Slotted metasurface capable of enhancing third-order nonlinearity

Abstract

The invention relates to the technical field of micro-nano photonics and nonlinear optics, in particular to a slotted metasurface capable of enhancing third-order nonlinearity, which comprises a silicon dimer metasurface structure unit, and a quartz substrate is arranged at the bottom of the silicon dimer metasurface structure unit; each silicon dimer metasurface structure unit is composed of two symmetrically-arranged nano-plates, the thickness of each nano-plate is 90 nm, the radius of each nano-plate is 180 nm, the refractive index of each nano-plate is 3.48, each nano-plate is provided with a narrow slit with the width of 20 nm and the length of 60 nm, the distance between the two nano-plates is 10 nm, ED / TD destructive interference is achieved through slotted dimer design, and the traditional structure Q factor limitation (Qgt; the method has the advantages that the THG efficiency is improved to 4.6 * 10 <-4 > (the highest level of similar silicon structures) and the parameter regulation and control flexibility (polarization and geometric dimensions), and a new normal form is provided for an on-chip nonlinear optical system.

Description

Technical Field

[0001] The invention relates to the field of micro-nano photonics and nonlinear optical technology, and in particular to a slotted metasurface capable of enhancing third-order nonlinearity. Background Art

[0002] Traditional metal plasma metamaterials have significant Ohmic loss and radiation loss due to their high light absorption characteristics, which not only limits their Q factor and resonance efficiency, but also makes the response spectrum wider, making it difficult to achieve efficient light field localization and energy conversion. Secondly, traditional optical metamaterials and nonlinear structures have the following technical bottlenecks in achieving efficient third-order nonlinear effects:

[0003] Intrinsic defects of metal plasmonic metamaterials

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

[0005] Spectral broadening: High loss increases the resonance linewidth (FWHM) and broadens the response spectrum, making it difficult to achieve narrow-band, high-precision light field control.

[0006] Nonlinear saturation: The nonlinear polarizability of metals is low (χ (3) ≈10 -18 m 2 / V 2 ), and thermal effects and electron saturation are prone to occur 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 capability is limited (|E / E0| < 100), making it difficult to achieve efficient third-order nonlinearity at the nanoscale (such as third harmonic THG efficiency < 10 -5 ).

[0009] Phase matching is difficult: nonlinear processes (such as THG) need to meet 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 controllability

[0011] The contradiction between Q factor and localization: It is difficult for traditional designs to achieve both high Q factor (narrow linewidth) and strong electric field localization. For example, high-Q resonant cavities usually rely on weakly localized modes, while strongly localized structures (such as nanoantennas) have low Q factors due to radiation losses.

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

[0013] Limited application scenarios

[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] Nonlinear device performance bottleneck: Existing technologies cannot meet cutting-edge demands such as high-sensitivity detection and low-power nonlinear signal processing. Summary of the invention

[0016] 1. Technical issues to be resolved

[0017] In view of the deficiencies in the prior art, the present invention provides a slotted metasurface that can enhance third-order nonlinearity.

[0018] (II) Technical solution

[0019] To achieve the above object, the present invention provides the following technical solution: A slotted metasurface capable of enhancing third-order nonlinearity of the present invention comprises:

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

[0021] The silicon dimer metasurface structural unit is composed of two symmetrically arranged nanodisks, each of which has a thickness of 90 nm, a radius of 180 nm, and a refractive index of 3.48;

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

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

[0024] Preferably, the silicon dimer supersurface structure unit is single crystal silicon, and its refractive index in the 1100-1200nm band is ≥3.4;

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

[0026] Further preferably, the silicon dimer metasurface structure unit exhibits an extremely narrow linear resonance at λ=1107 nm, and the fitted half-maximum full width of the resonance is only 0.16 nm, corresponding to a Q factor of about 6918.

[0027] Again preferably, the electric field enhancement factor |E / E0| of the Anapole state of the silicon dimer supersurface structure unit is ≥250 within the range of λ=1100-1110nm;

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

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

[0030] By changing the polarization angle of the pump light (0-90°), the THG intensity can be dynamically changed by ≥10 times.

[0031] Further preferably, the silicon dimer supersurface structure unit can be prepared by the following steps:

[0032] Depositing a silicon film on a silicon dioxide substrate using low pressure physical vapor deposition (LPCVD);

[0033] The desired removal portion pattern was customized in the resist layer (ZEP520) covering the sample using electron beam lithography (EBL), and the desired groove portion was obtained by inductively coupled plasma etching (ICP) after development and fixation;

[0034] The resist is removed and then plasma cleaned to obtain the grooved silicon dimer building blocks.

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

[0036] (III) Beneficial effects

[0037] Compared with the prior art, the present invention provides a slotted 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 non-radiative Anapole state is formed through the destructive interference of the electric dipole (ED) and the toroidal dipole (TD), and an ultra-narrow linewidth (FWHM=0.16nm) Fano resonance is achieved in the near-infrared band (λ=1107nm). The Q factor is nearly 70 times higher than that of traditional metal plasma structures (Q<100).

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

[0041] Strong electric field localization and nonlinear enhancement

[0042] Electric field enhancement factor |E / E0|=280~529: The slot design (a=20nm, b=60nm, g=10nm) forms a subwavelength 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 strength is more than 5 times that of the traditional silicon nanodisk structure.

[0043] Third-order nonlinear efficiency breakthrough: At the fundamental wave λ = 1107nm, the third harmonic (THG) conversion efficiency reaches 4.6×10 -4 , compared with traditional dielectric nanostructures (efficiency ~10 -5 ) increased by more than 10 times.

[0044] Flexible and adjustable dynamic control capability

[0045] Resonance wavelength tuning: By adjusting the slit length b (50-90nm), the resonance wavelength continuous tuning range ≥40nm (λ=1080-1120nm) can be achieved to meet the needs of multi-band applications.

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

[0047] High-precision preparation and scalability

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

[0049] Process compatibility: The preparation process based on LPCVD silicon film deposition and quartz substrate (n=1.45) can be adapted to existing semiconductor processes and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0052] Figure 3 Schematic diagram of the tuning effect of different slit lengths b on the resonance wavelength of the present invention;

[0053] Figure 4 Schematic diagram of the curve of the electric field enhancement factor according to the present invention varying with b (peak value 529);

[0054] Figure 5 The cubic dependence of THG efficiency on pump power (efficiency 4.6×10 -4 ) Schematic diagram;

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

[0056] In the figure: 1. Quartz substrate; 2. Nanodisk; 3. Narrow slit. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] See also Figure 1-6 , a slotted metasurface capable of enhancing third-order nonlinearity of the present invention comprises:

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

[0060] The silicon dimer metasurface structural unit is composed of two symmetrically arranged nanodisks 2, each of which has a thickness of 90 nm, a radius of 180 nm, and a refractive index of 3.48;

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

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

[0063] The slotted metasurface that can enhance the third-order nonlinearity achieves a narrow linewidth (FWHM = 0.16nm) and exhibits a Fano-shaped transmission drop in the near-infrared region, corresponding to a quality factor Q of 6918. In addition, the electric field enhancement factor |E / E0| reaches 280. By adjusting the geometric parameters, the resonance position and energy positioning can be precisely tuned. The structure significantly improves the generation efficiency of the tripled frequency (THG) and allows the intensity of THG to be precisely controlled by adjusting the polarization angle. The following is a description of the working principle:

[0064] Nonradiative Anapole State Formation Mechanism

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

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

[0067] Fano resonance regulation: The anapole state forms a resonance peak with a narrow linewidth (FWHM = 0.16nm) and a 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 when b=80nm).

[0070] Third-order nonlinear effect: Local electric field and high third-order nonlinear susceptibility of silicon (χ (3) ) combined with the third harmonic (THG) efficiency (4.6×10 -4 ).

[0071] Simplified phase matching: The energy localization of Anapole states at the subwavelength scale breaks the limitations of traditional phase matching conditions and achieves efficient frequency conversion.

[0072] How the Optimal Technology Solution Works

[0073] Structural parameter optimization

[0074] The size of the nanodisk 2 is 90 nm thick and 180 nm in radius. The high refractive index of single-crystal silicon (n=3.48@1107 nm) is combined to enhance the Mie resonance effect.

[0075] Slotted Design:

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

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

[0078] Unit cell period: 420nm, suppressing interference of high-order diffraction modes and ensuring a single resonance peak.

[0079] Performance Control Optimization

[0080] Wavelength tuning: adjust the slit length b (50-90nm) and adjust the resonant wavelength by changing the local current distribution (tuning range ≥40nm).

[0081] Polarization control: Change the polarization angle of the pump light (0-90°) to adjust the ED and TD excitation ratio to achieve a dynamic change of THG intensity ≥10 times.

[0082] Preparation process optimization

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

[0084] Electron beam lithography: Using ZEP520 resist, the minimum feature size can be ≤20nm (corresponding to the slit width accuracy).

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

[0086] Detailed workflow

[0087] Materials and structure preparation

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

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

[0090] Photolithography patterning:

[0091] ZEP520 resist was spin coated (thickness -200 nm).

[0092] Electron beam lithography (EBL) defined the 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 200W, etching rate ~50nm / min.

[0096] Etch endpoint detection: Optical emission spectroscopy (OES) is used to monitor the complete etching of the silicon layer to the quartz interface.

[0097] Post-processing:

[0098] Oxygen plasma cleaning removes residual resist.

[0099] The final structure period is 420nm and the unit size matches the design requirements.

[0100] Performance verification and control

[0101] Linear Optics Test:

[0102] The transmission spectrum was measured using a supercontinuum laser light source (1000-1200 nm) to verify the Fano resonance (Q=6918) at λ=1107 nm.

[0103] Non-linear test:

[0104] Pump source: tunable laser (λ=1107nm), power range 1~100mW / μm 2 .

[0105] THG detection: The spectrometer measures the third harmonic signal at 369nm and calculates the conversion efficiency (4.6×10 -4 ).

[0106] Dynamic control experiment:

[0107] The polarization angle of the pump light was rotated (0-90°) and the THG intensity change was recorded (dynamic range ≥10 times).

[0108] The slit length b was adjusted (50 to 90 nm) and the resonance wavelength shift was observed (Δλ≥40 nm).

[0109] Key innovations and applications

[0110] Innovation:

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

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

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

[0114] Application areas:

[0115] Nanolasers: low-threshold lasing using high-Q resonances.

[0116] Quantum optics: Strong local electric fields enhance the nonlinear effects of single photons.

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

Claims

1. A slotted metasurface capable of enhancing third-order nonlinearity, characterized in that: include: A silicon dimer supersurface structure unit, wherein a quartz substrate (1) is arranged at the bottom of the silicon dimer supersurface structure unit; The silicon dimer supersurface structural 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) is provided with a narrow slit (3) with a width of 20 nm and a length of 60 nm, and the distance between two nanodisks (2) is 10 nm; The silicon dimer metasurface structure unit exhibits a Fano-shaped transmission drop in the near-infrared region, corresponding to a quality factor Q of 6918 and an electric field enhancement factor |E / E0| reaching 280.

2. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 1, characterized in that: The silicon dimer supersurface structural unit is single crystal silicon, and its refractive index in the 1100-1200nm band is ≥3.4; The slit length b and the dimer spacing g satisfy a proportional relationship of b / g=5-10.

3. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 2, characterized in that: The silicon dimer metasurface structural unit exhibits an extremely narrow linear resonance at λ=1107 nm, and the fitted half-maximum full width of the resonance is only 0.16 nm, corresponding to a Q factor of about 6918.

4. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 3, characterized in that: The silicon dimer supersurface structure unit has an electric field enhancement factor of |E / E0| of the Anapole state ≥ 250 within the range of λ = 1100-1110 nm; The corresponding third harmonic (THG) conversion efficiency is ≥4×10 -4 .

5. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 4, characterized in that: The silicon dimer metasurface structure unit achieves a resonance wavelength tuning range of ≥40nm by adjusting the slit length b=50-90nm; By changing the polarization angle of the pump light (0-90°), the THG intensity can be dynamically changed by ≥10 times.

6. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 5, characterized in that: The silicon dimer super surface structural unit can be prepared by the following steps: Depositing a silicon film on a silicon dioxide substrate using low pressure physical vapor deposition (LPCVD); The desired removal portion pattern was customized in the resist layer (ZEP520) covering the sample using electron beam lithography (EBL), and the desired groove portion was obtained by inductively coupled plasma etching (ICP) after development and fixation; Plasma cleaning is performed after the resist removal to obtain the grooved silicon dimer building blocks.

7. The slotted metasurface capable of enhancing third-order nonlinearity according to claim 6, characterized in that: The electron beam lithography uses ZEP520 resist, and the minimum feature size formed after development is ≤20nm.

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