Angle insensitive optical filter based on metasurface structure

Abstract

The invention discloses an angle insensitive optical filter based on a metasurface structure. The angle insensitive optical filter comprises a substrate and a multilayer film structure on the surface of the substrate, the multilayer film structure is formed by alternately overlapping silicon dioxide layers and gallium arsenide layers; a groove array is etched on the multilayer film structure, the depth of each groove in the groove array is equal to the total thickness of the multilayer film structure, and the grooves are filled with metal silver. According to the narrow-band optical filter, the function that the central wavelength of the narrow-band optical filter changes extremely in a large-angle incidence range is achieved, and the narrow-band optical filter has important guiding significance on research of optical instruments.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical instruments and relates to an angle-insensitive filter based on a metasurface structure, which can be applied to optical analysis instruments and optical detectors. Background Art

[0002] Narrowband filters have high transmittance in a narrow wavelength range and high cutoff in other wavelength ranges. They are key components of many optical systems and are widely used in optical detection and optical measurement. Traditional thin-film Fabray-Perot narrowband filters and long- and short-wavelength superposition filters are widely used. However, when light is incident at an angle, the center wavelength of the thin-film narrowband filter will move toward the short-wave direction, such as Figure 1 As shown, this limits its scope of application. Summary of the Invention

[0003] The present invention aims to overcome these shortcomings by providing an angle-insensitive filter based on a metasurface structure. This solution addresses the technical issue of existing narrowband filters, where the central wavelength varies with the angle of incidence. This invention achieves minimal variation in the central wavelength of narrowband filters over a wide range of incident angles, providing important insights into the research of optical instruments.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] An angle-insensitive filter based on a metasurface structure comprises: a substrate and a multilayer film structure on the surface of the substrate;

[0006] The multilayer film structure is formed by alternating layers of silicon dioxide and gallium arsenide;

[0007] A groove array is etched on the multilayer film structure. The depth of each groove in the groove array is equal to the total thickness of the multilayer film structure, and the interior of the groove is filled with metallic silver.

[0008] Furthermore, the substrate is a K9 substrate.

[0009] Furthermore, suppose the total number of silicon dioxide layers and gallium arsenide layers in the multilayer film structure is n, and the layers are the 1st, 2nd, ..., nth layers, wherein the 1st layer contacts the substrate, and n>2;

[0010] The first layer and the nth layer are both silicon dioxide layers.

[0011] Furthermore, n is an odd number;

[0012] The thickness of each gallium arsenide layer is equal;

[0013] The thicknesses of the other silicon dioxide layers except the (n+1) / 2th layer are equal;

[0014] The thickness of the (n+1) / 2th silicon dioxide layer is twice the thickness of the other silicon dioxide layers.

[0015] Furthermore, the groove array divides the multilayer film structure into several sub-regions. Let the width of each sub-region be W, and the sum of the widths of a sub-region and an adjacent groove be P.

[0016] Determine the values ​​of W and P based on the center wavelength of the filter.

[0017] Furthermore, the larger the center wavelength of the filter, when the P value is constant, the larger the W value is, and the narrower the groove is.

[0018] Furthermore, when the central wavelength of the incident light is 970 nm, n = 13;

[0019] The thickness of each GaAs layer is 81 nm;

[0020] The thickness of the seventh silicon dioxide layer is 383 nm, and the thickness of the remaining silicon dioxide layers is 191.5 nm.

[0021] Furthermore, when the central wavelength of the incident light is 970 nm, W=600 nm, and P=750 nm.

[0022] Furthermore, when the central wavelength of the incident light is 1050 nm, n = 13;

[0023] The thickness of each gallium arsenide layer is 87.5 nm;

[0024] The thickness of the seventh silicon dioxide layer is 413 nm, and the thickness of the remaining silicon dioxide layers is 206.5 nm;

[0025] W=655nm, P=750nm.

[0026] Furthermore, when light with a central wavelength of 970 nm enters the filter at an incident angle of 0° to 60°, the central wavelength of the filter shifts by ±0.12 nm.

[0027] Furthermore, the method for determining the multilayer film structure includes:

[0028] The initial thickness and number of film layers in the multilayer film structure are determined based on the target central wavelength and half-width of the passband of the incident light. The product of the initial thickness of each film layer except the (n+1) / 2th layer and the refractive index of the layer is equal to one-quarter of the central wavelength. The narrower the half-width of the passband, the more film layers there are.

[0029] Then the groove width is changed to further adjust the precise position of the filter center wavelength;

[0030] When changing the groove width cannot change the position of the filter's central wavelength, the thickness and number of each film layer in the multilayer film structure are adjusted to make the central wavelength reach the target central wavelength position.

[0031] The present invention realizes the central wavelength drift of the narrow-band filter with a central wavelength of 970nm within the incident angle range of 0° to 60° by ±0.12nm, and realizes the function of minimal change of the central wavelength of the narrow-band filter within the large incident angle range.

[0032] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0033] (1) The present invention creatively proposes an angle-insensitive filter with a surface superstructure, which greatly reduces the dependence of the center wavelength of traditional narrow-band filters on the incident angle and improves the integration and system performance of the optical system.

[0034] (2) The narrow-band filter with a central wavelength of 970 nm of the present invention has an excellent performance with a central wavelength drift of ±0.12 nm within the incident angle range of 0° to 60°.

[0035] (3) The present invention uses conventional thin film materials and a film system design to achieve an angle-insensitive effect, with low cost and strong process applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the angular characteristics of a thin-film narrow-band filter;

[0037] Figure 2 Schematic diagram of the metasurface structure of the present invention, where (a) is an overall schematic diagram and (b) is a schematic diagram of the multilayer structure;

[0038] Figure 3 The present invention designs the transmittance spectrum of the narrowband filter when the incident angle is 0° to 40°;

[0039] Figure 4 The present invention designs the transmittance spectrum of the narrowband filter when the incident angle is 40° to 60°;

[0040] Figure 5 The present invention designs the change of the central wavelength of the narrowband filter with the W value. DETAILED DESCRIPTION

[0041] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0042] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0043] Compared with traditional thin film structures, three-dimensional structures based on metasurface design have extremely strong light manipulation capabilities. The present invention provides a filter that is insensitive to the angle of incidence. In a specific embodiment, the filter of the present invention includes a multilayer film structure composed of a K9 substrate and a certain thickness of silicon dioxide and gallium arsenide alternately stacked. The initial center wavelength and passband half-width parameters of the narrowband filter are determined by adjusting the film thickness and the number of film layers. The initial value of the film optical thickness is one-quarter of the center wavelength. The narrower the half-width, the more film layers there are. Changing the groove width (PW) further adjusts the precise position of the filter center wavelength. In a specific embodiment, the first layer is connected to the K9 substrate, and the 13th layer is in contact with the incident air. The structural parameters are shown in Table 1.

[0044] In a specific embodiment, grooves with a certain interval are etched on the multilayer film, and the grooves are filled with metallic silver. Figure 2 As shown, W = 600nm, P = 750nm, as Figure 5 By adjusting the values ​​of W and P, the central wavelength can be adjusted.

[0045] Table 1. Structural parameters of the multilayer film portion of the metasurface structure with a central wavelength of 970 nm.

[0046]

[0047] The materials of the present invention can be selected based on actual conditions. In the present invention, thin film materials SiO2 and GaAs are selected, and the incident medium is air with a refractive index of n = 1.0. SiO2 and GaAs film layers are alternately deposited according to the parameters and sequence shown in Table 1. After the deposition is completed, a narrow slit array with a width of 150nm is etched on the surface of the component using a semiconductor etching process. Then, metallic silver is evaporated to fill the narrow slit array. The grooves on both sides of the multilayer film stack form reflection wells, making the structure insensitive to the angle of incidence.

[0048] The present invention overcomes the disadvantage of existing thin film narrow band filters that the central wavelength changes with the incident angle. Figure 3 and Figure 4 The central wavelength of the narrow-band filter with a central wavelength of 970nm of the present invention drifts by ±0.12nm within the incident angle range of 0° to 60°, which greatly reduces the dependence of the central wavelength of the traditional narrow-band filter on the incident angle and improves the integration and system performance of the optical system.

[0049] By varying the thickness of the multilayer film and the width of the etched grooves in the metasurface structure of the present invention, angle-insensitive filters with varying center wavelengths can be obtained. Table 2 shows the parameters of the multilayer film portion of the metasurface structure with a center wavelength of 1050nm, where W = 655nm and P = 750nm. The center wavelength of the narrowband filter of the present invention with a center wavelength of 1050nm drifts by ±0.45nm within an incident angle range of 0° to 60°.

[0050] Table 2. Structural parameters of the multilayer film portion of the metasurface structure with a central wavelength of 1050 nm.

[0051]

[0052] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

[0053] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. An angle-insensitive filter based on a metasurface structure, characterized in that: include: a substrate and a multilayer film structure on the substrate surface; The multilayer film structure is formed by alternating layers of silicon dioxide and gallium arsenide; A groove array is etched on the multilayer film structure. The depth of each groove in the groove array is equal to the total thickness of the multilayer film structure, and the interior of the groove is filled with metallic silver.

2. The angle-insensitive filter based on a metasurface structure according to claim 1, characterized in that: The base is K9 base.

3. The angle-insensitive filter based on a metasurface structure according to claim 1, characterized in that: Assume that the total number of silicon dioxide layers and gallium arsenide layers in the multilayer film structure is n, and each layer is the 1st, 2nd, ..., nth layer, where the 1st layer is in contact with the substrate, and n>2; The first layer and the nth layer are both silicon dioxide layers.

4. The angle-insensitive filter based on a metasurface structure according to claim 3, characterized in that: n is an odd number; The thickness of each gallium arsenide layer is equal; The thicknesses of the other silicon dioxide layers except the (n+1) / 2th layer are equal; The thickness of the (n+1) / 2th silicon dioxide layer is twice the thickness of the other silicon dioxide layers.

5. The angle-insensitive filter based on a metasurface structure according to claim 4, characterized in that: The groove array divides the multilayer film structure into several sub-regions. Let the width of each sub-region be W, and the sum of the width of a sub-region and an adjacent groove be P. Determine the values ​​of W and P based on the center wavelength of the filter.

6. The angle-insensitive filter based on a metasurface structure according to claim 5, characterized in that: The larger the center wavelength of the filter, when the P value is constant, the larger the W value is and the narrower the groove is.

7. The angle-insensitive filter based on a metasurface structure according to claim 5, characterized in that: When the central wavelength of the incident light is 970 nm, n = 13; The thickness of each GaAs layer is 81 nm; The thickness of the seventh silicon dioxide layer is 383 nm, and the thickness of the remaining silicon dioxide layers is 191.5 nm; W=600nm, P=750nm.

8. The angle-insensitive filter based on a metasurface structure according to claim 5, characterized in that: When the central wavelength of the incident light is 1050 nm, n = 13; The thickness of each gallium arsenide layer is 87.5 nm; The thickness of the seventh silicon dioxide layer is 413 nm, and the thickness of the remaining silicon dioxide layers is 206.5 nm; W=655nm, P=750nm.

9. The angle-insensitive filter based on a metasurface structure according to claim 5, characterized in that: When light with a central wavelength of 970nm enters the filter at an incident angle of 0° to 60°, the central wavelength of the filter drifts by ±0.12nm.

10. The angle-insensitive filter based on a metasurface structure according to claim 4, characterized in that: Methods for determining multilayer film structures include: The initial thickness and number of film layers in the multilayer film structure are determined based on the target central wavelength and half-width of the passband of the incident light. The product of the initial thickness of each film layer except the (n+1) / 2th layer and the refractive index of the layer is equal to one-quarter of the central wavelength. The narrower the half-width of the passband, the more film layers there are. Then the groove width is changed to further adjust the precise position of the filter center wavelength; When changing the groove width cannot change the position of the filter's central wavelength, the thickness and number of each film layer in the multilayer film structure are adjusted to make the central wavelength reach the target central wavelength position.

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