Environmental refractive index sensor and monitoring method based on enhanced positive and negative Goos-Hanchen shifts

Abstract

The invention provides an environment refractive index sensor based on enhanced positive and negative Goos-Haenchen shift and a monitoring method, relates to the technical field of metasurface sensors, and is used for solving the technical problem that the sensitivity of an existing environment refractive index sensor is low as the Goos-Haenchen shift is difficult to enhance. The sensor includes: a substrate; the Bragg reflector, the top layer and the double gratings are sequentially stacked on the substrate; the double grating is formed by periodically arranging unit structures composed of two same grating strips, and the width of an air channel between the two grating strips is different from the width of air channels on the two sides of the two grating strips, so that the unit structures have asymmetry. When incident light enters the double grating at a non-vertical angle, the double grating can convert an ideal bound state into a double quasi bound state with a high-quality factor by utilizing asymmetry of a unit structure, so that positive and negative Goos-Haenchen shift is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurface sensors, and more specifically, to an environmental refractive index sensor and a monitoring method based on enhanced positive and negative Goos-Hanchen shifts. Background Art

[0002] With the rapid development of the Internet of Things, atmospheric monitoring and biosensing technology, the demand for high-sensitivity, fast-response and high-precision environmental refractive index sensors is increasing. Traditional refractive index sensors usually rely on technologies such as optical fiber sensing and surface plasmon resonance wavelength changes. Although they can achieve a certain degree of detection accuracy, they have certain limitations in responding to tiny changes in environmental refractive index. Existing technologies still have room for improvement in sensor sensitivity, response speed and the ability to monitor extremely small changes in refractive index.

[0003] The Goos-Hänchen (GH) shift has been a hot topic in optical research since its discovery. This shift is a tiny shift caused by the phase change of reflected light at the interface of optical media. Sensors based on the Goos-Hänchen shift have extremely high accuracy and sensitivity. However, in general, the size of the Goos-Hänchen shift is only a few times the wavelength, which makes it extremely difficult to observe the Goos-Hänchen shift experimentally. Since the Goos-Hänchen shift is proportional to the partial differential of the reflected phase with the incident angle. Therefore, the greater the change of the reflected phase with the incident angle, the greater the Goos-Hänchen shift, which is extremely important for improving the sensitivity of the sensor. In recent years, researchers have used various methods to increase the Goos-Hänchen shift, among which the method of using the properties of the continuous domain bound state of the metasurface to achieve high quality factor resonance has received widespread attention. However, to date, the existing environmental refractive index sensors still have low sensitivity due to the difficulty in enhancing the Goos-Hänchen shift. Summary of the invention

[0004] In view of this, the present invention provides an environmental refractive index sensor and a monitoring method based on enhancing positive and negative Goos-Hanchen shifts, so as to solve the technical problem that the existing environmental refractive index sensors have low sensor sensitivity due to the difficulty in enhancing the Goos-Hanchen shifts.

[0005] One aspect of the present invention provides an environmental refractive index sensor based on enhancing positive and negative Goos-Hanchen shifts, comprising: a substrate; a Bragg reflector, a top layer and a double grating stacked in sequence on the substrate; the double grating is formed by a unit structure composed of two identical grating strips arranged periodically, the width of the air channel between the two grating strips is different from the width of the air channels 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-vertical angle, the double grating utilizes the asymmetry of the unit structure to convert an ideal bound state into a double quasi-bound state with a high quality factor, thereby enhancing the positive and negative Goos-Hanchen shifts.

[0006] According to an embodiment of the present invention, a Bragg reflector is formed by a periodic arrangement of 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; wherein the top layer on the upper part of the Bragg reflector can destroy the translational symmetry of the Bragg reflector, thereby forming an optical resonance cavity to excite Bloch surface waves on the surface of the Bragg reflector.

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

[0008] According to an embodiment of the present invention, the material above the refractive index threshold in the Bragg reflector includes GaAs, with a thickness d H =199nm.

[0009] According to an embodiment of the present invention, the material below the refractive index threshold in the Bragg reflector includes AlGaAs, with a thickness d L =235nm.

[0010] According to an embodiment of the present invention, the material of the top layer includes GaAs, with a thickness d T =130nm.

[0011] According to an embodiment of the present invention, 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 an embodiment of the present invention, the width of the air channel between two grating strips in the double grating is d=91 nm.

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

[0014] Another aspect of the present invention provides an environmental refractive index monitoring method based on enhanced positive and negative Goos-Hanchen shifts, comprising: incident light excites Bloch surface waves under the joint action of a double grating, a top layer and a Bragg reflector, and obtains a dual 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; by fixing the dual 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-Hanchen shift angular spectrum is calculated, wherein the Goos-Hanchen 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-Hanchen shift near the resonance peak incident angle will change dramatically, and the environmental refractive index monitoring is achieved by observing the Goos-Hanchen shift fluctuation caused by the environmental refractive index change.

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

[0016] (1) The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided by the present invention is different from most existing refractive index sensors based on changes in resonant wavelength. Instead, it realizes 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 oblique incident excitation field. Then, based on the dual quasi-bound state, the positive and negative Goos-Hanchen shifts are enhanced respectively, thereby greatly improving the sensitivity of the sensor.

[0017] (2) The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided by 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 double quasi-bound state in the continuous domain.

[0018] (3) The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided by the present invention has a higher applicability because the resonant wavelength and quality factor of the dual quasi-bound state can be flexibly adjusted by the structural asymmetry and the incident angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0020] Figure 1 A three-dimensional structural diagram of an environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention is schematically shown;

[0021] Figure 2 The xz plane structure diagram of an environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention is schematically shown;

[0022] Figure 3 A comparison diagram of the continuous domain quasi-bound state supported by the sensor structure when the incident angle θ=0° vertical incidence and θ=5° oblique incidence according to an embodiment of the present invention is schematically shown;

[0023] Figure 4 A response parameter diagram for ambient refractive index sensing after positive Goos-Hanchen shift enhancement using a resonance wavelength of 893.12 nm according to an embodiment of the present invention is schematically shown;

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

[0025] 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.

[0026] [Reference Signs]

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

[0028] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0030] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0031] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0032] With the rapid development of the Internet of Things, atmospheric monitoring and biosensing technology, the demand for high-sensitivity, fast-response and high-precision environmental refractive index sensors is increasing. Traditional refractive index sensors usually rely on technologies such as optical fiber sensing and surface plasmon resonance wavelength changes. Although they can achieve a certain degree of detection accuracy, they have certain limitations in responding to tiny changes in environmental refractive index. Existing technologies still have room for improvement in sensor sensitivity, response speed and the ability to monitor extremely small changes in refractive index.

[0033] Goos-Hanchen shift has been a hot topic in optical research since its discovery. This shift is a tiny shift caused by the phase change of reflected light at the interface of optical media. Sensors based on Goos-Hanchen shift have extremely high accuracy and sensitivity. However, in general, the size of the Goos-Hanchen shift is only a few times the wavelength, which makes it extremely difficult to observe the Goos-Hanchen shift experimentally. Since the Goos-Hanchen shift is proportional to the partial differential of the reflected phase with the incident angle. Therefore, the greater the change of the reflected phase with the incident angle, the greater the Goos-Hanchen shift, which is extremely important for improving the sensitivity of the sensor. In recent years, researchers have used various methods to increase the Goos-Hanchen shift, among which the method of using the properties of the continuous domain bound state of the metasurface to achieve high quality factor resonance has received widespread attention. However, to date, the existing environmental refractive index sensors still have low sensitivity due to the difficulty in enhancing the Goos-Hanchen shift.

[0034] The continuum bound state is a non-radiative mode in a radiative continuum. Ideally, the bound state has infinite quality factor and zero line width, so it cannot be excited by the outside world. Usually, the bound state can be converted into a quasi-bound state with high quality factor resonance by breaking the symmetry of the excitation field or introducing structural asymmetry by oblique incidence. The quasi-bound state is manifested as ultra-narrow line width and high quality factor resonance in the spectrum, which has great application prospects in high-sensitive refractive index sensors.

[0035] Bloch surface waves are electromagnetic surface waves excited at the interface between a truncated periodic dielectric multilayer and the surrounding medium. Similar to surface plasmons on metal films, Bloch surface waves also have the inherent properties 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 plasmons, Bloch surface waves have lower absorption, narrower mode resonance, longer propagation length, and spectral and polarization sustainability.

[0036] Based on this, the present invention provides an environmental refractive index sensor and a monitoring method based on enhancing positive and negative Goos-Hanchen shifts, so as to solve the technical problem that the existing environmental refractive index sensors have low sensor sensitivity due to the difficulty in enhancing the Goos-Hanchen shifts.

[0037] 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 composed of two identical grating strips arranged periodically, the width of the air channel between the two grating strips is different from the width of the air channels 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-vertical angle, the double grating 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.

[0038] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided in the embodiments of the present invention is different from most existing refractive index sensors based on changes in resonant wavelength. Instead, it designs a double-period grating and utilizes the combined effects of structural symmetry breaking and oblique-incident excitation fields to achieve a continuous-domain dual quasi-bound state with a high quality factor. Then, based on the dual quasi-bound state, the positive and negative Goos-Hanchen shifts are enhanced respectively, thereby greatly improving the sensitivity of the sensor.

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0040] Figure 1 The three-dimensional structure diagram of an environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention is schematically shown.

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

[0042] Substrate 1;

[0043] A DBR 2 , a top layer 3 and a double grating 4 are sequentially stacked on a substrate 1 .

[0044] The double grating 4 is formed by a unit structure composed of two identical grating strips arranged periodically, and the width of the air channel between the two grating strips (ie, the grating strip spacing) is different from the width of the air channel on both sides of the two grating strips, so that the unit structure has asymmetry.

[0045] When the incident light is incident on the double grating 4 at a non-vertical angle (i.e., oblique incidence), the double grating 4 utilizes the asymmetry of the unit structure to transform 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 double 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 the incident light is coupled to the Bragg reflector 2 through the double grating 4, the light can be localized in the top layer 3 to resonate, thereby causing a sharp resonance peak to appear in the reflection spectrum. The angular reflection spectrum and reflection phase can be obtained by fixing the wavelength of the double quasi-bound state resonance peak and changing the incident angle θ. 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 change of the reflection phase with the incident angle becomes more dramatic, 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. The ambient refractive index can be monitored by observing the fluctuation of the Goos-Hanchen shift caused by the change of the ambient refractive index.

[0050] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided in the embodiments of the present invention is different from most existing refractive index sensors based on changes in resonant wavelength. Instead, it designs a double-period grating and utilizes the combined effects of structural symmetry breaking and oblique-incident excitation fields to achieve a continuous-domain dual quasi-bound state with a high quality factor. Then, based on the dual quasi-bound state, the positive and negative Goos-Hanchen shifts are enhanced respectively, thereby 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 resonance 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 of periodically superimposed high-refractive index materials and low-refractive index materials, and generally has translational symmetry, that is, the light field can be evenly distributed in each layer. When a top layer structure is introduced on the top of the Bragg reflector 2, that is, the top layer 3, this design will break the original symmetry. Due to the existence of the top layer, the light field will form a stronger localization at the interface between the top layer 3 and the Bragg reflector 2, thereby forming an efficient optical resonant cavity. The material and thickness of the top layer 3 are optimized to strongly localize the mode distribution of the light field in the top layer 3. The enhancement of this localized field helps to more efficiently excite Bloch surface waves.

[0054] Bloch surface wave is a standing wave mode generated on the surface of 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 enhance 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 in the top layer 3 as a Bloch mode, 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, and maximize the Bloch surface wave effect.

[0056] The environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts provided in the embodiment of the present invention further improves the sensitivity of the sensor to changes in 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 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 xz plane structure diagram of an environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts according to an embodiment of the present invention is schematically shown.

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

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

[0062] In the Bragg reflector 2, the high refractive index material may be GaAs, for example, with a thickness d H =199nm, the low refractive index material can be, for example, AlGaAs, with a thickness of d L =235nm, 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, with a thickness d T =130nm.

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

[0065] It should be understood that the dimensions and values ​​in the above structures are merely exemplary and are not intended to limit the present invention.

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

[0067] like Figure 3 As shown, when the incident angle θ=0° is vertical incidence, there is a continuous domain quasi-bound state with a resonance wavelength of 909.62nm; when the incident angle θ=5°, there are double continuous domain quasi-bound states with resonance wavelengths of 893.12nm and 939.21nm respectively.

[0068] Figure 4 The schematic diagram shows the response parameter diagram for ambient refractive index sensing after positive Goos-Hanchen shift enhancement using 893.12 nm resonant wavelength according to an embodiment of the present invention, specifically including Figure 4 a and Figure 4 b.

[0069] Figure 4 a schematically shows a characteristic diagram of a reflectivity angle spectrum and a phase angle spectrum at a wavelength of 893.12 nm according to an embodiment of the present invention.

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

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

[0072]

[0073] Among them, 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 reflection phase gradient. As can be seen from the figure, the reflectivity peak is distributed around 5°, and the reflection phase changes dramatically at 5°, indicating that a more obvious Goos-Hanchen shift may occur near 5°.

[0075] Figure 4 b schematically shows an angular spectrum characteristic diagram of the positive Goos-Hanchen shift at different ambient refractive indices with a wavelength of 893.12 nm according to an embodiment of the present invention.

[0076] like Figure 4 As shown in b, it is the angular spectrum of the positive Goos-Hanchen shift under different ambient refractive indices with an incident wavelength of 893.12 nm, which intuitively reflects the response characteristics of the sensor to changes in the ambient refractive index.

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

[0078]

[0079] Where S represents sensitivity, dS GH represents the Goos-Hanchen shift change, and dn represents the ambient refractive index change. When the ambient refractive index changes from 1 to 1.001, the Goos-Hanchen shift change at an incident angle of about 5° is 1733 times the resonant wavelength, and the sensor sensitivity is 1.5×10 6 μm / RIU.

[0080] Figure 5 The schematic diagram shows the response parameter diagram for environmental refractive index sensing after negative Goos-Hanchen shift enhancement using 939.21 nm resonant wavelength according to an embodiment of the present invention, specifically including Figure 5 a and Figure 5 b.

[0081] Figure 5a schematically shows a characteristic diagram of a reflectivity angle spectrum and a phase angle spectrum at a wavelength of 939.21 nm according to an embodiment of the present invention.

[0082] like Figure 5 As shown in a, the reflectivity angle spectrum and reflection phase angle spectrum are obtained when the incident wavelength is fixed at 939.21nm and the incident angle is changed from 4 to 6°.

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

[0084]

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

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

[0087] Figure 5 b schematically shows an angular spectrum characteristic diagram of the negative Goos-Hanchen shift at different ambient refractive indices with a wavelength of 939.21 nm according to an embodiment of the present invention.

[0088] like Figure 5 As shown in b, when the ambient refractive index is 1.000, the enhanced negative Goos-Hanchen shift of the continuum quasi-bound state obtained at around 5° is as high as 10280 times the resonance wavelength.

[0089] When the ambient refractive index changes slightly from 1.000 to 1.003, the negative Goos-Hanchen shift angular spectrum shifts significantly to smaller incident angles. The sensitivity of the sensor can be defined by the Goos-Hanchen shift and the change in the ambient refractive index, that is:

[0090]

[0091] Where S represents sensitivity, dS GH represents the Goos-Hanchen shift change, and dn represents the ambient refractive index change. When the ambient refractive index changes from 1 to 1.001, the negative Goos-Hanchen shift change at an incident angle of about 5° is 9561 times the resonant wavelength, and the sensor sensitivity 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 Gous-Hanchen shift which is only several times of 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 of 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 Gous-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 climate monitoring, biochemical detection and other fields 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 the 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, 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.

[0099] In operation S3, a positive and negative Goos-Hanchen shift angular spectrum is calculated based on the angular reflection 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. The ambient refractive index can be monitored by observing the Goos-Hanchen shift fluctuation caused by the ambient refractive index change.

[0101] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions. It can be understood by those skilled in the art that the features recorded in the various embodiments of the present invention can be combined and / or combined in various ways, even if such a combination or combination is not explicitly recorded in the present invention. In particular, without departing from the spirit and teachings of the present invention, the features recorded in the various embodiments of the present invention can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present invention.

[0102] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination advantageously. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. An environmental refractive index sensor based on enhanced positive and negative Goos-Hanchen shifts, characterized in that: The sensor comprises: substrate; A Bragg reflector, a top layer and a double grating are sequentially stacked on the substrate; The double grating is formed by a unit structure composed of two identical grating strips arranged periodically, and the width of the air channel between the two grating strips is different from the width of the air channels 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-vertical angle, the double grating 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.

2. The sensor according to claim 1, characterized in that The Bragg reflector is formed by periodically arranging two materials with different refractive indexes, wherein the refractive index of one material is higher than the refractive index threshold, and the refractive index of the other material is lower than the refractive index threshold; The top layer on the upper part of the Bragg reflector can destroy the translational symmetry of the Bragg reflector, thereby forming an optical resonance cavity to excite Bloch surface waves on the surface of the Bragg reflector.

3. The sensor according to claim 1, characterized in that The width of the air channel between the two grating strips in the double grating is adjustable. By adjusting the width of the air channel between the two grating strips, the asymmetry degree of the unit structure can be adjusted.

4. The sensor according to claim 2, characterized in that The material above the refractive index threshold in the Bragg reflector includes GaAs, with a thickness d H =199nm.

5. The sensor according to claim 2, characterized in that The material below the refractive index threshold in the Bragg reflector includes AlGaAs, with a thickness d L =235nm.

6. The sensor according to claim 2, characterized in that The material of the top layer includes GaAs, with a thickness of d T =130nm.

7. The sensor according to claim 2, characterized in that The double grating material includes GaAs, the period Λ=288nm, the width w=43nm, and the thickness d G =140nm.

8. The sensor according to claim 2, characterized in that The width of the air channel between two grating strips in the double grating is d=91 nm.

9. The sensor according to claim 2, characterized in that The substrate material includes GaAs, with a thickness of d S =5um.

10. A method for monitoring environmental refractive index based on enhanced positive and negative Goos-Hanchen shifts, applied to the sensor according to any one of claims 1 to 9, 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 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; 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-Hanchen shift angular spectrum is calculated, wherein the Goos-Hanchen shift is proportional to the partial derivative of the reflection phase with respect to the incident angle θ; When the ambient refractive index changes, the Goos-Hanchen shift near the resonance peak incident angle will change dramatically. The ambient refractive index can be monitored by observing the Goos-Hanchen shift fluctuation caused by the change in ambient refractive index.

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