CN113552072B - Optical sensor based on total reflection enhancement mechanism - Google Patents
Optical sensor based on total reflection enhancement mechanism Download PDFInfo
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- CN113552072B CN113552072B CN202110398466.1A CN202110398466A CN113552072B CN 113552072 B CN113552072 B CN 113552072B CN 202110398466 A CN202110398466 A CN 202110398466A CN 113552072 B CN113552072 B CN 113552072B
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/19—Dichroism
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/21—Polarisation-affecting properties
- G01N2021/216—Polarisation-affecting properties using circular polarised light
Abstract
The invention discloses an optical sensor based on a total reflection enhancement mechanism, which comprises a substrate, a double-layer super-structure surface and a medium spacing layer, wherein the super-structure surface is a metal nano-structure body, the two metal nano-structure bodies are respectively positioned on the upper surfaces of two opposite planes of the medium spacing layer, the two metal nano-structure bodies can rotate relatively, and the medium spacing layer is arranged above the substrate; when the circularly polarized light is incident from the substrate direction, the incident angle is larger than the critical angle and is not 0 degrees and not 90 degrees, the incident angle is the included angle between the incident light direction and the substrate vertical direction, and the circularly polarized light is totally reflected on the interface between the double-layer super-structure surface and the air. The invention has simple structure and greatly reduces the processing difficulty; the change of the characteristics such as the refractive index, the concentration, the chiral characteristic and the like of the external environment can be judged by utilizing the change of the resonant frequency of the external chiral response and the circular dichroism amplitude, and the method can be expanded to the fields of online optical detection, biological sensing and the like.
Description
Technical Field
The invention belongs to the field of optical sensors, and relates to an optical sensor based on a total reflection enhancement mechanism, which is mainly used for sensing and measuring refractive index, concentration, chiral characteristics and the like of an external environment.
Background
The sensor is a detection device which can sense the measured information and convert the sensed information into an electric signal or other information in a required form according to a certain rule to output so as to meet the requirements of information transmission, processing, storage, display, recording, control and the like. Optical sensors perform measurements on the basis of optical principles, which have many advantages such as non-contact and non-destructive measurements, little interference, high-speed transmission, and the possibility of remote sensing, remote control, etc.
The metamaterial is an artificial material consisting of structural units with characteristic dimensions far smaller than the working wavelength, and has extraordinary physical properties which are not possessed by natural materials. The optical metamaterial is one of important branches of the metamaterial, has freely designed electromagnetic characteristics, and has great potential in the application aspects of devices with special functions, such as holography, super-diffraction limit resolution, polarization conversion and the like.
The chiral material can control circularly polarized electromagnetic waves, but the cross-coupling efficiency between an electric field and a magnetic field in a natural chiral material is weak, and the chiral metamaterial can improve the cross-coupling efficiency and greatly improve the polarization control characteristics of the material, such as circular dichroism, optical rotation and the like. The active optical chiral metamaterial can be applied to novel optical sensors, modulators, optical switches and the like. Circular dichroism refers to the property of a metamaterial that its absorption properties for left-handed circularly polarized light and right-handed circularly polarized light are different, resulting in different transmittances. This property can be used to determine the asymmetric structure of the molecule, etc.
Disclosure of Invention
Aiming at the prior art, the invention aims to provide a novel optical sensor based on a total reflection enhancement mechanism, which has a simple structure and is convenient to manufacture.
In order to solve the technical problem, the optical sensor based on the total reflection enhancement mechanism comprises a substrate, a double-layer super-structure surface and a medium spacing layer, wherein the super-structure surface is a metal nano-structure body, the two metal nano-structure bodies are respectively positioned on the upper surfaces of two opposite planes of the medium spacing layer, the two metal nano-structure bodies can rotate relatively, and the medium spacing layer is arranged above the substrate; when the circularly polarized light is incident from the substrate direction, the incident angle is larger than the critical angle and is not 0 degrees and not 90 degrees, the incident angle is the included angle between the incident light direction and the substrate vertical direction, and the circularly polarized light is totally reflected on the interface between the double-layer super-structure surface and the air.
The invention also includes:
1. the coupling strength of the sensor can be changed by adjusting the rotation angle and the separation distance between the two metal nanostructures.
2. The optical sensor judges the changes of the refractive index, the concentration and the chiral characteristic by using the change of the resonant frequency of the external chiral response or the circular dichroism amplitude.
3. The dielectric spacing layer is made of silicon dioxide, magnesium fluoride or zinc oxide.
4. The substrate is made of quartz glass or silicon nitride.
The invention has the beneficial effects that: the invention relates to a novel optical sensor for sensing and measuring the change of an external environment by utilizing a total reflection enhancement mechanism. Because the sensitivity of evanescent waves generated by total reflection to the environment change of the air interface is simply utilized to sense, the changes of the characteristics such as the refractive index, the concentration, the chiral characteristic and the like of the external environment can be judged according to the changes of the resonant frequency of the external chiral response and the circular dichroism amplitude. The novel optical sensor based on the total reflection enhancement mechanism can easily optimize the system performance by adjusting the incident angle and the azimuth angle of incident circularly polarized light to obtain the optimal external chiral response enhancement effect. The novel optical sensor based on the total reflection enhancement mechanism can change system performance parameters through simple adjustment, has a simple structure, is convenient to manufacture, and can be expanded to the fields of online optical detection, biosensing and the like.
The invention has simple structure and greatly reduces the processing difficulty; the change of the characteristics such as the refractive index, the concentration, the chiral characteristic and the like of the external environment can be judged by utilizing the change of the resonance frequency of the external chiral response and the circular dichroism amplitude, and the method can be expanded to the fields of online optical detection, biological sensing and the like. The interlayer coupling strength of the metal nanostructure can be adjusted by simply changing the thickness of the dielectric spacer layer.
Drawings
FIG. 1 (a) is a cell geometry for a novel optical sensor;
FIG. 1 (b) is a front view of the cell geometry of the novel optical sensor;
FIG. 1 (c) is a top view of the cell geometry of the novel optical sensor;
FIG. 2 is a schematic diagram of circularly polarized light incidence;
FIG. 3 is a simulated reflectance spectrum of the novel optical sensor;
FIG. 4 is a circular dichroism spectrum of the novel optical sensor;
FIG. 5 is a schematic view of a dielectric layer overlying a sensor;
fig. 6 is a graph of simulation results of measuring refractive indices of different dielectric layers.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The novel optical sensor based on the total reflection enhancement mechanism can utilize strong outward circular dichroism to develop sensing application, and the novel optical sensor consists of a substrate, a double-layer super-structure surface and a medium spacing layer. The double-layer super-structure surface is composed of two metal nano-structures which are periodically distributed, the two metal nano-structures are respectively positioned on the upper side and the lower side of the medium spacing layer, and a rotation angle exists between the two metal nano-structures, so that a rotation structure body is formed. When the circularly polarized light is incident from the substrate direction at an azimuth angle which is not 0 degrees and is not 90 degrees and the incident angle is larger than the critical angle, the circularly polarized light is totally reflected at the interface between the double-layer super-structure surface and the air, no transmission signal exists, very strong reflecting circular dichroism is generated at the moment, and the change of the external environment can be detected by utilizing the change of the circular dichroism amplitude value.
The total reflection enhancement mechanism refers to total reflection generated on a double-layer super-structure surface and an air interface, and the optical sensor has no transmission signal under the condition of large-angle incidence, so that chiral response of the total reflection enhancement mechanism is formed.
The double-layer super-structure surface is composed of two metal nano structures, a structure rotation angle exists between the two metal nano structures, and the coupling strength of the sensor can be changed by adjusting the rotation angle and the spacing distance between the upper metal nano structure and the lower metal nano structure.
The medium spacing layer is mainly used for bearing the metal nano structure, the thickness change of the medium spacing layer can adjust the interlayer coupling strength of the metal nano structure, and the medium spacing layer can be made of silicon dioxide, magnesium fluoride, zinc oxide and other media.
The substrate is used for supporting the whole structure, and the material of the substrate can be quartz glass, silicon nitride and the like.
Incident circular polarized light is incident at an azimuth angle of not 0 degrees or not 90 degrees, which means that the direction of the incident circular polarized light cannot coincide with the directions of the two metal nanostructures, and at the moment, a system formed by the double-layer super-structure surface and the incident wave vector cannot coincide with the mirror image of the system, so that the system shows strong exo-chiral response.
The external chiral optical response depends on the incident angle and azimuth angle of incident circularly polarized light, and the optimal external chiral response enhancement effect can be obtained by optimizing the system performance. The incident angle and azimuth angle of incident circularly polarized light are adjusted, and the optimal external chiral response enhancement effect can be obtained by optimizing the system performance.
The sensitivity of evanescent waves generated by total reflection to the change of the air interface environment is sensed.
The change of the characteristics such as the refractive index, the concentration, the chiral characteristic and the like of the external environment can be judged by utilizing the change of the resonant frequency of the external chiral response and the circular dichroism amplitude, and the sensor can be expanded to the fields of online optical detection, biological sensing and the like.
Since the novel optical sensor is a sub-wavelength structure, the thickness of the structure can be ignored in practical application.
With reference to fig. 1 (a), 1 (b) and 1 (c), fig. 1 (a) is a cell geometry of the sensor, fig. 1 (b) is a front view of the cell geometry, and fig. 1 (c) is a top view of the cell geometry. Wherein 1 is a rotating structure body formed by two metal nano structures, one of which is positioned at the top of the medium 2, and the other is positioned at the bottom of the medium 2, and gold is adopted as a material of the metal nano structures. The Au nanostructure has a length of 240nm, a width of 50nm and a thicknessThe degree is set to 30nm, the rotation angle of the two nanostructures is 90 °, and the separation distance between the two metal nanostructures is 150nm.2 is a dielectric layer and adopts MgF 2 The dielectric layer is set to be 300nm in length and width and 180nm in thickness. The dielectric layer mainly plays a role in bearing the metal nano structure and fixing the metal nano structure. And 3, taking glass as a substrate of the structure, setting the length and the width of the glass substrate to be 300nm, forming a cube by the dielectric layer and the substrate, and enabling the substrate to be equivalent to a base of the structure. Incident light is made to enter from the substrate direction, and the included angle between the incident light direction and the vertical direction of the sensor is 70 degrees, as shown in fig. 2, we can observe that light is totally reflected, the incident light is right-handed polarized light, and the reflected light is left-handed polarized light. The reflection spectrum obtained by simulation using CST is shown in FIG. 3, wherein R ++ Denotes the reflection coefficient, R, of a right-hand polarized wave +- Denotes the circular cross-polarized reflection coefficient, R -+ Denotes the circular cross-polarized reflection coefficient, R -- Indicating the left-hand circularly polarized reflection coefficient. Observing fig. 3, it can be seen that the reflection curves of the left-handed polarized wave and the right-handed polarized wave are always coincident. The circular cross-polarization reflection curve shows two distinct resonance peaks, which appear at 221THz and 341THz, respectively. In order to more intuitively study the circular dichroism of the material, the calculation formula of the circular dichroism is delta R = R -+ -R +- The circular dichroism spectrum of the obtained material is shown in figure 4. Observing fig. 4, it can be seen that there are two distinct extrema for circular dichroism. At 221THz, the circular dichroism reaches negative 0.5498. At 341THz, the value of circular dichroism is 0.4301. It is shown that at these two frequencies, the polarization conversion effect of the structure is the best.
Looking at fig. 5, we add the analyzed dielectric layer 4 to the sensor unit structure, and we get the simulation result shown in fig. 6 by simulating dielectric layers with different refractive indexes. As can be seen from fig. 6, the maximum values of the amplitudes of the circular dichroism curves of the medium layers having different refractive indexes are different, and the frequency value points at which the circular dichroism takes the extreme values are also different. Therefore, we can measure the refractive index of the medium by detecting the change of the resonance frequency and the change of the circular dichroism amplitude.
Claims (5)
1. An optical sensor based on a total reflection enhancement mechanism, characterized in that: the metamaterial comprises a substrate, a double-layer metamaterial surface and a dielectric spacing layer, wherein the metamaterial surface comprises two metal nanostructures which are perpendicular to each other, the first metal nanostructure is positioned at the top of the dielectric spacing layer, the second metal nanostructure is positioned at the bottom of the dielectric spacing layer, and the dielectric spacing layer is arranged above the substrate; when circularly polarized light is incident from the substrate direction, the incident angle is larger than the critical angle and is not 0 degrees and not 90 degrees, the incident angle is the included angle between the incident light direction and the substrate vertical direction, and the circularly polarized light is totally reflected on the interface between the double-layer super-structure surface and the air; the height interval distance between the first metal nanostructure and the second metal nanostructure is 150nm; the first metal nanostructure and the second metal nanostructure are both strip-shaped; the length is 240nm, the width is 50nm, and the thickness is 30nm; the length and width of the dielectric spacing layer are 300nm, and the thickness is 180nm; the length and width of the substrate were 300nm.
2. An optical sensor based on a total reflection enhancement mechanism according to claim 1, characterized in that: the coupling strength of the sensor can be changed by adjusting the rotation angle and the separation distance between the two metal nanostructures.
3. An optical sensor based on a total reflection enhancement mechanism according to claim 1 or 2, characterized in that: the optical sensor judges the changes of refractive index, concentration and chiral characteristics by using the change of the resonant frequency of the external chiral response or the circular dichroism amplitude.
4. An optical sensor based on a total reflection enhancing mechanism according to claim 1 or 2, characterized in that: the dielectric spacing layer is made of silicon dioxide, magnesium fluoride or zinc oxide.
5. An optical sensor based on a total reflection enhancement mechanism according to claim 1 or 2, characterized in that: the substrate is made of quartz glass or silicon nitride.
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