Longitudinal gradient grating structure-based guided-mode resonance refractive index detection device and method
By introducing a longitudinally gradient grating structure into the guided mode resonant chip and using a CCD/CMOS image detector to acquire spectral information, the problem of insufficient structural control dimension in the existing technology is solved, and high-sensitivity, low-cost image-based refractive index detection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-21
- Publication Date
- 2026-03-31
AI Technical Summary
Existing guided-mode resonance structures do not fully utilize structural modulation capabilities in the vertical direction, limiting the dimensions of resonance control and the complexity of spectral functional modulation.
A guided-mode resonance refractive index detection device employing a longitudinally gradient grating structure achieves spatial distribution control of the monochromatic light resonance response position by introducing longitudinal structural gradient characteristics into the guided-mode resonance chip. It then uses a CCD/CMOS image detector to acquire spectral information and invert the refractive index.
It achieves image-based refractive index sensing without a spectrometer, simplifies system architecture, reduces costs, improves sensitivity and response speed, is suitable for refractive index detection in various media, and has modular features and wide spectral range operation capabilities.
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Figure CN120539109B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical sensing and image-based spectral detection technology, and in particular to a guided mode resonance refractive index detection device and method based on a longitudinally gradient grating structure. 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] Guided mode resonance (GMR) structures, as a highly sensitive optical filtering and sensing mechanism, have been widely used in fields such as biosensing, refractive index detection, color filtering, and spectral modulation. GMR structures are typically composed of periodic one-dimensional or two-dimensional nanogratings and waveguide layers. By coupling incident light to waveguide modes, resonant absorption occurs at specific wavelengths, thereby generating sharp resonance peaks in the transmission or reflection spectrum.
[0004] In recent years, researchers have introduced gradients in structural parameters into GMR structures, such as spatial gradients in grating period or nanostrip width, to achieve wavelength-to-position mapping (λ-to-position mapping). This allows them to replace traditional spectrometers and achieve spectrometer-less imaging spectral detection. These width-gradient GMR structures show broad application prospects in refractive index sensing, respiration monitoring, and gas detection.
[0005] However, current structural gradations are typically limited to a single linear change in the grating along the planar direction, failing to fully utilize the multidimensional control capabilities of the structure along the depth or vertical direction. For example, if gradations in refractive index or filling ratio could be achieved in the vertical direction, it would be possible to further expand the dimensions of resonance control, thereby enabling more complex spectral functional modulation. Summary of the Invention
[0006] To address the aforementioned issues, this invention proposes a guided-mode resonance refractive index detection device and method based on a longitudinally gradient grating structure. The overall structure is simple and portable. By introducing longitudinal structural gradient characteristics into the guided-mode resonance chip, spatial distribution control of the monochromatic light resonance response position is achieved, ultimately realizing image-based refractive index sensing without the need for a beam splitter.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] In a first aspect, the present invention provides a guided mode resonance refractive index detection device based on a longitudinally gradient grating structure, comprising a light source, an optical isolator, a polarization controller, a collimating beam expander, a guided mode resonance sensing chip, an image detector, and a signal processing unit connected in sequence.
[0009] The light source is used to emit laser light;
[0010] The optical isolator is used to eliminate back reflections;
[0011] The polarization controller is used to control the polarization state of the incident light;
[0012] The collimating beam expander is used to expand the laser beam to a suitable spot.
[0013] The guided mode resonance sensing chip has a transmissive structure, with a strip-shaped nanostructure with a consistent period but a gradual change in length on its top, and an image detector below it.
[0014] The image detector is used to receive the transmitted light signal after passing through the guided mode resonant sensing chip, generate a transmitted light image, and transmit the transmitted light image to the signal processing unit.
[0015] The signal processing unit is used to analyze the transmitted light image and invert the refractive index of the medium under test based on the structure mapping model.
[0016] As a further realization, the longitudinally gradient strip nanostructures have the same period spacing and have gradient characteristics in refractive index, structural width, or structural thickness in a direction perpendicular to their periodic direction.
[0017] 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. The high refractive index layer is a strip-shaped nanostructure with a consistent period but a longitudinal gradient.
[0018] 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. The low refractive index layer is a strip-shaped nanostructure with a consistent period but a longitudinal gradient.
[0019] 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.
[0020] 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.
[0021] As a further implementation, the light source is a wavelength-tunable monochromatic laser with an operating range covering the visible to infrared bands, and the incident light wavelength is greater than the period length of the strip nanostructure.
[0022] As a further implementation, the image detector is a CCD or CMOS array camera;
[0023] The signal processing unit includes image processing software and an algorithm module for establishing the mapping relationship between pixel position and refractive index.
[0024] As a further implementation, the structure mapping model is as follows:
[0025] The guided mode resonance refractive index detection device is calibrated using a set of reference samples with known refractive indices, resulting in a mapping model between the refractive index and the pixel position.
[0026] A second aspect of the present invention provides a method for detecting the guided-mode resonant refractive index based on a longitudinally graded grating structure, and a guided-mode resonant refractive index detection device based on a longitudinally graded grating structure as described in the first aspect of the present invention, comprising the following steps:
[0027] S1. Using a refractive index detection device to detect materials with unknown refractive index;
[0028] S2. Acquire the transmitted light image below the guided mode resonance sensing chip through an image detector;
[0029] S3. Transmit the image to the signal processing unit and extract the light intensity distribution of each pixel in the image;
[0030] S4. Based on the correspondence between pixel position and light intensity, obtain the changes in transmission spectrum intensity at different positions;
[0031] 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.
[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0033] The present invention provides a guided-mode resonance refractive index detection device and method based on a longitudinally graded grating structure. This device employs a guided-mode resonance structure design with a longitudinally graded grating structure to convert spectral information into spatial information, thereby inverting the refractive index of the medium under test. It has the following significant advantages:
[0034] (1) Achieving spectrometer-free image-based refractive index detection. This invention introduces a longitudinally gradient grating structure, transforming the traditional spectroscopic identification process that relies on spectrometers or dispersive systems into a spatial location information detection process. The resonant wavelength position can be identified solely through CCD / CMOS image acquisition, greatly simplifying the system architecture and reducing size and cost.
[0035] (2) Flexible structural design and strong feasibility of processing technology. By adopting a design with continuous gradient of longitudinal refractive index, material filling ratio (structural width) or structural thickness, it can be realized through conventional photolithography or deposition processes such as multi-step exposure, mask stacking or oblique deposition, which significantly improves the stability and yield of chip structure processing.
[0036] (3) High sensitivity and adjustable response of refractive index control. Different longitudinal structural positions correspond to different resonance conditions. The system can achieve high sensitivity recognition of external refractive index by changing the brightness of pixels, and has a natural spatial reuse capability; it can be further extended to two-dimensional imaging sensing applications.
[0037] (4) Applicable to a variety of media and wide spectrum range. This sensor system is suitable for refractive index detection of transparent or semi-transparent media such as liquids and gases. The working wavelength range can cover the visible light to near-infrared range (350 nm~2500 nm), and it has good material compatibility and environmental adaptability.
[0038] (5) It has scalability and modularity. The structure of this invention can be integrated with existing microfluidic chips and biofunctional modification layers, and is easy to modularly package and industrialize; at the same time, it has the potential to be extended to two-dimensional gradient (lateral + vertical) or nonlinear gradient structures, supporting more complex wavelength-space mapping functions.
[0039] It offers direct imaging, fast demodulation, and strong anti-interference capabilities. By identifying the location of resonant dark bands through image processing, it eliminates the need for point-by-point spectral scanning or high-frequency modulation, improving demodulation speed and stability, making it particularly suitable for dynamic detection and rapid response scenarios. Attached Figure Description
[0040] 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.
[0041] Figure 1 This is a schematic diagram of the overall structure of the guided mode resonance refractive index detection device based on a longitudinally gradient grating structure provided in Embodiment 1 of the present invention.
[0042] Figure 2 This is a schematic diagram of a substrate + high refractive index nanostrip structure (gradually varying longitudinal width, refractive index, and height) sensor chip structure provided in Embodiment 1 of the present invention, wherein (a) is a schematic diagram of a sensor chip structure with gradually varying longitudinal width, (b) is a schematic diagram of a sensor chip structure with gradually varying longitudinal refractive index, and (c) is a schematic diagram of a sensor chip structure with gradually varying longitudinal height.
[0043] Figure 3 This is a schematic diagram of a sensor chip structure with a substrate + waveguide layer + low refractive index strip structure (gradually changing longitudinal width, refractive index, and height) provided in Embodiment 1 of the present invention. (a) is a schematic diagram of a sensor chip structure with gradually changing longitudinal width, (b) is a schematic diagram of a sensor chip structure with gradually changing longitudinal refractive index, and (c) is a schematic diagram of a sensor chip structure with gradually changing longitudinal height.
[0044] Figure 4This is a schematic diagram of the image detector imaging provided in Embodiment 1 of the present invention;
[0045] Figure 5 The electric field distribution diagram of a substrate + high refractive index nanostrip structure (with gradually varying longitudinal width) provided in Embodiment 1 of the present invention, which locally satisfies guided mode resonance under single-wavelength incident light;
[0046] Figure 6 The electric field distribution diagram of a substrate + waveguide layer + low refractive index strip structure (with gradually changing longitudinal width) provided in Embodiment 1 of the present invention, which locally satisfies guided mode resonance under single wavelength incident light;
[0047] Figure 7 The electric field distribution diagram of a substrate + high refractive index nanostrip structure (longitudinal non-gradient width) provided in Embodiment 1 of the present invention satisfies the guided mode resonance condition;
[0048] Figure 8 The electric field distribution diagram of a substrate + high refractive index nanostrip structure (longitudinal non-gradient width) provided in Embodiment 1 of the present invention does not satisfy the guided mode resonance condition;
[0049] Figure 9 The electric field distribution diagram of a substrate + waveguide layer + low refractive index nanostrip structure (longitudinal non-gradient width) provided in Embodiment 1 of the present invention satisfies the guided mode resonance condition;
[0050] Figure 10 The electric field distribution diagram of a substrate + waveguide layer + low refractive index nanostrip structure (longitudinal non-gradient width) provided in Embodiment 1 of the present invention does not satisfy the guided mode resonance condition;
[0051] Figure 11 The flowchart shows the guided mode resonance refractive index detection method based on a longitudinally gradient grating structure provided in Embodiment 2 of the present invention.
[0052] 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
[0053] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0054] 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.
[0055] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.
[0056] Example 1
[0057] like Figure 1 As shown, this embodiment provides a guided-mode resonance refractive index detection device based on a longitudinally graded grating structure. It includes 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 resonance sensing chip 5. The guided-mode resonance sensing chip 5 is configured as a transmissive structure, with a strip-shaped nanostructure on its top that has a consistent period but a longitudinally graded shape. The period spacing of each strip-shaped nanostructure is the same, and it exhibits a gradient characteristic in refractive index, structural width, or structural thickness in a direction perpendicular to its periodic direction. An image detector 6 is located below the guided-mode resonance sensing chip 5. The image detector 6 receives the transmitted light signal after passing through the guided-mode resonance 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 a structure mapping model.
[0058] 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.
[0059] 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.
[0060] Image detector 6 acquires transmitted images. In this embodiment, the image detector is a CCD or CMOS array camera.
[0061] 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.
[0062] 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.
[0063] 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 there are two structures respectively as shown in the figure. Figure 2and Figure 3 As shown, the cross-sectional shape of the strip nanostructure can be rectangular, square, semi-circular, elliptical, sinusoidal, triangular, trapezoidal, or other regular shapes.
[0064] like Figure 2 As shown, the substrate + high refractive index nanostrip structure (gradual width, gradual refractive index, and gradual height) sensor chip structure proposed in this invention consists of the following parts:
[0065] (1) Base layer 10: Material such as quartz or glass, with a refractive index of n s ;
[0066] (2) The top longitudinally gradient grating structure is composed of periodic nanostrips, and the material is a high refractive index material 9 thin film layer (e.g. , , Composed of ) with a thickness of 50 nm to 500 nm and a refractive index of n h The period is P ,along X Axial periodic arrangement, its refractive index or geometric parameters (such as height, width) change continuously and gradually along the vertical direction (i.e., longitudinal direction, Y direction). The refractive index gradient is achieved by material doping, and the geometric parameter gradient is achieved by directly adjusting the geometric parameters.
[0067] like Figure 3 As shown, 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 parts:
[0068] (1) Base layer 10: Material such as quartz or glass, with a refractive index of n s ;
[0069] (2) Waveguide layer: composed of a thin film layer of high refractive index material (such as...) , , Composed of ) with a thickness of 20 nm to 500 nm and a refractive index of n h ;
[0070] (3) The top longitudinally gradient grating structure is composed of periodic nanostrips, and the material is a low refractive index material 8 thin film layer (such as... Composed of ) with a thickness of 50 nm to 500 nm and a refractive index of n l The period is P ,along XAxial periodic arrangement, its refractive index or geometric parameters (such as height, width) change continuously and gradually along the vertical direction (i.e., longitudinal direction, Y direction). The refractive index gradient is achieved by material doping, and the geometric parameter gradient is achieved by directly adjusting the geometric parameters.
[0071] Figure 2 , Figure 3 The structure given in the figure satisfies the following refractive index constraints: 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).
[0072] Nanostructure Periodic P Fixed (e.g.) P =500 nm The width w, refractive index n, and height h vary with position. y Changes create a gradual distribution, for example:
[0073] Δ w The gradient is a constant, with typical values of 2~100 nm / μm;
[0074] Δ n The gradient is constant, with typical values of 0.001~0.01 / μm;
[0075] Δ h The gradient is a constant, typically 2~10 nm / μm.
[0076] Each width w (Or refractive index n, height h) corresponds to a unique resonant wavelength λ R Their relationship can be preset through simulation. λ R = f ( w )(or f ( n ), f ( h )).because w ( y )(or n ( y ), h ( y ) is a monotonic function. λ R ( y Also followed yMonotonic change, therefore: spectral information λ R Spatial location information y R One-to-one correspondence.
[0077] like Figure 4 As shown in (a), the incident light produces strong absorption regions at different positions, and the transmission intensity exhibits local dark bands, which appear as intensity troughs in the image detector, corresponding to the resonant wavelength. λ R Place.
[0078] To further verify that the width-gradient guided-mode resonant grating structure used in this invention can achieve the "wavelength-position mapping" demodulation method, a longitudinally width-gradient grating structure will be used below. Its core is to change the filling ratio in each row of nanostrips to achieve a gradual change in the longitudinal equivalent refractive index. This characteristic is also present in grating structures with longitudinally varying refractive index and longitudinally varying height, and will not be discussed further. This gradual change causes different responses to the same wavelength λ at different positions, thus generating spatially distributed resonance of monochromatic light at different positions of the structure.
[0079] The following two typical examples, combined with electric field distribution simulation and imaging effects, illustrate that when the incident wavelength is fixed, local areas in the structure that meet the guided mode resonance condition will produce light absorption, thus presenting dark bands in the imaging, reflecting the function of "indicating the position of a specific wavelength in the structure".
[0080] Example 1: Substrate + high refractive index nanostrip structure (gradually varying longitudinal width) — single-wavelength incident, locally satisfying guided mode resonance
[0081] This example structure includes a glass substrate (n) s =1.45), above which is High refractive index 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 longitudinal direction (e.g. from w min =50 nm to w max =400 nm, gradient Δw=70 nm / um). The incident light is monochromatic with wavelength λ=710 nm, incident perpendicularly, and polarized in the TE mode.
[0082] like Figure 5 As shown, simulation results indicate that the structure satisfies the guided-mode resonance condition only near a stripe width of approximately w = 200 nm, where the electromagnetic field is locally coupled into the waveguide mode and strongly absorbed; in other regions, the resonance condition is not met, and light passes through. 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. Thus, the mapping of wavelength information to spatial position is realized.
[0083] Example 2: Substrate + waveguide layer + low refractive index strip structure (gradually varying longitudinal width) — single wavelength incident, locally satisfying guided mode resonance
[0084] 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 varying from w min =50 nm to w max =400 nm. The incident light wavelength is λ=850 nm, perpendicularly incident, TE polarized.
[0085] like Figure 6 As shown, simulation results indicate that near a stripe width of approximately w = 200 nm, the structure satisfies the guided-mode resonance condition, with strong coupling of the electric field within the waveguide layer, resulting in resonant absorption; no resonance occurs in other regions. Ultimately, a narrow dark band is clearly observed in the image detector imaging. Figure 4 (a)), whose position is the structural position corresponding to this wavelength, thus realizing wavelength identification without the need for a beam splitter.
[0086] These two examples are the core implementation methods of this 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.
[0087] Furthermore, to more clearly illustrate the principle of this invention, several comparative examples of longitudinal 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.
[0088] Example 3: Substrate + High-refractive-index nanostrip structure (longitudinal non-gradual width) — Satisfying the guided mode resonance condition
[0089] This example structure includes a refractive index of n. s A 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 =2.0 The structure has a period of P=500 nm, a fixed width of w=300 nm, a thickness of h=100 nm, and the incident light is monochromatic light with a wavelength of λ=715 nm, incident perpendicularly, and the polarization direction of the incident light is TE mode.
[0090] 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. Figure 4 (c)), such as Figure 7 The electric field distribution diagram is shown.
[0091] Example 4: Substrate + High-refractive-index nanostrip structure (longitudinal non-gradual width) — does not satisfy the guided mode resonance condition.
[0092] This structure is consistent with Example 3, except that the incident wavelength is set to λ = 800 nm, which does not satisfy 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. For example... Figure 8 As shown in the simulated electric field distribution diagram, no local field enhancement occurs in the visible light, and the energy distribution on the back of the chip is uniform with high transmittance, resulting in almost full brightness in the image detector image. Figure 4 (b)).
[0093] Example 5: Substrate + Waveguide Layer + Low-Refractive-Index Nanostrip Structure (Longitudinal Non-Gradual Width) — Satisfying the Guided Mode Resonance Condition
[0094] 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=855 nm, which satisfies the guided mode resonance condition.
[0095] like Figure 9 As shown, simulation results reveal a significant guided-mode resonance phenomenon within the waveguide layer. The electric field is concentrated inside the waveguide and periodically distributed, resulting in extremely low transmitted energy and a completely dark image from the image detector. Figure 4 (c)).
[0096] Example 6: Substrate + Waveguide Layer + Low-Refractive-Index Nanostrip Structure (Longitudinal Non-Gradual Width) — Does Not Satisfy the Guided Mode Resonance Condition
[0097] The structural parameters are the same as in Example 5, except that the incident wavelength is adjusted to λ=900 nm, which does not satisfy the guided mode resonance condition. For example... Figure 10 As shown, the simulated electric field distribution diagram shows no obvious electric field concentration or beam coupling, the transmitted energy is almost lossless, and the image detector image is approximately fully bright. Figure 4 (b) verifies that no guided mode resonance occurred.
[0098] The four examples above all use nanostrip structures with non-gradually wide longitudinal sections as a comparative reference for the longitudinally tapered 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, 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.
[0099] Example 2
[0100] This embodiment provides a guided-mode resonance refractive index detection method based on a longitudinally graded grating structure, and a guided-mode resonance refractive index detection device based on a longitudinally graded grating structure according to Embodiment 1, including the following steps:
[0101] S1. Using a refractive index detection device to detect materials with unknown refractive index;
[0102] S2. Acquire the transmitted light image below the guided mode resonance sensing chip through an image detector;
[0103] S3. Transmit the image to the signal processing unit and extract the light intensity distribution of each pixel in the image;
[0104] S4. Based on the correspondence between pixel position and light intensity, obtain the changes in transmission spectrum intensity at different positions;
[0105] 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.
[0106] like Figure 11 The refractive index inversion method of the present invention includes two stages, as detailed below:
[0107] (1) System calibration stage:
[0108] a) Input a series of known refractive indices n i Reference sample;
[0109] b) Corresponding resonance location on the recorded image x R ;
[0110] c) Create function x R ( n This allows us to obtain inverse lookup table data or a fitted model.
[0111] (2) Actual measurement stage:
[0112] a) Identify the location xR of pixels with extremely low transmission intensity in the image detector;
[0113] b) Look up the table xR(n) by matching the pixel position, and then obtain the corresponding refractive index n by mapping xR(n).
[0114] 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.
[0115] 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 device for detecting refractive index based on longitudinal graded grating structure of resonant guided mode, characterized in that, The device comprises a light source, a light isolator, a polarization controller, a collimating lens, a guided-mode resonance sensor chip, an image detector and a signal processing unit connected in sequence. The light source is configured to emit laser light. The light isolator is configured to eliminate back reflection. The polarization controller is configured to control the polarization state of the incident light. The collimating lens is configured to expand the laser light into a suitable light spot. The guided-mode resonance sensor chip has a transmissive structure, and a strip-shaped nanostructure with consistent periods and longitudinal gradient is arranged on the top of the chip. The image detector is configured to receive the transmitted light signal after passing through the guided-mode resonance sensor chip, generate a transmitted light image and transmit the transmitted light image to the signal processing unit. The signal processing unit is configured to analyze the transmitted light image and inversely calculate the refractive index of the medium to be measured according to a structure mapping model. The longitudinal gradient strip-shaped nanostructure has the same period in each cycle and has a gradient feature of refractive index, structure width or structure thickness in a direction perpendicular to the period direction. The guided-mode resonance sensor chip comprises a substrate layer, a high refractive index layer arranged on the substrate layer and a low refractive index layer arranged on the top.
2. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, The guided-mode resonance sensor chip comprises a substrate layer and a high refractive index layer arranged on the substrate layer.
3. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, 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 satisfy a set condition.
4. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, The cross-sectional shape of the strip-shaped nanostructure is rectangular, square, semicircular, elliptical, sinusoidal, triangular, trapezoidal or other regular shape.
5. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, The light source is a wavelength-tunable monochromatic laser, and the working range covers visible light to infrared waveband, and the wavelength of the incident light is greater than the period length of the strip-shaped nanostructure.
6. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, The image detector is a CCD or CMOS array camera. The signal processing unit comprises image processing software and an algorithm module for establishing a mapping relationship between pixel positions and refractive indexes.
7. The longitudinal grating structure based guided mode resonant refractive index detection device according to claim 1, wherein, The structure mapping model is: A set of reference samples with known refractive indexes are used to calibrate the guided-mode resonance refractive index detection device, and a mapping relationship model between the refractive index and the pixel position is obtained.
8. A method for detecting refractive index based on longitudinal graded grating structure of guided mode resonance, characterized in that, A guided-mode resonance refractive index detection device based on a longitudinal gradient grating structure according to any one of claims 1-7 comprises the following steps: S1, using the refractive index detection device to detect a material with unknown refractive index; S2, collecting the transmitted light image below the guided-mode resonance sensor chip through the image detector; S3, transmitting the image to the signal processing unit and extracting the light intensity distribution of each pixel in the image; S4, obtaining the transmission spectrum intensity variation at different positions according to the corresponding relationship between the pixel position and the light intensity; S5, using the preset mapping relationship between the refractive index and the pixel position to inversely calculate the refractive index value of the medium to be measured.