LIDAR SYSTEM INCLUDING HOLOGRAPHIC IMAGING OPTICS

Abstract

A LIDAR system for detecting objects within an observation area. The LIDAR system includes an illumination unit for illuminating the observation area using multiple light radiations, each having a different wavelength, multiple separate spatial areas of the observation area, which are presently detected by a detection area of the LIDAR system, being temporally consecutively illuminated in each case with another of the light radiations; and a detection unit for detecting the light radiations reflected by objects, including at least one detection array, which is individually assigned to the particular detection area and is made of up of a detector for detecting the light radiations from the spatial areas presently detected by the detection area, and a holographic imaging optics for focusing the respective light radiations onto the detector.

Claims

1-11. (canceled)

12. A LIDAR system for detecting objects within an observation area, comprising: an illumination unit configured to illuminate the observation area using multiple light radiations, each having a different wavelength and being emitted in the form of light beams, multiple separate spatial areas of the observation area, which are presently covered by a detection area of the LIDAR system, being temporally consecutively illuminated in each case with another of the light radiations; and a detection unit configured to detect the light radiations reflected by objects in the observation area, including at least one detection array, which is individually assigned to the particular detection area and is made of up of a detector configured to detect the light radiations from the spatial areas presently covered by the detection area and a holographic imaging optics configured to focus the respective light radiations onto the detector, the holographic imaging optics being configured, for each of the light radiations which are focused onto the detector, to focus a particular light radiation of the light radiations from only one spatial area, which is individually assigned to the particular light radiation and presently covered by the detection area, onto the detector.

13. The LIDAR system as recited in claim 12, wherein the holographic imaging optics includes at least one holographic optical element.

14. The LIDAR system as recited in claim 13, wherein the holographic optical element includes multiple holograms, which are configured to each focus one of the light radiations from a respective other of the spatial areas presently detected by the particular detection area onto the detector.

15. The LIDAR system as recited in claim 14, wherein at least one of the holograms is a transmission geometry volume hologram.

16. The LIDAR system as recited in claim 12, wherein the illumination unit includes a photoemitter array including multiple photoemitters, which each emit one of the light radiations.

17. The LIDAR system as recited in claim 16, wherein a respective passive optics made up of at least one diffractive optical element and/or a holographic optical element is assigned to individual ones of the photoemitters, the passive optics being configured to split the light radiation emitted by the particular photoemitter in the form of a light beam into at least two subbeams, each illuminating a different spatial area of the observation area.

18. The LIDAR system as recited in claim 12, wherein the detection unit includes multiple detection arrays which are situated spatially offset from one another and are each made up of a respective detector and a respective holographic optical element individually assigned to the detection arrays, detection areas of the detection arrays each covering different spatial areas of the observation area.

19. The LIDAR system as recited in claim 18, wherein the detection arrays of the detection unit are situated in a focal plane of a shared imaging optics.

20. The LIDAR system as recited in claim 12, wherein all spatial areas of the observation area which are presently covered by detectors of the detection unit define a present field of view of the LIDAR system, the LIDAR system being configured to scan the entire observation area using a scanning movement of the present field of view along a predefined scanning direction.

21. The LIDAR system as recited in claim 12, wherein an optical bandpass filter is assigned to at least one of the at least one detection array, which only allows light radiation having certain wavelengths to pass.

22. A holographic imaging optics for a LIDAR system, comprising: at least one holographic optical element including multiple holograms, each particular hologram of the holograms being configured to focus a particular light radiation which is individually assigned to the particular hologram, from a respective spatial area which is individually assigned to the particular light radiation onto a detector which is individually assigned to the holographic optical element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows a scanning LIDAR system while scanning an observation area.

[0018] FIG. 2 schematically shows a detection unit of a conventional LIDAR system.

[0019] FIG. 3 schematically shows a detection unit of a LIDAR system including a holographic imaging optics made up of a holographic optical element, in accordance with an example embodiment of the present invention.

[0020] FIG. 4 shows a detailed view of the holographic optical element including multiple holograms from FIG. 3, in accordance with an example embodiment of the present invention.

[0021] FIG. 5 schematically shows an expanded detection unit including multiple detection arrays according to FIG. 3 and a shared imaging optics, in accordance with an example embodiment of the present invention.

[0022] FIG. 6 shows an illumination unit of the LIDAR system including a diffractive optics made up of multiple diffractive optical elements, in accordance with an example embodiment of the present invention.

[0023] FIG. 7 schematically shows the configuration of a LIDAR system including a reduced number of detection arrays, in accordance with an example embodiment of the present invention.

[0024] FIG. 8 schematically shows a modification of the system from FIG. 7 in which the number of photoemitters of the LIDAR system was reduced with the aid of multiple diffractive optical elements, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0025] FIG. 1 schematically illustrates the principle of a scanning

[0026] LIDAR system 100, which scans a defined observation area 210 of its immediate surroundings 200 with the aid of light beams 311.sub.j.

[0027] LIDAR system 100 includes an illumination unit 130, which is situated in a rotating housing 110 and includes multiple photoemitters for generating one or multiple light radiation(s), which is/are emitted in the form of separate light or laser beams 311.sub.j into different spatial directions. In the process, each of light beams 311.sub.j illuminates a spatial area 211.sub.j which is individually assigned to the particular light beam 311.sub.j, in the present example spatial areas 211.sub.j detected simultaneously by illumination unit 130 at a certain point in time being situated vertically beneath one another, so that the present field of view 213 of LIDAR system 100 forms a more or less coherent strip. Housing 110 and illumination unit 130 situated therein are pivoted along a predefined scanning direction by a scanning movement 101 so that, during an entire scanning period, field of view 213 detects all spatial areas 211.sub.j of the present observation area 210 of LIDAR system 100.

[0028] During the measuring process, light beams 311.sub.j emitted by LIDAR system 100 strike objects 201 in surroundings 200 and are reflected by them to LIDAR system 100, where they are detected with the aid of a detection unit 140. Based on the runtimes of the received light beams 312.sub.j, a control unit 120 of LIDAR system 100 ascertains the distance from object 201 illuminated by the particular light beam for each of these light beams 311.sub.j, 312.sub.j. After an entire scanning period, LIDAR system 100 supplies a point cloud as the measuring result, which represents the relative arrangement of objects 201 within observation area 210 of LIDAR system 100.

[0029] The detection of light beams 312.sub.j reflected from the different spatial areas 211.sub.j of the present field of view 213 takes place individually in the process. In the case of a conventional LIDAR system 100, a dedicated detector 142.sub.j is thus in each case individually assigned to each viewing angle. In this regard, FIG. 2 shows a corresponding detailed view of a typical detection unit 140 of a conventional LIDAR system 100. Detection unit 140 includes an imaging optics 146 and a group 141 of detectors 142.sub.1-142.sub.m, which are situated in a column-shaped manner beneath one another in a focal plane 147 of imaging optics 146. In the process, imaging optics 146 focuses light from different spatial directions onto different spots in its focal plane 147, each of light beams 312.sub.j reflected from one of spatial areas 211.sub.1-211.sub.j of the present field of view 213 being mapped onto a detector 142.sub.1-142.sub.j individually assigned to the particular spatial area 211.sub.1-211.sub.j. LIDAR system 100 thus has a total number of j viewing directions 214.sub.j.

[0030] LIDAR system 100 uses avalanche diodes (APDs) or single-photon avalanche diode (SPADs) as detectors 142.sub.1-142.sub.j. In the process, the diodes may be present in isolated instances or as part of a monolithic array. Furthermore, it may also be advantageous to interconnect an entire array or a portion of an array of SPADs into an individual detector (“solid-state photomultiplier”). Depending on the application, imaging optics 146 shown symbolically here as an individual lens may be made up of an individual optical component, such as for example a lens or a concave mirror, or of an array of multiple such components, such as for example a lens triplet and an inverting mirror.

[0031] To be able to reduce the number of detectors in such a scanning LIDAR system, with the same resolution, according to the present invention the conventional imaging optics based on lenses and/or mirrors is replaced or supplemented with a holographic imaging optics 145 including holographic elements, which generates multiple viewing directions for each of the m detectors 142.sub.1-142.sub.j. For this purpose, FIG. 3 schematically shows a detection array 141 of an accordingly modified detection unit 140 of LIDAR system 100, including a detector 142 and a holographic imaging optics 145 including a holographic optical element 143 assigned to detector 142. Holographic optical element 143 formed of holograms is designed to focus multiple light radiations 310.sub.1-310.sub.3, each having different wavelengths, from different directions onto detector 142. A total of three different light radiations 310.sub.1-310.sub.3 are shown in the present example, which strike in the form of reflected light beams 312.sub.1-312.sub.3, each from different spatial directions, and are mapped onto detector 142 by holographic optical element 143. In contrast to a traditional refractive optics, it is a fundamental property of holograms to only work well for certain wavelengths and spatial directions, and to have only a limited tolerance with respect to this property. The use of holograms for the application in a LIDAR system thus has the advantage that neither light from spatial directions other than those intended, nor light having wavelengths other than those intended, is guided onto detector 142. Due to this wavelength selectivity, for example an additional bandpass filter is ideally not required, however may nonetheless be advantageous, depending on the application.

[0032] Holographic optics 145 is made up of at least one holographic optical element 143, which includes n holograms 144.sub.1-144.sub.n, n≥2 applying. Each of these n holograms 144.sub.1-144.sub.n is characterized in that it focuses a certain bundle of rays onto detector 142 for a corresponding number of n wavelengths λ.sub.1-λ.sub.n. Formulated in the wave representation, an ideally flat wave from a certain spatial direction is converted into a spherical wave front in the case of a hologram, which is centered on the detector position. In the present exemplary embodiment, a total of three light radiations 310.sub.1, 310.sub.2, 310.sub.3, which each have a different wavelength and which are reflected onto detector array 141 in the form of three light beams 312.sub.1, 312.sub.2, 312.sub.3 from different spatial areas, are mapped onto the shared detector 142 by holographic optical element 143. FIG. 4 shows a detailed view of holographic optical element 143 from FIG. 3. In the process, it becomes apparent that holographic optical element 143 is made up of a total of three consecutively situated holograms 144.sub.1, 144.sub.2, 144.sub.3, which each map a light radiation 310.sub.1, 310.sub.2, 310.sub.3 which is individually assigned to the respective hologram, from a spatial direction individually assigned to the particular light radiation 310.sub.1, 310.sub.2, 310.sub.3, onto detector 142. Holographic optical element 143, including its three holograms 144.sub.1, 144.sub.2, 144.sub.3, thus generates a total of three viewing directions in the present exemplary embodiment for the assigned detector 142. In the process, the number of viewing directions thus generated may be adapted as needed in each particular case by providing a corresponding number of holograms. In particular, additional viewing directions may be implemented relatively easily by adding further holograms to holographic optical element 143.

[0033] However, it may be useful to limit the number of holograms combined in a holographic optical element 143 since each additional hologram is generally also accompanied by a deterioration of the optical properties of holographic optical element 143. For example, the efficiency with which the individual holograms focus light having the corresponding wavelength as desired decreases as a result of the multiplexing of multiple holograms. At the same time, diffuse scattering increases, so that light radiation having undesirable wavelengths λ also reaches the detector. The involved deterioration of the signal-to-background ratio may, in particular, prove to be particularly critical in LIDAR applications.

[0034] To be able to increase the number of the viewing directions of the LIDAR system without these disadvantages, an array is selected in which the different viewing directions are distributed among multiple detectors, each equipped with a dedicated holographic optical element. For this purpose, FIG. 5 shows a corresponding detection unit 140 including a group of in total m detection arrays 141.sub.1-141.sub.m, made up in each case of a detector 142.sub.1-142.sub.m and a holographic optical element 143.sub.1-143.sub.m individually assigned to the detection arrays. Detection arrays 141.sub.1-141.sub.m situated in a row-shaped manner beneath one another each have different viewing directions. In the process, each detection array 141.sub.1-141.sub.m includes a holographic optical element 143.sub.1-143.sub.m, which, in turn, in total includes n holograms 144.sub.1-144.sub.n for wavelengths λ.sub.1-λ.sub.n, and thus has n different viewing directions. The entire group of detection arrays 141.sub.1-141.sub.n thus includes a total of j holograms, and thus viewing directions, j=m*n applying. The group having in each case m=3 holograms or viewing directions per detection array 141.sub.1-141.sub.n shown in FIG. 5 thus has a total of m*3 viewing directions. Even though the embodiment shown in FIG. 5 includes more detectors compared to the individual holographic optical element from FIG. 4 having n holograms or viewing directions, it has the advantage that the lower number of holograms per holographic optical element results in better optical quality. Furthermore, each of wavelengths λ.sub.1-λ.sub.n may be used for a total of m paths or viewing directions since only a single viewing direction is assigned to each of the m detection arrays 141.sub.1-141.sub.n for each wavelength λ.sub.1-λ.sub.n, and thus up to m individual measurements may take place simultaneously.

[0035] To increase the light efficiency, in the present exemplary embodiment all optical paths of detection unit 140 are collected by a conventional imaging optics 146 and only distributed downstream therefrom among the individual detection arrays 141.sub.1-141.sub.n, which are situated in a focal plane 147 of the shared imaging optics 146. In principle, however, it is also possible to situate detection arrays 141.sub.1-141.sub.n next to one another even without the shared traditional imaging optics 146. However, the equipment is thus made smaller, which is rather disadvantageous in a LIDAR system. With the aid of the traditional imaging optics 146 shown in FIG. 5, in contrast, it is possible to collect as much light as possible, and to distribute it among the individual holographic optical elements only thereafter.

[0036] For the implementation of the total of j viewing directions, a corresponding number of separate light paths or light beams is required. These may be implemented, for example, by a corresponding number (j) of photoemitters. Since the individual detection arrays 141.sub.1-141.sub.n carry out measurements independently of one another in the embodiment variant shown in FIG. 5, it is useful to use in each case the same light radiations or wavelengths for all detection arrays 141.sub.1-141.sub.n. Since, in this case, a total of n viewing directions or spatial areas are simultaneously excited or illuminated with the same light radiation or wavelength, it is possible to use only n photoemitters, whose emitted light beams are split by passive optics. In this regard, FIG. 6 shows an accordingly designed illumination unit 130 of LIDAR system 100. Illumination unit 130 includes a photoemitter system 131 including a total of i individual photoemitters 132.sub.1-132.sub.i, each emitting a light radiation 310.sub.1-310.sub.i having a different wavelength λ.sub.1-λ.sub.i in the form of a light beam 311.sub.1-311.sub.i, in the present exemplary embodiment only three individual photoemitters 132.sub.1, 132.sub.2, 132.sub.3 being shown. Each of photoemitters 132.sub.1-132.sub.i is assigned a respective passive optics 134.sub.1-134.sub.i in the form of a diffractive optical element (DOE), which splits light beam 311.sub.1-311.sub.i of the respective photoemitter 132.sub.1-132.sub.i into two or multiple individual subbeams 311.sub.i,1-311.sub.i,2, which are emitted in the different spatial directions in each case. As an alternative to the use of the total of n DOEs as passive optics 134.sub.1-134.sub.i, it is generally also possible to use one or multiple holographic optical element(s) for this purpose (not shown here).

[0037] FIG. 7 shows a schematic representation of a LIDAR system 100 according to the variant from FIG. 5, including an illumination unit 130 including a photoemitter array 131 made up of a total of six photoemitters 132.sub.1-132.sub.6, and a detection unit 140 including a total of two detection arrays 141.sub.1, 141.sub.2. For the sake of clarity, illumination unit 130 and detection unit 140 of LIDAR system 100 were shown on opposite sides of observation area 110. In the case of a typical LIDAR system 100, these units are situated in a shared housing so that the light paths of the transmission and reception light beams 311.sub.1-311.sub.6, 312.sub.1-312.sub.6 essentially extend next to one another. Observation area 210, which is only hinted at here, in general encompasses a plurality of separate spatial areas, for the sake of clarity only six spatial areas 211.sub.1-211.sub.6 being shown, which are presently detected by detection areas 212.sub.1, 212.sub.2 of the two detection arrays 141.sub.1, 141.sub.2. The first three photoemitters 132.sub.1-132.sub.3 of photoemitter system 131 consecutively illuminate the first three of spatial areas 211.sub.1-211.sub.3 with their respective separately generated transmission light beams 311.sub.1-311.sub.3. In parallel thereto, the remaining three photoemitters 132.sub.4-132.sub.6 of photoemitter array 131 consecutively illuminate the remaining three spatial areas 211.sub.4-211.sub.6 with their respective separately generated transmission light beams 311.sub.4-311.sub.6. During a regular operation of LIDAR system 100, a respective spatial area 211.sub.1-211.sub.6 from each of detection areas 212.sub.1, 212.sub.2 is thus illuminated, at any arbitrary measuring point in time, with light radiation 310.sub.1-310.sub.k individually assigned to the particular spatial area 211.sub.1-211.sub.6. On the reception side, the light radiations reflected or scattered from the presently illuminated spatial areas 211.sub.1-211.sub.6 in the form of reception light beams 312.sub.1-312.sub.6 back to reception unit 140 are received by the two detection arrays 141.sub.1, 141.sub.2. In the process, holographic optical elements 143.sub.1, 143.sub.2 situated in each case upstream of detectors 142.sub.1, 142.sub.2 cause each detector 142.sub.1, 142.sub.2 to only receive light radiations 310.sub.1-310.sub.k which are individually assigned to this detector 142.sub.1, 142.sub.2 from only one spatial area 211.sub.1-211.sub.6 which is individually assigned to the particular detector 142.sub.1, 142.sub.2.

[0038] Since the measurements for each of detection areas 212.sub.1, 212.sub.2 occur independently of one another, light radiations 310.sub.1-310.sub.k having the same wavelengths λ.sub.1-λ.sub.k may be used for all detection areas 211.sub.1, 211.sub.2. As is indicated in FIG. 7 with the aid of differently dotted lines, the total of six spatial areas 211.sub.1-211.sub.6 of the two detection areas 211.sub.1, 211.sub.2 are thus only illuminated with three different light radiations 310.sub.1, 310.sub.2, 310.sub.3. As is illustrated in FIG. 8, the number of photoemitters 132.sub.1-132.sub.1 of illumination unit 130 may thus be reduced to a total of three. For this purpose, LIDAR system 100 includes illumination unit 130 shown in FIG. 6, in which a respective passive optics 134.sub.1, 134.sub.2, 134.sub.3 is connected downstream from each photoemitter 132.sub.1, 132.sub.2, 132.sub.3 as a beam splitter. Each of passive optics 134.sub.1, 134.sub.2, 134.sub.3, for example in the form of a diffractive optical element (DOE), in each case splits light beam 311.sub.1, 311.sub.2, 311.sub.3 generated by the particular photoemitter 132.sub.1, 132.sub.2, 132.sub.3 into two subbeams 311.sub.1,1, 311.sub.1,2, 311.sub.2,1, 311.sub.2,2, 311.sub.3,1, 311.sub.3,2, which in each case scan a spatial area 211.sub.1-211.sub.6 in different detection areas 211.sub.1, 211.sub.2.

[0039] Holograms 144.sub.1, 144.sub.2, 144.sub.3 used in the above-described exemplary embodiments are preferably transmission geometry volume holograms. This embodiment is advantageous since in this way greater efficiencies are possible. However, a corresponding holographic optics may also be implemented with the aid of other types of holograms, for example with the aid of reflection holograms.

[0040] In the above description, the term “reflected light radiation” shall be understood to mean the light radiation reflected by the objects in the surroundings of the LIDAR system in the direction of the detection unit by reflection, diffuse reflection or scattering.

[0041] Although the present invention was illustrated and described in detail by the preferred exemplary embodiments, the present invention is not limited by the described examples. Rather, other variations may be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention, in view of the disclosure herein.