Refractive index detection device and method based on a width-graded guided-mode resonance grating

Abstract

The application discloses a refractive index detection device and method based on a width-gradually-changing guided-mode resonance grating, and belongs to the technical field of optical sensing. Light emitted by a light source is incident on a guided-mode resonance sensing chip after passing through a light isolator, a polarization controller and a collimating and expanding mirror. The guided-mode resonance sensing chip is of a transmission type structure, and a strip-shaped nano structure with gradually-changing strip width is arranged on the top of the guided-mode resonance sensing chip. An image detector is arranged below the guided-mode resonance sensing chip. The image detector receives a transmission light signal after passing through the guided-mode resonance sensing chip, generates a transmission light image, and transmits the transmission light image to a signal processing unit for analysis. The refractive index of a medium to be measured is inversely calculated according to the mapping relationship between the strip width and the refractive index. The application maps the resonance wavelength into image position information through spatial structure design, and does not need a traditional light splitting device for refractive index inversion, so that high-precision, image-based and real-time refractive index detection is realized, and the problems of the traditional guided-mode resonance sensor, such as the need of complex optical elements, large volume and high cost, are solved.

Description

Refractive index detection device and method based on width-gradient guided mode resonant grating Technical Field

[0001] This invention relates to the field of optical sensing technology, and in particular to a refractive index detection device and method based on a width-gradient guided-mode resonant grating. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Existing optical refractive index sensing technologies mostly employ interferometers, gratings, or plasmonic structures to achieve refractive index detection. These technologies largely rely on bulky and expensive spectroscopic analysis equipment, such as spectrometers or spectrometers, resulting in low system integration, high cost, and slow demodulation speed, making them unsuitable for portable or on-chip system integration requirements. Guided-mode resonant gratings, which excite waveguide modes through periodic gratings and exhibit strong transmission / reflection changes at specific wavelengths, have been applied to refractive index detection and offer advantages such as simple structure, narrow resonance peaks, and high sensitivity. However, conventional guided-mode resonant sensors face two main bottlenecks: (1) reliance on expensive equipment such as spectrometers: monitoring the resonance wavelength λ R High-resolution spectrometers or spectrometer systems are usually required, which is not conducive to low-cost, portable system integration; (2) lack of spatial coding mechanism: traditional equal-width guided mode resonance structures cannot realize structure-wavelength-space mapping, cannot simplify the demodulation process in a graphical way, and are difficult to combine with efficient demodulation methods. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a refractive index detection device and method based on a width-gradient guided-mode resonant grating. By designing a spatial structure, the refractive index is mapped to image position information, eliminating the need for refractive index inversion using traditional beam splitting devices. This achieves high-precision, image-based, and real-time refractive index detection, solving the problems of traditional guided-mode resonant sensors requiring complex optical components, large size, and high cost.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a refractive index detection device based on a width-gradient guided mode resonant grating, comprising a light source, wherein the light emitted by the light source passes through an optical isolator, a polarization controller and a collimating beam expander and then is incident on a guided mode resonant sensing chip, wherein the top of the guided mode resonant sensing chip is provided with a strip-shaped nanostructure with a consistent period but a gradually changing strip width.

[0007] The guided mode resonant sensing chip has a transmission structure with an image detector below it. The image detector receives the transmitted light signal after passing through the guided mode resonant sensing chip, generates a transmitted light image, and transmits the transmitted light image to the signal processing unit. The signal processing unit analyzes the transmitted light image and inverts the refractive index of the medium under test based on the mapping relationship between the stripe width and the refractive index.

[0008] As a further implementation, the guided mode resonant sensing chip includes a substrate layer and a high refractive index layer disposed on the substrate layer, wherein the high refractive index layer is a strip-shaped nanostructure.

[0009] As a further implementation, the guided mode resonant sensing chip includes a substrate layer, a high refractive index layer disposed on the substrate layer, and a low refractive index layer located on top, wherein the low refractive index layer is a strip-shaped nanostructure.

[0010] As a further implementation, the refractive index of the substrate, the refractive index of the high-refractive-index layer, and the refractive index of the low-refractive-index layer satisfy the set conditions.

[0011] As a further implementation, the cross-sectional shape of the strip nanostructure can be rectangular, square, semi-circular, elliptical, sinusoidal, triangular, trapezoidal, or other regular shapes.

[0012] As a further implementation, the strip nanostructures are spaced at the same intervals in each period, and the width of the strip nanostructures in adjacent periods gradually changes by a fixed increment.

[0013] As a further implementation, the light source is a wavelength-tunable monochromatic laser, whose operating range covers the visible to infrared bands, and the incident light wavelength is greater than the period length of the strip nanostructure.

[0014] As a further implementation, the image detector is a CCD or CMOS array camera;

[0015] The signal processing unit includes image processing software and an algorithm module for establishing the mapping relationship between pixel position and refractive index.

[0016] As a further implementation method, a mapping relationship between pixel position and refractive index is established, specifically as follows:

[0017] A set of reference samples with known refractive indices are tested, and the resonance position of each sample on the transmitted light image is recorded. A function between pixel position and refractive index is established to obtain an inversion lookup table or fitting model.

[0018] A second aspect of the present invention provides a refractive index detection method based on a width-gradient guided-mode resonant grating, and a refractive index detection device based on a width-gradient guided-mode resonant grating as described in the first aspect of the present invention, comprising the following steps:

[0019] S1. Using a refractive index testing device to test materials with unknown refractive index;

[0020] S2. Acquire the transmitted light image below the guided mode resonance sensing chip through an image detector;

[0021] S3. Transmit the image to the signal processing unit and extract the light intensity distribution of each pixel in the image;

[0022] S4. Based on the correspondence between pixel position and light intensity, obtain the changes in transmission spectrum intensity at different positions;

[0023] S5. Using the preset mapping relationship between refractive index and pixel position, the refractive index value of the medium under test is obtained by inversion.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention discloses a refractive index detection device and method based on a width-gradient guided-mode resonant grating. The guided-mode resonant sensing chip is designed as a one-dimensional strip-shaped nanostructure with a consistent period but gradually varying strip width. Utilizing the spatial correspondence between structural parameters and resonant wavelengths, combined with a monochromatic light source, spectral information is directly mapped to spatial position information on an image detector. Then, the refractive index of the medium under test is inverted using acquired lookup table data or a fitted model, achieving image demodulation. The system achieves a refractive index inversion method without a spectrometer through image recognition and pixel intensity analysis, simplifying the hardware system and making the system compact and easily integrated into on-chip sensors or portable devices. It is suitable for various light sources and detection environments, exhibiting high sensitivity and real-time performance. It possesses advantages such as simple overall structure, low cost, fast image demodulation, and wide applicability, and can be widely used for high-sensitivity real-time refractive index detection of liquids, gases, and other media. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 is a schematic diagram of the overall structure of the refractive index detection device based on the width-gradient guided mode resonant grating provided in Embodiment 1 of the present invention;

[0028] Figure 2 is a schematic diagram of the substrate + high refractive index nanostrip structure (width gradient) sensing chip provided in Embodiment 1 of the present invention, wherein (a) is a schematic diagram of the front view of the sensing chip and (b) is a schematic diagram of the three-dimensional structure of the sensing chip.

[0029] Figure 3 is a schematic diagram of the structure of the substrate + waveguide layer + low refractive index strip structure (width gradient) sensor chip provided in Embodiment 1 of the present invention, wherein (a) is a schematic diagram of the front view of the sensor chip, and (b) is a schematic diagram of the three-dimensional structure of the sensor chip.

[0030] Figure 4 is a schematic diagram of the image detector imaging provided in Embodiment 1 of the present invention;

[0031] Figure 5 shows the electric field distribution of the substrate + high refractive index nanostrip structure (width gradient) provided in Embodiment 1 of the present invention, which locally satisfies guided mode resonance under single-wavelength incident light.

[0032] Figure 6 shows the electric field distribution of the substrate + waveguide layer + low refractive index strip structure (width gradually changing) provided in Embodiment 1 of the present invention, which locally satisfies guided mode resonance under single wavelength incident.

[0033] Figure 7 shows the electric field distribution of the substrate + high refractive index nanostrip structure (non-gradient width) provided in Embodiment 1 of the present invention, which satisfies the guided mode resonance condition;

[0034] Figure 8 shows the electric field distribution of the substrate + high refractive index nanostrip structure (non-gradient width) provided in Embodiment 1 of the present invention, which does not meet the guided mode resonance condition;

[0035] Figure 9 shows the electric field distribution of the substrate + waveguide layer + low refractive index nanostrip structure (non-gradient width) provided in Embodiment 1 of the present invention, which satisfies the guided mode resonance condition.

[0036] Figure 10 shows the electric field distribution of the substrate + waveguide layer + low refractive index nanostrip structure (non-gradient width) provided in Embodiment 1 of the present invention, which does not meet the guided mode resonance condition.

[0037] Figure 11 is a flowchart of the refractive index detection method based on a width-gradient guided mode resonant grating provided in Embodiment 2 of the present invention.

[0038] The components include: 1. Light source; 2. Optical isolator; 3. Polarization controller; 4. Collimating beam expander; 5. Mode-guided resonance sensor chip; 6. Image detector; 7. Signal processing unit; 8. Low refractive index layer; 9. High refractive index layer; and 10. Substrate layer. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0041] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0042] Example 1

[0043] As shown in Figure 1, this embodiment provides a refractive index detection device based on a width-gradient guided-mode resonant grating, including a light source 1, an optical isolator 2, a polarization controller 3, and a collimating beam expander 4 connected in sequence. Monochromatic light output from the collimating beam expander 4 is incident perpendicularly onto a guided-mode resonant sensing chip 5. The guided-mode resonant sensing chip 5 is configured as a transmissive structure, with a one-dimensional strip-shaped nanostructure on its top that has a consistent period but a gradually changing strip width. An image detector 6 is located below the guided-mode resonant sensing chip 5. The image detector 6 receives the transmitted light signal after passing through the guided-mode resonant sensing chip 5, generates a transmitted light image, and transmits the transmitted light image to a signal processing unit 7. The signal processing unit 7 analyzes the light intensity of each pixel in the transmitted light image and inverts the refractive index of the medium under test based on the mapping relationship between the strip width (corresponding to the spatial position of the pixel) and the refractive index.

[0044] In this embodiment, the light source 1 is a wavelength-tunable monochromatic laser, such as a DFB laser or a picometer-level tunable laser, with an operating range of 350 nm to 2500 nm, covering the visible to infrared bands. The incident light wavelength is greater than the period length of the strip nanostructure, that is, the incident light λ satisfies λ>P.

[0045] Optical isolator 2 is used to eliminate back reflection; polarization controller 3 ensures that the polarization state of the incident light is consistent; collimating beam expander 4 expands the laser beam to a suitable spot; guided mode resonance sensing chip 5 is the core sensing component of this invention.

[0046] Image detector 6 acquires transmitted images. In this embodiment, the image detector is a CCD or CMOS array camera.

[0047] The signal processing unit 7 is used to analyze the image and calculate the refractive index. The signal processing unit 7 includes image processing software and an algorithm module for establishing the mapping relationship between pixel position, resonant wavelength, and refractive index.

[0048] Monochromatic light emitted from light source 1 passes through optical isolator 2, polarization controller 3, and collimating beam expander 4 before being incident perpendicularly on the surface of guided mode resonant chip 5. Image detector 6 is positioned below the chip to receive the transmitted light and form an image. Signal processing unit 7 processes the image data in real time and performs refractive index demodulation.

[0049] The core sensing component of this invention, the guided-mode resonant sensing chip 5, has a structural layer number N≥1, and a one-dimensional periodically arranged strip nanostructure is provided at the top. The strip nanostructure is made of a high-refractive-index material or a low-refractive-index material, and two structures are shown in Figures 2 and 3 respectively. The cross-sectional shape of the strip nanostructure can be rectangular, square, semi-circular, elliptical, sinusoidal, triangular, trapezoidal or other regular shapes.

[0050] As shown in Figure 2, the substrate + high refractive index nanostrip structure (gradually varying width) sensor chip structure proposed in this invention consists of the following parts:

[0051] (1) Base layer 10: Material such as quartz or glass, refractive index n s ;

[0052] (2) One-dimensional strip nanostructures: composed of high refractive index material 9 thin film layers (such as Si3N4, , Composed of ) with a thickness of 50 nm to 500 nm and a refractive index of n h The period is P, arranged along the Y-axis, and the width of the stripes gradually changes along the X-direction.

[0053] As shown in Figure 3, the sensor chip structure proposed in this invention, consisting of a substrate + waveguide layer + low refractive index strip structure (gradually varying width), comprises the following components:

[0054] (1) Base layer 10: Material such as quartz or glass, refractive index n s ;

[0055] (2) Waveguide layer: composed of a thin film layer of high refractive index material (such as Si3N4, ...). , Composed of ) with a thickness of 20 nm to 500 nm and a refractive index of n h ;

[0056] (3) One-dimensional strip nanostructure: composed of 8 thin film layers of low refractive index material (such as...) Composed of elements with a period of P, arranged along the Y-axis, and with a gradually changing stripe width along the X-direction, the refractive index is n. l .

[0057] The structures shown in Figures 2 and 3 satisfy the following refractive index constraint: n h -n s >0.2 (Ensure support for the guide mold); |n l -n s |≤ 0.2 (to avoid distortion of the resonance signal).

[0058] The period P of the strip nanostructure is fixed (e.g., P = 500 nm), while the strip width w i A gradual distribution is formed as the position x changes, for example:

[0059] Δw is a constant gradient, typically 2~10 nm / μm;

[0060] Gradient design range: Δw = 1 pm to 100 nm, supporting high-precision spatial resolution.

[0061] Each stripe width w corresponds to a unique resonant wavelength λ R Their relationship can be preset to λ through simulation. R =f(w). Since w(x) is a monotonic function, λ R (x) also changes monotonically with x, therefore, the spectral information λ R With spatial location information x R One-to-one correspondence.

[0062] As shown in Figure 4(a), the incident light produces strong absorption regions at different positions, and the transmission intensity appears as local dark bands, which are represented as intensity troughs in the image detector image, corresponding to the resonant wavelength λ. R Place.

[0063] To further verify that the width-gradient guided-mode resonant grating structure used in this invention can realize the demodulation method of "wavelength-position mapping", two typical examples are given below. Combined with electric field distribution simulation and imaging effect, it is shown that when the incident wavelength is fixed, the local area in the structure that meets the guided-mode resonance condition will generate light absorption, thus presenting a dark band in the imaging, reflecting the function of "position indication of a specific wavelength in the structure".

[0064] Example 1: Substrate + high refractive index nanostrip structure (gradually varying width) — single wavelength incident, locally satisfying guided mode resonance

[0065] This example structure includes a glass substrate (n) s =1.45), above which is a high-refractive-index Si3N4 strip structure (n h =2.0, thickness h=100 nm), the period of the nanostrips is fixed at P=500 nm, and the width of the strip structure changes linearly in the length direction (e.g. from w min =125 nm to w max =300 nm, increasing by Δw=35 nm per period). The incident light is monochromatic, with a wavelength of λ=710 nm, incident perpendicularly, and polarized in the TE mode.

[0066] As shown in Figure 5, the simulation results show that the structure satisfies the guided mode resonance condition only near a strip width of approximately w = 195 nm, where the electromagnetic field is locally coupled into the waveguide mode and strongly absorbed; the resonance condition is not met in the remaining areas, and light passes through. The final image detector image shows a clear dark band (Figure 4(a)), whose lateral position corresponds to a specific resonance width, i.e., the "marker position" for this wavelength. Therefore, the mapping of wavelength information to spatial position is realized.

[0067] Example 2: Substrate + waveguide layer + low refractive index strip structure (gradually varying width) — single wavelength incident, locally satisfying guided mode resonance

[0068] This example structure consists of three layers: the base is n. s =1.45 glass, with a high refractive index waveguide layer in the middle, the material is (n) h =2.0, thickness H=200 nm), the topmost part is a low-refractive-index nanostrip structure, the material is (n) l =1.45, thickness h=100 nm), period fixed at P=500 nm, stripe width linearly varied, from w min =125 nm to w max =300 nm. The incident light wavelength is λ=850 nm, perpendicularly incident, TE polarized.

[0069] As shown in Figure 6, the simulation results show that near a strip width of approximately w = 195 nm, the structure satisfies the guided mode resonance condition, and the electric field is strongly coupled within the waveguide layer, forming resonant absorption; no resonance occurs in other regions. Finally, a narrow dark band is clearly observed in the image detector imaging (Figure 4(a)), and its location is the structural location corresponding to this wavelength, thus achieving wavelength identification without a beam splitter.

[0070] These two examples represent the core implementation of the present invention, intuitively demonstrating the basic idea of ​​using spatially gradual changes in structural parameters to guide wavelength positioning. They are particularly suitable for building a high-bandwidth, high-resolution, and low-cost spectral identification and refractive index demodulation system.

[0071] Furthermore, to more clearly illustrate the principle of this invention, several comparative examples of non-width gradient structures are given below, combining different structural conditions and incident wavelengths, to demonstrate the correspondence between the guided mode resonance state and the image brightness and darkness response, thereby reflecting the technical advantage of this invention in spatially mapping the resonance wavelength.

[0072] Example 3: Substrate + High-refractive-index nanostrip structure (non-gradient width) — Satisfying the guided-mode resonance condition

[0073] This example structure includes a refractive index of n. sA glass substrate with a refractive index of 1.45 and a high-refractive-index nanostrip structure on it, wherein the nanostrip material is n h The Si3N4 with a density of 2.0 has a structural period of P=500 nm, a fixed width of w=300 nm for the nanostrips, a thickness of h=100 nm, and is incident with monochromatic light of wavelength λ=710 nm, perpendicularly incident, and polarized in the TE mode.

[0074] The structure satisfies the guided mode resonance condition (i.e., the incident wavelength matches the eigenfrequency of the guided mode). Electromagnetic simulation results show that a strong local electric field enhancement is generated in the waveguide layer and strip region. Photons are strongly coupled into the guided mode and almost no energy is transmitted, resulting in a completely dark image of the image detector (Fig. 4(c)). The electric field distribution is shown in Fig. 7.

[0075] Example 4: Substrate + High-refractive-index nanostrip structure (non-gradient width) — does not satisfy the guided-mode resonance condition.

[0076] The structure is consistent with Example 3, except that the incident wavelength is set to λ=800 nm, which does not meet the resonance condition. At this time, the incident light cannot be effectively coupled into the guided mode channel, and the light directly penetrates the structure. As shown in Figure 8, the visible light in the simulated electric field distribution diagram does not undergo local field enhancement, and the energy distribution on the back of the chip is uniform with high transmittance, and the image detector image is almost fully bright (Figure 4(b)).

[0077] Example 5: Substrate + Waveguide Layer + Low-Refractive-Index Nanostrip Structure (Non-Graduated Width) — Satisfying the Guided Mode Resonance Condition

[0078] The structure includes a glass substrate (n s =1.45), high refractive index waveguide layer (n h =2.0, thickness H=200 nm), and the low-refractive-index strip structure on it ( n l =1.45, thickness h=100 nm). The period of the strip structure is P=500 nm, and the width is w=300 nm. The incident light wavelength is set to λ=850 nm, which satisfies the guided mode resonance condition.

[0079] As shown in Figure 9, the simulation results show that a significant guided mode resonance phenomenon occurs in the waveguide layer, the electric field is concentrated inside the waveguide and periodically distributed, the transmitted energy is extremely low, and the image detector imaging result is completely dark (Figure 4(c)).

[0080] Example 6: Substrate + Waveguide Layer + Low-Refractive-Index Nanostrip Structure (Non-Graduated Width) — Does Not Satisfy the Guided Mode Resonance Condition

[0081] The structural parameters are the same as in Example 5, except that the incident wavelength is adjusted to λ=900 nm, which does not meet the guided mode resonance condition. As shown in Figure 10, the simulated electric field distribution diagram shows that there is no obvious electric field concentration or beam coupling, the transmitted energy is almost lossless, and the image detector image is almost fully bright (Figure 4(b)), verifying that guided mode resonance has not occurred.

[0082] The four examples above all use nanostrip structures with non-gradient widths as a comparative reference for the gradient width design in this invention. These comparative examples clearly demonstrate that, under certain structural parameters, the phenomenon of "resonance absorption—image darkening" only occurs when the incident wavelength matches the resonant frequency of the guided mode. Utilizing this relationship, if the structural width is set to a gradient form, different wavelengths can resonate at different positions, thereby realizing a mapping mechanism from "resonant wavelength to spatial position," and thus achieving image demodulation without the need for spectral splitting.

[0083] Establish a mapping relationship between pixel position (corresponding to the spatial position of the corresponding strip width) and refractive index, specifically as follows:

[0084] A set of reference samples with known refractive indices are tested, and the resonance position of each sample on the transmitted light image is recorded. A function between pixel position and refractive index is established to obtain an inversion lookup table or fitting model.

[0085] Example 2

[0086] As shown in Figure 11, this embodiment provides a refractive index detection method based on a width-gradient guided-mode resonant grating, and a refractive index detection device based on a width-gradient guided-mode resonant grating according to Embodiment 1, including the following steps:

[0087] S1. Using a refractive index testing device to test materials with unknown refractive index;

[0088] S2. Acquire the transmitted light image below the guided mode resonance sensing chip through an image detector;

[0089] S3. Transmit the image to the signal processing unit and extract the light intensity distribution of each pixel in the image;

[0090] S4. Based on the correspondence between pixel position and light intensity, obtain the changes in transmission spectrum intensity at different positions;

[0091] S5. Using the preset mapping relationship between refractive index and pixel position, the refractive index value of the medium under test is obtained by inversion.

[0092] The refractive index inversion method of the present invention includes two stages, as detailed below:

[0093] (1) System calibration stage:

[0094] a) Input a series of known refractive indices n i Reference sample;

[0095] b) Corresponding resonance position x on the recorded image R ;

[0096] c) Establish the function x R (n) yields inversion lookup table data or a fitted model.

[0097] (2) Actual measurement stage:

[0098] a) Identify the location xR of pixels with extremely low transmission intensity in the image from the image detector;

[0099] b) Look up the table xR(n) by matching the pixel position, and then obtain the corresponding refractive index n by mapping xR(n).

[0100] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0101] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A refractive index detection device based on a width-gradient guided-mode resonant grating, characterized in that, The system includes a light source. The light emitted from this light source passes through an optical isolator, a polarization controller, and a collimating beam expander before being incident on a guided-mode resonant sensing chip. The top of the guided-mode resonant sensing chip has a strip-shaped nanostructure with a consistent period but gradually varying strip width. The guided-mode resonant sensing chip is a transmission-type structure, with an image detector located below it. The image detector receives the transmitted light signal after passing through the guided-mode resonant sensing chip, generates a transmitted light image, and transmits the transmitted light image to a signal processing unit. The signal processing unit analyzes the transmitted light image and, based on the mapping relationship between strip width and refractive index, inverts the refraction of the medium under test. The refractive index of the guided mode resonant sensing chip includes a substrate layer and a high refractive index layer disposed on the substrate layer; or the guided mode resonant sensing chip includes a substrate layer, a high refractive index layer disposed on the substrate layer and a low refractive index layer located on top; the refractive index of the substrate layer, the refractive index of the high refractive index layer and the refractive index of the low refractive index layer meet the set conditions; the set conditions are that the refractive index difference between the high refractive index layer and the substrate layer is greater than 0.2 and the refractive index difference between the low refractive index layer and the substrate layer does not exceed 0.2; the spacing of the strip nanostructures is the same in each period, and the width of the strip nanostructures in adjacent periods gradually changes according to a fixed increment.

2. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 1, characterized in that, The high refractive index layer is a strip-shaped nanostructure.

3. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 1, characterized in that, The low-refractive-index layer is a strip-shaped nanostructure.

4. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 1, characterized in that, The cross-sectional shape of the strip nanostructure is rectangular, square, semi-circular, elliptical, sinusoidal, triangular, trapezoidal, or other regular shapes.

5. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 1, characterized in that, The light source is a wavelength-tunable monochromatic laser, whose operating range covers the visible to infrared bands, and the incident light wavelength is greater than the period length of the strip nanostructure.

6. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 1, characterized in that, The image detector is a CCD or CMOS array camera; the signal processing unit includes image processing software and an algorithm module for establishing the mapping relationship between pixel position and refractive index.

7. The refractive index detection device based on a width-gradient guided-mode resonant grating as described in claim 6, characterized in that, To establish the mapping relationship between pixel position and refractive index, specifically: a set of reference samples with known refractive index are detected, and the resonance position of each sample on the transmitted light image is recorded accordingly. A function between pixel position and refractive index is established to obtain an inversion lookup table or fitting model.

8. A method for refractive index detection based on a width-gradient guided-mode resonant grating, characterized in that, The refractive index detection device based on the width-gradient guided-mode resonant grating as described in any one of claims 1-7 includes the following steps: S1, detecting a material with an unknown refractive index using the refractive index detection device; S2, acquiring a transmitted light image below the guided-mode resonant sensing chip using an image detector; S3, transmitting the image to a signal processing unit and extracting the light intensity distribution of each pixel in the image; S4, obtaining the transmission spectrum intensity change at different positions based on the correspondence between pixel position and light intensity; S5, using a preset mapping relationship between refractive index and pixel position to invert and obtain the refractive index value of the medium under test.

Images