All-medium high-sensitivity refractive index sensor based on continuous domain bound state
By breaking the symmetry design on the metasurface unit and converting it to QBIC mode, the contradiction between sensitivity and figure of merit in existing optical sensors is resolved, realizing a high-sensitivity and high-figure-of-mercury refractive index sensor suitable for biochemical detection and environmental monitoring.
Patent Information
- Application Number
- CN202511436366.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-09
- Publication Date
- 2025-11-21
AI Technical Summary
There is a trade-off between sensitivity and figure of merit in existing optical sensors. While SPR sensors have high sensitivity, they suffer from high losses, while dielectric resonator sensors have insufficient sensitivity, making it difficult to achieve both high sensitivity and high figure of merit simultaneously.
A refractive index sensor based on continuous domain bound states is designed. By creating fan-shaped columnar notches on the metasurface unit to break the symmetry, the bound state is converted into a quasi-continuous domain bound state, and its mode is tuned to improve sensitivity and figure of merit.
It achieves refractive index sensing with high sensitivity and high figure of merit, with a Q factor of 7×104, a sensitivity of 310 nm/RIU, and a figure of merit of 1.55×104 RIU-1. It has strong anti-interference ability, high material stability, and is easy to prepare.
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Figure CN120992555A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of optical sensing technology, in particular to a full dielectric high-sensitivity refractive index sensor based on bound states in the continuum. BACKGROUND
[0002] Refractive index sensing is the core technology in the field of biochemical detection, and its performance is determined by the sensitivity (S) and figure of merit (FOM) of the device. However, the mainstream technology such as SPR (Surface Plasmon Resonance) sensor has inherent contradictions: SPR sensor can achieve high sensitivity by using localized field enhancement, but the ohmic loss of metal leads to a wide resonance peak and low FOM, which seriously limits the detection limit. The resonant cavity using dielectric material can obtain high FOM, but its localized field capacity is often weak, resulting in insufficient sensitivity. Therefore, developing a sensing platform that can simultaneously have ultra-high FOM and high sensitivity, and low loss, is the key to breaking through the bottleneck of existing technology.
[0003] BIC (Bound States in the Continuum) provides an ideal solution to break the above bottleneck. BIC is a special physical phenomenon existing in full dielectric photonic structures, and its ideal mode has an infinite Q (Quality) factor and zero radiation loss. By structural design, such as breaking the symmetry of the structure, the ideal BIC can be converted into a QBIC (Quasi-Bound States in the Continuum) mode, which realizes an extremely high FOM far beyond SPR and traditional resonant cavities in experiments, and can strongly localize the optical field in the sensing region, thereby ensuring high sensitivity. This full dielectric design based on dielectric materials fundamentally avoids the problem of metal loss, and has the potential for high stability and low cost, laying a solid foundation for the next generation of optical sensors with high sensitivity and high FOM. Although some full dielectric BICs have achieved some results in the field of refractive index sensing, the regulation of the symmetry breaking of the unit structure is not fine enough, and it is difficult to realize high sensitivity and high FOM. SUMMARY
[0004] The present application provides a full dielectric high-sensitivity refractive index sensor based on bound states in the continuum, which aims to improve the sensitivity, quality factor, robustness and anti-interference ability of the refractive index sensor.
[0005] In order to achieve the above purpose, the present application provides a full dielectric high-sensitivity refractive index sensor based on bound states in the continuum, comprising:
[0006] a substrate arranged to extend along an x-axis direction and a y-axis direction arranged perpendicularly;
[0007] a metasurface unit arranged in an array on the substrate, the metasurface unit being configured in a quadrangular prism shape, a surface of the metasurface unit parallel to the substrate being a preset surface, one diagonal of the preset surface being a preset diagonal, the preset diagonal being parallel to the x-axis direction or the y-axis direction, the metasurface unit being provided with a first notch and a second notch both in a fan-shaped column shape, the first notch in a fan-shaped column shape having a first end of the preset diagonal as a center, the second notch in a fan-shaped column shape having a second end of the preset diagonal as a center, a radius of the first notch being different from a radius of the second notch, so as to change symmetry of the metasurface unit and convert BIC of the metasurface unit into QBIC.
[0008] In an embodiment, arrangement periods of the metasurface unit in the x-axis direction and the y-axis direction are both in a range of 400nm-500nm.
[0009] In an embodiment, a side length of the preset surface is in a range of 200nm-300nm, and a height of the metasurface unit is in a range of 300nm-400nm.
[0010] In an embodiment, an absolute value of a difference between the radius of the first notch and the radius of the second notch is in a range of 0-40nm.
[0011] In an embodiment, a working wavelength of the refractive index sensor is in a range of 800nm-1000nm.
[0012] The above scheme of the present application has the following advantages:
[0013] In the embodiments of the present application, the first notch and the second notch in a fan-shaped column shape are arranged on the metasurface unit, and the radius of the first notch is not equal to the radius of the second notch to break the symmetry of the structure, so as to convert BIC into QBIC mode for regulation, which is beneficial to improve the sensitivity and merit figure of the all-dielectric high-sensitivity refractive index sensor, and the Q factor can reach 7x10 4 Through simulation, the sensitivity and the merit figure of the refractive index sensor can reach 310nm / RIU and 1.55x10 4 RIU -1, and the response in the near-infrared band is more advantageous. Since the morphology of the first gap and the second gap changes little, the effective refractive index of the metasurface unit remains constant, so that the QBIC resonance wavelength position is very stable, and the robustness is high. Moreover, when the external refractive index changes, the modulation depth of the resonance peak is always close to 100%, and the anti-interference ability is strong. In addition, the refractive index sensor of the present application is easy to prepare, and the material is not easy to be oxidized and corroded.
[0014] Other benefits of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS
[0015] Figure 1 It is an assembly schematic diagram of a single metasurface unit and a substrate in an embodiment of the present application.
[0016] Figure 2 It is a structural schematic diagram of a refractive index sensor in an embodiment of the present application.
[0017] Figure 3 It is a top view structural schematic diagram of a metasurface unit in an embodiment of the present application.
[0018] Figure 4 It is a transmission spectrum, a transmission scanning result and a Q factor test diagram of a refractive index sensor in different △r in an embodiment of the present application, wherein, Figure 4 (a) is a transmission spectrum schematic diagram of a refractive index sensor in different △r, Figure 4 (b) is a transmission scanning result schematic diagram of a refractive index sensor about △r, Figure 4 (c) is a Q factor calculation result schematic diagram of a refractive index sensor in different △r.
[0019] Figure 5 It is a multipole decomposition schematic diagram of a refractive index sensor in a symmetry breaking case in an embodiment of the present application, wherein, Figure 5 (a) is an electric field diagram of the xz cross section at the resonance peak position when △r=40nm, Figure 5 (b) is a magnetic field diagram of the xy cross section at the resonance peak position when △r=40nm, Figure 5 (c) is a schematic diagram of performing multi-level decomposition for the case of △r=40nm.
[0020] Figure 6 It is a test diagram of a refractive index sensor in a symmetry breaking case in an embodiment of the present application placed in different refractive index media, wherein, Figure 6 (a) is a transmission spectrum schematic diagram placed in different refractive index media when △r=40nm, Figure 6 (b) is a resonance peak position schematic diagram placed in different media environments under different △r, Figure 6(c) is a schematic diagram of Q factor under different Δr and in different medium environment, Figure 6 (d) is a schematic diagram of merit factor under different Δr and in different medium environment.
[0021] [Legend of the figures]
[0022] 1, substrate; 2, metasurface unit; 21, preset surface; 211, preset diagonal; 22, first notch; 23, second notch. DETAILED DESCRIPTION
[0023] In order to make the technical problems solved by the present application, the technical solutions and advantages clearer, the following will be described in detail with reference to the drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application. In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.
[0024] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.
[0025] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be a locking connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.
[0026] In the related art, as a key device for real-time monitoring of the composition and concentration of a substance, an optical refractive index sensor plays an indispensable role in the fields of biomolecular detection, medical diagnosis, and environmental monitoring. Therefore, in the field of optical sensing, it is an important topic to study a refractive index sensor with high sensitivity and high quality factor. As a kind of ideal singular state existing in the continuous spectrum of radiation and theoretically having infinite high quality factor and zero radiation loss, BIC is a powerful way to achieve this topic. Based on this, the present application proposes a full dielectric high-sensitivity refractive index sensor based on continuous domain bound state, which breaks the symmetry of the structure by changing the radius of the fan-shaped columnar notch at one of the diagonal positions.
[0027] Specifically, please refer to Figure 1 、 Figure 2 and Figure 3 , the refractive index sensor of the present application comprises a substrate 1 and a metasurface unit 2. For example, the material of the substrate 1 can be silicon dioxide with a refractive index of 1.45, and the material of the metasurface unit 2 can be silicon with a refractive index of 3.2. The substrate 1 and the metasurface unit 2 are both placed in air with a refractive index of 1. It should be noted that the metasurface refers to a special case of metamaterial, specifically referring to the arrangement of subwavelength devices in two-dimensional space to achieve specific electromagnetic properties.
[0028] Please refer to Figure 1 , the substrate 1 is arranged along the x-axis direction and the y-axis direction, and the x-axis direction and the y-axis direction are arranged vertically.
[0029] The metasurface unit 2 is arrayed on the substrate 1. The shape of the metasurface unit 2 is configured as a quadrangular prism. The surface of the metasurface unit 2 parallel to the substrate 1 is a preset surface 21. One of the diagonal lines of the preset surface 21 is a preset diagonal line 211, which is parallel to the x-axis direction or the y-axis direction. For example, as shown in Figure 3 , the preset diagonal line 211 is parallel to the x-axis direction and perpendicular to the y-axis direction. For example, the angle between the edge of the preset surface 21 and the x-axis direction is 45°. The metasurface unit 2 is provided with a first notch 22 and a second notch 23, both of which are fan-shaped columns. It should be noted that the initial shape of the metasurface unit 2 is a quadrangular prism, and after the first notch 22 and the second notch 23 are opened, the metasurface unit 2 has a shape similar to a prism. The first notch 22 of the fan-shaped column has the first end of the preset diagonal line 211 as the center, and the extension direction of the first notch 22 is parallel to the z-axis direction as shown in Figure 1 . The second notch 23 of the fan-shaped column has the second end of the preset diagonal line 211 as the center, and the extension direction of the second notch 23 is parallel to the z-axis direction as shown in Figure 1The z-axis direction is shown in the middle. The radius of the first notch 22 is not equal to the radius of the second notch 23 to change the symmetry of the metasurface unit 2 to convert the BIC of the metasurface unit 2 into QBIC.
[0030] Exemplarily, the refractive index sensor of the present application can be modeled and numerically simulated by electromagnetic simulation software. For example, periodic boundary is used in the x-axis direction and the y-axis direction, so that the metasurface unit 2 is distributed in an array on the substrate 1. PML (Perfectly Matched Layer) is used in the z-axis direction. PML is a kind of efficient absorbing boundary condition, which can effectively simulate the propagation behavior of electromagnetic field in infinite space, and is suitable for most electromagnetic field simulation scenarios. By reasonably setting the thickness and absorption coefficient of PML, the simulation accuracy and calculation efficiency can be further improved. The wavelength of the incident light is between 800 nm and 1000 nm, and the electric field (E) direction is along the x-axis direction. The simulation results of the refractive index sensor are shown in Figure 4 、 Figure 5 and Figure 6 .
[0031] Exemplarily, to achieve a super high Q factor resonance for sensing, the embodiment of the present application changes the radius of one of the sector-shaped columnar notches to destroy its structural symmetry, so as to realize the conversion of BIC to QBIC. Please refer to Figure 3 , the radius of the first notch 22 on the right side can be r1, which can be 40 nm and fixed, and the radius of the second notch 23 on the left side is r2, the breakage degree of the second notch 23 relative to the first notch 22 can be described by△r, r2=r1+△r,△r>0. Please refer to Figure 4 (a), when△r=0nm, the metasurface unit 2 is in BIC mode, and the resonance peak cannot be observed. With the change of r2, the symmetry of the metasurface unit 2 is destroyed, so that the symmetry-protected BIC of the metasurface unit 2 is converted into QBIC mode, and the resonance of the QBIC mode can be observed, which is manifested as a Fano resonance in the transmission spectrum. Fano resonance is a kind of asymmetric scattering resonance phenomenon in physics caused by discrete state and continuous state, which will not be described here. With the increase of△r, the resonance peak appears slight blue shift and the resonance line width increases. Figure 4 (b) shows the scanning diagram of△r on the transmission spectrum, it can be seen that the resonance peak changes from nothing to gradually obvious, and the resonance peak basically remains near 836 nm, showing high robustness, so that when△r changes, the refractive index sensor of the present application has strong ability to maintain stable operation of its own function. Figure 4 (c) shows the calculation results of the Q factor of the resonance peak under different△r, when△r tends to 0, a high Q factor of 10 7The theoretical value of the Q factor can be infinite. The Q factor can represent the efficiency of the interaction between light and matter. The coupling effect caused by the periodically arranged metasurface unit 2 in the refractive index sensor can produce an optical response with a high quality factor in the spectrum, which means that the refractive index sensor has higher sensitivity and smaller energy loss.
[0032] For example, for the above regulated QBIC, a multipole decomposition method can be used to analyze it in a deeper level to study the physical characteristics of the QBIC resonance. When electromagnetic waves interact with matter, charge and current distributions are excited inside the material, thereby producing electromagnetic responses. This response can be characterized by scattering properties. In order to analyze the overall scattering properties of the material, the material can be equivalent to a series of point-like multipole sources, such as electric dipoles, magnetic dipoles, electric quadrupoles, etc., and the scattering power of these multipole sources is calculated. This process is called multipole scattering power decomposition, simply referred to as multipole decomposition. It is found that this resonance is mainly supported by ED (electric dipole) and EQ (electric quadrupole) modes, of which ED makes the main contribution. As shown in Figure 5 (a) shows the electric field diagram of the xz plane at the resonance peak position when △r is 40 nm, and the white arrow in the figure indicates the vector direction of the electric field under this condition. It can be seen that the direction of the electric field is along the z axis from the negative direction to the positive direction. As shown in Figure 5 (b) shows the magnetic field diagram of the xy plane at the resonance peak position when △r is 40 nm. It can be seen that the magnetic field forms a clockwise magnetic field closed loop along the metasurface unit 2, thereby exciting an electric field along the z axis direction, forming an electric dipole. This is consistent with the principle that ED mode makes the main contribution to QBIC resonance in multipole decomposition. The multipole decomposition calculation of the QBIC resonance mode excited by the metasurface unit 2 when △r is 40 nm is shown in Figure 5 (c). From the figure, the contribution of each mode to the QBIC resonance mode can be clearly observed. The QBIC resonance is mainly excited by ED (electric dipole) and EQ (electric quadrupole), of which ED makes the main contribution. The excited resonance Q factor can be as high as 7x10 4 orders of magnitude, and the refractive index sensor with ultra-high sensitivity is designed by using the ultra-high Q factor, and the refractive index sensitivity is about 310 nm / RIU, and the merit is as high as 1.55x10 4 RIU -1 .
[0033] Exemplarily, different refractive index liquids to be measured are respectively filled above the metasurface unit 2, and the metasurface unit 2 is irradiated along the z-axis direction by using a near-infrared polarized light with a polarization direction along the x-axis direction, and the change of the refractive index will cause the shift of the resonance peak in the transmission spectrum of the metasurface unit 2, and the shift of the resonance peak position corresponds to different liquid components. By changing the refractive index of the filled liquid to simulate different refractive index environments, the refractive index of the liquid to be measured is analyzed by the shift of the resonance peak, and the sensitivity and figure of merit of the refractive index sensor are calculated.
[0034] Exemplarily, the sensitivity S is defined as the shift of the resonance peak under unit refractive index, and the formula is S = Δλ / Δn, wherein Δn is the difference of the refractive indices of the two liquids to be measured, and Δλ is the difference of the wavelengths corresponding to the resonance peaks of the two liquids to be measured. It should be noted that the change of the environmental refractive index will cause the drift of the optical element spectrum (transmission / reflection) or the change of the resonance angle. By measuring the wavelength drift or the angle change, the refractive index sensing can be realized. Figure 6 (b) shows the curve of the wavelength change with the refractive index, and the slope is the sensitivity of the refractive index sensor, with the unit of nm / RIU. Since the refractive index itself has no unit, RIU (Refractive Index Unit) can be translated as refractive index unit. The figure of merit FOM is defined as the ratio of the sensitivity S to the full width at half maximum FWHM of the resonance peak, and the formula is F = S / FWHM.
[0035] Exemplarily, Figure 6 (a) is the transmission spectrum of the refractive index sensor placed in the liquid to be measured with different refractive indices when Δr = 40 nm. As the refractive index of the liquid to be measured increases, the resonance peak of the liquid to be measured obviously red shifts (the wavelength becomes longer), and the resonance line width almost does not change. In addition, the modulation depth of the resonance peak is close to 100%, which indicates that the anti-interference ability of the refractive index sensor is relatively strong. Figure 6 (b) shows that the resonance peak position and the refractive index present an obvious linear relationship, and the refractive index of the environment can be calculated by the resonance peak position. Based on this linear relationship, a high-sensitivity refractive index sensor device can be developed. When the break degree Δr is 20 nm, 30 nm or 40 nm, the sensitivity of the refractive index sensor of the present application remains at about 310 nm / RIU, and has relatively high stability. Figure 6 (c) and Figure 6 (d) respectively show the relationship between the Q factor and the FOM and the refractive index. When Δr is 20 nm, the Q factor and the FOM can be up to 7×10 4 , respectively, and 1.55×10 4 RIU -1 . With the increase of the break degree Δr, the Q factor and the FOM of the resonance peak obviously decrease.
[0036] In the embodiments of the present application, the symmetry of the structure is broken by opening the first notch 22 and the second notch 23 in the form of a fan-shaped column on the metasurface unit 2, and the radius of the first notch 22 is not equal to the radius of the second notch 23, so as to convert the BIC into the QBIC mode for regulation, which is conducive to improving the sensitivity and figure of merit of the all-dielectric high-sensitivity refractive index sensor of the present application, and the Q factor can reach 7x10 4 . Through simulation, the sensitivity and figure of merit of the refractive index sensor can reach 310nm / RIU and 1.55x10 4 RIU -1 , respectively, and the response in the near-infrared band is more advantageous. Since the topography of the first notch 22 and the second notch 23 does not change much, the effective refractive index of the metasurface unit 2 remains constant, so that the QBIC resonance wavelength position is very stable, and the robustness is high. Furthermore, when the external refractive index changes, the modulation depth of the resonance peak is always close to 100%, and the anti-interference ability is strong. In addition, the refractive index sensor of the present application is easy to prepare, and the material is not easy to be oxidized and corroded.
[0037] In an embodiment, referring to Figure 2 and Figure 3 , the arrangement period of the metasurface unit 2 in the x-axis direction and the y-axis direction is in the range of 400nm-500nm. For example, the arrangement period of the metasurface unit 2 in the x-axis direction and the y-axis direction is 500nm, so that the sensitivity and figure of merit of the refractive index sensor are higher. For example, the distance represented by P in Figure 3 may represent the arrangement period of the metasurface unit 2, P=500nm. That is, the distance between a certain point in the metasurface unit 2 and the corresponding same point of the adjacent metasurface unit 2 is 500nm.
[0038] In an embodiment, referring to Figure 1 and Figure 3 , the side length of the preset surface 21 is in the range of 200nm-300nm, and the height of the metasurface unit 2 is in the range of 300nm-400nm, so that the sensitivity and figure of merit of the refractive index sensor are higher. For example, all the side lengths of the preset surface 21 are 250nm, so that the initial shape of the metasurface unit 2 is a regular quadrangular prism, and then the first notch 22 and the second notch 23 are opened on the metasurface unit 2 which is a regular quadrangular prism. For example, the distance represented by L in Figure 3 may represent the side length of the preset surface 21, L=250nm. For example, the height of the metasurface unit 2 is 400nm. For example, the distance represented by H in Figure 1 may represent the height of the metasurface unit 2.
[0039] In an embodiment, referring to Figure 3The absolute value of the difference between the radius of the first gap 22 and the radius of the second gap 23 ranges from 0 to 40 nm, i.e. the range of Δr is from 0 to 40 nm, so that the sensitivity and merit of the refractive index sensor are higher. For example, Δr can be 20 nm, 30 nm or 40 nm.
[0040] In an embodiment, the working wavelength of the refractive index sensor ranges from 800 nm to 1000 nm. When the wavelength of the incident light is between 800 nm and 1000 nm, the refractive index sensor of the present application has higher sensitivity and merit, so that the refractive index sensor is more sensitive to the incident light with a wavelength between 800 nm and 1000 nm, and in turn the response of the refractive index sensor to the incident light with a wavelength between 800 nm and 1000 nm is more advantageous.
[0041] The above describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered as the protection scope of the present application.
Claims
1. A high-sensitivity refractive index sensor based on continuous domain bound states in an all-dielectric medium, characterized in that, include: A substrate extends along the x-axis and y-axis directions, wherein the x-axis and y-axis directions are perpendicular to each other; Metasurface cells are arrayed on the substrate. The shape of each metasurface cell is configured as a quadrangular prism. The surface of each metasurface cell parallel to the substrate is a preset surface. One diagonal of the preset surface is a preset diagonal, which is parallel to either the x-axis or the y-axis. Each metasurface cell has a first notch and a second notch that are both fan-shaped prisms. The first notch is centered at the first end of the preset diagonal, and the second notch is centered at the second end of the preset diagonal. The radii of the first notch and the second notch are not equal to change the symmetry of the metasurface cell, thereby converting the BIC of the metasurface cell into QBIC.
2. The all-dielectric high-sensitivity refractive index sensor based on continuous domain bound states according to claim 1, characterized in that, The arrangement period of the metasurface units in both the x-axis and y-axis directions ranges from 400 nm to 500 nm.
3. The all-dielectric high-sensitivity refractive index sensor based on continuous domain bound states according to claim 1, characterized in that, The side length of the preset surface is in the range of 200nm~300nm, and the height of the metasurface unit is in the range of 300nm~400nm.
4. The all-dielectric high-sensitivity refractive index sensor based on continuous domain bound states according to claim 1, characterized in that, The absolute value of the difference between the radius of the first notch and the radius of the second notch ranges from 0 to 40 nm.
5. The all-dielectric high-sensitivity refractive index sensor based on continuous domain bound states according to claim 1, characterized in that, The refractive index sensor operates in the wavelength range of 800nm to 1000nm.