Composite superstructure surface infrared refractive index sensing system

Abstract

The invention discloses a composite superstructure surface infrared refractive index sensing system, and relates to the technical field of infrared sensing. The system comprises a first metasurface, a medium separation layer, a second metasurface and an infrared detector which are sequentially arranged in the positive direction of an optical axis by taking the direction of vertically downward incident infrared electromagnetic waves as the positive direction of the optical axis; the first metasurface and the second metasurface are respectively arranged on the upper surface and the lower surface of the dielectric separation layer; the infrared detector is arranged on a focal plane of a focusing light spot of the second metasurface; the first metasurface is a resonance type metasurface; and the second metasurface is a phase type metasurface. The detection rate of the refractive index sensing system is increased.

Description

Technical Field

[0001] The present invention relates to the field of infrared sensing technology, and in particular to a composite metasurface infrared refractive index sensing system. Background Art

[0002] Optical refractive index sensing technology is a technology that detects the refractive index of the target material as it changes with its temperature, concentration and other parameters and maps it to the target state. It has the advantages of high sensitivity, non-destructive, real-time, and label-free. It is particularly suitable for trace substance detection and has very important application value in medical diagnosis, environmental testing, biometrics and other fields. The basic principle of infrared optical refractive index sensing is to sense the refractive index by detecting the absorption of the infrared spectrum transmitted and reflected by the measured object, the peak position shift of the resonance peak or the intensity change. This requires the device to be sensitive to changes in the refractive index and have a narrow response bandwidth at the resonant wavelength to achieve rapid changes in the intensity of the response spectrum line. It is often necessary to be equipped with a high-performance infrared spectrometer to detect weak changes in the infrared spectrum.

[0003] The performance of optical refractive index sensors is extremely dependent on the material and structure of the sensor. Due to its advantages in refractive index sensitivity and spectral width control, metasurface sensors have become a feasible and reliable way to improve the performance of infrared refractive index sensing. By introducing subwavelength-scale micro-nanostructure arrays, the spectral response characteristics of the device can be effectively controlled by changes in the material, structure, arrangement and other parameters of the micro-nanostructures, thereby achieving efficient refractive index sensing. Inducing the occurrence of narrow-linewidth optical resonance modes with high quality factors of metasurfaces through methods such as symmetry breaking is an effective way to improve the refractive index sensing performance, but the refractive index sensor using this method also needs to be equipped with a high-precision infrared spectrometer to detect fine changes in the infrared spectrum, resulting in increased system complexity and cost. If the intensity change of a specific spectral line is detected, the response rate of the system will also be affected due to the weak intensity of the narrowband signal. Therefore, exploring efficient refractive index sensing system solutions that do not require an infrared spectrometer is of great significance to solving the above problems. Summary of the invention

[0004] In order to solve the problems existing in the existing metasurface refractive index sensing technology, the present invention provides a composite metasurface infrared refractive index sensing system, which converts the refractive index information into intensity information containing position information through two layers of metasurfaces. There is no need to detect changes in the infrared spectrum, which reduces the complexity of the refractive index sensing system. At the same time, the focusing of the light beam increases the system's weak signal detection capability and improves the sensing quality.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A composite metasurface infrared refractive index sensing system, the system comprising: a first metasurface, a dielectric separation layer, a second metasurface and an infrared detector are sequentially arranged along the positive direction of the optical axis, with the direction of the infrared electromagnetic wave incident vertically downward being the positive direction of the optical axis;

[0007] The first metasurface and the second metasurface are respectively arranged on the upper surface and the lower surface of the dielectric separation layer;

[0008] The infrared detector is arranged on the focal plane of the focused light spot of the second metasurface;

[0009] The first metasurface is a resonant metasurface; the second metasurface is a phase metasurface.

[0010] Optionally, the first metasurface is composed of a plurality of uniformly arranged sub-wavelength periodic micro-nano structures.

[0011] Optionally, the second metasurface is composed of non-uniformly arranged sub-wavelength micro-nano structures.

[0012] Optionally, the sub-wavelength micro-nano structures of the second metasurface are arranged according to a phase gradient function.

[0013] Optionally, the sub-wavelength periodic micro-nano structure includes a circular structure, a ring structure, a cross structure, a triangle structure and a polygonal structure.

[0014] Optionally, the sub-wavelength periodic micro-nano structure has a thickness ranging from 0.5 μm to 10 μm.

[0015] Optionally, the dielectric separation layer is a substrate composed of a material with high infrared transmittance.

[0016] Optionally, the material of the dielectric separation layer includes silicon, germanium, silicon dioxide, zinc sulfide, zinc selenide, calcium fluoride, magnesium fluoride, barium fluoride and lithium fluoride.

[0017] Optionally, the dielectric separation layer has a thickness ranging from 100 μm to 1000 μm.

[0018] Optionally, the size of the pixel of the infrared detector ranges from 10 μm to 100 μm.

[0019] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0020] The present invention discloses a composite metasurface infrared refractive index sensing system. Based on the design concept of efficient conversion and enhanced detection, the refractive index information is converted into intensity information containing position information on the infrared focal plane through two layers of metasurfaces with clear functions. This method only requires the detection of light intensity and distribution, and the refractive index information can be obtained without the infrared spectrometer to obtain the change of the spectrum, which reduces the complexity of the refractive index sensing system. At the same time, the focusing of the light beam increases the weak signal detection capability of the system and improves the sensing quality. The present invention realizes efficient sensing of infrared refractive index, simplifies the structural design of the refractive index sensing system, and has the advantages of being light and thin and easy to integrate, which is beneficial to improving detection stability and effectively reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a schematic diagram of the structure of the composite metasurface infrared refractive index sensing system of the present invention;

[0023] Figure 2 A schematic diagram of some possible shapes of the first metasurface of the present invention;

[0024] Figure 3 A schematic diagram of a specific structure of the first metasurface placed on the upper surface of the dielectric layer according to the present invention;

[0025] Figure 4 Another specific structural schematic diagram of the first metasurface placed on the upper surface of the dielectric layer according to the present invention;

[0026] Figure 5 The present invention Figure 3 A cross-sectional view of the structure of the first metasurface embodiment shown;

[0027] Figure 6 The transmission spectra of the first metasurface embodiment of the present invention under different refractive index conditions;

[0028] Figure 7 A schematic diagram of a unit structure of the second metasurface embodiment of the present invention;

[0029] Figure 8 Schematic diagram of the structure of the second metasurface embodiment of the present invention.

[0030] Description of the accompanying drawings:

[0031] Infrared detector—1, second metasurface—2, dielectric separation layer—3, first metasurface—4. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The purpose of the present invention is to provide a composite metasurface infrared refractive index sensing system, aiming to increase the detection rate of the refractive index sensing system.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] like Figure 1 As shown, the composite metasurface infrared refractive index sensing system in this embodiment includes: taking the direction of the infrared electromagnetic wave incident vertically downward as the positive direction of the optical axis, a first metasurface 4, a dielectric separation layer 3, a second metasurface 2 and an infrared detector 1 are arranged one by one along the positive direction of the optical axis.

[0037] The first metasurface 4 and the second metasurface 2 are respectively arranged on the upper surface and the lower surface of the dielectric separation layer 3 .

[0038] The infrared detector 1 is arranged on the focal plane of the focused light spot of the second metasurface 2 .

[0039] The first metasurface 4 is a resonant metasurface; the second metasurface 2 is a phase metasurface.

[0040] Specifically, the first metasurface 4 is a uniformly arranged sub-wavelength periodic micro-nanostructure array, the micro-nanostructure is composed of metal or dielectric materials, the optional materials of the micro-nanostructure are metal or dielectric materials, the optional metal materials include: gold, silver, copper, aluminum, titanium, chromium, nickel, tungsten and other materials, the optional dielectric materials include silicon, germanium, silicon dioxide, silicon nitride, titanium dioxide and other materials. The specific function of the first metasurface 4 is to efficiently sense the change of the refractive index of the environment and induce the generation of a narrow-band transmitted light signal with high sensitivity and high spectral resolution. Figure 2 , Figure 3 and Figure 4As shown, the first metasurface 4 array structure is a periodic array preferably composed of a circular, annular, cross, triangular, polygonal structure or a combination of the above structures, with a thickness of 0.5 μm to 10 μm and a unit structure period of 0.1 μm to 10 μm.

[0041] As a specific implementation method, Figure 3 The structure shown is an embodiment of the first metasurface 4. The material of the first metasurface 4 is low-loss infrared high-refractive-index material germanium to increase the ability to manipulate light and maintain low loss. Figure 5 As shown in the figure, the structural parameters of the unit size of the micro-nano structure array are as follows: the unit period P is 0.5μm to 10μm, the side length D of the germanium block is 0.5μm to 5μm, and the thickness T1 is 0.5μm to 5μm. The side length D should be smaller than the period P. For ease of processing, the difference between the two should be more than 100nm to ensure a certain gap width. The size of the unit structure must generally be smaller than the working wavelength.

[0042] The function of the first metasurface 4 is to efficiently sense and conduct the refractive index change of the external environment, and to achieve this by inducing the generation of high-sensitivity, high-spectral resolution narrow-band transmitted light through high-quality factor optical resonance modes such as plasmon resonance, Fano resonance, and bound state effects (BICs) in the continuous state excited by the metasurface, and converting the refractive index change into the resonant wavelength change of the narrow-band transmitted light. The generation and coupling of optical resonance modes are controlled by parameters such as the structure, shape, material, and arrangement of the micro-nano structure.

[0043] The performance of the refractive index sensor can be characterized by two parameters: wavelength sensitivity S and performance quality factor FOM, which can be expressed by the following equation:

[0044]

[0045] FOM = S / FWHM;

[0046] Among them, λ is the response wavelength, n is the ambient refractive index, and FWHM is the half-maximum width of the resonance peak.

[0047] Improving the refractive index sensing performance requires increasing the wavelength sensitivity S and reducing the half-width at half maximum FWHM of the resonance peak. The change in the ambient refractive index essentially changes the refractive index at the top of the nanopillar array and the refractive index difference with the gap, which then perturbs the induced electromagnetic resonance mode, causing the resonance peak wavelength to shift. Therefore, one way to improve S is to increase the intensity of the local electromagnetic field leaking from the resonance mode into the gap to expand the effect of external perturbations on the resonance. Since high-order electromagnetic modes often have higher sensitivity to parameter changes, another way to improve S is to increase the order of the optical resonance mode. The quality factor Q of the optical resonance mode determines its FWHM, and Q can be expressed as follows:

[0048] 1 / Q=1 / Q r +1 / Q in ;

[0049] Among them, Q r and Q in are the radiative and non-radiative Q factors, respectively.

[0050] Figure 6 The relationship between the transmission spectrum of the embodiment and the ambient refractive index is shown. As the ambient refractive index increases, the spectrum of the transmitted light gradually redshifts, and there is a positively correlated mapping relationship between the transmitted light frequency and the refractive index. The refractive index information can be obtained by detecting the frequency change of the transmitted light signal.

[0051] The dielectric separation layer 3 is a substrate made of infrared high transmittance material, and the optional materials include silicon, germanium, silicon dioxide, zinc sulfide, zinc selenide, calcium fluoride, magnesium fluoride, barium fluoride, lithium fluoride, etc., and its thickness is 100 μm to 1000 μm.

[0052] The dielectric layer 3 plays the role of optical transmission and structural support in the system. First, the dielectric layer 3 acts as an optical spacer to prevent mode coupling between two metasurfaces with different functions, so that their optical properties do not interfere with each other. Secondly, the dielectric layer has the property of high transmittance, which reduces the loss of light transmitted therein. Finally, the dielectric spacer layer 3 with a certain thickness serves as the supporting layer of the device. The optical films composed of the first metasurface 4 and the second metasurface 2 are placed on the upper and lower surfaces respectively.

[0053] The second metasurface 2 is a preferred non-uniformly arranged sub-wavelength micro-nano structure array, which is arranged on the lower surface of the dielectric layer according to the preferred phase gradient function law, and is set as a multi-focal meta-lens, which plays the role of focusing and spectral separation, and focuses the narrow spectrum light signals with different wavelengths transmitted through the first metasurface 4 on different positions of the focal plane of the detector. The second metasurface 2 is composed of a preferred infrared high-transmittance material. In order to reduce the difficulty of processing and the steps of the micro-nano processing procedure, its material can be consistent with the material of the dielectric layer. Considering the optical modulation capability, the preferred material is high-refractive-index silicon, germanium, etc., and its thickness is 0.5μm to 10μm.

[0054] The optional material type of the second metasurface 2 is consistent with that of the first metasurface 4. The array unit structure of the second metasurface 2 is preferably a circular, annular, cross, triangular, polygonal structure or a combination of the above structures.

[0055] by Figure 7The structure shown is an embodiment of the second metasurface 2, and the material of the second metasurface 2 is germanium, a high refractive index medium. The second metasurface 2 is composed of metaunits arranged in a certain order. The structural parameters of the micro-nanostructure size of the metaunit are as follows: the unit period P is 0.5μm to 10μm, the long side length L of the germanium rectangular column is 2μm to 5μm, the short side length thickness W is 0.5μm to 2μm, and the height T2 is 2μm to 10μm. The size of the unit structure must generally be smaller than the working wavelength. The increase in height is conducive to increasing the optical modulation capability of the structure, but the transmission efficiency needs to be guaranteed by changing the size and rotation angle of the metaunit, through the coordinated control of its transmission phase and geometric phase, while achieving full coverage of 0-2π phase, while satisfying the mapping relationship between wavelength and phase.

[0056] The second metasurface 2 is composed of relatively independent phase-controlled meta-units arranged in a certain order. The phase function of the meta-lens used for focusing can be expressed as:

[0057]

[0058] Where f is the focal length of the lens, r is the distance from a point on the lens to its center,

[0059]

[0060] Consider the wavelength λ i The light is focused at the focal plane position (x i ,y i ), adding the wavelength and position information offset, the above formula becomes:

[0061]

[0062] The second metasurface 2 constitutes a multi-focal metalens. The dispersion control function of the metalens controls the focusing position of the dispersed light, and focuses light signals of different wavelengths on different positions of the same focal plane. The frequency and intensity of the received light can be sensed by detecting the intensity change of the received light intensity of each pixel of the infrared detector 1 on the focal plane, and the refractive index can be efficiently sensed through the known mapping relationship between the first metasurface 4 and the refractive index.

[0063] The infrared detector 1 is an infrared surface array detector, which is arranged on the focal plane of the multi-focus meta-lens formed by the second meta-surface 2, and plays the role of receiving the position and intensity of the light signal. The pixel size is 10μm to 100μm.

[0064] The present invention solves the problems of existing metasurface refractive index sensing technology, such as the need for a spectrometer to detect infrared spectra and the low intensity of narrowband optical signals. The system includes, in sequence along the positive direction of the optical axis: a first metasurface, a dielectric separation layer, a second metasurface, and an infrared detector. The first metasurface is a periodic subwavelength resonator array, which converts refractive index information into wavelength-related narrowband spectral information; the second metasurface is a multi-focus metalens, which is used for focusing and spectral focus separation of narrow-spectrum optical signals. The present invention converts the target refractive index information into intensity information containing position information via two layers of metasurfaces. It can directly and efficiently sense refractive index changes without detecting changes in infrared spectrum intensity, thereby reducing system complexity. At the same time, signal focusing increases the detection rate of the system and improves the overall sensing quality.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. By setting metasurfaces on the upper and lower surfaces of the dielectric separation layer respectively, the resonant metasurface with a high quality factor on the upper surface is used to improve the refractive index sensing performance, and the multi-focus metalens formed by the phase-type metasurface on the lower surface is used to achieve spectral focusing, thereby improving the intensity and signal-to-noise ratio of the detection signal, and solving the problem of mutual restriction between spectral resolution and signal intensity in refractive index sensing.

[0067] 2. The refractive index information can be obtained by inverting the position and intensity of the received signal of the infrared detector on the focal plane. Therefore, the present invention can directly sense the environmental refractive index. Compared with other metasurface refractive index sensors in the field, it does not require an infrared spectrum detector, which can reduce system complexity and manufacturing costs.

[0068] 3. The present invention is a coaxial structure with strong system stability. This structural design reduces the difficulty of installing and adjusting the optical system and improves its anti-interference level in complex environments.

[0069] 4. The composite metasurface device described in the present invention is a planar optical element that can be independently packaged and used as an additional component of an existing infrared detector to improve infrared detection performance. It can also be directly integrated into the detector, and has the advantages of integrated manufacturing and mass production.

[0070] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A composite metasurface infrared refractive index sensing system, characterized in that: The system comprises: taking the direction of the infrared electromagnetic wave incident vertically downward as the positive direction of the optical axis, a first metasurface, a dielectric separation layer, a second metasurface and an infrared detector are sequentially arranged along the positive direction of the optical axis; The first metasurface and the second metasurface are respectively arranged on the upper surface and the lower surface of the dielectric separation layer; The infrared detector is arranged on the focal plane of the focused light spot of the second metasurface; The first metasurface is a resonant metasurface; the second metasurface is a phase metasurface.

2. The composite metasurface infrared refractive index sensing system according to claim 1, characterized in that: The first metasurface is composed of a plurality of uniformly arranged sub-wavelength periodic micro-nano structures.

3. The composite metasurface infrared refractive index sensing system according to claim 2, characterized in that: The second metasurface is composed of non-uniformly arranged sub-wavelength micro-nano structures.

4. The composite metasurface infrared refractive index sensing system according to claim 3, characterized in that: The sub-wavelength micro-nano structures of the second metasurface are arranged according to a phase gradient function.

5. The composite metasurface infrared refractive index sensing system according to claim 3, characterized in that: The sub-wavelength periodic micro-nano structure includes a circular structure, a ring structure, a cross structure, a triangle structure and a polygonal structure.

6. The composite metasurface infrared refractive index sensing system according to claim 2, characterized in that: The thickness of the sub-wavelength periodic micro-nano structure ranges from 0.5 μm to 10 μm.

7. The composite metasurface infrared refractive index sensing system according to claim 1, characterized in that: The medium separation layer is a substrate composed of infrared high transmittance material.

8. The composite metasurface infrared refractive index sensing system according to claim 7, characterized in that: The material of the dielectric separation layer includes silicon, germanium, silicon dioxide, zinc sulfide, zinc selenide, calcium fluoride, magnesium fluoride, barium fluoride and lithium fluoride.

9. The composite metasurface infrared refractive index sensing system according to claim 7, characterized in that: The thickness of the dielectric separation layer ranges from 100 μm to 1000 μm.

10. The composite metasurface infrared refractive index sensing system according to claim 7, characterized in that: The size of the pixel of the infrared detector ranges from 10 μm to 100 μm.

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