Phase optimization method of metasurface optical element and continuous line laser projection module

Abstract

The invention relates to a metasurface optical element phase optimization method and a continuous line laser projection module, and belongs to the technical field of optical elements, the metasurface optical element phase optimization method comprises the following steps: S1, using Zemax to design a lens capable of converting approximately parallel incident Gaussian plane waves into continuous line laser at a certain emission angle, converting the rise of the lens into a phase surface curve; s2, performing full-wave simulation by using FDTD to obtain a series of atomic parameters, and selecting a high-transmittance region in the atomic parameters as an optimized initial target monomer; s3, solving units in all periods within a certain space angle range according to a formula; and S4, solving a group of slopes ki every 2 pi from the center of the lens in the S1 to the two sides, and matching the value of ki with the optimized unit library until the filling of the phase surface type of the whole lens is completed. According to the invention, through algorithm optimization, the phase surface type after the arrangement of the nanorods is close to continuous arrangement, and the projection of continuous line laser is realized.

Description

Technical Field

[0001] The present invention belongs to the field of optical elements, and in particular relates to a phase optimization method of a metasurface optical element and a continuous line laser projection module. Background Art

[0002] Line lasers are widely used in fields such as 3D scanning and ranging. The traditional way to achieve the conversion of point lasers to line lasers requires the use of cylindrical lenses, and their total length and structural dimensions do not meet the design requirements of miniaturization. In application scenarios with FOV120° and above, there are great challenges in the lens volume, material refractive index, and processing difficulty, and compromises need to be made. Diffractive optical elements (DOEs) have the potential to replace optical lenses, but the diffraction efficiency is often difficult to improve. DEO's large-angle line laser projection has problems with discontinuous distribution and uneven brightness. Summary of the invention

[0003] The present application provides a phase optimization method for a metasurface optical element and a continuous line laser projection module to at least solve the above technical problems existing in the prior art.

[0004] An embodiment of the present application provides a phase optimization method for a metasurface optical element, comprising the following steps:

[0005] S1. Use Zemax to design a lens that can transform a nearly parallel incident Gaussian plane wave into a continuous line laser of a certain emission angle, and convert the sag of the lens into a phase surface curve.

[0006] S2. Use FDTD to perform full-wave simulation to obtain a series of atomic parameters, and select the high-transmittance area as the initial target monomer for optimization;

[0007] S3. Solve the units of all periods within a certain spatial angle range according to the formula dsinθ=λ;

[0008] S4. Starting from the center of the lens in S1, a set of slopes ki are solved every 2pi on both sides, and the values ​​of ki are matched with the optimized unit library until the entire lens phase surface is filled.

[0009] In one embodiment, at least 8 discrete values ​​are taken at equal intervals between 0-2pi to find the corresponding nanorods as the initial monomers.

[0010] In one possible implementation, in S2, at least 32 discrete values ​​are taken at equal intervals between 0-2pi to find the corresponding nanorods as the initial monomers.

[0011] In one possible implementation, in S3, the parameters in the unit are optimized, and during the optimization process, the efficiency of each unit is ensured to be higher than 90%.

[0012] In one possible implementation, the optimization of the large cell is performed in 0.5° intervals within the range of 0 to 60°.

[0013] On the other hand, an embodiment of the present application provides a continuous line laser projection module, including a light source, a collimating mirror and a metasurface optical element.

[0014] In one possible implementation, the metasurface optical element consists of a transparent substrate and nanorods on the substrate.

[0015] In one embodiment, the size of the nanorods is determined by the phase distribution and the transmittance curve.

[0016] In one embodiment, the size of the nanorods is between 180-300 nm.

[0017] In one embodiment, the height of the nanorods is 740 nm.

[0018] Compared with the prior art, this application has the following advantages:

[0019] 1. This application uses algorithm optimization to make the phase surface of the nanopillars arranged close to a continuous arrangement, thus realizing the design of a continuous phase metasurface;

[0020] 2. This application uses the optimization results to achieve continuous line laser projection, solving the problem of discontinuous phase modulation of the DOE device, which leads to discontinuous and uneven line laser projection; BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the phase arrangement of a traditional diffraction device;

[0022] Figure 2 It is a phase surface distribution diagram of the sagittal height phase transition in the embodiment of the present application;

[0023] Figure 3 is a phase curve diagram of the unit optimization target in the embodiment of the present application;

[0024] Figure 4 is a schematic diagram of an optimization parameter model in an embodiment of the present application;

[0025] Figure 5 This is a schematic diagram of the arrangement of the vcsel lamp beads in the embodiment of the present application;

[0026] Figure 6 It is a structural schematic diagram of a linear laser projection module in an embodiment of the present application;

[0027] Description of reference numerals:

[0028] 61. Light source; 62. Collimating lens; 63. Metasurface optical element; 64. Receiving plane. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0030] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0031] The diffractive optical element takes 2nd order (4th order or 8th order) discrete values ​​at equal intervals between 0 and 2pi to realize the function of the device. Figure 1 As shown in Figure 1, this discrete sampling will cause a large difference between the actual phase plane of the device and the designed target phase plane.

[0032] The present application adopts a phase gradient matching optimization method to solve the above problems. Specifically, the present application discloses a phase optimization method for a metasurface optical element, comprising the following steps:

[0033] S1. Use Zemax to design a lens that can transform a nearly parallel incident Gaussian plane wave into a continuous line laser of a certain emission angle, and convert the sag of the lens into Figure 2 The phase surface curve shown;

[0034] S2. Use FDTD to perform full-wave simulation to obtain a series of atomic parameters, and select the high-transmittance area as the initial target monomer for optimization.

[0035] Specifically, at least 8 discrete values ​​are taken at equal intervals between 0-2pi to find the corresponding nanopillars as the initial monomers, preferably 32 or more, and the higher the order, the more conducive it is to reduce the step size and increase the accuracy of subsequent optimization.

[0036] S3. Solve the units under all periods within a certain spatial angle range according to the formula d sinθ=λ; where d is the period of the structural unit, θ is the preset deflection angle, and Δθ is the interval change. By optimizing the parameters within the unit, the phase curve distribution of each unit is as follows: Figure 3 The optimization process ensures that the efficiency of each unit is higher than 90%, and the optimization of the large unit is completed in the range of 0 to 60° with an interval of 0.5°.

[0037] The parameters that can be optimized are Figure 4As shown, including but not limited to (nano-pillar radius Ri, gap between nano-pillars Gi, nano-pillar displacement in y direction). During the optimization process, the efficiency of each unit is guaranteed to be higher than 90%.

[0038] S4. Starting from the center of the lens in S1, a set of slopes ki are solved every 2pi on both sides, and the values ​​of ki are matched with the optimized unit library until the entire lens phase surface is filled.

[0039] The above phase optimization method realizes a quasi-continuous large structure by optimizing the overall large unit. It can cover the entire phase space from 0 to 2pi. It solves the problem that the phase is discontinuous when the overall phase surface analysis is not performed during discrete phase sampling, resulting in discontinuous line laser.

[0040] One implementation of the above phase optimization method is as follows:

[0041] First, determine the arrangement of the incident light source as follows Figure 5 As shown. It is clear that the divergence angle of the output line light source is 120°. In the optical design software, a cylindrical lens that can achieve this function is designed, and its sag data is converted into phase distribution φ(x,y).

[0042] Full-wave simulation was performed to determine the initial radius and height of the single nanocolumn to ensure that the transmittance of the single nanocolumn was above 90%. The optimization of the large unit was completed in the range of 0 to 60° with an interval of 0.5°.

[0043] The period of the large unit is determined according to d sinθ = λ, and the optimization goal is to make the phase curve close to Figure 3 The phase curve and high diffraction efficiency are shown. The higher the efficiency, the closer the slope of the curve is to the ideal value, and the optimization is effective.

[0044] After completing the design of the large unit at all angles, the phase change slope k is calculated from the center to the edge at intervals of 2pi according to the obtained phase surface φ(x,y) θ , find the slope and k in the large unit curve obtained above θ The unit with the highest matching degree is filled until the filling and matching of the entire phase surface is completed.

[0045] The present application also discloses a line laser projection module, including a light source 61, a collimator 62 and a metasurface optical element 63, wherein the metasurface optical element 63 is a metasurface device obtained by any of the above-mentioned phase optimization methods. The metasurface optical element 63 is composed of a transparent substrate and nanocolumns on the substrate. The size of the nanocolumns is determined by the phase distribution and the transmittance curve. The size of the nanocolumns is between 180-300nm, and the height of the nanocolumns is 740nm. The light source 61 is a VCSEL light source, and the arrangement of its lamp beads is as follows: Figure 5As shown, its arrangement includes but is not limited to this, and different arrangement effects can produce different projection schemes. The collimator 62 is a collimating lens, which modulates the divergent light source into plane waves propagating in different directions. The light is modulated by the metasurface optical element 63 to form a line laser with a certain divergence angle in one-dimensional direction. When the light source 61 on the light board is driven to emit light in turn, the outgoing line laser realizes scanning in the designed direction. The divergence angle of the line laser is determined by the design parameters of the metasurface device.

[0046] The divergent light emitted by the light source 61 is collimated by the collimator 62 and becomes a plane wave emitted at different angles. The multi-angle plane waves are irradiated to the metasurface optical element 63, and are modulated by the metasurface optical element 63 to generate a continuous line laser distribution, which hits the receiving plane 64.

[0047] The above are only specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure, which should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. A phase optimization method for a metasurface optical element, characterized in that: The steps include: S1. Use Zemax to design a lens that can transform a nearly parallel incident Gaussian plane wave into a continuous line laser of a certain emission angle, and convert the sag of the lens into a phase surface curve. S2. Use FDTD to perform full-wave simulation to obtain a series of atomic parameters, and select the high-transmittance area as the initial target monomer for optimization; S3. Solve the units of all periods within a certain spatial angle range according to the formula dsinθ=λ; S4. Starting from the center of the lens in S1, a set of slopes ki are solved every 2pi on both sides, and the values ​​of ki are matched with the optimized unit library until the entire lens phase surface is filled.

2. The phase optimization method of a metasurface optical element according to claim 1, characterized in that: In S2, at least 8 discrete values ​​are taken at equal intervals between 0 and 2pi to find the corresponding nanopillars as the initial monomers.

3. The phase optimization method of a metasurface optical element according to claim 2, characterized in that: In S2, at least 32 discrete values ​​are taken at equal intervals between 0 and 2pi to find the corresponding nanopillars as the initial monomers.

4. The phase optimization method of a metasurface optical element according to claim 1, characterized in that: In S3, the parameters in the unit are optimized, and the efficiency of each unit is ensured to be higher than 90% during the optimization process.

5. The phase optimization method of a metasurface optical element according to claim 4, characterized in that: The optimization of the large unit was done in 0.5° intervals over the range of 0 to 60°.

6. A continuous line laser projection module, characterized in that: It includes a light source, a collimating lens and a metasurface optical element.

7. A continuous line laser projection module according to claim 6, characterized in that: The super-surface optical element consists of a transparent substrate and nano-columns on the substrate.

8. The continuous line laser projection module according to claim 7, characterized in that: The size of the nanorods is determined by the phase distribution and the transmittance curve.

9. A continuous line laser projection module according to claim 8, characterized in that: The size of the nanorods is between 180-300 nm.

10. A continuous line laser projection module according to claim 8 or 9, characterized in that: The height of the nanorods is 740 nm.

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