A double-layer metasurface beam scanning element for lidar

Abstract

The application discloses a kind of double-layer metasurface beam scanning elements for laser radar, including two parallel dielectric metasurfaces arranged in turn with optical axis;Incident light sequentially passes through two layers of dielectric metasurfaces, realizes twice different phase control, and then realizes the deflection of incident light;Rotating two layers of dielectric metasurfaces around optical axis respectively, the regular deflection of outgoing light beam in any direction within a certain field of view angle, and then realize the directional scanning of light beam.The element has polarization insensitive characteristics, and when controlling the incident light beam of different polarization state, the scanning positions obtained on the object to be scanned are completely consistent.The double-layer metasurface beam scanning element provided by the application can realize the deflection in any direction within a certain field of view angle according to the rotation angle of metasurface, and can perform directional scanning within the field of view range, which has great application potential in the field of laser radar.Meanwhile, the introduction of metasurface solves the problem of complex and large traditional laser radar optical system, and meets the requirements of modern optical element miniaturization and integration.

Description

Technical Field

[0001] This invention belongs to the field of lidar scanning technology, and in particular to a dual-layer metasurface beam scanning element for lidar. Background Technology

[0002] Since its advent, lidar has rapidly become a core technology in the fields of scanning and ranging due to its high precision, high resolution, and fast response. LiDAR scans emit laser pulses and receive their reflected signals, using the time-of-flight principle to calculate the time difference between emission and return, thus accurately measuring the distance to a target object. This method can not only achieve single-point ranging but also acquire omnidirectional, high-density 3D point cloud data of the surrounding environment through scanning mechanisms (such as mechanical rotation, MEMS micromirrors, or optical phased arrays). Traditional lidar systems rely on bulky mechanical rotating parts and complex optical components to achieve beam scanning and target detection. These systems typically contain multiple lenses, mirrors, and prisms for focusing and guiding the laser beam. This design results in a large size and weight of the internal optical system, and its extremely high requirements for mechanical alignment accuracy pose significant challenges to the cost and reliability of traditional lidar. Furthermore, the presence of moving mechanical parts limits scanning speed and system lifespan, while also increasing power consumption and maintenance requirements. With the rapid development of autonomous driving, robot navigation, and intelligent sensing, the demand for miniaturization, integration, and high performance of lidar systems is becoming increasingly urgent.

[0003] Recently, the emergence of metasurfaces has provided new possibilities for the innovation of lidar systems. Compared with traditional optical elements, metalenses have advantages such as small size, light weight, and ease of integration. Applying metalenses to lidar systems can significantly simplify the optical system structure, eliminate mechanical moving parts, and thus achieve all-solid-state beam scanning. This design not only improves the reliability and scanning speed of the system, but also reduces power consumption and manufacturing costs. In 2020, He et al. (He M, Guo Y, Li C, et al. Metasurface-based wide-angle beam steering for optical trapping[J]. IEEE Access, 2020, 8: 37275-37280) achieved beam deflection by changing the metasurface unit structure. They changed the geometric phase by adjusting two structural units of the metasurface to achieve beam deflection and scanning within a certain area. However, adjusting the structural units inevitably increases the complexity of the design. In the same year, Yin et al. (Yin S, He F, Kubo W, et al. Coherently tunable metalens tweezers for optofluidic particle routing[J]. Optics Express, 2020, 28(26): 38949-38959) achieved the filtering of different beams by changing the incident conditions of the incident beam, ensuring that the phase of the output light depends only on the geometry of the nanopillar and the illumination conditions. Compared with the former work, the latter reduced the design complexity of the metasurface, but using only a single metasurface makes it difficult to meet the current application requirements in terms of the scanning field of view and scanning accuracy of the beam. Summary of the Invention

[0004] The purpose of this invention is to address the problems of high complexity, small scanning field of view, and low scanning accuracy of existing metasurface beam scanning elements, and to provide a dual-layer metasurface beam scanning element for lidar.

[0005] The technical solution to achieve the purpose of this invention is: a dual-layer metasurface beam scanning element for lidar, wherein the dual-layer metasurface beam scanning element comprises two parallel dielectric metasurfaces arranged sequentially along the same optical axis;

[0006] An incident beam passes through two layers of dielectric metasurfaces in sequence, achieving two different phase modulations, thereby deflecting the incident beam. By rotating the two layers of dielectric metasurfaces around the optical axis, the outgoing beam deflects regularly in any direction within a certain field of view, thereby achieving directional scanning of the beam.

[0007] Furthermore, each of the dielectric metasurfaces comprises several metasurface structural units arranged in an array, and the entire dielectric metasurface has the same phase gradient from left to right and from top to bottom.

[0008] Furthermore, the metasurface structural unit is a symmetrical cylindrical nanounit structure.

[0009] Furthermore, the phase change of the incident light by the metasurface structural unit satisfies:

[0010]

[0011] Where, φ WG The variable λ represents the phase of the metasurface structural unit with respect to incident light. d The wavelength of the incident light is represented by n, h is the height of the dielectric cylinder, and n is the wavelength of the incident light. eff β is the effective refractive index, β is the propagation function, and k0 is the free plane wavenumber.

[0012] Furthermore, the symmetrical cylindrical nanounit structure includes a glass substrate and a high-refractive-index titanium dioxide cylinder disposed on the glass substrate.

[0013] Furthermore, the radius of the high-refractive-index titanium dioxide cylinder is adjustable, ranging from 30 nm to 120 nm, to cover phase changes from 0 to 2π.

[0014] Furthermore, the parameters set for the dual-layer metasurface beam scanning element and its theoretical operating performance must meet the following requirements:

[0015]

[0016] Where (X,Y) are the coordinates of the beam projected onto the object to be scanned, D1 is the distance between the two dielectric metasurfaces, D2 is the distance between the second dielectric metasurface and the object to be scanned, θ1 is the rotation angle of the first dielectric metasurface around the optical axis, θ2 is the rotation angle of the second dielectric metasurface around the optical axis, ψ is the acute angle between the path of the beam after passing through the second dielectric metasurface and the z-axis, and φ is the acute angle between the perpendicular line of the optical axis passing through the final beam landing point and the x-axis; G1 is the phase gradient of the first dielectric metasurface, k0 is the free plane wavenumber; the z-axis is the direction along the optical axis, and the x-axis is the horizontal direction perpendicular to the z-axis in the plane where the dielectric metasurface is located.

[0017] Furthermore, the dual-layer metasurface beam scanning element has polarization insensitivity characteristics, and when the incident beams with different polarization states are controlled, the scanning positions obtained on the object to be scanned are completely consistent.

[0018] Compared with the prior art, the significant advantages of this invention are:

[0019] (1) The optical metasurface in this invention can replace the combined functions of traditional optical elements such as spatial light modulators and diffractive optical elements in traditional radar systems. Its core function relies on the micro-nano arrangement structure of titanium dioxide nanocylinders, and different optical control effects can be achieved by adjusting the arrangement. This design can achieve flexible control of incident light while meeting the requirements of miniaturization and integration of optical systems.

[0020] (2) Compared with existing single-layer metasurface scanning elements, after the design of two-layer dielectric metasurface is completed, the present invention only needs to adjust its rotation angle to achieve beam scanning within a certain range, which is efficient, simple and easy to implement.

[0021] (3) The double-layer superlens beam scanning element used to replace the laser radar beam deflection element in this invention has advantages such as a larger scanning angle and higher accuracy compared with the traditional double-layer optical wedge system and galvanometer.

[0022] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a dual-layer metasurface beam scanning element for lidar in one embodiment.

[0024] Figure 2 This is a diagram showing the scanning range of a small-sized double-layer superlens system obtained theoretically in one embodiment.

[0025] Figure 3(a) is a three-dimensional schematic diagram of a metasurface structure unit in one embodiment, and Figure 3(b) is a schematic diagram of the cross-section of the metasurface structure unit in the xoy plane.

[0026] Figure 4 This is a partially enlarged schematic diagram of the metasurface in one embodiment.

[0027] Figure 5(a) shows the xoz plane phase distribution result obtained by phase modulation of a double-layer metasurface with rotation angles of (45°, 45°) in one embodiment, and Figure 5(b) shows the beam deflection result under this condition.

[0028] Figure 6 This is a simulation result of the scanning range of a scanning element that rotates simultaneously on a dual-layer metasurface in one embodiment. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0031] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0032] In one embodiment, combined Figure 1 A dual-layer metasurface beam scanning element for lidar is provided, the dual-layer metasurface beam scanning element comprising two parallel dielectric metasurfaces arranged sequentially along the optical axis;

[0033] The incident light passes through two layers of dielectric metasurface in sequence, achieving two different phase modulations, thereby deflecting the incident light; by rotating the two layers of dielectric metasurface around the optical axis, the outgoing beam deflects regularly in any direction within a certain field of view, thereby achieving directional scanning of the beam.

[0034] The dual-layer metasurface beam scanning element has polarization insensitivity characteristics, and when the incident beams with different polarization states are controlled, the scanning positions obtained on the object to be scanned are completely consistent.

[0035] Furthermore, in one embodiment, the dielectric metasurface comprises several metasurface structural units arranged in an array, and the entire dielectric metasurface has the same phase gradient from left to right and from top to bottom.

[0036] Preferably, in some embodiments, the metasurface structural unit is a symmetrical cylindrical nanounit structure, whose phase change with incident light satisfies:

[0037]

[0038] Where, φ WG The variable λ represents the phase of the metasurface structural unit with respect to incident light. d The wavelength of the incident light is represented by n, h is the height of the dielectric cylinder, and n is the wavelength of the incident light. effβ is the effective refractive index, β is the propagation function, and k0 is the free plane wavenumber.

[0039] More preferably, the symmetrical cylindrical nanounit structure includes a glass substrate and a high-refractive-index titanium dioxide cylinder disposed on the glass substrate, as shown in Figures 3(a) and 3(b).

[0040] Preferably, each layer of the dielectric metasurface has a size of 6μm*6μm and includes 24*24 structural units.

[0041] Preferably, the entire dielectric metasurface has the same phase gradient of 3141.5 rad / mm from left to right and from top to bottom.

[0042] Preferably, the lattice constant of the metasurface structural unit is 250 nm.

[0043] Preferably, the height of the high-refractive-index titanium dioxide cylinder is 600 nm, and the radius is adjustable, ranging from 30 nm to 120 nm, to cover phase changes from 0 to 2π.

[0044] Here, according to the propagation phase calculation formula, the amount of phase delay added to the beam by the nano-phase pillar is related to the radius of the phase pillar. Therefore, the phase delay applied to the beam within the range of 0-2π can be changed by altering the radius of the nano-phase pillar. Simulation measurements can reveal the relationship between the phase delay values ​​applied to the beam by phase pillars of different radii within one period. To obtain this specific relationship, parameter scanning is required within the simulation software. In this embodiment, Lumerical FDTD Solutionos simulation software is used for simulation.

[0045] In a database of circular nanopillar radii and phase delays, eight high-refractive-index dielectric cylinders with radii ranging from 30 nm to 120 nm were discretely selected. The eight basic structural units basically covered the phase change from 0 to 2π, with radii of 37.8 nm, 54.2 nm, 64.2 nm, 72.8 nm, 80.8 nm, 88.4 nm, 96.2 nm, and 104.2 nm, respectively.

[0046] Furthermore, in one embodiment, the parameters set for the dual-layer metasurface beam scanning element and its theoretical operating performance must meet the following requirements:

[0047]

[0048] Where (X,Y) are the coordinates of the beam projected onto the object to be scanned, D1 is the distance between the two dielectric metasurfaces, D2 is the distance between the second dielectric metasurface and the object to be scanned, θ1 is the rotation angle of the first dielectric metasurface around the optical axis, θ2 is the rotation angle of the second dielectric metasurface around the optical axis, ψ is the acute angle between the path of the beam after passing through the second dielectric metasurface and the z-axis, and φ is the acute angle between the perpendicular line of the optical axis passing through the final beam landing point and the x-axis; G1 is the phase gradient of the first dielectric metasurface, k0 is the free plane wavenumber; the z-axis is the direction along the optical axis, and the x-axis is the horizontal direction perpendicular to the z-axis in the plane where the dielectric metasurface is located.

[0049] As a specific example, the invention is further verified in some embodiments.

[0050] In this embodiment, the object to be scanned is a light screen, D1 is set to 4μm, D2 is set to 3μm, and other parameters adopt the above-mentioned preferred parameters. The dual-layer metasurface beam scanning element of this invention can control the beam to deflect in different directions by controlling the different rotation angles of the two metasurfaces, so that the beam, after being modulated by the dual-layer metasurface system, ultimately lands at different points on the light screen. Finally, the landing points are all displayed on the light screen, showing that the landing points basically cover a circular area, as shown... Figure 4 As shown, this region represents the theoretical scanning range of the double-layer superlens system.

[0051] In the superlens simulation system, two far-field monitors are placed between the first and second dielectric metasurfaces and at the screen, respectively, to observe the far-field results of the light beam after passing through the first and second dielectric metasurfaces.

[0052] Figure 5(a) shows the xz-plane phase distribution results obtained by phase modulation of a bilayer dielectric metasurface with rotation angles of (45°, 45°). It can be seen that after phase modulation by the bilayer dielectric metasurface with rotation angles of (45°, 45°), the phase direction of the incident light is clearly at an angle to the z-axis, indicating that the incident light is deflected after modulation by the nanorods. Figure 5(b) shows the beam deflection results under this condition, proving that the invention can achieve beam deflection on demand. In the figure, lens1 and lens2 represent the first and second dielectric metasurface layers, respectively.

[0053] The scanning range and accuracy of this invention are verified by modifying the rotation angle of the metasurface. While keeping the structural parameters of the metasurface and the system settings unchanged, the rotation angle of the first layer of the metasurface is fixed at 0°, and the second layer of the metasurface rotates in a certain step. The point of impact on the screen after the beam is deflected by the double-layer metasurface beam scanning element can be approximated as a teardrop shape. Based on this, the first layer of the metasurface is rotated in a certain step, while keeping the second layer of the metasurface rotating one revolution unchanged. Thus, the final scanning result can be seen as rotating the deflected beam obtained by rotating only the second layer of the metasurface around the incident light axis for one revolution. The annular area swept by the teardrop is the range that the deflected beam can reach, and it is also the scanning result after the beam is deflected and emitted in different directions. Figure 6 As shown, it can be seen that the scanning coverage of a certain area has been basically achieved, while ensuring extremely high scanning accuracy.

[0054] In summary, the dual-layer metasurface beam scanning element provided by this invention can achieve deflection in any direction within a certain field of view based on the rotation angle of the metasurface, enabling directional scanning within this field of view and possessing great application potential in the field of lidar. Simultaneously, the introduction of the metasurface solves the problem of the complexity and bulkiness of traditional lidar optical systems, meeting the requirements of miniaturization and integration of modern optical components.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention without departing from its spirit and scope should be included within the protection scope of the present invention.

Claims

1. A dual-layer metasurface beam scanning element for lidar, characterized in that, The dual-layer metasurface beam scanning element includes two parallel dielectric metasurfaces arranged sequentially along the same optical axis. The incident light passes through two layers of dielectric metasurface in sequence, achieving two different phase modulations, thereby deflecting the incident light; by rotating the two layers of dielectric metasurface around the optical axis, the outgoing beam deflects regularly in any direction within a certain field of view, thereby achieving directional scanning of the beam. The parameters and theoretical performance of the dual-layer metasurface beam scanning element must meet the following requirements: Where (X,Y) are the coordinates of the beam projected onto the object to be scanned, D1 is the distance between the two dielectric metasurfaces, D2 is the distance between the second dielectric metasurface and the object to be scanned, θ1 is the rotation angle of the first dielectric metasurface around the optical axis, θ2 is the rotation angle of the second dielectric metasurface around the optical axis, ψ is the acute angle between the path of the beam after passing through the second dielectric metasurface and the z-axis, and φ is the acute angle between the perpendicular line of the optical axis passing through the final beam landing point and the x-axis; G1 is the phase gradient of the first dielectric metasurface, k0 is the free plane wavenumber; the z-axis is the direction along the optical axis, and the x-axis is the horizontal direction perpendicular to the z-axis in the plane where the dielectric metasurface is located.

2. The dual-layer metasurface beam scanning element for lidar according to claim 1, characterized in that, Each of the dielectric metasurfaces comprises several metasurface structural units arranged in an array, and the entire dielectric metasurface has the same phase gradient from left to right and from top to bottom.

3. The dual-layer metasurface beam scanning element for lidar according to claim 2, characterized in that, The metasurface structural unit is a symmetrical cylindrical nanounit structure.

4. The dual-layer metasurface beam scanning element for lidar according to claim 3, characterized in that, The phase change of the incident light by the metasurface structural unit satisfies: Where, φ WG λ represents the phase change of the metasurface structural unit with respect to incident light. d The wavelength of the incident light is represented by n, h is the height of the dielectric cylinder, and n is the wavelength of the incident light. eff β is the effective refractive index, β is the propagation function, and k0 is the free plane wavenumber.

5. The dual-layer metasurface beam scanning element for lidar according to claim 3, characterized in that, The symmetrical cylindrical nanounit structure includes a glass substrate and a high-refractive-index titanium dioxide cylinder disposed on the glass substrate.

6. The dual-layer metasurface beam scanning element for lidar according to claim 5, characterized in that, The radius of the high-refractive-index titanium dioxide cylinder is adjustable, ranging from 30 nm to 120 nm, to cover phase changes from 0 to 2π.

7. The dual-layer metasurface beam scanning element for lidar according to claim 1, characterized in that, The dual-layer metasurface beam scanning element has polarization insensitivity characteristics, and when the incident beams with different polarization states are controlled, the scanning positions obtained on the object to be scanned are completely consistent.

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