Silicon-based metasurface wide-range refractive index sensor

Abstract

The invention relates to a silicon-based metasurface wide-range refractive index sensor which comprises a substrate and a superstructure. The substrate is a double-sided polished flat plate made of a uniform material, the refractive index of the material is n (0), one surface of the double-sided polished flat plate is a structural surface, the other surface is a non-structural surface, and the superstructure is attached to the upper surface of the structural surface; a refractive index to-be-measured medium is attached above the structural surface and covers the superstructure; the superstructure is composed of elements which are periodically arranged according to crystal lattices, and each element comprises three silicon material cubes with different angles. The lattice construction method comprises the following steps: establishing a square lattice with a period of p; firstly, a basic element is constructed, the basic element is composed of three silicon material cubes with the length of 1, the width of w and the height of h, the height h direction is perpendicular to a coordinate system, and the basic element periodically translates according to crystal lattices to obtain other elements. Through reasonable design of the metasurface structure, optical resonance effects of electric quadrupole, magnetic quadrupole and the like can be realized, and the metasurface has a narrow resonance spectrum peak, so that wide-range and high-sensitivity refractive index measurement is realized.

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 detection is one of the most important optical measurement methods, and has important application significance in industry, life, and scientific research. For example, using refractive index to determine liquid type, solution concentration, crystal type, gas concentration, etc. can provide important qualitative information.

[0003] Abbe refractometer is the most commonly used instrument for measuring the refractive index of liquids. It measures the refractive index based on the principle of interface refraction. Because it requires the setting of a refractive prism and an imaging lens optical path, its volume is difficult to miniaturize. Ellipsometer is the most commonly used instrument for measuring the refractive index. It measures the refractive index based on the principle of interface reflection. It is also difficult to miniaturize. In practical applications, a more miniaturized and flexible refractive index measuring device is needed.

[0004] To this end, the academic community has proposed a variety of refractive index measurement metasurfaces, which are usually based on the principle that the optical resonance spectrum peak is disturbed by the refractive index change. They can obtain very high measurement sensitivity, but most of them can only achieve measurement in 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 the metasurface for measurement, which is inconvenient to use. In practical applications, the refractive index of liquids can be between 1.2-1.75, 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 has 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 of uniform material, 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, and the primitives include three silicon cubes at different angles;

[0011] The lattice construction method is as follows: establish a Cartesian two-dimensional coordinate system (x, y) on the base structure surface, take the x-axis and y-axis directions as lattice vectors, and establish 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 x. The center coordinates of the second cube are (0.18p, 0.66p) and the l direction is parallel to y. 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: 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 spectral wavelength range tested by the sensor is between p and 3p, and the substrate is transparent at the p-3p light wavelength.

[0021] Furthermore: the surface of the superstructure has 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 or a conjugated polymer or 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. When measuring the refractive index, the device designed in this application is placed in the substance to be measured, or the substance to be measured is coated on its surface, illuminated by 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, and the measurement accuracy can reach 0.001, which can almost meet the needs of all industries and biomedicines; multi-mode covers the refractive index range of 1-3, and the measurement accuracy can reach 0.0001, and it can be further expanded to meet the needs of the scientific research community.

[0025] By rationally designing the metasurface structure, the present application can realize optical resonance effects such as electric quadrupole and magnetic quadrupole, with a narrow resonance spectrum peak. When the metasurface contacts different media with a large refractive index range, the resonance will not be destroyed, thereby realizing a large-range 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 distributed 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 the single-device single-spectrum measurement of refractive index 1-3 through reasonable structural design, and has the unique advantages of small device size, large measurement 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

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

[0033] Figure 2 : A three-dimensional schematic diagram of the lattice and primitives of the device of the present application;

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

[0035] Figure 4 : The 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 the present 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, in the absence of 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 by no means 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 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 exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates 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 described in these embodiments, the numerical expressions and numerical values ​​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 technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0042] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the 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 contours 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 here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. 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 figure. For example, if the device in the accompanying 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. If not 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, 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 cell of the superstructure is arranged in each lattice. The unit cell is composed of three silicon cubes at different angles, and supports 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: establish a Cartesian two-dimensional coordinate system (x, y) on the structural surface of the substrate 2, take the x-axis and y-axis directions as lattice vectors, and establish a square lattice with a period of p;

[0054] First, a basic primitive is constructed. The basic primitive is composed 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 3 to be measured is added to the structural surface to cover the superstructure, and then the transmission or reflection spectrum of the silicon-based metasurface large-range refractive index sensor is tested, and the refractive index of the medium 3 to be measured is calculated by combining the shape of the spectrum curve with the principle of wave optics.

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

[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 spectral wavelength range tested by the sensor is between p and 3p, and the substrate 2 is transparent at the p-3p light wavelength.

[0064] Furthermore, it also includes a transparent protective layer in the range of light wavelength p to 3p on the surface of the superstructure 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 or a conjugated polymer or 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 are the same as superstructures. They are very thin and their thickness can be ignored in optical applications, so they are called metasurfaces. When designing and manufacturing, thickness must be considered, so they are called superstructures. This patent discusses design and manufacturing, and most of the time it is called superstructures.

[0068] The super surface of the present invention realizes its function by setting a super structure of silicon material on the surface of a silicon dioxide (fused quartz) substrate. Specifically, the super structure is a two-dimensional periodic structure, and three micro silicon cubes with different placement directions are set in each period. By optimizing the structural parameters, optical resonance effects such as electric quadrupoles and magnetic quadrupoles can be realized. These optical resonance effects can form very narrow transmission and reflection spectrum peaks. When the space around the super structure is filled with substances to be tested with different refractive indices, the spectrum peak moves to different wavelengths, but unlike the common super surface design, the spectrum peak does not disappear, thereby realizing ultra-wide range refractive index measurement with high measurement accuracy.

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

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

[0071] Sensor device structure Figure 1 : Schematic diagram of the lattice and unit plane of the device of the present application; Figure 2 : A three-dimensional schematic diagram of the lattice and primitives 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 sheet 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 has 3 silicon cubes 1-1 to 1-3 distributed 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 respectively, and the size of the device 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 3 to be measured 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 8 obvious resonance peaks #1-#8 in the range of 700-900nm. The nature of the spectrum peak 8 is the electric quadrupole resonance mode peak, which is characterized by that when the refractive index of the medium 3 to be measured is in the range of 1-2.2, the spectrum peak #8 always exists, maintains high intensity and narrow line width, and is an isolated peak in the range of about + / -30nm. The relationship between its peak position and the refractive index of the medium 3 to be measured is shown in the attached figure. Figure 5The Mode1 curve is a monotonic curve. The refractive index value of the medium 3 to be tested 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 the transmission spectrum to be tested, the reflection spectrum can also be tested. The peak position of the reflection spectrum is equivalent to the attached Figure 4 The mechanism by which the spectrum peak #8 allows the refractive index of the medium 3 to change greatly is that part of its corresponding resonant mode electric field is distributed in the silicon superstructure, another part is distributed in the substrate 1, and the rest is distributed in the medium 3 to be measured. Each part supports each other to form a stable large-range refractive index measurement mode.

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

[0074] The device structure of the second embodiment is still the same as that of the first embodiment, but when measuring the refractive index, multiple modes are used, including the modes corresponding to the spectrum peaks #1-#8. At this time, the device allows the refractive index range of the medium 3 to be measured to be 1.33-1.62. The drift rates of the spectrum peaks #1-#8 as the refractive index of the medium 3 to be measured are different, and are not simply scaled with the wavelength. Therefore, the refractive index of the medium 3 to be measured can be determined with high precision by testing the spacing between the spectrum peaks, with an accuracy of up to 0.0001.

[0075] Embodiment 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 the spectrum peak #8 (Mode 1) and the high-order collective lattice resonance mode, namely, Figure 5 Mode2 and Mode3 are shown. Mode2 and Mode3 only work when the medium 3 to be measured has a high refractive index. Mode1 to 3 form a relay, and the refractive index range that can be tested is 1-3, with an accuracy of up to 0.001, which can meet the measurement needs of scientific research exploration.

[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 basis for explanation, a 50nm thick transparent inert material, such as silicon dioxide, aluminum oxide, polyethylene, etc., is coated on the superstructure 1 using a general coating device, and then covered with the medium to be measured 3. At this time, the medium to be measured 3 is not in direct contact with the superstructure 1, which increases the inertness of the device. At this time, the lower limit of the refractive index range of the device is still 1, but the upper limit is reduced to about 1.8. The device strikes a balance between measurement capability and stability, and can measure the refractive index of more chemically unstable substances.

[0079] Embodiment 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 working 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 a longer wavelength 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned 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: Includes substrate and superstructure; The substrate is a double-sided polished flat plate of uniform material, 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, and the primitives include three silicon cubes at different angles; The lattice construction method is as follows: establish a Cartesian two-dimensional coordinate system (x, y) on the base structure surface, take the x-axis and y-axis directions as lattice vectors, and establish 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 x. The center coordinates of the second cube are (0.18p, 0.66p) and the l direction is parallel to y. 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 primitive is 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 shapes.

3. The silicon-based metasurface large-range refractive index sensor according to claim 1, characterized in that: The described 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 silica, and n(0) of the fused silica 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 light wavelength range of 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 onto the structural surface to cover the superstructure, wherein the gain medium is a laser dye solution or a conjugated polymer or a laser dye doped polymer or a direct bandgap semiconductor, and laser generation is achieved by exciting the gain medium.

10. A refractive index measuring instrument using a 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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