A silicon-based metasurface large-range refractive index sensor

Abstract

The application discloses a silicon-based metasurface large-range refractive index sensor, which comprises a substrate and a superstructure; the substrate is a double-side polished flat plate with uniform material, the material has a refractive index n(0), one side of the double-side polished flat plate is a structure surface, and the other side is a non-structure surface; the upper surface of the structure surface is attached with the superstructure; a medium with a refractive index to be measured is attached above the structure surface and covers the superstructure; the superstructure is formed by units arranged periodically according to a lattice, and the unit comprises three silicon material cubes with different angles; the lattice construction method is as follows: a square lattice with a period p is established; a basic unit is first constructed, the basic unit is composed of three silicon material cubes with a length l, a width w and a height h, the height h is perpendicular to a coordinate system, and other units are obtained by periodically translating the basic unit according to the lattice. The application can realize optical resonance effects of electric quadrupole, magnetic quadrupole and the like by reasonably designing the metasurface structure, has a narrow resonance spectrum peak, and thus realizes large-range and high-sensitivity refractive index measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement, and in particular to a device for measuring refractive index, in particular to a silicon-based metasurface large-range refractive index sensor. Background Art

[0002] Refractive index measurement is one of the most important optical measurement methods, with significant applications in industry, life, and research. For example, using refractive index to determine liquid type, solution concentration, crystal type, gas concentration, and other aspects can provide important qualitative information.

[0003] The Abbe refractometer is the most commonly used instrument for measuring the refractive index of liquids, utilizing the principle of interfacial refraction. However, due to the need for a refracting prism and an imaging lens optical path, miniaturization is difficult. Ellipsometers are also the most commonly used refractive index measuring instruments, utilizing the principle of interfacial reflection. Miniaturization is also difficult. In practical applications, more miniaturized and flexible refractive index measurement equipment is needed.

[0004] To this end, the academic community has proposed a variety of refractive index measurement metasurfaces. These are usually based on the principle that the optical resonance spectrum peak is disturbed by the refractive index change. They can achieve high measurement sensitivity, but most of them can only measure a small refractive index range, such as measuring the refractive index change within a range of 0.01. If you need to measure samples with a large refractive index change range, or measure multiple samples, you need to frequently switch metasurfaces for measurement, which is inconvenient to use. In practical applications, the refractive index of liquids can be between 1.2 and 1.75, the refractive index of gases can be close to 1, and the refractive index of soluble polymers, soluble semiconductors, and conjugated polymers can be as high as 2.5. Therefore, various industries need a refractive index measurement device that combines a large range, high sensitivity, and a small size. Summary of the Invention

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a silicon-based metasurface large-range refractive index sensor, comprising a substrate and a metastructure;

[0006] The substrate is a double-sided polished flat plate made of uniform material, and the refractive index of the material is n(0).

[0007] One side of the double-sided polished plate is a structural surface, and the other side is a non-structural surface.

[0008] A superstructure is attached to the upper surface of the structural surface;

[0009] A medium to be measured for refractive index is attached above the structural surface and covers the superstructure;

[0010] The superstructure is composed of primitives arranged periodically in a lattice, wherein the primitives include three silicon cubes at different angles;

[0011] The lattice construction method is as follows: establishing a Cartesian two-dimensional coordinate system (x, y) on the base structure surface, using the x-axis and y-axis directions as lattice vectors, and establishing a square lattice with a period of p;

[0012] First, construct a basic primitive. The basic primitive consists of three silicon cubes with a length of l, a width of w, and a height of h. The height h is perpendicular to the coordinate system. The center coordinates of the first cube are (0.66p, 0.18p) and the l direction is parallel to the x direction. The center coordinates of the second cube are (0.18p, 0.66p) and the l direction is parallel to the y direction. The center coordinates of the third cube are (0.62p, 0.62p) and the l direction is parallel to the (1,1) vector direction.

[0013] The basic primitive is translated periodically according to the lattice to obtain other primitives,

[0014] The number of cycles is ≥ 1,000,000.

[0015] Furthermore: the primitives are arranged as a square or circular finite envelope lattice.

[0016] Furthermore: the 500nm≤p≤1000nm, 0.45p≤l≤0.55p, 0.18p≤w≤0.22p, 0.1p≤h≤0.22p, 1.40≤n(0)≤1.55.

[0017] Furthermore: the substrate is made of fused quartz, and n(0) of fused quartz is 1.46.

[0018] Furthermore: the center coordinates of the third cube of the basic primitive move on the line connecting the points (0.62p, 0.62p) to (0.68p, 0.68p).

[0019] Furthermore: the silicon material is single crystal silicon, polycrystalline silicon or amorphous silicon.

[0020] Furthermore, the sensor is tested in a spectral wavelength range of p to 3p, and the substrate is transparent at the p-3p light wavelength.

[0021] Furthermore: the surface of the superstructure is provided with a transparent protective layer in the light wavelength range of p to 3p.

[0022] According to a collective lattice resonance laser with a silicon-based metasurface large-range refractive index sensor as a resonant cavity, a gain medium is added to the structural surface to cover the metastructure. The gain medium is a laser dye solution, a conjugated polymer, a laser dye-doped polymer, or a direct bandgap semiconductor. Laser generation is achieved by exciting the gain medium.

[0023] A refractive index measuring instrument using the silicon-based metasurface large-range refractive index sensor comprises the silicon-based metasurface large-range refractive index sensor, a light source for testing the transmission and reflection spectra of the sensor, and a spectrometer.

[0024] The present invention provides a silicon-based metasurface large-range refractive index sensor. To measure refractive index, the device designed in this application is placed in the substance to be measured, or coated with the substance to be measured, illuminated with a broadband collimated light source, and the peak position of the transmission or reflection spectrum is measured to calculate the refractive index. A single optical mode can cover the refractive index range of 1-2.2 with a measurement accuracy of up to 0.001, meeting almost all industrial and biomedical needs. Multi-modes can cover the refractive index range of 1-3 with a measurement accuracy of up to 0.0001, and further expansion is possible to meet the needs of the scientific research community.

[0025] By rationally designing the metasurface structure, this application can realize optical resonance effects such as electric quadrupoles and magnetic quadrupoles, with narrow resonance spectrum peaks. When the metasurface contacts different media with a large refractive index range, the resonance will not be destroyed, thereby realizing large-scale and high-sensitivity refractive index measurement.

[0026] The device is made of silicon dioxide and silicon materials, has good inertness, can be in contact with a variety of substances to be tested, and has a long service life.

[0027] The device allows the measurement of the two-dimensional spatial distribution of the refractive index, as well as the joint measurement of multiple device arrays.

[0028] The device can also be used as a laser resonant cavity, supporting laser gain media with almost arbitrary refractive index, such as liquid gain media and semiconductor thin film gain media.

[0029] The device can be used as a narrowband tilt-tuned filter, and the size of the device can be arbitrarily scaled to support different operating wavelength ranges.

[0030] The present invention realizes single-device single-spectrum measurement of refractive index 1-3 through reasonable structural design, and has the unique advantages of small device size, large range and high measurement resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1 : Schematic diagram of the lattice and unit cell plane of the device of the present application;

[0033] Figure 2 : Schematic diagram of the lattice and unit cell of the device of the present application;

[0034] Figure 3 : A side view of the device structure of the present application;

[0035] Figure 4 : Transmission spectrum peak of the device of the present application;

[0036] Figure 5 : The spectral peak response refractive index change curve when the device of this application is used to test the refractive index.

[0037] Reference numerals: 1 - silicon cube, 2 - substrate, 3 - medium to be measured. DETAILED DESCRIPTION

[0038] It should be noted that, unless there is any conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0042] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0043] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0044] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0045] A silicon-based metasurface large-range refractive index sensor, comprising a substrate 2 and a metastructure;

[0046] The substrate 2 is a double-sided polished flat plate made of uniform material, and the refractive index of the material is n(0).

[0047] One side of the double-sided polished plate is a structural surface, and the other side is a non-structural surface. The upper surface of the structural surface is attached with a superstructure; not only the upper part of the superstructure, but also the gaps in the superstructure (exposed parts of the structural surface) are covered.

[0048] A medium to be measured for refractive index is attached above the structural surface and covers the superstructure;

[0049] The substrate 2 is a transparent substrate;

[0050] The superstructure is composed of primitives arranged periodically in a lattice.

[0051] The superstructure has a square lattice, and a unit of the superstructure is set in each lattice. The unit is composed of three silicon cubes at different angles, supporting collective lattice resonance optical modes such as electric quadrupole resonance.

[0052] A medium to be measured for refractive index is attached above the superstructure.

[0053] The lattice construction method is as follows: a Cartesian two-dimensional coordinate system (x, y) is established on the structural surface of the substrate 2, with the x-axis and y-axis directions as lattice vectors, and a square lattice with a period of p is established;

[0054] First, construct a basic primitive. The basic primitive consists of three silicon cubes 1 with a length of l, a width of w, and a height of h. The height h is perpendicular to the coordinate system. The center coordinates of the first cube are (0.66p, 0.18p) and the l direction is parallel to the x direction. The center coordinates of the second cube are (0.18p, 0.66p) and the l direction is parallel to the y direction. The center coordinates of the third cube are (0.62p, 0.62p) and the l direction is parallel to the (1,1) vector direction.

[0055] The basic primitive is translated periodically according to the lattice to obtain other primitives,

[0056] The number of cycles is ≥ 1,000,000.

[0057] A method for using a silicon-based metasurface large-range refractive index sensor is as follows: when measuring the refractive index, a medium to be measured 3 is added to the structural surface to cover the metastructure, and then the transmission or reflection spectrum of the silicon-based metasurface large-range refractive index sensor is tested. The refractive index of the medium to be measured 3 is calculated using the shape of the spectral curve combined with the principles of wave optics.

[0058] Furthermore: the lattice always has a boundary, and the primitives are arranged as a square or circular lattice.

[0059] Furthermore, the 500nm≤p≤1000nm, the 0.45p≤l≤0.55p, 0.18p≤w≤0.22p, 0.1p≤h≤0.22p, and 1.40≤n(0)≤1.55.

[0060] The substrate 2 is made of fused quartz, and n(0) of fused quartz is 1.46.

[0061] Furthermore, the center coordinates of the third cube of the basic primitive move on the line connecting the points (0.62p, 0.62p) to (0.68p, 0.68p).

[0062] Furthermore, the material is single crystal silicon, polycrystalline silicon or amorphous silicon.

[0063] Furthermore, the sensor tests a spectral wavelength range of p to 3p, and the substrate 2 is transparent at the p-3p light wavelength.

[0064] Furthermore, the superstructure further comprises a transparent protective layer in the wavelength range of p to 3p on the surface not attached to the substrate 2. The protective layer isolates the medium to be measured from the sensor.

[0065] A collective lattice resonance laser using the silicon-based metasurface large-range refractive index sensor as a resonant cavity, wherein a gain medium is added to the structural surface to cover the metastructure, wherein the gain medium is a laser dye solution, a conjugated polymer, a laser dye-doped polymer, or a direct bandgap semiconductor, and laser generation is achieved by exciting the gain medium.

[0066] A refractive index measuring instrument using the silicon-based metasurface large-range refractive index sensor comprises the silicon-based metasurface large-range refractive index sensor, a light source for testing the transmission and reflection spectra of the sensor, and a spectrometer.

[0067] Metasurfaces and metastructures are similar. They are so thin that their thickness can be ignored in optical applications, so they are called metasurfaces. When thickness is a factor in design and manufacturing, they are called superstructures. This patent discusses design and manufacturing, but mostly refers to them as superstructures.

[0068] The metasurface of the present invention achieves its function by placing a silicon superstructure on the surface of a silicon dioxide (fused quartz) substrate. Specifically, the superstructure is a two-dimensional periodic structure, with three micro-silicon cubes arranged in different orientations within each period. By optimizing the structural parameters, optical resonance effects such as electric quadrupoles and magnetic quadrupoles can be achieved. These optical resonance effects can form very narrow transmission and reflection spectral peaks. When the space around the superstructure is filled with substances to be measured with different refractive indices, the spectral peaks shift to different wavelengths. However, unlike common metasurface designs, the spectral peaks do not disappear, thus achieving ultra-wide refractive index measurement with high measurement accuracy.

[0069] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0070] Example 1: A single-mode, large-range refractive index sensor

[0071] Sensor device structure such as Figure 1 : Schematic diagram of the lattice and unit cell plane of the device of the present application; Figure 2 : Schematic diagram of the lattice and unit cell of the device of the present application; Figure 3 : As shown in the side schematic diagram of the device structure of the present application, it contains a fused quartz polished flat plate as a substrate 2, a superstructure 1 made of single crystal silicon attached to the substrate 2, and a medium to be tested 3. The superstructure 1 is a periodic structure, and its two-dimensional lattice is a square lattice. The lattice vectors are along the x and y directions, and the lattice period p = 500nm. The superstructure 1 distributes 3 silicon cubes 1-1 to 1-3 in each lattice. The length of each cube is l = 250nm, the width is w = 100nm, and the height is h = 100nm. Taking the lower left corner of the lattice as the origin, the coordinates of the center point of the cube are specifically (330nm, 90nm) for cube 1-1, (90nm, 330nm) for cube 1-2, and (310nm, 310nm) for cube 1-3. The superstructure 1 has 2000 periods in the x and y dimensions, and the size of the device's usable area is 1mm. 2 The device can be manufactured using a common deposition-electron beam lithography-development process.

[0072] The refractive index sensing method of the sensor device is to test the transmission or reflection spectrum peak position. If the refractive index of the medium to be measured 3 is consistent with that of fused quartz, the horizontal polarization normal transmission spectrum peak of the device is as shown in the following figure. Figure 4 As shown, there are eight distinct resonance peaks #1-#8 in the range of 700-900nm. Peak 8 is an electric quadrupole resonance mode peak. Its characteristics are that when the refractive index of the test medium 3 is in the range of 1-2.2, peak #8 always exists, maintains high intensity, and has a narrow linewidth. It is an isolated peak within the range of approximately + / -30nm. The relationship between its peak position and the refractive index of the test medium 3 is shown in the attached figure. Figure 5The Mode 1 curve is a monotonic curve. The refractive index value of the medium 3 to be measured can be determined based on the measured spectrum peak #8 wavelength with an accuracy of 0.001. It is recommended to test the normal transmission spectrum when the device is in use, but the incident light can also be deflected at an angle within 10° and the device can still work normally. If the working conditions do not allow testing the transmission spectrum, the reflection spectrum can also be tested. The peak position of the reflection spectrum is the same as the attached Figure 4 The mechanism by which peak #8 allows for large variations in the refractive index of the medium 3 being measured is that part of the electric field in the corresponding resonant mode is distributed in the silicon superstructure, another part in the substrate 1, and the remaining part in the medium 3 being measured. These parts support each other, forming a stable, large-range refractive index measurement mode.

[0073] Example 2: A multi-mode high-precision refractive index sensor

[0074] The device structure of Example 2 remains the same as that of Example 1, but multiple modes are used for refractive index measurement, including modes corresponding to peaks #1-#8. This device now allows the refractive index of the test medium 3 to range from 1.33 to 1.62. The drift rates of peaks #1-#8 as the refractive index of the test medium 3 changes vary, not simply scaling with wavelength. Therefore, by measuring the spacing between the peaks, the refractive index of the test medium 3 can be determined with high precision, reaching an accuracy of 0.0001.

[0075] Example 3: A multi-mode, large-range refractive index sensor

[0076] The device structure of the third embodiment is still the same as that of the first embodiment, but when measuring the refractive index, multiple modes are used, including peak #8 (Mode 1) and high-order collective lattice resonance mode, namely Figure 5 Mode 2 and Mode 3 are shown. Mode 2 and Mode 3 only work when the medium 3 to be measured has a high refractive index. Modes 1 to 3 form a relay, and the testable refractive index range is 1-3 with an accuracy of up to 0.001, which can meet the measurement needs of scientific research.

[0077] Example 4: A single-mode, large-range refractive index sensor with enhanced inertness

[0078] The device structure of the fourth embodiment is improved on the basis of the first embodiment, Figure 3 As a basic example, a 50nm-thick layer of transparent, inert material, such as silicon dioxide, aluminum oxide, or polyethylene, is deposited on superstructure 1 using a standard coating system. This layer then covers the test medium 3. This prevents direct contact between the test medium 3 and superstructure 1, increasing the device's inertness. The lower limit of the device's refractive index range remains 1, but the upper limit is reduced to approximately 1.8. This device strikes a balance between measurement capability and stability, enabling the measurement of the refractive index of a wider range of chemically unstable substances.

[0079] Example 5: A long-wave single-mode large-range refractive index sensor

[0080] The device structure of the fifth embodiment is a scaled-up version of the first embodiment, which is enlarged to 100%-200% of the original size. At this time, the operating wavelength of the device is also approximately red-shifted to 100%-200% of the original wavelength. Figure 5 Modes such as Mode 1 shown still work normally and can test the refractive index of the medium 3 under test at longer wavelengths of light.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based metasurface large-range refractive index sensor, characterized in that: including substrate and superstructure; The substrate is a double-sided polished flat plate made of uniform material, and the refractive index of the material is n(0). One side of the double-sided polished plate is a structural surface, and the other side is a non-structural surface. A superstructure is attached to the upper surface of the structural surface; A medium to be measured for refractive index is attached above the structural surface and covers the superstructure; The superstructure is composed of primitives arranged periodically in a lattice, wherein the primitives include three silicon cubes at different angles; The lattice construction method is as follows: establishing a Cartesian two-dimensional coordinate system (x, y) on the base structure surface, using the x-axis and y-axis directions as lattice vectors, and establishing a square lattice with a period of p; First, construct a basic primitive. The basic primitive consists of three silicon cubes with a length of l, a width of w, and a height of h. The height h is perpendicular to the coordinate system. The center coordinates of the first cube are (0.66p, 0.18p) and the l direction is parallel to the x direction. The center coordinates of the second cube are (0.18p, 0.66p) and the l direction is parallel to the y direction. The center coordinates of the third cube are (0.62p, 0.62p) and the l direction is parallel to the (1,1) vector direction. The basic primitives are translated periodically according to the lattice to obtain other primitives, The number of cycles is ≥ 1,000,000.

2. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The primitives are arranged as a finite envelope lattice of square or circular elements.

3. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: 500nm≤p≤1000nm, 0.45p≤l≤0.55p, 0.18p≤w≤0.22p, 0.1p≤h≤0.22p, 1.40≤n(0)≤1.

55.

4. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The substrate is made of fused quartz, and n(0) of fused quartz is 1.

46.

5. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The center coordinates of the third cube of the basic primitive move on the line connecting the points (0.62p, 0.62p) to (0.68p, 0.68p).

6. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The silicon material is single crystal silicon, polycrystalline silicon or amorphous silicon.

7. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The sensor is tested in the spectral wavelength range of p-3p, and the substrate is transparent at the p-3p light wavelength.

8. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The surface of the superstructure is provided with a transparent protective layer in the range of light wavelength p to 3p.

9. A collective lattice resonance laser with a silicon-based metasurface large-range refractive index sensor as a resonant cavity according to claims 1-8, characterized in that: A gain medium is added to the structural surface to cover the superstructure. The gain medium is a laser dye solution, a conjugated polymer, a laser dye-doped polymer, or a direct bandgap semiconductor. Laser generation is achieved by exciting the gain medium.

10. A refractive index measuring instrument using the silicon-based metasurface large-range refractive index sensor according to claims 1-8, characterized in that: It includes a silicon-based metasurface large-range refractive index sensor, a light source and a spectrometer for testing the transmission and reflection spectra of the sensor.

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