Broadband Tunable Refractive Index Sensor and Detection System Based on the PIT Effect

Abstract

The invention provides a wide-band tunable refractive index sensor and detection system based on the PIT effect, comprising: a silicon dioxide substrate, a grating layer, a calcium difluoride spacer layer and a bias voltage-controlled two-dimensional material film layer arranged in sequence from bottom to top; a sample area for placing an object to be tested is arranged on the upper surface of the two-dimensional material film layer; under the action of an incident light beam, the grating layer exhibits a bright mode, and the two-dimensional material film layer exhibits a dark mode; the grating layer and the two-dimensional material film layer waveguide are combined to achieve bright and dark mode coupling, generate a PIT effect, and form a dynamically tunable transparent window; the invention has the beneficial effect of dynamic tuning and is suitable for the technical field of optical sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of optical sensors, and particularly to a broadband tunable refractive index sensor and a detection system based on the PIT effect. Background Art

[0002] Refractive index sensors have the advantages of real-time monitoring, label-free detection of biomolecules to be detected, high measurement accuracy, easy operation, and small detection error, and are widely used in the fields of environmental monitoring, food safety, biomedical detection, chemical processing, etc. With the increasing requirements for the volume of sensors, the working environment, and ease of operation, it is very important to realize a refractive index sensor with small size, high sensing accuracy and sensitivity, and broadband dynamic tunability.

[0003] However, once the current passive sensors based on optical resonance structures are fabricated, it is very difficult to regulate them through external excitation, resulting in their inability to achieve dynamic regulation of the sensing band. In this case, the sensing bandwidth of the sensor is very narrow and cannot meet the actual requirements for a wide sensing bandwidth. In addition, for surface plasmon sensors made of metal microstructures, there are large ohmic losses, strong radiative damping leads to a wide resonance linewidth, low detection accuracy, and poor practicability. Summary of the Invention

[0004] In order to solve the above technical problems existing in the prior art, the present invention provides a broadband tunable refractive index sensor and a detection system based on the PIT effect, and solves the technical problems of inflexible tuning, limited resonance band, and low sensitivity of refractive index sensors in the prior art.

[0005] The present invention provides a broadband tunable refractive index sensor based on the PIT effect, including: a silica substrate, a grating layer, a calcium fluoride spacer layer, and a two-dimensional material thin film layer controlled by a bias voltage, which are sequentially arranged from bottom to top;

[0006] A sample area for placing a test substance is provided on the upper surface of the two-dimensional material thin film layer;

[0007] Under the action of an incident light beam, the grating layer exhibits a bright mode, the two-dimensional material thin film layer exhibits a dark mode, and the waveguide combination of the grating layer and the two-dimensional material thin film layer realizes bright-dark mode coupling, generates the PIT effect, and forms a dynamically tunable transparent window.

[0008] Optionally, the grating layer is composed of periodically arranged grating structures, and each grating structure includes: a slit and a metal spacer;

[0009] The width W of the slit is 180 nm; the period P of the grating structure is 250 nm; the thickness t of the grating structure is 10 nm.

[0010] Optionally, the material of the metal spacer is gold, silver or sodium.

[0011] Optionally, the material of the two-dimensional material thin film layer is borophene.

[0012] Optionally, the conductivity of the borophene is expressed by the Drude model as:

[0013]

[0014]

[0015] In formula (1), j is the optical axis of the borophene crystal, ω is the angular frequency of the incident light, and τ is the electron relaxation time; D j is the weight;

[0016] In formula (2), e is the electron charge, m j is the effective electron mass in the two crystal axis directions, and n s is the electron concentration. Under the control of the bias voltage, the electron concentration of the borophene can be adjusted.

[0017] Optionally, the thickness d of the calcium fluoride spacer layer is 150 nm.

[0018] The present invention also provides a wide-band tunable refractive index detection system based on the PIT effect, including: a refractive index sensor, an incident light beam generating device, and a signal processing device; the refractive index sensor is the refractive index sensor as described above;

[0019] The refractive index sensor is respectively connected to the incident light beam generating device and the signal processing device.

[0020] Optionally, the incident light beam generating device emits an incident light beam in the same polarization direction.

[0021] Optionally, the signal processing device is a spectral analyzer.

[0022] Optionally, when the incident light beam irradiates the object to be measured in the sample area through the silica substrate, the grating layer, the calcium fluoride spacer layer, and the two-dimensional material thin film layer:

[0023] The signal processing device measures the transmission spectrum of the object to be measured with different refractive indices according to the absorption of surface plasmon resonance for a specific light wavelength, and determines the refractive index of the object to be measured; and obtains the sensitivity characteristics of the refractive index sensor according to the change of the transmission spectrum of the object to be measured with different refractive indices.

[0024] The advantages of the technical solution provided by this application are as follows:

[0025] 1. In this application, by adjusting the bias voltage, the electron concentration of the two-dimensional material thin film layer can be changed, causing changes in the position and size of the PIT spectrum (transparent window). At the same time, using the coupling structure between the grating layer and the two-dimensional material thin film layer, the sensing bandwidth of the sensor can be dynamically regulated in the near-infrared band, with extremely strong practicality.

[0026] 2. In the detection system of this application, during detection, only the object to be measured (gas or liquid analyte) needs to be placed in the sample area on the surface of the refractive index sensor for detection, which is convenient for sample measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 is a schematic structural diagram of a broadband tunable refractive index sensor based on the PIT effect provided by an embodiment of the present invention;

[0029] Figure 2 is a schematic circuit diagram of a broadband tunable refractive index detection system based on the PIT effect provided by an embodiment of the present invention;

[0030] Figure 3 is a refractive index transmission spectrogram of different objects to be measured provided by an embodiment of the present invention;

[0031] Figure 4 is a sensitivity schematic diagram of a refractive index sensor under different electron concentrations and different refractive indices provided by an embodiment of the present invention;

[0032] In the figure:

[0033] 1 is a refractive index sensor, 2 is a signal processing device, 3 is a light source, 4 is a first optical fiber, 5 is a first lens, 6 is a first polarizer, 7 is a first aperture;

[0034] 41 is a second optical fiber, 51 is a second lens, 61 is a second polarizer;

[0035] 10 is a silicon dioxide substrate, 20 is a grating layer, 30 is a calcium fluoride spacer layer, 40 is a two-dimensional material thin film layer, 50 is a bias voltage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Electromagnetically induced transparency (EIT) stems from the quantum interference effect in a laser-driven three-level atomic system, generating a narrow transparent window over a wide absorption spectral range; the EIT effect is usually accompanied by extreme optical dispersion, which significantly reduces the group velocity of light and enhances optical nonlinearity. However, realizing traditional quantum EIT in an atomic system generally requires harsh experimental conditions. To break these limitations, metamaterials have been designed to achieve an EIT-like effect, also known as surface plasmon-induced transparency (PIT); PIT can be obtained through direct destructive interference between a bright mode and a dark mode or the detuning of two bright modes; in recent years, many PIT systems have been proposed, including optical sensors, optical switches, and optical storage, etc.

[0037] Based on the PIT effect, this application designs a broadband tunable refractive index sensor and detection system based on the PIT effect, which has high sensing sensitivity and a wide detection range, and can be used for the determination of a series of chemical substances and biomolecules, and has good application prospects in the fields of biosensing and chemical substance detection, etc.

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] Embodiment 1

[0040] Refer to Figure 1 , a broadband tunable refractive index sensor based on the PIT effect, comprising: a silica substrate 10, a grating layer 20, a calcium fluoride spacer layer 30, and a two-dimensional material thin film layer 40 controlled by a bias voltage 50, which are sequentially arranged from bottom to top;

[0041] A sample area for placing a test substance is arranged on the upper surface of the two-dimensional material thin film layer 40;

[0042] Under the action of an incident light beam, the grating layer 20 exhibits a bright mode, and the two-dimensional material thin film layer 40 exhibits a dark mode. The grating layer 20 and the two-dimensional material thin film layer 40 are waveguide combined to achieve bright-dark mode coupling, generate the PIT effect, and form a dynamically tunable transparent window.

[0043] It should be noted that under the action of the incident light beam, strong local surface plasmon resonance is excited at the slit 201 of the grating layer 20, causing strong radiative loss of the signal light and forming a transmission spectrum, so that the grating layer 20 exhibits a bright mode; in the two-dimensional material thin film layer 40 itself, due to the large wave vector mismatch, it cannot be directly excited by the incident light and requires the grating layer to provide wave vector compensation, so that the conduction mode on the two-dimensional material thin film layer 40 can be excited, which exhibits a dark mode; the surface PIT effect occurs through hybrid coupling between the bright and dark modes, forming a dynamically tunable transparent window.

[0044] After the structural dimensions of the sensor are determined, the traditional sensor geometry is not easy to change, and dynamic regulation of the sensing band cannot be achieved. Therefore, the sensing bandwidth of the sensor is very narrow and cannot meet the actual requirements for a wide sensing bandwidth.

[0045] In this application, by adjusting the bias voltage 50, the electron concentration of the two-dimensional material thin film layer 40 can be changed, causing changes in the position and size of the PIT spectrum (transparent window); at the same time, this application uses the coupling structure between the grating layer 20 and the two-dimensional material thin film layer 40 to enable dynamic regulation of the sensing bandwidth of the sensor in the near-infrared band, with extremely strong practicality.

[0046] Embodiment 2

[0047] Based on the wide-band tunable refractive index sensor based on the PIT effect in Embodiment 1, the grating layer 20 is composed of a periodically arranged grating structure, and each grating structure includes: a slit 201 and a metal spacer 202;

[0048] The width W of the slit 201 is 180 nm; the period P of the grating structure is 250 nm; the thickness t of the grating structure is 10 nm.

[0049] It should be noted that the material of the metal spacer 202 is gold, silver or sodium; in addition, the material of the metal spacer 202 can also be other surface plasmon materials with metal characteristics, such as doped semiconductors, transparent conductive oxides, etc.

[0050] It should be noted that the material of the two-dimensional material thin film layer 40 is borophene; in addition, the material of the two-dimensional material thin film layer 40 can also be two-dimensional materials such as transition metal sulfides.

[0051] It should be noted that the conductivity of the borophene is expressed by the Drude model as:

[0052]

[0053]

[0054] In Equation (1), j is the optical axis of the borophene crystal, ω is the angular frequency of the incident light, and τ is the electron relaxation time; D j is the weight;

[0055] In Equation (2), e is the electron charge, and m j is the effective electron mass in the two crystal axis directions, and n s is the electron concentration, which can be adjusted under the control of the bias voltage to regulate the electron concentration of borophene.

[0056] In this embodiment, the optical axis of the borophene crystal can be selected as the x-axis or the y-axis, and the initial value of τ can be set to 65 fs;

[0057] The effective electron masses in the two crystal axis directions can be respectively: m x = 1.4m0, m y = 3.4m0, where m0 is the rest mass of the standard electron.

[0058] It should be noted that the thickness d of the calcium fluoride spacer layer 30 is 150 nm.

[0059] In addition, the present application also provides a wide-band tunable refractive index detection system based on the PIT effect.

[0060] Referring to Figure 2 , a wide-band tunable refractive index detection system based on the PIT effect includes: a refractive index sensor 1, an incident light beam generating device, and a signal processing device 2;

[0061] The refractive index sensor 1 is the refractive index sensor as described above;

[0062] The refractive index sensor 1 is respectively connected to the incident light beam generating device and the signal processing device 2.

[0063] It should be noted that the incident light beam generating device emits an incident light beam in the same polarization direction; the signal processing device 2 is a spectral analyzer.

[0064] In this embodiment, the incident light beam generating device includes: a light source 3, a first optical fiber 4, a first lens 5, a first polarizer 6, and a first aperture 7;

[0065] During use, the light beam generated by the light source 3 through the first optical fiber 4 is expanded by the first lens 5 and polarized by the first polarizer 6, and then the almost uniform polarized light in the center of the light spot is selected by the first aperture 7 to pass through; the polarized light emitted from the first aperture 7 is the incident light beam;

[0066] The light emitted after the incident light beam passes through the refractive index sensor 1 passes through an outgoing light beam generating device to generate an outgoing light beam. The outgoing light beam generating device includes: a second polarizer 61, a second lens 51, and a second optical fiber 41. The outgoing light beam is transmitted to a spectral analyzer so that the spectral analyzer performs spectral analysis on the outgoing light beam.

[0067] It should be noted that when the incident light beam irradiates the object to be measured on the sample area through the silica substrate 10, the grating layer 20, the calcium fluoride spacer layer 30, and the two-dimensional material thin film layer 40:

[0068] The signal processing device 2 measures the transmission spectra of objects to be measured with different refractive indices according to the absorption of surface plasmon resonance for specific light wavelengths, and judges the refractive index of the object to be measured; and obtains the sensitivity characteristics of the refractive index sensor according to the changes in the transmission spectra of objects to be measured with different refractive indices.

[0069] In this embodiment, air (refractive index of 1.00), water (refractive index of 1.33), ethanol (refractive index of 1.361), glycerol (refractive index of 1.473), and a high refractive index matching liquid (refractive index of 1.636) are respectively selected as samples for transmission spectrum detection.

[0070] See Figure 3 , the PIT effect occurs in the near-infrared band. As the refractive index of the object to be measured increases, the resonance wavelength moves successively to longer wavelengths, that is, the red shift phenomenon; it can be seen from this that changing the refractive index of the object to be measured can change the spectral position, thereby obtaining the sensitivity characteristics of the refractive index sensor in this application; at the same time, through the sensitivity characteristics, various samples can be detected and identified according to the properties of the refractive indices of different objects to be measured, so that the application value of sensing can be realized.

[0071] This application also gives the transmission spectra of the refractive index changes of the object to be measured under different electron concentrations of the two-dimensional material thin film layer, as well as the sensitivity and linear correlation coefficient schematic diagrams of the refractive index sensor under different electron concentrations.

[0072] See Figure 4 , the abscissa represents the change in the refractive index of the object to be measured, and the ordinate represents the resonance wavelength at the PIT resonance peak position. The three lines shown respectively take the boronene electron concentration as: 5.4×10 -19 m -2 、8.8×10 -19 m -2 、12.2×10 - 19 m -2 .

[0073] In this application, the sensitivity of the refractive index sensor refers to the ratio S of the output change Δλ to the input change Δn of the refractive index sensor under stable working conditions, which can be obtained by the following formula:

[0074] S = Δλ / Δn (3);

[0075] In formula (3), Δλ is the difference in wavelengths corresponding to the PIT resonance peaks of the objects to be measured with different refractive indices, Δn is the difference in refractive indices of the objects to be measured, and the static sensitivity S of the refractive index sensor is a constant.

[0076] From formula (3), we can see that Figure 4 The slope of the straight line is the sensitivity of the refractive index sensor of this application. In the refractive index range of 1-1.7, the electron concentration is 5.4×10 -19 m -2 When the sensitivity of the refractive index sensor is S = 601nm / RIU, the linear correlation coefficient R 2 =0.99855, indicating that the peak wavelength and the refractive index have a good linear relationship;

[0077] Similarly, the electron concentration is 8.8×10 -19 m -2 When the sensitivity of the refractive index sensor is S = 498nm / RIU, the linear correlation coefficient R 2 =0.99823;

[0078] The electron concentration is 12.2×10 -19 m -2 When the sensitivity of the refractive index sensor is S = 438nm / RIU, the linear correlation coefficient R 2 =0.99752;

[0079] It can be seen from this that the refractive index sensor provided in the present application has a maximum sensitivity of up to 601nm / RIU; it has high sensing sensitivity and a wide detection range, can be used for the determination of a series of chemical substances and biological molecules, and has good application prospects in the fields of biosensing and chemical substance detection.

[0080] In summary, the wide-band tunable refractive index sensor and detection system based on the PIT effect provided by the present application, the resonance wavelength of the surface plasmon of the two-dimensional material thin film layer is tunable in the near-infrared band. Therefore, the refractive index sensor based on the present invention can have a good application prospect in the detection of biological molecules and chemical substances in the near-infrared band.

[0081] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0082] In the present invention, unless otherwise clearly specified and defined, terms such as "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0083] In addition, those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0084] As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A broadband tunable refractive index sensor based on the PIT effect, characterized in that Including: A silicon dioxide substrate (10), a grating layer (20), a calcium fluoride spacer layer (30), and a two-dimensional material thin film layer (40) controlled by a bias voltage (50), which are arranged successively from bottom to top; A sample area for placing a test object is arranged on the upper surface of the two-dimensional material thin film layer (40); Under the action of an incident light beam, the grating layer (20) exhibits a bright mode, the two-dimensional material thin film layer (40) exhibits a dark mode, and the grating layer (20) and the two-dimensional material thin film layer (40) are waveguide combined to achieve bright-dark mode coupling, generate a PIT effect, and form a dynamically tunable transparent window; The grating layer (20) is composed of periodically arranged grating structures, and each grating structure includes: a slit (201) and a metal spacer (202); The width W of the slit (201) is 180 nm; the period P of the grating structure is 250 nm; the thickness t of the grating structure is 10 nm; The material of the two-dimensional material thin film layer (40) is borophene; The conductivity of the borophene is expressed by the Drude model as: （1）； （2）； In formula (1), j is the optical axis of the borophene crystal, ω is the angular frequency of the incident light, and τ is the electron relaxation time; is the weight; In formula (2), e is the electron charge, is the effective electron mass in the directions of two crystal axes, is the electron concentration, which can be adjusted under the control of the bias voltage to regulate the electron concentration of borophene.

2. The broadband tunable refractive index sensor based on the PIT effect according to claim 1, characterized in that The material of the metal spacer (202) is gold, silver or sodium.

3. The broadband tunable refractive index sensor based on the PIT effect according to claim 1, characterized in that, The thickness d of the calcium fluoride spacer layer (30) is 150 nm.

4. A wide-band tunable refractive index detection system based on the PIT effect, characterized in that Including: A refractive index sensor (1), an incident light beam generating device, and a signal processing device (2); The refractive index sensor (1) is the refractive index sensor according to any one of claims 1 to 3; The refractive index sensor (1) is respectively connected to the incident light beam generating device and the signal processing device (2).

5. The broadband tunable refractive index detection system based on the PIT effect according to claim 4, characterized in that, The incident light beam generating device emits an incident light beam in the same polarization direction.

6. The broadband tunable refractive index detection system based on the PIT effect according to claim 4, wherein The signal processing device (2) is a spectral analyzer.

7. The broadband tunable refractive index detection system based on the PIT effect according to claim 5, wherein When the incident light beam irradiates the test object on the sample area through the silicon dioxide substrate (10), the grating layer (20), the calcium fluoride spacer layer (30), and the two-dimensional material thin film layer (40): The signal processing device (2) measures the transmission spectrum of test objects with different refractive indices according to the absorption of surface plasmon resonance for a specific light wavelength, judges the refractive index of the test object; and obtains the sensitivity characteristic of the refractive index sensor (1) according to the change of the transmission spectrum of test objects with different refractive indices.

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