Micro-nano structure-based adjustable window sheet and design method thereof

Abstract

The application belongs to the technical field of infrared light field regulation and infrared photoelectric detection, and particularly relates to a tunable window sheet based on a micro-nano structure and a design method thereof, comprising a substrate and a phase change superlattice algorithm optimization area arranged on the substrate, wherein the phase change superlattice algorithm optimization area comprises a plurality of period units, each period unit is divided into MxN square units, and the state of each square unit is air or a phase change material; the application has modulation performances of anti-reflection and high reflection, can realize switching of high reflection and high transmission in a working wavelength range, and has high transmittance and reflectance. Compared with general optimization, the four-part optimization design method exhibits the advantage of polarization insensitivity in device design, and greatly improves the application potential of the device.

Description

Technical Field

[0001] This invention belongs to the field of infrared light field modulation and infrared photoelectric detection technology, specifically relating to an adjustable window based on micro-nano structures and its design method. Background Technology

[0002] Infrared light field manipulation has always been a core focus of infrared technology research, with the anti-reflection (high transmission) and high emissivity of windows directly impacting the performance of infrared optoelectronic systems. Since Professor Soref proposed silicon photonics in the 1980s, the fabrication process for silicon-based optoelectronic devices has become quite mature, offering advantages such as diverse methods, low cost, and stable performance. However, due to silicon's high refractive index and relatively high intrinsic absorptivity, silicon is generally not used for long-wavelength infrared imaging or window optical elements. However, in Mie scattering research, the transmission (anti-reflection) of Si-based windows has been enhanced by introducing Si-based superlattices. To date, no infrared modulation device can simultaneously function as both a window and a mirror, which severely hinders the integration of optoelectronic systems and impedes cost reduction.

[0003] In the field of infrared spectroscopy, obtaining the infrared transmittance and reflectance of a sample requires two different infrared optical systems. However, using a modulated infrared window with transmission / reflection capabilities can replace this complex optical system and enable in-situ transmission and reflectance measurement, something traditional infrared spectroscopy cannot achieve. In optoelectronic countermeasures, infrared detectors receive infrared light transmitted through an infrared window for imaging. Laser damage often involves blinding the detector with a high-power laser. If adaptive switching between high transmittance and high reflectance could be implemented, compatibility between infrared detector imaging and protection could be achieved. However, infrared modulators based on absorption and reflection cannot reach the detector through the modulator, thus limiting their application in this field. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a tunable window based on micro / nano structures and its design method, which simultaneously possesses anti-reflection and high-reflection modulation properties to achieve switching between high reflection and high transmission within the operating wavelength range, resulting in high transmittance and reflectivity. Compared with general optimization, this quartic optimization design method demonstrates its advantage of polarization insensitivity in device design, greatly enhancing the application potential of the device.

[0005] This invention provides an adjustable window based on micro / nano structures, including a substrate and a phase change superlattice algorithm optimization region disposed on the substrate. The phase change superlattice algorithm optimization region includes multiple periodic units, each periodic unit is divided into M×N square units, and the state of each square unit is either air or phase change material.

[0006] The state of the periodic unit is determined by the following design method: an initial population composed of multiple square units is constructed; a transmittance and reflectance evaluation function is constructed based on the target wavelength range to obtain performance index values; genetic operations are performed on the initial population to generate a new generation population; the genetic operations include replication, selection, crossover, and mutation operations; the genetic algorithm is judged to meet the stopping optimization condition by detecting whether the performance index value of the best individual in the new generation population tends to stabilize after multiple optimizations; wherein, the best individual is the genetic individual with the best performance index value; if the condition is met, the periodic unit corresponding to the best individual is obtained.

[0007] In one embodiment, the transmittance and reflectance evaluation function is:

[0008] FOM trans For the transmittance evaluation function in the operating wavelength range of 7–14 μm and the wavelength range of 9–11 μm, FOM is used. ref It is a reflectivity evaluation function for the working wavelength range of 7–14 μm and the wavelength range of 9–11 μm.

[0009] In one embodiment, the side length of the periodic unit is 0.1-14 μm, and the thickness of the periodic unit is 0.1-2 μm.

[0010] In one embodiment, the phase change material is VO2, Ge2Sb2Te5, Ge3Sb2Te6, Ge2Sb2Se4Te1, or In3SbTe. 2， The preferred phase change material is In3SbTe2.

[0011] In one embodiment, the periodic unit has a side length of 5 μm and a thickness of 1 μm.

[0012] In one embodiment, M equals N, and the phase transition superlattice algorithm optimization region includes four periodic units: B1, B2, B3, and B4. The B1 periodic unit is obtained by rotating 90° around the center of the phase transition superlattice algorithm optimization region to obtain the B2 periodic unit. The B2 periodic unit is obtained by rotating 90° around the center of the phase transition superlattice algorithm optimization region to obtain the B3 periodic unit. The B3 periodic unit is obtained by rotating 90° around the center of the phase transition superlattice algorithm optimization region to obtain the B4 periodic unit.

[0013] In one embodiment, "0" represents no phase change material filling, i.e., an air state, and "1" represents a phase change material filling state, with M equal to 5; the state of the phase change superlattice algorithm optimization region is:

[0014] The state of cell 01 is: 1,0,0,1,0,1,0,1,1,1;

[0015] The state of cell 02 is: 1,0,1,0,1,1,0,1,0,0;

[0016] The state of cell 03 is: 1,1,1,1,0,0,1,1,1,0;

[0017] The state of cell 04 is: 0,0,1,1,0,0,1,1,0,1;

[0018] The state of cell 05 is: 1,1,0,0,1,1,0,0,1,0;

[0019] The state of cell 06 is: 0,1,0,0,1,1,0,0,1,1;

[0020] The state of cell 07 is: 1,0,1,1,0,0,1,1,0,0;

[0021] The state of cell 08 is: 0,1,1,1,0,0,1,1,1,1;

[0022] The state of cell 09 is: 0,0,1,0,1,1,0,1,0,1;

[0023] The state of cell 10 is: 1,1,1,0,1,0,1,0,0,1.

[0024] In one embodiment, the substrate is a Si substrate.

[0025] This invention provides a design method for tunable windows based on micro / nano structures. The state of the periodic unit is determined by the following design method: an initial population composed of multiple square units is constructed; transmittance and reflectance evaluation functions are constructed based on the target wavelength range to obtain performance index values; genetic operations are performed on the initial population to generate a new generation population; the genetic operations include replication, selection, crossover, and mutation; the genetic algorithm is judged to meet the stopping condition by detecting whether the performance index value of the best individual in the new generation population tends to stabilize after multiple optimizations; wherein, the best individual is the genetic individual with the best performance index value; if the condition is met, the periodic unit corresponding to the best individual is obtained.

[0026] The beneficial effects of this invention are as follows:

[0027] Phase change materials (PCMs) are often opaque absorbers. Due to intrinsic loss issues, bulk PCMs often struggle to achieve high reflectivity. Typically, intrinsic absorption is modulated in PCMs to increase transmittance, rather than enhancing reflection. High-reflectivity structures usually employ Bragg gratings composed of transparent media or metal coatings. In this invention, a rationally designed PCM superlattice achieves enhanced light field reflection, a property not inherent in typical PCMs. Based on the modulating properties of PCMs, the inventors used a reverse design algorithm to design a tunable silicon-based window based on a PCM superlattice. This allows the silicon-based window to simultaneously possess anti-reflection and high-reflection modulation properties, which is significant for infrared light field modulation and the integration and expansion of infrared systems.

[0028] This invention proposes a tunable silicon-based window based on a phase change superlattice and its design / manufacturing method, thereby achieving compatibility between high transmittance (anti-reflection) and high reflectance light field modulation characteristics of the silicon-based window. When the phase change material is in an amorphous state, the broadband average transmittance of 7–14 μm reaches 90.7%, a 35% improvement compared to silicon wafers. When the phase change material is in a crystalline state, the broadband average reflectance of 7–14 μm reaches 91.5%, a 60% improvement compared to silicon wafers. This tunable silicon-based window further solves the compatibility problem of simultaneously achieving high reflectance and high transmittance in infrared light field modulation, providing a new integrated solution for infrared light field modulation. Attached Figure Description

[0029] Figure 1 This is a three-dimensional schematic diagram of the periodic structure of the adjustable window based on the phase transition superlattice of the present invention.

[0030] Figure 2 This is a top view of the optimization region of the phase transition superlattice algorithm in an embodiment of the present invention.

[0031] Figure 3 This is a top view of the optimization region of the phase transition superlattice algorithm in the final optimized embodiment of the present invention.

[0032] Figure 4 The infrared spectrum under high reflectance and high transmittance conditions is ultimately optimized for the structure of this invention.

[0033] Figure 5 This is a comparison of the infrared transmittance of the present invention with that of a silicon window wafer.

[0034] Figure 6 This is a comparison of the infrared reflectivity of the present invention with that of a silicon window wafer.

[0035] Figure 7 This is the light field distribution at 10 μm in the high transmission mode of this embodiment of the invention.

[0036] Figure 8 This is the light field distribution at 10 μm in the high-reflectivity mode of this embodiment of the invention.

[0037] Figure 9 This invention compares the infrared transmittance of the optimal structure obtained by the quartic optimization algorithm and the genetic algorithm through direct discretization in an embodiment of the invention.

[0038] Figure 10 This invention compares the infrared reflectance of the optimal structure obtained by the quartic optimization algorithm and the genetic algorithm through direct discretization in an embodiment of the invention.

[0039] Figure 11 The mid-infrared polarization sensitivity of the optimal structure directly discretized by the genetic algorithm is determined by normal incidence of light with different polarizations. Detailed Implementation

[0040] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] A tunable silicon-based window based on a phase change superlattice includes a silicon substrate 1. A phase change superlattice algorithm optimization region 2 is formed on the silicon substrate 1. The phase change superlattice algorithm optimization region 2 is composed of periodic porous phase change material micro / nano structure patterns, i.e., periodic units. Materials include VO2, Ge2Sb2Te5, Ge3Sb2Te6, Ge2Sb2Se4Te1, In3SbTe2, etc. One periodic structure is divided into 2M×2N equally sized square units B. 2M2N That is, square unit 21, by adjusting the square unit B 2M2N The state (phase change material or air) forms a porous array based on the phase change material. The operating bandwidth of this adjustable window is 7–14 μm. To satisfy the subwavelength periodicity condition within the operating bandwidth, the structural period is smaller than the operating wavelength, and the side length P of a periodic unit satisfies 0.1 μm ≤ P ≤ 14 μm, and the thickness T satisfies 0.1 μm ≤ T ≤ 2 μm. Figure 1 As shown, taking a 10×10 grid as an example (2M=2N=10), we present a schematic diagram of the array structure of periodic units and identify the two basic regions, A and B. In actual fabrication, the superlattice structure on the window will be arranged periodically with structural units of side length P and thickness T.

[0043] In this embodiment, the material of the phase transition superlattice algorithm optimization region B is In3SbTe2, the side length of the periodic unit is P = 5μm, and the thickness is T = 1μm.

[0044] The structure of the optimized region in this invention is intelligently designed using a genetic algorithm, and includes the following steps:

[0045] Step 1: Determine the function of the device. Define the quality factor function representing the device's function:

[0046]

[0047] In the formula, FOM trans and FOM ref These are the transmittance and reflectance evaluation functions for the operating wavelength range (7–14 μm) and the preferred wavelength range (9–11 μm), respectively; T a (λ) represents the transmittance at wavelength λ when the filling phase change material is in an amorphous state (a); R c (λ) represents the reflectance at wavelength λ when the phase change material is in the crystalline state (c). The optimization function aims to maximize the value of the Formal Image Model (FOM), enabling the silicon-based tunable window designed using a genetic algorithm to achieve switchable high transmittance and high reflectance infrared light field modulation.

[0048] Step 2: Discretizing the optimization region of the device. The inventors discovered that the periodic structure is square (M=N). The phase transition superlattice algorithm optimization region B is divided into four equal regions: B1, B2, B3, and B4. Regions B2, B3, and B4 are obtained by rotating B1 by 90° around the periodic center, thus achieving a four-part symmetric structure. The 5μm×5μm phase transition superlattice algorithm optimization region B is divided into 10×10 equally sized square pixel cells B. 2M2N We know that the side length of the pixel cell is L = 0.5 μm; each square pixel cell has two states: filled with phase change material and not filled with phase change material, i.e., phase change material state and air state. Figure 2 The diagram shows a schematic of a randomized initial periodic structure, with four regions labeled B1, B2, B3, and B4. A pixel grid with side length L is defined using dashed lines, where white pixels are unfilled (air) pixels, and gray pixels are filled with phase change material.

[0049] The inventors discovered that by directly rotating individual periodic units sequentially by 90°, not only can the optimization process be simplified and the optimization speed accelerated, but the resulting tunable silicon-based window also has higher transmittance and reflectivity, while making the incident light less sensitive to polarization.

[0050] Step 3: Genetic Algorithm Optimization. The initial population structure consists of 200 randomized array individuals. Each individual is represented by 25 binary numbers of "0" or "1", representing that the square pixel unit has two states: "0" indicates no phase change material (air) filling, and "1" indicates phase change material filling. For example... Figure 2As shown, we present a schematic diagram of the optimization region of a stochastic periodic algorithm, and label the four regions B1, B2, B3, and B4. For each individual, the evaluation function FOM (Form of Meaning) for high transmittance in amorphous states and high reflectance in crystalline states is calculated twice. The individual with the best FOM directly becomes the next generation of individuals. Except for the best individual, which is retained in the next generation, all other offspring are generated through parent crossover and mutation processes. Parent individuals are randomly selected from the previous generation, with a number of 170. The crossover process involves randomly selecting the crossover point between the binary codes of two parents and replacing and recombining them to form a new individual. The mutation process involves the random mutation point of the binary code of the new individual generated by the crossover process changing (i.e., the original code 0 mutates to 1, and the original code 1 mutates to 0). The entire algorithm iterates 20 times, terminating when there are individuals with FOM greater than 99% in the offspring, or when 20 iterations are completed. The mutation rate (Mutation_rate) is set to 0.3.

[0051] Step 4: Obtain the final structure. Each iteration involves calculating the FOM (Form of Meaning) for 200 individuals in each generation of the population (400 calculations). After 20 iterations, the final structure is obtained. Figure 3 As shown in the iterative process, the optimal individual was found in the 8th iteration and retained until the 20th generation. To describe the specific device structure, "0" represents no filling, and "1" represents filling the square pixel unit with phase-change material. The pixel distribution of the optimal structure period is as follows:

[0052] The state of cell 01 is: 1,0,0,1,0,1,0,1,1,1;

[0053] The state of cell 02 is: 1,0,1,0,1,1,0,1,0,0;

[0054] The state of cell 03 is: 1,1,1,1,0,0,1,1,1,0;

[0055] The state of cell 04 is: 0,0,1,1,0,0,1,1,0,1;

[0056] The state of cell 05 is: 1,1,0,0,1,1,0,0,1,0;

[0057] The state of cell 06 is: 0,1,0,0,1,1,0,0,1,1;

[0058] The state of cell 07 is: 1,0,1,1,0,0,1,1,0,0;

[0059] The state of cell 08 is: 0,1,1,1,0,0,1,1,1,1;

[0060] The state of cell 09 is: 0,0,1,0,1,1,0,1,0,1;

[0061] The state of cell 10 is: 1,1,1,0,1,0,1,0,0,1.

[0062] exist Figure 4 In comparison, a tunable silicon-based window with the optimal phase change superlattice structure was used. It was found that when the phase change layer was in the amorphous state, the average transmittance of the proposed tunable window in the working bandwidth was 90.7%; while in the crystalline state, the average reflectance in the working bandwidth was 91.5%.

[0063] like Figure 5 and 6 As shown, compared with silicon wafers, the proposed configuration significantly improves both infrared transmission and infrared reflection modulation capabilities, with an average transmittance increase of 35% and an average reflectance increase of 60%. This further illustrates the application value of the proposed tunable silicon-based window based on phase change superlattices in the field of infrared light field modulation.

[0064] Figure 7 The local electromagnetic field distribution within a periodic cell at 10 μm in the high transmission mode is presented. It can be seen that in the high transmission mode, due to the coupling of the resonant modes of polarization and magnetic polarization, the incident light is confined in the superlattice, thereby achieving transmission enhancement and further improving the transmittance of the window.

[0065] Figure 8 The local electromagnetic field distribution within a periodic cell at 10 μm in the high-reflection mode is presented. It can be seen that in the high-reflection mode, due to the metal-like properties of the phase change material, an equivalent metal layer is formed, which effectively blocks the downward transmission of incident light and suppresses the transmission of incident light.

[0066] Figure 9 and Figure 10 The transmittance and reflectance within the working bandwidth window of the structure designed by direct discretization using a genetic algorithm (i.e., directly optimizing all square pixel units using the genetic algorithm in step 3) and the quaternary symmetric structure were compared. It can be seen that the transmittance performance of the quaternary symmetric genetic algorithm is not significantly different from that of the direct discretization result (0.92). However, in terms of crystallization reflectance, the structure optimized by the quaternary symmetric genetic algorithm can effectively achieve high in-band reflectance (0.92), while the direct discretization design, due to the insignificant effect of the large resonant field constraint in the sample space, results in an average reflectance of only 0.72, a difference of approximately 20%. This further illustrates the performance advantage of the quaternary symmetric algorithm design method in this invention compared to general optimization design methods in device design.

[0067] also, Figure 11The reflectance of the structure directly discrete by the genetic algorithm is given for normal incidence of light with different polarizations. It can be seen that the in-band reflectance of the structure varies greatly under different polarizations, with different reflection peaks. However, the structure with quartic symmetry exhibits good polarization insensitivity to polarized light, and the reflectance is basically the same for normal incidence of different polarizations.

[0068] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0069] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. An adjustable window based on micro / nano structures, characterized in that, It includes a substrate (1) and a phase change superlattice algorithm optimization region (2) disposed on the substrate (1). The phase change superlattice algorithm optimization region (2) includes multiple periodic units, each periodic unit is divided into M×N square units (21), and each square unit (21) is in the state of air or phase change material. The state of the periodic unit is determined by the following design method: an initial population composed of multiple square units (21) is constructed, and a transmittance and reflectance evaluation function is constructed based on the target wavelength range to obtain performance index values; genetic operations are performed on the initial population to generate a new generation population; the genetic operations include replication, selection, crossover and mutation operations; the genetic algorithm is judged to meet the stopping optimization condition by detecting whether the performance index value of the best individual in the new generation population tends to be stable after multiple optimizations; wherein, the best individual is the genetic individual with the best performance index value; if it is satisfied, the periodic unit corresponding to the best individual is obtained; M equals N. The phase transition superlattice algorithm optimization region (2) includes four periodic units: B1, B2, B3, and B4. The B1 periodic unit is rotated 90° around the center of the phase transition superlattice algorithm optimization region (2) to obtain the B2 periodic unit. The B2 periodic unit is rotated 90° around the center of the phase transition superlattice algorithm optimization region (2) to obtain the B3 periodic unit. The B3 periodic unit is rotated 90° around the center of the phase transition superlattice algorithm optimization region (2) to obtain the B4 periodic unit.

2. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, The transmittance and reflectance evaluation functions are as follows: , FOM trans This is a transmittance evaluation function for operating wavelength ranges of 7~14μm and 9~11μm. FOM ref It is a reflectivity evaluation function for the working wavelength range of 7~14μm and the wavelength range of 9~11μm.

3. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, The side length of the periodic unit is 0.1-14 μm, and the thickness of the periodic unit is 0.1-2 μm.

4. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, The phase change material is VO2, Ge2Sb2Te5, Ge3Sb2Te6, Ge2Sb2Se4Te1 or In3SbTe2.

5. The adjustable window based on micro / nano structures as described in claim 4, characterized in that, The phase change material is In3SbTe2.

6. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, The periodic unit has a side length of 5 μm and a thickness of 1 μm.

7. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, "0" indicates no phase change material is filled, i.e., the air state; "1" indicates the state filled with phase change material; M equals 5; the state of the phase change superlattice algorithm optimization region (2) is: The state of cell 01 is: 1,0,0,1,0,1,0,1,1,1; The state of cell 02 is: 1,0,1,0,1,1,0,1,0,0; The state of cell 03 is: 1,1,1,1,0,0,1,1,1,0; The state of cell 04 is: 0,0,1,1,0,0,1,1,0,1; The state of cell 05 is: 1,1,0,0,1,1,0,0,1,0; The state of cell 06 is: 0,1,0,0,1,1,0,0,1,1; The state of cell 07 is: 1,0,1,1,0,0,1,1,0,0; The state of cell 08 is: 0,1,1,1,0,0,1,1,1,1; The state of cell 09 is: 0,0,1,0,1,1,0,1,0,1; The state of cell 10 is: 1,1,1,0,1,0,1,0,0,1.

8. The adjustable window based on micro / nano structures as described in claim 1, characterized in that, The substrate is a Si substrate.

9. A design method for an adjustable window based on a micro / nano structure as described in any one of claims 1-8, characterized in that, The state of the periodic unit is determined by the following design method: an initial population composed of multiple square units (21) is constructed, and a transmittance and reflectance evaluation function is constructed based on the target wavelength range to obtain performance index values; genetic operations are performed on the initial population to generate a new generation population; the genetic operations include replication, selection, crossover and mutation operations; by detecting whether the performance index value of the best individual in the new generation population tends to be stable after multiple optimizations, it is determined whether the genetic algorithm meets the stopping optimization condition; wherein, the best individual is the genetic individual with the best performance index value; if it is satisfied, the periodic unit corresponding to the best individual is obtained.

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