Metasurface Spectral Modulator and Spectral Imaging System Based on Continuum Quasi-Bound States

Abstract

The present invention discloses a metasurface spectral modulator and a spectral imaging system based on continuum quasi-bound states. The modulator in the present invention is an all-dielectric metasurface made of silicon material, and its structural parameters can be designed and optimized by comparing the reconstructed image quality corresponding to different structural heights. In an efficient short-wave infrared computational spectral imaging system, the incident light carrying the spectral information of all spatial points of the target object is spectrally modulated by the metasurface spectral modulator based on continuum quasi-bound states according to the spatial position, and then compressed and sampled by a photodetector. The spectra of each spatial point of the target object are reconstructed through the ADMM algorithm and stitched according to the spatial point positions, and finally a spatial-spectral three-dimensional data cube of the target object is obtained. The present invention has high executability and realizes short-wave infrared spectral imaging with both high spectral accuracy and wide wavelength range.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral imaging, and in particular relates to a metasurface spectral modulator based on a continuum quasi-bound state and a high-efficiency short-wave infrared computational spectral imaging system having the spectral modulator. Background Art

[0002] Short-wave infrared spectral imaging technology can obtain spatial-spectral three-dimensional data cubes in the range of 0.9-1.7 μm. It is a new type of visual perception technology that surpasses human perception and is widely used in remote sensing, military, agriculture, medical and security fields. However, traditional short-wave infrared spectral imaging systems rely on large components, which limits miniaturization and portability. At the same time, in practical applications, there are problems such as large data volume, high redundancy, long acquisition time, and difficulty in balancing spatial and spectral resolution.

[0003] The computational spectral imaging system based on micro-nano photonic structures has the characteristics of compact structure, stable performance, no need for moving components and large components, and can achieve high spectral resolution and promote the miniaturization and integration of on-chip spectral imagers. The micro-nano spectral modulator used can be directly integrated into the photodetector pixels to facilitate rapid data acquisition. Combined with the computational reconstruction algorithm, the system can accurately decode spectral information and improve analysis efficiency. Therefore, the use of computational spectral imaging systems based on micro-nano structures to achieve miniaturized, low-cost, high-quality, and wide-imaging short-wave infrared spectral imaging has become a current research hotspot.

[0004] In computational spectral imaging systems based on micro-nano photonic structures, the response (transmittance, reflectance or absorptivity) of the spectral modulator is crucial to the reconstruction accuracy of the system. Micro-nano photonic spectral modulators with high spectral diversity in spectral response can provide better reconstruction quality and spectral resolution. Narrowband spectral modulators with sharp resonance peaks usually have lower correlation coefficients and are suitable for high spectral accuracy requirements; broadband spectral modulators provide a wider wavelength range, but may affect the spectral reconstruction accuracy. Therefore, in order to achieve short-wave infrared imaging with both high spectral accuracy and wide wavelength range, it is urgent to design a micro-nano photonic spectral modulator that combines the advantages of broadband and narrowband modulation, achieve high quality factor resonance while maintaining a flat response at other wavelengths, and balance the spectral range and reconstruction accuracy. Summary of the invention

[0005] The present invention proposes a metasurface spectral modulator based on a continuum quasi-bound state, and a computational spectral imaging system with the spectral modulator, which realizes high-quality reconstruction of short-wave infrared spectral images.

[0006] In a first aspect, the present invention provides a metasurface spectral modulator based on a continuum quasi-bound state, comprising:

[0007] A mirror-symmetric double-ellipsoidal cylinder array made of silicon material, and the double-ellipsoidal cylinder array is located on a silica substrate;

[0008] The size of the double-ellipsoidal cylinder array varies uniformly in the transverse direction, and the major axis, minor axis and period of the double-ellipsoidal cylinder are controlled by a transverse scale factor;

[0009] The metasurface spectral modulator is designed to excite the electric dipole mode in the continuum quasi-bound state (ED-QBIC) and the magnetic dipole mode (MD-QBIC), and precisely control the resonance wavelength of the mode;

[0010] The metasurface spectral modulator is further designed to achieve the collaborative modulation of narrowband and broadband spectral characteristics to cover the resonant peaks in the complete spectral range.

[0011] In a second aspect, the present invention provides a design method for a metasurface spectral modulator, and the method includes the following steps:

[0012] Step 1) Select a mirror-symmetric double-ellipsoidal cylinder as the basic structural unit of the metasurface spectral modulator, and the double-ellipsoidal cylinder is made of silicon material and located on a silica substrate;

[0013] Step 2) Determine the structural height, orientation angle, major axis, minor axis and period of the double-ellipsoidal cylinder as structural parameters;

[0014] Step 3) By uniformly varying the transverse scale factor, adjust the major axis, minor axis and period in the structural parameters to control the resonance wavelengths of the electric dipole mode and magnetic dipole mode in the continuum quasi-bound state;

[0015] Step 4) Design the double-ellipsoidal cylinder array to excite high-quality factor continuum quasi-bound state resonant peaks, and the resonant peaks cover the entire imaging spectral range;

[0016] Step 5) Realize the synergistic effect of narrowband continuum quasi-bound state resonance and metasurface wide-spectrum resonance modulation in the non-continuum quasi-bound state interaction band to meet the requirements of wide working bandwidth and high spectral resolution.

[0017] In a third aspect, the present invention provides a short-wave infrared computational spectral imaging system, which adopts the metasurface spectral modulator, and the metasurface spectral modulator is directly integrated onto the imaging pixels of a photodetector; the photodetector is used to detect the light modulated by the metasurface spectral modulator; the system further includes a light source for irradiating a target object;

[0018] The system reconstructs the detected signal through the alternating direction method of multipliers (ADMM) to obtain the spectral information of each spatial point of the target object, and splices them according to the spatial positions, and finally obtains the spatial-spectral three-dimensional data cube of the target object.

[0019] Advantages of the present invention:

[0020] (1) By directly integrating the metasurface spectrometer based on the continuum quasi-bound state onto the imaging pixels of the detector, the data acquisition process is effectively simplified, the data sampling rate is increased, and at the same time, it is beneficial to reduce the volume and cost of the short-wave infrared spectral imaging system.

[0021] (2) By realizing short-wave infrared spectral regulation through the metasurface based on the continuum quasi-bound state, as the transverse scale scaling factor uniformly changes to scale the structure, the resonance wavelengths of ED-QBIC and MD-QBIC can be precisely controlled simultaneously, and through the high-order resonance under a large scaling factor, imaging with a larger spectral range and higher spectral resolution can be achieved.

[0022] (3) By realizing short-wave infrared spectral regulation through the metasurface based on the continuum quasi-bound state, the sparse characteristics of the target object in the spectral dimension are fully utilized, greatly improving the sampling efficiency of the system and the reconstruction quality of the spectral image. Description of the drawings

[0023] Figure 1 Schematic diagram of the short-wave infrared computational spectral imaging system of the present invention;

[0024] Figure 2 Flowchart for optimizing the double elliptical cylinder metasurface in the present invention;

[0025] Figure 3 Schematic diagram of the basic structure of the metasurface spectrometer based on the continuum quasi-bound state of the present invention;

[0026] Figure 4 25 kinds of spectral transmittances that can be achieved by the metasurface spectrometer under the regulation of the scaling factor. Detailed implementation manners

[0027] The present invention will be further described below in conjunction with the drawings and examples.

[0028] The embodiment of the present application provides a computational spectral imaging system for short-wave infrared (0.9 - 1.7 μm) with narrowband and broadband collaborative modulation, including a light source, a metasurface spectrometer based on the continuum quasi-bound state, and a photodetector.

[0029] The compressive sampling and computational reconstruction process of this system includes the following steps:

[0030] 1) The light source irradiates the target object, generating incident light carrying the target spatial-spectral information;

[0031] 2) Image the incident light carrying the spectral information of the target object's spatial points onto the metasurface spectral modulator based on the continuum quasi-bound state integrated on the imaging pixels of the photodetector according to the spatial position. The metasurface spectral modulator based on the continuum quasi-bound state performs spectral modulation on the incident light carrying the spatial point spectrum numbered , where L is the total number of modulations of the spectral modulator;

[0032] 3) The modulated light is directly detected by the photodetector;

[0033] 4) Input the detected signal into the ADMM algorithm for reconstruction to obtain the spectral information of the target spatial point;

[0034] 5) Stitch the spectral information of the reconstructed spatial points according to the spatial position to finally obtain the spatial-spectral three-dimensional data cube of the target object.

[0035] In the step 1), the incident light carrying the spatial-spectral information of the target object after discretization can be written in vector form f, with a magnitude of , where M is the size of the spectral dimension of the image to be reconstructed, is the size of the spatial dimension.

[0036] In the step 2), the incident light carrying the spectral information at the spatial point of the target object can be written in vector form , with a magnitude of . The total number of spectral modulations performed by the metasurface spectral modulator based on the continuum quasi-bound state is , corresponding to types of spectral transmittances of the metasurface. The matrix form of the spectral modulation is H, with a size of .

[0037] In the step 3), the signal detected by the photodetector can be written in vector form g, with a magnitude of .

[0038] In the step 4), the sparse prior adopted by the ADMM algorithm is Ψ, with a size of , being the number of atoms in the sparse prior.

[0039] In the step 5), finally, the spatial-spectral three-dimensional data cube of the target object is obtained, with a size of .

[0040] Preferably, the spectral dimension size of the incident light at the spatial point is .

[0041] Preferably, the number of modulations of the dynamic spectral modulator.

[0042] Preferably, the spatial-spectral three-dimensional data cube of the target object .

[0043] The embodiment of the present application also provides a full-dielectric metasurface dynamic spectral modulator based on continuum quasi-bound states and a method for optimizing its structural parameters.

[0044] The metasurface structure consists of a mirror-symmetric double-elliptical cylinder array of silicon material located on a silica substrate. Silicon has low loss in the short-wave infrared region. As the lateral scale scaling factor changes uniformly, the size of the double-elliptical cylinder also changes laterally,

[0045] By uniformly changing the lateral scale scaling factor to simultaneously control the three structural parameters of the major axis, minor axis, and period of a pair of basic double-elliptical cylinders, and changing the lateral size of the structure, the resonance wavelengths of ED-QBIC and MD-QBIC can be precisely controlled simultaneously, so that the high-quality factor continuum quasi-bound state resonance peaks excited by different double-elliptical cylinder arrays cover the entire imaging spectral range; the narrowband continuum quasi-bound state resonance and the broadband spectral resonance modulation of the metasurface in the non-continuum quasi-bound state interaction band work together to achieve the collaborative modulation of narrowband and broadband spectral features in the entire spectral range, while meeting the requirements of wide working bandwidth and high spectral resolution.

[0046] The metasurface spectral modulator based on continuum quasi-bound states in the present application is directly integrated onto the imaging pixels of the detector, and 25 continuum quasi-bound state structures obtained from the scaling structure form the basic unit of single-pixel spatial spectral modulation.

[0047] Furthermore, the optimization of the metasurface parameters is to optimize the structural height, aiming to make the excitation position of the high-quality factor resonance peak of the continuum quasi-bound state cover the entire imaging band to obtain the optimal imaging effect. The specific optimization process includes the following steps:

[0048] 1) Select the structural parameters of the mirror-symmetric double-elliptical cylinder of the metasurface based on continuum quasi-bound states (including the major axis, minor axis, period, and orientation angle of the double-elliptical cylinder). When the lateral scale scaling factor S = 1, calculate the spectral transmittance that can be achieved when the structural height of the metasurface based on continuum quasi-bound states varies in the range of 300 nm to 600 nm through rigorous coupled-wave analysis simulation, and record the transmittance matrix corresponding to different structural heights;

[0049] 2) By analyzing the excitation of the high-quality factor resonance peak of the metasurface continuum quasi-bound state at different structural heights, screen the metasurface structures that can simultaneously excite ED-QBIC and MD-QBIC;

[0050] 3) Calculate the 25 spectral transmittances achievable when the selected metasurface structures vary uniformly with S in the range of S (0.52 - 1.48) through rigorous coupled-wave analysis simulation, and record the transmittance matrices of different structures;

[0051] 4) By analyzing the transmittance matrices recorded in step 3), screen out the metasurface structures whose quasi-bound states in the continuum resonances can cover the entire short-wave infrared imaging band;

[0052] 5) Select the structure with the highest average imaging quality by evaluating the imaging quality of the metasurfaces screened in step 4) for multiple real scenarios;

[0053] Preferably, the mirror-symmetric double elliptical cylinder has a fixed height of 500 nm, a fixed direction angle of 40°, and a structure where the major axis, minor axis, and period vary uniformly with S. When S = 1, the major axis is 452 nm, the minor axis is 266 nm, and the periods are 918 nm and 452 nm respectively.

[0054] Example:

[0055] As Figure 1 shown, the short-wave infrared computational spectral imaging system of this example includes a light source 1, a metasurface spectral modulator 2 based on quasi-bound states in the continuum, and a single-pixel detector 3.

[0056] The system sampling and reconstruction process includes:

[0057] 1) The light emitted by the light source 1 is projected onto the target object. The target object is discretized into a three-dimensional data cube with a spatial size of 8 * 8 and a spectral size of 161. Among them, the spectral range is 900 nm - 1700 nm, and the spectral interval is 5 nm;

[0058] 2) Each spatial point of the target object is imaged on the metasurface spectral modulator 2 based on quasi-bound states in the continuum for spectral modulation numbered ;

[0059] 3) Each spatial point of the target object is directly detected by the photodetector 3 after spectral modulation;

[0060] 4) The short-wave infrared spectral image of each spatial point of the target object is reconstructed through the ADMM algorithm;

[0061] 5) By stitching the spectra of each spatial point according to the spatial position, the complete short-wave infrared spectral image of the target object is finally obtained.

[0062] As Figure 2 shown, the structural parameter optimization process of the metasurface spectral modulator based on quasi-bound states in the continuum in this application:

[0063] 1) Select the major axis, minor axis, period, and direction angle of the mirror-symmetric double cylinder of the metasurface based on the continuum quasi-bound state. When S = 1, calculate the spectral transmittance that can be achieved when the height of the metasurface structure varies in the range of 300 nm to 600 nm through rigorous coupled-wave analysis simulation, record the corresponding spectral transmittance matrices respectively, with a size of 1×161;

[0064] 2) Screen the metasurface structures that can simultaneously excite ED-QBIC and MD-QBIC;

[0065] 3) Calculate the 25 spectral transmittances that can be achieved when S varies uniformly in the range of 0.52 to 1.48 at an interval of 0.04 for each metasurface structure screened in step 2) through rigorous coupled-wave analysis, and record the spectral transmittance matrix H corresponding to different structures, with a size of 25×161;

[0066] 4) Screen the metasurface structures whose continuum quasi-bound state resonance peaks can cover the entire short-wave infrared imaging band;

[0067] 5) Image the metasurfaces screened in step 4) for multiple real scenarios and evaluate the imaging quality, and select the structure with the highest average imaging quality.

[0068] As Figure 3 shown, on the silica substrate 32, after optimizing the structural parameters, the height of the mirror-symmetric double elliptical cylinder 31 is fixed at 500 nm, the direction angle is fixed at 40°, when S = 1, the major axis is 452 nm, the minor axis is 266 nm, and the periods are 918 nm and 452 nm respectively. By regulating S to vary uniformly in the range of 0.52 to 1.48 at an interval of 0.04, 25 different transmission spectra can be achieved in the wavelength range of 900 nm - 1700 nm in the short-wave infrared, as shown in Figure 4 . The excited high-quality factor continuum quasi-bound state resonance peaks cover the entire imaging band, and jointly act with the broadband spectral resonance modulation of the metasurface in the non-continuum quasi-bound state interaction band, so as to achieve the goal of synergistic modulation of narrowband and broadband spectral characteristics in the complete spectral range, and realize short-wave infrared spectral imaging with both a wide imaging band range and high spectral resolution.

[0069] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A metasurface spectral modulator based on a continuum quasi-bound state, characterized in that: include: A mirror-symmetrical double elliptical column array made of silicon material, wherein the double elliptical column array is located on a silicon dioxide substrate; The size of the double elliptical cylinder array varies uniformly in the lateral direction, and the major axis, minor axis and period of the double elliptical cylinder are controlled by a lateral scale scaling factor; The metasurface spectral modulator is designed to excite continuum quasi-bound state electric dipole modes and magnetic dipole modes, and precisely control the resonant wavelength of the modes; The metasurface spectral modulator is further designed to achieve coordinated modulation of narrowband and broadband spectral features to cover the resonance peaks in the complete spectral range; The double elliptical column array includes 25 different size variations to achieve resonance peak coverage within the imaging spectrum range; the double elliptical column array of silicon material is fixed on a silicon dioxide substrate, and the height of the double elliptical column is fixed at 500nm and the direction angle is fixed at 40°; the lateral scale scaling factor is S = 1, the major axis is 452 nm, the minor axis is 266 nm, and the periods are 918 nm and 452 nm, respectively. By adjusting the lateral scale scaling factor S It varies uniformly from 0.52 to 1.48 at intervals of 0.04, achieving 25 different transmission spectra in the wavelength range of short-wave infrared 900 nm-1700 nm.

2. A method for designing a metasurface spectral modulator according to claim 1, characterized in that: The method comprises the following steps: Step 1) selecting a mirror-symmetrical double elliptical cylinder as a basic structural unit of a metasurface spectrum modulator, wherein the double elliptical cylinder is made of silicon material and is located on a silicon dioxide substrate; Step 2) determining the structural height, orientation angle, major axis, minor axis and period of the double elliptical cylinder as structural parameters; Step 3) adjusting the major axis, minor axis and period in the structural parameters to control the resonant wavelength of the continuum quasi-bound state electric dipole mode and magnetic dipole mode by uniformly changing the lateral scale scaling factor; Step 4) designing the double elliptical cylinder array to excite a continuum quasi-bound state resonance peak with a high quality factor, wherein the resonance peak covers the entire imaging spectral range; Step 5) realizes the synergistic effect of narrow-band continuum quasi-bound state resonance and discontinuum quasi-bound state action band metasurface wide-spectrum resonance modulation to meet the requirements of wide working bandwidth and high spectral resolution.

3. The design method according to claim 2, characterized in that: In step 3), the lateral scale scaling factor is uniformly varied in the range of 0.52 to 1.48 at an interval of 0.

04.

4. The design method according to claim 2 or 3, characterized in that: In step 5), the synergy is achieved by optimizing the structural height of the double elliptical cylinders to maximize the imaging quality and spectral resolution.

5. The design method according to claim 4, characterized in that: It also includes using rigorous coupled wave analysis simulation to calculate the spectral transmittance that can be achieved when the height of the structure changes.

6. The design method according to claim 4, characterized in that: It also includes an evaluation of the imaging quality of a variety of real scenes to select the metasurface structure with the highest average imaging quality.

7. A short-wave infrared computational spectral imaging system, using the metasurface spectral modulator according to claim 1, characterized in that: The metasurface spectral modulator is directly integrated into the imaging pixel of the photodetector; the photodetector is used to detect the light modulated by the metasurface spectral modulator; the system also includes a light source for irradiating the target object; The system reconstructs the detected signals through an alternating direction multiplier algorithm to obtain the spectral information of each spatial point of the target object, and splices them according to the spatial position to finally obtain a spatial-spectral three-dimensional data cube of the target object.

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