Lidar system

Abstract

having lidar system (1) • a transmitting unit (2) for emitting laser radiation, • a receiving unit (3) for detecting laser radiation, • a rotating mirror unit (4), • at least one switchable optical element (5), • wherein the switchable optical element (5) is formed, ◯ to establish a first optical path (10) between the rotating mirror unit (4) and the transmitting unit (2) and / or receiving unit (3) in a first switching state, and ◯ in a second switching state to establish a second optical path (11) different from the first optical path (10) between the rotating mirror unit (4) and the transmitting unit (2) and / or receiving unit (3), and • wherein the rotating mirror unit (4) is configured to reflect laser radiation incident on the transmitting unit (2) along a third optical path (12) into an environment (13) and to reflect laser radiation incident on the environment (13) along the third optical path (12) to the receiving unit (3).

Description

State of the art

[0001] The present invention relates to a lidar system. The lidar system preferably has reduced vignetting.

[0002] Lidar systems can have a centrally located rotating mirror that is illuminated by an optical transmit path and detected by a receive path. A transmitting unit and a receiving unit can, for example, be located on the same side relative to the rotating mirror. Depending on the rotation angle of the rotating mirror, the laser beam strikes the mirror at different angles on both the transmitting and receiving sides. The shallower the angle of incidence, the larger the area over which the optical energy of the laser beam is distributed. At large rotation angles, the power density on the rotating mirror decreases, and consequently, so does the range of the lidar system. This decrease in range with increasing angle is called vignetting.

[0003] Alternatively, a lidar system can also have a distribution matrix to split an optical signal into several discrete spatial directions, as described in DE 10 2020 110 142 A1. Disclosure of the invention

[0004] The lidar system according to the invention enables the avoidance or at least reduction of vignetting. Thus, there is no, or at least only a reduced, decrease in range across the scanning angle of the surroundings. This also reduces the asymmetry of the scanning area that would occur with lateral illumination of the mirror. Distortions of the transmitted pulse are therefore avoided, which improves alignment with the reference pulse in the receive path (matched filter approach). As a result, the range is uniform across the entire scanning area of ​​the lidar system and does not decrease, or only decreases minimally, particularly at the edges.

[0005] The lidar system comprises a transmitter for emitting laser radiation and a receiver for detecting laser radiation. Furthermore, the lidar system comprises a rotating mirror unit and at least one switchable optical element. The rotating mirror unit preferably comprises a multi-sided mirror, for example, a four-sided mirror. Preferably, the multi-sided mirror has the contour of a polygon, with each edge of the polygon corresponding to a mirror surface. The switchable optical element is configured to switch between a first switching state and a second switching state. In the first switching state, the switchable optical element is configured to establish a first optical path between the rotating mirror unit and the transmitter and / or receiver unit.Furthermore, the switchable optical element is configured to establish a second optical path between the rotating mirror unit and the transmitter and / or receiver unit in the second switching state. This second optical path differs from the first. In particular, the first and second optical paths lead to the rotating mirror unit from different directions. The rotating mirror unit is configured to reflect laser radiation incident from the transmitter unit along a third optical path into an environment and to reflect laser radiation incident from the environment along the third optical path to the receiver unit.

[0006] The rotating mirror unit thus allows scanning of different directions of the environment with a fixed transmitter and / or receiver unit. In other words, the third optical path can be aligned in different directions. This creates a detection range for the lidar system.

[0007] Thus, laser radiation can be guided from the transmitting unit to the switchable optical element and then either along the first or second optical path to the rotating mirror unit. From the rotating mirror unit, the laser radiation can be guided into the environment along the third optical path. Alternatively or additionally, laser radiation reflected from the environment can be guided along the third optical path to the rotating mirror and from there along the first or second optical path to the switchable optical element. From the switchable optical element, the laser radiation can then be guided to the receiving unit.

[0008] By establishing both the first and second optical paths between the transmitting unit and the rotating mirror unit, and / or between the receiving unit and the rotating mirror unit, it is possible to avoid using the edge areas of the rotating mirror unit's mirror surfaces. In particular, this prevents the optical path from striking the rotating mirror unit at too shallow an angle, leading to an improved range of the lidar system and a more uniform distribution of the range across the detection area.

[0009] The dependent claims describe preferred embodiments of the invention.

[0010] Preferably, the rotating mirror allows the third optical path to be aligned along a predefined angular range. This angular range comprises a first sub-range and a second sub-range. The second sub-range adjoins the first sub-range, particularly directly and / or seamlessly. This achieves, in particular, the detection range described above. The rotating mirror unit and the switchable optical element are advantageously configured such that when the first optical path is established, the third optical path lies within the first sub-range, and when the second optical path is established, the third optical path lies within the second sub-range. In other words, the detection range of the lidar system is divided into two sub-ranges, with either the first or second optical path being active depending on the sub-range. Thus, depending on the detection direction, i.e.,The direction of the angular range along which laser radiation is emitted to or received from the environment is determined by whether the first or second optical path is used. This results in an optimized angle at which the respective optical path strikes the rotating mirror unit. This, in turn, enables optimal reflection of the laser radiation while minimizing vignetting effects.

[0011] The boundary between the first and second sub-areas is preferably a reference axis. This reference axis preferably divides the predefined angular range into two equal sub-areas; that is, the first and second sub-areas are preferably equal in size. The reference axis preferably represents an axis of symmetry of the angular range. It is also preferably provided that the first optical path intersects the rotating mirror unit from a first side with respect to the reference axis, and the second optical path intersects the rotating mirror unit from a second side opposite the reference axis of the first side. This allows for optimal adjustment of the angle at which the respective optical path intersects the rotating mirror unit for all operating states of the lidar system.

[0012] In an advantageous embodiment, the first optical path leads directly from the switchable optical element to the rotating mirror unit without any deflection. Alternatively or additionally, the second optical path leads from the switchable optical element to the rotating mirror unit via a deflection unit. This allows the transmitting unit and / or the receiving unit to be preferably arranged to the side of the rotating mirror. Nevertheless, it is possible to establish an optical path between the transmitting unit and / or the receiving unit from different sides of the rotating mirror unit. This ensures that an optimal angle is always maintained at which the respective optical paths meet the rotating mirror unit, while still covering the entire detection range.

[0013] The switchable optical element preferably has a first switchable area and a second switchable area distinct from the first. The first and second switchable areas can be configured to be switched together or independently. The first switchable area allows the laser radiation emitted by the transmitter to be switched between the first and second optical paths. The second switchable area allows the laser radiation directed to the receiver to be switched between the first and second optical paths. Thus, both a transmit and a receive path of the lidar system can be switched using the same optical element. Depending on the configuration of the respective switchable areas, the transmitter and receiver can be arranged, in particular, on the same side of the rotating mirror unit.Alternatively, the transmitting unit and the receiving unit can also be arranged on different sides of the rotating mirror unit, so that the rotating mirror unit is arranged in particular between the transmitting unit and the receiving unit.

[0014] A particularly advantageous feature is that the first switchable area is enclosed by the second switchable area with respect to one of the surrounding directions. The switchable optical element thus has the form of a pinhole mirror, with the hole formed by the first switchable area and the rest of the element by the second switchable area. The reference to the pinhole mirror is merely illustrative and does not imply that the second switchable area must necessarily be reflective.

[0015] The switchable optical element is preferably switchable between a reflective and a transparent switching state. A reflective element is preferably arranged behind at least a portion of the optical element, such that in the transparent switching state of the switchable optical element, a reflection caused by the reflective element occurs. This reflection occurs, in particular, in a direction different from a reflection caused by the switchable optical element in the reflective switching state. It is especially advantageous to position the reflective element behind the first or second switchable area described above. This allows for a separation between the transmit and receive paths, enabling the transmitting and receiving units to be located at different positions.

[0016] Preferably, the switchable optical element comprises a switchable holographic optical element. The switchable optical element is, in particular, a transmission hologram and / or a reflection hologram. The switchable holographic optical element preferably allows switching between two different types of reflection and / or switching between a reflective state and a transparent state. Thus, switching between the first and second optical paths is simple and requires minimal effort.

[0017] Preferably, the switchable holographic optical element comprises a holographic polymer-dispersed liquid crystal, also called holographic polymer-dispersed liquid crystal, abbreviated H-PDLC. These are special holographic materials that change their state when an electrical voltage is applied. The state change occurs during a rise time when the voltage is applied, which is shorter than the decay time when the state change occurs when the electrical voltage is removed. Therefore, switching during the decay time is particularly useful when the rotating mirror unit rotates around a corner, i.e., when the mirror surface onto which the first or second optical path intersects changes. In other words, the respective optical paths intersect different mirror surfaces of the rotating mirror unit before and after the switch.The corner of the rotating mirror unit is not used, so the transmitter is switched off. The rise time is significantly faster and should be used for switching within a single mirror surface of the rotating mirror unit; that is, before and after switching, the respective optical path intersects the same mirror surface of the rotating mirror unit. This switching preferably occurs when both the first and second optical paths lead to the same third optical path due to reflection at said mirror surface of the rotating mirror unit. If an intermediate state of the H-PDLC exists during switching, this angle is illuminated by both the first and second optical paths, and the laser beams add up at the correct solid angle.

[0018] The lidar system preferably comprises a housing. It is preferably provided that the transmitter, receiver, and rotating mirror unit are all arranged within the housing. The first and second optical paths, in particular, remain within the housing. Thus, only the third optical path leads from the rotating mirror unit to the surroundings and vice versa. For this purpose, the housing preferably has a window through which laser radiation can exit the housing along the third optical path and through which laser radiation can enter the housing along the third optical path. The transmitter and / or receiver unit and / or switchable optical element are fixedly arranged opposite the housing.

[0019] In a preferred embodiment, the switchable optical element also exhibits a filtering effect. In particular, it is provided that the switchable optical element attenuates wavelengths except for a predefined wavelength range. Brief description of the drawings

[0020] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows: Fig. 1 a first schematic view of a lidar system according to a first embodiment of the invention, Fig. 2 a second schematic view of the lidar system according to the first embodiment of the invention, Fig. 3 a schematic view of a switchable optical element for use in a lidar system according to one of the embodiments of the invention, Fig. 4 a first schematic view of a lidar system according to a second embodiment of the invention, Fig. 5 a second schematic view of the lidar system according to the second embodiment of the invention, Fig. 6 a first schematic view of a lidar system according to a third embodiment of the invention, and Fig. 7 a second schematic view of the lidar system according to the third embodiment of the invention. Embodiments of the invention

[0021] The Fig. 1 and Fig. Figure 2 shows a lidar system 1 according to a first embodiment of the invention. The lidar system 1 serves to detect an environment 13 and comprises a transmitting unit 2 and a receiving unit (in Fig. 1 and Fig. 2 not shown, see reference 3 in Fig. 4 to 7). Furthermore, the lidar system 1 has a rotating mirror unit 4, which in this embodiment is designed as a four-sided mirror, i.e., with four mirror surfaces 4A. Other forms of the rotating mirror unit 4 are also possible.

[0022] Furthermore, a switchable optical element 5 is provided. The switchable optical element is preferably a holographic switchable optical element, in particular a holographic polymer-dispersed liquid crystal. Laser radiation emitted by the transmitter unit 2 first strikes the switchable optical element 5. From the switchable optical element 5, the laser radiation can be directed to the rotating mirror. The switchable optical element 5 can switch between two optical paths 10, 11.

[0023] The switchable optical element 5 is configured to establish, in a first switching state, a first optical path 10 between the transmitter unit 2 and the rotating mirror unit 4, and, in a second switching state, a second optical path 11 between the transmitter unit 2 and the rotating mirror unit 4, which differs from the first optical path 10. The first optical path 10 leads directly to the rotating mirror unit 4, while the second optical path 11 leads to the rotating mirror unit 4 via an additional deflection element 6.

[0024] Starting from the rotating mirror unit 4, a third optical path 12 leads into the surroundings 13. The direction of the third optical path 12 depends on the rotation of the rotating mirror unit 4. By rotating the rotating mirror unit 4, a predefined angular range 12A, 12B can be covered, whereby the third optical path can be aligned in any direction within the angular range 12A, 12B. The angular range 12A, 12B is divided into a first sub-range 12A and a second sub-range 12B by a reference axis 12C. The first sub-range 12A and the second sub-range 12B are preferably of equal size, and the reference axis 12C is preferably an axis of symmetry of the predefined angular range 12A, 12B.

[0025] The transmitter unit 2 is laterally offset from the rotating mirror unit 4 with respect to the reference axis 12C. Depending on the orientation of the rotating mirror unit 4, there would be a risk that the laser radiation from the transmitter unit 2 would strike the mirror surface 4A at a very shallow angle, which would lead to vignetting effects. To avoid this, it is possible to switch between the first optical path 10 and the second optical path 11.

[0026] The rotating mirror unit 4 and the switchable optical element 5 interact in such a way that, when the first optical path 10 is established, the third optical path 12 is arranged within the first sub-area 12A, as shown in Fig. 1 shown, and that when the second optical path 11 is manufactured, the third optical path 12 is arranged within the second sub-area 12B, as shown in Fig. Figure 2 shows that the first optical path 10 and the second optical path 11 strike the rotating mirror unit 4 from different sides, ensuring that an optimal reflection angle is always present at the rotating mirror unit 4 over the entire predefined angular range 12A, 12B. In particular, shallow reflection angles can be avoided, thereby reducing or preventing vignetting effects.

[0027] A holographic material is used as a switchable optical element 5. This material changes its state when an electrical voltage is applied, with the state change occurring during a rise time that is shorter than the decay time during which the state change occurs when the electrical voltage is removed. When switching from the first optical path 10 to the second optical path 11, both the first optical path 10 and the second optical path 12 intersect the same mirror surface 4A of the rotating mirror unit 4, necessitating rapid switching. The rise time is significantly faster than the decay time.The fall-off time is used for switching from the second optical path 11 to the first optical path 10, whereby the first optical path 10 and the second optical path 11 intersect different mirror surfaces 4A, thus rotating the rotating mirror unit 4 around a corner, i.e., a change of mirror surface occurs. In other words, the respective optical paths 10 and 11 intersect different mirror surfaces 4A of the rotating mirror unit 4 before and after the switchover, meaning that a longer switching time due to the switchable optical element 5 has no or almost no effect. Specifically, the corner of the rotating mirror unit 4 is not used, so the transmitter unit 2 is switched off.

[0028] The transmitter unit 2, receiver unit 3, and rotating mirror unit 4 are arranged within a housing 9. Both the first optical path 10 and the second optical path 11 remain completely within the housing 9. Only the third optical path 12 leads to the environment 13 via a cover glass 8. The transmitter unit 2, receiver unit 3, and the switchable optical element 5 are preferably fixed relative to the housing 9, with only the rotating mirror unit 4 being movable relative to the housing 9, i.e., rotatable about a rotational axis 100. The rotational axis 100 is preferably oriented perpendicular to the first optical path 10 and / or the second optical path 11 and / or the third optical path 12.

[0029] In the embodiment according to Fig. 1 and Fig. Figure 2 shows the switching between the first optical path 10 and the second optical path 11 for emitting laser radiation. This is also possible for receiving laser radiation, as shown below. Fig. Figure 3 shows a schematic view of a switchable optical element 5 with a first switchable area 5A and a second switchable area 5B. The switchable optical element 5 thus enables the separation of the receive path and the transmit path, with these two paths running together between the switchable optical element 5 and the rotating mirror unit 4 along the first optical path 10 or the second optical path 11. By separating the transmit and receive paths using the switchable optical element 5, beam splitters, which are usually associated with high losses, can be dispensed with.

[0030] The Fig. 4 and Fig. Figure 5 shows the lidar system 1 according to a second embodiment of the invention. In this embodiment, Fig. 4 the same condition as in Fig. 1 shown, where in Fig. 5 the same condition as in Fig. 2 is shown. The only difference from the first embodiment is that the one shown in Fig. Figure 3 shows a switchable optical element 5 and a receiver unit 3. The transmit path is drawn with solid lines, and the receive path is shown with dotted lines. The switching function between the first optical path 10 and the second optical path 11 is the same as in the first embodiment, wherein, on the one hand, laser radiation travels from the transmitting unit 2 to the switchable optical element 5 and, on the other hand, laser radiation travels from the switchable optical element 5 to the receiver unit 3. The switchable optical element 5 is shown as in Figure 3. Fig. 4 and Fig. Figure 5 shows the first switchable range 5A and the second switchable range 5B as shown in Fig. 3 shown. The first switchable area 5A corresponds in its function to the entire switchable element 5 from the first embodiment as shown in Fig. 1 and Fig. The rotating mirror unit 4 is shown in Figure 2 and serves to switch the laser radiation from the transmitting unit 2 between the first optical path 10 and the second optical path 11. The received laser radiation from the environment 13 is guided by the rotating mirror unit 4 along the first optical path 10 or second optical path 11 to the second switchable area 5B of the switchable optical element 5 and from there to the receiving unit.

[0031] It is provided that the second switchable area 5B is reflective in the first switching state, in which the first optical path 10 is used. In the second switching state, in which the second optical path 11 is used, the second switchable area 5B is transparent, with a reflective element 7 located behind the second switchable area 5B. The reflection occurring at this reflective element 7 results in a direction that differs from that of a reflection caused by the second switchable area 5B in the reflective switching state.

[0032] In the Fig. 4 and Fig. 5. The transmitting unit 2 and the receiving unit 3 are located on the same side with respect to the reference axis 12C. Fig. 6 and Fig. Figure 7 shows a third embodiment in which the transmitter unit 2 and the receiver unit 3 are located on opposite sides of the reference axis 12C. In this embodiment, only the design of the switchable optical element is adapted to the changed position of the receiver unit 3 compared to the second embodiment; otherwise, the function is identical. The intersecting optical paths of the transmitting and receiving beams do not interfere with each other. Spatial correlation is achieved by temporal separation, whereby the transmitting pulses are separated from each other by at least the flight time of one pulse.

[0033] The in Fig. The embodiments shown in Figures 4 to 7 can alternatively also be configured with a transmitting unit 2 and a receiving unit 3 stacked perpendicular to the plane of the drawing. In this case, there is no switchable optical element 5 as shown in Figure 4. Fig.3 shown, but in particular two similarly stacked switchable optical elements 5 or one switchable optical element 5 with adjacent switchable areas 5A, B5 are used.

[0034] In all versions, the angles of the optical paths 10, 11 striking the rotating mirror unit 4 are optimized to reduce or avoid vignetting.

Claims

[1] Lidar system (1) • a transmitting unit (2) for emitting laser radiation, • a receiving unit (3) for detecting laser radiation, • a rotating mirror unit (4), • at least one switchable optical element (5), • wherein the switchable optical element (5) is formed, ◯ to establish a first optical path (10) between the rotating mirror unit (4) and the transmitting unit (2) and / or receiving unit (3) in a first switching state, and ◯ in a second switching state to establish a second optical path (11) different from the first optical path (10) between the rotating mirror unit (4) and the transmitting unit (2) and / or receiving unit (3), and • wherein the rotating mirror unit (4) is configured to reflect laser radiation incident from the transmitting unit (2) along a third optical path (12) into an environment (13) and to reflect laser radiation incident from the environment (13) along the third optical path (12) to the receiving unit (3). [2] Lidar system (1) according to claim 1, characterized by, that the third optical path (12) can be aligned along a predefined angular range (12A, 12B) by means of the rotating mirror (4), wherein the angular range (12A, 12B) has a first sub-range (12A) and a second sub-range (12B) adjoining the first sub-range (12A), wherein the rotating mirror unit (4) and the switchable optical element (5) are configured such that when the first optical path (11) is produced, the third optical path (12) is within the first sub-range (12A) and that when the second optical path (11) is produced, the third optical path (12) is within the second sub-range (12B). [3] Lidar system (1) according to claim 2, characterized by, that the boundary between first sub-area (12A) and second sub-area (12B) is a reference axis (12C), wherein the first optical path (10) from a first side with respect to the reference axis (12C) meets the rotating mirror unit (4) and the second optical path (11) from a second side opposite the first side with respect to the reference axis (12C) meets the rotating mirror unit (4). [4] Lidar system (1) according to any one of the preceding claims, characterized by , that the first optical path (11) leads from the switchable optical element (5) to the rotating mirror unit (4) without deflection and / or that the second optical path (12) leads from the switchable optical element (5) via a deflection unit (6) to the rotating mirror unit (4). [5] Lidar system (1) according to any one of the preceding claims, characterized by, that the switchable optical element (5) has a first switchable area (5A) and a second switchable area (5B) different from the first switchable area (5A), • wherein the laser radiation emitted by the transmitting unit (2) can be switched between the first optical path (10) and the second optical path (11) by means of the first switchable area (5A). • wherein the laser radiation to be directed to the receiving unit (3) can be switched between the first optical path (10) and the second optical path (11) by means of the second switchable area (5B). [6] Lidar system (1) according to claim 5, characterized by , that the first switchable area (5A) is enclosed by the second switchable area (5B) with respect to an ambient direction (50). [7] Lidar system (1) according to any one of the preceding claims, characterized by, that the switchable optical element (5) is switchable between a reflective switching state and a transparent switching state, wherein preferably a reflective element (7) is arranged behind at least a partial area of ​​the optical element (5), so that in the transparent switching state of the switchable optical element (5) a reflection caused by the reflective element (7) takes place in a direction that is different from a reflection caused by the switchable optical element (5) in the reflective switching state. [8] Lidar system (1) according to any one of the preceding claims, characterized by , that the switchable optical element (5) comprises a switchable holographic optical element, preferably a transmission hologram and / or a reflection hologram. [9] Lidar system (1) according to claim 8, characterized by, that the switchable holographic optical element has a holographic polymer-dispersed liquid crystal. [10] Lidar system (1) according to any one of the preceding claims, characterized by a housing (9) wherein the first optical path (10) and the second optical path (11) remain inside the housing (9).

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