the invention; and Fig. 3 a second embodiment of the present invention. Embodiments of the invention

[0031] In the Fig. Figure 1 shows a LiDAR system 1 according to a first embodiment of the present invention. The LiDAR system 1 has a curved protective glass 2. The LiDAR system 1 also has a transmitter 3, more precisely a laser source. A transmitter lens 4 with several optical components, in the present embodiment three lenses 5a-c, is arranged between the transmitter 3 and the protective glass 2. The transmitter 3 is arranged to send a laser beam through the transmitter lens 4. The transmitter lens 4 conditions the laser beam emitted by the transmitter 3 such that it is suitable for LiDAR measurements with the LiDAR system 1.

[0032] The LIDAR system 1 according to Fig. The device 1 further comprises a receiving unit 6, specifically a laser detector. Between the receiving unit 6 and the protective glass 2, a receiving lens 7 with several additional optical components is arranged, in this case four additional lenses 8a-d. The receiving lens 7 conditions the laser beam emitted by the transmitting unit 3, transmitted through the protective glass 2, and reflected by an object (not shown) located outside the protective glass 2, such that it is detectable by the receiving unit 6. The transmitting unit 3, the transmitting lens 4, the receiving lens 7, and the receiving unit 6 are fixed on a common, rotatably mounted carrier disk 9. The transmitting unit 3 and the receiving unit 6 together form a LIDAR sensor of the LIDAR system 1.

[0033] The carrier disk 9 is rotatably and driveably mounted on a central pivot axis 10. The receiver unit 6 and the transmitter unit 3 are arranged side by side on the carrier disk 9, i.e., laterally offset from each other. The transmitter unit 3 and the receiver unit 6 are also rotatably mounted about the central pivot axis 10, and thus, together with the carrier disk 9, are rotatably mounted about the central pivot axis 10. The central pivot axis 10 of the carrier disk 9 lies in the center of the protective glass 2 and represents a rotational symmetry axis of the protective glass 2. The protective glass 2 is decoupled from the rotation of the carrier disk 9 and therefore does not rotate with the carrier disk 9, the transmitter unit 3, the transmitting lens 4, the receiving lens 7, and the receiver unit 6 when the LIDAR system 1 is in its driven operating state.The protective glass 2 of the LIDAR system 1 is therefore stationary and protects the LIDAR sensor of the LIDAR system 1, which is rotatably mounted relative to it, from environmental influences.

[0034] The transmitter unit 3 and the receiver unit 6 are located on the carrier disk 9 on opposite sides of the axis of rotation 10. This means that the beam path of the exiting and incident laser beams through the protective glass 2 is not centered, but offset to the side. Therefore, the laser beam, originating from the transmitter unit 3, is not perpendicular to the inner surface of the protective glass 2. Consequently, the laser beam is refracted by the curved protective glass 2 both when exiting the LIDAR system 1 and when entering the LIDAR system 1. This would negatively affect the measurement quality of the LIDAR system 1 because the refraction of the laser beam by the protective glass 2 alters the direction of travel of the laser beam.

[0035] According to the invention, the LIDAR system 1 includes a compensation element 11 designed to compensate for light refraction caused by the protective glass 2. This improves, for example, the image quality of the LIDAR system 1. In this embodiment, the protective glass 2 incorporates the compensation element 11. More precisely, the compensation element 11 is mounted on an inner surface of the protective glass 2. This inner surface is an inward-facing interface of the protective glass 2, pointing towards the LIDAR sensor. Thus, the compensation element 11 is located between the protective glass 2 and the transmitting unit 3, as well as between the protective glass 2 and the receiving unit 6.

[0036] The compensation element 11 in the first embodiment according to Fig. 1 is a holographic optical element (HOE), more precisely a volume hologram. The compensation element 11 is mounted on the protective glass 2 on a 360° circumference, specifically in the horizontal scan plane of the transmitting unit 3 and the receiving unit 6. This is designed so that the transmitting unit 3 and the receiving unit 6 are rotatably mounted through 360° and therefore, during the rotation of the carrier disk 9 about the central axis of rotation 10 of the protective glass 2, the laser beam successively and repeatedly illuminates the full circle of the cylindrical, curved protective glass 2 in the scan plane.

[0037] The compensation element 11 is assigned a characteristic wavelength selectivity. Furthermore, the compensation element 11 is assigned a characteristic angle selectivity. Additionally, the compensation element 11 is assigned a filter function. Finally, the compensation element 11 has a pixel structure that is adapted to the curvature of the protective glass 2 depending on a calculated desired diffraction grating.

[0038] Fig. Figure 2 schematically illustrates an enlarged section of the first embodiment of the present invention. The case of a laser beam exiting the protective glass 2 is shown as an example. The path of the laser beam 2 is indicated by the dashed arrow. The same applies analogously, but in reverse, to the case (not shown) of a laser beam entering the protective glass 2.

[0039] A circular segment of a cross-section through the cylindrical, curved protective glass 2 is in Fig. Figure 2 shows a top-down view. The compensation element 11 pre-compensates for the curvature of the protective glass 2. This is an example of diffraction at the holographic grating in transmission. As a result, the laser beam exits the protective glass 2 in essentially the same direction as it entered the compensation element 11 from the transmitting unit. Snell's law of refraction is used here. An angle α2 is set by the compensation element such that the angle of incidence α1 into the compensation element 11 and the angle of exit α3 from the compensation element 11 are essentially exactly the same. The incident beam is thus diffracted at angle α1 at the holographic grating of the compensation element 11 to angle α2.

[0040] By orienting the holographic grating, α2 can be configured such that the subsequent distortion caused by the curvature of the cover glass, the protective glass 2, can be compensated. The direction of travel of the laser beam behind the protective glass 2 is then essentially exactly the same as the direction of travel of the laser beam in front of the compensation element 11, viewed from the transmitter unit 3. According to the invention, the compensation element 11 compensates for the refraction of light caused by the protective glass 2. More precisely, the diffraction of light at the volume grating of the compensation element 11, i.e., at the volume hologram, compensates for the refraction of light at the protective glass 2.In other words, the volume hologram is designed to bend the laser beam from α1 into the medium, i.e., the protective glass 2, at an angle α2, so that when the laser beam exits the surface of the protective glass 2, α1 = α3 again applies, as with a non-curved medium or with a central beam passage through the curved medium, perpendicular to the interface. The curvature of the cover glass, the protective glass 2, is compensated by the holographic optical element, the compensation element 11.

[0041] Fig. Figure 3 shows a second embodiment of the present invention. Many features of the second embodiment are identical to those of the first embodiment. However, the compensation element 11 is designed as a compensation plate separate from the protective glass 2. More precisely, the compensation element 11 is a flat, cuboid compensation plate. In the second embodiment, the compensation element 11 is arranged downstream of the transmitting lens with respect to the laser beam path and is fixed separately from the protective glass 2 on the carrier disk 9. In the second embodiment, the compensation element 11 is arranged upstream of the receiving lens 7 with respect to the laser beam path and is fixed separately from the protective glass 2 on the carrier disk 9. The compensation element 11 is arranged so as not to rotate with respect to the carrier disk 9, and thus rotates with the carrier disk 9 during operation.The compensation element 11 can in principle be arranged anywhere in the beam path of the laser beam and within the protective glass 2, separately from the protective glass 2, as long as it is ensured that the compensation element 11 remains continuously in the beam path of the laser beam when the carrier disk 9 is rotated, in order to guarantee continuous refractive compensation of the protective glass 2.

[0042] In the exemplary embodiment according to Fig. 3 A common compensation element 11 is provided for both the transmitting unit 3 and the receiving unit 6. In embodiments not shown, however, a separate compensation element 11 is provided for each of the transmitting unit 3 and the receiving unit 6, for example, two compensation plates, one for the transmitting unit 3 and one for the receiving unit 6. Some embodiments not shown have, in addition to one or more compensation plates on the carrier disk 9, a further compensation element 11 on the protective glass 2, as shown by Fig. 1 shown. In some embodiments, the compensation plate is curved, preferably with the same radius of curvature as the protective glass 2.

[0043] In other words, the invention describes a compensation for beam changes at a curved interface for LIDAR sensors. The core of the invention is the compensation of the influence of a curved protective glass 2 in LIDAR sensors using a compensation element 11, in particular holographic optical elements.

[0044] As shown by the Fig. Figures 1-3 illustrate a LIDAR system 1 which has a curved protective glass 2, wherein the LIDAR system 1 has a compensation element 11 which is configured to compensate for a refraction of light caused by the protective glass 2.

[0045] Furthermore, a curved protective glass 2, in this case for a LIDAR system 1, is proposed, wherein the protective glass 2 has a compensation element 11 which is designed to compensate for light refraction caused by the protective glass 2.

Claims

[1] LIDAR system (1) comprising a curved protective glass (2), characterized by , that the LIDAR system (1) has a compensation element (11) which is configured to compensate for light refraction caused by the protective glass (2), wherein the compensation element (11) is surrounded by or embedded in the protective glass (2). [2] LIDAR system (1) according to claim 1, wherein the compensation element (11) is a holographic optical element. [3] LIDAR system (1) according to claim 2, wherein the holographic optical element is a volume hologram. [4] LIDAR system (1) according to one of the preceding claims, wherein the compensation element (11) is assigned a characteristic wavelength selectivity and / or characteristic angle selectivity. [5] LIDAR system (1) according to one of the preceding claims, wherein the compensation element (11) is assigned a filter function. [6] LIDAR system (1) according to one of the preceding claims, wherein the compensation element (11) has a pixel structure which is adapted to a curvature of the protective glass (2) depending on a calculated desired diffraction grating. [7] Curved protective glass (2), preferably for a LIDAR system (1), characterized by , that the protective glass (2) has a compensation element (11) which is designed to compensate for a refraction of light caused by the protective glass (2), wherein the compensation element (11) is surrounded by or embedded in the protective glass (2).

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