Design method of wave infrared multispectral filter array in si-based metasurface structure

Abstract

The application belongs to the field of micro-nano optics and multispectral imaging technology, and relates to a design method of a mid-wave infrared multispectral filter array of Si-based metasurface structures. The application is characterized in that: the mid-wave infrared multispectral filter array is composed of Si-based metasurface structures with different structural parameters; the geometric structural size parameters of different Si-based metasurface structure units are different; the optical response of the Si-based metasurface structure is simulated and analyzed by using a finite difference time domain algorithm, different metasurface array structural parameters are scanned in the mid-wave infrared band, and the transmission spectrum of the Si-based metasurface structure is obtained according to a transmittance formula. By integrating metasurface arrays with different structural parameters on a photoelectric detector, the application can realize narrow-band full transmission of the mid-wave infrared, and realize a transmission-type metasurface multispectral filter array for mid-wave infrared tunable filtering. The transmission-type metasurface multispectral filter array designed by the application also has the advantages of simple structure and light weight.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics and multispectral imaging technology, and relates to a design method for a Si-based metasurface structure multispectral filter array for mid-wave infrared spectral modulation. Background Technology

[0002] Multispectral imaging, a technology capable of acquiring images of targets across multiple wavelength ranges, is an indispensable tool in agriculture, military, and environmental monitoring. Its core advantage lies in its ability to analyze the same target's behavior at different wavelengths, obtaining rich spectral information and revealing the object's physical, chemical, and biological properties. Because multispectral imaging can distinguish the spectral characteristics of different substances, it plays a crucial role in crop health monitoring, target identification, resource exploration, and pollution detection. However, the current development of multispectral photodetectors faces several key challenges, including how to improve spectral resolution and detectivity while minimizing the complexity and size of the optical system.

[0003] Currently, the main technical bottleneck facing traditional multispectral photodetectors is the difficulty in simultaneously achieving high detectivity and high spectral resolution. High detectivity is crucial for improving image quality because low detectivity leads to insufficient signal, affecting image clarity and contrast; while low spectral resolution causes crosstalk between different wavelength channels, resulting in spectral information confusion and reducing the accuracy of spectral imaging. To overcome these challenges, multispectral detectors typically require complex optical beam splitting systems, such as gratings and prisms. While these components effectively separate the spectrum, they significantly increase the system's size, weight, and manufacturing cost. Furthermore, these traditional beam splitting systems struggle to meet the requirements of miniaturization, lightweight design, and ease of integration when applied to portable devices such as drone monitoring.

[0004] The introduction of metasurface technology has provided a breakthrough for the development of multispectral photodetectors. A metasurface is a two-dimensional nanostructure composed of artificial atomic arrangements with special electromagnetic properties. Through meticulously designed subwavelength-scale units, it can uniquely manipulate incident light. This manipulation includes optical field properties such as amplitude, phase, and polarization. By flexibly adjusting the geometric parameters of the metasurface units, such as shape, size, arrangement, and azimuth, complex optical effects such as wavefront manipulation, anomalous reflection, transmission, dispersion control, and local field enhancement can be achieved. This characteristic makes metasurfaces a promising candidate for multispectral narrowband detector design. With a well-designed metasurface structure, spectral splitting and manipulation functions can be directly integrated into the detector, eliminating the size and complexity of traditional optical spectral splitting devices and greatly simplifying the optical system. Simultaneously, metasurfaces can achieve narrowband filtering characteristics, enabling detectors to have high spectral resolution and high detection efficiency at different wavelengths. These characteristics are particularly important in scenarios such as UAV monitoring, where there are extremely high requirements for device portability and system integration. Leveraging metasurface technology, future multispectral photodetectors will be able to achieve smaller size, higher integration, and superior spectral selectivity and imaging performance. This will drive their widespread adoption in various application areas, including agricultural monitoring, defense reconnaissance, and environmental surveillance, meeting the growing demand for high-performance imaging and detection. Summary of the Invention

[0005] To address the aforementioned problems and shortcomings, and in order to achieve crosstalk-free, high spectral resolution photoelectric detection in the mid-wave infrared, this invention aims to provide a design method for a Si-based metasurface structure mid-wave infrared multispectral filter array. By integrating metasurface arrays with different structural parameters onto a photodetector, tunable narrowband full transmission in the mid-wave infrared can be achieved, realizing a transmissive metasurface multispectral filter array for tunable filtering in the mid-wave infrared. The transmissive metasurface multispectral filter array designed in this invention also has the advantages of simple structure and lightweight design.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure disclosed in this invention is characterized by comprising the following steps:

[0008] Step 1: The mid-wave infrared multispectral filter array is composed of Si-based metasurface structures with different structural parameters; the geometric dimensions of different Si-based metasurface structure units are different; the geometric dimensions include the height H, diameter D, and spacing P of the silicon cylinders;

[0009] Step 2: The optical response of the Si-based metasurface structure is simulated and analyzed using the finite-difference time-domain algorithm. Different metasurface array structure parameters are scanned in the mid-infrared band, and the transmission spectrum of the Si-based metasurface structure is obtained by solving according to formula (1).

[0010]

[0011] Where P(f) is the Poynting vector at different frequencies; dS is the integral element; and sourcepower(f) is the power of the excitation source.

[0012] According to the requirements, select from the transmission spectrum, determine the corresponding H, D and P, and obtain the array. The requirements include transmittance and full width at half maximum (FWHM).

[0013] Furthermore, the selection of corresponding H, D, and P from the transmission spectrum is based on the following principles: transmittance is higher than 80%, and full width at half maximum (FWHM) is less than 200 nm.

[0014] Furthermore, a photodetector is constructed, and a unit structure integrating the photodetector with the Si metasurface structure is constructed. The unit structure includes a three-layer structure, from top to bottom: Si metasurface structure, SU-8 transition layer, and InSb mid-wave infrared photodetector.

[0015] Furthermore, Si metasurface structures with different structural parameters are integrated onto InSb photodetectors to achieve multispectral mid-infrared detection.

[0016] Beneficial effects:

[0017] 1. This invention discloses a design method for a Si-based metasurface structure mid-wave infrared multispectral filter array. This method integrates a Si metasurface structure with a mid-wave infrared photodetector, solving the problems of low absorption rate and large system size associated with traditional mid-wave infrared photodetectors combined with filters and corresponding optical paths for multispectral detection. By introducing a nanoscale metasurface structure, the spectrum of incident light can be precisely controlled, enabling the mid-wave infrared photodetector to achieve narrowband absorption. This invention achieves spectral width adjustment without relying on traditional filters, offering significant advantages such as simple optical path design, high system integration, and device miniaturization.

[0018] 2. The design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure disclosed in this invention, based on fine adjustment of the metasurface structure parameters, enables matching with mid-wave infrared photodetectors of different absorption spectral characteristics, thereby improving the applicability and versatility of this invention. This invention, by cooperating with the narrowband transmission spectrum of the Si metasurface structure, can achieve narrowband multi-channel spectral detection. This invention can be widely applied in various micro / nano photodetectors, providing an effective technical approach to achieving spectral tunability in the mid-infrared band.

[0019] 3. The design method for a Si-based metasurface structure mid-wave infrared multispectral filter array disclosed in this invention uses silicon nanocylinders, an all-dielectric material, to construct the metasurface, avoiding the ohmic losses of traditional metal plasmon metasurfaces. By selecting appropriate structural parameters, narrowband full transmission of the target wavelength can be achieved. Integrating this invention with a broadband mid-wave infrared detector can improve the spectral resolution of the photodetector.

[0020] 4. The design method of the Si-based metasurface structure mid-wave infrared multispectral filter array disclosed in this invention, based on achieving the beneficial effects 1, 2, and 3, can realize multispectral narrowband detection, ensure high responsivity in the mid-wave infrared band, thereby enhancing the spectral selectivity and color resolution of the detector, which helps to significantly improve the signal-to-noise ratio and overall imaging quality of the imaging system, and promotes the application and development of mid-wave infrared photodetectors in the field of multispectral imaging. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the design process for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure.

[0022] Figure 2 This is a schematic diagram of the narrowband multispectral photodetector structure and its periodic unit structure provided in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the Si metasurface structure in an embodiment of the present invention;

[0024] Figure 4 These are the absorption spectra of the InSb detector alone and the InSb detector with the SU-8 transition layer added in the embodiments of the present invention.

[0025] Figure 5 These are the transmission spectra of Si nanodisks under different structural parameters;

[0026] Figure 6 This is a multipole decomposition diagram with a diameter of 1.6 μm in an embodiment of the present invention;

[0027] Figure 7 This is a schematic diagram of the multi-channel narrowband absorption spectrum implemented in an embodiment of the present invention;

[0028] Figure 8 This is a schematic diagram of the structure of a multi-pixel multispectral detector for multispectral imaging in an embodiment of the present invention.

[0029] Among them: 1—Si metasurface structure, 2—SU-8 photoresist, 3—InSb photodetector, 4—Si nanocylinder, 5—metasurface structure array photodetector unit. Detailed Implementation

[0030] To more fully describe and illustrate the technical solutions and advantages of the present invention, the specific embodiments of the present invention will be described below in conjunction with the accompanying drawings and examples.

[0031] Figure 2 This invention demonstrates a unit structure integrating a mid-wave infrared photodetector with a Si metasurface, specifically comprising a three-layer structure: from top to bottom, a Si metasurface structure 1, an SU-8 photoresist 2, and an InSb mid-wave infrared photodetector 3. Multiple Si nanodisks 4 are periodically arranged on the upper surface of the SU-8 photoresist 2, forming the Si metasurface structure 1. The InSb mid-wave infrared photodetector typically has a broad spectral response to the target wavelength, limiting its further application in the multispectral field. By combining it with the narrowband transmission spectrum of the Si metasurface structure 1, narrowband multichannel spectral detection can be achieved.

[0032] The material used in the Si metasurface structure 1 in this embodiment is preferably amorphous Si. Since Si is a traditional semiconductor material with a high refractive index, its processing technology is already very mature, and it has lower ohmic loss compared to metals.

[0033] The SU-8 photoresist 2 used in this embodiment can protect the InSb mid-wave infrared photodetector from damage during the fabrication of the Si metasurface structure 1 after curing. At the same time, the appropriate transition thickness can suppress unnecessary optical effects caused by direct contact between the metasurface and the detector. The transition material is not limited to SU-8, but can also be a material with low absorption in the corresponding spectral range, such as silicon dioxide.

[0034] like Figure 1 As shown in this embodiment, the design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure is implemented using the following specific steps:

[0035] Step 1: Construct an existing Si metasurface array structure model by parameterizing the geometric dimensions of the Si metasurface unit: the geometric dimension parameters include the height (H), diameter (D), and spacing (P) of the silicon cylinders;

[0036] Step 2: Use FDTD simulation software to model the Si metasurface structure 1, which is an array of periodically arranged Si nanodisks 4, as shown below. Figure 3 As shown, the simulation is performed on a periodic element with structural parameters of height (H), diameter (D), and spacing (P). The boundary conditions in the x and y directions are set as periodic boundary conditions, and the boundary in the z direction is set as a perfectly matched layer (PML). The above structural parameters are scanned and the transmission spectrum and the multipole decomposition diagram of the scattering cross section are obtained by solving according to formulas (1) to (9). The transmission spectrum is calculated as shown in formula (1):

[0037]

[0038] Where P(f) is the Poynting vector at different frequencies, dS is the integral element, and the integration region is the surface where the monitor is located after the incident light passes through the metasurface.

[0039] The structure, under the excitation of incident light, generates electric quadrupole resonance (EQ) and electric dipole resonance (ED), achieving unidirectional radiation with two peaks. In the calculation of the multipole decomposition of the scattering cross section, the total scattering power is expanded into electric dipole (ED), magnetic dipole (MD), electric quadrupole (EQ), and magnetic quadrupole (MQ). Under the excitation of incident light, the scattering power I is expressed as:

[0040]

[0041] These four terms represent the scattering of ED, MD, EQ, and MQ, respectively. In this equation:

[0042] Electric dipole moment ED: Electric dipole moment ED: Magnetic dipole moment MD: Electric quadrupole torque EQ: Magnetic quadrupole moment MQ: Where j is the current density: j(r) = -iωε0(n 2 -1)E(r)(9) The relationship between the scattering cross section and the scattering power is as follows: Where i is an imaginary number, ω is the angular frequency of the incident wave; c is the speed of light in vacuum; r is the position vector; r α,β ε0 is the component of the position vector in Cartesian coordinates; ε0 is the dielectric constant in vacuum; μ0 is the permeability in vacuum; E inc is the incident photoelectric field vector; n is the refractive index, which is a function of the position vector r.

[0043] The structure alters its refractive index distribution by adjusting three parameters: P, D, and H, thereby changing the current density distribution and ultimately exciting electric quadrupole resonance (EQ) and electric dipole resonance (ED), resulting in a double-peak narrow-band full transmission spectrum. The scattering cross-section of the multipole decomposition at a diameter of 1.6 μm is shown below. Figure 6 As shown.

[0044] The multipolar resonance modes of the structure under incident light excitation were analyzed. Narrow-band transmission in the spectrum was achieved by adjusting the resonance modes. As an optimal choice, based on the obtained transmission curve, a transmittance higher than 80% and a full width at half maximum (FWHM) less than 200 nm were selected as targets. The corresponding structural parameters were selected as the results of the Si metasurface structural parameter scanning optimization.

[0045] The Si nanodisk 1 has a fixed height H, which can be selected between 1 μm and 1.5 μm. The relationship between the spacing P and the diameter D is defined according to formula (2). Figure 5 The image shows the transmission spectra of the Si metasurface structure 1 with a fixed height H and diameter D of 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm and 1.9 μm, respectively. The full width at half maximum (FWHM) can reach about 120 nm.

[0046] P = D + 0.5μm (11)

[0047] Step 3: After obtaining the influence characteristics of the three key structural parameters—height (H), diameter (D), and spacing (P)—on the transmission spectrum of the metasurface array, based on the obtained absorption spectrum of the InSb mid-wave infrared photodetector, a Si metasurface structure with a corresponding narrowband transmission spectrum is selected for matching. The absorption spectra of a single InSb detector and the absorption spectra of an InSb detector with an SU-8 transition layer are shown below. Figure 4 As shown, a Si metasurface structure was integrated onto a photodetector with broadband high absorption in the mid-infrared range, isolated by an SU-8 transition layer. The optimal SU-8 layer thickness was obtained through scanning optimization within the 0.6-1 μm range. Based on the obtained absorption curves, an absorptivity higher than 80% and a full width at half maximum (FWHM) less than 200 nm were selected as targets, and the optimal SU-8 transition layer thickness was obtained. The SU-8 layer not only avoids unnecessary optical effects caused by direct contact between the metasurface structure and the detector, but also enhances the absorptivity of the InSb detector.

[0048] Step 4: Connect the Si metasurface structure 1 with the corresponding InSb mid-wave infrared photodetector as follows... Figure 2 By integrating the overall structure and performing simulation analysis using the FDTD method, the structure of the multispectral photodetector with optimized backup narrowband absorption spectrum can be realized. Figure 7The results demonstrate the optimized 8-channel multispectral narrowband response in the mid-infrared spectral range obtained using this method, with a full width at half maximum (FWHM) of approximately 100 nm. Integrating Si metasurface-InSb photodetector pixels with different absorption peaks enables multispectral mid-infrared detection.

[0049] By integrating multiple metasurface structure array pixels optimized using the above methods onto the same chip, multispectral photoelectric detection can be achieved. A schematic diagram of the fabricated multi-pixel multispectral detector is shown below. Figure 8 As shown.

[0050] In a further specific implementation, the material of the mid-infrared photodetector that can be optimized by this method is not limited to InSb, but can also be mercury cadmium telluride, or the spectral response of photodetectors made of III-V compound semiconductor materials such as GaAs, InP, InGaAs, InAs, InAsSb and other materials can be optimized.

[0051] This demonstrates that the design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure disclosed in this embodiment can achieve narrowband multispectral detection in the mid-wave infrared band by integrating this structure with a mid-wave infrared detector. The metasurface is composed of several subwavelength-scale metasurface units. This invention uses silicon nanocylinders, an all-dielectric material, to construct the metasurface, avoiding the ohmic losses of traditional metal-plasma metasurfaces. By selecting appropriate structural parameters, narrowband full transmission at the target wavelength can be achieved. Integrating this invention with a broadband mid-wave infrared detector can effectively improve the spectral resolution of the photodetector. This invention has potential applications in numerous fields such as military equipment, aerospace, and road monitoring.

[0052] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure, characterized by: Includes the following steps, Step 1: The mid-wave infrared multispectral filter array is composed of Si-based metasurface structures with different structural parameters; the geometric dimensions of different Si-based metasurface structure units are different; the geometric dimensions include the height H, diameter D, and spacing P of the silicon cylinders; Step 2: The optical response of the Si-based metasurface structure is simulated and analyzed using the finite-difference time-domain algorithm. Different metasurface array structure parameters are scanned in the mid-infrared band, and the transmission spectrum of the Si-based metasurface structure is obtained by solving according to formula (1). Where P(f) is the Poynting vector at different frequencies; dS is the integral element; sourcepower(f) is the power of the excitation source; According to the requirements, select from the transmission spectrum, determine the corresponding H, D and P, and obtain the array. The requirements include transmittance and full width at half maximum (FWHM). A photodetector was constructed, and a unit structure integrating the photodetector with the Si metasurface structure was constructed. The unit structure consists of three layers, from top to bottom: Si metasurface structure, SU-8 transition layer, and InSb mid-wave infrared photodetector. Integrating Si metasurface structures with different structural parameters onto an InSb photodetector enables multispectral mid-infrared detection.

2. The design method for a mid-wave infrared multispectral filter array based on a Si-based metasurface structure as described in claim 1, characterized in that: The corresponding H, D, and P are selected from the transmission spectrum. The selection principle is that the transmittance is higher than 80% and the full width at half maximum (FWHM) is less than 200 nm.

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