Environmental refractive index sensor and monitoring method based on enhanced positive and negative goos-hanchen displacement

Abstract

The application provides an environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen displacement and a monitoring method, relates to the technical field of metasurface sensors, and aims to solve the technical problem of low sensor sensitivity of the existing environmental refractive index sensor due to the difficulty in enhancing the Goos-Haenchen displacement. The sensor comprises a substrate, a Bragg reflector, a top layer and a double grating which are sequentially stacked on the substrate. The double grating is formed by a unit structure of two identical grating strips arranged periodically, the air channel width between the two grating strips is different from the air channel width on the two sides of the two grating strips, so that the unit structure has asymmetry. When incident light is incident on the double grating at a non-perpendicular angle, the double grating can convert ideal bound states into double quasi-bound states with high quality factors by utilizing the asymmetry of the unit structure, thereby enhancing the positive and negative Goos-Haenchen displacement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metasurface sensors, and more particularly to an environmental refractive index sensor and a monitoring method based on enhanced positive and negative Goos-Hänchen displacements. BACKGROUND

[0002] With the rapid development of the Internet of Things, atmospheric monitoring and biosensing technology, there is an increasing demand for environmental refractive index sensors with high sensitivity, fast response and high precision. Traditional refractive index sensors usually rely on fiber sensing, surface plasmon resonance wavelength change and other technologies, which can achieve certain detection accuracy, but have certain limitations in responding to small environmental refractive index changes. The existing technology still has room for improvement in terms of sensor sensitivity, response speed and monitoring ability for extremely small refractive index changes.

[0003] Goos-Hänchen (GH) displacement has been a hot topic in optical research since it was discovered. The displacement is a small displacement caused by the phase change of reflected light at the interface of an optical medium. Sensors based on Goos-Hänchen displacement have high precision and sensitivity. However, the size of the Goos-Hänchen displacement is usually only a few times the wavelength, making it extremely difficult to observe the Goos-Hänchen displacement experimentally. Since the Goos-Hänchen displacement is proportional to the partial derivative of the reflection phase with respect to the incident angle. Therefore, the larger the change in the reflection phase with the incident angle, the larger the Goos-Hänchen displacement, which is important for improving the sensitivity of the sensor. In recent years, researchers have used various methods to increase the Goos-Hänchen displacement, among which the method of using the properties of continuous domain bound states of metasurfaces to achieve high-quality factor resonance has attracted widespread attention. However, so far, the existing environmental refractive index sensors still have low sensitivity due to the difficulty in enhancing the Goos-Hänchen displacement. SUMMARY

[0004] Therefore, the present application provides an environmental refractive index sensor and a monitoring method based on enhanced positive and negative Goos-Hänchen displacements to solve the technical problem of low sensor sensitivity due to the difficulty in enhancing the Goos-Hänchen displacement of the existing environmental refractive index sensors.

[0005] One aspect of the present application provides an environmental refractive index sensor based on enhanced positive and negative Goos-Hänchen displacements, comprising: a substrate; a Bragg reflector, a top layer and a double grating sequentially stacked on the substrate; the double grating is formed by a unit structure of two identical grating strips arranged periodically, the air channel width between the two grating strips is different from the air channel width on both sides of the two grating strips, so that the unit structure has asymmetry; wherein when the incident light is incident on the double grating at a non-perpendicular angle, the double grating utilizes the asymmetry of the unit structure to convert the ideal bound state into a double quasi-bound state with high quality factor, thereby enhancing the positive and negative Goos-Hänchen displacements.

[0006] According to the embodiment of the present application, the Bragg mirror is periodically arranged by two kinds of materials with different refractive indexes, one of which has a refractive index higher than a refractive index threshold, and the other of which has a refractive index lower than the refractive index threshold; wherein a top layer on the upper part of the Bragg mirror can destroy the translational symmetry of the Bragg mirror, thereby forming an optical resonant cavity to excite Bloch surface waves on the surface of the Bragg mirror.

[0007] According to the embodiment of the present application, the air channel width between the two grating strips in the double grating is adjustable, and by adjusting the air channel width between the two grating strips, the degree of asymmetry of the unit structure can be adjusted.

[0008] According to the embodiment of the present application, the material with a refractive index higher than the refractive index threshold in the Bragg mirror includes GaAs, and the thickness d H = 199nm.

[0009] According to the embodiment of the present application, the material with a refractive index lower than the refractive index threshold in the Bragg mirror includes AlGaAs, and the thickness d L = 235nm.

[0010] According to the embodiment of the present application, the material of the top layer includes GaAs, and the thickness d T = 130nm.

[0011] According to the embodiment of the present application, the material of the double grating includes GaAs, the period Λ = 288nm, the width w = 43nm, and the thickness d G = 140nm.

[0012] According to the embodiment of the present application, the air channel width d = 91nm between the two grating strips in the double grating.

[0013] According to the embodiment of the present application, the material of the substrate includes GaAs, and the thickness d S = 5um.

[0014] Another aspect of the present application provides a method for monitoring environmental refractive index based on enhanced positive and negative Goos-Haenchen shifts, comprising: exciting Bloch surface waves by incident light under the joint action of a double grating, a top layer and a Bragg mirror, and obtaining a double quasi-bound state resonance peak wavelength after reflection, wherein the incident light is a TE polarized plane wave with an angle of θ along the z axis; obtaining an angular reflection spectrum and a reflection phase by fixing the double quasi-bound state resonance peak wavelength and changing the incident angle θ; and calculating a positive and negative Goos-Haenchen shift angle spectrum according to the angular reflection spectrum and the reflection phase, wherein the Goos-Haenchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle θ; when the environmental refractive index changes, the Goos-Haenchen shift near the resonance peak incident angle changes dramatically, and the monitoring of the environmental refractive index is realized by observing the fluctuation of the Goos-Haenchen shift caused by the change of the environmental refractive index.

[0015] Compared with the prior art, the environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts provided by the present application has at least the following beneficial effects:

[0016] (1) The environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts provided by the present application is different from most existing refractive index sensors based on resonance wavelength changes, but through the joint action of the structural symmetry breaking and the oblique incidence excitation field, a continuous domain double quasi-bound state with a high quality factor is realized, and then the positive and negative Goos-Haenchen shifts are enhanced based on the double quasi-bound state, thereby greatly improving the sensitivity of the sensor.

[0017] (2) The environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts provided by the present application further improves the sensitivity of the sensor to the change of the environmental refractive index through the field enhancement effect of the Bloch surface wave on the basis of the continuous domain double quasi-bound state.

[0018] (3) The environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts provided by the present application can flexibly adjust the resonance wavelength and the quality factor of the double quasi-bound state by the structural asymmetry and the incident angle, and therefore has stronger applicability. BRIEF DESCRIPTION OF DRAWINGS

[0019] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 A perspective structural view of the environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts according to the embodiment of the present application is schematically shown;

[0021] Figure 2 An x-z plane structural view of the environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts according to the embodiment of the present application is schematically shown;

[0022] Figure 3 A comparative plot of the continuous domain quasi-bound states supported by the sensor structure for normal incidence (θ = 0°) and oblique incidence (θ = 5°) is schematically shown according to an embodiment of the present application;

[0023] Figure 4 A response parameter plot for environmental refractive index sensing using a positive Goos-Haenchen shift enhancement with a resonance wavelength of 893.12 nm is schematically shown according to an embodiment of the present application;

[0024] Figure 5 A response parameter plot for environmental refractive index sensing using a negative Goos-Haenchen shift enhancement with a resonance wavelength of 939.21 nm is schematically shown according to an embodiment of the present application;

[0025] Figure 6 A flow chart of a method for environmental refractive index monitoring based on enhanced positive and negative Goos-Haenchen shift according to an embodiment of the present application is schematically shown.

[0026] REFERENCE NUMERALS

[0027] 1 - substrate; 2 - Bragg mirror; 3 - top layer; 4 - double grating. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that the description is merely exemplary of the present application, and is intended to provide a thorough description for implementations of the present application, and to convey the best understanding of the embodiments of the present application. Accordingly, those skilled in the art will appreciate that the present application can be practiced with

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the term "includes" and tautological expressions thereof, such as "including," "includes," "include," "contains," "containing," and so forth, shall be read expansively and without limitation. The terms "comprising," "including," and "having," and tautological expressions thereof (e.g., "comprises," "comprising," "containing," "contains," "includes," "including," "have," etc.) serve to specify the presence of stated features, steps or components but do not preclude the presence or addition of one or more other features, steps, operations, elements, components or groups thereof.

[0030] All terms used herein including technical and scientific terms have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein are merely specific examples for the described embodiments and should not be limiting. Nothing herein is to be construed as limiting the scope of the application. The terms "a," "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. The terms "comprises," "comprising," "includes," "including," "has," "having" and the like can be used interchangeably with the term "consisting of" or "consisting only of." The term "consisting essentially of" or "consisting essentially of only" can be used interchangeably with the term "consisting of" or "consisting only of," unless the context clearly dictates otherwise. The term "plurality" refers to two or more.

[0031] In the case of using expressions like "at least one of A, B, and C", generally this is to be understood to mean one or more of A or B or C, but not necessarily including multiple instances of A, B, or C. For example, a compound can contain "at least one aryl group", but it cannot contain two aryl groups, or two instances of at least one aryl group. If it is intended to indicate multiple aryl groups, the expression "at least two", "a plurality of", or the like will be used.

[0032] With the rapid development of the Internet of Things, atmospheric monitoring and biosensing technology, there is an increasing demand for environmental refractive index sensors with high sensitivity, fast response and high precision. Traditional refractive index sensors usually rely on fiber sensing, surface plasmon resonance wavelength change and other technologies, which can achieve certain detection accuracy, but have certain limitations in responding to small environmental refractive index changes. The existing technology still has room for improvement in terms of sensor sensitivity, response speed and monitoring ability for extremely small refractive index changes.

[0033] Goos-Haunche shift has been a hot topic in optical research since it was discovered. The shift is a small displacement due to the phase change of reflected light at the interface of optical media. Sensors based on Goos-Haunche shift have extremely high precision and sensitivity. However, the size of the Goos-Haunche shift is usually only a few times the wavelength, which makes it extremely difficult to observe the Goos-Haunche shift in experiments. Since the Goos-Haunche shift is proportional to the partial derivative of the reflection phase with respect to the incident angle. Therefore, the larger the change of the reflection phase with the incident angle, the larger the Goos-Haunche shift, which is important for improving the sensitivity of the sensor. In recent years, researchers have used various methods to increase the Goos-Haunche shift, among which the method of using the properties of continuous domain bound states of super surface to achieve high quality factor resonance has attracted widespread attention. However, so far, the existing environmental refractive index sensors still have low sensitivity due to the difficulty of enhancing the Goos-Haunche shift.

[0034] Continuous domain bound state is a non-radiative mode in a continuous domain of radiation. In an ideal case, the bound state has an infinite quality factor and zero line width, so it cannot be excited by the outside world. Generally, the symmetry of the excitation field can be broken by oblique incidence or structural asymmetry, which can convert the bound state into a quasi-bound state with high quality factor resonance. Quasi-bound state shows super-narrow line width and high quality factor resonance in the spectrum, which has great application prospect in high sensitivity refractive index sensors.

[0035] Bloch surface wave is an electromagnetic surface wave excited at the interface between a truncated periodic dielectric multilayer and the surrounding medium. Similar to surface plasmon polaritons on metal films, Bloch surface waves also have inherent characteristics of optical near-field confinement and enhancement, and are widely used in chemical and biological sensing, gas sensing, fluorescence radiation enhancement, etc. Compared with surface plasmon polaritons, Bloch surface waves have lower absorption, narrower mode resonance, longer propagation length, and maintainability of spectrum and polarization.

[0036] Based on this, the application provides an environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts and a monitoring method, to solve the technical problem of low sensor sensitivity of the existing environmental refractive index sensor due to the difficulty in enhancing the Goos-Haenchen shift.

[0037] The sensor comprises a substrate, a Bragg reflector, a top layer and a double grating which are sequentially stacked on the substrate.

[0038] The environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts provided by the embodiments of the application is different from most existing refractive index sensors based on resonance wavelength change, but through the design of a double-period grating, the common action of structure symmetry breaking and oblique incidence excitation field is utilized to realize continuous domain double quasi-bound states with high quality factors, and then the enhancement of positive and negative Goos-Haenchen shifts is realized based on the double quasi-bound states, so that the sensitivity of the sensor is greatly improved.

[0039] To make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below with reference to the specific embodiments and the accompanying drawings.

[0040] Figure 1 The schematic diagram of the environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts according to the embodiments of the application is shown.

[0041] As shown in the figure, the environmental refractive index sensor based on enhanced positive and negative Goos-Haenchen shifts of this embodiment may, for example, comprise: Figure 1

[0042] a substrate (Substrate) 1;

[0043] a Bragg reflector (DBR) 2, a top layer 3 and a double grating 4 which are sequentially stacked on the substrate 1. ​

[0044] The double grating 4 is formed by a unit structure consisting of two identical grating strips arranged periodically. The width of the air channel between the two grating strips (i.e., the grating strip spacing) is different from the width of the air channel on both sides of the two grating strips, making the unit structure asymmetric.

[0045] When the incident light is incident on the double grating 4 at a non-perpendicular angle (i.e., oblique incidence), the double grating 4 utilizes the asymmetry of the unit structure to convert the ideal bound state into a double quasi-bound state with a high quality factor, thereby enhancing the positive and negative Goos-Hanchen shifts.

[0046] In this embodiment, a dual-grating coupling structure is used, which has two effects:

[0047] One is to use the periodic modulation of the double grating structure to fold the Brillouin zone of the energy band and realize the continuous domain bound state.

[0048] The second is to provide phase matching conditions to couple light of free-space wavelength into the Bloch surface wave mode.

[0049] When incident light is coupled into the Bragg reflector 2 through the double grating 4, it can localize the light to the top layer 3 and resonate, resulting in a sharp resonance peak in the reflection spectrum. By fixing the wavelength of the double quasi-bound state resonance peak and changing the incident angle θ, the angular reflection spectrum and reflection phase can be obtained. The Goos-Hanchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle. When asymmetry is introduced into the structure, the reflection phase changes more dramatically with the incident angle, thereby significantly amplifying the positive and negative Goos-Hanchen shifts. When the ambient refractive index changes, the Goos-Hanchen shift near the resonance peak incident angle changes dramatically. By observing the fluctuations in the Goos-Hanchen shift caused by changes in the ambient refractive index, the ambient refractive index can be monitored.

[0050] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided in an embodiment of the present invention is different from most existing refractive index sensors based on changes in resonant wavelength. Instead, it achieves a high-quality factor continuous domain dual quasi-bound state by designing a double-period grating and utilizing the combined effects of structural symmetry breaking and the oblique-incident excitation field. Then, based on the dual quasi-bound state, the positive and negative Goos-Hanchen shifts are enhanced respectively, greatly improving the sensitivity of the sensor.

[0051] According to an embodiment of the present invention, the Bragg reflector 2 is formed by periodically arranging two materials with different refractive indices, wherein the refractive index of one material is higher than a refractive index threshold, and the refractive index of the other material is lower than the refractive index threshold.

[0052] The top layer 3 on the upper part of the Bragg reflector 2 can destroy the translational symmetry of the Bragg reflector, thereby forming an optical resonant cavity to excite Bloch surface waves on the surface of the Bragg reflector.

[0053] In this embodiment, the Bragg reflector 2 itself is a structure composed of a periodic stack of high-refractive-index materials and low-refractive-index materials, typically exhibiting translational symmetry, meaning that the light field can be evenly distributed across each layer. However, the addition of a top layer, namely, the top layer 3, on top of the Bragg reflector 2 disrupts this inherent symmetry. Due to the presence of the top layer, the light field becomes more strongly localized at the interface between the top layer 3 and the Bragg reflector 2, thereby forming a highly efficient optical resonant cavity. The material and thickness of the top layer 3 have been optimized to strongly localize the mode distribution of the light field within the top layer 3. This enhanced localized field facilitates more efficient excitation of Bloch surface waves.

[0054] Bloch surface waves are a standing wave pattern generated on the surface of the Bragg reflector 2 due to the interaction between light and the interface. Its electric field intensity reaches its maximum at the interface. This localized light field enhancement can significantly improve the interaction between light and the surrounding environment (such as the refractive index of the medium), allowing tiny environmental changes to be efficiently detected.

[0055] In this embodiment, the Bloch surface wave exists as a Bloch mode in the top layer 3, decays exponentially along the Bragg reflector 2, and decays rapidly along the environment. The Bragg reflector 2 is used to promote the coupling between the Bloch surface wave and the resonant mode, maximizing the Bloch surface wave effect.

[0056] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided in an embodiment of the present invention further improves the sensitivity of the sensor to changes in the environmental refractive index through the field enhancement effect of Bloch surface waves on the basis of the continuous domain dual quasi-bound state.

[0057] According to an embodiment of the present invention, the width of the air channel between the two grating strips in the double grating 4 is adjustable, that is, the spacing between the two grating strips can be flexible. By adjusting the width of the air channel between the two grating strips, the asymmetry of the unit structure can be adjusted.

[0058] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided by the embodiment of the present invention has a higher applicability because the resonance wavelength and quality factor of the dual quasi-bound state can be flexibly adjusted by the structural asymmetry and the incident angle.

[0059] Figure 2 The diagram schematically shows the xz plane structure of an ambient refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention.

[0060] like Figure 2 As shown, in this embodiment of the environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts, the relevant parameters such as the materials and dimensions of each structure can be designed as follows:

[0061] The material of the substrate 1 can be GaAs, for example, and the thickness d S = 5 um.

[0062] In the Bragg mirror 2, the high refractive index material can be GaAs, for example, and the thickness d H = 199 nm, and the low refractive index material can be AlGaAs, for example, and the thickness d L = 235 nm, wherein the high refractive index material GaAs and the low refractive index material AlGaAs are arranged periodically, and the periodicity N = 5.5.

[0063] The material of the top layer 3 can be GaAs, for example, and the thickness d T = 130 nm.

[0064] The material of the double grating 4 can be GaAs, for example, the period A = 288 nm, the width w = 43 nm, and the thickness d G = 140 nm, and the spacing d = 91 nm between the two grating bars in the double grating.

[0065] It should be understood that the sizes and values in the above structure are only exemplary and do not limit the present application.

[0066] Figure 3 A comparison diagram of the continuous domain quasi-bound state supported by the sensor structure according to the embodiment of the present application is schematically shown when the incident angle is 0° vertical incidence and 5° oblique incidence.

[0067] As shown in Figure 3 , when the incident angle is 0° vertical incidence, there is one continuous domain quasi-bound state, and the resonance wavelength is 909.62 nm; when the incident angle is 5°, there are two continuous domain quasi-bound states, and the resonance wavelengths are 893.12 nm and 939.21 nm, respectively.

[0068] Figure 4 A response parameter diagram for environmental refractive index sensing after positive Goos-Ha-nchen shift enhancement using the resonance wavelength of 893.12 nm according to the embodiment of the present application is schematically shown, and specifically includes Figure 4 a and Figure 4 b.

[0069] Figure 4 a shows the reflectivity angle spectrum and the phase angle spectrum feature diagram of the wavelength of 893.12 nm according to the embodiment of the present application.

[0070] As shown in Figure 4 a, the reflectivity angle spectrum and the reflection phase angle spectrum obtained when the incident wavelength is fixed at 893.12 nm and the incident angle is changed from 4° to 6°.

[0071] For the incident beam with a sufficiently wide beam waist, the Goos-Ha nchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle, that is:

[0072]

[0073] where S GH represents the Goos-Hanchen shift, λ represents the resonance wavelength, φ r represents the reflection phase, and θ represents the incident angle.

[0074] The Goos-Hanchen shift is determined by the gradient of the reflection phase. As can be seen from the figure, the reflectivity peak is distributed at about 5°, and the reflection phase changes sharply at 5°, indicating that the Goos-Hanchen shift may be more obvious near 5°.

[0075] Figure 4 b schematically shows the angular spectrum feature map of the positive Goos-Hanchen shift under different environmental refractive indexes of the wavelength of 893.12 nm according to an embodiment of the present application.

[0076] As Figure 4 b shows the angular spectrum of the positive Goos-Hanchen shift under different environmental refractive indexes of the incident wavelength of 893.12 nm, which intuitively reflects the response characteristics of the sensor to the change of the environmental refractive index.

[0077] It can be seen that when the environmental refractive index is 1.000, the continuous domain quasi-bound state enhanced positive Goos-Hanchen shift obtained at about 5° is as high as 3895 times the resonance wavelength. When the environmental refractive index changes slightly from 1.000 to 1.003, the positive Goos-Hanchen shift angular spectrum obviously shifts to a smaller incident angle. The sensitivity of the sensor can be defined by the change of the Goos-Hanchen shift and the environmental refractive index, that is:

[0078]

[0079] where S represents the sensitivity, dS GH represents the change of the Goos-Hanchen shift, and dn represents the change of the environmental refractive index. When the change range of the environmental refractive index is 1-1.001, the change amount of the Goos-Hanchen shift at about 5° incident angle is 1733 times the resonance wavelength, and the sensitivity of the sensor is 1.5×10 6 μm / RIU.

[0080] Figure 5 Schematically shows the response parameter map of the negative Goos-Hanchen shift enhanced for environmental refractive index sensing using a resonance wavelength of 939.21 nm according to an embodiment of the present application, specifically including Figure 5 a and Figure 5 b.

[0081] Figure 5a shows the reflectivity angular spectrum and phase angular spectrum characteristics of wavelength 939.21 nm according to an embodiment of the present application.

[0082] As shown in Figure 5 a, for fixed incident wavelength 939.21 nm, the reflectivity angular spectrum and reflection phase angular spectrum obtained by changing the incident angle from 4° to 6° are shown.

[0083] For an incident light beam with a sufficiently wide beam waist, the Goos-Haun shift is proportional to the partial derivative of the reflection phase with respect to the incident angle, that is:

[0084]

[0085] wherein S GH represents the Goos-Haun shift, λ represents the resonance wavelength, φ r represents the reflection phase, and θ represents the incident angle.

[0086] The Goos-Haun shift is determined by the gradient of the reflection phase. As can be seen from the figure, the reflectivity peak is distributed at about 5°, and the reflection phase changes sharply at 5°, indicating that a relatively obvious Goos-Haun shift may occur near 5°.

[0087] Figure 5 b shows the angular spectrum characteristics of negative Goos-Haun shift under different environmental refractive indexes of wavelength 939.21 nm according to an embodiment of the present application.

[0088] As shown in Figure 5 b, when the environmental refractive index is 1.000, the negative Goos-Haun shift of the continuous domain quasi-bound state enhancement obtained at about 5° is as high as 10280 times the resonance wavelength.

[0089] When the environmental refractive index changes slightly from 1.000 to 1.003, the negative Goos-Haun shift angular spectrum obviously shifts to a smaller incident angle. The sensitivity of the sensor can be defined by the change of the Goos-Haun shift and the environmental refractive index, that is:

[0090]

[0091] wherein S represents the sensitivity, dS GH represents the change of the Goos-Haun shift, and dn represents the change of the environmental refractive index. When the change range of the environmental refractive index is 1-1.001, the change amount of the negative Goos-Haun shift at about 5° incident angle is 9561 times the resonance wavelength, and the sensitivity of the sensor is 9×10 6 μm / RIU.

[0092] The environmental refractive index sensor based on enhanced positive and negative Gous-Hanchen shifts provided in the embodiments of the present invention is different from the case where the Gous-Hanchen shift is only a few times the wavelength without the assistance of external resonance enhancement. With the assistance of the quasi-bound state, the Gous-Hanchen shift can be increased to several thousand times the resonance wavelength, and the maximum Gous-Hanchen shift is located near the reflectivity peak, which makes the Gous-Hanchen shift easier to detect and utilize.

[0093] By enhancing the positive and negative Goos-Hanchen shifts based on the continuum double quasi-bound states and Bloch surface waves, the sensitivities can reach 1.5×10 6 μm / RIU and 9×10 6 μm / RIU, which makes the sensor widely used in fields such as climate monitoring and biochemical detection that are extremely sensitive to tiny changes in the environmental refractive index.

[0094] An embodiment of the present invention also provides an environmental refractive index monitoring method based on enhanced positive and negative Goos-Hanchen shifts.

[0095] Figure 6 The flowchart of the environmental refractive index monitoring method based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention is schematically shown.

[0096] like Figure 6 As shown, the environmental refractive index monitoring method based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention may include operations S1 to S4:

[0097] In operation S1, the incident light excites Bloch surface waves under the joint action of the double grating, the top layer and the Bragg reflector, and obtains the double quasi-bound state resonance peak wavelength after reflection, wherein the incident light adopts a TE polarized plane wave with an angle of θ along the z-axis.

[0098] In operation S2 , the angular reflection spectrum and the reflection phase are obtained by fixing the double quasi-bound state resonance peak wavelength and changing the incident angle θ.

[0099] In operation S3 , a positive and negative Goos-Hanchen shift angular spectrum is calculated based on the angular reflectance spectrum and the reflection phase, wherein the Goos-Hanchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle θ.

[0100] In operation S4, when the ambient refractive index changes, the Goos-Hanchen shift near the resonance peak incident angle will change dramatically. By observing the Goos-Hanchen shift fluctuation caused by the ambient refractive index change, the ambient refractive index can be monitored.

[0101] The computer program product of the present application can be a computer program product that comprises a computer-readable medium having stored thereon instructions that can be executed by a processor of a computer to cause the processor to perform steps of any of the above-described methods of the present application. Those of skill would further appreciate that the various illustrative logical blocks, modules, processors, means, circuits, and algorithm steps described in connection with the implementations disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. The

[0102] The above-described embodiments of the application are presented for purposes of illustration and description. They are not intended to limit the scope of the application in that the various concepts taught herein can be combined in a number of ways. Other situations or modifications, obvious to those skilled in the art, can be made without departing from the spirit and scope of the application.

Claims

1. An ambient refractive index sensor based on enhanced positive and negative Goos-Ha nchen displacement, characterized in that, The sensor comprises: a substrate; a Bragg mirror, a top layer and a double grating arranged on the substrate in sequence; the Bragg mirror is periodically arranged by two materials with different refractive indexes, one of which has a refractive index higher than a refractive index threshold, and the other has a refractive index lower than the refractive index threshold; the top layer on the upper part of the Bragg mirror can destroy the translational symmetry of the Bragg mirror, thereby forming an optical resonant cavity to excite Bloch surface waves on the surface of the Bragg mirror; the double grating is periodically arranged by a unit structure composed of two identical grating strips, and the air channel width between the two grating strips is different from the air channel width on both sides of the two grating strips, so that the unit structure has asymmetry; when the incident light is incident on the double grating at a non-perpendicular angle, the double grating can convert ideal bound states into double quasi-bound states with high quality factors by using the asymmetry of the unit structure, thereby enhancing positive and negative Goos-Ha-nchen shifts.

2. The sensor of claim 1, wherein, The air channel width between the two grating strips in the double grating is adjustable, and the degree of asymmetry of the unit structure can be adjusted by adjusting the air channel width between the two grating strips.

3. The sensor of claim 1, wherein, The material in the Bragg mirror above the refractive index threshold comprises GaAs, with a thickness d H = 199 nm.

4. The sensor of claim 1, wherein, The material below the refractive index threshold in the Bragg mirror comprises AlGaAs, with a thickness d L = 235 nm.

5. The sensor of claim 1, wherein, The material of the top layer comprises GaAs, thickness d T = 130 nm.

6. The sensor of claim 1, wherein, The material of the double grating comprises GaAs, period Λ = 288 nm, width w = 43 nm, thickness d = 140 nm. G = 140 nm.

7. The sensor of claim 1, wherein, The air channel width between the two grating strips in the double grating is d=91nm.

8. The sensor of claim 1, wherein, The material of the substrate comprises GaAs, the thickness d S = 5 um.

9. A method for monitoring the environmental refractive index based on enhanced positive and negative Goos-Ha nchen displacement, applied to the sensor according to any one of claims 1 to 8, characterized in that, The method comprises: the incident light excites Bloch surface waves under the joint action of the double grating, the top layer and the Bragg mirror, and obtains a double quasi-bound state resonance peak wavelength after reflection, wherein the incident light is a TE polarization plane wave with an angle θ along the z axis; by fixing the double quasi-bound state resonance peak wavelength and changing the incident angle θ, an angular reflection spectrum and a reflection phase are obtained; according to the angular reflection spectrum and the reflection phase, a positive and negative Goos-Ha-nchen shift angle spectrum is calculated, wherein the Goos-Ha-nchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle θ; when the environmental refractive index changes, the Goos-Ha-nchen shift near the resonance peak incident angle will change dramatically, and the environmental refractive index can be monitored by observing the fluctuation of the Goos-Ha-nchen shift caused by the change of the environmental refractive index.

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