A phase-compensated large-field-angle metalens and its design method

Abstract

The present invention belongs to the field of optical technology, specifically a phase-compensated large-field-of-view metalens and its design method, suitable for focal plane array imaging systems. The metalens provided by the present invention targets the specific large-angle conical light field in the focal plane array imaging system, adopts the phase compensation design principle, introduces a concave metalens phase to compensate the phase of the incident conical light field, thereby converting the incident light field into parallel light, and then focuses the light field into the focal plane array photosensitive pixel through an equivalent convex metalens; thereby solving the problem of the small angle of incident light collection by the microlens, improving the detection efficiency of the focal plane array imaging system, and providing an effective solution to the field-of-view angle problem faced by existing microlens arrays.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and specifically relates to a phase-compensated large-field-angle metalens and a design method thereof, which are suitable for focal plane array imaging systems. Background Art

[0002] Infrared focal plane array detectors have the advantages of high resolution, strong anti-electromagnetic interference ability, and all-weather operation. They can be applied to scenarios such as remote sensing and telemetry, autonomous driving, and virtual reality. As focal plane arrays develop towards high efficiency, high integration, high speed, intelligence, and miniaturization, the photosensitive pixel area of ​​the focal plane array is getting smaller and smaller. In order to ensure the collection efficiency of the focal plane array for incident light, it is necessary to integrate a microlens array on the focal plane array to ensure that the incident light can be effectively focused within the photosensitive pixel area. However, the existing microlens arrays mainly use refractive semicircular lenses, which have the problem of a small collection angle for incident light. When the angle of the incident light is large, the focus of the microlens will deviate outside the photosensitive pixel area, seriously limiting the detection efficiency of the focal plane array.

[0003] In recent years, with the development of metasurface technology, metalenses have gained a high degree of design freedom. Based on a specific incident light field, metalenses can be designed to combine a large field of view with high focusing efficiency. They are also compact and easy to integrate. Metalenses based on two-dimensional subwavelength structures have been widely studied, such as broadband achromatic metalenses and large-field-of-view metalenses. Existing large-field-of-view metalenses use apertures to limit the angle range of the incident light, but still have low utilization of the incident light, low focusing efficiency and resolution, and low detection efficiency. Summary of the Invention

[0004] In response to the above-mentioned problems or shortcomings, and to solve the problem that the existing microlens array has a small collection angle of incident light, resulting in low detection efficiency of the focal plane array, the present invention provides a large field of view angle metalens and a design method thereof, which can be applied to the focal plane array imaging system.

[0005] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0006] A phase-compensated large-field-angle metalens consists of a transparent substrate and a subwavelength micro-nanostructure.

[0007] The transparent substrate is used to transmit incident light and supports the sub-wavelength micro-nano structure arranged on one side of the transparent substrate.

[0008] The subwavelength micro-nanostructure is an M×M square matrix composed of n types of nano-dielectric columns, where n is 2, 4, 8 or 16; for the M×M square matrix composed of nano-dielectric columns, the side length of the matrix is ​​D, and the side length of each matrix unit (the square base of the nano-dielectric column) is P, and P×M=D.

[0009] The nano-dielectric column is a cylinder with a height of H and a radius of R. By changing the radius R of the nano-dielectric column, n types of nano-dielectric columns are obtained to realize the control of the transmission phase. After being arranged in an M×M square matrix, the transmission phases of the selected n types of nano-dielectric columns cover 0 to 2π, and at the same time meet the requirements of being insensitive to the size of the incident angle and the polarization of the incident light. It is used to perform phase control on the incident large-angle conical light beam, meet the phase distribution of the phase compensation super lens, and realize focus without focus offset.

[0010] According to the generalized Snell's law The refraction angle θ r The incident angle θ can be obtained by After substituting it into the differential equation, the phase distribution formula of the phase compensation superlens of each nano-dielectric column can be obtained:

[0011]

[0012] The surface of the metalens is taken as the xOy plane, its center point is the coordinate origin, and x and y are the coordinate positions. is the transmission phase that the nanocolumns at different positions need to satisfy, λ is the wavelength of the incident light, the first term of the formula is the equivalent convex superlens phase distribution, f is the focal length of the equivalent convex superlens, the second term of the formula is the phase distribution of the equivalent concave superlens, f1 is the negative focal length of the equivalent concave superlens, and r is the distance from the center of the nanocolumn to the coordinate origin

[0013] When the incident light cone angle is θ and the side length of a single metalens is D, the negative focal length f1 of the equivalent concave metalens is The incident light cone angle θ is calculated based on the aperture and focal length of the imaging lens. The equivalent concave metalens can compensate for the additional phase shift introduced by the incident light field, thereby achieving equivalent parallel light incidence. The focal length of the equivalent convex metalens is equal to the distance from the metalens to the photosensitive pixel (the actual working distance), aiming to focus equivalent parallel light onto the photosensitive pixel area.

[0014] Furthermore, the material of the nano-dielectric column is silicon nitride, titanium dioxide, amorphous silicon, silicon or gallium nitride.

[0015] Furthermore, the transparent substrate is a visible light, near infrared, mid-to-far infrared transparent substrate, and is made of a material with a transmittance greater than 95% in the infrared band, such as silicon dioxide, aluminum oxide, magnesium fluoride, barium fluoride, calcium fluoride, zinc sulfide or zinc selenide.

[0016] Furthermore, an anti-reflection film is provided on the side of the transparent substrate without the micro-nano structure to reduce reflection, and the coating material is magnesium fluoride or calcium fluoride.

[0017] Furthermore, the phase-compensated large-field-of-view metalenses are arranged into an array as a metalense array of a focal plane array imaging system, which better focuses the incident light on the photosensitive pixel area, thereby improving the detection efficiency of the focal plane array.

[0018] The design method of the phase-compensated large-field-angle metalens comprises the following steps:

[0019] Step 1: Calculate the incident light cone angle θ based on the clear aperture and focal length of the imaging lens in the focal plane array imaging system.

[0020] Step 2: Based on the incident light cone angle θ calculated in step 1 and the side length D of the single metalens to be designed, according to the formula: The negative focal length of the required equivalent concave metalens is calculated.

[0021] Step 3: Determine the focal length of the required equivalent convex metalens based on the distance between the metalens and the photosensitive pixel in the focal plane array imaging system.

[0022] Step 4: Use electromagnetic simulation software to calculate the transmittance and transmission phase of nano-dielectric columns of different sizes. When selecting the size of the nano-dielectric column, the transmittance is greater than 90%, and the transmission phase of the nano-dielectric column of different sizes covers 0 to 2π.

[0023] Step 5: Based on the focal length determined in steps 2 and 3, the phase distribution of the target superlens and the arrangement of the nano-dielectric columns are obtained using the phase compensation superlens phase distribution formula.

[0024]

[0025] In summary, the metalens provided by the present invention adopts a phase compensation design principle for the specific large-angle conical light field in the focal plane array imaging system. By introducing a concave metalens phase to compensate the phase of the incident conical light field, the incident light field is equivalent to parallel light incidence, and then the light field is focused into the focal plane array photosensitive pixel through an equivalent convex metalens; thereby solving the problem of the small collection angle of the incident light by the microlens, improving the detection efficiency of the focal plane array imaging system, and providing an effective solution to the field of view angle problem faced by existing microlens arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the focal plane array imaging system.

[0027] Figure 2 (a) is a diagram of the unit cell structure of the embodiment design, and (b) is a schematic diagram of the overall structure of the metalens.

[0028] Figure 3This is a distribution diagram of the transmittance and transmission phase of the nano-dielectric column at a wavelength of 1064nm as a function of the nano-column radius.

[0029] Figure 4 3 is a fitting diagram of the radial phase distribution function of the embodiment metalens at a wavelength of 1064nm.

[0030] Figure 5 2 is a structural diagram and focusing diagram of the embodiment metalens.

[0031] Figure 6 The theoretical focusing performance analysis diagram of the implemented super lens array. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] This embodiment provides a large field-of-view metalens array for phase compensation in a focal plane array imaging system.

[0034] like Figure 1 As shown, in the focal plane array imaging system, parallel incident light becomes a cone-shaped light beam when it passes through the imaging lens and enters the surface of the metalens array. The metalens array needs to effectively focus each cone-shaped light beam into the photosensitive pixel of the focal plane array.

[0035] Figure 2 (a) is a diagram of the unit cell structure designed in this embodiment, and (b) is a schematic diagram of the overall structure of a single metalens; in the figure, H is the height of the nanodielectric pillar, R is the radius of the nanodielectric pillar, and P is the structural period, that is, the side length of each nanodielectric pillar corresponding to the square structural period base on the transparent substrate.

[0036] The dimensions of a single large-field superlens in this embodiment are: D = 100 μm, H = 800 nm, P = 500 nm, and the radius R is between 80 nm and 146 nm. The transmittance and transmission phase of nanopillars with different radius sizes are shown in Figure 2. Figure 3 shown.

[0037] In this embodiment, eight basic units were selected to achieve a phase variation of 0 to 2π, while all exhibiting transmittances greater than 92%. The target metalens phase distribution was obtained by assuming a convex metalens focal length of f = 100 μm and a concave metalens negative focal length of f1 = 208.26 μm. Based on the target phase distribution, the nanopillars were arranged to match the desired phase distribution, yielding the final large-field-of-view metalens.

[0038] Figure 4 This is the fitting diagram of the radial phase distribution function of the metalens at a wavelength of 1064nm. It can be seen that 8 structural units meet the required phase distribution, and there is no need to select 16 different structural units. Figure 5(a) is a structural diagram of the large field-of-view metalens array of this embodiment under a microscope, (b) is a structural diagram of a single metalens under a microscope, (c) is the focusing condition of the metalens array under the incidence of parallel light with a wavelength of 1064nm, and the focusing effect is obvious, (d) is the focusing condition of the metalens array under the incidence of large-angle light with a wavelength of 1064nm, and it can still maintain a high focusing ability under large-angle light.

[0039] like Figure 6 As shown in Figure 3, the theoretical focusing performance analysis of the metalens array in this embodiment is performed, with the metalens surface as the xOy plane, the center of the metalens as the coordinate origin, and the normal direction of the metalens as the z direction. The incident light cone angle is ±20°. (a), (b), and (c) are the xy plane focused light intensity distribution and xz plane focused light intensity distribution of the device at a wavelength of 1064nm, as well as the one-dimensional point spread function in the x-axis direction. (d) is the one-dimensional distribution profile of the light intensity at the dotted line in Figure (b). The calculation results show that the focusing efficiency of the device can reach 84.54%, the focal spot diameter is 8μm, and the focal length is 100μm.

[0040] It can be seen from the above embodiments that the metalens provided by the present invention adopts a phase compensation design principle for the specific large-angle conical light field in the focal plane array imaging system. By introducing a concave metalens phase to compensate the phase of the incident conical light field, the incident light field is equivalent to parallel light incidence, and then the light field is focused into the focal plane array photosensitive pixel through an equivalent convex metalens; thereby solving the problem of the small collection angle of the incident light by the microlens, improving the detection efficiency of the focal plane array imaging system, and providing an effective solution to the field of view angle problem faced by existing microlens arrays.

Claims

1. A phase-compensated metalens with a large field of view, characterized by: It consists of a transparent substrate and sub-wavelength micro-nanostructure; The transparent substrate is used to transmit incident light and support the sub-wavelength micro-nano structure provided on one side of the transparent substrate; The subwavelength micro-nano structure is an M×M square matrix composed of n types of nano-dielectric pillars, where n is 2, 4, 8 or 16; for the M×M square matrix composed of nano-dielectric pillars, the side length of the matrix is ​​D, the side length of each matrix unit is P, and P×M=D; The nano-dielectric column is a cylinder with a height of H and a radius of R. By changing the radius R of the nano-dielectric column, n types of nano-dielectric columns are obtained. After being arranged in an M×M square matrix, the transmission phase of the selected n types of nano-dielectric columns covers 0 to 2π, and at the same time meets the requirements of being insensitive to the magnitude of the incident angle and the polarization of the incident light. It is used to control the phase of the incident large-angle conical light beam, meet the phase distribution of the phase compensation super lens, and achieve focus without focus offset. Phase distribution formula of the phase compensation superlens of each nano-dielectric column: The surface of the metalens is taken as the xOy plane, its center point is the coordinate origin, and x and y are the coordinate positions. is the transmission phase that the nanopillars at different positions need to satisfy, λ is the wavelength of the incident light, the first term of the formula is the equivalent convex metalens phase distribution, f is the focal length of the equivalent convex metalens, the second term of the formula is the equivalent concave metalens phase distribution, f1 is the negative focal length of the equivalent concave metalens; The negative focal length f1 of the equivalent concave metalens is The incident light cone angle θ is calculated based on the aperture and focal length of the imaging lens, and then combined with the side length D of the single metalens to be designed to compensate for the phase of the incident light field and obtain equivalent parallel light incidence; the focal length of the equivalent convex metalens is equal to the distance from the metalens to the photosensitive pixel.

2. The phase-compensated, wide-angle metalens according to claim 1, wherein: The material of the nano-medium column is silicon nitride, titanium dioxide, amorphous silicon, silicon or gallium nitride.

3. The phase-compensated, wide-angle metalens according to claim 1, wherein: The transparent substrate is a visible light, near infrared, mid-infrared and far infrared transparent substrate, and its transmittance in the infrared band is greater than 95%.

4. The phase-compensated, wide-angle metalens according to claim 3, wherein: The material of the transparent substrate is silicon dioxide, aluminum oxide, magnesium fluoride, barium fluoride, calcium fluoride, zinc sulfide or zinc selenide.

5. The phase-compensated, wide-angle metalens according to claim 1, wherein: An anti-reflection film is provided on the side of the transparent substrate without microstructure.

6. The phase-compensated, wide-angle metalens according to claim 5, wherein: The material of the anti-reflection film is magnesium fluoride or calcium fluoride.

7. The phase-compensated, wide-angle metalens according to claim 1, wherein: The phase-compensated large-field-angle metalenses are arranged in an array as a metalense array of a focal plane array imaging system to focus the incident light into the photosensitive pixel area.

8. The method for designing a phase-compensated large-angle metalens according to claim 1, wherein: The following steps are involved: Step 1: Calculate the incident light cone angle θ based on the aperture and focal length of the imaging lens in the focal plane array imaging system; Step 2: Based on the incident light cone angle θ calculated in step 1 and the side length D of the single metalens to be designed, the formula Calculate the negative focal length of the required equivalent concave metalens; Step 3: Determine the focal length of the required equivalent convex metalens based on the distance between the metalens and the photosensitive pixel in the focal plane array imaging system; Step 4: Use electromagnetic simulation software to calculate the transmittance and transmission phase of nano-dielectric columns of different sizes. The size of the nano-dielectric columns is selected so that the transmittance is greater than 90% and the transmission phase of the nano-dielectric columns of different sizes covers 0 to 2π. Step 5: Based on the focal length determined in steps 2 and 3, the phase distribution of the target superlens and the arrangement of the nano-dielectric columns are obtained using the phase compensation superlens phase distribution formula;

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