QBIC metasurface based on nanowire hyperbolic metamaterial

Abstract

The invention discloses a nanowire hyperbolic metamaterial-based QBIC (Quantum Balanced Integrated Circuit) super-structure surface, which belongs to the field of optical super-structure surfaces and comprises a substrate and a dielectric layer on the substrate, and a metal nanowire array is vertically embedded into the dielectric layer to form a metamaterial; the method comprises the following steps of: photoetching the metamaterial in a partial region to form two cylinders with the same height, namely a dimer cell, and photoetching the metamaterial in the rest partial region according to a mode that a plurality of dimer cells are periodically arranged to form a QBIC (Quadrature Balanced Integrated Circuit) metasurface based on the nanowire hyperbolic metamaterial. The refractive index is accurately adjusted by adjusting the size, spacing and material characteristics of dimer cells and the arrangement mode of a periodic array, a QBIC structure with a high Q value and high sensitivity is designed, and the QBIC structure has wide application prospects in the aspects of high-sensitivity sensing, quantum optics, nonlinear enhancement, low-loss lasers and the like.

Description

Technical Field

[0001] The present invention belongs to the field of optical metasurfaces, and in particular relates to a QBIC metasurface based on nanowire hyperbolic metamaterials. Background Art

[0002] Bound States in the Continuum (BIC) is a unique optical phenomenon. Although it exists in the continuous radiation spectrum, due to its special symmetry or topological protection mechanism, the resonant mode will not couple with the external radiation field, thereby greatly reducing energy loss and theoretically obtaining an infinitely high Q factor (Q value). The BIC mode is an idealized state. This non-radiative dark mode is only of practical significance in enhancing the interaction between light and matter when it is coupled with external radiation and converted into a leakage mode with an ultra-narrow linewidth, namely the quasi-bound states in the continuous spectrum (QBIC). The QBIC mode with a high quality factor has broad application prospects in many aspects such as high-sensitivity sensing, quantum optics, nonlinear enhancement, and low-loss lasers.

[0003] In recent years, research on BICs has made significant progress, especially in the field of artificial structures such as metasurfaces and photonic crystals. By destroying structural symmetry, introducing defect states, or using special materials, researchers have designed periodic nanostructures that can precisely control the resonant frequency, quality factor, and electromagnetic field distribution of BICs. This type of high-Q resonance mode theoretically has an infinite Q factor. However, due to material loss and processing precision limitations, it is still challenging to achieve infinite Q in reality.

[0004] Metal structures can achieve ultra-high sensitivity due to their ability to excite surface plasmon resonances, but their Q value is limited by the metal's ohmic loss. Compared to plasmas, dielectric nanoresonators are not affected by inherent material absorption losses, and they can support BIC modes, especially high-refractive-index dielectric structures, which can produce extremely sharp resonances and strong light confinement, but most of the electromagnetic energy of this resonance will be confined inside the structure, thus greatly limiting the sensing sensitivity of the device.

[0005] In the prior art, researchers have developed a variety of BIC metasurface structure sensors. For example, the invention application with publication number CN115096848A discloses a BIC metasurface structure sensor based on all-dielectric materials. The patent proposes a BIC metasurface structure based on all-dielectric materials for optical biosensing. The BIC metasurface uses silicon nitride or titanium dioxide as the dielectric material, and the refractive index of the material ranges from 1.8 to 2.5. The array structure is composed of four cylindrical cells, each cubic column has a height H of 50nm-500nm, a radius of 100nm-350nm, a center spacing P of 400nm, and a cell period of 800nm. Although high-refractive-index dielectric materials can limit electromagnetic fields, this limitation is usually not as significant as the field enhancement brought about by the plasmon effect of metal materials, and the area where the electric field of the high-refractive-index dielectric material is enhanced is located inside the high-refractive-index material. This means that under the same refractive index change, the sensing signal of the dielectric metasurface is relatively weak.

[0006] For another example, the invention application with publication number CN116183559A discloses a terahertz metal metasurface sensor based on bound states in a continuum. The patent proposes a BIC structure based on a metal metasurface unit for sensing detection in the terahertz band. The metasurface structure is an array structure composed of a plurality of periodically arranged square metal metasurface units, each unit including a bottom dielectric layer and a metal resonator layer covering the dielectric layer. The metal resonator layer is composed of a large resonant ring and a small resonant ring. The large resonant ring is composed of a metal resonant ring A and a metal resonant ring B, and the small resonant ring is composed of a metal resonant ring C and a metal resonant ring D. However, the sensor also faces some challenges, such as the difficulty of processing due to the complex structure, the high cost caused by the use of precious metals, the inherent loss problem of the metal itself, and the signal attenuation and background noise interference commonly found in terahertz sensing technology, which limit the detection performance and reliability in certain environments.

[0007] Therefore, developing a QBIC structure that combines the high Q value of dielectric materials and the high sensitivity S of metal materials has become the focus of current research. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention proposes a QBIC metasurface structure based on nanowire hyperbolic metamaterials, which is used to develop a QBIC structure that has both the high Q value of dielectric materials and the high sensitivity S of metal materials, thereby reducing energy loss.

[0009] To achieve the above-mentioned invention object, the present invention provides a QBIC metasurface based on nanowire hyperbolic metamaterial, comprising a substrate and a dielectric layer on the substrate, wherein a metal nanowire array is vertically embedded in the dielectric layer to form a metamaterial;

[0010] First, the metamaterial in some areas is photolithographically formed into two highly consistent cylinders, which is a dimer cell. The metamaterial in the remaining areas is photolithographically arranged in a periodic manner to form a QBIC metasurface based on nanowire hyperbolic metamaterials.

[0011] The present invention uses metal nanowire arrays to support surface plasmon resonance, generating strong local electromagnetic field enhancement at specific wavelengths; the metal nanowire arrays are vertically embedded into a dielectric layer to form a composite structure, so that the propagation mode of light at the nanoscale exhibits hyperbolic characteristics within a specific frequency range; the frequency and field distribution of the QBIC mode are controlled by regulating the structural parameters of the cylinders in the dimer cells and arranging them periodically, thereby achieving large-area electromagnetic field control.

[0012] Preferably, the substrate is quartz, magnesium fluoride, low-refractive index glass or a porous silicon oxide composite substrate.

[0013] Further preferably, the porous silicon oxide composite substrate comprises a nanoscale porous silicon oxide array and a centimeter-thick quartz substrate.

[0014] A low refractive index or transparent low-loss medium is selected as the substrate to support the overall structure, thereby increasing the refractive index and thus the sensitivity.

[0015] Optionally, the nanoscale porous silicon oxide array is obtained by etching silver nanowires in a silver silicon oxide nanowire composite film by a solution method.

[0016] The porous material is obtained by solution etching. Controlling the porosity of the porous silicon oxide material can reduce the refractive index of the substrate material, thereby improving the sensitivity.

[0017] Preferably, the array period of the nanoscale porous silicon oxide material is 6nm to 8nm, the pore size is 1.0 nm to 4.8nm, the porosity is 5% to 35%, the change value of the pore size is 0.1nm to 0.8nm, the diameter of the solid-state nanopores is 1nm to 10nm, the average spacing of the solid-state nanopores is 3nm to 20nm, the array period is 6nm to 40nm, and the porosity is 5% to 50%.

[0018] The pore size and porosity of the porous silicon oxide material are regulated by adjusting the ratio of the etching solution concentration to obtain a low refractive index, thereby improving the detection sensitivity.

[0019] Preferably, the metal nanowire array is formed by arranging metal nanowires at intervals, the diameter of the metal nanowires is 2nm to 6nm, the length of the metal nanowires is the same as the thickness of the dielectric layer, and the spacing between the metal nanowires is 1nm to 6nm.

[0020] Preferably, the metal nanowires are one or more of gold, silver, platinum, copper and aluminum.

[0021] Low-resistance metals such as gold, silver, and platinum are selected as nanowire materials. They have low ohmic loss, and the staggered arrangement to form a metal nanowire array not only reduces the ohmic loss but also obtains low dispersion characteristics, thereby greatly reducing the overall energy loss.

[0022] Preferably, the volume percentage of the metal nanowires in the metamaterial is 5% to 35%.

[0023] Preferably, the dielectric layer is a semiconductor transparent medium or a ceramic transparent medium.

[0024] A semiconductor transparent medium or a ceramic transparent medium is selected as the medium layer, and the refractive index is adjusted by adjusting the composition and structure to achieve dynamic tuning of the Q value and the sensitivity S.

[0025] Further preferably, the semiconductor transparent medium is one of silicon, germanium, tantalum pentoxide, zinc sulfide, zinc selenide, and silicon carbide;

[0026] The ceramic transparent medium is one of oxides, nitrides and carbides.

[0027] Preferably, the radius of the first and second cylinders in the dimer cell is 50nm to 400nm, and the height is 50nm to 500nm; the period L of the dimer cell in the x direction of the two-dimensional plane is x is 500nm~2000nm, and the period L in the y direction of the two-dimensional plane y It is 500nm~2000nm.

[0028] By changing the height of the dimer cylindrical material, the cylindrical radius, and the period L of the dimer cell in the x direction of the two-dimensional plane x , the period in the y direction of the two-dimensional plane is L y To dynamically tune the Q value.

[0029] Further preferably, the distance between the centers of the two cylinders is L0 under the initial high translational symmetry. The distance between the centers of the two cylinders after breaking the translational symmetry in the x direction is L.

[0030] By changing the distance L between the centers of cylinders 1 and 2 in the dimer cell unit structure, the translational symmetry in the x direction is destroyed. This method of destroying the translational symmetry of the cell can realize the transformation of the QBIC metasurface with infinite Q value to the QBIC metasurface with high Q value.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Selecting metal nanowires and vertically embedding the metal nanowire array into the dielectric layer can produce strong local electromagnetic field enhancement at a specific wavelength, significantly improve the interaction between light and matter, and achieve improved sensitivity;

[0033] (2) By adjusting the size, spacing, material properties and arrangement of the periodic array of dimer cells, the refractive index can be precisely adjusted to achieve dynamic tuning of Q value and sensitivity, and a QBIC structure with both high Q value and high sensitivity can be designed.

[0034] (3) The QBIC metasurface design provided by the present invention has broad application prospects in many aspects such as high-sensitivity sensing, quantum optics, nonlinear enhancement, and low-loss lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 1.

[0036] Figure 2 This is the infrared transmission spectrum of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 1.

[0037] Figure 3 Infrared transmission spectra of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 1 under different liquid environments.

[0038] Figure 4 Schematic diagram of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 2.

[0039] Figure 5 This is the infrared transmission spectrum of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 2.

[0040] Figure 6 Infrared transmission spectra of the QBIC metasurface structure based on nanowire hyperbolic metamaterial provided in Example 2 under different liquid environments. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described and illustrated in detail below in conjunction with examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1

[0043] Figure 1The schematic diagram of the designed QBIC metasurface unit structure is shown. Specifically, the selected substrate material is a SiO2 porous composite substrate with a porosity of 30%. The unit structure of the metasurface unit cell is obtained through micro-nanostructure design. The period L of the unit structure of the metasurface unit cell in the x direction of the two-dimensional plane is x is 1000nm, and the period in the y direction of the two-dimensional plane is L y The radius of the first and second cylinders is 500nm, the center distance L of the first and second cylinders is 570nm, the radius r of the first and second cylinders is 150nm, and the height h is 140nm. The dimer unit cell is composed of Ag-Ta2O5 nanowire composite thin film material with a metal volume filling rate of 15%.

[0044] For the Ag-Ta2O5 nanowire composite thin film material with a metal volume filling rate of 15%, the array period is 7±0.2nm and the pore size is 3.06±0.2nm; while for the Ag-SiO2 nanowire composite thin film material with a metal volume filling rate of 30%, the array period is 6.8±0.2nm and the pore size is 4.2±0.2nm. The Ag-SiO2 nanowire composite thin film material with a metal volume filling rate of 30% is etched by solution method to obtain a SiO2 porous composite substrate with a porosity of 30%.

[0045] Solution etching was performed using hydrogen peroxide, while the dimer structure was fabricated using electron beam lithography.

[0046] Then, the dielectric constants of silver (Ag), tantalum oxide (Ta2O5) and silicon oxide (SiO2) were extracted using ellipsometer software, and the dielectric constants of the metamaterials were extracted based on the equivalent medium theory calculations:

[0047]

[0048] ε z =(1-f)ε d +fε m

[0049]

[0050] where ε x，y represents the equivalent dielectric constant of the metamaterial in the xy plane, ε z represents the equivalent dielectric constant of the metamaterial in the z plane, ε m is the metal dielectric constant, ε d is the dielectric constant of the dielectric, and f is the metal filling rate. The transmission spectrum of the bulk material film is simulated in the electromagnetic simulation software, where the bulk material film is substituted into the optical constant of the anisotropic nanowire hyperbolic metamaterial film extracted by the equivalent medium theory, and the results of the electromagnetic simulation are compared with the test results to verify the accuracy of the dielectric constant extraction.

[0051] like Figure 2 As shown in Figure 2, the infrared transmission spectra of the designed metasurface cells in aqueous solution environments with different refractive indices (1.33 to 1.36) show high Q values ​​(defined as the ratio between the resonant frequency and the resonant half-peak width) in the transmission valley. Figure 3 As shown, when the solution environment is changed, the resonance valley in the simulated infrared transmission spectrum shifts, indicating that the designed metasurface cell has high sensitivity (S, defined as the ratio between the resonant wavelength shift and the refractive index change).

[0052] Example 2

[0053] like Figure 4 The schematic diagram of the QBIC metasurface unit structure designed in Example 2 is shown. Specifically, the selected substrate material is a SiO2 porous composite substrate with a porosity of 30%. The unit structure of the metasurface unit cell is obtained by micro-nanostructure design. The period L of the unit structure of the metasurface unit cell in the x direction of the two-dimensional plane is x is 1000nm, and the period in the y direction of the two-dimensional plane is L y is 500nm, the center distance L of cylinder one and cylinder two is 530nm, the radius r of cylinder one and cylinder two is 150nm, the height h is 180nm, and the dimer cell is a porous Si metamaterial with a porosity of 30%.

[0054] For the Ag-Si nanowire composite thin film material with a metal volume filling rate of 30%, the array period is 6.8±0.2nm and the pore size is 4.2±0.2nm. The Ag-SiO2 nanowire composite thin film material with a metal volume filling rate of 30% is etched by solution method to obtain a porous Si metamaterial with a porosity of 30%.

[0055] The solution etching was performed using hydrogen peroxide, while the dimer cell structure was fabricated using electron beam lithography.

[0056] Then, the dielectric constants of silver (Ag), silicon (Si) and silicon oxide (SiO2) materials were extracted using ellipsometer software, and the dielectric constant of the metamaterial was extracted based on the equivalent medium theory calculation:

[0057]

[0058] ε z =(1-f)ε d +fε m

[0059]

[0060] where ε x，yrepresents the equivalent dielectric constant of the metamaterial in the xy plane, ε z represents the equivalent dielectric constant of the metamaterial in the z plane, ε m is the metal dielectric constant, ε d is the dielectric constant of the dielectric, and f is the metal filling rate. The transmission spectrum of the bulk material film is simulated in the electromagnetic simulation software, where the bulk material film is substituted into the optical constant of the anisotropic nanowire hyperbolic metamaterial film extracted by the equivalent medium theory, and the results of the electromagnetic simulation are compared with the test results to verify the accuracy of the dielectric constant extraction.

[0061] like Figure 5 As shown in Figure 2, the infrared transmission spectra of the designed metasurface cells in aqueous solution environments with different refractive indices (1.33 to 1.36) show high Q values ​​(defined as the ratio between the resonant frequency and the resonant half-peak width) in the transmission valley. Figure 6 As shown, when the solution environment is changed, the resonance valley in the simulated infrared transmission spectrum shifts, indicating that the designed metasurface cell has high sensitivity (S, defined as the ratio between the resonant wavelength shift and the refractive index change).

Claims

1. A QBIC metasurface based on nanowire hyperbolic metamaterial, characterized in that: It includes a substrate and a dielectric layer on the substrate, wherein a metal nanowire array is vertically embedded in the dielectric layer to form a metamaterial; First, the metamaterial in some areas is photolithographically formed into two highly consistent cylinders, which is a dimer cell. The metamaterial in the remaining areas is photolithographically arranged in a periodic manner to form a QBIC metasurface based on nanowire hyperbolic metamaterials.

2. The QBIC metasurface according to claim 1, characterized in that: The substrate is quartz, magnesium fluoride, low-refractive index glass or porous silicon oxide composite substrate.

3. The QBIC metasurface according to claim 2, characterized in that: The porous silicon oxide composite substrate comprises a nanometer-scale porous silicon oxide array and a centimeter-thick quartz substrate, wherein the nanometer-scale porous silicon oxide array is obtained by etching the silver nanowires in the silver silicon oxide nanowire composite film by a solution method.

4. The QBIC metasurface according to claim 3, characterized in that: The array period of the nanoscale porous silicon oxide array is 6nm to 8nm, the pore size is 1.0nm to 4.8nm, the porosity is 5% to 35%, the change value of the pore size is 0.1nm to 0.8nm, the diameter of the solid nanopores after etching is 1nm to 10nm, the average spacing of the solid nanopores is 3nm to 20nm, the array period is 6nm to 40nm, and the porosity is 5% to 50%.

5. The QBIC metasurface according to claim 1, characterized in that: The metal nanowire array is formed by arranging metal nanowires at intervals, the diameter of the metal nanowires is 2nm-6nm, the length of the metal nanowires is the same as the thickness of the dielectric layer, and the spacing between the metal nanowires is 1nm-6nm.

6. The QBIC metasurface according to claim 6, characterized in that: The metal nanowires are one or more of gold, silver, platinum, copper and aluminum.

7. The QBIC metasurface according to claim 1, characterized in that: The dielectric layer is a semiconductor transparent medium or a ceramic transparent medium.

8. The QBIC metasurface according to claim 7, characterized in that: The semiconductor transparent medium is one of silicon, germanium, tantalum pentoxide, zinc sulfide, zinc selenide, and silicon carbide; The ceramic transparent medium is one of oxides, nitrides and carbides.

9. The QBIC metasurface according to claim 1, characterized in that: The radius of cylinder 1 and cylinder 2 in the dimer cell is 50nm to 400nm, and the height is 50nm to 500nm; The period L of the dimer cell in the x direction of the two-dimensional plane x is 500nm~2000nm, and the period L in the y direction of the two-dimensional plane y It is 500nm~2000nm.

10. The QBIC metasurface according to claim 1, characterized in that: The distance between the centers of the two cylinders of the dimer cell is L0 under the initial high translational symmetry. The distance between the centers of the two cylinders after breaking the translational symmetry in the x direction is L.

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