Coaxial optical system for full solid state lidar transceiver based on polarization multiplexing

Abstract

The utility model relates to a kind of full solid-state laser radar transmitting and receiving coaxial optical systems based on polarization multiplexing, comprising: transmitting structure, polarization modulation structure, optical lens assembly and receiver;The light beam emitted by the transmitting structure is reflected by the reflecting surface of polarization modulation structure, forms first reflected light, first reflected light is irradiated on target object by optical lens assembly, target object forms second reflected light for detecting target object based on the laser illumination, the second reflected light and the first reflected light are sequentially passed through optical lens assembly, and pass through the transmission surface of polarization modulation structure, and are received by receiver;The utility model solves the technical problem that the laser radar of non-coaxial optical system exists shading effect, assembly and calibration cost are high, are easily influenced by mechanical vibration or temperature deformation, long-term stability is insufficient, system volume is large, integration is low, difficult to meet the needs of miniaturization of automatic driving, robot navigation, surveying and mapping and security scene.

Description

Technical Field

[0001] This utility model relates to the field of lidar optical technology, and in particular to an all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing. Background Technology

[0002] LiDAR (Light Detection and Ranging) is an active remote sensing technology that measures the distance, velocity, or three-dimensional shape of a target by emitting a laser beam and detecting its reflection signal. LiDAR emits pulsed or continuous laser beams towards the target. The laser beam is reflected upon encountering the target and received by the LiDAR's sensors. The LiDAR calculates the time difference between emission and reception, the time of flight, and combines this with the speed of light to calculate the distance. Multiple sets of distance data are combined with the scanning angle to construct a three-dimensional model. As a high-precision three-dimensional environmental perception technology, LiDAR is widely used in fields such as autonomous driving, robot navigation, surveying and mapping, and security.

[0003] Traditional lidar faces technical problems such as ambient light interference, specular reflection misjudgment, and low optical path efficiency.

[0004] 1. Ambient light interference: The irradiance of sunlight in the near-infrared band (such as the wavelength commonly used in 905nm lidar) is as high as 500W / m2, which forms strong background noise with the lidar echo signal (usually at the milliwatt level). The lidar detector will introduce a large amount of random noise (such as thermal noise and shot noise) under strong ambient light, which will cause the effective signal to be submerged and the signal-to-noise ratio to drop by more than 20dB.

[0005] 2. Specular reflection misjudgment: Smooth surfaces (car windows or water accumulation) reflect the laser beam, causing the beam to deviate from its original path or form multiple reflections, resulting in pseudo-range measurement. The actual path is different from the expected one, resulting in a ranging error of more than ±10m.

[0006] 3. Low optical path efficiency: LiDAR systems with coaxial optical systems typically use beam splitters to split the incident light into two beams, one transmitted and one reflected, resulting in a loss of ≥50% of optical energy. LiDAR systems with co-aperture optical systems require additional filters to suppress light leakage at the transmitting end, further reducing the optical path efficiency (total efficiency may be <30%).

[0007] To address the aforementioned technical challenges, current lidar systems primarily employ mechanical scanning or MEMS (Micro-Electro-Mechanical Systems) micro-mirror solutions. However, these solutions suffer from low reliability, large size, and high cost. Lidar systems using non-coaxial optical systems employ separate transmit and receive optical structures, separating the emission and reception optical paths, with the emission and reception axes parallel to each other. This approach also presents issues such as light-blocking effects and difficulties in field-of-view calibration.

[0008] Therefore, it is desirable to have a polarization-multiplexed all-solid-state lidar transceiver coaxial optical system that can solve the problems existing in the current technology. Utility Model Content

[0009] (a) Technical problems to be solved

[0010] In view of the above-mentioned shortcomings and deficiencies of the prior art, this utility model provides a coaxial optical system for transmitting and receiving all-solid-state lidar based on polarization multiplexing. It solves the technical problems of lidar in non-coaxial optical systems, such as light-shielding effect, high assembly and calibration costs, susceptibility to mechanical vibration or temperature deformation, insufficient long-term stability, large system size, low integration, and difficulty in meeting the miniaturization requirements of autonomous driving, robot navigation, surveying and mapping, and security scenarios.

[0011] (II) Technical Solution

[0012] To achieve the above objectives, this utility model employs a polarization-multiplexed all-solid-state lidar transceiver coaxial optical system, comprising: a transmitting structure, a polarization modulation structure, an optical lens assembly, and a receiver; the beam emitted by the transmitting structure is reflected by the reflective surface of the polarization modulation structure to form a first reflected light, which is then irradiated onto a target object by the optical lens assembly; the target object generates a second reflected light based on the irradiated laser for detecting the target object; the second reflected light and the first reflected light coaxially pass through the optical lens assembly and the transmission surface of the polarization modulation structure in sequence, and are received by the receiver;

[0013] The polarization modulation structure includes two right-angled triangular polarization beam splitters, and the inclined surfaces of the two right-angled triangular polarization beam splitters are attached to form a cube-shaped polarization modulation structure.

[0014] Each polarization beam splitter has a semi-transparent and semi-reflective coating on its inclined surface. The semi-transparent and semi-reflective coating serves as a reflective surface to form the first reflected light and as a transmitting surface to transmit the second reflected light.

[0015] This invention employs a polarization multiplexing coaxial architecture to achieve single-lens transmission and reception along the same optical path, thereby eliminating the light-blocking effect and enabling lossless switching between emission reflection and reception transmission.

[0016] Preferably, the emission structure includes a polarizing light source and a collimating lens, wherein the beam emitted from the polarizing light source is collimated into a parallel beam by the collimating lens.

[0017] Preferably, the polarization light source is a VCSEL-based polarization light source or an EEL-based polarization light source.

[0018] Preferably, the emitting structure further includes a polarizer, and the parallel light beam passing through the collimating lens is incident on the polarizer to output polarized light.

[0019] Preferably, the polarizer is a high-power linear grid polarizer, and the parallel beam incident on the high-power linear grid polarizer outputs high-purity linearly polarized light.

[0020] Preferably, the polarization modulation structure further includes a dual-channel quarter-wave plate group formed by two quarter-wave plates closely fitted together. The high-purity linearly polarized light is incident on the polarization beam splitter. The high-purity linearly polarized light reflected by the polarization beam splitter is converted into circularly polarized light after being phase-delayed by λ / 4 of the dual-channel quarter-wave plate group. The circularly polarized light is the first reflected light. The circularly polarized light is incident on the optical lens assembly. The optical lens assembly calibrates the circularly polarized light into a parallel beam suitable for long-distance propagation and directs it toward the target object. After the beam hits the target surface, it is reflected to form reflected circularly polarized light, i.e., the second reflected light. The reflected circularly polarized light is incident in the opposite direction on the optical lens assembly. The optical lens assembly converges the diverging reflected light into a parallel beam. The reflected circularly polarized light after passing through the optical lens assembly is again phase-delayed by λ / 4 of the dual-channel quarter-wave plate group, and the reflected circularly polarized light is converted into orthogonal linearly polarized light. The orthogonal linearly polarized light is incident on the polarization beam splitter. The orthogonal linearly polarized light transmitted through the polarization beam splitter is focused onto the receiver.

[0021] Preferably, the polarization modulation structure is a cubic structure with a size of 5mm*5mm, and the four right-angled surfaces of the polarization beam splitter are respectively provided with anti-reflection coatings.

[0022] Preferably, an ultra-narrow band filter is provided on the right-angle surface from which the orthogonally linearly polarized light exits from the polarization beam splitter line.

[0023] Preferably, the receiving unit is a single-photon avalanche diode array detector with an integrated nanowire grid polarizer.

[0024] Preferably, the transmitting structure is spatially matched to the receiver.

[0025] (III) Beneficial Effects

[0026] The advantages of this novel all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing include:

[0027] 1. This application adopts a polarization multiplexing coaxial architecture: single-lens transmission and reception along the same optical path are achieved through polarization state conversion, thereby eliminating the light-blocking effect;

[0028] 2. This application utilizes a polarization beam splitter and a dual-channel quarter-wave plate group to achieve lossless switching between transmission reflection and reception transmission;

[0029] 3. The spatial positions of the transmitting unit and the receiving unit in this application are matched to achieve all-solid-state electronic scanning. Attached Figure Description

[0030] Figure 1 A schematic diagram of a coaxial optical system for transmitting and receiving an all-solid-state lidar based on polarization multiplexing, provided in an embodiment of this utility model;

[0031] Figure 2 for Figure 1 Schematic diagram of the optical path of the optical system. Detailed Implementation

[0032] To better explain and facilitate understanding of this utility model, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] PBS: Polarizing Beam Splitter, used to split incident light into two linearly polarized beams with orthogonal polarization directions;

[0034] ROI: Region of Interest, which is the target region.

[0035] SPAD: Single-photon avalanche diode;

[0036] DOP: Degree of Polarization;

[0037] AOP: Angle of Polarization;

[0038] VCSEL: Vertical-cavity surface-emitting laser with a small divergence angle and a wavelength of 650-670nm;

[0039] EEL: Side-emitting laser with a large divergence angle and a wavelength of 630-670nm.

[0040] AR coating: Anti-reflective coating, used to reduce reflectivity and increase transmittance.

[0041] This utility model relates to a polarization-multiplexed all-solid-state lidar transceiver coaxial optical system, comprising: a transmitting structure, a polarization modulation structure, an optical lens assembly, and a receiver; the beam emitted by the transmitting structure is reflected by the reflective surface of the polarization modulation structure to form a first reflected light, which is then irradiated onto a target object by the optical lens assembly. The target object generates a second reflected light based on the irradiated laser, which is used for detection. The second reflected light and the first reflected light coaxially pass through the optical lens assembly and the transmission surface of the polarization modulation structure, and are received by the receiver; the polarization modulation structure includes two right-angled triangular polarization beam splitters, the inclined surfaces of which are joined to form a cubic polarization modulation structure; each inclined surface of the polarization beam splitter is provided with a semi-transparent and semi-reflective coating, which serves as a reflective surface to form the first reflected light and as a transmission surface to transmit the second reflected light.

[0042] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0043] Example 1

[0044] like Figure 1 As shown, the all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing in this embodiment includes: a transmitting structure, a polarization beam splitter, a dual-channel 1 / 4 waveplate group, an optical lens, and a SPAD array detector. The polarization beam splitter has a transmittance of >95%, which improves the light utilization rate by more than 1 times compared to the coaxial optical system using a beam splitter prism. The coaxial design in this embodiment reduces the size of the optical module by 40%, and the ROI scanning frequency of the transmitting structure can reach 10MHz, far exceeding the limit of mechanical scanning.

[0045] Polarized light is incident on a polarization beamsplitter. The polarized light reflected by the polarization beamsplitter is converted into circularly polarized light after being phase-delayed by a dual-channel 1 / 4 waveplate group (λ / 4). The circularly polarized light is then incident on an optical lens, which calibrates the circularly polarized light into a parallel beam suitable for long-distance propagation and directs it toward the target object. After the beam hits the target surface, it is reflected to form reflected circularly polarized light, carrying information such as the target's distance and outline. The reflected circularly polarized light is then incident back onto the optical lens, which converges the diverging reflected light into a parallel beam. The reflected circularly polarized light passing through the optical lens is again phase-delayed by a dual-channel 1 / 4 waveplate group (λ / 4), converting it into orthogonally linearly polarized light. The orthogonally linearly polarized light is then incident on a polarization beamsplitter, which focuses the projected orthogonally linearly polarized light onto a SPAD array detector. The orthogonal polarization design effectively suppresses ambient stray light.

[0046] The four right-angled surfaces of the polarization beam splitter are each coated with an anti-reflection coating, and the right-angled surfaces from which the linearly orthogonally polarized light exits are fitted with ultra-narrow band filters.

[0047] The transmitter structure ROI illumination control polarization light source switch, receiver SPAD array detector, and transmitter structure and receiver spatial position distribution are matched to achieve all-solid-state electronic scanning.

[0048] The advantages of anti-interference performance include: ambient light suppression ratio >45dB (22dB improvement over traditional solutions), and specular reflection false detection rate <1% compared to the average >30% of traditional solutions.

[0049] The polarization multiplexing architecture reduces optical components by 50% and mass production costs by 37%.

[0050] The detection accuracy is improved compared to traditional methods. In this embodiment, the ranging error range at a distance of 100 meters is ±1.5cm, while the ranging error range of the traditional method at a distance of 100 meters is ±5cm. The minimum angular interval between two adjacent targets can be distinguished by this embodiment of 0.05°, while it is 0.1° in the traditional method. In the point cloud data output by this embodiment, the proportion of effective measurement points to total emitted laser points is 98.7%, while it is 76.3% in the traditional method.

[0051] Example 2:

[0052] like Figure 2As shown, polarized light is incident on a polarization beamsplitter. The polarized light reflected by the polarization beamsplitter is converted into circularly polarized light after being phase-delayed by a dual-channel 1 / 4 waveplate group (λ / 4). The circularly polarized light is then incident on an optical lens, which calibrates the circularly polarized light into a parallel beam suitable for long-distance propagation and directs it toward the target object. After the beam hits the target surface, it is reflected to form reflected circularly polarized light, carrying information such as the target's distance and outline. The reflected circularly polarized light is then incident back onto the optical lens, which converges the diverging reflected light into a parallel beam. The reflected circularly polarized light, after passing through the optical lens, is again phase-delayed by a dual-channel 1 / 4 waveplate group (λ / 4), converting it into orthogonally linearly polarized light. The orthogonally linearly polarized light is then incident on a polarization beamsplitter, which focuses the projected orthogonally linearly polarized light onto a SPAD array detector.

[0053] The optical path, polarization state changes, and the functions of optical elements are shown in the table below:

[0054]

[0055] Example 3:

[0056] The transmitting structure has a peak power of 50W, a pulse width of 5ns, a polarization ratio of 100:1, and the lens is focused on the target area (ROI diameter ≤ 0.1°). The transmitting structure uses a VCSEL-based polarization source or an EEL-based polarization source, and the polarizer is a high-power linear grid polarizer to output high-purity linearly polarized light, thereby improving the polarization purity of the transmitted signal. The transmitting structure outputs S-polarized light (electric field vector parallel to the PBS reflector), which is reflected by the PBS and then passes through a 1 / 4 wave plate, forming right-hand circularly polarized light (ER = 0.98).

[0057] The ultra-narrowband filter has a bandwidth of 0.5nm, a center wavelength of 905nm, a transmittance of >90%, and an ambient light suppression of >30dB.

[0058] The dual-channel quarter-wave plate group uses quartz quarter-wave plates with a delay accuracy of λ / 500 and a temperature drift of <0.01° / ℃, ensuring polarization conversion stability. The reflected light processing stage includes diffuse reflection targets and specular reflection targets. The reflected light from diffuse reflection targets is depolarized and converted into non-uniform P-polarized light by the quarter-wave plate. For specular reflection targets, the circular polarization characteristics are maintained and the light is converted into ideal P-polarized light by the quarter-wave plate.

[0059] The polarization SPAD array detector has 762×576 pixels and integrates a nanowire grid polarizer to simultaneously acquire four-dimensional data of I light intensity, DoP polarization degree, AoP polarization angle, and ε ellipticity.

[0060] Example 4:

[0061] The detection of vehicle windshields and smog environments used the all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing in this application and a traditional scheme, respectively. The test conditions were: ambient light illuminance: 100klux (simulating midday sunlight), and interfering targets: windshield (specular reflection) and dense fog (Mie scattering).

[0062] The application's emission structure has a laser peak power of 30W, a pulse width of 905nm, a ROI scanning density of 256 independently controlled zones, and a receiver polarization camera frame rate of 100fps.

[0063] Comparison of effects:

[0064]

[0065] Example 5:

[0066] The polarization light source uses an 8×8 VCSEL array (wavelength 905nm) with an integrated polarizer to output S-polarized light. The PBS cube beam splitter is 5mm×5mm in size, with a zero-order quartz quarter-wave plate, a delay accuracy of λ / 300, and a SPAD array. The pixel size corresponds to the VCSEL light-emitting area in a 1:1 ratio.

[0067] The VCSEL emitted pulse is reflected by the PBS and converted into right-hand circularly polarized light by a λ / 4 waveplate. The light is then projected onto a target 50m away through an f / 2.0 lens. The reflected light is converted into P-polarized light again by a λ / 4 waveplate. The PBS has a transmittance of over 98% and is directly imaged onto the SPAD array.

[0068] In the description of this utility model, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0069] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0070] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "beneath" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0071] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A coaxial optical system for transmitting and receiving all-solid-state lidar based on polarization multiplexing, characterized in that, include: The system comprises a transmitting structure, a polarization modulation structure, an optical lens assembly, and a receiver. The light beam emitted by the transmitting structure is reflected by the reflective surface of the polarization modulation structure to form a first reflected light. The first reflected light is irradiated onto a target object by the optical lens assembly. The target object forms a second reflected light based on the irradiated laser to detect the target object. The second reflected light and the first reflected light are coaxially connected and sequentially pass through the optical lens assembly and the transmission surface of the polarization modulation structure, and are received by the receiver. The polarization modulation structure includes two right-angled triangular polarization beam splitters, and the inclined surfaces of the two right-angled triangular polarization beam splitters are attached to form a cube-shaped polarization modulation structure. Each polarization beam splitter has a semi-transparent and semi-reflective coating on its inclined surface. The semi-transparent and semi-reflective coating serves as a reflective surface to form the first reflected light and as a transmitting surface to transmit the second reflected light.

2. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 1, characterized in that: The emission structure includes a polarizing light source and a collimating lens. The beam emitted from the polarizing light source is collimated into a parallel beam by the collimating lens.

3. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 2, characterized in that: The polarization light source is a VCSEL-based polarization light source or an EEL-based polarization light source.

4. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 3, characterized in that: The emitting structure also includes a polarizer. The parallel light beam that passes through the collimating lens is incident on the polarizer and outputs polarized light.

5. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 4, characterized in that: The polarizer is a high-power linear grid polarizer. When the parallel beam is incident on the high-power linear grid polarizer, it outputs high-purity linearly polarized light.

6. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 5, characterized in that: The polarization modulation structure also includes a dual-channel quarter-wave plate group formed by two quarter-wave plates closely fitted together. The high-purity linearly polarized light is incident on the polarization beam splitter. The high-purity linearly polarized light reflected by the polarization beam splitter is converted into circularly polarized light after being phase-delayed by λ / 4 of the dual-channel quarter-wave plate group. The circularly polarized light is the first reflected light. The circularly polarized light is incident on the optical lens assembly. The optical lens assembly calibrates the circularly polarized light into a parallel beam suitable for long-distance propagation and directs it toward the target object. After the beam hits the target surface, it is reflected to form reflected circularly polarized light, i.e., the second reflected light. The reflected circularly polarized light is incident in the opposite direction on the optical lens assembly. The optical lens assembly converges the diverging reflected light into a parallel beam. The reflected circularly polarized light after passing through the optical lens assembly is again phase-delayed by λ / 4 of the dual-channel quarter-wave plate group, and the reflected circularly polarized light is converted into orthogonal linearly polarized light. The orthogonal linearly polarized light is incident on the polarization beam splitter. The orthogonal linearly polarized light transmitted through the polarization beam splitter is focused onto the receiver.

7. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 6, characterized in that: The polarization modulation structure is a cubic structure with a size of 5mm*5mm, and the four right-angled surfaces of the polarization beam splitter are respectively coated with anti-reflection coatings.

8. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 7, characterized in that: An ultra-narrow band filter is set on the right-angle surface from which the orthogonally linearly polarized light from the polarization beam splitter line is emitted.

9. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 1, characterized in that: The receiver is a single-photon avalanche diode array detector with an integrated nanowire grid polarizer.

10. The all-solid-state lidar transceiver coaxial optical system based on polarization multiplexing according to claim 9, characterized in that: The transmitting structure is matched to the spatial distribution of the receiver.

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