Refractive index detection device and method based on width gradient guided mode resonance grating

Abstract

The invention discloses a refractive index detection device and method based on a width-gradually-changed guided mode resonance grating, and belongs to the technical field of optical sensing. Light emitted by a light source enters a guided mode resonance sensing chip after passing through an optical isolator, a polarization controller and a collimation beam expander, the guided mode resonance sensing chip is of a transmission type structure, and the width of the guided mode resonance grating is gradually changed; a strip-shaped nano structure with gradually-changed strip width is arranged at the top of the substrate; and an image detector is arranged below the guided-mode resonance sensing chip, receives a transmission light signal passing through the guided-mode resonance sensing chip, generates a transmission light image, transmits the transmission light image to a signal processing unit for analysis, and inverts the refractive index of the medium to be measured according to the mapping relation between the strip width and the refractive index. Resonance wavelength is mapped into image position information through space structure design, a traditional light splitting device is not needed for refractive index inversion, high-precision, imaging and real-time refractive index detection is achieved, and the problems that a traditional guided-mode resonance sensor needs complex optical elements and is large in size and high in cost are solved.

Description

Technical Field

[0001] The present 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 resonance grating. Background Art

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

[0003] Existing optical refractive index sensing technologies mostly use interferometers, gratings or plasmon structures to achieve refractive index detection. Most of them rely on bulky and expensive spectral analysis equipment such as spectrometers or spectrometers. The system has low integration, high cost, and slow demodulation speed, which is not suitable for portable or on-chip system integration requirements. Guided mode resonance gratings excite waveguide modes through periodic gratings, causing strong transmission / reflection changes at specific wavelengths. They have been applied to refractive index detection and have the advantages of simple structure, narrow resonance peak, and high sensitivity. However, conventional guided mode resonance sensors face two major bottlenecks: (1) Reliance on expensive equipment such as spectrometers: Monitoring the resonance wavelength λ R Usually a high-resolution spectrometer or spectrometer system is 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 achieve structure-wavelength-space mapping, cannot simplify the demodulation process in an image-based manner, and are difficult to combine with efficient demodulation methods. Summary of the Invention

[0004] To address the above problems, the present invention proposes a refractive index detection device and method based on a width-gradient guided mode resonance grating. Through spatial structure design, the refractive index is mapped into image position information, and no traditional spectroscopic device is required for refractive index inversion. High-precision, image-based, and real-time refractive index detection is achieved, solving the problems of traditional guided mode resonance sensors requiring complex optical components, large size, and high cost.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a refractive index detection device based on a gradient-width guided mode resonance grating, comprising a light source. Light emitted by the light source passes through an optical isolator, a polarization controller, and a collimating beam expander before being incident on a guided mode resonance sensor chip. The top of the guided mode resonance sensor chip is provided with a strip-shaped nanostructure with a uniform period but gradient width. The guided mode resonance sensor chip is a transmission structure with an image detector underneath. The image detector receives the transmitted light signal after passing through the guided mode resonance sensor 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 to be measured based on the mapping relationship between the strip width and the refractive index.

[0006] As a further implementation, the guided mode resonance sensor chip includes a base layer and a high refractive index layer disposed on the base layer, wherein the high refractive index layer is a strip-shaped nanostructure.

[0007] As a further implementation, the guided mode resonance sensor chip includes a base layer, a high refractive index layer disposed on the base layer, and a low refractive index layer located on the top, wherein the low refractive index layer is a strip-shaped nanostructure.

[0008] As a further implementation manner, the refractive index of the base layer, the refractive index of the high refractive index layer, and the refractive index of the low refractive index layer meet set conditions.

[0009] As a further implementation, the cross-sectional shape of the strip-shaped nanostructure is a rectangle, a square, a semicircle, an ellipse, a sinusoid, a triangle, a trapezoid or other regular shapes.

[0010] As a further implementation method, the spacing between the strip nanostructures in each period is the same, and the width of the strip nanostructures in adjacent periods gradually changes according to a fixed increment.

[0011] As a further implementation method, the light source is a wavelength-tunable monochromatic laser, whose operating range covers the visible light to infrared band, and the wavelength of the incident light is greater than the period length of the strip nanostructure.

[0012] As a further implementation, the image detector is a CCD or CMOS array camera; The signal processing unit includes image processing software and an algorithm module for establishing a mapping relationship between pixel position and refractive index.

[0013] As a further implementation method, a mapping relationship between pixel position and refractive index is established, specifically: A set of reference samples with known refractive index are tested, 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.

[0014] A second aspect of the present invention provides a refractive index detection method based on a gradient-width guided mode resonance grating. The refractive index detection device based on a gradient-width guided mode resonance grating described in the first aspect of the present invention comprises the following steps: S1. Using a refractive index detection device to detect a material with an unknown refractive index; S2. collecting a transmitted light image below the guided mode resonance sensor chip through 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 intensity change of the transmission spectrum at different positions based on the correspondence between the pixel position and the light intensity; S5. Using the preset mapping relationship between the refractive index and the pixel position, the refractive index value of the medium to be measured is inverted and obtained.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a refractive index detection device and method based on a gradient-width guided mode resonance grating. The guided mode resonance sensor chip is designed as a one-dimensional strip nanostructure with a uniform period but gradient width. Utilizing the spatial correspondence between structural parameters and resonance wavelength, combined with a monochromatic light source, spectral information is directly mapped to spatial position information on an image detector. The refractive index of the medium being measured is then inverted using acquired lookup table data or a fitted model, achieving image-based demodulation. The system implements a spectrometer-free refractive index inversion method 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. The system is suitable for a variety of light sources and detection environments, exhibiting high sensitivity and real-time performance. Its advantages include a simple overall structure, low cost, fast image-based demodulation, and a wide range of applications. It can be widely used for high-sensitivity, real-time refractive index detection of liquids, gases, and other media. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0017] Figure 1 A schematic diagram of the overall structure of a refractive index detection device based on a width-gradient guided mode resonance grating provided in Example 1 of the present invention; Figure 2 Schematic diagram of the structure of the sensor chip with a substrate + high-refractive-index nanostrip structure (gradually varying width) provided in Example 1 of the present invention, wherein (a) is a schematic diagram of the structure of the sensor chip in a front view, and (b) is a schematic diagram of the three-dimensional structure of the sensor chip; Figure 3 Schematic diagram of the structure of a sensor chip with a substrate + waveguide layer + low-refractive-index strip structure (gradually varying width) provided in Example 1 of the present invention, wherein (a) is a schematic diagram of the structure of the sensor chip from a front view, and (b) is a schematic diagram of the three-dimensional structure of the sensor chip; Figure 4 A schematic diagram of imaging by an image detector provided in Example 1 of the present invention; Figure 5 The electric field distribution diagram of the substrate + high refractive index nanostrip structure (with gradient width) provided in Example 1 of the present invention, which locally satisfies guided mode resonance under single wavelength incidence; Figure 6The electric field distribution diagram of the substrate + waveguide layer + low refractive index strip structure (with gradient width) provided in Example 1 of the present invention, which locally satisfies guided mode resonance under single wavelength incidence; Figure 7 The electric field distribution diagram of the substrate + high refractive index nanostrip structure (non-gradient width) provided in Example 1 of the present invention that meets the guided mode resonance condition; Figure 8 The electric field distribution diagram of the substrate + high refractive index nanostrip structure (non-gradient width) provided in Example 1 of the present invention does not meet the guided mode resonance condition; Figure 9 The electric field distribution diagram of the substrate + waveguide layer + low-refractive-index nanostrip structure (non-gradient width) provided in Example 1 of the present invention, which meets the guided-mode resonance condition; Figure 10 The electric field distribution diagram of the substrate + waveguide layer + low-refractive-index nanostrip structure (non-gradient width) provided in Example 1 of the present invention does not meet the guided-mode resonance condition; Figure 11 This is a flow chart of a refractive index detection method based on a width-gradient guided mode resonance grating provided in Example 2 of the present invention.

[0018] Among them, 1. light source; 2. optical isolator; 3. polarization controller; 4. collimating beam expander; 5. guided mode resonance sensor chip; 6. image detector; 7. signal processing unit; 8. low refractive index layer; 9. high refractive index layer; 10. base layer. DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0021] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0022] Example 1 like Figure 1As shown, this embodiment provides a refractive index detection device based on a width-gradient guided mode resonance grating, comprising a light source 1, an optical isolator 2, a polarization controller 3, and a collimating beam expander 4 connected in sequence. The monochromatic light output by the collimating beam expander 4 is vertically incident on a guided mode resonance sensor chip 5; the guided mode resonance sensor chip 5 is configured as a transmission structure, and a one-dimensional strip nanostructure with a uniform period but a gradient strip width is provided on the top of the guided mode resonance sensor chip 5; the image detector 6 is located below the guided mode resonance sensor chip 5, and the image detector 6 receives the transmitted light signal after passing through the guided mode resonance sensor 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 to be measured based on the mapping relationship between the strip width (corresponding to the spatial position of the pixel) and the refractive index.

[0023] In this embodiment, light source 1 is a wavelength-tunable monochromatic laser, such as a DFB laser or a picometer-level tunable laser, whose operating range is 350 nm to 2500 nm, covering the visible light to infrared band. The wavelength of the incident light is greater than the period length of the strip nanostructure, that is, the incident light λ satisfies λ>P.

[0024] The optical isolator 2 is used to eliminate back reflections; the polarization controller 3 ensures that the polarization state of the incident light is consistent; the collimating beam expander 4 expands the laser beam to a suitable light spot; and the guided mode resonance sensor chip 5 is the core sensing component of the present invention.

[0025] The image detector 6 collects the transmission image. In this embodiment, the image detector is a CCD or CMOS array camera.

[0026] 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 a mapping relationship between pixel position, resonance wavelength, and refractive index.

[0027] Monochromatic light from light source 1 passes through optical isolator 2, polarization controller 3, and collimating beam expander 4 before being perpendicularly incident on the surface of guided mode resonance chip 5. An image detector 6, located beneath the chip, receives the transmitted light and forms an image. A signal processing unit 7 processes the image data in real time and performs refractive index demodulation.

[0028] The core sensing component of the present invention is a guided mode resonance sensor chip 5. The number of structural layers N is greater than or equal to 1, and a one-dimensional periodically arranged strip nanostructure is provided on the top. The strip nanostructure is made of a high refractive index material or a low refractive index material. There are two structures as follows: Figure 2 and Figure 3 The cross-sectional shape of the strip-shaped nanostructure can be rectangular, square, semicircular, elliptical, sinusoidal, triangular, trapezoidal or other regular shapes.

[0029] like Figure 2As shown, the substrate + high refractive index nano-strip structure (width gradient) sensor chip structure proposed by the present invention is composed of the following parts: (1) Base layer 10: made of quartz or glass, with a refractive index of n s ; (2) One-dimensional strip nanostructure: composed of 9 thin film layers of high refractive index materials (such as Si3N4, 、 ) with a thickness of 50 nm~500 nm and a refractive index of n h ; The period is P ,along Y Axis arrangement, along X Directional bar width gradient.

[0030] like Figure 3 As shown, the substrate + waveguide layer + low refractive index strip structure (width gradient) sensor chip structure proposed in the present invention is composed of the following parts: (1) Base layer 10: made of quartz or glass, with a refractive index of n s ; (2) Waveguide layer: It is made of high refractive index material 9 thin film layer (such as Si3N4, 、 ) with a thickness of 20 nm~500 nm and a refractive index of n h ; (3) One-dimensional strip nanostructure: composed of 8 thin film layers of low refractive index material (such as ) with a period of P ,along Y Axis arrangement, along X Directional strip width gradient, refractive index n l .

[0031] Figure 2 、 Figure 3 The structure given in satisfies the following refractive index constraints: n h - n s >0.2 (ensure guided mode support); | n l - n s |≤ 0.2 (to avoid resonance signal distortion).

[0032] Periodicity of strip nanostructures P Fixed (such as P =500 nm ), and the strip width wi Any location x The changes form a gradual distribution, for example: , Δ w It is a constant gradient, with a typical value of 2~10 nm / μm; Gradient design range: Δw = 1 pm to 100 nm, supporting high-precision spatial resolution.

[0033] Each strip width w Corresponding to the only resonant wavelength λ R , the relationship can be preset through simulation as λ R = f ( w ).because w ( x ) is a monotonic function, λ R ( x ) also follows x Monotonically changing, therefore, the spectral information λ R and spatial location information x R One to one correspondence.

[0034] like Figure 4 As shown in (a), the incident light produces strong absorption areas at different positions, and the transmitted intensity is a local dark band, which appears as an intensity valley in the image detector image, corresponding to the resonance wavelength λ R Place.

[0035] To further verify that the width-gradient guided mode resonance grating structure used in this invention can implement the "wavelength-position mapping" demodulation method, two typical examples are given below. Combined with electric field distribution simulation and imaging effects, it is shown that when the incident wavelength is fixed, the local area in the structure that meets the guided mode resonance conditions will produce light absorption, resulting in dark bands in the imaging, reflecting the "position indication of a specific wavelength in the structure" function.

[0036] Example 1: Substrate + high refractive index nanostrip structure (width gradient) - single wavelength incidence, local satisfied guided mode resonance The structure of this example includes a glass substrate (n s =1.45), on which is a Si3N4 high refractive index strip structure (n h = 2.0, thickness h = 100 nm), the nanostrip period is fixed at P = 500 nm, and the strip width changes linearly in the length direction (e.g., from w min =125 nm to w max=300 nm, with Δw=35 nm added per cycle). The incident light is monochromatic with a wavelength of λ=710 nm, incident vertically, and polarized in the TE mode.

[0037] like Figure 5 As shown in the figure, the simulation results show that only near the strip width of about w = 195 nm, the structure meets the guided mode resonance condition, the electromagnetic field is locally coupled into the waveguide mode and is strongly absorbed; the rest of the area does not meet the resonance condition, and the light is transmitted. The final image detector image shows a clear dark band ( Figure 4 (a) ), its lateral position corresponds to a specific resonance width, which is also the "marking position" of this wavelength. This achieves the mapping of wavelength information to spatial position.

[0038] Example 2: Substrate + waveguide layer + low-refractive-index strip structure (width gradient) - single-wavelength incidence, locally satisfying guided-mode resonance The structure of this example consists of three layers: the base is n s =1.45 glass, with a high refractive index waveguide layer in the middle, made of (n h =2.0, thickness H=200 nm), the top is a low refractive index nanostrip structure, the material is (n l =1.45, thickness h=100 nm), the period is fixed at P=500 nm, and the strip width is linearly gradient from w min =125 nm to w max =300 nm. The incident light has a wavelength of λ = 850 nm, is incident vertically, and is TE polarized.

[0039] like Figure 6 As shown in the figure, the simulation results show that: near the strip width of about w = 195 nm, the structure meets the guided mode resonance condition, the electric field is strongly coupled in the waveguide layer, forming resonant absorption; no resonance occurs in other areas. Finally, a narrow dark band is clearly observed in the image detector imaging ( Figure 4 (a)), its position is the structural position corresponding to this wavelength, thus realizing wavelength identification without the need for a spectrometer.

[0040] These two examples represent the core implementation methods of the present invention, intuitively embodying the basic idea of using spatial gradients of structural parameters to guide wavelength positioning, and are particularly suitable for building large-bandwidth, high-resolution, low-cost spectral recognition and refractive index demodulation systems.

[0041] Furthermore, to more clearly illustrate the principles of the present invention, several comparative examples under 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 dark response, thereby reflecting the technical advantage of the present invention in spatially mapping the resonant wavelength.

[0042] Example 3: Substrate + High-Refractive-Index Nanostrip Structure (Non-Gradual Width)—Satisfying Guided-Mode Resonance Conditions The structure of this example includes a refractive index of n s =1.45 glass substrate and a high refractive index nano-strip structure located thereon, the nano-strip material is n h =2.0 Si3N4, the structural period is P=500 nm, the nanostrip width is a fixed value w=300 nm, the thickness is h=100 nm, the incident light is monochromatic light with a wavelength of λ=710 nm, the incident light is vertically incident, and the polarization direction of the incident light is TE mode.

[0043] This 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 the strip region. Photons are strongly coupled into the guided mode, with almost no energy passing through, resulting in a completely dark image on the image detector ( Figure 4 (c)), such as Figure 7 The electric field distribution diagram is shown.

[0044] Example 4: Substrate + High-Refractive-Index Nanostrip Structure (Non-Gradual Width)—Does Not Satisfy Guided-Mode Resonance Conditions This structure is consistent with Example 3, except that the incident wavelength is set to λ = 800 nm, which does not meet the resonance condition. In this case, the incident light cannot be effectively coupled into the guided mode channel and the light directly penetrates the structure. Figure 8 As shown in the simulated electric field distribution diagram, it can be seen that there is no local field enhancement in the light, and the energy distribution on the back of the chip is uniform and the transmittance is high. The image detector is almost fully bright ( Figure 4 (b)).

[0045] Example 5: Substrate + waveguide layer + low-refractive-index nanostrip structure (non-gradient width)—meeting the guided-mode resonance condition 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 stripe structure thereon ( , n l =1.45, thickness h = 100 nm). The stripe structure period 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.

[0046] like Figure 9 As shown in the simulation results, an obvious guided mode resonance phenomenon is generated in the waveguide layer. The electric field is concentrated inside the waveguide and distributed periodically. The transmitted energy is extremely low, and the imaging result of the image detector is completely dark ( Figure 4 (c)).

[0047] Example 6: Substrate + waveguide layer + low-refractive-index nanostrip structure (non-gradient width) - does not meet the guided-mode resonance condition The structural parameters are the same as those in Example 5, except that the incident wavelength is adjusted to λ = 900 nm, which does not meet the guided mode resonance condition. Figure 10 As shown in the simulation, the 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 imaging is almost full brightness ( Figure 4 (b)), verifying that no guided mode resonance occurs.

[0048] The four examples above all use nanostrip structures with non-gradient widths, serving as a comparison for the width gradient design employed in the present invention. These comparative examples clearly demonstrate that, under certain structural parameters, the "resonant absorption-image darkening" phenomenon occurs only when the incident wavelength matches the guided mode resonant frequency. Leveraging this relationship, by gradually varying the structural width, different wavelengths can resonate at different locations, thereby achieving a "resonant wavelength to spatial location" mapping mechanism and enabling image demodulation without the need for optical splitting.

[0049] A mapping relationship between pixel position (corresponding to the spatial position of the corresponding strip width) and refractive index is established, specifically: A set of reference samples with known refractive index are tested, 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.

[0050] Example 2 like Figure 11 As shown, this embodiment provides a refractive index detection method based on a width-varying guided mode resonance grating, and a refractive index detection device based on a width-varying guided mode resonance grating according to the first embodiment, comprising the following steps: S1. Using a refractive index detection device to detect a material with an unknown refractive index; S2. collecting a transmitted light image below the guided mode resonance sensor chip through 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 intensity change of the transmission spectrum at different positions based on the correspondence between the pixel position and the light intensity; S5. Using the preset mapping relationship between the refractive index and the pixel position, the refractive index value of the medium to be measured is inverted and obtained.

[0051] The refractive index inversion method of the present invention includes two stages, as follows: (1) System calibration stage: a) Input a series of known refractive indicesn i Reference samples; b) Corresponding resonance position on the recorded image x R ; c) Create a function x R ( n ) to obtain the inversion table data or fitting model.

[0052] (2) Actual measurement stage: a) Identify the pixel position xR with the minimum transmission intensity in the image detector image; b) Look up the table xR(n) by matching the pixel position, and then map xR(n) to obtain the corresponding refractive index n.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0054] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it 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 on the basis of the technical solution of the present invention without any creative work 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 resonance grating, characterized in that: The device comprises 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 is incident on a guided mode resonance sensor chip. The top of the guided mode resonance sensor chip is provided with a strip nanostructure with a uniform period but a gradually varying strip width; The guided mode resonance sensor chip is a transmission structure, and an image detector is provided underneath it. The image detector receives the transmitted light signal after passing through the guided mode resonance sensor 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 inverts the refractive index of the medium to be measured based on the mapping relationship between the strip width and the refractive index.

2. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The guided mode resonance sensor chip comprises a base layer and a high refractive index layer arranged on the base layer, and the high refractive index layer is a strip-shaped nanostructure.

3. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The guided mode resonance sensor chip comprises a base layer, a high refractive index layer arranged on the base layer, and a low refractive index layer located on the top, wherein the low refractive index layer is a strip-shaped nanostructure.

4. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 3, characterized in that: The refractive index of the base layer, the refractive index of the high refractive index layer, and the refractive index of the low refractive index layer satisfy set conditions.

5. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The cross-sectional shape of the strip-shaped nanostructure is a rectangle, a square, a semicircle, an ellipse, a sinusoid, a triangle, a trapezoid or other regular shapes.

6. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The strip-shaped nanostructures have the same spacing in each period, and the widths of the strip-shaped nanostructures in adjacent periods gradually change according to fixed increments.

7. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The light source is a wavelength-tunable monochromatic laser, whose operating range covers the visible light to infrared band, and the wavelength of the incident light is greater than the period length of the strip nanostructure.

8. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 1, wherein: The image detector is a CCD or CMOS array camera; The signal processing unit includes image processing software and an algorithm module for establishing a mapping relationship between pixel positions and refractive indices.

9. The refractive index detection device based on a width-graded guided mode resonance grating according to claim 8, characterized in that: Establish a mapping relationship between pixel position and refractive index, specifically: A set of reference samples with known refractive index are tested, 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.

10. A refractive index detection method based on a width-gradient guided mode resonance grating, characterized in that: The refractive index detection device based on the width-gradient guided mode resonance grating according to any one of claims 1 to 9 comprises the following steps: S1. Using a refractive index detection device to detect a material with an unknown refractive index; S2, collecting a transmitted light image below the guided mode resonance sensor chip through 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 intensity change of the transmission spectrum at different positions based on the correspondence between the pixel position and the light intensity; S5. Using the preset mapping relationship between the refractive index and the pixel position, the refractive index value of the medium to be measured is obtained by inversion.

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