Long-wave infrared chromatic dispersion suppression narrow-band polarization super-structure surface and preparation method thereof

Abstract

This invention discloses a narrowband polarization metasurface for suppressing long-wave infrared angular dispersion and its fabrication method, relating to the field of optical component technology. Addressing the problems of difficult fabrication and strong angular dispersion inherent in existing polarizers, the metasurface of this invention comprises a barium fluoride substrate and a double-layer composite grating structure disposed on its surface. The composite grating includes a bottom arsenic selenide grating and a top metal layer. By limiting the period of the composite grating to 5.5-6.25 micrometers and the width of a single double-layer grating structure to 4.5-5.5 micrometers, the downward-leaking guided modes and Fabry-Perot cavity modes within the structure undergo strong compression in momentum space, resulting in band folding and anti-crossing flat-band effects. This invention not only relaxes the feature size to the micrometer level, significantly reducing fabrication difficulty, but also fundamentally suppresses the strong angular dispersion of plasmon resonance in narrowband, achieving a high polarization extinction ratio under large angle tolerance and greatly reducing the collimation requirements of practical optical paths.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics technology, and more specifically, to a narrow-band polarized metasurface for suppressing long-wave infrared spectral dispersion and its preparation method. Background Technology

[0002] Polarizers, as core components in optical imaging and sensing systems, play a crucial role in fields such as infrared imaging and gas detection. Currently, mainstream long-wave infrared polarizers are primarily based on the principle of diffraction. Specifically, parallel metal gratings are typically fabricated on an infrared-transparent substrate. The long-wave infrared transmittance and polarization extinction ratio of these gratings are highly dependent on the period and characteristic size of the metal gratings. Generally, to achieve both high extinction ratio and high transmittance simultaneously, the characteristic size of these metal gratings must be designed to be much smaller than the wavelength of their operating band; currently, the mainstream characteristic size is approximately 200 nanometers. At this extreme subwavelength scale, when the polarization direction of the incident light is perpendicular to the metal grating, because the wavelength of the light is much larger than the characteristic size of the grating, the light energy can pass through the metal grating through the diffraction effect, thus achieving high transmittance. However, when the polarization direction of the incident light is parallel to the metal grating, the incident light will undergo plasmon resonance with the surface metal structure, causing most of the light energy of this polarization state to be lost or dissipated. This is the conventional technical route for achieving high polarization extinction ratios based on the principle of diffraction.

[0003] However, the aforementioned conventional techniques have significant drawbacks in practical applications: because the feature size of the metal wire grid is much smaller than the working wavelength, polarizers based on pure diffraction inevitably exhibit "low-pass filter" characteristics in their spectral transmittance. Furthermore, as the size of the metal wire grid increases, its polarization extinction ratio gradually decreases. On the one hand, maintaining high performance requires extremely small feature sizes (e.g., around 200 nanometers), which significantly increases the difficulty of fabricating the corresponding polarizers; on the other hand, their inherent broadband low-pass characteristics are insufficient to meet the application requirements in specific wavelength bands (e.g., infrared gas detection applications that are extremely sensitive to specific target absorption lines).

[0004] To reduce the fabrication difficulty of traditional polarization gratings and improve device performance, several improvements have emerged in existing technologies. For example, Chinese patent application CN106950635A discloses a double-layer grating polarizer for the long-wave infrared band. This technology proposes over-etching the dielectric substrate layer under the subwavelength metal grating line to form a composite structure of metal / dielectric double-layer material in the grating region, simplifying the grating fabrication process. Another example is US patent US10809426B2, which discloses "WIDEBAND RESONANT REFLECTORS WITH ZERO-CONTRAST GRATINGS". However, while these two existing technologies improve the structure or reflection characteristics to some extent, they are essentially still based on the requirements of wideband infrared polarization or resonance, and still fail to overcome the wideband low-pass filtering characteristics of traditional devices, thus failing to meet the practical engineering requirements of narrowband polarization filtering at specific target wavelengths.

[0005] Furthermore, to meet the demands of narrowband applications, when the feature size of micro / nano structures gradually increases to be close to the operating wavelength, the structure can interact with incident light to form subwavelength resonance. This subwavelength resonance often exhibits excellent narrowband characteristics. For polarizers, introducing high-loss metallic materials is indispensable for efficiently dissipating light energy in specific polarization directions. However, for this type of metal plasmon microstructure based on subwavelength dimensions, the plasmon resonance mode generated by the internal metal inevitably exhibits extremely strong angle dispersion characteristics. Specifically, when the angle of the incident light changes slightly, its resonant wavelength (i.e., the narrowband filter channel) will drift drastically. Currently, some research is attempting to solve this angle-sensitive problem, such as the World Intellectual Property Organization patent application with international publication number WO2019136166A1, which discloses an “ANGLE-DEPENDENT OR POLARIZATION-DEPENDENT METASURFACES WITH WIDE FIELD OF VIEW”. This technology attempts to improve angle dependence in large field-of-view conditions through the complex design of metasurfaces. However, for narrowband metallic plasmon filters in the long-wave infrared band, this approach fails to fundamentally solve the inherent problem of strong angular dispersion when resonant modes interact with light. It remains difficult to simultaneously achieve high polarization extinction ratios, extremely narrowband resonance, and extremely low optical path collimation requirements while significantly reducing the difficulty of micro / nano fabrication. This strong angular dispersion characteristic greatly increases the collimation requirements of narrowband devices in practical optical systems; even slight alignment deviations can lead to device failure, severely limiting their practical application.

[0006] Given the technical shortcomings of the existing technologies, such as high processing difficulty, low-pass filtering characteristics that cannot meet the requirements of narrowband applications, and strong angular dispersion of existing narrowband plasmon microstructures that makes the actual optical path collimation requirements extremely demanding, there is an urgent need for a new type of long-wave infrared polarization metasurface that can simultaneously achieve low fabrication difficulty, narrowband filtering characteristics, and extremely low angular dispersion to significantly reduce the difficulty of optical path collimation. Summary of the Invention

[0007] One of the technical problems to be solved by the present invention is to provide a narrow-band polarization metasurface for suppressing long-wave infrared angular dispersion, so as to solve the technical problems in the prior art where the feature size of infrared polarization devices is extremely small, resulting in difficult processing, the broadband low-pass characteristics are difficult to meet the narrow-band filtering requirements, and the strong angular dispersion of narrow-band plasmonic devices leads to stringent requirements for actual optical path collimation.

[0008] To overcome the shortcomings of the prior art, the present invention provides a long-wave infrared angular dispersion suppression narrow-band polarization metasurface, comprising: a barium fluoride substrate, and a composite grating structure disposed on the surface of the barium fluoride substrate;

[0009] The composite grating structure is a double-layer grating structure, which includes an arsenic selenide grating at the bottom and a metal layer at the top of the arsenic selenide grating.

[0010] The period of the composite grating structure is 5.5-6.25 micrometers, the width of a single double-layer grating structure is 4.5-5.5 micrometers, and the height of the arsenic selenide grating is 4.5-5.5 micrometers.

[0011] Compared with existing technologies, the long-wave infrared spectral dispersion suppression narrowband polarization metasurface of this invention has the following advantages: This invention transforms the broadband diffraction mechanism relying on extremely small feature sizes to achieve polarization in existing technologies into a narrowband subwavelength resonance mechanism based on micrometer-scale dimensions. The 4.5-5.5 micrometer width of a single grating and the 4.5-5.5 micrometer height of the arsenic selenide grating synergistically establish the reference resonance position of the device in the long-wave infrared band and provide sufficient longitudinal waveguide space. The increased feature size significantly reduces the overall micro / nano fabrication difficulty. Furthermore, the barium fluoride substrate, in conjunction with the arsenic selenide grating with a metal layer, excites downward-leaking first-order... The first guided mode and the second Fabry-Perot cavity mode resonating between adjacent gratings, within a periodic range of 5.5-6.25 micrometers, can independently adjust the position of the second Fabry-Perot cavity mode, causing a strong energy interaction between the first guided mode and the second Fabry-Perot cavity mode. The mode within the above-mentioned range can induce band folding and anti-crossing effects, causing the two bands to squeeze each other and exhibit an anti-crossing flat band state in momentum space. This flat band mechanism effectively suppresses the inherent wave dispersion characteristics of subwavelength metal structures, ensuring that the target narrowband resonant wavelength does not drift significantly under oblique incidence conditions, thus reducing the difficulty of optical path collimation in optical system integration.

[0012] In one possible implementation, the period of the composite grating structure is 5.60-5.70 micrometers.

[0013] Compared with the prior art, in this embodiment, by using a periodic condition of 5.60-5.70 micrometers, the energy exchange between the first guided mode and the second Fabry-Perot cavity mode enters a balanced coupling range, the mutual squeezing effect of the two energy bands is further enhanced, and a smoother anti-crossing state is formed in the momentum space. This reduces the resonant wavelength drift that is easily caused by oblique incidence of micro-nano structures, reduces the sensitivity of the polarizer to the collimation angle of the optical path, and improves the working stability of the optical system in actual use environment.

[0014] In one possible implementation, the period of the composite grating structure is 5.65 micrometers, the width of a single double-layer grating structure in the composite grating structure is 5.05 micrometers, and the height of the arsenic selenide grating is 5 micrometers.

[0015] Compared with the prior art, in this embodiment, by limiting the period to 5.65 micrometers, the width to 5.05 micrometers, and the height to 5 micrometers, the resonant cavity length of the Fabry-Perot cavity and the spatial distribution of the guided modes achieve a high physical matching state, while the energy exchange between modes reaches a critical state. The energy band of the second Fabry-Perot cavity mode is approximately a straight line, which minimizes the polarization of the device and ensures that the metasurface can still maintain a high polarization extinction ratio and extremely stable narrowband infrared transmittance under a wide range of oblique incidence conditions of 0-15 degrees.

[0016] In one possible implementation, the metal layer is a chromium metal layer with a thickness of 50-80 nanometers.

[0017] Compared with existing technologies, chromium metal possesses the required high optical loss characteristics. With a chromium metal layer thickness of 50-80 nanometers, when the polarization direction of the incident light is parallel to the grating, the metal layer in the 50-80 nanometer thickness range can generate strong surface plasmon resonance with the incident light, efficiently absorbing and dissipating the light energy of a specific polarization state. This avoids the additional blocking loss caused by excessive thickness to vertically polarized transmitted light, ensuring the excellent anisotropic polarization filtering performance of the metasurface, and playing a reliable hard mask protection role in micro-nano etching processes.

[0018] In one possible implementation, the thickness of the chromium metal layer is 65 nanometers.

[0019] Compared with existing technologies, 65-nanometer chromium metal can absorb energy parallel to the direction of the metal grating to the maximum extent, while reducing the transmission loss of the orthogonal polarization state to an extremely low level. This enables the metasurface to achieve a transmittance of more than 75% and a polarization extinction ratio of more than 30 dB at the infrared working wavelength, thereby improving the signal-to-noise ratio of signal extraction in infrared sensing and gas detection applications.

[0020] Another technical problem to be solved by the present invention is to provide a method for preparing a narrow-band polarized metasurface for suppressing long-wave infrared angular dispersion, so as to solve the technical problems in the prior art where the feature size of infrared polarization devices is extremely small, resulting in complicated micro-nano fabrication processes, extremely high alignment accuracy requirements, and low fabrication yield.

[0021] To overcome the shortcomings of the prior art, this invention provides a method for preparing a narrow-band polarized metasurface with long-wave infrared angular dispersion suppression, used to prepare the aforementioned narrow-band polarized metasurface with long-wave infrared angular dispersion suppression. The preparation method includes the following steps:

[0022] S1: Deposit a thin film of arsenic selenide on the cleaned barium fluoride substrate;

[0023] S2: Spin-coat photoresist onto a barium fluoride substrate with the arsenic selenide thin film, and perform photolithography exposure and development to obtain a pattern;

[0024] S3: Deposit metal onto the developed pattern surface to form a hard mask;

[0025] S4: Remove excess photoresist with a solution, retaining the hard mask;

[0026] S5: Using the hard mask as a shield, plasma etching is performed to obtain a composite grating structure containing the arsenic selenide grating and the metal layer.

[0027] Compared with existing technologies, the method for fabricating a narrow-band polarized metasurface with long-wave infrared dispersion suppression according to the present invention has the following advantages: The fabrication method of the present invention changes the highly difficult patterning transfer process for extremely small nanoscale feature sizes in existing technologies to a standard micro-nano fabrication process for micrometer-level subwavelength sizes. After sequentially completing arsenic selenide deposition, photolithography, and metal deposition on a barium fluoride substrate, the retained metal pattern serves as a hard mask to protect the underlying thick arsenic selenide layer during the plasma etching step, and directly serves as an optical loss layer to induce plasmon resonance in the final composite device; the design that integrates the mask and the optical functional layer eliminates the need for... The additional mask stripping and secondary coating steps in traditional processes shorten the process flow, while the enlarged micron-level feature size significantly reduces the stringent requirements for equipment resolution and process tolerance in the photolithography exposure stage. Combined with solution stripping technology and plasma dry etching, the pattern can be accurately transferred to the deep arsenic selenide film with a high etching selectivity, ensuring the morphological integrity and sidewall perpendicularity of the high aspect ratio composite grating with a large thickness. This solves the problem of high processing barriers and low yield caused by the small feature size of traditional diffractive polarization devices, and provides a highly feasible implementation plan for the engineering manufacturing of high-performance infrared narrowband polarizers.

[0028] In one possible implementation, in step S1, the barium fluoride substrate is subjected to double-sided polishing, and the method for depositing the arsenic selenide thin film is electron beam evaporation deposition.

[0029] In one possible implementation, in step S2, the photolithography exposure and development process is electron beam exposure and development.

[0030] Compared with existing technologies, in the above embodiments, the combination of double-sided polished barium fluoride substrate and electron beam evaporation deposition process conditions effectively eliminates the roughness and undulation of the substrate surface, reduces surface scattering loss and background noise during long-wave infrared light penetration, and at the same time, electron beam evaporation deposition can grow a dense and uniformly thick arsenic selenide film on the substrate, providing a dielectric layer for subsequent deep trench etching; further, combined with high-resolution electron beam exposure and development process, the fine contour of the micron-level grating is precisely defined using a high-energy electron beam, ensuring strict consistency of the array period and high fidelity of the sidewall dimensions, improving the overall processing yield of metasurface feature dimensions and the uniformity of the device's optical response in the infrared band.

[0031] In one possible implementation, in step S3, the method for depositing the metal is electron beam evaporation deposition.

[0032] In one possible implementation, in step S4, the solution is an acetone solution.

[0033] Compared with existing technologies, the above-mentioned technical solution employs electron beam evaporation to deposit chromium metal, combined with acetone solution for stripping. The high orientation of electron beam evaporation ensures that the deposited chromium metal layer has excellent density and adhesion. As a high-hardness mask, it exhibits a high etching selectivity in plasma etching, effectively resisting the physical bombardment during deep trench etching. The acetone solution stripping can quickly and gently dissolve the residual photoresist on the underlying layer, allowing for processing without damaging the fragile arsenic selenide film and barium fluoride substrate. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a narrow-band polarized metasurface for suppressing long-wave infrared irradiance provided in an embodiment of the present invention. Figure 1 In the diagram, a is a schematic diagram of the overall structure, and b is a schematic diagram of the cross-sectional parameters of the composite grating structure;

[0035] Figure 2 The flowchart illustrates the fabrication process of a narrow-band polarized metasurface for suppressing long-wave infrared spectral dispersion, as provided in this embodiment of the invention.

[0036] Figure 3 Transmittance spectra, electric field strengths, and band structure diagrams of metasurfaces under different structural parameters provided in embodiments of the present invention; Figure 3 In the diagram, a shows the transmittance spectrum of the metasurface at an oblique incidence angle of 15° and a schematic diagram of the electric field distribution of the corresponding mode; b shows a comparison of transmittance spectra under different grating widths w; c shows a comparison of transmittance spectra under different periods p; and d shows the curves of electric field intensity as a function of incidence angle θ under different periods p. Figure 3 The eh diagrams in the figure represent the band structure evolution of the transmittance of the metasurface as a function of wavelength and incident angle θ when the period p is 5.5 μm, 5.75 μm, 6.0 μm, and 6.25 μm, respectively.

[0037] Figure 4 The present invention provides the band structure, resonant wavelength, and transmittance and polarization extinction ratio spectra of the metasurface under specific periods in an embodiment of the invention. Figure 4 In the diagram, a is the band structure of transmittance as a function of wavelength and incident angle θ when the period p is 5.65 μm; b is the curve of full width at half maximum (FWHM) (left axis) and resonance wavelength (right axis) as a function of incident angle θ; c is the transmittance spectrum at different incident angles θ; and d is the polarization extinction ratio (PER) spectrum at different incident angles θ.

[0038] Figure 5 This is a frontal SEM image of the metasurface structure prepared in Example 1 of the present invention.

[0039] Figure 6The measured spectra of transmittance and polarization extinction ratio of the metasurface prepared in Example 1 of the present invention under normal incidence are shown.

[0040] Explanation of reference numerals in the attached figures: 10, barium fluoride substrate; 20, composite grating structure; 21, arsenic selenide grating; 22, metal layer; p, period; w, grating width; h, arsenic selenide grating height; t, metal layer thickness. Detailed Implementation

[0041] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0042] The present invention provides a narrow-band polarization metasurface for suppressing long-wave infrared angular dispersion, comprising: a barium fluoride substrate 10, and a composite grating structure 20 disposed on the surface of the barium fluoride substrate 10;

[0043] The composite grating structure 20 is a double-layer grating structure, which includes an arsenic selenide grating 21 at the bottom and a metal layer 22 at the top of the arsenic selenide grating 21.

[0044] The composite grating structure 20 has a period of 5.5-6.25 micrometers. The width of a single double-layer grating structure in the composite grating structure 20 is 4.5-5.5 micrometers, and the width of a single double-layer grating structure is less than the period of the composite grating structure 20. The height of the arsenic selenide grating 21 is 4.5-5.5 micrometers.

[0045] As a preferred embodiment, the period of the composite grating structure 20 is 5.60-5.70 micrometers.

[0046] As a preferred embodiment, the composite grating structure 20 has a period of 5.65 micrometers, the width of a single double-layer grating structure in the composite grating structure 20 is 5.05 micrometers, and the height of the arsenic selenide grating 21 is 5 micrometers.

[0047] As a preferred embodiment, the metal layer 22 is a chromium metal layer with a thickness of 50-80 nanometers.

[0048] As a preferred option, the thickness of the chromium metal layer is 65 nanometers.

[0049] This invention also provides a method for preparing a narrow-band polarized metasurface with long-wave infrared angular dispersion suppression. The preparation method includes the following steps:

[0050] S1: Deposit an arsenic selenide thin film on the cleaned barium fluoride substrate 10;

[0051] S2: Spin-coat photoresist onto a barium fluoride substrate 10 with an arsenic selenide thin film, and perform photolithography exposure and development to obtain a pattern;

[0052] S3: Deposit metal onto the developed pattern surface to form a hard mask;

[0053] S4: Remove excess photoresist with a solution, leaving the hard mask intact;

[0054] S5: Using a hard mask as a shield, plasma etching is performed to obtain a composite grating structure 20 containing an arsenic selenide grating 21 and a metal layer 22.

[0055] As a preferred embodiment, in step S1, the barium fluoride substrate 10 undergoes double-sided polishing, and the method for depositing the arsenic selenide thin film is electron beam evaporation deposition.

[0056] As a preferred option, in step S2, the photolithography exposure and development process is electron beam exposure and development.

[0057] As a preferred option, in step S3, the method for depositing the metal is electron beam evaporation deposition.

[0058] As a preferred option, in step S4, the solution used is an acetone solution.

[0059] This invention overcomes the technical bottleneck of traditional infrared polarization devices relying on extreme subwavelength diffraction effects. It innovatively proposes achieving narrowband resonance through a subwavelength grating structure: this invention significantly increases the characteristic size of the traditional wire grating to the micrometer scale, successfully transforming the device's working mechanism from diffraction to subwavelength resonance, reducing the fabrication difficulty and cost in micro / nano processing, while simultaneously achieving high-performance narrowband infrared filtering at the subwavelength scale. Furthermore, addressing the inherent strong angular dispersion defect in traditional narrowband plasmonic polarizers, this invention innovatively introduces bandgap engineering design. Through precise control of structural parameters such as the grating period, energy interaction between internal modes (guided modes and FP cavity modes) is induced, successfully achieving bandgap folding and anti-crossover effects. This alters the angular dispersion characteristics of the resonant mode, effectively flattening the target bandgap in momentum space and endowing the device with extremely low angular dispersion. This design allows the device to maintain excellent polarization performance over a wide angular tolerance range, solving the technical challenge of extremely stringent optical path collimation requirements in practical applications of traditional devices, and broadening its application scope in practical engineering fields such as infrared imaging and gas detection.

[0060] The following are embodiments incorporating specific data to further elaborate on the above-described technical solutions of the present invention:

[0061] Example 1:

[0062] This embodiment provides a narrowband polarized metasurface for suppressing long-wave infrared irradiance and its preparation method.

[0063] In this embodiment, the overall structure of the metasurface is as follows: Figure 1 As shown in Figure a, it includes: a barium fluoride substrate 10, and a composite grating structure 20 disposed on the surface of the barium fluoride substrate 10; the composite grating structure 20 is a double-layer grating structure, which includes an arsenic selenide grating 21 at the bottom and a metal layer 22 at the top of the arsenic selenide grating 21.

[0064] Combination Figure 1 As shown in Figure b, the parameters of this embodiment are set as follows: the period p of the composite grating structure 20 is 5.65 micrometers, the grating width w is 5.05 micrometers, and the height h of the bottom arsenic selenide grating 21 is 5 micrometers; wherein, the period p is the repetition distance between adjacent repeating grating structures, the grating width w is the width of a single grating in the periodic direction; the top metal layer 22 is a chromium (Cr) metal layer, and the thickness t of the chromium metal layer is 65 nanometers.

[0065] Combination Figure 2 The fabrication process flow diagram shown illustrates the preparation method of this long-wave infrared angular dispersion-suppressing narrow-band polarized metasurface in this embodiment, which specifically includes the following steps:

[0066] S1: Deposit an arsenic selenide film on the cleaned barium fluoride substrate 10; specifically, select a double-sided polished barium fluoride substrate 10, and after standard cleaning, deposit an arsenic selenide film with a thickness of 5 micrometers on the barium fluoride substrate 10 by electron beam evaporation deposition process.

[0067] S2: Spin-coat photoresist onto a barium fluoride substrate 10 with an arsenic selenide thin film, and perform photolithography exposure and development to obtain a pattern; specifically, after spin-coating the photoresist, obtain a preset grating pattern on the photoresist through an electron beam exposure and development process.

[0068] S3: Deposit metal on the surface of the developed pattern to form a hard mask; specifically, deposit a 65-nanometer thick chromium metal on the sample surface using an electron beam evaporation deposition process as a hard mask for subsequent etching.

[0069] S4: Remove excess photoresist with a solution, leaving the hard mask; specifically, immerse the sample in an acetone solution for a stripping process to remove excess photoresist, leaving only the chromium hard mask pattern.

[0070] S5: Using a hard mask as a shield, plasma etching is performed to obtain a composite grating structure 20 containing an arsenic selenide grating 21 and a chromium metal layer, thus obtaining the final micro-nano composite metasurface. The front SEM top view of the actual object is shown below. Figure 5 As shown.

[0071] Example 2

[0072] This embodiment provides a narrowband polarized metasurface for suppressing long-wave infrared irradiance and its preparation method.

[0073] The structure and preparation steps of this embodiment are basically similar to those of Example 1, the difference being in the relevant parameter settings:

[0074] The composite grating structure 20 has a period of 5.5 micrometers and a grating width of 4.5 micrometers, while the arsenic selenide grating 21 has a height of 4.5 micrometers; the thickness of the top chromium metal layer is 50 nanometers. Furthermore, in step S2, the photolithography exposure and development process employs ultraviolet photolithography exposure and development technology.

[0075] Example 3

[0076] This embodiment provides a narrowband polarized metasurface for suppressing long-wave infrared irradiance and its preparation method.

[0077] The structure and preparation steps of this embodiment are basically similar to those of Example 1, the difference being in the relevant parameter settings:

[0078] The composite grating structure 20 has a period of 6.25 micrometers, a grating width of 5.5 micrometers, and an arsenic selenide grating 21 with a height of 5.5 micrometers; the thickness of the top chromium metal layer is 80 nanometers.

[0079] Analysis and verification of physical mechanisms and technical effects:

[0080] To further elucidate the design principles of this invention and the control mechanism of each structural parameter on optical performance, this embodiment systematically analyzes and experimentally characterizes the physical process with period p in the range of 5.5-6.25 micrometers.

[0081] Depend on Figure 3 As shown in the oblique incidence (15°) transmittance spectrum in Figure a, the present invention excites two significant resonance characteristic peaks in the long-wave infrared band, denoted as Mode 1 and Mode 2, respectively. Combined with the corresponding electric field distribution diagram depth analysis, Mode 1 exhibits guided mode characteristics leaking towards the substrate, while Mode 2 manifests as a Fabry-Perot (FP) cavity mode formed between adjacent gratings.

[0082] To ensure that Mode 1 and Mode 2 can be effectively excited and precisely coupled in the target wavelength band, this invention performs synergistic optimization on the basic structural parameters of the composite grating:

[0083] The grating width w and the height h of the arsenic selenide grating 21 together establish the fundamental response characteristics of the resonant mode, such as... Figure 3As shown in Figure b, increasing the grating width w causes a synchronous redshift in both Mode 1 and Mode 2. By limiting w to 4.5-5.5 micrometers, the target infrared window near 9.78 micrometers can be precisely locked, preventing the overall response peak from deviating. Meanwhile, the arsenic selenide grating 21, as the core dielectric waveguide, provides ample longitudinal waveguide space for Mode 1 within its 4.5-5.5 micrometer height h, and also defines the physical boundary of the FP cavity, ensuring sufficient resonant optical path length for long-wave infrared light within the structure.

[0084] The chromium metal layer at the top serves as a loss control layer, and its thickness t of 50-80 nanometers directly determines the upper limit of the polarization extinction ratio. When the polarization direction of the incident light is parallel to the grating, the chromium metal layer of the above-mentioned specific thickness induces strong surface plasmon resonance, which efficiently dissipates the energy of the polarization state, thereby ensuring that the device has an extremely high polarization extinction ratio of more than 30dB while performing narrowband filtering.

[0085] The core innovation of this invention lies in achieving artificial tailoring of band structure characteristics through the parametric evolution of period p. Research has found that, for example... Figure 3 The transmittance spectrum comparison results for mode c show that although both mode 1 and mode 2 are modulated by the width w, the change in period p mainly affects mode 2 (FP cavity mode), while having almost no effect on mode 1 (guided mode). This asymmetric parameter sensitivity provides a physical prerequisite for precisely controlling the energy interaction between the two modes. Figure 3 Taking the case of p=6.05 micrometers shown in d as an example, as the incident angle increases, the electric field strength in the FP cavity decreases significantly after crossing the critical angle. This directly reflects the transfer and leakage of energy to the FP cavity mode, proving that adjusting the period p can substantially change the coupling strength between modes.

[0086] This invention further investigates the complete band structure evolution process within the range of Example 2 (5.5 μm) to Example 3 (6.25 μm). For example... Figure 3 As shown in e, f, g, and h:

[0087] When the parameters of Example 2 (p=5.5 micrometers) are used, the band of Mode 2 shows a downward bending trend, while the band of Mode 1 bends upward.

[0088] When p = 5.75 micrometers, the band structure of mode 2 begins to flatten due to the compression of the band structure of mode 1;

[0089] When p increases further to 6.0 micrometers, due to the strong compression of the mode 1 band, the mode 2 band is changed from being bent downwards to being bent upwards.

[0090] When the parameters of Example 3 (p=6.25 micrometers) are reached, this upward bending trend becomes even more pronounced.

[0091] The above evolution process fully demonstrates that by adjusting the period of the composite grating within the range of 5.5-6.25 micrometers, the coupling relationship between the energy bands of Mode 1 and Mode 2 can be effectively changed. This coupling alters the corresponding dispersion curvature, making it technically feasible for structures within this range to achieve subwavelength narrowband resonance. Ultimately, it was determined that under the optimal parameters of Example 1 (i.e., p=5.65 micrometers), the compression of the two energy bands reached an excellent energy exchange state, exhibiting a cross-shaped "anti-crossing" characteristic. The energy band of Mode 2, approximately a straight line, was successfully flattened, at which point dispersion reached its minimum.

[0092] Optical performance test results:

[0093] Taking Example 1 (p=5.65 micrometers) as an example, simulation results show that, Figure 4 As shown in Figures a and b, the resonant wavelength ( ) changes with the incident angle θ. Figure 4 The right-hand axis (b) remains stable at around 9.78 micrometers, and its full width at half maximum (FWHM) is... Figure 4 The left axis (of the b-axis) remains stable around 250 nanometers. For example... Figure 4 As shown in Figures c and d, within the oblique incidence angle range of 0° to 15°, the position of Mode 2 in the spectrum remains essentially unchanged, and the long-wave infrared polarization extinction ratio is consistently maintained at a high level of over 30dB.

[0094] Meanwhile, actual preparation experiments verified the above theory, such as Figure 6 The measured normal incident spectrum shows that the device prepared in Example 1 of this invention has a transmittance of 75.19% at a working wavelength of 9.78 micrometers, a mode half-width of 321 nanometers, a polarization extinction ratio as high as 33.69 dB, and a flat band (low angular dispersion) angle tolerance range of about 15°.

[0095] In summary, the above embodiments fully demonstrate that this invention overcomes the low-pass filtering defects and the bottleneck of extremely small feature size processing difficulties inherent in traditional infrared polarizers based on pure diffraction principles. By scaling up the size of the microstructure to the subwavelength level to excite narrowband resonance, and by cleverly utilizing the fine control of specific periodic parameters (5.5-6.25 micrometers) at the micrometer level, the downward-leaking guided modes and Fabry-Perot cavity modes within the structure undergo strong energy exchange and mutual compression in momentum space. The physical mechanism based on band folding and anti-crossover characteristics successfully flattens the bands of specific resonance modes, overcoming the inherent strong dispersion defects of plasmon narrowband microstructures. Furthermore, this invention not only achieves high transmittance and high polarization extinction ratio in the long-wave infrared band at micrometer-level processing dimensions, but also greatly reduces the difficulty of optical path collimation in practical optical systems with its excellent wide angular tolerance (0-15°), possessing extremely high engineering application value and broad industrial prospects.

[0096] In the description of the embodiments of the present invention, it should be noted that the terms "inner" and "outer" and other terms indicating the direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0097] In the description of this invention, the terms "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0098] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A narrow-band polarized metasurface for suppressing long-wave infrared spectral dispersion, characterized in that, include: A barium fluoride substrate (10), and a composite grating structure (20) disposed on the surface of the barium fluoride substrate (10); The composite grating structure (20) is a double-layer grating structure, which includes an arsenic selenide grating (21) at the bottom and a metal layer (22) at the top of the arsenic selenide grating (21). The period of the composite grating structure (20) is 5.5-6.25 micrometers, the width of a single double-layer grating structure is 4.5-5.5 micrometers, and the height of the arsenic selenide grating (21) is 4.5-5.5 micrometers; The metal layer (22) is a chromium metal layer with a thickness of 50-80 nanometers.

2. The long-wave infrared spectral dispersion suppression narrow-band polarized metasurface according to claim 1, characterized in that, The period of the composite grating structure (20) is 5.60-5.70 micrometers.

3. The long-wave infrared spectral dispersion suppression narrow-band polarized metasurface according to claim 2, characterized in that, The period of the composite grating structure (20) is 5.65 micrometers, the width of a single double-layer grating structure in the composite grating structure (20) is 5.05 micrometers, and the height of the arsenic selenide grating (21) is 5 micrometers.

4. The long-wave infrared angular dispersion suppression narrow-band polarized metasurface according to claim 1, characterized in that, The thickness of the chromium metal layer is 65 nanometers.

5. A method for preparing a narrow-band polarized metasurface with long-wave infrared angular dispersion suppression, used to prepare the narrow-band polarized metasurface with long-wave infrared angular dispersion suppression as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: S1: Deposit a thin film of arsenic selenide on the cleaned barium fluoride substrate (10); S2: Spin-coat photoresist onto a barium fluoride substrate (10) with the arsenic selenide film, and perform photolithography exposure and development to obtain a pattern; S3: Deposit metal onto the developed pattern surface to form a hard mask; S4: Remove excess photoresist with a solution, retaining the hard mask; S5: Using the hard mask as a shield, plasma etching is performed to obtain a composite grating structure (20) containing the arsenic selenide grating (21) and the metal layer (22).

6. The method for preparing a narrow-band polarized metasurface with long-wave infrared spectral dispersion suppression according to claim 5, characterized in that, In step S1, the barium fluoride substrate (10) is subjected to double-sided polishing, and the method for depositing the arsenic selenide thin film is electron beam evaporation deposition.

7. The method for preparing a narrow-band polarized metasurface with long-wave infrared spectral dispersion suppression according to claim 5, characterized in that, In step S2, the photolithography exposure and development process is electron beam exposure and development.

8. The method for preparing a narrow-band polarized metasurface with long-wave infrared spectral dispersion suppression according to claim 5, characterized in that, In step S3, the method for depositing the metal is electron beam evaporation deposition.

9. The method for preparing a narrow-band polarized metasurface with long-wave infrared spectral dispersion suppression according to claim 5, characterized in that, In step S4, the solution is an acetone solution.

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