A QBIC metasurface based on nanowire hyperbolic metamaterials

Abstract

This invention discloses a QBIC metasurface based on nanowire hyperbolic metamaterials, belonging to the field of optical metasurfaces. It includes a substrate and a dielectric layer on the substrate. A metal nanowire array is vertically embedded into the dielectric layer to form the metamaterial. First, a portion of the metamaterial is photolithographically formed into two cylinders of uniform height, constituting a dimer cell. The remaining portion of the metamaterial is then photolithographically formed by periodically arranging several dimer cells to create the QBIC metasurface based on nanowire hyperbolic metamaterials. This invention precisely adjusts the refractive index by modifying the size, spacing, material properties, and periodic array arrangement of the dimer cells, designing a QBIC structure that combines high Q-value and high sensitivity. It has broad application prospects in high-sensitivity sensing, quantum optics, nonlinear enhancement, low-loss lasers, and many other fields.

Description

Technical Field

[0001] This invention belongs to the field of optical metasurfaces, specifically relating to a QBIC metasurface based on nanowire hyperbolic metamaterials. Background Technology

[0002] Bound states in the continuous spectrum (BIC) are a unique optical phenomenon. Although they exist within the continuous radiation spectrum, their resonant modes do not couple with external radiation fields due to their special symmetry or topological protection mechanisms, thus greatly reducing energy loss and theoretically allowing for infinitely high Q factors (Q values). BIC modes are idealized states; these non-radiative dark modes only become practically significant in enhancing light-matter interactions when they couple with external radiation to transform into leakage modes with ultra-narrow linewidths, i.e., quasi-bound states in the continuous spectrum (QBIC). QBIC modes with high quality factors have broad application prospects in high-sensitivity sensing, quantum optics, nonlinear enhancement, and low-loss lasers.

[0003] In recent years, significant progress has been made in research on bipolar indices (BICs), particularly in the field of artificial structures such as metasurfaces and photonic crystals. By disrupting 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. These high-Q resonant modes theoretically possess an infinite Q factor. However, due to limitations in material loss and fabrication precision, achieving an infinite Q factor remains a challenge in reality.

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

[0005] Researchers have developed various BIC metasurface structure sensors in the prior art. For example, patent application CN115096848A discloses a BIC metasurface structure sensor based on an all-dielectric material, which proposes a BIC metasurface structure for optical biosensing. The BIC metasurface uses silicon nitride or titanium dioxide as the dielectric material, with a refractive index ranging from 1.8 to 2.5. It consists of an array structure of four cylindrical cells, each with a height H of 50 nm to 500 nm, a radius of 100 nm to 350 nm, a center-to-center spacing P of 400 nm, and a cell period of 800 nm. Although high-refractive-index dielectric materials can confine electromagnetic fields, this confinement is usually not as significant as the field enhancement brought about by the plasmon effect in metallic materials, and the region of electric field enhancement in high-refractive-index dielectric materials 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 example, patent application CN116183559A discloses a terahertz metallic metasurface sensor based on bound states in a continuum. This patent proposes a BIC structure based on metallic metasurface units for sensing in the terahertz band. This metasurface structure is an array of multiple periodically arranged square metallic metasurface units. Each unit includes a bottom dielectric layer and a metallic resonator layer covering the dielectric layer. The metallic resonator layer consists of large resonant rings and small resonant rings. The large resonant rings are composed of metallic resonant rings A and B, and the small resonant rings are composed of metallic resonant rings C and D. However, this sensor also faces some challenges, such as the difficulty of fabrication due to its complex structure, the high cost of using precious metals, the inherent loss problems of the metal itself, and the signal attenuation and background noise interference commonly found in terahertz sensing technology. These factors limit the detection performance and reliability under certain conditions.

[0007] Therefore, developing QBIC structures that combine the high Q value of dielectric materials with the high S sensitivity of metallic materials has become a current research focus. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention proposes a QBIC metasurface structure based on nanowire hyperbolic metamaterials, which is used to develop QBIC structures that simultaneously possess the high Q value of dielectric materials and the high S sensitivity of metallic materials, thereby reducing energy loss.

[0009] To achieve the above-mentioned objectives, this invention provides a QBIC metamaterial based on a hyperbolic nanowire metamaterial, comprising a substrate and a dielectric layer on the substrate, wherein a metal nanowire array is vertically embedded into the dielectric layer to form a metamaterial.

[0010] First, the metamaterial in a certain area is photolithographically formed into two cylinders of the same height, which are a dimer cell. The metamaterial in the remaining area is photolithographically formed in a periodic arrangement of several dimer cells to form a QBIC metamaterial based on nanowire hyperbolic metamaterial.

[0011] This invention employs a metal nanowire array to support surface plasmon resonance, generating a strong local electromagnetic field enhancement at a specific wavelength; the metal nanowire array is vertically embedded into a dielectric layer to form a composite structure, enabling the light propagation mode to exhibit hyperbolic characteristics within a specific frequency range at the nanoscale; the frequency and field distribution of the QBIC mode are controlled by adjusting the structural parameters of the cylinders in the dimer cell and arranging them periodically, thereby achieving large-area electromagnetic field modulation.

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

[0013] More preferably, the porous silica composite substrate comprises a nanoscale porous silica array and a centimeter-thick quartz substrate.

[0014] Choosing a low-refractive-index or transparent, low-loss medium as a substrate to support the overall structure increases the refractive index and thus improves sensitivity.

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

[0016] Porous materials are obtained by etching using a solution method. By controlling the porosity of the porous silicon oxide material, the refractive index of the substrate material can be reduced, thereby improving sensitivity.

[0017] Preferably, the array period of the nanoscale porous silica material is 6nm to 8nm, the pore size is 1.0nm to 4.8nm, the porosity is 5% to 35%, and the pore size variation is 0.1nm to 0.8nm. The solid nanopore diameter 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%.

[0018] By adjusting the concentration ratio of the etching solution, the pore size and porosity of porous silica materials can be controlled to obtain a low refractive index, thereby improving 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] Using low-resistance metals such as gold, silver, and platinum as nanowire materials results in low ohmic loss. The spaced arrangement of these metal nanowires not only reduces ohmic loss but also achieves low dispersion characteristics, thereby significantly reducing 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 dielectric or a ceramic transparent dielectric.

[0024] By selecting a semiconductor transparent medium or a ceramic transparent medium as the dielectric layer, the refractive index can be adjusted through composition and structure to achieve dynamic tuning of the Q value and sensitivity S.

[0025] More 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 radii of cylinder one and cylinder two in the dimer cell are 50 nm to 400 nm, and the height is 50 nm to 500 nm; the period L of the dimer cell in the x-direction of the two-dimensional plane is... x The period L in the y-direction of the two-dimensional plane is 500nm to 2000nm. y The range is 500nm to 2000nm.

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

[0029] A further preferred embodiment, under the initial height translation symmetry, has a distance of L0 between the centers of the two cylinders. 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 one and two in the dimer cellular unit structure, the translational symmetry in the x-direction is disrupted. This method of disrupting cellular translational symmetry can achieve the transformation from an infinite Q-value QBIC metasurface to a high Q-value QBIC metasurface.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) By selecting metal nanowires and embedding the metal nanowire array vertically into the dielectric layer, a strong local electromagnetic field enhancement can be generated at a specific wavelength, which significantly improves the interaction between light and matter and achieves an increase in sensitivity.

[0033] (2) By adjusting the size, spacing, material properties and arrangement of the periodic array of the 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 this invention has broad application prospects in many fields such as high-sensitivity sensing, quantum optics, nonlinear enhancement, and low-loss lasers. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the QBIC metasurface structure based on nanowire hyperbolic metamaterials provided in Example 1.

[0036] Figure 2 The infrared transmission spectrum of the QBIC metasurface structure based on nanowire hyperbolic metamaterials 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 This is a schematic diagram of the QBIC metasurface structure based on nanowire hyperbolic metamaterials provided in Example 2.

[0039] Figure 5 The infrared transmission spectrum of the QBIC metasurface structure based on nanowire hyperbolic metamaterials 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 Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described and illustrated below with reference to examples. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the 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 cell is obtained through micro-nano structure design. The period L of the unit structure of the metasurface cell in the x-direction of the two-dimensional plane is shown. x The wavelength is 1000 nm, and the period in the y-direction of the two-dimensional plane is L. y The diameter is 500 nm, the center distance L between cylinder one and cylinder two is 570 nm, the radius r of cylinder one and cylinder two is 150 nm, and the height h is 140 nm. The dimer cell is composed of Ag-Ta2O5 nanowire composite film material with a metal volume fill rate of 15%.

[0044] For Ag-Ta2O5 nanowire composite film with a metal volume fill rate of 15%, the array period is 7±0.2nm and the pore size is 3.06±0.2nm; while for Ag-SiO2 nanowire composite film with a metal volume fill rate of 30%, the array period is 6.8±0.2nm and the pore size is 4.2±0.2nm. By etching Ag-SiO2 nanowire composite film with a metal volume fill rate of 30% using a solution method, a SiO2 porous composite substrate with a porosity of 30% is obtained.

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

[0046] Subsequently, the dielectric constants of silver (Ag), tantalum oxide (Ta2O5), and silicon oxide (SiO2) were extracted using ellipsometer software. Based on the equivalent medium theory, the dielectric constant of the metamaterial was then calculated.

[0047]

[0048] ε z =(1-f)ε d +fε m

[0049]

[0050] Where ε x，y ε represents the equivalent dielectric constant of the metamaterial in the xy plane. z ε represents the equivalent dielectric constant of the metamaterial in the z-plane. m ε is the dielectric constant of the metal. d Let f be the dielectric constant of the dielectric material and f be the metal filling rate. The transmission spectrum of the bulk material thin film was simulated in electromagnetic simulation software. The optical constants of the anisotropic nanowire hyperbolic metamaterial thin film were extracted by substituting the equivalent medium theory. The results obtained from the electromagnetic simulation were compared with the test results to verify the accuracy of the dielectric constant extraction.

[0051] like Figure 2 As shown, the infrared transmission spectra of the designed metasurface cells in aqueous solutions with different refractive indices (1.33–1.36) exhibit a high Q value (defined as the ratio between the resonant frequency and the full width at half maximum) 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 diagram shown is a schematic of the QBIC metasurface unit structure designed in Example 2. Specifically, the selected substrate material is a SiO2 porous composite substrate with a porosity of 30%. The unit structure of the metasurface cell is obtained through micro-nano structure design. The period L of the unit structure of the metasurface cell in the x-direction of the two-dimensional plane is... x The wavelength is 1000 nm, and the period in the y-direction of the two-dimensional plane is L. y The center distance L between cylinders 1 and 2 is 530 nm, the radius r of cylinders 1 and 2 is 150 nm, the height h is 180 nm, and the dimer cell is a porous Si metamaterial with a porosity of 30%.

[0054] For Ag-Si nanowire composite thin film material with a metal volume fill rate of 30%, an array period of 6.8±0.2nm, and a pore size of 4.2±0.2nm, porous Si supermaterial with a porosity of 30% is obtained by etching Ag-SiO2 nanowire composite thin film material with a metal volume fill rate of 30% through solution method.

[0055] Solution etching uses hydrogen peroxide, while the dimer cellular structure is fabricated using electron beam lithography.

[0056] Subsequently, the dielectric constants of silver (Ag), silicon (Si), and silicon oxide (SiO2) materials were extracted using ellipsometer software. Based on the equivalent medium theory, the dielectric constant of the metamaterial was then calculated.

[0057]

[0058] ε z =(1-f)ε d +fε m

[0059]

[0060] Where ε x，yε represents the equivalent dielectric constant of the metamaterial in the xy plane. z ε represents the equivalent dielectric constant of the metamaterial in the z-plane. m ε is the dielectric constant of the metal. d Let f be the dielectric constant of the dielectric material and f be the metal filling rate. The transmission spectrum of the bulk material thin film was simulated in electromagnetic simulation software. The optical constants of the anisotropic nanowire hyperbolic metamaterial thin film were extracted by substituting the equivalent medium theory. The results obtained from the electromagnetic simulation were compared with the test results to verify the accuracy of the dielectric constant extraction.

[0061] like Figure 5 As shown, the infrared transmission spectra of the designed metasurface cells in aqueous solutions with different refractive indices (1.33–1.36) exhibit a high Q value (defined as the ratio between the resonant frequency and the full width at half maximum) 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 metamaterials, characterized in that, The material includes a substrate and a dielectric layer on the substrate. A metal nanowire array is vertically embedded into the dielectric layer to form a metamaterial, wherein the dielectric layer is a semiconductor transparent dielectric or a ceramic transparent dielectric. First, the metamaterial in a certain region is photolithographically formed into two cylinders of the same height, which form a dimer cell. The metamaterial in the remaining region is photolithographically formed in a periodic arrangement of several dimer cells to form a QBIC metamaterial based on nanowire hyperbolic metamaterial. In the dimer cell, the radius of cylinder one and cylinder two is 50 nm~400 nm, and the height is 50 nm~500 nm. Dimeric cells in a two-dimensional plane Cycle in direction The wavelength range is 500 nm to 2000 nm, in a two-dimensional plane. Cycle in direction The range is 500 nm to 2000 nm; The distance between the centers of the two cylinders in the dimer cell under the initial height translation symmetry is: , ,destroy The distance between the centers of the two cylinders after directional translation symmetry is , .

2. The QBIC metasurface according to claim 1, characterized in that, The substrate is a 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 silica composite substrate comprises a nanoscale porous silica array and a centimeter-thick quartz substrate, wherein the nanoscale porous silica array is obtained by etching silver nanowires in a silver silica nanowire composite film using a solution method.

4. The QBIC metasurface according to claim 3, characterized in that, The nanoscale porous silica array has an array period of 6 nm to 8 nm, a pore size of 1.0 nm to 4.8 nm, a porosity of 5% to 35%, a pore size variation of 0.1 nm to 0.8 nm, a solid nanopore diameter of 1 nm to 10 nm after etching, an average spacing of 3 nm to 20 nm between solid nanopores, an array period of 6 nm to 40 nm, and a porosity of 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 2 nm to 6 nm, the length of the metal nanowires is the same as the thickness of the dielectric layer, and the spacing between the metal nanowires is 1 nm to 6 nm.

6. The QBIC metasurface according to claim 5, 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 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.

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