Large field of view scanning method of laser radar based on liquid crystal phased array

Abstract

The present invention discloses a large-field-of-view scanning method for a laser radar based on a liquid crystal phased array, comprising the following steps: expanding and deflecting a laser light source according to the aperture size of the liquid crystal phased array to obtain a target beam; phase-modulating the target beam using the liquid crystal phased array to achieve beam deflection, continuously changing the applied phase modulation to achieve annular scanning of the beam; reflecting the annular scanning beam using a conical reflector to achieve spatial transformation, thereby converting the circular scan into an arcuate scan and obtaining a preliminary large-field-of-view arcuate scan; reasonably setting the parameters of the conical reflector and the distance between the conical reflector and the liquid crystal phased array to filter out stray light such as grating lobes outside the scanning beam, thereby obtaining a final large-field-of-view arcuate scan. The present invention improves the scanning field of view of a phased array laser radar, filters out stray light such as grating lobes outside the scanning beam, and obtains high-quality large-field-of-view arcuate scans.

Description

Technical Field

[0001] The present invention relates to the field of light beam deflection and scanning, and in particular to a large field of view scanning method of a laser radar based on a liquid crystal phased array. Background Art

[0002] The core of the LiDAR scanning method is to achieve a scanning effect by continuously deflecting the light beam through a specific optomechanical structure, thereby realizing three-dimensional laser imaging. Currently, this technology has been widely applied in a variety of applications, such as autonomous driving, topographic mapping, atmospheric sounding, VR / AR, and other popular fields. LiDAR can be divided into three categories based on the scanning method: mechanical, hybrid solid-state, and pure solid-state. Mechanical LiDARs use a rotary motor for 360° horizontal rotation. For the vertical direction, additional laser transceiver modules are required to scan different vertical fields of view. Currently, mechanical LiDARs have 8, 16, 32, and 40 lines, where "line" refers to the number of laser transceiver modules. Consequently, they suffer from large size, low reliability, high cost, and extremely difficult assembly. Hybrid solid-state LiDARs use scanning modules such as MEMS galvanometers, rotating mirrors, and rotating biprisms to replace the traditional mechanical one-dimensional rotation. These achieve two-dimensional beam scanning while the laser transceiver module is fixed, thereby improving system reliability and integration. However, these systems suffer from a reduced field of view and the wear and tear of mechanical moving components. Purely solid-state phased array technology, by modulating the phase of the optical beam, enables flexible, fast, and precise non-mechanical beam directional scanning, and is a promising future development direction. Silicon-based optical waveguide phased arrays, currently a hot topic of research, offer the advantage of on-chip integration, but this results in a reduced array dimension, resulting in a one-dimensional array. Therefore, to achieve two-dimensional beam deflection and scanning, wavelength tuning in another orthogonal dimension is required, significantly increasing system cost and complexity. Leveraging mature liquid crystal processing, liquid crystal phased arrays can achieve large-area two-dimensional arrays, enabling flexible two-dimensional beam deflection and scanning at a single wavelength, such as bow scanning, circular scanning, and hopping scanning. However, like optical waveguide phased arrays, the intercoherent element spacing in liquid crystal phased arrays is still larger than the wavelength, severely limiting the maximum beam deflection angle and resulting in a limited scanning field of view. This also generates a series of grating lobes, which interfere with mainlobe detection and echo reception. Consequently, phased array lidars face challenges such as a small scanning field of view and the presence of grating lobes that affect echo detection and recognition at the receiver. Summary of the Invention

[0003] The purpose of the present invention is to provide a large field of view scanning method of a laser radar based on a liquid crystal phased array, so as to solve the problems existing in the above-mentioned prior art, improve the scanning field of view of the phased array laser radar, and remove the interference of grating lobes on echo detection and identification.

[0004] To achieve the above objectives, the present invention provides the following solution: The present invention provides a large field of view scanning method of a laser radar based on a liquid crystal phased array, comprising the following steps:

[0005] The laser light source is expanded and aligned according to the aperture size of the liquid crystal phased array to obtain the target beam;

[0006] Continuously applying target adjacent phase differences to the liquid crystal phased array to obtain an annular scanning beam;

[0007] Reflecting the annular scanning beam to obtain a preliminary large-field-of-view arcuate scanning beam;

[0008] The grating lobes outside the preliminary large-field-of-view bow scanning beam are filtered out to obtain the final large-field-of-view bow scanning result.

[0009] Optionally, the target light beam covers the aperture of the liquid crystal phased array and has the same polarization direction.

[0010] Optionally, continuously applying the target adjacent phase differences to the liquid crystal phased array to obtain the annular scanning beam includes:

[0011] Corresponding adjacent phase differences are applied in two orthogonal dimensions of the liquid crystal phased array to form a two-dimensional deflection of the target light beam, and the adjacent phase differences applied in the two dimensions are continuously changed to perform annular scanning of the light beam.

[0012] Optionally, a conical reflector is used in the process of reflecting the annular scanning light beam.

[0013] Optionally, reflecting the annular scanning beam to obtain the preliminary large-field-of-view arcuate scanning beam includes:

[0014] The annular scanning light beam is reflected by the conical reflector, and the beam rotation angle in the annular scanning is converted into a horizontal deflection angle, and the beam deflection angle in the annular scanning is converted into a vertical deflection angle, so as to realize the conversion from annular scanning to bow scanning to obtain the preliminary large-field-of-view bow scanning light beam.

[0015] Optionally, when unfolded along the optical axis, the cone tip of the conical reflector is aligned with the aperture center of the liquid crystal phased array, and the cone bottom of the conical reflector is parallel to the surface of the liquid crystal phased array.

[0016] Optionally, the distance between the conical reflector and the liquid crystal phased array is set to an intrinsic distance.

[0017] Optionally, the intrinsic distance is:

[0018] L=R / tanθ max

[0019] Where L is the intrinsic distance, R is the radius of the cone bottom of the conical reflector, θ max is the maximum value of the deflection angle of the circular scanning beam.

[0020] The present invention discloses the following technical effects:

[0021] The invention discloses a method for scanning a large field of view of a laser radar based on a liquid crystal phased array. The method converts the annular scanning realized by the liquid crystal phased array into an arcuate scanning by using a conical reflector, so that the scanning field of view is reduced from the original device process parameters and the wavelength of light to the θ max ×θ max Transformed to 360°×θ max The large field of view greatly improves the scanning field of view; by reasonably setting the parameters of the conical reflector and the distance from the liquid crystal phased array, the grating removal effect can be achieved without changing the process structure of the liquid crystal phased array or increasing the complexity of the beam control model, thereby obtaining high-quality large-field bow scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of a flow chart of a large field of view scanning method of a laser radar based on a liquid crystal phased array in an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of annular scanning in an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of spatial transformation after reflection by a conical reflector in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The present invention provides a large field of view scanning method of laser radar based on liquid crystal phased array, such as Figure 1 As shown, the following steps are included:

[0029] The laser light source used in this example has a wavelength of 1064 nm, a beam diameter of 500 μm, and a vertical polarization direction of the linear polarization. The spatial light modulator used in this embodiment by Meadowlark Optics is used as a liquid crystal phased array, with a pixel count of 1920 × 1200, a pixel pitch of d = 8 μm × 8 μm, an aperture size of 15.36 mm × 9.6 mm, and the required polarization direction of the incident linear polarization is horizontal.

[0030] S1: Expand the laser light source and align it according to the aperture size of the liquid crystal phased array; ensure that the light beam covers the entire aperture, and play the role of phase modulation of the light beam by the liquid crystal phased array.

[0031] The half-wave plate used in this example has its fast axis at a 45° angle to the polarization direction of the linearly polarized light emitted by the laser. This alters the polarization direction of the incident linearly polarized light so that it aligns horizontally with the polarization direction required by the liquid crystal phased array. An inverted telescope system is then used to expand and collimate the beam, with an expansion ratio of approximately 30. The expanded beam covers the entire aperture of the liquid crystal phased array.

[0032] S2: applying corresponding phase modulation to the liquid crystal phased array according to the desired beam scanning result; continuously changing the applied phase modulation to achieve circular scanning.

[0033] The liquid crystal spatial light modulator (LCSLM), the primary component of the LC phased array, controls the wavefront phase of the beam. This control is achieved by loading a kinoform pattern onto the target surface via the HDMI interface. The 8-bit kinoform pattern provides the phase modulation level for each pixel on the SLM target surface.

[0034] For a two-dimensional liquid crystal phased array, corresponding adjacent phase differences are applied in two orthogonal dimensions to form a two-dimensional deflection of the light beam. By continuously changing the applied phase modulation, annular scanning of the light beam is achieved. The annular scanning model is shown in Equation 1:

[0035]

[0036] Thus forming Figure 2 The circular scan shown. and are the adjacent phase differences in the two orthogonal dimensions X and Y, θ x0 and θ y0 are the deflection angles of the light beam in the X and Y dimensions respectively; in a two-dimensional liquid crystal phased array, d x =d y =d, d is the pixel spacing; k is the wave number, is the two-dimensional adjacent phase difference, θ0 is the two-dimensional deflection angle of the light beam, that is, the deflection angle of the circular scanning of the light beam; φ is the rotation angle of the circular scanning of the light beam.

[0037] S3: The circular scan obtained in S2 is reflected by a conical reflector to achieve spatial transformation; the beam rotation angle in the circular scan is converted into a horizontal deflection angle, and the beam deflection angle in the circular scan is converted into a vertical deflection angle; the circular scan is converted into an arcuate scan, and the maximum scanning field of view is increased from the theoretical θ max ×θ max Transformed to 360°×θ max .

[0038] like Figure 3 As shown, the model of spatial transformation is as follows:

[0039] The deflected light beam located in the XOZ plane (i.e., φ = 0) is reflected by the conical reflector and then emitted. The emitted light beam is located in the X'O'Z plane. The angle φ' between the projection of the emitted light beam on the X'O'Y' plane and the X' axis is easy to know. φ' = φ. The angle between the emitted light beam and the X'O'Y' plane is θ'. when When θ′=θ0, where α is the cone angle. Thus, the rotation angle φ of the annular scan is converted into the horizontal deflection angle φ' in the new spatial coordinate system, and the deflection angle θ0 of the annular scan is converted into the vertical deflection angle θ′. The transformation from annular scanning to bow scanning is achieved, and the scanning field of view is changed from the theoretical θ max ×θ max Transformed to 360°×θ max .

[0040] In this example, If the wavelength is 1550nm, θ max =5.559°, based on the wavelength of 1550nm, if a device with a smaller pixel pitch is used, for example, d = 3μm, then θ max =14.971°.

[0041] S4: Reasonably set the conical reflector parameters and the distance between them to filter out stray light such as grating lobes outside the scanning beam, and finally obtain high-quality large-field bow scanning.

[0042] Expanded along the optical axis, the cone tip of the conical reflector is aligned with the center of the liquid crystal phased array, and the cone base is parallel to the surface of the liquid crystal phased array. The cone base size R of the selected conical reflector in this example is 10mm; the distance between the two is the intrinsic distance L, L = R / tanθ max≈150mm. Under this setting, the deflected beam within the deflection range, or the main lobe, is reflected by the conical reflector, achieving spatial transformation, while all grating lobes are filtered out. Ultimately, at the transmitting scanning end, only the scanning beam, or the main lobe, is emitted, effectively filtering out the grating lobes and achieving high-quality, large-field-of-view arcuate scanning.

[0043] The present invention relates to a liquid crystal phased array-based laser radar large-field-of-view scanning method. This method primarily utilizes the liquid crystal phased array's two-dimensional beam deflection capability to achieve circular scanning by continuously varying the applied phase modulation. This light is then reflected by a conical reflector, achieving spatial transformation to complete the transition from circular scanning to large-field-of-view bow scanning, thereby expanding the field of view. Reasonable settings for the conical reflector parameters and its distance from the liquid crystal phased array enable filtering of grating lobes. Compared to traditional optical phased array methods, this method achieves a larger scanning field of view while eliminating the interference of grating lobes on echo detection and identification, ultimately resulting in high-quality, large-field-of-view bow scanning.

[0044] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. However, such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. They should all be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A large field of view scanning method for laser radar based on liquid crystal phased array, characterized in that: The following steps are involved: The laser light source is expanded and aligned according to the aperture size of the liquid crystal phased array to obtain the target beam; Continuously applying target adjacent phase differences to the liquid crystal phased array to obtain an annular scanning beam; Reflecting the annular scanning beam to obtain a preliminary large-field-of-view arcuate scanning beam, wherein a conical reflector is used in the process of reflecting the annular scanning beam; In order to filter out the grating lobes outside the preliminary large-field-of-view arcuate scanning beam and obtain the final large-field-of-view arcuate scanning result, the distance between the bottom surface of the conical reflector and the liquid crystal phased array is set to the intrinsic distance, where the intrinsic distance is: L=R / tanθ max Where L is the intrinsic distance, R is the radius of the cone bottom of the conical reflector, θ max is the maximum value of the deflection angle of the circular scanning beam.

2. The liquid crystal phased array-based laser radar large field of view scanning method according to claim 1, characterized in that: The target light beam covers the aperture of the liquid crystal phased array and has the same polarization direction.

3. The liquid crystal phased array-based laser radar large field of view scanning method according to claim 1, characterized in that: Continuously applying the target adjacent phase differences to the liquid crystal phased array to obtain an annular scanning beam includes: Corresponding adjacent phase differences are applied in two orthogonal dimensions of the liquid crystal phased array to form a two-dimensional deflection of the target light beam, and the adjacent phase differences applied in the two dimensions are continuously changed to perform annular scanning of the light beam.

4. The liquid crystal phased array-based laser radar large field of view scanning method according to claim 1, characterized in that: Reflecting the annular scanning beam to obtain the preliminary large-field-of-view bow-shaped scanning beam includes: reflecting the annular scanning beam using the conical reflector, converting the beam rotation angle in the annular scanning into a horizontal deflection angle, and converting the beam deflection angle in the annular scanning into a vertical deflection angle, thereby realizing the conversion from annular scanning to bow-shaped scanning to obtain the preliminary large-field-of-view bow-shaped scanning beam.

5. The liquid crystal phased array-based laser radar large field of view scanning method according to claim 1, characterized in that: Expanded along the optical axis, the cone tip of the conical reflector is aligned with the aperture center of the liquid crystal phased array, and the cone bottom of the conical reflector is parallel to the surface of the liquid crystal phased array.

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