Design method of medium-wave infrared multispectral optical filter array in Si-based metasurface structure

Abstract

The invention discloses a method for designing a medium-wave infrared multispectral optical filter array in a Si-based metasurface structure, and belongs to the technical field of micro-nano optics and multispectral imaging. The realization method comprises the following steps: the medium-wave infrared multispectral optical filter array is composed of Si-based metasurface structures with different structure parameters; geometric structure size parameters of different Si-based metasurface structure units are different; and performing simulation analysis on optical response of the Si-based metasurface structure by adopting a finite difference time domain algorithm, scanning different metasurface array structure parameters in a medium-wave infrared band, and solving according to a transmissivity formula to obtain a transmission spectrum of the Si-based metasurface structure. According to the invention, metasurface arrays with different structural parameters are integrated on a photoelectric detector, so that medium-wave infrared adjustable narrow-band total transmission can be realized, and the transmission type metasurface multispectral optical filter array for medium-wave infrared tunable filtering is realized. The transmission-type metasurface multispectral optical filter array designed by the invention also has the advantages of simple structure and portability.

Description

Technical Field

[0001] The invention belongs to the field of micro-nano optics and multi-spectral imaging technology, and relates to a design method for a Si-based super-surface structure multi-spectral filter array for medium-wave infrared spectrum regulation. Background Art

[0002] Multispectral imaging, as a technology that can acquire target images in multiple wavelength ranges, is an indispensable tool in the fields of agriculture, military, environmental monitoring, etc. The core advantage of this technology is that it can obtain rich spectral information by analyzing the performance of the same target at different wavelengths, thereby revealing the physical, chemical and biological properties of the object. Since multispectral imaging can distinguish the spectral characteristics of different substances, it plays an important role in crop health monitoring, target identification, resource detection and pollution detection. However, the current technological development of multispectral photoelectric detectors faces some key challenges, including how to reduce the complexity and volume of the optical system as much as possible while improving the spectral resolution and detection rate.

[0003] At present, the main technical bottleneck faced by traditional multispectral photodetectors is the difficulty in achieving high detection rate and high spectral resolution at the same time. High detection rate is crucial to improving imaging quality, because low detection rate will lead to insufficient signal, thus affecting the clarity and contrast of the image; while low spectral resolution will cause crosstalk between different wavelength channels, confusing the spectral information, thereby reducing the accuracy of spectral imaging. In order to overcome these challenges, multispectral detectors usually require complex optical spectroscopic systems, such as gratings, prisms and other spectroscopic devices. Although these components can effectively separate the spectrum, they significantly increase the volume, weight and manufacturing cost of the system. In addition, these traditional spectroscopic systems are difficult to meet the requirements of miniaturization, lightweight and easy 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. Metasurfaces are two-dimensional nanostructures composed of artificial atomic arrangements with special electromagnetic properties. Through finely designed subwavelength-scale units, they can uniquely regulate the incident light. This regulation includes light field properties such as amplitude, phase, and polarization. By flexibly adjusting the geometric parameters of metastructure units, such as shape, size, arrangement, and azimuth, complex optical effects such as wavefront manipulation, abnormal reflection, transmission, dispersion control, and local field enhancement can be achieved. This feature makes metasurfaces show great application potential in the design of multispectral narrowband detectors. Through reasonable metasurface structure design, the splitting and regulation functions can be directly integrated into the detector, eliminating the volume and complexity of traditional optical splitting devices, thereby greatly simplifying the optical system. At the same time, metasurfaces can also achieve narrowband filtering characteristics, so that the detector has high spectral resolution and high detection efficiency at different wavelengths. Such characteristics are particularly important in scenarios such as drone monitoring, because these scenarios have extremely high requirements for the portability and system integration of equipment. With the help of metasurface technology, future multispectral photodetectors will be able to achieve smaller size, higher integration, and excellent spectral selectivity and imaging performance. This will promote its widespread adoption in various application fields including agricultural monitoring, defense reconnaissance, and environmental monitoring, meeting the growing demand for high-performance imaging and detection. Summary of the invention

[0005] In view of the above problems or deficiencies, in order to achieve photoelectric detection of mid-wave infrared without crosstalk and with high spectral resolution, the purpose of the present invention is to provide a design method of a mid-wave infrared multi-spectral filter array of a Si-based metasurface structure, which can achieve adjustable narrow-band full transmission of mid-wave infrared by integrating a metasurface array with different structural parameters on a photodetector, and realize a transmission-type metasurface multi-spectral filter array for tunable filtering of mid-wave infrared. The transmission-type metasurface multi-spectral filter array designed by the present invention also has the advantages of simple structure and light weight.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] The design method of the Si-based supersurface structure medium-wave infrared multi-spectral filter array disclosed in the present invention is characterized by comprising the following steps:

[0008] Step 1, the medium-wave infrared multi-spectral filter array is composed of Si-based supersurface structures with different structural parameters; the geometric structure size parameters of different Si-based supersurface structural units are different; the geometric structure size parameters include the height H, diameter D and spacing P of the silicon cylinder;

[0009] Step 2: Use the finite-difference time-domain algorithm to simulate and analyze the optical response of the Si-based metasurface structure, scan different metasurface array structure parameters in the mid-wave infrared band, and solve the transmission spectrum of the Si-based metasurface structure according to formula (1);

[0010]

[0011] Where P(f) is the Poynting vector at different frequencies; dS is the integral surface element; and sourcepower(f) is the power of the excitation light 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 corresponding H, D and P are selected and determined from the transmission spectrum according to the following principles: the transmittance is higher than 80% and the full width at half maximum (FWHM) is less than 200 nm.

[0014] Furthermore, a photodetector is constructed, and a unit structure integrating the photodetector and the Si supersurface structure is constructed. The unit structure includes a three-layer structure, namely, a Si supersurface structure, a SU-8 transition layer, and an InSb medium-wave infrared photodetector from top to bottom.

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

[0016] Beneficial effects:

[0017] 1. The design method of the Si-based metasurface structure medium-wave infrared multi-spectral filter array disclosed in the present invention integrates the Si metasurface structure with the medium-wave infrared photodetector, which can solve the problems of low absorption rate and large system volume of the traditional medium-wave infrared photodetector combined with the filter and the corresponding optical path to realize multi-spectral detection. By introducing the nanoscale metasurface structure, the spectrum of the incident light is precisely controlled, so that the medium-wave infrared photodetector can achieve narrow-band absorption. The present invention does not need to rely on traditional filters, that is, it can realize the adjustment of the spectrum width, and has significant advantages such as simple optical path design, high system integration, and miniaturization of devices.

[0018] 2. The design method of the Si-based metasurface structure mid-wave infrared multi-spectral filter array disclosed in the present invention can achieve matching with mid-wave infrared photodetectors with different absorption spectrum characteristics based on fine adjustment of the parameters of the metasurface structure, thereby improving the applicability and versatility of the present invention. The present invention can achieve narrow-band multi-channel spectral detection by coordinating with the narrow-band transmission spectrum of the Si metasurface structure. The present invention can be widely used in various micro-nano photodetectors, providing an effective technical approach to achieve spectral adjustability in the mid-infrared band.

[0019] 3. The design method of the Si-based metasurface structure mid-wave infrared multi-spectral filter array disclosed in the present invention uses all-dielectric silicon nano-cylinders to form the metasurface, avoiding the ohmic loss of the traditional metal plasma metasurface. By selecting appropriate structural parameters, the narrow-band full transmission of the target wavelength can be achieved. The present invention can be integrated with a broadband mid-wave infrared detector to improve the spectral resolution of the photodetector.

[0020] 4. The design method of the Si-based metasurface structure medium-wave infrared multi-spectral filter array disclosed in the present invention can realize multi-spectral narrow-band detection on the basis of achieving beneficial effects 1, 2, and 3, and ensure a high response rate in the medium-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 promote the application and development of medium-wave infrared photoelectric detectors in the field of multi-spectral imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the design method of Si-based metasurface structure mid-wave infrared multi-spectral filter array;

[0022] Figure 2 It is a schematic diagram of a narrow-band multi-spectral photoelectric detector structure and a periodic unit structure thereof provided by an embodiment of the present invention;

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

[0024] Figure 4 It is the absorption spectrum of the InSb detector alone and the InSb detector with the SU-8 transition layer added in the embodiment of the present invention;

[0025] Figure 5 is the transmission spectrum of Si nanodisk under different structural parameters;

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

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

[0028] Figure 8 It is a schematic diagram of the structure of a multi-pixel multi-spectral detector realizing multi-spectral imaging in an embodiment of the present invention.

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

[0030] In order to more completely describe and illustrate the technical solutions and advantages of the present invention, the specific implementation methods of the present invention will be described below in conjunction with the accompanying drawings and embodiments.

[0031] Figure 2 The unit structure of the present invention integrating the medium-wave infrared photodetector with the Si metasurface is shown, which specifically includes a three-layer structure, which is composed of a Si metasurface structure 1, a SU-8 photoresist 2, and an InSb medium-wave infrared photodetector 3 from top to bottom. A plurality of Si nanodisks 4 are periodically arranged on the upper surface of the SU-8 photoresist 2 to form the Si metasurface structure 1. The spectral response of the InSb medium-wave infrared photodetector to the target band is usually wide, which limits its further application in the multi-spectral field. By cooperating with the narrow-band transmission spectrum of the Si metasurface structure 1, narrow-band multi-channel spectral detection can be achieved.

[0032] The material of the Si supersurface structure 1 used in this embodiment is preferably amorphous Si. Since Si is a traditional semiconductor material with a high refractive index, the processing technology is very mature, and it has lower loss than the ohmic loss of metal.

[0033] The SU-8 photoresist 2 used in this embodiment can protect the InSb medium-wave infrared photodetector from being damaged when preparing the Si supersurface structure 1 after curing. At the same time, the appropriate excess thickness can suppress unnecessary optical effects caused by direct contact between the supersurface and the detector. The transition material is not limited to SU-8, and materials with low absorption rate in the corresponding spectral range, such as silicon dioxide, can also be selected.

[0034] like Figure 1 As shown, the design method of the Si-based metasurface structure mid-wave infrared multi-spectral filter array disclosed in this embodiment is specifically implemented in the following steps:

[0035] Step 1: construct an existing Si supersurface array structure model by parameterizing the geometric structure size of the Si supersurface unit: the geometric structure size parameters include the height (H), diameter (D) and spacing (P) of the silicon cylinder;

[0036] Step 2: Use FDTD simulation software to model the structure of the Si supersurface structure 1, which is a periodically arranged array of Si nanodisks 4, such as Figure 3 As shown, the simulation is performed on a periodic unit, the structural parameters are 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 solved according to formulas (1) to (9) to obtain its transmission spectrum and multipolar decomposition diagram of the scattering cross section; the calculation of the transmission spectrum is shown in formula (1):

[0037]

[0038] Where P(f) is the Poynting vector at different frequencies, dS is the integration surface element, and the integration area is the surface where the incident light is transmitted through the monitor on one side of the metasurface.

[0039] The structure generates electric quadrupole resonance (EQ) and electric dipole resonance (ED) under the excitation of incident light, realizing double-peak unidirectional radiation. In the calculation of multipolar 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). In the case of incident light excitation, the scattering power I is expressed as:

[0040]

[0041] Among them, 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 moment 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: Where i is an imaginary number, ω is the circular frequency of the incident wave, c is the speed of light in vacuum, r is the position vector, and r α,β is the component of the position vector in the Cartesian coordinate system; ε0 is the dielectric constant in vacuum; μ0 is the magnetic permeability in vacuum; E inc is the incident light electric field vector; n is the refractive index, which is a function of the position vector r.

[0043] The structure changes the refractive index distribution of the structure by adjusting the three parameters of P, D, and H, thereby changing the distribution of current density, and finally exciting electric quadrupole resonance (EQ) and electric dipole resonance (ED), which is manifested as double-peak narrow-band full transmission in the spectrum. The scattering cross section of the multipole decomposition when the diameter is 1.6 μm is as follows: Figure 6 shown.

[0044] The multipolar resonance mode of the structure under the excitation of incident light is analyzed, and the narrow-band transmission in the spectrum is achieved by adjusting the resonance mode. As a preference, according to the obtained transmission curve, a transmittance higher than 80% and a full width at half maximum (FWHM) less than 200nm are selected as the target, and the corresponding structural parameters are selected as the scanning optimization results of the Si metasurface structure parameters.

[0045] The Si nanodisk 1 has a fixed height H, which can be selected in the range of 1 μm to 1.5 μm. The relationship between the spacing P and the diameter D is defined according to formula (2): Figure 5 Shown is the transmission spectrum of the Si metasurface structure 1 when the Si nanodisk 1 has a fixed height H and a diameter D of 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm and 1.9 μm, respectively, and its 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 of height (H), diameter (D), and spacing (P) on the transmission spectrum of the metasurface array, according to the absorption spectrum of the InSb mid-wave infrared photodetector obtained, select the Si metasurface structure with the corresponding narrow-band transmission spectrum to match it. The absorption spectrum of a single InSb detector and the absorption spectrum of the InSb detector with a SU-8 transition layer are shown in Figure 2. Figure 4 As shown. The Si metasurface structure is integrated on a photodetector with broadband high absorption in the mid-wave infrared, isolated by a SU-8 transition layer in the middle, and the optimal SU-8 layer thickness is obtained by scanning optimization in the range of 0.6-1μm; according to the obtained absorption curve, the absorption rate is higher than 80%, and the full width at half maximum FWHM is less than 200nm as the target, and the optimal SU-8 transition layer thickness is 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 absorption rate of the InSb detector;

[0048] Step 4: Press the Si metasurface structure 1 and the corresponding InSb medium-wave infrared photodetector Figure 2 The overall structure is integrated and simulated by the FDTD method to achieve a multi-spectral photodetector structure with optimized backup narrow-band absorption spectrum. Figure 7 The results show that the method can be used to optimize the multi-spectral narrow-band response of 8 channels in the mid-wave infrared spectrum, and its half-maximum FWHM can reach about 100nm. By integrating Si metasurface-InSb photodetector pixels with different absorption peaks, multi-spectral mid-infrared detection can be achieved.

[0049] By integrating multiple metasurface structure array pixels optimized by the above method onto the same chip, multi-spectral photoelectric detection can be realized. The schematic diagram of the prepared multi-pixel multi-spectral detector is shown in the figure. Figure 8 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. The spectral response of photodetectors made of III-V compound semiconductor materials such as GaAs, InP, InGaAs, InAs, InAsSb and other materials can also be optimized.

[0051] This shows that the design method of a Si-based metasurface structure mid-wave infrared multi-spectral filter array disclosed in this embodiment can realize narrow-band multi-spectral detection in the mid-infrared band by integrating this structure with a mid-wave infrared detector. The metasurface is composed of a number of sub-wavelength-scale metasurface units. The present invention uses all-dielectric material silicon nano-cylinders to form the metasurface, avoiding the ohmic loss of traditional metal plasma metasurfaces. By selecting appropriate structural parameters, narrow-band full transmission of the target wavelength can be achieved. By integrating the present invention with a broadband mid-wave infrared detector, the spectral resolution of the photoelectric detector can be effectively improved. The present invention has potential application value in many fields such as military equipment, aerospace, and road monitoring.

[0052] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above 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 in the scope of protection of the present invention.

Claims

1. A design method for a Si-based metasurface structure mid-wave infrared multi-spectral filter array, characterized in that: The following steps are included: Step 1, the medium-wave infrared multi-spectral filter array is composed of Si-based supersurface structures with different structural parameters; the geometric structure size parameters of different Si-based supersurface structural units are different; the geometric structure size parameters include the height H, diameter D and spacing P of the silicon cylinder; Step 2: Use the finite-difference time-domain algorithm to simulate and analyze the optical response of the Si-based metasurface structure, scan different metasurface array structure parameters in the mid-wave infrared band, and solve the transmission spectrum of the Si-based metasurface structure according to formula (1); Where P(f) is the Poynting vector at different frequencies; dS is the integral bin; sourcepower(f) is the power of the excitation light 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.

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

3. The design method of the Si-based metasurface structure mid-wave infrared multi-spectral filter array as claimed in claim 1, characterized in that: A photodetector is constructed, and a unit structure integrating the photodetector and the Si supersurface structure is constructed. The unit structure includes a three-layer structure, namely, a Si supersurface structure, a SU-8 transition layer, and an InSb medium-wave infrared photodetector from top to bottom.

4. The design method of the Si-based metasurface structure mid-wave infrared multi-spectral filter array as claimed in claim 3, characterized in that: Si metasurface structures with different structural parameters are integrated on InSb photodetectors to achieve multi-spectral mid-infrared detection.

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