CN115220015A - Liquid crystal phased array-based laser radar large-field-of-view scanning method - Google Patents
Liquid crystal phased array-based laser radar large-field-of-view scanning method Download PDFInfo
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- CN115220015A CN115220015A CN202210936732.6A CN202210936732A CN115220015A CN 115220015 A CN115220015 A CN 115220015A CN 202210936732 A CN202210936732 A CN 202210936732A CN 115220015 A CN115220015 A CN 115220015A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
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Abstract
The invention discloses a liquid crystal phased array-based laser radar large-field scanning method, which comprises the following steps of: expanding the beam of the laser light source and polarizing and aligning the beam according to the aperture size of the liquid crystal phased array to obtain a target light beam; performing phase modulation on the target light beam by using a liquid crystal phased array based on the target light beam to realize light beam deflection, and continuously changing the applied phase modulation to realize annular scanning of the light beam; reflecting the annular scanning light beam by using a conical reflector to realize space transformation, and realizing conversion from annular scanning to bow-shaped scanning to obtain primary large-field bow-shaped scanning; the parameters of the conical reflector and the distance between the conical reflector and the liquid crystal phased array are reasonably set, stray light such as grating lobes outside scanning beams is filtered, and final large-field-of-view bow-shaped scanning is obtained. The invention improves the scanning field of view of the phased array laser radar, filters stray light such as grating lobes except scanning beams and the like, and obtains high-quality large-field-of-view bow-shaped scanning.
Description
Technical Field
The invention relates to the field of light beam deflection and scanning, in particular to a liquid crystal phased array-based laser radar large-field-of-view scanning method.
Background
The laser radar scanning method has the core that the scanning effect is achieved by realizing the continuous deflection of light beams through a specific optical machine structure, so that the laser three-dimensional imaging is realized. Currently, this technology has been widely used in a variety of applications, such as: many popular fields such as autopilot, topographic mapping, atmospheric sounding, VR/AR, etc. The laser radar can be divided into three types, namely a mechanical type, a mixed solid state and a pure solid state according to a scanning method, wherein the mechanical type adopts a rotating motor to rotate 360 degrees in the horizontal direction, and in the vertical direction, a laser transceiving module needs to be added to scan different vertical fields of view, at present, the mechanical type laser radar has 8, 16, 32 and 40 lines, and the 'line' represents the number of the laser transceiving module groups. Therefore, the device has the problems of large volume, low reliability, high cost and extremely high assembly difficulty. The mixed solid state adopts a scanning module, such as an MEMS (micro-electromechanical system) galvanometer, a rotating mirror, a rotating double prism and the like to replace the original mechanical one-dimensional rotation, and realizes the two-dimensional scanning of light beams under the fixation of a laser transceiving module, thereby improving the reliability and the integration level of the system, but the problems of reduced view field, loss of mechanical moving parts and the like are still existed. The pure solid-state phased array technology can realize flexible, fast and accurate non-mechanical light beam directional scanning by modulating the phase of a light beam, and is the direction of future development. The hot silicon-based optical waveguide phased array currently studied has the advantage of on-core integration, but the consequence is a reduction in array dimensions, i.e. a one-dimensional array. Therefore, to achieve two-dimensional deflection and scanning of the beam, the deflection angle needs to be controlled in another orthogonal dimension by wavelength tuning, which greatly increases the system cost and complexity. By means of a mature liquid crystal process, the liquid crystal phased array can be a two-dimensional array of a large area array, so that flexible two-dimensional light beam deflection and scanning, such as bow-shaped scanning and annular scanning and hopping type scanning, can be realized under the condition of a single wavelength. However, as with the optical waveguide phased array, the coherence element spacing in the liquid crystal phased array is still above the wavelength, which severely limits the maximum deflection angle of the beam and results in a limited scan field. A series of grating lobes will be generated at the same time, thereby interfering with the identification of the main lobe and the reception of the echo. Therefore, the phased array laser radar faces the problems that the scanning field of view is small, grating lobes influence echo detection and identification of a receiving end and the like.
Disclosure of Invention
The invention aims to provide a liquid crystal phased array-based laser radar large-view-field scanning method, which is used for solving the problems in the prior art, improving the scanning view field of a phased array laser radar and removing the interference of grating lobes on echo detection and identification.
In order to achieve the purpose, the invention provides the following scheme: the invention provides a liquid crystal phased array-based laser radar large-field-of-view scanning method, which comprises the following steps of:
expanding the beam of the laser light source according to the aperture size of the liquid crystal phased array, polarizing and aligning to obtain a target light beam;
continuously applying target adjacent phase difference to the liquid crystal phased array to obtain annular scanning beams;
reflecting the annular scanning beam to obtain a preliminary large-field-of-view arched scanning beam;
and filtering grating lobes except the preliminary large-field-of-view arched scanning beam to obtain a final large-field-of-view arched scanning result.
Optionally, the target beam covers an aperture of the liquid crystal phased array and has a uniform polarization direction.
Optionally, the continuously applying the target neighboring phase difference to the liquid crystal phased array, and obtaining an annular scanning beam comprises:
and respectively applying corresponding adjacent phase differences on two orthogonal dimensions of the liquid crystal phased array to form two-dimensional deflection of the target light beam, and continuously changing the adjacent phase differences applied on the two dimensions to carry out annular scanning of the light beam.
Optionally, a conical mirror is used in the process of reflecting the annular scanning beam.
Optionally, reflecting the annular scanning beam to obtain the preliminary large-field-of-view arcuate scanning beam comprises:
and reflecting the annular scanning beams by using the conical reflector, converting the rotation angle of the beams in annular scanning into a horizontal deflection angle, converting the deflection angle of the beams in the annular scanning into a vertical deflection angle, and converting the annular scanning into bow-shaped scanning to obtain the primary large-field bow-shaped scanning beams.
Optionally, spreading 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 surface of the conical reflector is parallel to the surface of the liquid crystal phased array.
Optionally, the distance between the conical mirror and the liquid crystal phased array is set as an intrinsic distance.
Optionally, the intrinsic distance is:
L＝R/tanθ max
wherein L is the intrinsic distance, R is the radius of the cone bottom of the cone-shaped reflector, and theta max The maximum value of the deflection angle of the beam circular scan.
The invention discloses the following technical effects:
the invention discloses a liquid crystal phased array-based laser radar large-field-of-view scanning method, which converts annular scanning realized on the basis of a liquid crystal phased array into bow-shaped scanning through a conical reflector, so that the scanning field of view is limited by the original device process parameters and optical wavelength max ×θ max Conversion to 360 DEG x theta max The scanning field of view is greatly improved due to the large field of view; by reasonably setting parameters of the conical reflector and the distance between the conical reflector and the liquid crystal phased array, the grating lobe removing effect can be realized without changing the process structure of the liquid crystal phased array and increasing the complexity of a beam control model, and finally high-quality large-view-field bow-shaped scanning is obtained.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic flow chart of a liquid crystal phased array-based laser radar large-field-of-view scanning method in an embodiment of the present invention;
FIG. 2 is a schematic view of a circular scan in an embodiment of the present invention;
fig. 3 is a schematic diagram of spatial transformation after being reflected by a conical reflector in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, the present invention is described in detail with reference to the accompanying drawings and the detailed description thereof.
The invention provides a liquid crystal phased array-based laser radar large-field-of-view scanning method, which comprises the following steps of:
the wavelength of the laser light source adopted in the example is 1064nm, the diameter of the light beam is 500 mu m, and the linear polarization direction is vertical; the spatial light modulator of Meadowlark Optics company adopted in this embodiment is used as a liquid crystal phased array, the number of pixels is 1920 × 1200, the pixel pitch d =8 μm × 8 μm, the aperture size is 15.36mm × 9.6mm, and the required incident linearly polarized polarization direction is horizontal.
S1: expanding the beam of the laser light source according to the aperture size of the liquid crystal phased array, polarizing and aligning; the light beam is ensured to cover the whole aperture, and the phase modulation effect of the liquid crystal phased array on the light beam is achieved.
The fast axis of the half-wave plate adopted by the embodiment forms an included angle of 45 degrees with the linear polarization direction emitted by the laser so as to change the incident linear polarization direction and enable the incident linear polarization direction to be horizontally aligned with the polarization direction required by the liquid crystal phased array. And then, an inverted telescope system is adopted to expand and collimate the light beam, the expansion multiplying power is about 30, and the expanded light beam covers the aperture of the whole liquid crystal phased array.
S2: applying corresponding phase modulation to the liquid crystal phased array according to a light beam scanning result to be realized; the applied phase modulation is continuously varied to achieve circular scanning.
The liquid crystal spatial light modulator is used as a main device of a liquid crystal phased array, and plays a role in controlling the wave front phase of a light beam. The control mode is to load the kinoform onto the target surface through the HDMI interface. The phase modulation size of each pixel point on the target surface of the spatial light modulator can be obtained through the 8-bit kinoform.
For a two-dimensional liquid crystal phased array, corresponding adjacent phase differences are respectively applied to two orthogonal dimensions to form two-dimensional deflection of a light beam, and annular scanning of the light beam is realized by continuously changing applied phase modulation. The annular scanning model is shown in formula 1:
thereby forming a circular scan as shown in fig. 2. Wherein
And
adjacent phase differences in two orthogonal dimensions, X and Y, respectively, theta x0 And theta y0 Deflection angles of the light beam in the X and Y dimensions, respectively; in two-dimensional liquid crystal phased arrays, d is usually x ＝d y D, d is the pixel pitch; k is the number of waves and is the number of waves,
for two-dimensional adjacent phase difference, θ 0 Is the two-dimensional deflection angle of the light beam, i.e. the deflection angle of the circular scanning of the light beam; phi is the rotation angle of the beam circular scan.
S3: reflecting the annular scanning obtained in the step S2 by using a conical reflector to realize space transformation; converting a light beam rotation angle in annular scanning into a horizontal deflection angle, and converting a light beam deflection angle in the annular scanning into a vertical deflection angle; the conversion from annular scanning to arcuate scanning is realized, and the maximum scanning field of view is changed from theta in theory max ×θ max Conversion to 360 DEG x theta max 。
As shown in fig. 3, the model of the spatial transformation is as follows:
the deflected light beam in the XOZ plane (i.e. phi = 0) is reflected by the conical reflector and then exits, and the exiting light beam is positioned in the X 'O' Z plane; the projection of the emergent light beam on the X 'O' Y 'plane and the X' axis form an included angle phi ', and phi' = phi is known easily; the angle between the emergent light beam and the X 'O' Y 'plane is theta',
when in use
When, θ' = θ 0 Where α is the cone angle. Thereby, the rotation angle φ of the ring scan is converted into a horizontal deflection angle φ' of the ring scan in a new spatial coordinate system 0 To a vertical deflection angle theta'. The conversion from annular scanning to arcuate scanning is realized, so that the scanning field of view is changed from theta in theory max ×θ max Conversion to 360 DEG x theta max 。
In the present example, it is shown that,
e.g. using a wavelength of 1550nm, theta max =5.559 °, on the basis of the 1550nm wavelength, if a device with a smaller pixel pitch is used again, for example, d =3 μm, then θ max ＝14.971°。
S4: the parameters of the conical reflector and the distance between the conical reflector and the conical reflector are reasonably set, stray light such as grating lobes outside scanning beams is filtered, and finally high-quality large-view-field bow-shaped scanning is obtained.
The cone-shaped reflector is unfolded along the optical axis, the cone tip of the cone-shaped reflector is aligned with the center of the liquid crystal phased array, and the bottom surface of the cone is parallel to the surface of the liquid crystal phased array. The size R =10mm of the conical bottom surface of the conical reflector selected in the example; the distance between the two is an intrinsic distance L, L = R/tan theta max About 150mm. Under the arrangement, the deflected light beams in the deflection range, namely the main lobe, are reflected by the conical reflector to realize space transformation, and all grating lobes are filtered. So that finally at the emission scanning end onlyThe scanning beam, namely the main lobe, is emitted finally, the effect of filtering grating lobes is achieved, and finally high-quality large-field-of-view bow-shaped scanning is obtained.
The invention relates to a liquid crystal phased array-based laser radar large-field-of-view scanning method, which mainly utilizes the two-dimensional deflection capability of light beams of a liquid crystal phased array and realizes annular scanning by continuously changing applied phase modulation. Then the conical reflector is used for reflecting the scanning object, and the conversion from annular scanning to large-field arcuate scanning is completed by space transformation, so that the field of view is enlarged. And parameters of the conical reflector and the distance between the conical reflector and the liquid crystal phased array are reasonably set, so that grating lobes are filtered. Compared with the traditional optical phased array method, the method has the advantages that the scanning field of view is larger, the interference of grating lobes on echo detection and identification is eliminated, and finally high-quality large-field-of-view bow-shaped scanning is obtained.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: those skilled in the art can still make modifications or changes to the embodiments described in the foregoing embodiments, or make equivalent substitutions for some features, within the scope of the disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the present invention in its spirit and scope. Are intended to be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. The liquid crystal phased array-based laser radar large-field scanning method is characterized by comprising the following steps:
expanding the beam of the laser light source and polarizing and aligning the beam according to the aperture size of the liquid crystal phased array to obtain a target light beam;
continuously applying target adjacent phase difference to the liquid crystal phased array to obtain annular scanning beams;
reflecting the annular scanning light beam to obtain a preliminary large-field-of-view bow-shaped scanning light beam;
and filtering grating lobes except the preliminary large-field-of-view arched scanning beams to obtain a final large-field-of-view arched scanning result.
2. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 1, wherein: the target light beam covers the aperture of the liquid crystal phased array and the polarization directions are consistent.
3. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 1, wherein: the continuously applying the target neighboring phase difference to the liquid crystal phased array to obtain an annular scanning beam comprises:
and respectively applying corresponding adjacent phase differences on two orthogonal dimensions of the liquid crystal phased array to form two-dimensional deflection of the target light beam, and continuously changing the adjacent phase differences applied on the two dimensions to carry out annular scanning of the light beam.
4. The liquid crystal phased array-based lidar large field-of-view scanning method according to claim 1 or 3, wherein: and a conical reflector is adopted in the process of reflecting the annular scanning light beam.
5. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 4, wherein: reflecting the annular scanning beam to obtain the preliminary large-field-of-view arcuate scanning beam comprises:
and reflecting the annular scanning beams by using the conical reflector, converting the rotation angle of the beams in annular scanning into a horizontal deflection angle, converting the deflection angle of the beams in the annular scanning into a vertical deflection angle, and converting the annular scanning into bow-shaped scanning to obtain the primary large-field bow-shaped scanning beams.
6. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 4, wherein: the conical reflector is unfolded along an optical axis, the conical tip of the conical reflector is aligned with the aperture center of the liquid crystal phased array, and the conical bottom surface of the conical reflector is parallel to the surface of the liquid crystal phased array.
7. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 4, wherein: the distance between the conical reflector and the liquid crystal phased array is set as an intrinsic distance.
8. The liquid crystal phased array-based lidar large field-of-view scanning method of claim 7, wherein: the intrinsic distance is:
L＝R/tanθ max
wherein L is the intrinsic distance, R is the radius of the cone bottom of the cone-shaped reflector, and theta max The maximum value of the deflection angle of the beam circular scan.
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