A collimation system based on MEMS scanning mirror and laser radar

Abstract

The application provides a collimation system based on a MEMS mirror and a laser radar, the collimation system based on the MEMS mirror comprises: a laser emission unit for emitting a modulated laser beam; a front light beam shaping unit for shaping the laser emitted by the laser emission unit; a MEMS mirror scanning unit for scanning a field of view of a to-be-measured plane after resonant reflection of the light beam shaped by the front light beam shaping unit by using a MEMS mirror; and a rear collimation unit for performing secondary shaping on the light beam reflected by the MEMS mirror scanning unit, so that the edge light beam and the center light beam deflected by the MEMS mirror have equal optical paths at an entrance pupil of the rear collimation unit. The collimation system based on the MEMS mirror can improve the energy coupling efficiency of the system, reduce the beam divergence angle and the system volume, and make the ranging capabilities of the center field of view and the edge field of view uniform.

Description

Technical Field

[0001] This invention relates to the field of lidar technology, specifically to a collimation system based on MEMS galvanometers and a lidar. Background Technology

[0002] As one of the key core technologies for autonomous vehicles, LiDAR technology has become the most effective solution for environmental sensing in autonomous driving due to its advantages such as high ranging accuracy, fast response, strong directionality, and immunity to ground clutter. It can also effectively provide the information required by the vehicle's decision-making and control system.

[0003] Currently, when using lidar technology for detection, mechanical rotating devices are typically employed, utilizing multiple emitting lasers and multiple receiving detectors to achieve multi-line scanning. The lasers are placed on a rotating platform that can rotate at a uniform speed, and the laser beams emitted by the lasers are controlled to scan the target object, recording the corresponding azimuth information. This results in low scanning frequency and poor angular resolution, and the system structure is also relatively complex, affecting the overall stability of the system. To address these issues, researchers are constantly searching for lidar with high stability, high resolution, and a simple structure. Consequently, MEMS-based lidar has gradually developed.

[0004] However, MEMS-based lidar has many problems, with energy coupling efficiency and emitted beam size being among the key issues. Because MEMS mirrors need to achieve high vibration frequencies, their mirror size cannot be too large; typically, MEMS mirrors are circles with a diameter of 1mm to 2mm. The laser beam emitted by the laser usually needs to be collimated and shaped, but the aperture size of the collimated beam is much larger than the MEMS mirror size. The beam cannot be fully emitted onto the MEMS mirror, resulting in low energy coupling efficiency and significantly reducing the ranging capability of MEMS-based lidar. Therefore, some solutions on the market use solid-state lasers with better beam quality as the light source, ensuring higher energy coupling efficiency. However, solid-state lasers require cooling systems and are typically large in size and volume, leading to a large overall lidar system size. Furthermore, solid-state lasers are relatively expensive, thus reducing the applicability of this solution.

[0005] MEMS-based lidar requires a very small size and generally uses cost-effective semiconductor lasers. However, the inherent astigmatism of semiconductor lasers causes the fast and slow axis emitting surfaces to be on different planes. When collimating and shaping the optical path, the fast and slow axis beams cannot be collimated and shaped at the same time. This results in the light spot diverging at a distance, which leads to insufficient ranging capability and low system resolution. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a collimation system and lidar based on MEMS galvanometers. This invention can improve the energy coupling efficiency of the system, reduce the beam divergence angle, and simultaneously make the ranging capabilities of the central field of view and the edge field of view uniform and consistent.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a collimation system based on a MEMS galvanometer, comprising:

[0009] The laser emitting unit is used to emit a modulated laser beam;

[0010] A front beam shaping unit is used to shape the laser emitted by the laser emitting unit;

[0011] The MEMS galvanometer scanning unit is used to perform field-of-view scanning on the plane of the object under test by resonating and reflecting the beam shaped by the front beam shaping unit using a MEMS galvanometer.

[0012] The rear collimation unit is used to perform secondary shaping on the beam reflected by the MEMS galvanometer scanning unit, so that the optical path lengths of the edge beam and the center beam after deflection by the MEMS galvanometer are equal at the entrance pupil of the rear collimation unit.

[0013] Preferably, the rear collimation unit includes: a toric mirror;

[0014] The toric mirror is used to reshape the light beam reflected by the MEMS galvanometer scanning unit, so that the edge beam and the center beam after being deflected by the MEMS galvanometer have the same optical path at the entrance pupil of the toric mirror.

[0015] Preferably, the laser emitting unit includes a semiconductor laser and a semiconductor laser driving unit; the semiconductor laser driving unit is used to modulate the beam emitted by the semiconductor laser.

[0016] Preferably, the front beam shaping unit includes a shaping lens; the shaping lens is used to shape the beam emitted by the laser emitting unit.

[0017] Preferably, the shaping lens consists of at least one aspherical or freeform lens or multiple ordinary lenses.

[0018] Preferably, the pre-beam shaping unit further includes a microlens encapsulated at the beam exit of the laser emitting unit; the microlens is used to perform preliminary shaping of the beam emitted by the laser emitting unit.

[0019] Preferably, the front beam shaping unit further includes a field stop; the field stop is used to limit the size of the shaped beam spot so that the outgoing beam can be fully incident on the MEMS galvanometer and intercept excess stray light.

[0020] Preferably, the MEMS galvanometer scanning unit includes: a MEMS galvanometer scanning component and a MEMS scanning driving component; the MEMS scanning driving component is used to drive and control the MEMS galvanometer scanning component; the driving method of the MEMS scanning driving component includes one or more of piezoelectric driving, electrothermal driving, electrostatic driving and electromagnetic driving.

[0021] Preferably, the MEMS galvanometer scanning component is composed of a single or multiple MEMS galvanometer arrays, which scan and reflect the shaped beam according to the corresponding scanning drive signal.

[0022] Secondly, the present invention also provides a lidar, including the above-described collimation system based on MEMS galvanometers.

[0023] As can be seen from the above technical solution, the collimation system based on a MEMS galvanometer provided by the present invention includes a rear collimation unit for secondary shaping of the beam reflected by the MEMS galvanometer scanning unit, ensuring that the optical path lengths of the edge beam and the center beam after deflection by the MEMS galvanometer are equal at the entrance pupil of the rear collimation unit. Therefore, the present invention can improve the energy coupling efficiency of the system, reduce the beam divergence angle, and ensure consistent ranging capabilities between the center and edge fields of view, thereby improving the system's detection capability in the edge field of view. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the collimation system based on a MEMS galvanometer provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the structure of the rear collimation unit using a toroidal mirror, as provided in an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram illustrating the working principle of the collimation system based on a MEMS galvanometer provided in an embodiment of the present invention;

[0028] Figure 4This is a schematic diagram of the collimation system based on a MEMS galvanometer provided in an embodiment of the present invention in the slow axis direction;

[0029] Figure 5 This is a schematic diagram of the collimation system based on a MEMS galvanometer provided in an embodiment of the present invention in the fast axis direction;

[0030] The meanings of the labels in the above figures are as follows:

[0031] 101 represents the laser emitting unit; 102 represents the front beam shaping unit; 103 represents the MEMS galvanometer unit; 104 represents the rear collimation unit; 105 represents the target object under test; 201 represents the semiconductor laser; 202 represents the microlens; 203 represents the shaping lens; 204 represents the field stop; 205 represents the MEMS galvanometer; 206 represents the toroidal mirror; 207 represents the plane of the target object under test. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a collimation system based on a MEMS galvanometer, see [link to documentation]. Figure 1 The collimation system includes: a laser emitting unit 101, a front beam shaping unit 102, a MEMS galvanometer scanning unit 103, and a rear collimation unit 104, wherein:

[0034] Laser emitting unit 101 is used to emit modulated laser beams;

[0035] The front beam shaping unit 102 is used to shape the laser emitted by the laser emitting unit 101;

[0036] MEMS galvanometer scanning unit 103 is used to perform field scanning on the plane of the object under test by resonating and reflecting the beam shaped by the front beam shaping unit 102 using a MEMS galvanometer.

[0037] The rear collimation unit 104 is used to perform secondary shaping on the beam reflected by the MEMS galvanometer scanning unit 103, so that the optical path lengths of the edge beam and the center beam after deflection by the MEMS galvanometer are equal at the entrance pupil of the rear collimation unit.

[0038] Furthermore, the laser emitting unit 101 includes a semiconductor laser and a semiconductor laser driving unit; the semiconductor laser driving unit is used to modulate the beam emitted by the semiconductor laser.

[0039] Furthermore, the front beam shaping unit 102 includes a shaping lens; the shaping lens is used to shape the beam emitted by the semiconductor laser 201. Preferably, the shaping lens is composed of at least one aspherical or freeform lens or multiple ordinary lenses.

[0040] Furthermore, in order to perform preliminary shaping of the beam emitted by the laser emitting unit 101, the front beam shaping unit 102 further includes a microlens encapsulated at the outlet of the laser emitting unit; the microlens is used to perform preliminary shaping of the beam emitted by the laser emitting unit.

[0041] Furthermore, in order to limit the size of the shaped beam spot so that the entire outgoing beam can be incident on the MEMS galvanometer and intercept excess stray light, the front beam shaping unit 102 further includes a field stop; the field stop is used to limit the size of the shaped beam spot so that the entire outgoing beam can be incident on the MEMS galvanometer and intercept excess stray light.

[0042] Furthermore, the MEMS galvanometer scanning unit 103 includes a MEMS galvanometer scanning component and a MEMS scanning driving component. The MEMS scanning driving component is used to drive and control the MEMS galvanometer scanning component. The driving method of the MEMS scanning driving component includes one or more of piezoelectric driving, electrothermal driving, electrostatic driving, and electromagnetic driving. It can be understood that, depending on the size of the actual scanning field range, the MEMS galvanometer scanning component can be composed of a single or multiple MEMS galvanometer arrays. The single or multiple MEMS galvanometer arrays scan and reflect the shaped light beam according to the corresponding scanning driving signal.

[0043] See Figure 1 The laser emitted by the laser emitting unit 101 is shaped by the pre-beam shaping unit 102 and then incident on the MEMS galvanometer scanning unit 103. After being resonantly reflected by the MEMS galvanometer scanning unit 103, the laser is shaped again by the post-collimation unit 104. The beam after the second shaping is emitted onto the target object 105, forming a light spot of a preset size. The MEMS galvanometer scanning unit 103 oscillates according to a certain signal pattern, so that the emitted light spot forms regular detection points on the target object 105, thus completing the scanning of the target object 105.

[0044] It should be noted that since the laser emitting unit uses a semiconductor laser, the beam collimation and shaping principle provided in this embodiment is to process the beam in two directions, that is, the fast axis and slow axis of the semiconductor laser collimate and shape the beam respectively.

[0045] As described above, the collimation system based on a MEMS galvanometer provided in this embodiment includes a post-collimation unit for secondary shaping of the beam reflected by the MEMS galvanometer scanning unit. This ensures that the optical path lengths of the edge beam and the center beam, after deflection by the MEMS galvanometer, are equal at the entrance pupil of the post-collimation unit. Therefore, this invention improves the system's energy coupling efficiency, reduces the beam divergence angle, and ensures uniform ranging capabilities in both the center and edge fields of view, thereby enhancing the system's detection capability in the edge field of view.

[0046] In a preferred embodiment of the present invention, such as Figure 2 As shown, the rear collimation unit 104 is preferably implemented using a toric mirror. Specifically, the toric mirror is used to perform secondary shaping on the beam reflected by the MEMS galvanometer scanning unit, so that the edge beam and the center beam after being deflected by the MEMS galvanometer have equal optical path lengths at the entrance pupil of the toric mirror.

[0047] Further, see Figure 3 The diagram illustrates the working principle of the collimation system based on a MEMS galvanometer. A light beam exits from a semiconductor laser 201, enters a microlens 202, and is initially compressed before entering a shaping lens 203. After exiting the shaping lens 203, the beam enters the MEMS galvanometer 205. Before reaching the MEMS galvanometer 205, stray light from the edges is intercepted by a field stop 204. The beam is reflected by the MEMS galvanometer 205 and enters a toric mirror 206 for secondary shaping, ensuring that the optical path lengths of the edge and center beams after deflection by the MEMS galvanometer are equal at the entrance pupil of the toric mirror. Finally, the beam exits from the toric mirror 206 and reaches the target object plane 207. During this process, the MEMS galvanometer 205 oscillates according to a specific pattern, thus completing the scanning of the target object plane 207.

[0048] Further, see Figure 4The diagram illustrates the principle of the MEMS-based collimation system in the slow-axis direction. The laser beam emitted by the semiconductor laser 201, after passing through the microlens 202 of the pre-shaping unit, has its divergence angle initially compressed, increasing the energy entering the next shaping lens 203. After entering the shaping lens 203, the initially compressed beam is collimated into parallel light along the fast axis. Furthermore, the slow-axis photosensitive surface of the semiconductor laser is in front, and the fast-axis photosensitive surface is behind. The distance between the slow-axis photosensitive surface and the shaping lens 203 is greater than that of the fast-axis photosensitive surface. Therefore, a converging beam forms along the slow axis, creating a minimal convergence point on the MEMS mirror 205. Simultaneously, before entering the MEMS mirror 205, the beam passes through a field-of-view aperture 204, intercepting stray light at the beam edges and improving beam quality.

[0049] Depend on Figure 4 It is known that in the slow axis direction, the beam becomes a divergent beam after passing through the MEMS galvanometer 205. Without processing, at long distances, the beam divergence angle is large, the energy of the spot is not concentrated, and the energy efficiency is low. Therefore, after passing through the MEMS galvanometer 205, the beam enters the toric mirror 206. The toric mirror 206 can be equivalent to a single cylindrical mirror or a set of cylindrical mirrors with curvature only in the slow axis direction, performing a second collimation and shaping on the spot. In this way, after passing through the toric mirror 206, the beam forms a spot with a smaller divergence angle and exits onto the target object plane 207.

[0050] Further, see Figure 5 The diagram illustrates the principle of the MEMS-based collimation system along the fast axis. In the fast axis direction, the laser emitted from the semiconductor laser 201 is initially compressed after passing through the microlens 202, ensuring that as much of its energy as possible enters the shaping lens 203. After passing through the shaping lens 203, the beam is collimated and incident on the MEMS mirror 205. The beam then exits through the MEMS mirror 205 onto the toroidal mirror 206.

[0051] Depend on Figure 5 As can be seen, in the fast axis direction, the toric mirror 206 can be equivalent to a curved flat glass plate, and the convergence point of the light spot on the MEMS galvanometer 205 is at the center of curvature of the toric mirror 206. In the fast axis direction, due to the oscillation of the MEMS galvanometer, the light beam passes through various regions of the toric mirror 206 and is scanned, forming a central field of view and an edge field of view. Due to the curved shape of the toric mirror 206, the optical path length of each part from the light spot exit point on the MEMS galvanometer is equal, so the optical aberrations of each field of view are also consistent. The benefit of this is that the divergence angles of the central field of view and the edge field of view are consistent, thereby improving the system's detection capability in the edge field of view and ensuring uniform ranging capability in each field of view.

[0052] Depend on Figure 5As can be seen, in the fast axis direction, the light spot emitted from the MEMS galvanometer 205 can enter the flat plate faster at the edge of the field of view compared to a non-curved flat plate. Therefore, the size of the toric mirror 206 can be smaller. The MEMS galvanometer 205 needs to perform large field-of-view oscillation. Therefore, the toric mirror 206 behind the MEMS galvanometer 205 is the largest module in this embodiment. Thus, the reduction in the size of the toric mirror 206 leads to a corresponding reduction in the overall system volume.

[0053] according to Figures 3-5 As can be seen from the above analysis, the first surface of the toric mirror (the surface facing the light beam emitted from the MEMS galvanometer scanning unit) can be equivalent to a cylindrical surface, processing only one direction of the light beam (the fast axis direction); the second surface of the toric mirror (the surface opposite to the first surface) can be equivalent to a cylindrical surface in two directions (the fast axis and the slow axis), processing the two directions of the light beam respectively, wherein the curvature of the second surface equivalent to the cylindrical surface in the fast axis direction is the same as the curvature of the first surface.

[0054] The above analysis shows that due to the large beam divergence angle of semiconductor lasers, a beam shaping unit is usually required after the laser. However, because the mirror size of a MEMS galvanometer is small, and the beam shaping unit behind the semiconductor laser has a relatively large aperture to collect the laser beam energy, only a small portion of the energy is received by the MEMS galvanometer when it strikes the laser, resulting in low energy coupling efficiency. To solve this problem, the beam after the beam shaping unit can be converged through appropriate optical path design, forming a convergence point on the MEMS galvanometer. This would allow most of the energy to be received and utilized, improving energy coupling efficiency. However, in this case, since the beam incident on the MEMS galvanometer is a converged beam, it becomes a divergent beam when leaving the galvanometer. If it is directly emitted to a distance, the divergence angle is large, the energy is not concentrated, and the signal will be very low if combined with other receiving systems. To address the issue of large beam divergence after passing through a MEMS galvanometer, current technologies typically employ a plano-convex cylindrical lens or other plane mirror behind the MEMS galvanometer for secondary beam reshaping. However, because MEMS galvanometers require large field-of-view scanning, the plano-convex cylindrical lens behind the galvanometer needs to be quite large in the scanning direction to collect and emit all the scanning light, which does not meet the size requirements of lidar. Furthermore, the plano-convex cylindrical lens cannot simultaneously solve the problem of beam collimation and shaping on both the fast and slow axes.

[0055] To address this, this embodiment of the invention adds a toric mirror after the MEMS galvanometer to reshape the light spot in the slow-axis direction, reducing the beam divergence angle and concentrating the energy of the distant light spot. Simultaneously, in the fast-axis direction, due to the curved shape of the toric mirror, the optical path length of each part from the light spot exit point on the MEMS galvanometer is equal. This results in consistent divergence angles in the central and peripheral fields of view, improving the system's detection capability in the peripheral fields of view and ensuring uniform ranging capabilities across all fields of view. Furthermore, because the toric mirror is curved on both sides, light from the peripheral fields of view can quickly enter the rear collimating unit. This curved shape reduces the size of the rear collimating unit, thus reducing the overall system size.

[0056] As can be seen, the collimation system based on MEMS galvanometers provided in this embodiment uses a complex toroidal mirror for secondary beam shaping, which greatly simplifies the size and structure of the lidar system, reduces the weight and volume of the lidar, and enables the system as a whole to have high angular resolution and scanning frequency. It is also easy to integrate, which is conducive to promoting the development of lidar technology towards miniaturization, lightweighting and integration.

[0057] Another embodiment of the present invention provides a lidar, including the MEMS galvanometer-based collimation system described in the above embodiments.

[0058] The lidar provided in this embodiment includes the collimation system based on MEMS galvanometers described in the above embodiments, so its technical principle and beneficial effects are similar and will not be repeated here.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A collimation system based on a MEMS galvanometer, characterized in that, include: The laser emitting unit is used to emit a modulated laser beam; The front beam shaping unit is used to shape the laser emitted by the laser emitting unit so that the beam in the fast axis direction is collimated and shaped into parallel light, and the beam in the slow axis direction is shaped into a converging beam. The MEMS galvanometer scanning unit is used to perform field-of-view scanning on the plane of the object under test by resonating and reflecting the beam shaped by the front beam shaping unit using a MEMS galvanometer. The rear collimation unit includes a toric mirror, which is used to perform secondary shaping on the light beam reflected by the MEMS galvanometer scanning unit, so that the optical path lengths of the edge beam and the center beam after deflection by the MEMS galvanometer are equal at the entrance pupil of the rear collimation unit, so that the divergence angle of the light spot in the center field of view and the edge field of view are consistent.

2. The system according to claim 1, characterized in that, The laser emitting unit includes a semiconductor laser and a semiconductor laser driving unit; the semiconductor laser driving unit is used to modulate the beam emitted by the semiconductor laser.

3. The system according to claim 1, characterized in that, The front beam shaping unit includes a shaping lens; the shaping lens is used to shape the beam emitted by the laser emitting unit.

4. The system according to claim 3, characterized in that, The shaping lens consists of at least one aspherical or freeform lens or multiple ordinary lenses.

5. The system according to claim 3, characterized in that, The pre-beam shaping unit further includes a microlens encapsulated at the beam exit of the laser emitting unit; the microlens is used to perform preliminary shaping of the beam emitted by the laser emitting unit.

6. The system according to claim 3 or 4, characterized in that, The front beam shaping unit also includes a field stop; the field stop is used to limit the size of the beam spot after shaping, so that the outgoing beam can be fully incident on the MEMS galvanometer and intercept excess stray light.

7. The system according to claim 1, characterized in that, The MEMS galvanometer scanning unit includes a MEMS galvanometer scanning component and a MEMS scanning driving component; the MEMS scanning driving component is used to drive and control the MEMS galvanometer scanning component; the driving method of the MEMS scanning driving component includes one or more of piezoelectric driving, electrothermal driving, electrostatic driving and electromagnetic driving.

8. The system according to claim 7, characterized in that, The MEMS galvanometer scanning component consists of a single or multiple MEMS galvanometer arrays, which scan and reflect the shaped beam according to the corresponding scanning drive signal.

9. A lidar, characterized in that, Including the collimation system based on MEMS galvanometers as described in any one of claims 1 to 8.

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