Optical refractive index sensor based on pea-shaped metasurface and its manufacturing method

Abstract

An optical refractive index sensor based on a pea-shaped metasurface and a method for fabricating the same relate to the field of optical sensing technology, specifically to an optical refractive index sensor based on a pea-shaped metasurface and a method for fabricating the same. The sensor comprises a dielectric substrate and a metastructure, wherein the dielectric substrate comprises a plurality of square substrates, and the metastructure comprises a plurality of superstructure units. The superstructure units are arranged corresponding to the square substrates and constitute microstructure units. The microstructure units form a matrix distribution and are periodically arranged in the X and Y directions. By employing metasurface materials with different refractive indices to break symmetry, the sensor can generate two sharp Fano resonances within the sensor's operating wavelength range, achieving a high quality factor.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular to an optical refractive index sensor based on a pea-shaped metasurface and a manufacturing method thereof. Background Art

[0002] Sensing technology, which enables people to perceive, acquire, and detect information, is one of the three pillars of the global information industry. With the continuous development of sensing technology, its integration with disciplines such as optics, chemistry, and biology has led to the emergence of a number of promising interdisciplinary fields. This has also led to the development of various types of refractive index sensors. Among these, refractive index sensors based on superstructure optical structures have garnered increasing research interest and technical support due to their smaller size, enhanced information capture capabilities, and higher levels of integration.

[0003] Currently, research on refractive index sensors has largely focused on plasmonic metasurfaces composed of metals. However, these metal plasmonic metasurfaces suffer from high ohmic losses, high manufacturing costs, and low integration, which have limited their development and application in micro- and nano-optics. However, the emergence of dielectric metasurfaces has addressed these issues. Compared to traditional metal plasmonic metasurfaces, dielectric metasurfaces do not have internal free electron oscillations, thereby eliminating the influence of ohmic losses. The resulting resonance-generated transmission and reflection spectra are much narrower than those of traditional plasmonic sensors, making it easier to achieve high quality factors and high sensitivity. Furthermore, the simple fabrication process for dielectric metasurfaces reduces production costs, providing new approaches for the manufacture of miniaturized and integrated optical devices.

[0004] Fano resonance is a phenomenon that produces asymmetric linear scattering resonance and is widely used in fields such as optical switching, optical sensing, and nonlinear optics. Bound states in the continuum (BIC) are waves that exist in the continuous spectrum of radiation waves that can carry away energy while remaining localized. They are ubiquitous in fluid mechanics, acoustics, and optics. By breaking the asymmetry of the structure and introducing a radiation channel to the outside world, the BIC mode can be transformed into a quasi-BIC mode with a high Q (maximum quality) factor. This is manifested by the generation of a high-performance Fano peak in the transmission spectrum, realizing a high-quality refractive index sensor.

[0005] In summary, based on the current research status of optical refractive index sensors and the advantages of Fano resonance, the inventors proposed an optical refractive index sensor based on a pea-shaped metasurface and a method for manufacturing the same. Summary of the Invention

[0006] The purpose of the present invention is to provide an optical refractive index sensor based on a pea-shaped metasurface and a method for manufacturing the same, so as to achieve the purpose of breaking the symmetry by adopting metasurface materials with different refractive indices, generating two sharp Fano resonances within the operating wavelength range of the sensor, and obtaining a high quality factor.

[0007] The present invention provides an optical refractive index sensor based on a pea-shaped metasurface, characterized in that it includes a dielectric substrate and a metastructure, wherein the dielectric substrate includes a plurality of square substrates, and the metastructure includes a plurality of metastructure units. The superstructure units are arranged corresponding to the square substrates and constitute microstructure units. The plurality of microstructure units form a matrix distribution and are periodically arranged in the X and Y directions.

[0008] Furthermore, the dielectric substrate material is silicon dioxide with a thickness of 260 nm.

[0009] Furthermore, the superstructure unit includes a first structure and a second structure, wherein the first structure and the second structure are symmetrically arranged pea-shaped defect elliptical cylinder structures, both of which have a thickness of 270 nm, wherein the material of the first structure is Si, and the refractive index of Si is 3.56; the material of the second structure is GaAs, and the refractive index of GaAs is 3.52.

[0010] Furthermore, the arrangement period of the microstructure units in the X and Y directions is 530 nm.

[0011] Furthermore, the major axis of the pea-shaped defect elliptical cylinder is 225 nm, the minor axis is 64 nm, and the center interval between the two pea-shaped defect elliptical cylinders is 258 nm.

[0012] Furthermore, the optical refractive index sensor of the present invention can generate two sharp Fano resonances in the transmission spectrum, and the operating wavelength of the sensor is 960nm-1050nm.

[0013] The present invention provides a method for manufacturing an optical refractive index sensor based on a pea-shaped metasurface, characterized by comprising the following steps:

[0014] Step 1: Rinse the silicon dioxide substrate with a deionized water solution to remove contaminants;

[0015] Step 2: Depositing a silicon film on a silicon dioxide substrate sample by low-pressure chemical vapor deposition;

[0016] Step 3: Spin-coat the sample with a resist thickness of 330 nm to 340 nm, and then bake the sample for 2 to 4 minutes.

[0017] Step 4: After the sample cools to room temperature, the sample is etched with the required pattern using electron beam lithography. The corresponding pea-shaped defect elliptical column is not irradiated by the electron beam, and the exposure dose is set at 195μC / cm 2 about;

[0018] Step 5: Use an inorganic weak alkaline aqueous solution to dissolve the soluble area of ​​the photoresist after exposure, perform a development operation, dissolve unnecessary photoresist, and obtain the desired shape;

[0019] Step 6: Heat and bake the sample to make the glue in the area not exposed by the electron beam adhere more firmly to the sample surface, thereby increasing the etching resistance of the glue layer;

[0020] Step 7: Deposit a GaAs film on the sample by low-pressure chemical vapor deposition, and then repeat steps 3-6 to obtain a GaAs piea-shaped defect elliptical column;

[0021] Step 8: Remove the masks on the Si and GaAs cylinders to obtain the required element surface, and obtain a pea-shaped defect elliptical cylinder array through inductively coupled plasma etching;

[0022] Step 9: Use an organic solvent to dissolve the photoresist to obtain the desired refractive index sensor.

[0023] The present invention provides an optical refractive index sensor based on a pea-shaped metasurface and a method for fabricating the same. By using materials with different refractive indices to break symmetry and generate a high-Q-factor Fano resonance peak, the sensor provides an excellent alternative to geometrically asymmetric metasurface structures. The main advantages of the present invention include the following aspects:

[0024] 1. The superstructure unit uses semiconductor materials, which have higher sensitivity and Q factor compared with metal structures;

[0025] 2. The superstructure unit breaks the symmetry by using materials with different refractive indices, generating a high-Q-factor Fano resonance peak, providing a good alternative to geometrically asymmetric metasurface structures;

[0026] 3. Solve the problems of high ohmic loss and low quality factor on the surface of metal plasmons, and promote the development of dielectric superstructures;

[0027] 4. The microstructure unit of the present invention supports Mie resonance, and can enhance the interaction between light and matter through strong confinement of the electromagnetic field, thereby obtaining high-quality Fano resonance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the present invention;

[0029] Figure 2 Schematic diagram of the structure of the microstructure unit of the present invention;

[0030] Figure 3 is a side view of the microstructure unit of the present invention;

[0031] Figure 4 The transmission spectra of the two pisiform defect elliptical cylinders of the present invention when the materials are the same (n1=n2=3.56) and when the materials are different (n1=3.56, n2=3.52);

[0032] Figure 5 The transmission curve of the resonance mode with the first Fano peak (first dip) at different refractive indices of the medium to be measured according to the present invention;

[0033] Figure 6 The second Fano peak (second dip) of the present invention is the transmission curve of the resonance mode under different refractive indices of the medium to be measured;

[0034] Figure 7 The graphs are the resonance position change curves of the two resonance modes of the present invention at different refractive indices. DETAILED DESCRIPTION

[0035] like Figure 1-3 As shown, the present invention provides an optical refractive index sensor based on a pea-shaped metasurface and a method for manufacturing the same, comprising a dielectric substrate and a superstructure. The dielectric substrate material is silicon dioxide and has a thickness of 260 nm. Specifically, the dielectric substrate includes a plurality of square substrates 1, and the superstructure includes a plurality of superstructure units. The superstructure unit includes a first structure 2 and a second structure 3. The first structure and the second structure are symmetrically arranged pea-shaped defect elliptical cylinder structures, each with a thickness h of 270 nm. The major axis R of the pea-shaped defect elliptical cylinder is 225 nm, the minor axis r is 64 nm, and the center spacing d between the two pea-shaped defect elliptical cylinders is 258 nm. The first structure is made of Si, and the refractive index of Si is 3.56; the second structure is made of GaAs, and the refractive index of GaAs is 3.52. The superstructure unit is arranged corresponding to the square substrate and constitutes a microstructure unit. The plurality of microstructure units form a matrix distribution and are periodically arranged in the X and Y directions with an arrangement period of 530 nm.

[0036] When the present invention is used, the optical refractive index sensor of the present invention can generate two sharp Fano resonances on the transmission spectrum, and the operating wavelength of the sensor is 960nm-1050nm.

[0037] The present invention also provides a method for manufacturing an optical refractive index sensor based on a pea-shaped metasurface, the specific steps of which are as follows:

[0038] Step 1: Rinse the silicon dioxide substrate with a deionized water solution to remove contaminants;

[0039] Step 2: Depositing a silicon film on a silicon dioxide substrate sample by low-pressure chemical vapor deposition (LPCVD);

[0040] Step 3: Spin-coat the sample with a resist thickness of 330nm to 340nm, then bake the sample for 2 to 4 minutes.

[0041] Step 4: After the sample cools down to room temperature, electron beam lithography is used to etch the desired pattern. The corresponding pea-shaped defect elliptical column is not irradiated by the electron beam. The exposure dose can be set at 195μC / cm 2 about;

[0042] Step 5: Use an inorganic weak alkaline aqueous solution to dissolve the soluble area of ​​the photoresist after exposure, perform a development operation, dissolve unnecessary photoresist, and obtain the desired shape;

[0043] Step 6: Heat and bake the sample to make the glue in the area not exposed by the electron beam adhere more firmly to the sample surface, thereby increasing the etching resistance of the glue layer;

[0044] Step 7: Deposit a GaAs film on the sample by low-pressure chemical vapor deposition (LPCVD), and then repeat steps 3-6 to obtain a GaAs piea-shaped defect elliptical column;

[0045] Step 8: Remove the masks on the Si and GaAs cylinders to obtain the required element surface, and obtain a pea-shaped defect elliptical cylinder array through inductively coupled plasma etching;

[0046] Step 9: Use an organic solvent to dissolve the photoresist to obtain the desired refractive index sensor.

[0047] like Figure 4 The transmission spectra of the two pisiform defect elliptic cylinders of the inventive microstructure unit are shown when the materials are symmetric (n1=n2=3.56) and asymmetric (n1=3.56, n2=3.52). When the two pisiform elliptic cylinders are made of the same material, no energy leaks from the bound state into free space, and only a single resonance peak is observed in the transmission spectrum. However, when the refractive indices of the two pisiform elliptic cylinders differ, the symmetry of the structure is broken, and the continuum interacts with the bound state, generating energy leakage. This creates a new channel for energy radiation to free space, transforming the symmetry-protected BIC mode into a quasi-BIC mode, thereby exciting a high-Q-factor Fano resonance.

[0048] like Figure 5 、 Figure 6The transmission curves of the resonance mode of the present invention, shown below, show the first and second Fano peaks at different refractive indices of the test medium. When incident light is incident vertically and interacts with the dielectric element surface, two narrow-linewidth Fano peaks are observed in the transmission spectrum. The corresponding refractive indices of the test materials are 1.31, 1.32, 1.33, 1.34, and 1.35, respectively. When the refractive index of the test material above the superstructure changes, the resonance peaks shift significantly. By measuring the shift in the resonance peaks, the sensitivity of the structure can be determined, enabling sensing of the test material.

[0049] like Figure 7 The following curves show the change in the resonance position of the two resonance modes at different refractive indices. The sensitivity of the refractive index sensor is defined as S = Δλ / Δn, where Δn is the change in the refractive index of different substances, and Δλ is the shift of the Fano resonance at different refractive indices of the substance to be measured. The two Fano peaks appearing in the transmission spectrum are defined as P1 and P2. When the refractive index of the substance to be measured changes, P1 and P2 shift to the right to a certain extent. The shift corresponding to the P1 resonance wavelength is Δλ1 = 1.149nm, Δn1 = 0.01; the shift corresponding to the P2 resonance wavelength is Δλ2 = 1.52nm, Δn2 = 0.01. The calculated sensitivities of the two Fano resonances are S(P1) = 114.9nm / RIU and S(P2) = 152nm / RIU, and the maximum modulation depth is close to 100%.

[0050] In summary, simulation experiments have demonstrated the performance of the proposed refractive index sensor based on a pea-shaped defect elliptical cylinder metasurface. By employing semiconductor materials, the present invention addresses the issue of ohmic loss and reduces manufacturing costs, further contributing to the development of miniaturized and integrated optical devices. The present invention can be applied to detecting the refractive indices of different gases and liquids, offering advantages such as low cost and simple structure. It provides a promising alternative to geometrically asymmetric metasurface structures and holds great research potential.

Claims

1. An optical refractive index sensor based on a pea-shaped metasurface, characterized in that: The invention comprises a dielectric substrate and a superstructure, wherein the dielectric substrate comprises a plurality of square substrates, the superstructure comprises a plurality of superstructure units, the superstructure units are arranged corresponding to the square substrates and constitute microstructure units, and the plurality of microstructure units form a matrix distribution and are periodically arranged in the X and Y directions; The dielectric substrate material is silicon dioxide with a thickness of 260nm; The superstructure unit includes a first structure and a second structure. The first structure and the second structure are symmetrically arranged pea-shaped defect elliptical cylinder structures, each with a thickness of 270 nm. The first structure is made of Si, with a refractive index of 3.56; the second structure is made of GaAs, with a refractive index of 3.

52. The arrangement period of the microstructure units in the X and Y directions is 530 nm; The major axis of the pea-shaped defect elliptical cylinder is 225 nm, the minor axis is 64 nm, and the center distance between the two pea-shaped defect elliptical cylinders is 258 nm.

2. The optical refractive index sensor based on the pea-shaped metasurface according to claim 1, further characterized in that: The optical refractive index sensor can generate two sharp Fano resonances in the transmission spectrum, and the operating wavelength of the sensor is 960nm-1050nm.

3. The optical refractive index sensor based on a pea-shaped metasurface according to any one of claims 1 to 2, further characterized in that: The following steps are involved: Step 1: Rinse the silicon dioxide substrate with a deionized water solution to remove contaminants; Step 2: Depositing a silicon film on a silicon dioxide substrate sample by low-pressure chemical vapor deposition; Step 3: Spin-coat the sample with a resist thickness of 330 nm to 340 nm, and then bake the sample for 2 to 4 minutes. Step 4: After the sample cools to room temperature, electron beam lithography is used to etch the desired pattern. The corresponding pea-shaped defect elliptical column is not exposed to the electron beam, and the exposure dose is set at approximately 195μC / cm2. Step 5: Use an inorganic weak alkaline aqueous solution to dissolve the soluble area of ​​the photoresist after exposure, perform a development operation, dissolve unnecessary photoresist, and obtain the desired shape; Step 6: Heat and bake the sample to make the glue in the area not exposed by the electron beam adhere more firmly to the sample surface, thereby increasing the etching resistance of the glue layer; Step 7: Deposit a GaAs film on the sample by low-pressure chemical vapor deposition, and then repeat steps 3-6 to obtain a GaAs piea-shaped defect elliptical column; Step 8: Remove the masks on the Si and GaAs cylinders to obtain the required element surface, and obtain a pea-shaped defect elliptical cylinder array through inductively coupled plasma etching; Step 9: Use an organic solvent to dissolve the photoresist to obtain the desired refractive index sensor.

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