A beam scanning system based on polarization multiplexing metalens group and its design method

Abstract

The present invention belongs to the field of micro-nano optical technology and discloses a light beam scanning system based on a polarization multiplexing metalens group and a design method thereof. The present invention includes a polarization adjustment unit, a first metalens, a second metalens and a displacement adjustment unit. The polarization adjustment unit is used to adjust the polarization state of the incident light. The first metalens is used to generate an off-axis focusing phase symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light. The second metalens is used to generate the same phase modulation for the x-polarized light and the y-polarized light, and modulate the light beam focused by the first metalens into a parallel light beam before emitting. The displacement adjustment unit is used to adjust the position of the second metalens. The light beam scanning system mentioned in the present invention realizes scanning of the output light beam angle of 0 to θ in half a scanning cycle, and realizes scanning of the output light beam angle of 0 to θ in the other half a scanning cycle. The present invention can expand the light beam scanning angle without sacrificing the scanning frequency.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optical technology, and more specifically, relates to a light beam scanning system based on a polarization multiplexing superlens group and a design method thereof. Background Art

[0002] Beam scanning, as an important light wave modulation technology, is widely used in many fields, including lidar and scanning imaging. However, existing beam scanning technologies have many problems. For example, the use of mechanical mechanisms to rotate the beam emission device leads to low scanning frequencies. For example, the use of optical phased array technology to modulate the output beam phase leads to small scanning angles. Furthermore, while some scanning solutions based on superlenses can achieve high-speed beam scanning, the beam scanning angle is often still very small. How to expand the beam scanning angle without sacrificing scanning frequency is a technical issue that needs to be addressed in this field. Summary of the Invention

[0003] The present invention solves the problem of small beam scanning angle in the prior art by providing a beam scanning system based on a polarization multiplexing super lens group and a design method thereof.

[0004] The present invention provides a light beam scanning system based on a polarization multiplexing superlens group, comprising: a polarization adjustment unit, a first superlens, a second superlens, and a displacement adjustment unit; the polarization adjustment unit, the first superlens, and the second superlens are arranged in sequence along an optical path, and the second superlens is mounted on the displacement adjustment unit;

[0005] The polarization adjustment unit is used to adjust the polarization state of the incident light; the first superlens and the second superlens constitute a polarization multiplexing superlens group, the first superlens is used to generate an off-axis focusing phase symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light, and the second superlens is used to generate the same phase modulation for the x-polarized light and the y-polarized light, and modulate the light beam focused by the first superlens into a parallel light beam before emitting; the displacement adjustment unit is used to adjust the position of the second superlens;

[0006] Under the adjustment of the polarization adjustment unit and the displacement adjustment unit, the beam scanning system based on the polarization multiplexing metalens group realizes scanning of the output beam angle of 0 to θ in half a scanning cycle, and realizes scanning of the output beam angle of 0 to -θ in the other half of the scanning cycle, where θ is the maximum angle of the output beam.

[0007] Preferably, the first superlens includes a first substrate and a nanobrick array located on the first substrate, and the second superlens includes a second substrate and a nanocolumn array located on the second substrate.

[0008] Preferably, the nanobrick array includes several nanobricks with the same height and different major axis or minor axis sizes, and the nanobrick array achieves a phase modulation amount covering 0 to 2π under incident light with a working wavelength; the nanocolumn array includes several nanocolumns with the same height and different diameters, and the nanocolumn array achieves a phase modulation amount covering 0 to 2π under incident light with a working wavelength.

[0009] Preferably, the first substrate and the second substrate are both made of silicon dioxide, and the nanobrick array and the nanocolumn array are both made of silicon.

[0010] Preferably, the polarization adjustment unit includes an electro-optical crystal and a first voltage source; the displacement adjustment unit includes a piezoelectric ceramic, a second voltage source and a support platform;

[0011] The electro-optical crystal is connected to the first voltage source, and the output voltage of the first voltage source switches between the half-wave voltage and zero voltage of the electro-optical crystal, so that the electro-optical crystal generates polarization modulation in half a scanning cycle and does not generate polarization modulation in the other half of the scanning cycle, thereby realizing the switching of the incident light beam between two orthogonal linear polarization states; the piezoelectric ceramic is connected to the second superlens through the support platform, and the piezoelectric ceramic is connected to the second voltage source, and the elongation of the piezoelectric ceramic is adjusted by controlling the output voltage of the second voltage source.

[0012] On the other hand, the present invention provides a design method for the above-mentioned beam scanning system based on the polarization multiplexing type metalens group, comprising the following steps:

[0013] Determine the operating wavelength, the maximum angle of the output light beam, and the maximum displacement adjustment amount of the displacement adjustment unit, design the phase equations of the first superlens and the second superlens, and step the phase equations;

[0014] Obtaining a phase modulation amount based on the stepped phase equation, and constructing the first superlens and the second superlens based on the phase modulation amount;

[0015] The second superlens is installed on the displacement adjustment unit, and the polarization adjustment unit, the first superlens, and the second superlens are placed in sequence along the optical path to form a beam scanning system based on a polarization multiplexing superlens group.

[0016] Preferably, the phase equation φ2(x,y) of the second superlens is the phase function The result of phase folding from 0 to 2π is: The calculation formula is as follows:

[0017]

[0018] in,

[0019]

[0020] Wherein, L is the maximum displacement adjustment amount of the displacement adjustment unit, λ is the operating wavelength, and θ is the maximum angle of the output light beam.

[0021] Preferably, the phase equation of the first superlens satisfies the following condition: when the light beam focused by the first superlens propagates to the second superlens, the phase of the light wave is the inverse of the phase equation of the second superlens;

[0022] The phase equation φ of the first metalens for linearly polarized light along the x-axis is designed using the inverse diffraction method. 1x (x,y), and the phase equation for linearly polarized light along the y-axis φ 1y (x,y).

[0023] Preferably, the complex amplitude distribution E at the position of the first super lens is calculated using the following Rayleigh-Sommerfeld diffraction formula: 1t (x′1,y′1,0):

[0024]

[0025] Wherein, (x′1, y′1) is the coordinate of the sampling point on the plane of the first superlens, (x′2, y′2) is the coordinate of the sampling point on the plane of the second superlens, d is the distance between the first superlens and the second superlens, E2(x′2, y′2, d) is the initial complex amplitude distribution of the inverse diffraction, and R is the distance between the sampling point on the plane of the first superlens and the sampling point on the plane of the second superlens;

[0026] Among them, when When the phase equation φ1x(x, y) is the complex amplitude distribution E 1t The opposite of the phase angle of (x′1, y′1, 0); when When the phase equation φ 1y (x, y) is the complex amplitude distribution E 1t Δx is the off-axis amount of the off-axis phase of the first metalens for x-polarized light and y-polarized light.

[0027] Preferably, the plane of the first superlens is sampled with the period size of the nanobrick as the coordinate interval, and the coordinates of the center point of each nanobrick (x1, y1) are substituted into the phase equation of the first superlens to calculate the first phase modulation amount φ 1x (x1, y1) and the second phase modulation amount φ 1y (x1, y1); select the nanobrick structure with the phase modulation amount of x polarized light closest to φ from the nanobrick structure library 1x(x1, y1), and the phase modulation amount of the y-polarized light is closest to φ 1y The nanobricks of (x1, y1) are arranged at this position to construct the first superlens;

[0028] The plane of the second superlens is sampled using the periodic size of the nanopillars as the coordinate interval, and the coordinates of the center point of each nanopillar (x2, y2) are substituted into the phase equation of the second superlens to calculate the third phase modulation amount φ2(x2, y2). The nanopillar with the phase delay closest to φ2(x2, y2) is selected from the nanopillar structure library and arranged at that position to construct the second superlens.

[0029] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0030] The present invention provides a light beam scanning system based on a polarization multiplexing metalens group, comprising a polarization adjustment unit, a first metalens, a second metalens, and a displacement adjustment unit; the polarization adjustment unit is used to adjust the polarization state of the incident light; the first metalens and the second metalens constitute a polarization multiplexing metalens group, wherein the first metalens is used to generate off-axis focusing phases symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light, the second metalens is used to generate the same phase modulation for the x-polarized light and the y-polarized light, and modulate the light beam focused by the first metalens into a parallel light beam before emitting; the displacement adjustment unit is used to adjust the position of the second metalens; under the adjustment of the polarization adjustment unit and the displacement adjustment unit, the light beam scanning system based on the polarization multiplexing metalens group realizes scanning of the output beam angle from 0 to θ in half a scanning cycle, and realizes scanning of the output beam angle from 0 to -θ in the other half a scanning cycle, where θ is the maximum angle of the output beam. The present invention utilizes the polarization multiplexing function of the metalens to design complementary scanning ranges for x-polarized light and y-polarized light, respectively, thereby expanding the beam scanning angle without sacrificing the scanning frequency. That is, the present invention can design two symmetrical off-axis focal points for two orthogonal polarization states of linear polarization based on the polarization multiplexing metalens. By switching the polarization state of the light beam incident on the metalens group, a complementary scanning range can be achieved, thereby expanding the scanning angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of a light beam scanning system based on a polarization multiplexing metalens assembly provided in Example 1 of the present invention;

[0032] Figure 2 A schematic diagram of a nanobrick structure unit in a beam scanning system based on a polarization multiplexing superlens group provided in Example 1 of the present invention;

[0033] Figure 3The simulation results of the nanobrick structure unit in the beam scanning system based on the polarization multiplexing type super lens group provided in Example 1 of the present invention are as follows; wherein, Figure 3 (a) is the phase modulation of x-polarized light by nanobricks with different structural parameters. Figure 3 (b) is the transmittance of x-polarized light by nanobricks with different structural parameters. Figure 3 (c) is the phase modulation of y-polarized light by nanobricks with different structural parameters. Figure 3 (d) is the transmittance of nanobricks with different structural parameters to y-polarized light;

[0034] Figure 4 A schematic diagram of a nanorod structure unit in a beam scanning system based on a polarization multiplexing superlens group provided in Example 1 of the present invention;

[0035] Figure 5 The simulation results of the nanorod structure unit in the beam scanning system based on the polarization multiplexing superlens group provided in Example 1 of the present invention;

[0036] Figure 6 The phase distribution diagram of the first metalens in a beam scanning system based on a polarization multiplexing metalens group provided in Example 1 of the present invention; wherein, Figure 6 (a) is the phase distribution diagram of the first super lens for x-polarized light. Figure 6 (b) is the phase distribution diagram of the first metalens for y-polarized light;

[0037] Figure 7 Phase distribution diagram of the second metalens in a beam scanning system based on a polarization multiplexing metalens group provided in Example 1 of the present invention;

[0038] Figure 8 This is a simulation diagram of the beam scanning process of the first and second metalens in a beam scanning system based on a polarization multiplexing metalens group provided in Example 1 of the present invention; wherein, Figure 8 (a) is the simulation result when a plane wave with polarization direction along the x-axis is incident on the first super lens and the x-coordinate of the center of the second super lens is 100 μm. Figure 8 (b) is the simulation result when a plane wave with polarization direction along the x-axis is incident on the first metalens and the x-coordinate of the center of the second metalens is 0. Figure 8 (c) is the simulation result when a plane wave with polarization direction along the x-axis is incident on the first super lens and the x-coordinate of the center of the second super lens is -100 μm. Figure 8 (d) is the simulation result when a plane wave with polarization along the y-axis is incident on the first metalens and the x-coordinate of the center of the second metalens is -100 μm. Figure 8(e) is the simulation result when the plane wave with polarization direction along the y-axis is incident on the first metalens and the x-coordinate of the center of the second metalens is 0. Figure 8 (f) is the simulation result when a plane wave with polarization along the y-axis is incident on the first superlens and the x-coordinate of the center of the second superlens is 100 μm.

[0039] Among them, 1-electro-optic crystal, 2-first super lens, 3-second super lens, 4-support platform, 5-piezoelectric ceramic. DETAILED DESCRIPTION

[0040] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0041] Example 1:

[0042] Example 1 provides a beam scanning system based on a polarization multiplexing superlens group, including: a polarization adjustment unit, a first superlens, a second superlens and a displacement adjustment unit; the polarization adjustment unit, the first superlens, and the second superlens are arranged in sequence along the optical path, and the second superlens is installed on the displacement adjustment unit.

[0043] The polarization adjustment unit is used to adjust the polarization state of the incident light; the first superlens and the second superlens constitute a polarization multiplexing superlens group, the first superlens is used to generate an off-axis focusing phase symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light, the second superlens is used to generate the same phase modulation for the x-polarized light and the y-polarized light, and modulate the light beam focused by the first superlens into a parallel light beam before emitting; the displacement adjustment unit is used to adjust the position of the second superlens.

[0044] Under the adjustment of the polarization adjustment unit and the displacement adjustment unit, the beam scanning system based on the polarization multiplexing metalens group realizes scanning of the output beam angle of 0 to θ in half a scanning cycle, and realizes scanning of the output beam angle of 0 to -θ in the other half of the scanning cycle, where θ is the maximum angle of the output beam.

[0045] The first superlens includes a first substrate and a nanobrick array located on the first substrate, and the second superlens includes a second substrate and a nanocolumn array located on the second substrate.

[0046] The nanobrick array includes several nanobricks with the same height and different major or minor axis sizes, and the nanobrick array achieves a phase modulation amount covering 0 to 2π under incident light with a working wavelength; the nanopillar array includes several nanopillars with the same height and different diameters, and the nanopillar array achieves a phase modulation amount covering 0 to 2π under incident light with a working wavelength.

[0047] The first substrate and the second substrate may both be made of silicon dioxide, and the nanobrick array and the nanocolumn array may both be made of silicon.

[0048] For example, the polarization adjustment unit may specifically include an electro-optical crystal and a first voltage source; the displacement adjustment unit may specifically include a piezoelectric ceramic, a second voltage source and a support platform; the electro-optical crystal is connected to the first voltage source, and the output voltage of the first voltage source switches between the half-wave voltage and zero voltage of the electro-optical crystal, so that the electro-optical crystal generates polarization modulation in half a scanning cycle and does not generate polarization modulation in the other half of the scanning cycle, thereby realizing the switching of the incident light beam between two orthogonal linear polarization states; the piezoelectric ceramic is connected to the second superlens through the support platform, and the piezoelectric ceramic is connected to the second voltage source, and the elongation of the piezoelectric ceramic is adjusted by controlling the output voltage of the second voltage source.

[0049] The present invention will be described below in its entirety by taking the above device combination as an example.

[0050] See also Figure 1 The present invention provides a light beam scanning system based on a polarization multiplexing metalens group, which mainly includes an electro-optical crystal 1, a first metalens 2, a second metalens 3, a support platform 4, and a piezoelectric ceramic 5. The first metalens 2 and the second metalens 3 constitute a polarization multiplexing metalens group. The first metalens 2 generates an off-axis focusing phase symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light. The second metalens 3 modulates the light beam focused by the first metalens 2 into a parallel light beam for output. The second metalens 3 is a polarization-independent metalens and has only one on-axis focus under the illumination of light beams with different polarization states. Therefore, different exit angles are generated for x-polarized light and y-polarized light. When the second metalens 3 undergoes vertical axis displacement, the angle of the exiting beam changes, realizing beam scanning. Within a scanning cycle, in the first half of the scanning cycle, x-polarized parallel light or y-polarized parallel light is perpendicularly incident on the metalens group. In the second half of the scanning cycle, the polarization state of the incident light is switched to the orthogonal polarization state of the first half of the scanning cycle. The off-axis amount of the first metalens 2 for x-polarized light and y-polarized light is designed to be the maximum displacement of the second metalens 3 relative to the optical axis, so that the exiting beams of the polarization-multiplexed metalens group have complementary scanning ranges, realizing large-angle beam scanning.

[0051] The first superlens 2 produces different off-axis focusing phases for x-polarized light and y-polarized light, and adopts an anisotropic nanostructure, consisting of the first substrate and an array of nanobricks arranged at equal intervals on the working plane of the first substrate. The second superlens 3 produces the same phase modulation for x-polarized light and y-polarized light, and adopts an isotropic nanostructure, consisting of the second substrate and an array of nanopillars arranged at equal intervals on the working plane of the second substrate.

[0052] In the present invention, the first superlens arranged along the optical path is polarization-multiplexed, and the second superlens is polarization-independent. Therefore, the two superlenses are constructed in the form of nanobrick arrays and nanopillar arrays, respectively. This ensures that the size of the second superlens meets the requirements. This is also the design result after considering process limitations.

[0053] The piezoelectric ceramic 5 is externally connected to the second voltage source. Changes in the signal voltage cause the elongation of the piezoelectric ceramic 5 to change. The signal frequency is the resonant frequency of the piezoelectric ceramic 5. The piezoelectric ceramic 5 is connected to the second superlens 3 via the support platform 4 to achieve vertical axis displacement of the second superlens 3. Therefore, the scanning frequency of the light beam scanning device is the resonant frequency of the piezoelectric ceramic 5.

[0054] Specifically, the support platform 4 can be a right-angled triangular prism structure, one right-angled cross-section is bonded to the conical cap of the piezoelectric ceramic 5 using epoxy resin, the conical cap of the piezoelectric ceramic 5 is bonded to the spherical contact of the piezoelectric ceramic 5 using epoxy resin, and the other right-angled cross-section of the support platform 4 and the lower edge of the second substrate of the second superlens 3 are bonded using photoresist.

[0055] The electro-optical crystal 1 is externally connected to the first voltage source, which switches between outputting a half-wave voltage and zero voltage to the electro-optical crystal 1 at a switching frequency that is twice the resonant frequency of the piezoelectric ceramic 5. This causes the electro-optical crystal 1 to generate polarization modulation during half a scanning cycle and not generate polarization modulation during the other half of the scanning cycle, thereby switching the incident light beam between two orthogonal linear polarization states. In other words, the essence of this voltage switching is to allow the electro-optical crystal 1 to operate in two states: one in which no polarization modulation is generated for the incident light, and the other in which x-polarized light is converted to y-polarized light.

[0056] Example 1 uses anisotropic nanounits to construct a superlens, which can have different responses under incident light of different polarization states, bringing new ideas for expanding the scanning angle of the beam scanning system.

[0057] Example 2:

[0058] Example 2 provides a design method for a beam scanning system based on a polarization multiplexing metalens assembly as described in Example 1, comprising the following steps:

[0059] Determine the operating wavelength, the maximum angle of the output light beam, and the maximum displacement adjustment amount of the displacement adjustment unit, design the phase equations of the first superlens and the second superlens, and step the phase equations;

[0060] Obtaining a phase modulation amount based on the stepped phase equation, and constructing the first superlens and the second superlens based on the phase modulation amount;

[0061] The second superlens is installed on the displacement adjustment unit, and the polarization adjustment unit, the first superlens, and the second superlens are placed in sequence along the optical path to form a beam scanning system based on a polarization multiplexing superlens group.

[0062] The phase equation of the second super lens φ2(x, y) is the phase function The result of phase folding from 0 to 2π is: The calculation formula is as follows:

[0063]

[0064] in,

[0065]

[0066] Wherein, L is the maximum displacement adjustment amount of the displacement adjustment unit, λ is the operating wavelength, and θ is the maximum angle of the output light beam.

[0067] The phase equation of the first superlens satisfies the following conditions: when the light beam focused by the first superlens propagates to the second superlens, the phase of the light wave is the inverse of the phase equation of the second superlens; the phase equation φ of the first superlens for linearly polarized light along the x-axis is designed by using the reverse diffraction method. 1x (x, y), and the phase equation for linearly polarized light along the y-axis is φ 1y (x, y).

[0068] The complex amplitude distribution E at the position of the first super lens is calculated using the following Rayleigh-Sommerfeld diffraction formula: 1t (x′1,y′1,0):

[0069]

[0070] Wherein, (x′1, y′1) are the coordinates of the sampling point on the plane of the first superlens, (x′2, y′2) are the coordinates of the sampling point on the plane of the second superlens, d is the distance between the first superlens and the second superlens, E2(x′2, y′2, d) is the initial complex amplitude distribution of the inverse diffraction, and R is the distance between the sampling point on the plane of the first superlens and the sampling point on the plane of the second superlens.

[0071] Among them, when When the phase equation φ1x(x, y) is the complex amplitude distribution E 1t The opposite of the phase angle of (x′1, y′1, 0); when When the phase equation φ 1y (x, y) is the complex amplitude distribution E 1t Δx is the off-axis amount of the off-axis phase of the first metalens for x-polarized light and y-polarized light.

[0072] The plane of the first superlens is sampled with the period size of the nanobrick as the coordinate interval, and the coordinates of the center point of each nanobrick (x1, y1) are substituted into the phase equation of the first superlens to calculate the first phase modulation amount φ 1x (x1, y1) and the second phase modulation amount φ 1y (x1, y1); select the nanobrick structure with the phase modulation amount of x polarized light closest to φ from the nanobrick structure library 1x (x1, y1), and the phase modulation amount of the y-polarized light is closest to φ 1y Nanobricks with a diameter of (x1, y1) are arranged at this position to construct the first superlens; the plane of the second superlens is sampled with the period size of the nanopillar as the coordinate interval, and the coordinates of the center point of each nanopillar (x2, y2) are substituted into the phase equation of the second superlens to calculate the third phase modulation amount φ2(x2, y2); the nanopillar with a phase delay closest to φ2(x2, y2) is selected from the nanopillar structure library and arranged at this position to construct the second superlens.

[0073] The present invention is further described below in conjunction with parameters.

[0074] In the design method of the beam scanning system based on the polarization multiplexing superlens group provided by the present invention, physical models of the first superlens and the second superlens are constructed, the center of the nanobrick array of the first superlens is used as the coordinate origin, the directions of the two sides parallel to the working plane of the first substrate of the first superlens are used as the x-axis direction and the y-axis direction, and the direction perpendicular to the working plane of the first substrate of the first superlens and pointing to the second superlens is used as the positive direction of the z-axis to establish a coordinate system, the nanobricks included in the first superlens are a rectangular structure, and the two sides of the bottom surface of the rectangular parallelepiped are parallel to the x-axis and the y-axis, respectively, and the nanocolumns included in the second superlens are cylindrical structures.

[0075] A nanobrick structure library and a nanopillar structure library are constructed through electromagnetic simulation. The nanobricks in the nanobrick structure library have the same height and different major or minor axis sizes. When illuminated by incident light with a wavelength equal to the working wavelength and polarization states of x and y, respectively, a phase modulation amount covering 0 to 2π is achieved. The nanopillars in the nanopillar structure library have the same height and different diameters. When illuminated by incident light with a wavelength equal to the working wavelength, a phase modulation amount covering 0 to 2π is achieved.

[0076] The present invention designs the phase equation φ2(x, y) of the second super lens according to the design indicators and the device parameters of the piezoelectric ceramic. The phase equation of the first super lens needs to meet the following conditions: when the light beam focused by the first super lens propagates to the position of the second super lens, the light wave phase needs to be the opposite of the phase equation of the second super lens, so that the second super lens can modulate the light beam into a parallel light beam for emission. Therefore, the reverse diffraction method is used to design the phase equation φ2(x, y) of the first super lens for linearly polarized light along the x-axis. 1x (x, y), the phase equation for linearly polarized light along the y-axis is φ 1y (x, y), the phase equations of the first super lens and the second super lens are stepped.

[0077] Then, the plane of the first superlens is sampled with the period size of the nanobrick as the coordinate interval, and the coordinates of the center point of each nanobrick (x1, y1) are substituted into the phase equation of the first superlens to calculate the phase modulation amount φ 1x (x1, y1) and φ 1y (x1, y1), select the nanobrick structure whose phase modulation amount for x polarized light is closest to φ from the nanobrick structure library 1x (x1, y1), the phase modulation amount of y-polarized light is closest to φ 1yThe nanobricks of (x1, y1) are arranged at this position; similarly, the plane of the second superlens is sampled with the periodic size of the nanopillars as the coordinate interval, and the coordinates of the center point of each nanopillar (x2, y2) are substituted into the phase equation of the second superlens to calculate the phase modulation amount φ2(x2, y2). The nanopillar with the phase delay closest to φ2(x2, y2) is selected from the nanopillar structure library and arranged at this position.

[0078] For example, at an operating wavelength of 1550 nm, Figure 2 The figure shows the structure of the nanobrick unit. The base material is silicon dioxide, the nanobrick material is silicon, the height H is set to 1820nm, the interval C between the center points of adjacent nanobricks is 500nm, and the periodic boundary conditions are used to perform parametric scanning on the major axis L and minor axis W of the nanobrick. The scanning range is 200-420nm. Figure 3 (a) shows the phase modulation of x-polarized light by nanobricks with different structural parameters. Figure 3 (b) shows the transmittance of x-polarized light by nanobricks with different structural parameters. Figure 3 (c) shows the phase modulation of y-polarized light by nanobricks with different structural parameters. Figure 3 (d) shows the transmittance of nanobricks with different structural parameters for y-polarized light, achieving phase coverage of 0 to 2π for x-polarized light and y-polarized light.

[0079] At the operating wavelength of 1550nm, Figure 4 The figure shows the structure of the nanopillar unit. The substrate material is silicon dioxide, the nanopillar material is silicon, the height H is set to 1260nm, the interval C between the center points of adjacent nanopillars is 500nm, and the diameter D of the nanopillar is parametrically scanned using periodic boundary conditions. The scanning range is 150-420nm. Figure 5 The figure shows the phase modulation amount and transmittance of the incident light by nanopillars with different structural parameters, achieving phase coverage of the incident light from 0 to 2π.

[0080] Figure 7 The phase distribution diagram of the second super lens is shown. The phase equation of the second super lens φ2(x, y) is the phase function The result of phase folding from 0 to 2π is: The calculation formula is as follows:

[0081]

[0082] in,

[0083]

[0084] Wherein, L is the maximum displacement adjustment amount of the displacement adjustment unit, which may be specifically the maximum elongation of the piezoelectric ceramic, λ is the operating wavelength of the incident light, and θ is the maximum angle of the outgoing light beam.

[0085] Figure 6 The phase distribution diagram of the first metalens is shown in FIG. Figure 6 (a) is the phase distribution diagram of the first metalens for x-polarized light, Figure 6 (b) is the phase distribution diagram of the first superlens for y-polarized light.

[0086] The reverse diffraction method used in the design of the phase equation of the first superlens of the present invention is as follows: the planes of the first superlens and the second superlens are sampled, the coordinates of the plane sampling point of the first superlens are (x′1, y′1), the coordinates of the plane sampling point of the second superlens are (x′2, y′2), the distance between the first superlens and the second superlens is d, and the complex amplitude distribution of the light wave incident on the second superlens is known to be The phase of the complex amplitude distribution is negated and used as the initial complex amplitude distribution of reverse diffraction. The complex amplitude distribution E at the position of the first super lens is calculated using the following Rayleigh-Sommerfeld diffraction formula: 1t (x′1,y′1,0):

[0087]

[0088] Among them, when the distance between the sampling point on the first metalens plane and the sampling point on the second metalens plane is When the phase equation φ 1x (x, y) is the complex amplitude distribution E 1t The opposite number of the phase angle of (x′1, y′1, 0); when the sampling point on the first metalens plane is the distance from the sampling point on the second metalens plane to When the phase equation φ 1y (x, y) is the complex amplitude distribution E 1t Δx is the off-axis amount of the off-axis phase of the first metalens to the x-polarized light and the y-polarized light.

[0089] For example, the maximum elongation of the piezoelectric ceramic is L, the resonant frequency of the piezoelectric ceramic is f, the switching frequency of the electro-optical crystal is 2f, and the off-axis amount of the first metalens for x-polarized light and y-polarized light is The center coordinates of the initial position of the second metalens are When the x-polarized parallel beam is incident vertically on the beam scanning device, the working process of the beam scanning device is as follows: During this time, the output voltage of the first voltage source is 0, the electro-optical crystal does not generate polarization modulation, and the elongation of the piezoelectric ceramic changes continuously from 0 to L, so that the center coordinate of the second metalens changes from Continuously change to The output beam angle can be scanned from 0 to θ. During this time, the output voltage of the first voltage source is the half-wave voltage of the electro-optical crystal, and the electro-optical crystal switches the polarization state of the incident light beam to a linear polarization state along the y-axis. At this time, the angle of the outgoing light beam switches from θ to 0, and the elongation of the piezoelectric ceramic changes continuously from L to 0, so that the center coordinate of the second metalens changes from Continuously change to The output beam angle can be scanned from 0 to -θ.

[0090] For example, in order to illustrate the effectiveness of the beam scanning system based on the polarization multiplexing type metalens group, L = 200 μm, θ = 30°, and the metalens group is simulated, as shown in FIG. Figure 8 As shown in FIG, the simulation results of the beam scanning effect of the first superlens and the second superlens are shown. The first superlens is placed at z = 0, and the x-coordinate at the center is 0. The second superlens is placed at z = 1 mm, and the x-coordinate at the center is 100 μm. First, a plane wave with a wavelength of 1550 nm, polarization direction along the x-axis, and propagation direction parallel to the z-axis is incident on the first superlens. The x-coordinate of the center of the second superlens changes from 100 μm to -100 μm. Figure 8 (a), (b), and (c) are the simulation results when the x-coordinate of the center of the second super-lens is 100 μm, 0, and -100 μm, respectively. The angle of the outgoing beam is deflected from 0° to 30°. Then, a plane wave with a wavelength of 1550 nm, polarization direction along the y-axis, and propagation direction parallel to the z-axis is incident on the first super-lens. The x-coordinate of the center of the second super-lens changes from -100 μm to 100 μm. Figure 8 (d), (e), and (f) are the simulation results when the x-coordinates of the center of the second super lens are -100 μm, 0, and 100 μm, respectively, and the angle of the output light beam is deflected from 0° to -30°.

[0091] It can be seen that the beam scanning scheme based on the polarization-multiplexed superlens group provided by the present invention can realize the design of the polarization-multiplexed superlens group. When the electro-optical crystal switches the polarization state of the incident light, it can realize high-speed beam scanning at a large angle and expand the beam scanning angle without sacrificing the scanning frequency.

[0092] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A design method for a beam scanning system based on a polarization multiplexing metalens group, characterized in that: The light beam scanning system based on the polarization multiplexing metalens group includes a polarization adjustment unit, a first metalens, a second metalens and a displacement adjustment unit; the polarization adjustment unit is used to adjust the polarization state of the incident light; the first metalens and the second metalens constitute a polarization multiplexing metalens group, the first metalens is used to generate an off-axis focusing phase symmetrical with respect to the optical axis for vertically incident x-polarized parallel light and y-polarized parallel light, the second metalens is used to generate the same phase modulation for x-polarized light and y-polarized light, and modulate the light beam focused by the first metalens into a parallel light beam before emitting; the displacement adjustment unit is used to adjust the position of the second metalens; under the adjustment action of the polarization adjustment unit and the displacement adjustment unit, the light beam scanning system based on the polarization multiplexing metalens group realizes an output light beam angle of The scanning of the other half scanning cycle realizes the output beam angle of Scan, is the maximum angle of the outgoing light beam; The design method of a beam scanning system based on a polarization multiplexing metalens group includes the following steps: Determining an operating wavelength, a maximum angle of an outgoing light beam, and a maximum displacement adjustment amount of the displacement adjustment unit, designing phase equations of the first superlens and the second superlens, and stepping the phase equations; Obtaining a phase modulation amount based on the stepped phase equation, and constructing the first superlens and the second superlens based on the phase modulation amount; The second superlens is mounted on the displacement adjustment unit, and the polarization adjustment unit, the first superlens, and the second superlens are placed in sequence along the optical path to form a beam scanning system based on a polarization multiplexing superlens group.

2. The design method of the beam scanning system based on the polarization multiplexing type metalens group according to claim 1 is characterized in that: The phase equation of the second metalens is the phase function conduct The result of phase folding is The calculation formula is as follows: in, in, L is the maximum displacement adjustment amount of the displacement adjustment unit, is the operating wavelength, is the maximum angle of the outgoing beam.

3. The design method of a beam scanning system based on a polarization multiplexing metalens assembly according to claim 2, characterized in that: The phase equation of the first superlens satisfies the following condition: when the light beam focused by the first superlens propagates to the second superlens, the phase of the light wave is the inverse of the phase equation of the second superlens; The phase equation of the first metalens for linearly polarized light along the x-axis is designed using the inverse diffraction method. , and the phase equation for linearly polarized light along the y-axis .

4. The design method of the beam scanning system based on the polarization multiplexing type metalens group according to claim 3 is characterized in that: The complex amplitude distribution at the first superlens position is calculated using the following Rayleigh-Sommerfeld diffraction formula: : Where, are the sampling point coordinates on the plane of the first metalens, is the sampling point coordinate on the plane of the second metalens, d is the distance between the first superlens and the second superlens, is the initial complex amplitude distribution of inverse diffraction, is the distance between the sampling point on the plane of the first metalens and the sampling point on the plane of the second metalens; Among them, when When the phase equation is the complex amplitude distribution The opposite of the phase angle; when When the phase equation is the complex amplitude distribution The opposite of the phase angle; is the off-axis amount of the off-axis phase of the first metalens to the x-polarized light and the y-polarized light.

5. The design method of the beam scanning system based on the polarization multiplexing type metalens group according to claim 3 is characterized in that: The first superlens includes a first substrate and a nanobrick array located on the first substrate, and the second superlens includes a second substrate and a nanopillar array located on the second substrate; The nanobrick array includes a plurality of nanobricks with the same height and different major or minor axis sizes, and the nanobrick array achieves a phase modulation amount covering 0 to 2π under incident light with an operating wavelength; the nanopillar array includes a plurality of nanopillars with the same height and different diameters, and the nanopillar array achieves a phase modulation amount covering 0 to 2π under incident light with an operating wavelength; The plane of the first metalens is sampled with the period size of the nanobrick as the coordinate interval, and the coordinate of the center point of each nanobrick is Substitute into the phase equation of the first super lens and calculate the first phase modulation amount and the second phase modulation amount ; Select the nanobrick structure library with the phase modulation amount closest to x-polarized light , and the phase modulation amount of y-polarized light is closest to The nanobricks are arranged at the position to construct the first superlens; The plane of the second super lens is sampled with the period size of the nanocolumn as the coordinate interval, and the coordinate of the center point of each nanocolumn is Substituting into the phase equation of the second metalens, the third phase modulation amount is calculated ; Select the nanopillar structure library with the closest phase delay The nanopillars are arranged at this position to construct the second superlens.

6. The design method of a beam scanning system based on a polarization multiplexing metalens assembly according to claim 5, characterized in that: The first substrate and the second substrate are both made of silicon dioxide, and the nanobrick array and the nanocolumn array are both made of silicon.

7. The design method of a beam scanning system based on a polarization multiplexing metalens assembly according to claim 1, characterized in that: The polarization adjustment unit includes an electro-optical crystal and a first voltage source; the displacement adjustment unit includes a piezoelectric ceramic, a second voltage source and a support platform; The electro-optical crystal is connected to the first voltage source, and the output voltage of the first voltage source switches between the half-wave voltage and zero voltage of the electro-optical crystal, so that the electro-optical crystal generates polarization modulation in half a scanning cycle and does not generate polarization modulation in the other half of the scanning cycle, thereby realizing the switching of the incident light beam between two orthogonal linear polarization states; the piezoelectric ceramic is connected to the second superlens through the support platform, and the piezoelectric ceramic is connected to the second voltage source, and the elongation of the piezoelectric ceramic is adjusted by controlling the output voltage of the second voltage source.

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