A slotted metasurface that can enhance third-order nonlinearity

Abstract

The application relates to the fields of micro-nano photonics and nonlinear optical technology, in particular to a slotted metasurface capable of enhancing third-order nonlinearity, which comprises a silicon dimer metasurface structure unit, and a quartz substrate arranged at the bottom of the silicon dimer metasurface structure unit; the silicon dimer metasurface structure unit is composed of two symmetrically arranged nanodisks, the thickness of each nanodisk is 90 nm, the radius of each nanodisk is 180 nm, and the refractive index of each nanodisk is 3.48; a slit with a width of 20 nm and a length of 60 nm is arranged on each nanodisk, and the spacing between the two nanodisks is 10 nm; ED / TD destructive interference is realized through slotted dimer design, the limitation of a traditional structure Q factor (Q>5000) is broken, the Anapole state is combined with the high nonlinear characteristic of silicon, and the THG efficiency is improved to 4.6*10 ‑4 (the highest level of similar silicon structures), and the parameter control flexibility (polarization, geometric size) provides a new paradigm for an on-chip nonlinear optical system.

Description

Technical Field

[0001] This invention relates to the fields of micro-nano photonics and nonlinear optics, specifically to a grooved metasurface that can enhance third-order nonlinearity. Background Technology

[0002] Traditional metallic plasmonic metamaterials suffer from significant ohmic and radiative losses due to their high light absorption characteristics. This not only limits their Q-factor and resonant efficiency but also broadens their response spectrum, making it difficult to achieve efficient optical field localization and energy conversion. Furthermore, traditional optical metamaterials and nonlinear structures face the following technical bottlenecks in achieving efficient third-order nonlinear effects:

[0003] Inherent defects of metallic plasma metamaterials

[0004] High loss problem: Metallic materials (such as gold and silver) have significant ohmic and radiation losses in the optical frequency band, resulting in a resonant quality factor (Q factor) that is usually below 100 and insufficient energy localization efficiency (electric field enhancement factor |E / E0|<50).

[0005] Spectral broadening: High loss increases the resonance linewidth (FWHM), resulting in broadened response spectrum, making it difficult to achieve narrowband, high-precision optical field modulation.

[0006] Nonlinear saturation: Metals have low nonlinear polarizability (χ²) ( ³ ) ≈10 - ¹ 8 (m² / V²), and is prone to thermal effects and electron saturation under high pump intensity, limiting the improvement of nonlinear conversion efficiency.

[0007] Limitations of traditional nonlinear optical structures

[0008] Insufficient electric field enhancement: Although nanostructures based on dielectrics (such as silicon and silicon nitride) have low losses, their electric field localization ability is limited (|E / E0|<100), making it difficult to achieve efficient third-order nonlinearity (such as third harmonic THG efficiency <10) at the nanoscale. -5 ).

[0009] Phase matching difficulties: Nonlinear processes (such as THG) require phase matching conditions, but the subwavelength characteristics of nanodevices are incompatible with the phase matching mechanism of traditional bulk materials, resulting in a significant reduction in energy conversion efficiency.

[0010] Insufficient resonance characteristics and modulation capabilities

[0011] The contradiction between Q-factor and localization: Traditional designs struggle to simultaneously achieve a high Q-factor (narrow linewidth) and strong electric field localization. For example, high-Q resonators typically rely on weak localization modes, while strongly localized structures (such as nanoantennas) suffer from low Q-factors due to radiation losses.

[0012] Poor tuning flexibility: The resonance characteristics of metal / dielectric structures are limited by fixed geometric parameters (such as size and period), making it difficult to achieve dynamic response through simple adjustments (such as polarization and slit parameters).

[0013] Application scenarios are limited

[0014] Integration challenges: The high loss, low efficiency, and phase matching requirements of traditional structures limit their application in on-chip integrated optical systems (such as nanolasers and optical sensors).

[0015] Performance bottleneck of nonlinear devices: Existing technologies cannot meet the cutting-edge demands such as high-sensitivity detection and low-power nonlinear signal processing. Summary of the Invention

[0016] (a) Technical problems to be solved

[0017] To address the shortcomings of existing technologies, this invention provides a slotted metasurface that can enhance third-order nonlinearity.

[0018] (II) Technical Solution

[0019] To achieve the above objectives, the present invention provides the following technical solution: A grooved metasurface that enhances third-order nonlinearity, comprising:

[0020] A silicon dimer metasurface structure unit, wherein a quartz substrate is disposed at the bottom of the silicon dimer metasurface structure unit;

[0021] The silicon dimer metasurface structure unit consists of two symmetrically arranged nanodisks, each with a thickness of 90 nm, a radius of 180 nm, and a refractive index of 3.48.

[0022] Each nanodisk has a slit with a width of 20 nm and a length of 60 nm, and the spacing between two nanodisks is 10 nm;

[0023] The silicon dimer metasurface structure unit exhibits a Fano-shaped decrease in transmission in the near-infrared region, corresponding to a quality factor Q of 6918 and an electric field enhancement factor |E / E0| of 280.

[0024] Preferably, the silicon dimer metasurface structure unit is single-crystal silicon with a refractive index ≥3.4 in the 1100-1200nm wavelength range;

[0025] The slit length b and the dimer spacing g satisfy the proportional relationship b / g=5-10.

[0026] More preferably, the silicon dimer metasurface structural unit exhibits an extremely narrow linear resonance at λ=1107 nm, with a full width at half maximum (FWHM) of only 0.16 nm, corresponding to a Q factor of 6918.

[0027] Preferably, the non-radiative electric field enhancement factor |E / E0| of the silicon dimer metasurface structural unit is ≥250 in the range of λ=1100-1110nm;

[0028] The corresponding third harmonic conversion efficiency is ≥4×10 -4 .

[0029] Preferably, the silicon dimer metasurface structure unit achieves a resonant wavelength tuning range of ≥40nm by adjusting the slit length b=50-90nm;

[0030] By changing the polarization angle of the pump light from 0 to 90°, the intensity of THG can be dynamically varied by ≥10 times.

[0031] More preferably, the silicon dimer metasurface structural unit can be prepared by the following steps:

[0032] Silicon films were deposited on silicon dioxide substrates using low-pressure physical vapor deposition.

[0033] Electron beam lithography is used to customize the pattern of the desired removal portion in the resist layer covering the sample, and the desired groove portion is obtained by inductively coupled plasma etching after development and fixation.

[0034] Plasma cleaning was performed after removing the resist to obtain grooved silicon dimer structural units.

[0035] Preferably, the electron beam lithography uses ZEP520 resist, and the minimum feature size formed after development is ≤20nm.

[0036] (III) Beneficial Effects

[0037] Compared with the prior art, the present invention provides a grooved metasurface that can enhance third-order nonlinearity, and has the following beneficial effects:

[0038] Ultra-high Q factor and narrow linewidth resonance

[0039] The Q factor reaches 6918: a nonradiative Anapole state is formed by the destructive interference of an electric dipole (ED) and a toroidal dipole (TD), achieving an ultra-narrow linewidth (FWHM=0.16 nm) Fano resonance in the near-infrared band (λ=1107 nm), with a Q factor nearly 70 times higher than that of traditional metal plasma structures (Q<100).

[0040] Far-field scattering suppression: Anapole states localize energy in the near-field region, reducing far-field scattering loss by more than 90% and significantly improving resonance efficiency.

[0041] Strong electric field localization and nonlinear enhancement

[0042] Electric field enhancement factor |E / E0|=280~529: The slotted design (a=20 nm, b=60 nm, g=10 nm) forms a subwavelength level electric field localization at the edge of the slit. Combined with the high refractive index of single-crystal silicon (n=3.48), the maximum electric field intensity is more than 5 times that of the traditional silicon nanodisk structure.

[0043] Breakthrough in third-order nonlinear efficiency: At the fundamental frequency λ=1107 nm, the third harmonic (THG) conversion efficiency reaches 4.6×10⁻⁶. -4 Compared to traditional dielectric nanostructures (efficiency ~10), -5 It has increased by more than 10 times.

[0044] Flexible and adjustable dynamic control capabilities

[0045] Resonant wavelength tuning: By adjusting the slit length b (50~90 nm), the continuous tuning range of the resonant wavelength can be ≥40 nm (λ=1080~1120 nm), meeting the requirements of multi-band applications.

[0046] Dynamic polarization control: By changing the polarization angle of the pump light (0~90°), the dynamic range of THG intensity changes by ≥10 times, providing a real-time control method for nonlinear optical devices.

[0047] High-precision fabrication and scalability

[0048] Nanoscale processing precision: Electron beam lithography (EBL) and ICP etching processes are used to achieve a minimum feature size of ≤20 nm (slit width a=20 nm), ensuring structural consistency.

[0049] Process compatibility: Based on the LPCVD silicon film deposition and quartz substrate (n=1.45) fabrication process, it can be adapted to existing semiconductor processes and is suitable for large-scale production. Attached Figure Description

[0050] Figure 1This is a schematic diagram of the slotted silicon dimer metasurface unit structure of the present invention;

[0051] Figure 2 This is a schematic diagram of the transmission spectrum and Fano resonance fitting curve (Q=6918, FWHM=0.16nm) of the present invention;

[0052] Figure 3 This is a schematic diagram illustrating the tuning effect of different slit lengths b on the resonant wavelength of the present invention.

[0053] Figure 4 This is a schematic diagram of the electric field enhancement factor of the present invention as a function of b (peak value 529);

[0054] Figure 5 The THG efficiency of this invention has a cubic dependence on pump power (efficiency 4.6 × 10⁻⁶). -4 ) Schematic diagram;

[0055] Figure 6 This is a schematic diagram of the control curve of the vibration angle on the THG intensity (dynamic range > 10 times) of the present invention;

[0056] In the figure: 1. Quartz substrate; 2. Nanodisk; 3. Slit. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Please see Figure 1-6 The present invention provides a grooved metasurface that enhances third-order nonlinearity, comprising:

[0059] A silicon dimer metasurface structure unit, wherein a quartz substrate 1 is disposed at the bottom of the silicon dimer metasurface structure unit;

[0060] The silicon dimer metasurface structure unit consists of two symmetrically arranged nanodisks 2, each nanodisk 2 having a thickness of 90 nm, a radius of 180 nm, and a refractive index of 3.48.

[0061] Each nanodisk 2 has a slit 3 with a width of 20 nm and a length of 60 nm, and the spacing between two nanodisks 2 is 10 nm;

[0062] The silicon dimer metasurface structure unit exhibits a Fano-shaped decrease in transmission in the near-infrared region, corresponding to a quality factor Q of 6918 and an electric field enhancement factor |E / E0| of 280.

[0063] This grooved metasurface, which enhances third-order nonlinearity, achieves a narrow linewidth (FWHM = 0.16 nm) and exhibits a Fano-shaped transmission drop in the near-infrared region, corresponding to a quality factor Q of 6918. Furthermore, the electric field enhancement factor |E / E0| reaches 280. By adjusting the geometric parameters, the resonant position and energy localization can be precisely tuned. This structure significantly improves the generation efficiency of third harmonic generation (THG) and allows for precise control of THG intensity by adjusting the polarization angle. The working principle is explained below:

[0064] Nonradiative Anapole state formation mechanism

[0065] Core principle: Non-radiative properties are achieved through the destructive interference of electric dipoles (ED) and toroidal dipoles (TD).

[0066] ED and TD interference: When ED and TD are excited simultaneously and spatially overlap, their far-field radiation amplitudes are the same but their phases are opposite, resulting in significant suppression (or even disappearance) of far-field scattering, and energy localization in the near-field region.

[0067] Fano resonance modulation: The Anapole state forms a resonance peak with narrow linewidth (FWHM=0.16 nm) and high Q factor (Q=6918) through the Fano interference mechanism (destructive interference between different modes).

[0068] Nonlinear enhancement mechanism

[0069] Electric field localization: The Anapole state localizes the energy in the slit region of the nanodisk 2 (near field), and the electric field enhancement factor |E / E0| reaches 280~529 (peak value at b=80nm).

[0070] Third-order nonlinear effects: Local electric field and high third-order nonlinear polarizability of silicon (χ²) ( ³ ) The combination of these technologies significantly improves the efficiency of the third harmonic (THG) (4.6 × 10⁻⁶). -4 ).

[0071] Phase matching simplification: Energy localization of Anapole states at subwavelength scales breaks the limitations of traditional phase matching conditions, enabling efficient frequency conversion.

[0072] Working principle of the preferred technical solution

[0073] Structural parameters preferred

[0074] Nanodisk 2 dimensions: 90 nm thickness and 180 nm radius, combined with the high refractive index of single-crystal silicon (n=3.48@1107nm) to enhance the Mie resonance effect.

[0075] Slotted design:

[0076] Slit 3 parameters: width a = 20 nm, length b = 60 nm, enhancing electric field localization through edge effect (|E / E0| = 280).

[0077] Dimer spacing: g=10 nm, optimize the spatial overlap between ED and TD, and enhance destructive interference.

[0078] Cell period: 420 nm, suppressing interference from higher-order diffraction modes and ensuring a single resonance peak.

[0079] Performance tuning optimization

[0080] Wavelength tuning: Adjust the length b of slit 3 (50~90 nm) to adjust the resonant wavelength by changing the local current distribution (tuning range ≥40 nm).

[0081] Polarization modulation: By changing the polarization angle of the pump light (0~90°), the excitation ratio of ED and TD can be adjusted to achieve dynamic changes in THG intensity of ≥10 times.

[0082] Optimal preparation process

[0083] Silicon film deposition: A 90 nm silicon film was deposited on a quartz substrate 1 (n=1.45) using the LPCVD method, ensuring high refractive index and low defect density.

[0084] Electron beam lithography: ZEP520 resist is used to achieve a minimum feature size of ≤20 nm (corresponding to slit width accuracy 3).

[0085] ICP etching: Dry etching of the silicon layer down to the quartz interface to avoid the influence of sidewall roughness on the Q factor.

[0086] Detailed Workflow

[0087] Materials and Structure Preparation

[0088] Substrate treatment: Clean quartz substrate 1 (SiO2, n=1.45) to ensure the surface is free of contaminants.

[0089] Silicon film deposition: A 90 nm thick single-crystal silicon film (refractive index 3.48@1107nm) was deposited on the substrate by LPCVD.

[0090] Photolithographic patterning:

[0091] Spin-coating ZEP520 resist (thickness ~200 nm).

[0092] Electron beam lithography (EBL) defines a grooved dimer pattern (a=20 nm, b=60 nm, g=10 nm).

[0093] After development, a high-precision resist mask is formed.

[0094] ICP etching:

[0095] Etching conditions: Cl2 / Ar mixed gas, power 200 W, etching rate ~50 nm / min.

[0096] Etching endpoint detection: The complete etching of the silicon layer to the quartz interface is monitored by optical emission spectroscopy (OES).

[0097] Post-processing:

[0098] Oxygen plasma cleaning removes residual resist.

[0099] The final structure has a period of 420 nm, and the unit size matches the design requirements.

[0100] Performance verification and tuning

[0101] Linear optical testing:

[0102] Transmission spectra were measured using a supercontinuum laser source (1000~1200 nm) to verify the Fano resonance (Q=6918) at λ=1107 nm.

[0103] Nonlinear testing:

[0104] Pump source: tunable laser (λ=1107 nm), power range 1~100 mW / μm².

[0105] THG detection: The third harmonic signal at 369 nm was measured using a spectrometer, and the conversion efficiency (4.6 × 10⁻⁶) was calculated. -4 ).

[0106] Dynamic regulation experiment:

[0107] Rotate the pump light polarization angle (0~90°) and record the THG intensity change (dynamic range ≥10 times).

[0108] Adjust the length b of slit 3 (50~90 nm) and observe the resonant wavelength shift (Δλ≥40 nm).

[0109] Key innovations and applications

[0110] Innovation points:

[0111] The ED / TD destructive interference is achieved through a slotted dimer design, breaking through the Q factor limitation of traditional structures (Q>5000).

[0112] By combining the Anapole state with the high nonlinearity of silicon, the THG efficiency is increased to 4.6 × 10⁻⁶. -4 (The highest level among similar silicon structures).

[0113] The flexibility of parameter tuning (polarization, geometry) provides a new paradigm for on-chip nonlinear optical systems.

[0114] Application areas:

[0115] Nanolasers: Low-threshold laser emission is achieved by utilizing high Q resonance.

[0116] Quantum optics: Strong local electric fields enhance single-photon nonlinear effects.

[0117] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A slotted metasurface that can enhance third-order nonlinearity, characterized in that, include: A silicon dimer metasurface structure unit, wherein a quartz substrate is disposed at the bottom of the silicon dimer metasurface structure unit (1). The silicon dimer metasurface structure unit is composed of two symmetrically arranged nanodisks (2), each nanodisk (2) having a thickness of 90 nm, a radius of 180 nm, and a refractive index of 3.

48. Each nanodisk (2) has a slit (3) with a width of 20 nm and a length of 60 nm, and the spacing between two nanodisks (2) is 10 nm; The silicon dimer metasurface structure unit exhibits a Fano-shaped decrease in transmission in the near-infrared region, corresponding to a quality factor Q of 6918 and an electric field enhancement factor |E / E0| of 280.

2. The slotted metasurface of claim 1, wherein, The silicon dimer metasurface structure unit is a single-crystal silicon with a refractive index ≥3.4 in the 1100-1200nm wavelength range; The length b of the slit (3) and the dimer spacing g satisfy the proportional relationship b / g=5-10.

3. The slotted metasurface that can enhance the third-order nonlinearity of claim 2, wherein, The silicon dimer metasurface structural unit exhibits an extremely narrow linear resonance at λ=1107 nm, with a full width at half maximum (FWHM) of only 0.16 nm, corresponding to a Q factor of 6918.

4. The slotted metasurface of claim 3, wherein, The non-radiative electric field enhancement factor |E / E0| of the silicon dimer metasurface structural unit in the range of λ=1100-1110nm is ≥250. The corresponding third harmonic conversion efficiency is ≥ 4 x 10 -4 .

5. The slotted metasurface of claim 4, wherein, The silicon dimer metasurface structure unit achieves a resonant wavelength tuning range of ≥40nm by adjusting the slit (3) length b=50-90nm; By changing the polarization angle of the pump light from 0 to 90°, the intensity of THG can be dynamically varied by ≥10 times.

6. The slotted metasurface that can enhance the third-order nonlinearity of claim 5, wherein, The silicon dimer metasurface structural unit can be prepared by the following steps: Silicon films were deposited on silicon dioxide substrates using low-pressure physical vapor deposition. Electron beam lithography is used to customize the pattern of the desired removal portion in the resist layer covering the sample, and the desired groove portion is obtained by inductively coupled plasma etching after development and fixation. Plasma cleaning is performed after removing the resist to obtain slotted silicon dimer structural units.

7. The slotted metasurface that can enhance the third-order nonlinearity according to claim 6, wherein, The electron beam lithography uses ZEP520 resist, and the minimum feature size formed after development is ≤20nm.

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