Narrowband filter based on all-dielectric fishbone metasurface and its manufacturing method

Abstract

A narrowband filter based on an all-dielectric fishbone metasurface and its fabrication method relate to the field of optical sensing technology, specifically to a narrowband filter based on an all-dielectric fishbone metasurface and its fabrication method. The filter comprises a dielectric substrate and a superstructure. The dielectric substrate comprises several square substrates, and the superstructure comprises several superstructure units made of all-dielectric materials. 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. The invention excites sharp Fano resonances with a modulation depth approaching 100%, which is conducive to achieving a high-q-factor Fano resonance peak.

Description

Technical Field

[0001] The present invention relates to the field of optical sensing technology, and in particular to a narrowband filter based on an all-dielectric fishbone metasurface and a manufacturing method thereof. Background Art

[0002] With advances in nanodevice processing, surface plasmons in metallic nanostructures have become a hot topic of research. However, due to strong radiative losses caused by free electron oscillations in metallic structures, the high quality factor of metallic structures is typically low, limiting the application of metallic plasmon structures in nanophotonics. The emergence of all-dielectric superstructures addresses these issues. All-dielectric superstructures offer low loss, easy tunability, and compatibility with CMOS technology, while also supporting ultrahigh sensitivity. This provides a new path to achieving high-performance, compact, and highly integrated optical devices.

[0003] Fano resonance, a special form of surface plasmon, can be generated in nanostructures. Due to its asymmetric, sharp linear shape, Fano resonance is highly sensitive to changes in the surrounding environment and is often used in fields such as filters and biosensors.

[0004] Fano resonance has garnered widespread attention from researchers because it can produce narrower spectra and higher field intensities, achieving superior sensitivity. Fano resonance is caused by destructive interference between discrete and continuous states. Fano resonance-based all-dielectric metastructure optical biorefractive index sensors utilize the significant electromagnetic field enhancement generated by Fano resonance at its resonant frequency. This approach offers high sensitivity while avoiding ohmic losses caused by the material, making them a current research hotspot in the field of optical filters.

[0005] In summary, based on the current research status of optical filters and the advantages of all-dielectric metastructures and Fano resonance, the inventors proposed a narrowband filter based on an all-dielectric fishbone metasurface. Summary of the Invention

[0006] The purpose of the present invention is to provide a narrowband filter based on an all-dielectric fishbone metasurface and a manufacturing method thereof, which excites a sharp Fano resonance with a modulation depth close to 100%, so as to achieve a Fano resonance peak that is conducive to achieving a high q factor.

[0007] The present invention provides a narrowband filter based on an all-dielectric fishbone metasurface, characterized in that it includes a dielectric substrate and a superstructure, wherein the dielectric substrate includes a plurality of square substrates, and the superstructure includes a plurality of superstructure units composed of all-dielectric materials. 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 300 nm and a corresponding refractive index of 1.48, and the superstructure material is single crystal silicon with a corresponding refractive index of 3.45.

[0009] Furthermore, the superstructure unit is a silicon cylinder, the center of the bottom surface of the silicon cylinder coincides with the center of the upper surface of the square substrate, and a fishbone-shaped hollow section is provided on the silicon cylinder.

[0010] Furthermore, the arrangement period of the microstructure units in the X and Y directions is 610 nm; the radius of the silicon cylinder is 278 nm; the height of the silicon cylinder is 171 nm, and the depth of the hollow section is 171 nm.

[0011] Furthermore, the silicon cylinder has three hollow sections, the depth of the hollow sections is consistent with the height of the silicon cylinder, the hollow sections are fishbone-shaped bilaterally symmetrical structures, and the hollow sections gradually shrink from one end of the cylinder to the other end.

[0012] Furthermore, a 90° corner is formed in the middle of each hollow segment, and the corner is located on an axis passing through the center of the bottom surface of the silicon cylinder.

[0013] Furthermore, along the direction in which the hollow segments gradually shrink, take half of the measurement data of each hollow segment:

[0014] Outer hollow section: outer side length is 350nm, width is 100nm, inner side length is 250nm;

[0015] The middle hollow section has an outer side length of 180 nm, a width of 60 nm, and an inner side length of 120 nm.

[0016] Inner hollow section: outer side length is 80nm, width is 40nm, inner side length is 40nm;

[0017] The minimum distance between the outermost corner of the outer hollow segment and the bottom circle of the silicon cylinder is 38 nm, and the minimum distance between the innermost corner of the inner hollow segment and the bottom circle of the silicon cylinder is 135 nm.

[0018] Furthermore, when incident light irradiates the superstructure, electromagnetic waves interact with the microstructure units, and two narrow-linewidth Fano resonance peaks appear in the transmission spectrum. The operating wavelength of the filter of the present invention is 1050nm-1350nm.

[0019] Furthermore, the q factor of the narrowband filter of the present invention is calculated by the following formula: q=resonant wavelength / full width at half maximum.

[0020] The present invention provides a method for manufacturing a narrowband filter based on an all-dielectric fishbone metasurface, characterized by comprising the following steps:

[0021] Step 1: Rinse the silica substrate with deionized water to remove contaminants;

[0022] Step 2: Depositing a silicon thin film on a silicon dioxide substrate wafer using a low-pressure chemical vapor deposition method;

[0023] Step 3: Clean the wafer, spin-coat the photoresist evenly onto the silicon film and bake it;

[0024] Step 4: Project the pattern using electron beam lithography technology to illuminate the area of ​​the wafer that needs to be etched. The area on the silicon film that does not need to be etched is not exposed by the electron beam.

[0025] Step 5: Develop the photoresist remaining in the corresponding positions after electron beam exposure. Immerse the wafer in an inorganic weak alkaline aqueous solution. After soaking in the developer, bake it at high temperature to harden the photoresist in the area not exposed by the electron beam and make it corrosion-resistant.

[0026] Step 6: Obtain a superstructure unit array by inductively coupled plasma etching;

[0027] Step 7: Remove the photoresist and clean with plasma to obtain the superstructure narrowband filter of the present invention. The present invention provides a narrowband filter based on an all-dielectric fishbone-type supersurface and a method for manufacturing the same. The superstructure solves the problems of high ohmic loss, high manufacturing cost and incompatibility with CMOS in metal micro-nanostructures by using all-dielectric silicon-based materials instead of metal materials. Simulation and experimental results show that double Fano resonances are generated in the system, and the resonance wavelength and resonance line shape can be adjusted by changing the geometry of the device. Combined with the BIC theory, a high q-factor Fano peak is excited, thereby achieving tunable multi-wavelength filtering performance. The all-dielectric superstructure is based on the Mie resonance principle. When a plane wave along the negative direction of the z-axis is used to be vertically incident on the all-dielectric superstructure, its light field is mainly confined inside the device, which is beneficial to enhance the interaction between light and matter inside the device, and two sharp Fano resonances appear in the transmission spectrum. In summary, the present invention has the following positive effects:

[0028] 1. All-dielectric material, no ohmic loss, the transmission and reflection spectra generated by Fano resonance can be much narrower than traditional plasma sensors, making it easier to achieve high quality factor, high sensitivity and high quality factor.

[0029] 2. The two Fano resonance peaks with narrow line widths in the transmission spectrum are easy to detect and measure, and can provide multiple detection points simultaneously.

[0030] 3. The superstructure uses all-dielectric materials, is compatible with CMOS technology, has low manufacturing costs, and is expected to achieve high-performance, miniaturized and highly integrated photonic devices.

[0031] 4. The narrowband filter described in the present invention can be applied to related fields such as gas, liquid and biological sensing, and can bring great convenience to industry experimental measurements.

[0032] Figures in the specification

[0033] Figure 1 A top view of the overall structure of the present invention;

[0034] Figure 2 A top view of the microstructure unit of the present invention;

[0035] Figure 3 is a side view of the microstructure unit of the present invention;

[0036] Figure 4 Make a flow chart for the process of the present invention;

[0037] Figure 5 The transmission spectra of the incident plane wave of the silicon cylinder of the microstructure unit of the present invention at different heights;

[0038] Figure 6 The transmission spectra of the silicon cylinder of the microstructure unit of the present invention under different radius states of the incident plane wave. DETAILED DESCRIPTION

[0039] like Figure 1-3 As shown, the narrowband filter based on the all-dielectric fishbone metasurface provided by the present invention is specifically composed of a dielectric substrate and a superstructure stacked in sequence. Specifically, the dielectric substrate is composed of a plurality of square substrates 1, and the superstructure is composed of a plurality of superstructure units 2 composed of all-dielectric materials. Preferably, the dielectric substrate material is silicon dioxide with a thickness of 300nm and a corresponding refractive index of 1.48, and the superstructure material is single-crystal silicon with a corresponding refractive index of 3.45. The superstructure unit is a silicon cylinder, and the center of the bottom surface of the silicon cylinder coincides with the center of the upper surface of the square substrate. The superstructure unit and the square substrate are correspondingly arranged to form a microstructure unit. The plurality of microstructure units form a matrix distribution and are periodically arranged in the X and Y directions.

[0040] A fishbone-shaped hollow section 3 is provided on the silicon cylinder. Figure 1-3 As shown, the silicon cylinder has three hollow sections. The depth of each hollow section matches the height of the silicon cylinder. The hollow sections have a fishbone-shaped bilaterally symmetrical structure and gradually decrease in size from one end of the cylinder to the other. In addition, each hollow section has a 90° corner in the middle, located on the axis of the silicon cylinder's bottom surface that passes through the center.

[0041] In a specific embodiment of the present invention, the arrangement period of the microstructure units in the X and Y directions is 610 nm; the radius of the silicon cylinder is 278 nm; the height of the silicon cylinder is 171 nm, and the depth of the hollow section is 171 nm. The measurement data of half of each hollow section is taken along the direction in which the hollow section gradually decreases:

[0042] Outer hollow section: outer side length is 350nm, width is 100nm, inner side length is 250nm;

[0043] The middle hollow section has an outer side length of 180 nm, a width of 60 nm, and an inner side length of 120 nm.

[0044] Inner hollow section: outer side length is 80nm, width is 40nm, inner side length is 40nm;

[0045] The minimum distance between the outermost corner of the outer hollow segment and the bottom circle of the silicon cylinder is 38 nm, and the minimum distance between the innermost corner of the inner hollow segment and the bottom circle of the silicon cylinder is 135 nm.

[0046] When incident light strikes the superstructure, the electromagnetic wave interacts with the microstructure units, resulting in two narrow-linewidth Fano resonance peaks appearing in the transmission spectrum. The filter operates at a wavelength between 1050 nm and 1350 nm. The q factor of the narrowband filter is calculated using the following formula: q = resonance wavelength / full width at half maximum.

[0047] like Figure 4 As shown, the present invention provides a method for manufacturing a narrowband filter based on an all-dielectric fishbone metasurface, which is characterized by comprising the following steps:

[0048] Step 1: Rinse the silica substrate with deionized water to remove contaminants;

[0049] Step 2: Depositing a silicon thin film on a silicon dioxide substrate wafer using a low-pressure chemical vapor deposition method;

[0050] Step 3: Clean the wafer, spin-coat the photoresist evenly onto the silicon film and bake it;

[0051] Step 4: Project the pattern using electron beam lithography technology to illuminate the area of ​​the wafer that needs to be etched. The area on the silicon film that does not need to be etched is not exposed by the electron beam.

[0052] Step 5: Develop the photoresist remaining in the corresponding positions after electron beam exposure. Immerse the wafer in an inorganic weak alkaline aqueous solution. After soaking in the developer, bake it at high temperature to harden the photoresist in the area not exposed by the electron beam and make it corrosion-resistant.

[0053] Step 6: Obtaining a superstructure unit array through inductively coupled plasma etching;

[0054] Step 7: Remove the photoresist and clean with plasma to obtain the superstructure narrowband filter of the present invention.

[0055] like Figure 5 Shown is a silicon cylinder with a hollowed-out section of the microstructure unit of the present invention, and the transmission spectra of the incident plane wave at different heights. It can be seen that the Fano resonance point is adjustable as the structural parameters change, and the present invention can be used as a filter.

[0056] like Figure 6 The microstructure unit of the present invention shown has a silicon cylinder with a hollow section. The transmission spectrum of the incident plane wave under different radius states, the change of structural parameters, leads to corresponding changes in the position of the resonance peak. The resonance positions of the two peaks show an obvious red shift when R is 278nm to 284nm, that is, the resonance wavelength and resonance line shape can be adjusted by changing the geometry of the device.

[0057] like Figure 5 、 6 The transmission spectra of the present invention in the two resonance modes are shown as q = resonance wavelength / full width at half maximum. Taking into account the various situations of experimental parameter changes, it can be calculated that the optimal q factor of the first Fano resonance peak can reach 5319, and the optimal q factor of the second Fano resonance peak can reach 1614.

[0058] In summary, simulation experiments have verified the specific implementation of the all-dielectric fishbone narrowband filter proposed in this invention, which can induce two high-performance Fano resonances to provide multiple detection points. Due to its excellent performance and adjustable Fano resonance points, the all-dielectric fishbone narrowband filter structure proposed in this invention is of great significance for the manufacture of narrowband filters. It has the advantages of low cost, simple structure, real-time monitoring, and no calibration required. It can play an important role in fields such as chemistry, medicine, and integrated optics.

Claims

1. A narrowband filter based on an all-dielectric fishbone metasurface, characterized in that: The invention comprises a dielectric substrate and a superstructure. The dielectric substrate comprises a plurality of square substrates. The superstructure comprises a plurality of superstructure units made entirely of dielectric materials. The superstructure units are arranged corresponding to the square substrates and constitute microstructure units. The microstructure units are arranged in a matrix and are periodically arranged in the X and Y directions. The superstructure units are silicon cylinders. The center of the bottom surface of the silicon cylinder coincides with the center of the top surface of the square substrate. The silicon cylinder has three hollow sections. The depth of the hollow sections is consistent with the height of the silicon cylinder. The hollow sections are fishbone-shaped and bilaterally symmetrical. The hollow sections gradually decrease from one end of the cylinder to the other. A 90° corner is formed in the middle of each hollow section, and the corner is located on the axis of the silicon cylinder bottom surface passing through the center.

2. The narrowband filter based on the all-dielectric fishbone metasurface according to claim 1, further characterized in that: The dielectric substrate material is silicon dioxide with a thickness of 300 nm and a corresponding refractive index of 1.

48. The superstructure material is single crystal silicon with a corresponding refractive index of 3.

45.

3. The narrowband filter based on the all-dielectric fishbone metasurface according to claim 1, further characterized in that: The arrangement period of the microstructure units in the X and Y directions is 610 nm; the radius of the silicon cylinder is 278 nm; the height of the silicon cylinder is 171 nm, and the depth of the hollow section is 171 nm.

4. The narrowband filter based on the all-dielectric fishbone metasurface according to claim 1, further characterized in that: Along the direction in which the hollow segments gradually shrink, half of the measurement data of each hollow segment are taken: outer hollow segment: outer side length is 350nm, width is 100nm, and inner side length is 250nm; middle hollow segment: outer side length is 180nm, width is 60nm, and inner side length is 120nm; inner hollow segment: outer side length is 80nm, width is 40nm, and inner side length is 40nm; among them, the minimum distance between the outermost corner of the outer hollow segment and the bottom circle of the silicon cylinder is 38nm, and the minimum distance between the innermost corner of the inner hollow segment and the bottom circle of the silicon cylinder is 135nm.

5. The narrowband filter based on the all-dielectric fishbone metasurface according to claim 1, further characterized in that: When incident light irradiates the superstructure, electromagnetic waves interact with the microstructure units, and two Fano resonance peaks with narrow line widths appear in the transmission spectrum. The operating wavelength of the narrowband filter is 1050nm-1350nm.

6. The narrowband filter based on the all-dielectric fishbone metasurface according to claim 1, further characterized in that: The q factor of the narrowband filter is calculated by the following formula: q=resonance wavelength / full width at half maximum.

7. A method for manufacturing a narrowband filter based on an all-dielectric fishbone metasurface according to any one of claims 1 to 6, characterized in that: The following processes are included: Step 1: Rinse the silica substrate with deionized water to remove contaminants; Step 2: Depositing a silicon thin film on a silicon dioxide substrate wafer using a low-pressure chemical vapor deposition method; Step 3: Clean the wafer, spin-coat the photoresist evenly onto the silicon film and bake it; Step 4: Project the pattern using electron beam lithography technology to illuminate the area of ​​the wafer that needs to be etched. The area on the silicon film that does not need to be etched is not exposed by the electron beam. Step 5: Develop the photoresist remaining in the corresponding positions after electron beam exposure. Immerse the wafer in an inorganic weak alkaline aqueous solution. After soaking in the developer, bake it at high temperature to harden the photoresist in the area not exposed by the electron beam and make it corrosion-resistant. Step 6: Obtain a superstructure unit array by inductively coupled plasma etching; Step 7: Remove the photoresist and clean with plasma to obtain the narrowband filter.

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