Switchable dual-band high-quality factor metasurface sensor and system

Abstract

The present invention discloses a dual-band high-quality metasurface sensor and system that can be switched. The metasurface sensor of the present invention includes a substrate and an all-dielectric metasurface structure array; the all-dielectric metasurface structure array includes a plurality of all-dielectric metasurface structure units, and the all-dielectric metasurface structure unit is in a four-leaf clover structure, consisting of four cylinders with equal radius and a cube in the middle. The material is GST, and the switching control of the sensor is achieved by changing the crystal state of the material; cylindrical air holes are also provided on the all-dielectric metasurface structure unit to form a spatially asymmetric structure. The sensor of the present invention has an extremely high Q factor and high refractive index sensitivity. The sensor has two working wavelengths in the near-infrared band, which is suitable for detection in a variety of application scenarios, and the switching control of the sensor can be achieved by changing the crystal state of the material.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano metasurface sensing technology, and relates to a switch-controllable dual-working-band high-quality factor metasurface sensor and system, which can be applied to technical fields such as gas sensing and biosensing. Background Art

[0002] Metasurfaces with high-quality (Q)-factor resonances and strong light focusing on the subwavelength scale hold broad application prospects in fields such as sensors, nonlinear optics, and nanolasers. However, conventional surface plasmon metal metasurfaces, due to factors such as ohmic losses, exhibit broad spectral lines with low quality (Q) factors, significantly limiting their application. This can also lead to significant errors in sensor measurements. All-dielectric metasurfaces composed of dielectric materials, due to their lower constitutive losses, can achieve high-Q-factor resonant lines.

[0003] Bound states in the continuum (BICs) were first proposed in quantum mechanics by von Neumann and Wigner. Research has shown that the relationship between the asymmetry of metasurface structures and the resonant Q factor can be described by the characteristic inverse-square law. This symmetry-protected BIC arises from the coupling between the resonator's eigenmodes and external propagating modes due to symmetry mismatch, resulting in the embedding of localized states into the continuum. Ideally, BICs exhibit infinite Q factors and zero resonant linewidth in completely symmetric nanostructures, making them undetectable in spectroscopy. In practical applications, BICs can be induced to transform into quasi-BICs by breaking the structural symmetry, changing the refractive index of the local structural material, or adjusting the incident angle of the light source. Quasi-BICs possess ultrahigh Q factors, extremely narrow linewidths, and large electric field enhancements, offering promising applications in biosensing, nonlinear optics, gas sensing, and optical modulators. In recent years, quasi-BIC resonances have been realized in structures with asymmetric dielectric constants, such as tetramer arrays, silicon rectangular rods, silicon nanodisk arrays, and slotted disks, and have been applied to sensing applications.

[0004] Ge2Sb2Te5 (GST) is a high-refractive-index phase-change material with two states: crystalline (c-GST) and amorphous (a-GST). GST thin films deposited by magnetron sputtering are in the amorphous state. Annealing above 160°C transforms them into the crystalline state. Rapid annealing at 640°C returns the crystalline state to the amorphous state. The real part of the refractive index of GST changes by Δn≈2 during the transition between the amorphous and crystalline states. At room temperature, GST can maintain its current state for years, maintaining its stable properties and making it a promising nonvolatile optoelectronic material. Furthermore, its rapid crystallization, excellent stability, and low power consumption make it suitable for applications such as thermal emission and optical switching. Furthermore, GST is a high-refractive-index dielectric material, which meets the requirements for quasi-BIC generation. Combining these two materials can create a quasi-BIC metasurface device with a high-quality switching factor. Summary of the Invention

[0005] The purpose of the present invention is to design a switch-controllable dual-band high-quality factor metasurface sensor and sensing system to solve the problems of low quality factor of metal metasurfaces and the lack of switch switching of conventional sensors.

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

[0007] One aspect of the present invention provides a switchable dual-band high-quality factor metasurface sensor, comprising a substrate and an all-dielectric metasurface structure array on the substrate;

[0008] The all-dielectric metasurface structure array includes a plurality of all-dielectric metasurface structure units, and the plurality of all-dielectric metasurface structure units are arranged in a matrix;

[0009] The all-dielectric metasurface structure unit is a four-leaf clover structure, consisting of four cylinders of equal radius and a cube in the middle. Its material is Ge2Sb2Te5. By changing the crystal state of the material, the switch control of the sensor is achieved;

[0010] When the all-dielectric metasurface structural unit is in an amorphous state, there are two quasi-bound state resonance peaks in its transmission spectrum;

[0011] A cylindrical air hole is also provided on the all-dielectric metasurface structural unit to form a spatially asymmetric structure, thereby obtaining a high-quality quasi-bound state resonance peak.

[0012] Preferably, the substrate material is CaF2.

[0013] Preferably, the radius of the cylinder is 110 nm, and the diameter of the cylindrical air pore is 140 nm.

[0014] Another aspect of the present invention provides an all-medium metasurface sensing and detection system, which includes a near-infrared light source, a switch-controllable dual-working band high-quality factor metasurface sensor, a near-infrared detector and a data analysis and acquisition device. The light emitted by the near-infrared light source passes through the metasurface sensor and is received by the near-infrared detector. The near-infrared detector is signal-connected to the data analysis and acquisition device.

[0015] The beneficial effects of the present invention are:

[0016] 1. The quasi-BIC sensor designed in the present invention has an extremely high Q factor and high refractive index sensitivity.

[0017] 2. The quasi-BIC sensor designed in the present invention has two operating wavelengths in the near-infrared band and is suitable for detection in a variety of application scenarios.

[0018] 3. In the present invention, the switch control of the sensor can be achieved by changing the crystal state of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the all-dielectric metasurface structure based on the GST-like "four-leaf clover" structure;

[0020] Figure 2 Transmission spectra of a-GST and c-GST under different parameters D;

[0021] Figure 3 This is a curve showing the effect of the asymmetry parameter D on the Q factor;

[0022] Figure 4 Sensing curves at different refractive indices;

[0023] Figure 5 This is a graph showing the relationship between different analyte thicknesses and sensing sensitivity.

[0024] Figure 6 Schematic diagram of the sensing detection system built based on a switchable dual-working-band high-quality factor metasurface sensor. DETAILED DESCRIPTION

[0025] A switchable dual-band high-quality factor metasurface sensor consists of a CaF2 substrate and a "four-leaf clover"-shaped structure on the substrate. The structure consists of four cylinders with equal radii and a cube in the middle. The structural material is GST.

[0026] To overcome the structural asymmetry, cylindrical air holes are introduced. By shifting the positions of the air holes, a spatially asymmetric structure is formed, resulting in a resonant peak with a high Q factor. The resonant wavelength of the quasi-BIC exhibits a significant electric field enhancement, greatly increasing the interaction between light and matter and providing exceptional sensitivity to changes in material concentration, thus enabling applications in sensing measurements.

[0027] This structure can stimulate two quasi-BIC resonances at different wavelengths. Both quasi-BIC resonance peaks have ultra-high Q factors, greatly ensuring the accuracy of measurement results. By varying the crystalline state of the GST material, the generation and disappearance of the two quasi-BIC resonances can be controlled, realizing a switchable BIC sensor.

[0028] Based on the above technical concept, the present invention provides a switch-controllable dual-working-band high-quality factor metasurface sensor and system.

[0029] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, identical or corresponding parts are denoted by identical reference numerals, and repeated descriptions are omitted. Furthermore, the dimensional ratios of the drawings are not necessarily consistent with the actual ratios.

[0030] In one example of this application, a schematic diagram of the all-dielectric metasurface structure based on the GST-type "four-leaf clover" structure is shown in FIG. Figure 1 , including a four-leaf clover structure 1 composed of GST material, arranged in a matrix, a CaF2 substrate 2, and a cylindrical air hole 3; the structural parameters P x =P y =830nm, H=200nm, R1=110nm, R2=70nm, L=240nm, D is the moving distance between the center of the air hole and the center of the four-leaf clover.

[0031] Furthermore, if Figure 2 Figure 2 shows the transmission spectra of a-GST and c-GST under different parameters D. When GST is amorphous, two quasi-BIC resonance peaks are present in the transmission spectrum, designated Quasi-BIC I and Quasi-BIC II. When GST is crystalline, these two quasi-BIC resonance peaks disappear. This suggests that by varying the crystalline state of GST, the generation of the two quasi-BIC resonances in the four-leaf clover structure can be controlled, demonstrating a switching characteristic.

[0032] Furthermore, if Figure 3The graph below shows the effect of the asymmetry parameter D on the Q factor. When the air hole gradually moves, the Q of the two quasi-BICs (Quasi-BICⅠ and Quasi-BICⅡ) changes dramatically. The reason is that after the air hole moves, the spatial asymmetry of the four-leaf clover structure becomes larger. When D = 0, the four-leaf clover structure is in a completely symmetrical state; when D ≠ 0, the symmetry of the four-leaf clover structure is destroyed. The larger the air hole movement distance D, the smaller the Q factor of Quasi-BICⅠ and Quasi-BICⅡ. When D = 5nm, the Q factors of Quasi-BICⅠ and Quasi-BICⅡ are 1.71×10 5 and 1.1×10 5 ; When D = 60nm, the Q factors of Quasi-BICⅠ and Quasi-BICⅡ are 1054 and 814; by comparison, the Q factors have changed by orders of magnitude.

[0033] Furthermore, if Figure 4 The following plots the sensing curves of Quasi-BIC I and Quasi-BIC II at different refractive indices. When the refractive index of the material covering the metasurface structure changes, both Quasi-BIC I and Quasi-BIC II quasi-BIC resonance peaks undergo a redshift, while the Q factors of these peaks remain unaffected. Calculations show that the sensing sensitivities of the two quasi-BIC resonance peaks of Quasi-BIC I and Quasi-BIC II are S1 = 337.6 nm / RIU and S2 = 104.5 nm / RIU, respectively, demonstrating high sensitivity.

[0034] Furthermore, if Figure 5 The relationship between different analytes on the surface of the structure and the sensor sensitivity is shown in Figure 2. After studying the different thicknesses of analytes on the surface of the structure, it was found that the thickness of the analyte will seriously affect the sensitivity of the sensor. When the thickness of the analyte is thin, H analyte =50nm, the sensing sensitivities of the two quasi-BIC resonance peaks are only 68nm / RIU and 16.5nm / RIU, which are very low. When the analyte thickness exceeds 400nm, the sensing sensitivity reaches its maximum; as the analyte thickness increases further, the sensing sensitivity remains unchanged.

[0035] In another example of this application, a schematic diagram of a quasi-BIC all-medium metasurface sensor sensing detection system is given, see Figure 6 ; The system includes a near-infrared light source 4, a switchable dual-working band high-quality factor metasurface sensor 5, a near-infrared detector 6 and a data analysis and acquisition device 7.

[0036] Although the present invention has been described with reference to certain aspects and embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

1. A switchable dual-band high-quality metasurface sensor, characterized in that: comprising a substrate and an array of all-dielectric metasurface structures on the substrate; The all-dielectric metasurface structure array includes a plurality of all-dielectric metasurface structure units, and the plurality of all-dielectric metasurface structure units are arranged in a matrix; The all-dielectric metasurface structure unit is a four-leaf clover structure, consisting of four cylinders of equal radius and a cube in the middle. Its material is Ge2Sb2Te5. By changing the crystal state of the material, the switch control of the sensor is achieved; When the all-dielectric metasurface structural unit is in an amorphous state, there are two quasi-bound state resonance peaks in its transmission spectrum; A cylindrical air hole is also provided on the all-dielectric metasurface structural unit to form a spatially asymmetric structure, thereby obtaining a high-quality quasi-bound state resonance peak.

2. The switchable dual-band high-quality factor metasurface sensor according to claim 1, characterized in that: The substrate material is CaF2.

3. The switchable dual-band high-quality factor metasurface sensor according to claim 1, characterized in that: The radius of the cylinder is 110 nm, and the pore diameter of the cylindrical air pore is 140 nm.

4. An all-medium metasurface sensing detection system, characterized by: It comprises a near-infrared light source, a switchable dual-working band high-quality factor metasurface sensor according to any one of claims 1 to 3, a near-infrared detector and a data analysis and acquisition device, wherein the light emitted by the near-infrared light source passes through the metasurface sensor and is received by the near-infrared detector, and the near-infrared detector is signal-connected to the data analysis and acquisition device.

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