Optical system having an improved aberration behavior, and lidar device including a system of this type

Abstract

An optical system is described, in particular for a LIDAR device, which includes a lens array having a multitude of microlenses and a lens system for deflecting beams out of a scanning area or into the scanning area, the lens system being situated in the beam path between the scanning area and the lens array, the system including at least one wedge array having a multitude of wedge elements situated upstream or downstream from the lens array in the radiation direction, a number of wedge elements equaling a number of microlenses. A LIDAR device is also described.

Claims

1-10. (canceled)

11. An optical system for a LIDAR device, comprising: a lens array including a multitude of microlenses; a lens system configured to deflect beams out of a scanning area or into the scanning area, the lens system being situated in a beam path of the beams between the scanning area and the lens array; and at least one wedge array situated upstream or downstream from the lens array in a radiation direction, the wedge array including a multitude of wedge elements, a number of wedge elements equaling a number of microlenses.

12. The system as recited in claim 11, wherein the wedge array is a diffractive or holographic optical element, which is mounted on the lens array at least on one side or is situated at a distance from the lens array in the beam path of the beams.

13. The system as recited in claim 11, wherein the wedge elements of the wedge array each have a triangular cross section with an inclined surface and a planar surface, the planar surface of at least one of the wedge elements facing a planar surface of at least one of the microlenses.

14. The system as recited in claim 13, wherein the at least one of the wedge elements has a height, which is equal to a height of the at least one of the microlenses or is less than the height of the at least one of the microlenses.

15. The system as recited in claim 11, wherein the wedge array is situated at a distance from the lens array in the radiation direction or is connected to the lens array.

16. The system as recited in claim 11, wherein the wedge array is integral with the lens array.

17. The system as recited in claim 11, wherein at least one microlens of the lens array is inclined by a rotation angle with respect to at least one wedge element of the wedge array.

18. The system as recited in claim 11, wherein each microlens of the lens array has a separate rotation angle.

19. The system as recited in claim 18, wherein the rotation angle of at least one of the microlenses corresponds to a deflection angle of at least one of the wedge elements which is assigned to the at least one of the microlenses.

20. A LIDAR device for scanning a scanning area using beams, comprising: a transmission unit configured to generate the beams and to deflect the beams along the scanning area; and a receiving unit, which includes at least one detector, configured to receive reflected beams; wherein the transmission unit and/or the receiving unit includes an optical system including: a lens array including a multitude of microlenses; a lens system configured to deflect beams out of the scanning area or into the scanning area, the lens system being situated in a beam path of the beams between the scanning area and the lens array; and at least one wedge array situated upstream or downstream from the lens array in a radiation direction, the wedge array including a multitude of wedge elements, a number of wedge elements equaling a number of microlenses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a schematic representation of a LIDAR device according to one exemplary embodiment of the present invention.

[0029] FIGS. 2 and 3 show schematic representations of setpoint and actual transmission spot arrangements at a target distance in the scanning area.

[0030] FIG. 4 shows a detailed view of an optical system according to one specific embodiment of the present invention.

[0031] FIG. 5 shows a detailed view of an optical system according to a further specific embodiment of the present invention.

[0032] FIG. 6 shows a sectional representation of a microlens array.

[0033] FIG. 7 shows a perspective representation of the microlens array from FIG. 6.

[0034] FIGS. 8 through 17 show schematic representations of microlenses including wedge elements of an optical system in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0035] FIG. 1 shows a schematic representation of a LIDAR device 1 according to one exemplary embodiment of the present invention. LIDAR device 1 is used to generate beams 2 and to scan a scanning area A using beams 2. LIDAR device 1 includes a transmission unit 4, which includes a laser 6 as the radiation source for generating beams 2.

[0036] Generated beams 2 are successively deflected via a movable mirror 8 of transmission unit 4. Movable mirror 8 may be designed as a pivotable micromirror and periodically oscillate, by which scanning area A is scanned. Mirror 8 is used by transmission unit 4 together with a receiving unit 10.

[0037] Beams 2 deflected by mirror 8 are bundled or preferably formed in parallel by a collimator lens 12 and deflected transversely to the radiation direction of laser 6 by a deflection mirror 14. Deflected beams 3 are emitted onto an optical system 16 along a first optical axis OA1.

[0038] Optical system 16 includes a microlens array 17 and is described in greater detail below. Optical system 16 acts upon beams 3 before they are deflected onto a beam splitter 18 and onto optical transmitting system 20. Optical transmitting system 20 is used to emit beams 3 into scanning area A.

[0039] According to the exemplary embodiment, optical transmitting system 20 is designed as a combined optical transceiver system 20 and is also used by receiving unit 10. Optical transceiver system 20 includes a lens system 22 and an aperture 24. Lens system 22 may also be designed as part of optical system 16. Depending on the design of LIDAR device 1, in particular, only one optical system 16 may be provided, which is usable for generated beams 3 and received beams 28 alike.

[0040] Backscattered or reflected beams 28 are received by optical transceiver system 20 in scanning area A, for example on an object 26, and deflected onto optical system 16 of receiving unit 10 via beam splitter 18. The optical system of receiving unit 10 and transmission unit 4 may be provided with the same or different designs.

[0041] After passing optical system 16, beams 28 are deflected onto a deflection mirror 30. The deflected beams are deflected onto a second optical axis OA2 by deflection mirror 30, second optical axis OA2 being able to run in parallel to first optical axis OA1. Deflected beams 28 are again deflected onto a detector 34 via a focusing lens 32 and via pivotable mirror 8.

[0042] Transmission beam 2, 3 are scanned via optical system 16 with the aid of the movement of mirror 8 and its alternating movement. A divergent transmission beam is then projected onto optical transceiver system 20 by each microlens element of lens array 17 before it may, in an expanded manner, exit LIDAR device 1 into scanning area A. After being reflected/scattered on an object 26 situated in field A, signal 28 again passes through optical transceiver system 20 and is deflected onto detector 34 via the optical elements described above.

[0043] FIG. 2 and FIG. 3 illustrate schematic representations of a setpoint and actual transmission spot system at a target distance in scanning area A to clarify the problem in the related art. FIG. 2 shows three different setpoint spot arrangements. The effective actual spot arrangements illustrated in FIG. 2 are shown in FIG. 3. An inherent problem with the usual scanner systems is the fact that, during the transmission-side scanning on microlens elements aside from the optical axis, differently sized areas of the transmission signal are deflected directly into aperture 24 of the transceiver lens, depending on the design of the expanded transmission beam diameter and the distance of an impacted microlens element from the optical axis. This is illustrated in FIG. 4. These cut-off parts 36 thus no longer reach scanning area A or lens system 22 of optical transceiver system 20, by which gaps of different sizes occur in the target distance of the measuring area between adjacent spots, depending on the scanning angle of mirror 8. The cut off spots are illustrated in FIG. 3 on a left side.

[0044] This means that the full field angle of lens system 22 used may never be utilized without a spot section 36 occurring of no more than half the original diameter.

[0045] Depending on the diameter of expanded transmission beam 3, transmission beam 3 is cut off by aperture 24 of optical transceiver system 20, starting at a certain microlens height with respect to optical axis OA1. The distance of a microlens element 17 from optical axis OA1 is translated into a deflection angle in the field (field angle, FoV). The larger the transmission beam diameter, the smaller the field angle at which the full diameter of transmission spot 3 has already been cut.

[0046] FIG. 4 shows a detailed view of an optical system 16 according to one exemplary embodiment of the present invention. A wedge element 42 of a wedge array 40 is illustrated, which is not integrated into microlens 17 of a microlens array but is situated at a distance from particular microlens 17. For the sake of simplicity, only one wedge element 42 and one microlens 17, which are part of an optical system 16, are illustrated in FIG. 4. However, optical system 16 includes a multitude of wedge elements 42 and microlenses 17, which are each arranged over a wide area as arrays. In particular, an optical function of optical system 16 with and without wedge element 42 is illustrated. The beam path through a microlens 17 and downstream lens system 22 on the transmission and reception sides is illustrated. In particular, beam paths are shown in a comparison between beams 3 without wedge element 42 and beams 3 with wedge element 42.

[0047] Not only a part of signal 3 incident through microlenses 17 is deflected at an angle in such a way that it does not strike objective aperture 24, but rather entire signal 3.

[0048] Signal 3 is deflected through wedge element 42 onto lens system 22 on the transmission side with the aid of an angle difference, whereby it strikes lens system 22 and not objective aperture 24 in a different position. The angle difference is selected in such a way that the beams or the transmission signal illuminate the same object point in the target distance of detection space A.

[0049] LIDAR device 1 is thus also able to recapture light 28 backscattered by illuminated object point 26 at the same angle without any spot section 36 and to deflect it in an axis-parallel manner downstream from wedge array 40 in the direction of detector 34.

[0050] FIG. 5 shows a detailed view of an optical system 16 according to a further exemplary embodiment of the present invention. In contrast to FIG. 4, beams 3 in optical system 16 do not strike microlens 17 in parallel to optical axis OA1, due to the beam deflection of wedge element 42 around angle .sub.K. The occurrence of aberrations, in particular astigmatisms, may be avoided hereby. These mapping errors result in the fact that the mapping quality of emitted beam 3 in scanning area A deteriorates, and no defined spot may be projected at an increasing object distance. The consequence is a significant reduction in the system range and the system angle resolution.

[0051] In optical system 16 including the wedge element/microlens combination, the problem of the mapping errors may be eliminated by rotating particular microlens 17. Rotation angle .sub.L of microlens 17 always corresponds to deflection angle .sub.K of wedge element 42. This rotation angle .sub.L may vary for each individual wedge element 42 or each individual microlens 17 and focuses on the radial distance from optical axis OA1 (FIG. 6). Exit angle .sub.obj,MK of the beams may be varied on the focal plane of lens system 22 via the selected rotation center. For illustrative purposes, an exit angle .sub.Obj,MK including a wedge element 42 and an exit angle .sub.Obj,OK without a wedge element 42 of beams 3 are illustrated.

[0052] According to the illustrated exemplary embodiment, beams 3, 3 are deflected onto optical system 16 in radiation direction Z.

[0053] FIG. 6 and FIG. 7 show representations of a microlens array 27. To be able to place the particular focal points on the focal plane of lens system 22, despite a rotation of individual microlenses 17, a concave design of entire lens array 27 is necessary. The distance between lens system 22 and microlens array 27 may be minimized hereby. To illustrate the dome shape of microlens array 27, microlenses 27 are not shown in FIG. 7.

[0054] Depending on a distance from optical axis OA1, particular microlenses 27 have a different rotation angle .sub.L in the x-direction and/or y-direction. In particular, a larger rotation angle .sub.L may be selected as the distance increases.

[0055] Schematic representations of microlenses 17, including corresponding wedge elements 42 of an optical system 16, are illustrated in FIGS. 8 through 17. In particular, different designs of the individual element combinations are shown.

[0056] FIGS. 8, 10, 12, 14 show designs, in which first wedge element 42 and then microlens 17 are connected in radiation direction Z. Wedge elements 42 may be situated at a distance from particular microlens 17, or they may be integrally connected to particular microlens 17. Since the beams deflected by wedge elements 42 strike flat surfaces 44 of microlenses 17 at an angle, aberrations may arise, since the beam deflection by wedge element 40 around angle .sub.K takes place only downstream from microlens 17.

[0057] FIGS. 9, 11, 13, 15, as opposed to FIGS. 8, 10, 12, 14, show mirror-inverted arrangements of microlenses 17 and wedge elements 42. First a microlens 17 and then a wedge element 42 are thus situated in radiation direction Z. Microlenses 17 are arranged in such a way that flat surface 44 is facing the incoming beams from radiation direction Z. As a result, one incident beam 3 may be maintained in parallel to optical axis OA for each microlens 17. This may be implemented without rotating particular microlenses 17. Since microlens array 27 may thus have a flat or plate-shaped design, the use of standard components is possible.

[0058] Although the arrangement of microlenses 17 and wedge elements 42 in FIGS. 16 and 17 is similar to that in FIGS. 8, 10, 12, 14, a rotation of microlenses 17 with respect to wedge elements 42 is provided, whereby the installation space requirements and the occurrence of aberrations are minimized.