Compensation device for a biaxial LIDAR system

Abstract

A compensation device for a biaxial LIDAR system includes two holographic optical elements, which are locatable between a receiving optical system and a detector element, and which are designed to compensate for a parallax effect of the biaxial LIDAR system, incident light being guidable onto the detector element with the aid of the two holographic optical elements.

Claims

1. A compensation device for a biaxial LIDAR system, comprising: at least two holographic optical elements that are locatable between a receiving optical system and a detector element of the biaxial LIDAR system; wherein the at least two holographic optical elements compensate for a parallax effect of the biaxial LIDAR system, and wherein an incident light is guidable onto the detector element with the aid of the at least two holographic optical elements, and wherein a diffraction efficiency of the at least two holographic optical elements is adjusted in a defined manner.

2. The compensation device as recited in claim 1, wherein the at least two holographic optical elements are reflection holograms.

3. The compensation device as recited in claim 2, wherein the at least two holographic optical elements are planar reflection holograms.

4. The compensation device as recited in claim 2, wherein the at least two holographic optical elements are curved reflection holograms.

5. The compensation device as recited in claim 1, wherein: a first holographic optical element of the at least two holographic optical elements is a coupling hologram, a second holographic optical element of the at least two holographic optical elements is a decoupling hologram, and an optical waveguide is disposed between the at least two holographic optical elements.

6. The compensation device as recited in claim 1, wherein the at least two holographic optical elements include a defined optical function for compensating for an imaging error.

7. A biaxial LIDAR system, comprising: a compensation device that includes at least two holographic optical elements that are locatable between a receiving optical system and a detector element of the biaxial LIDAR system; wherein the at least two holographic optical elements compensate for a parallax effect of the biaxial LIDAR system, and wherein an incident light is guidable onto the detector element with the aid of the at least two holographic optical elements, and wherein a diffraction efficiency of the at least two holographic optical elements is adjusted in a defined manner.

8. A method for manufacturing a compensation device for a biaxial LIDAR system, comprising: providing at least two holographic optical elements for compensating for a parallax effect of the biaxial LIDAR system; wherein an incident light is guidable onto a detector element of the biaxial LIDAR system with the aid of the at least two holographic optical elements, and wherein a diffraction efficiency of the at least two holographic optical elements is adjusted in a defined manner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a representation of a conventional biaxial LIDAR system.

(2) FIG. 2 schematically shows a representation of a parallax problem of a biaxial LIDAR system.

(3) FIG. 3 schematically shows a correlation between parallax effect and detector size.

(4) FIGS. 4 through 7 schematically show representations of a proposed compensation device, including two reflection holograms.

(5) FIG. 8 schematically shows a representation of a compensation device, including an optical waveguide.

(6) FIG. 9 schematically shows a representation of a creation of a coupling hologram of FIG. 8.

(7) FIG. 10 schematically shows a representation of an alternative creation of the coupling hologram of FIG. 8.

(8) FIG. 11 schematically shows a representation of a creation of a decoupling hologram of FIG. 8.

(9) FIG. 12 schematically shows a design of a decoupling hologram for separating direct incident radiation from diffracted radiation.

(10) FIG. 13 shows a basic representation of a diffraction efficiency in various materials and wavelengths.

(11) FIG. 14 shows a block diagram of a biaxial LIDAR system, including the proposed compensation device.

(12) FIG. 15 shows a basic representation of the sequence of one specific embodiment of a method for manufacturing a compensation device for a biaxial LIDAR system.

DETAILED DESCRIPTION

(13) FIG. 4 shows a first specific embodiment of a proposed compensation device 40 for a biaxial LIDAR system. A first holographic optical element 11 is apparent in the form of a reflection hologram, which is struck by beams from distant or nearby objects 20, 30 (not depicted). This first holographic optical element 11 directs the beams to a second holographic optical element 12 in the form of a second reflection hologram, which guides the beams to detector element 4 of the biaxial LIDAR system (not depicted). As a result, detector element 4 need advantageously only be of a size that would be necessary for a coaxial LIDAR system. It may, of course, be designed somewhat larger, so that the parallax effect is distributed in particular proportions to the size of detector element 4 and in particular proportions to holographic optical elements 11, 12.

(14) This advantageously utilizes, in particular, the possibility of specifically adjusting the diffraction efficiency of holographic optical elements 11, 12. It may be meaningful, for example, to select the diffraction efficiency in area p1 (radiation from distant object 30) to be very high, whereas in area p2 (radiation from nearby object 20) a lower diffraction efficiency may be selected. In the case of nearby objects 20, a significantly higher percentage of the emitted output returns, so that the lower diffraction efficiency is able to protect detector element 4 from saturation.

(15) Since LIDAR systems are operated at a fixed wavelength (for example, at 905 nm), the use of holographic optical elements in the form of holographic optical elements 11, 12 is particularly advantageous in this case, since they are likewise designed for a particular wavelength and function optimally for this wavelength, whereas other wavelengths are not influenced by the holographic function. In this way, it is possible through the use of the holographic optical elements 11, 12 in the form of reflection holograms to advantageously also realize an intrinsic filter effect.

(16) The reflection holograms are preferably analogously recorded, but may also be written pixel by pixel by a holographic printer. This offers the possibility of printing specific holograms with an optical function that varies pixel by pixel. The contact copy method may then be used for mass production.

(17) FIG. 5 shows another specific embodiment of proposed compensation device 40, in this case, it being apparent that holographic optical elements 11, 12 are situated on the same side of detector element 4. Arbitrary geometrical arrangements are, in principle, conceivable here. Diagonally positioned and curved holographic optical elements 11, 12 are also possible for implementing compensation device 40, as depicted, in principle, in FIGS. 6, 7.

(18) Holographic optical elements 11, 12 in the form of reflection holograms are designed preferably together with receiving optical system 3. In this design, it is then also possible to implement a part of the image quality via holographic optical elements 11, 12, and thus to design the lens system of receiving optical system 3 more compactly and/or more cost-efficiently and/or more simply. At a greater angle, it is difficult to achieve the required image quality using a lens system that includes few lenses. However, two holographic optical elements 11, 12 in the form of reflection holograms are present specifically in this angle range, which are able to assume optical functions.

(19) Another advantageous specific embodiment of proposed compensation device 40 provides a beam guidance with the aid of an optical waveguide 13. In this embodiment, the signal is coupled via a first holographic element 11 in the form of a coupling hologram into optical waveguide 13, which causes a deflection in the angle of the total reflection and is diffracted out again from the structure at a defined angle via an optical holographic element 12 in the form of a decoupling hologram. This is depicted, in principle, in FIG. 8.

(20) A basic representation of a recording of the coupling hologram is depicted in FIG. 9. In the process, an interference pattern, which is stored in a light-sensitive material (for example, photopolymer), is generated by the superposition of two coherent waves (object wave OW, reference wave RW. During the reconstruction, light is diffracted on the structure and, with the wavelength remaining the same,
λ.sub.recording=λ.sub.reconstruction=λ.sub.LIDAR system
λ.sub.recording . . . recording wavelength
λ.sub.reconstruction . . . reconstruction wavelength
λ.sub.LIDAR system . . . system wavelength
is directed again at the diffraction angle of the original object wave OW.

(21) Laser diodes having a high coherence length (not cost-efficient and not space-saving) are necessary for recording holographic optical elements 11, 12, “normal” (cost-efficient and space-saving) laser diodes being sufficient for the reproduction. Given the fact that the wavelengths of the laser diodes having a high coherence length and the wavelengths of the normal diodes are different, the holographic material with its dyes is selective only in certain ranges. Thus, the later system wavelength λ.sub.LIDAR system often does not correspond to the recording wavelength λ.sub.recording. This difference in the wavelength during the recording and the reconstruction may be pre-compensated for during the recording by an angle allowance Δθ, which is depicted, in principle, in FIG. 10. One measure of the pre-compensation in this case is described by the Bragg's equation:
λ=2d×sin θ
d describing the grating distance of the holographic grating, which remains constant after the recording and storing of the volume hologram.

(22) The recording and reconstruction of the decoupling hologram is depicted in FIG. 11. Here, too, the wavelength difference between recording wave and reconstruction wave may be compensated for by a pre-compensation Δθ during recording of the hologram. The angle of the reference wave in this case corresponds to the diffraction angle θ.sub.B of the coupling hologram. Decoupling hologram θ.sub.1 may theoretically be freely selected. In the exemplary embodiment depicted, it should be noted that the useful light or the direct signal is not diffracted on the holograph structure.

(23) This is depicted in principle in FIG. 12, which shows a design of an optical holographic element 12 in the form of a decoupling hologram for separating the direct signal and the parallax-compensated signal. A useful light/direct signal NL emitted from above by a distant object 30 is apparent, which passes through optical waveguide 13 and directly strikes detector element 4. Also noticeable is the signal wave SW guided within optical waveguide 13, which is diffracted on holographic optical element 12 in the form of the decoupling hologram and is subsequently guided to detector element 4.

(24) As a result of the characteristic angle selectivity and wavelength selectivity of the volume hologram, it is possible to narrow the optical function to a certain angle range via the selection of the material parameters.

(25) All exemplary images of compensation device 40 are depicted in figures for telecentric lenses, however, the holographic optical elements may also be adapted to non-telecentric imaging systems (not depicted in the figures).

(26) The simulation of a defined structure is depicted in FIG. 13. In this case, the angle of incidence and the wavelength have been varied and the diffraction characteristic for different material parameters (thickness of the holographic layer and refractive index modulation) of two materials has been evaluated via the calculated intensity of the diffracted beam. No light is diffracted on the structure within the useful light range (angle of incidence −20° . . . −40°) defined by the wavelength and angle in the example depicted. Different refractive indices η for the two different materials are graphically depicted.

(27) In addition, a filter function is also produced as a result of the specific cascade-like arrangement of the holographic optical waveguide 13. Only light within a defined wavelength band is diffracted on the coupling structure and then also arrives under the right combination of wavelength and angle at the decoupling hologram.

(28) FIG. 14 symbolically shows a biaxial LIDAR system 100, including one specific embodiment of proposed compensation device 40.

(29) FIG. 15 shows a basic sequence of one specific embodiment of the proposed method for manufacturing a compensation device 40 for a biaxial LIDAR system 100.

(30) At least two holographic optical elements 11, 12 are provided in a step 200, holographical optical elements 11, 12 being designed in such a way that they compensate for a parallax effect of biaxial LIDAR system 100, incident light being guidable with the aid of the two holographic optical elements 11, 12, to a detector element 4 of biaxial LIDAR system 100.

(31) Using the compensation device, an improved biaxial scanning LIDAR system may be implemented as a result, which is distinguished, in particular, by the fact that the detector element is minimized in terms of surface area and, as a result, is cost-efficiently implementable.

(32) In summary, a compensation device for a biaxial, scanning LIDAR system is provided with the present invention. A biaxial LIDAR system implemented with the proposed compensation device may be used preferably in the motor vehicle sector for the distance measurement and speed measurement of objects.

(33) Those skilled in the art recognize that a multitude of modifications of the present invention are possible without departing from the core of the present invention.