Large-view-field FMCW laser radar system based on liquid crystal polarization grating and scanning control method

Abstract

The invention relates to a large-view-field FMCW laser radar system based on a liquid crystal polarization grating and a scanning control method, and belongs to the technical field of laser radars. The system comprises a laser emitting subsystem, a laser scanning subsystem, a laser receiving subsystem and a laser control subsystem, and the core of the system is that the laser scanning subsystem adopts a fast reflecting mirror to cooperate with a multi-level liquid crystal polarization grating module. The fast reflecting mirror performs high-precision and fast scanning in a small-angle range, the multi-level liquid crystal polarization grating module switches all levels of deflection states through electric control, discrete jumping of light beams in a large-angle range is achieved, and the fast reflecting mirror and the multi-level liquid crystal polarization grating module are overlapped to jointly cover a large view field. In addition, the emission subsystem processes the laser beam and regulates and controls the polarization state of the laser beam. The receiving subsystem adopts a perforated reflector to construct a coaxial receiving framework, receives a target echo signal in combination with an optical lens and a detector, and calculates distance and speed information in real time by a data processing module; and the control subsystem adopts an integrated controller to schedule signal generation, light beam modulation, scanning execution and data processing flow.

Description

Technical Field

[0001] This invention belongs to the field of lidar technology and relates to a large field-of-view FMCW lidar system and scanning control method based on a liquid crystal polarization grating. Background Technology

[0002] LiDAR systems utilize lasers to achieve all-weather, high-precision 3D measurement and imaging, providing core data support for key fields such as autonomous driving, industrial manufacturing, and aerospace. Based on their detection mechanisms, LiDAR is mainly divided into Time-of-Flight (TOF) and Frequency Modulated Continuous Wave (FMCW) types. TOF LiDAR calculates target distance by measuring the flight time of the reflected signal light, while FMCW LiDAR, based on coherent detection principles, offers significant advantages such as strong anti-interference capabilities, high ranging accuracy, and the ability to directly acquire target radial velocity, gradually becoming the preferred technology for high-reliability applications.

[0003] In terms of scanning mechanism, LiDAR can be divided into three categories: mechanical scanning, semi-solid scanning, and solid scanning.

[0004] Solid-state scanning is a significant trend. Optical Phased Array (OPA) technology, however, is limited by finite aperture and sidelobe issues, resulting in typically small scanning angles that struggle to meet large field-of-view requirements. Solid-state solutions based on Liquid Crystal Polarization Grating (LCPG) achieve beam deflection through the arrangement of liquid crystal molecules, offering advantages such as no mechanical movement, large deflection angles, and ease of integration. For example, existing technologies (such as Chinese patent CN111399218A) disclose schemes using rotating LCPGs or combinations of LCPGs and wedge prisms for beam scanning. However, these purely solid-state solutions have inherent limitations: the deflection angle of a single LCPG is fixed, requiring the integration of an electrically driven half-wave plate to switch polarization states for angle adjustment; when high-resolution scanning is required, a multi-level LCPG cascade design is necessary, leading to a significant decrease in optical efficiency and preventing dynamic resolution switching due to the rigidity of the hierarchical structure, making it difficult to simultaneously meet the dual requirements of large field-of-view coverage and fine scanning of local areas. In addition, existing LCPG solutions suffer from response delays when rapidly switching fields of view, and cannot support real-time staring functionality, which severely limits their practicality in dynamic environment monitoring.

[0005] In summary, existing scanning schemes based on liquid crystal polarization gratings still face a trade-off between large field-of-view coverage and fine scanning of local areas, and there is a lack of a system solution that can simultaneously achieve both. Summary of the Invention

[0006] In view of this, the present invention aims to overcome the inherent defects of existing solid-state lidar in terms of field of view, scanning efficiency and dynamic adjustment of resolution, and to provide a large field of view linear frequency modulated continuous wave (FMCW) lidar system and scanning control method based on liquid crystal polarization grating.

[0007] To achieve the above objectives, this invention is not a simple parallel or replacement of existing scanning devices, but rather addresses the contradiction between large field-of-view scanning and high-resolution ranging by dividing the scanning task into functional parts: a liquid crystal polarizing grating is used to handle large-angle field-of-view switching, and a fast reflector is used to handle continuous fine scanning within a sub-field of view, so that different scanning devices always work in their respective optimal working ranges.

[0008] This invention provides a large field-of-view FMCW lidar system based on a liquid crystal polarization grating, comprising a laser emitting subsystem for generating frequency-modulated continuous wave laser signals, a laser scanning subsystem for scanning the laser beam output by the laser emitting subsystem, a laser receiving subsystem for receiving the reflected echo light from the target, and a control subsystem for coordinating the scanning and receiving timing.

[0009] The laser scanning subsystem includes at least a fast reflector and a multi-level liquid crystal polarization grating module. The fast reflector is configured to perform two-dimensional scanning within its maximum mechanical deflection angle range. The multi-level liquid crystal polarization grating module is composed of at least two cascaded scanning units. Each scanning unit includes an electric half-wave plate and a liquid crystal polarization grating, configured to apply a preset fixed angle deflection to the passing light beam.

[0010] The control subsystem, including an integrated controller and a signal generator, is configured to coordinate the switching of the continuous scanning of the fast reflector and the discrete deflection state of the multi-level liquid crystal polarization grating module, such that the target scanning angle α1 is formed by the superposition of the fixed deflection angle α2 of the liquid crystal polarization grating and the scanning angle α3 of the fast reflector, where α1 = α2 + α3.

[0011] The laser emission subsystem includes at least a laser, an optical fiber beam splitter, and a polarization control module. The polarization control module consists of a linear polarizer and a quarter-wave plate, and is used to adjust the signal light split by the optical fiber beam splitter into circularly polarized light before it is incident on the laser scanning subsystem.

[0012] The laser emitted by the laser is split into signal light and intrinsic light by an optical fiber beam splitter. The signal light is polarized and then transmitted through a perforated mirror after polarization state conversion by a polarization control module. This completes the splitting, polarization control and emission of the laser beam.

[0013] The laser receiving subsystem adopts a coaxial receiving architecture based on a perforated mirror, including at least a perforated mirror, an optical lens, a balanced detector, and a data processing module. The perforated mirror is located at the intersection of the transmitting and receiving optical paths, with a through hole in its center for the transmitted beam to pass through, and its reflective surface is used to reflect the target echo signal light to the receiving optical path. The laser scanning subsystem also includes a quarter-wave plate disposed on the output optical path of the multi-level liquid crystal polarization grating module, which is used to ensure that the target echo signal light meets its polarization selection characteristics when it passes through the liquid crystal polarization grating again, thereby returning along the original transmitting optical path and being guided into the laser receiving subsystem by the perforated mirror.

[0014] The signal light returned by the target returns along the original optical path, passing sequentially through a quarter-wave plate, a liquid crystal polarization grating module, and a fast reflector. After passing through the quarter-wave plate again, it recovers to the same circular polarization state as the emitted light, satisfying the polarization selection characteristics of the liquid crystal polarization grating, and thus returns along the original emitted optical path to the perforated reflector. The perforated reflector reflects the target echo signal light to the receiving optical path, where it is collected by an optical lens and coupled into an optical fiber. It is then coherently mixed with the intrinsic light in a coupler, and finally the target distance and velocity information is demodulated by a balanced detector and a data processing module.

[0015] Furthermore, in the multi-level liquid crystal polarization grating module, the deflection angle of the first-level liquid crystal polarization grating is designed to match the scanning angle range of the fast reflector, and the deflection angle of subsequent levels is designed to be cascaded and matched based on the deflection angle of the previous level. Through multi-level collaboration, the large field-of-view angle deflection of the laser beam is achieved.

[0016] This invention also provides a scanning control method for the large field-of-view FMCW lidar system based on a liquid crystal polarization grating. This method employs a fast-reflecting mirror to perform high-precision scanning within a small angle range, while simultaneously using a liquid crystal polarization grating module to achieve stepped beam deflection within a large angle range. The method includes the following steps: (1) Divide the target large field of view into multiple sub-regions, each sub-region corresponding to a deflection state of the multi-level liquid crystal polarization grating module; (2) For each sub-region: a. Control the multi-level liquid crystal polarization grating module to switch to the corresponding deflection state; b. Control the fast-reflecting mirror to perform a two-dimensional scan within the corresponding sub-region; c. During the fast mirror scan, the target echo signal is received and processed to obtain target information; The scanning of the fast reflector is coordinated with the switching of the liquid crystal polarization grating module, thereby optimizing the overall scanning path.

[0017] Furthermore, the fast reflector and the liquid crystal polarizing grating module are controlled to perform a serpentine scanning path. After completing the scanning of a sub-region, the liquid crystal polarizing grating module is switched only once to enter the adjacent sub-region, and the fast reflector is controlled to scan in the opposite direction within the adjacent sub-region.

[0018] Furthermore, the method also includes a dynamic staring step: dividing the plurality of sub-regions into staring regions and non-staring regions; controlling the fast reflector to scan in the staring regions using a first angular resolution, and in the non-staring regions using a second angular resolution lower than the first angular resolution.

[0019] Furthermore, the method also includes a timing synchronization step: during the switching of the deflection state of the multi-level liquid crystal polarization grating module, the control subsystem controls the fast reflector to pause scanning and controls the laser receiving subsystem to pause signal acquisition until the liquid crystal polarization grating module completes the switching. During the switching of the liquid crystal polarization grating deflection state, by controlling the fast reflector to pause scanning and synchronously controlling the signal acquisition timing, the scanning control logic is matched with the physical response characteristics of the device, thereby avoiding interference with the FMCW coherent ranging process.

[0020] Furthermore, the deflection angle range of the liquid crystal polarizing grating and the scanning angle range of the fast reflector are configured according to a preset ratio or matching relationship, so that the scanning angles of the two are superimposed to form an overall scanning field of view that is greater than the scanning range of any single scanning device.

[0021] Optionally, the laser includes, but is not limited to, semiconductor lasers and fiber lasers; the polarization beam splitter includes, but is not limited to, fiber polarization and energy beam splitters; and the scanning mirror includes, but is not limited to, two-dimensional galvanometers and two-dimensional fast-reflection mirrors.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Through a hybrid scanning architecture, a large field of view scanning of the beam is achieved by using a fast reflector and a liquid crystal polarization grating module. The fast reflector has a fast response and is responsible for the main scanning motion, achieving high-precision scanning at small angles. The liquid crystal polarization grating is only responsible for discrete jumps between fields of view, and its switching speed is much faster than that of the mechanical rotation scheme, thus achieving a large field of view scanning of the lidar system. The combination of the two optimizes the path, which not only obtains the large-angle deflection capability of the liquid crystal polarization grating, but also retains the local high-precision scanning characteristics of the fast reflector, resulting in high overall scanning efficiency.

[0023] (2) A coaxial receiving architecture based on a perforated mirror and a quarter-wave plate is adopted. Through the design of optical path reversibility and polarization matching, the target echo signal can be efficiently returned along the original path. Thus, only ordinary optical lenses are needed to achieve large field of view signal reception, avoiding expensive large field of view field array detectors and receiving antennas, significantly reducing system complexity and cost, and facilitating mass production.

[0024] (3) Based on FMCW coherent detection, high-precision distance and velocity information of objects can be obtained simultaneously, which greatly improves the information dimension of the lidar system; dynamic resolution is used to enhance scene adaptability. Through the staring area division and resolution grading strategy, real-time performance and energy consumption ratio can be significantly optimized in various scenarios.

[0025] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This invention provides a structural framework for a large field-of-view FMCW lidar system based on a liquid crystal polarization grating. Figure 2 This is a schematic diagram showing the deflection of left- and right-hand circularly polarized light by a liquid crystal polarization grating unit. Figure 3 This is a schematic diagram of the composition of a single-stage liquid crystal polarization grating module; Figure 4 This is a schematic diagram of the two-dimensional deflection of circularly polarized light by a single-stage liquid crystal polarization grating module. Figure 5 This is a schematic diagram of a fast-reflecting mirror scanning a light beam. Figure 6 This is a schematic diagram of the composition of a multi-level liquid crystal polarization grating module; Figure 7 This is a schematic diagram of a two-dimensional large field-of-view beam scanning using a fast reflector and a liquid crystal polarization grating module. Figure 8 This is a schematic diagram of the coaxial receiving optical path proposed in this invention; Figure 9 This is a schematic diagram illustrating the logic switching for fast scanning with a wide field of view. Figure 10 A schematic diagram of a wide field-of-view, fast-scanning gaze function; Figure 11This is a schematic diagram of the beat frequency signal of the balanced detector when the system described in this invention performs distance and velocity measurement. Figure label: In Figure 1 In the middle: 1-Laser; 2-Fiber beam splitter; 3-Polarization control module; 4-Perforated mirror; 5-Fast mirror; 6-Liquid crystal polarization grating module; 7-Quarter-wave plate; 8-Target; 9-Optical lens; 10-Fiber optic cable; 11-Coupler; 12-Balanced detector; 13-Data processing module; 14-Integrated controller; 15-Signal generator. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0029] Example 1 illustrates the structure and workflow of a large field-of-view FMCW lidar system based on a liquid crystal polarization grating. The following description, in conjunction with the accompanying drawings, particularly... Figure 1 Please provide a detailed explanation.

[0030] like Figure 1 As shown, a large field-of-view FMCW lidar system based on a liquid crystal polarization grating mainly includes a laser emission subsystem, a laser scanning subsystem, a laser receiving subsystem, and a control subsystem.

[0031] The laser emission subsystem includes a laser 1, an fiber beam splitter 2, and a polarization control module 3. This embodiment uses a 1550nm fiber laser, driven by a linearly frequency-modulated continuous wave (FMCW) generated by a signal generator 15, to output a linearly frequency-changing laser beam. This laser beam is split into two paths by a 3dB fiber coupler: one path serves as the signal beam, and the other as the intrinsic beam. The signal beam enters the polarization control module 3, which consists of a linear polarizer and a quarter-wave plate, used to convert the signal beam into specifically circularly polarized light.

[0032] The laser scanning subsystem includes a perforated mirror 4, a fast reflector 5, a liquid crystal polarization grating module 6, and another quarter-wave plate 7. Circularly polarized signal light emitted from the polarization control module 3 exits through the central aperture of the perforated mirror 4, achieving beam splitting, polarization control, and directional emission, before being incident on the fast reflector 5. The fast reflector 5 employs a two-dimensional piezoelectric or electromagnetically driven fast reflector, and its working principle is as follows... Figure 5 As shown, it can deflect in two dimensions. Under the control of the integrated controller 14, the fast reflector 5 performs high-speed, high-precision two-dimensional grid or continuous scanning within a small angle range, achieving fine coverage in the pitch and horizontal dimensions. Subsequently, the beam enters the liquid crystal polarization grating module 6.

[0033] like Figure 3 and Figure 4 As shown, the liquid crystal polarization grating module 6 is composed of cascaded multi-level units, each unit consisting of an electrically driven half-wave plate and a liquid crystal polarization grating (LCPG). The electrically driven half-wave plate is used to switch the circular polarization direction of the incident light under voltage control. Figure 2 As shown, LCPG will deflect incident left-handed or right-handed circularly polarized light at a fixed angle in different directions, such as upward or downward.

[0034] The integrated controller 14 adjusts the circular polarization direction (left-hand or right-hand) of the beam incident on the next-stage LCPG by controlling the voltage applied to each stage of the motorized half-wave plate. This controls the LCPG to deflect the beam in a preset fixed direction, thus guiding the beam to a large field of view of the target. Subsequently, the integrated controller precisely controls the fast reflector to perform small-angle dynamic scanning within the deflected sub-field of view, achieving fine coverage in both pitch and horizontal dimensions.

[0035] The deflection angle of a single liquid crystal polarizing grating module depends on the arrangement period of its liquid crystal molecules and is a fixed angle. Therefore, multiple liquid crystal polarizing gratings can be used to achieve beam deflection at multiple angles. Using liquid crystal polarizing gratings with alternating combinations of up-down and left-right deflection can achieve beam deflection in two dimensions.

[0036] In this embodiment, to achieve a large field of view scanning, a multi-layer cascaded liquid crystal polarization grating module 6 is used, the composition of which is as follows: Figure 6 As shown. Specifically, to achieve a two-dimensional ±48° field of view, a three-stage design is adopted, requiring a total of 6 LCPGs. The deflection angle of the first-stage LCPG matches the scanning range of the fast reflector 5; the deflection angle of the second-stage LCPG is extended based on the first-stage; and the deflection angle of the third-stage LCPG is further extended. By combining different deflection directions at each stage, a pattern can be formed as shown... Figure 7The two-dimensional scanning dot array shown corresponds to a sub-region scanned by the fast reflector 5. The signal light is reflected by the fast reflector 5 and deflected at a large angle by the liquid crystal polarization grating module 6. Finally, it passes through the quarter-wave plate 7, where it is converted from circularly polarized light to linearly polarized light and emitted to illuminate the target 8.

[0037] The laser receiving subsystem includes a perforated mirror 4, an optical lens 9, an optical fiber 10, a coupler 11, a balanced detector 12, and a data processing module 13. This subsystem employs... Figure 8 The coaxial receiving optical path architecture shown depicts the return signal light reflected from target 8 along its original path, passing sequentially through a quarter-wave plate 7, a liquid crystal polarization grating module 6, and a fast reflector 5. During this process, the echo signal light scattered by the target propagates in reverse along the original emission path: the incident linearly polarized light is converted into outgoing circularly polarized light by the quarter-wave plate, ensuring its polarization state is the same as during emission. Finally, the signal light is reflected back to the apertured reflector 4 by the fast reflector 5. The reflective surface of the apertured reflector 4 reflects the signal light to the optical lens 9, where it is focused and coupled into the optical fiber 10. In the fiber coupler 11, the returned signal light is coherently mixed with the intrinsic light. The mixed light is received by the balanced detector 12 and converted into a beat frequency electrical signal containing target distance and velocity information. The data processing module 13 samples and performs FFT transformation on this signal to calculate the target distance D and radial velocity V.

[0038] The control subsystem includes an integrated controller 14 and a signal generator 15. The integrated controller 14, as the control core, has the following functions: controlling the signal generator 15 to generate FMCW modulated waveforms; generating scanning drive signals for the fast reflector 5 according to a preset scanning strategy; generating voltage switching logic for each stage of the motorized half-wave plate in the liquid crystal polarization grating module 6; controlling the signal acquisition and processing timing of the data processing module 13; and finally fusing the scanning angle information and processing results to generate a point cloud image of the target.

[0039] The system described in this invention achieves target ranging and velocity measurement based on the principle of frequency-modulated continuous wave coherent detection.

[0040] Specifically, the signal generator generates a triangular wave modulation signal under the scheduling of the integrated controller, which drives the laser to perform frequency modulation. The modulation period is T and the modulation bandwidth is B.

[0041] The laser output light is split into signal light and local oscillator light. The signal light passes through a laser scanning subsystem containing a fast reflector and a liquid crystal polarization grating module, completes a large field-of-view two-dimensional scan, and is then emitted. The target echo signal light returns through a coaxial receiving architecture with a perforated reflector as its core, and is coherently mixed with the local oscillator light in an optical fiber coupler. It is then converted into a beat frequency electrical signal by a balanced detector.

[0042] The data processing module acquires the beat frequency values ​​of the upper and lower frequency bands in real time. The beat frequency signals obtained from the laser's intrinsic light and signal light during the upper and lower frequency bands are as follows: Figure 11 As shown, the beat frequency signal value of the upper sweep frequency is f1, and the beat frequency signal value of the lower sweep frequency is f2. The distance and velocity information of the target can be obtained by using the distance formula D=[cT(f1+f2)] / 8B and the velocity calculation formula V=[λ(f2-f1)] / 4.

[0043] Example 2 provides a specific implementation of the liquid crystal polarization grating module and scanning principle described in Example 1, and details the key components of the scanning subsystem and their collaborative mechanism.

[0044] 2.1 Working principle of liquid crystal polarizing grating (LCPG) unit Figure 2 This diagram illustrates the deflection of left-handed or right-handed circularly polarized light by a liquid crystal polarization grating (LCPG) unit. The LCPG unit exhibits directional selectivity in deflecting circularly polarized light. When left-handed (right-handed) circularly polarized light passes through the liquid crystal polarization unit, the outgoing beam will be deflected upwards (downwards), resulting in right-handed (left-handed) circularly polarized light. The specific circular polarization state of the incident beam and the actual outgoing direction, whether the deflection is upwards or downwards, can be set according to actual conditions and are not limited here. The magnitude of the deflection angle can be designed based on the arrangement period of the liquid crystal grating according to actual conditions and is not limited here.

[0045] 2.2 Composition of a Single-Stage Controllable Deflection Module Figure 3 and Figure 4 The diagram shows a single-stage liquid crystal polarization grating module composed of a single electrodynamic half-wave plate and a single liquid crystal polarization grating unit, and a schematic diagram showing how the deflection direction is controlled by the electrodynamic half-wave plate.

[0046] Figure 3 The diagram shows a first-stage liquid crystal polarization grating module consisting of an electrically driven half-wave plate and a liquid crystal polarization grating unit. The electrically driven half-wave plate allows for the artificial alteration of the polarization state of the incident light beam, thereby controlling the outgoing deflection direction. When a zero voltage is applied to the electrically driven half-wave plate, it can convert left-handed circularly polarized light to right-handed circularly polarized light, or vice versa. When a non-zero voltage is applied to the electrically driven half-wave plate, the polarization state of the incident light beam remains unchanged. By controlling the voltage of the electrically driven half-wave plate, the deflection direction of the subsequent LCPG can be selected.

[0047] 2.3 Design of Multi-layer Cascaded Extended Field of View To achieve a large field of view, a multi-layered cascaded liquid crystal polarization grating module 6 is required, and its composition is as follows: Figure 6As shown. In a specific design of this embodiment, the operating wavelength is selected as 1550nm, and the scanning range of the fast reflector 5 is set to ±6°.

[0048] To achieve a two-dimensional field of view of ±48° horizontally and ±48° vertically, a three-level design is adopted, using a total of 6 LCPGs, 3 in the horizontal dimension and 3 in the vertical dimension.

[0049] The first-stage LCPG consists of one horizontal and one vertical LCPG, with a deflection angle designed to be ±6° to match the scanning range of the fast mirror, corresponding to a grating period of approximately 14.8μm.

[0050] The second-stage LCPG has a deflection angle designed to be ±12°. The corresponding grating period is approximately 7.46 μm.

[0051] The third-stage LCPG has a deflection angle designed to be ±24°. The corresponding grating period is approximately 3.81 μm.

[0052] The angles at each level are cascaded at 6°, 12°, and 24°. By controlling the electric half-wave plates at each level to select the positive or negative deflection direction of each level, a two-dimensional scanning dot array with 12° intervals can be formed, such as... Figure 7 As shown, each dot corresponds to the center of a sub-region, and the fast reflector 5 performs a fine scan of ±6° within the small region corresponding to each dot, ultimately synthesizing a complete ±48° large field of view.

[0053] The above parameter configuration is only a specific example of this embodiment, used to illustrate the matching relationship between the multi-level liquid crystal polarization grating and the fast reflector, and does not constitute a limitation on the scope of protection of this invention.

[0054] 2.4 The function of a fast reflecting mirror like Figure 5 As shown, the fast reflector 5 can achieve high dynamic deflection in both the X and Y dimensions. Its core function is to perform high-precision, high-density scanning in each sub-region determined by the LCPG module, filling in the detailed information of that region.

[0055] 2.5 Coaxial receiving optical path like Figure 8 As shown, the key to the coaxial receiving architecture of this system lies in the design of the perforated reflector 4: the reflective surface guides the return beam 100% to the receiving optical path, while the central aperture only allows the emitted beam to pass through, so as to eliminate the return light with a different polarization state than the emitted light and retain the target return light with the same polarization state as the emitted light.

[0056] In the coaxial receiving architecture, a perforated reflector is positioned at the intersection of the transmitting and receiving optical paths. Its central through-hole allows the transmitted beam to pass through, while the reflective surface guides the returned target echo signal light to the receiving optical path. A quarter-wave plate is placed on the output optical path of the liquid crystal polarization grating module, so that the emitted circularly polarized light is converted into linearly polarized light and emitted to the target. The signal light reflected by the target passes through the quarter-wave plate again and is restored to the same circularly polarized state as the emitted light, thereby satisfying the polarization selection characteristics of the liquid crystal polarization grating and ensuring that the echo light returns along the original transmitting optical path, realizing reversible optical path reception.

[0057] Example 3 details the scanning control method based on the system described in Example 1.

[0058] The large field-of-view scanning of the scanning system described in this invention is achieved through the coordinated operation of continuous scanning by the fast-reflecting mirror 5 and discrete deflection by the liquid crystal polarization grating module 6. Its control flow is as follows: 3.1 Regional Division like Figure 7 and Figure 9 As shown, Figure 7 This paper illustrates a two-dimensional large field-of-view scanning mechanism achieved through the collaborative operation of a fast reflector and a liquid crystal polarization grating module. The deflection angles of the first and second stage liquid crystal polarization grating modules are set to ±α to match the scanning range of the fast reflector. The deflection angles of the third and fourth stage liquid crystal polarization grating modules are set to ±2α, and a cascaded design is implemented based on the deflection angles of the first two stages. Through the combination of N stages of liquid crystal polarization grating modules (N being an even number), the system can achieve a total field-of-view angle of... Two-dimensional scanning; the field resolution is determined by the angular resolution β rad of the fast reflector; this architecture achieves high-precision large field coverage through the fine scanning of the fast reflector and the large-angle deflection of the liquid crystal polarization grating module, and the scanning range can be adjusted by dynamically switching the state of the liquid crystal polarization grating module; Figure 9 The logic switching mechanism of large field of view fast scanning is shown: the target scanning angle α1 is composed of the fixed deflection angle α2 of the liquid crystal polarization grating and the scanning angle α3 of the fast reflector (α1 = α2 + α3), where α1 is greater than the single scanning range α3 of the fast reflector, which needs to be achieved through the deflection coordination of the liquid crystal polarization grating module.

[0059] In this embodiment, the total field of view ±48° is divided into multiple sub-regions. The size of each sub-region corresponds to the maximum scanning range of the fast reflector 5, i.e., a square of 12° × 12°. The center point of each sub-region corresponds to a specific set of deflection states of the liquid crystal polarization grating module 6.

[0060] 3.2 Scanning Path Planning The integrated controller 14 plans a scanning path covering all target sub-regions. The preferred path is as follows: Figure 9The "snake-like" path shown.

[0061] Starting from the leftmost sub-region of the first row, control the fast reflector 5 to complete a grid scan from left to right and from top to bottom within this sub-region; then, switch the deflection state of the liquid crystal polarization grating module 6 only once to jump the beam to the adjacent sub-region on the right side of the first row, and control the fast reflector 5 to perform a reverse scan from right to left within this new sub-region; repeat this process.

[0062] This path planning allows the liquid crystal polarization grating module 6 to change the deflection state in only one dimension when switching between adjacent sub-regions. For example, the α2 of the left and right adjacent sub-regions differs by only 12° on the X-axis, reducing the number of switching times and the time consumed.

[0063] 3.3 Dynamic gaze Figure 10 The method of implementing the staring function is further illustrated: within the target angle range, a high-priority staring area and a regular non-staring area are divided. The staring area is finely scanned using a high-resolution β of a fast-reflecting mirror to obtain detailed information, while the non-staring area is scanned using N times the resolution (Nβ). By dynamically allocating scanning resources, the overall scanning speed is greatly improved while ensuring the detection accuracy of key areas.

[0064] Based on the regions of interest initially identified by the target detection algorithm, the integrated controller 14 marks certain sub-regions in the total field of view as "staring regions" (high priority) and others as "non-staring regions." During scanning, for sub-regions within the staring regions, the fast reflector 5 performs dense scanning at a high angular resolution of 0.1°; for sub-regions within the non-staring regions, it performs sparse scanning at a lower angular resolution of 1.0°. This dynamic resolution strategy ensures detail in critical areas while significantly improving the overall scanning frame rate.

[0065] 3.4 Timing Synchronization Because the response time of the liquid crystal polarization grating module 6, especially its relaxation time, is tens of milliseconds, much slower than the FMCW modulation period (in microseconds) and the stepping time of the fast reflector 5, the integrated controller 14 needs to perform precise timing control. During the angle switching process of the liquid crystal polarization grating module 6, a "dead time" matching the LCPG response time is set. During this period, the fast reflector scanning and signal acquisition are paused until the LCPG state stabilizes before resuming, in order to avoid generating invalid or erroneous beat frequency signals due to beam instability.

[0066] In summary, this invention, by combining the high-precision dynamic scanning capability of a fast reflector with the preset angle deflection characteristics of a liquid crystal polarizing grating, and by integrating a coaxial receiving architecture and a staring function optimization strategy, significantly improves the wide field-of-view coverage efficiency and system flexibility while ensuring ranging and velocity measurement accuracy.

[0067] Finally, it should be noted that 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A large field-of-view FMCW lidar system based on a liquid crystal polarization grating, comprising a laser emitting subsystem for generating a frequency-modulated continuous wave laser signal, a laser scanning subsystem for scanning the laser beam output by the laser emitting subsystem, a laser receiving subsystem for receiving the reflected echo light from the target, and a control subsystem for coordinating the scanning and receiving timing, characterized in that, The laser scanning subsystem includes at least a fast reflector and a multi-level liquid crystal polarization grating module. The fast reflector is configured to perform two-dimensional scanning within its maximum mechanical deflection angle range. The multi-level liquid crystal polarization grating module is composed of at least two cascaded scanning units. Each scanning unit includes an electric half-wave plate and a liquid crystal polarization grating, and is configured to apply a preset fixed angle deflection to the passing light beam. The control subsystem is configured to coordinate the switching of the continuous scanning of the fast reflector and the discrete deflection state of the multi-level liquid crystal polarization grating module, so that the target scanning angle α1 is formed by the superposition of the fixed deflection angle α2 of the liquid crystal polarization grating and the scanning angle α3 of the fast reflector, where α1 = α2 + α3.

2. The system according to claim 1, characterized in that, In the multi-level liquid crystal polarization grating module, the deflection angle of the first-level liquid crystal polarization grating is designed to match the scanning angle range of the fast reflector. The deflection angles of subsequent levels are designed to be cascaded and matched based on the deflection angles of the previous level. Through multi-level collaboration, the large field-of-view angle deflection of the laser beam is achieved.

3. The system according to claim 1, characterized in that, The laser emission subsystem includes at least a laser, an optical fiber beam splitter, and a polarization control module. The polarization control module consists of a linear polarizer and a quarter-wave plate, and is used to adjust the signal light split by the optical fiber beam splitter into circularly polarized light before it is incident on the laser scanning subsystem.

4. The system according to claim 1, characterized in that, The laser receiving subsystem adopts a coaxial receiving architecture based on a perforated mirror, including a perforated mirror, an optical lens, a balanced detector, and a data processing module. The perforated reflector is located at the intersection of the transmitting optical path and the receiving optical path. It has a through hole in the center for the transmitting beam to pass through, and its reflective surface is used to reflect the target echo signal light to the receiving optical path. The laser scanning subsystem also includes a quarter-wave plate disposed on the output optical path of the multi-level liquid crystal polarization grating module, which is used to ensure that the target echo signal light meets its polarization selection characteristics when it passes through the liquid crystal polarization grating again, so that it returns along the original emission optical path and is guided into the laser receiving subsystem by the perforated mirror.

5. A scanning control method for a large field-of-view FMCW lidar system based on a liquid crystal polarization grating as described in any one of claims 1-4, characterized in that, The scanning control method uses a liquid crystal polarizing grating to determine the sub-region orientation and a fast-reflecting mirror to complete continuous scanning within the sub-region. The method steps include: (1) Divide the target large field of view into multiple sub-regions, each sub-region corresponding to a deflection state of the multi-level liquid crystal polarization grating module; (2) For each sub-region: a. Control the multi-level liquid crystal polarization grating module to switch to the corresponding deflection state; b. Control the fast reflector to perform two-dimensional scanning in the corresponding sub-region; c. During the scanning of the fast reflector, receive and process the target echo signal to obtain target information; The scanning of the fast reflector is coordinated with the switching of the liquid crystal polarization grating module, thereby optimizing the overall scanning path.

6. The method according to claim 5, characterized in that, The fast reflector and the liquid crystal polarizing grating module are controlled to perform a serpentine scanning path. After completing the scanning of a sub-region, the liquid crystal polarizing grating module is switched only once to enter the adjacent sub-region, and the fast reflector is controlled to scan in the opposite direction within the adjacent sub-region.

7. The method according to claim 5, characterized in that, The method further includes a dynamic gaze step: dividing the plurality of sub-regions into gaze regions and non-gaze regions; controlling the fast reflector to scan in the gaze regions using a first angular resolution, and in the non-gaze regions using a second angular resolution lower than the first angular resolution.

8. The method according to claim 7, characterized in that, The method further includes a timing synchronization step: during the process of controlling the switching of the deflection state of the multi-level liquid crystal polarization grating module, the control subsystem controls the fast reflector to pause scanning and controls the laser receiving subsystem to pause signal acquisition until the switching of the liquid crystal polarization grating module is completed.

9. The method according to claim 5, characterized in that, The deflection angle range of the liquid crystal polarizing grating and the scanning angle range of the fast reflector are configured according to a preset ratio or matching relationship, so that the scanning angles of the two are superimposed to form an overall scanning field of view that is larger than the scanning range of any single scanning device.

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