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摘要

由高折射率介质材料制备的亚波长人工结构, 通过电磁谐振效应为在纳米尺度操控光提供了一种有效方法. 这类结构的吸收损耗通常较低, 然而辐射损耗降低了其非线性响应的效率. 通过连续域束缚态(bound states in the continuum, BICs)可望解决这个问题. BICs是一种处于连续域内而保持局域的非常规光学态, 存在于光锥线以内并且具有无限大的 Q值. 本文提出通过破坏硅纳米颗粒阵列原胞的对称性将BIC转变成准BIC, 使得结构的透射谱中出现高 Q的窄共振谷, 当调节泵浦波长至共振波长时, 非线性响应显著增强, 三次谐波激发的强度提高了6个数量级, 转化效率可提升至约2.6 × 10 ^–6, 该结果有望应用于硅基光学非线性器件的设计.

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Abstract

Subwavelength artificial structures of high refractive index dielectrics provide an effective way to control and manipulate light on a nanoscale by enhancing electric and magnetic fields. This kind of structure usually has low absorption loss, but its performance is also limited by radiation loss, which will reduce the efficiency of its nonlinear response. This problem can be solved by using bound states in the continuum (BICs). The BICs are a kind of unconventional state which is in continuous domain but remains localized. They exist within a light cone and have an infinite quality factor. By combining BICs with nonlinear optics, high- Qresonances from quasi-BICs are used to excite and enhance the nonlinear response. The simulation shows that when the symmetry of the unit cell of the silicon nanoparticle arrays is broken, the BIC become the quasi-BIC, and the transmission spectrum will produce a high- Qnarrow resonance valley. The resonance has polarization dependence of electric field. With the change of pump wavelength, the third-harmonic generation (THG) intensity first increases and then decreases gradually. The pump wavelength changed by several nanometers can change THG intensity by at least one order of magnitude. When the pump wavelength is adjusted to the resonance wavelength, the nonlinearity is significantly enhanced as a result of the strong field localization. The THG intensity is highly sensitive to the variation of asymmetric parameters. Only a change of 75 nm will result in a decrease of THG intensity by at least one order of magnitude. There is a third-order relationship between pump power and THG power. For the proposed structure, the factors affecting the conversion efficiency of THG include pump power, pump wavelength, polarization angle of pump light, and asymmetry parameter. When the polarization direction of electric field is along the short axis of the structure and the pump light at resonance wavelength is vertically incident to the structure with an asymmetric parameter of 0.125, the conversion efficiency of THG can be increased to ～2.6 × 10 ^–6and the intensity of THG is increased by six orders of magnitude. The results are expected to be applied to designing the silicon-based optical nonlinear devices.

Keywords:

high refractive index dielectric materials/
quasi bound states in the continuum/
third-harmonic generation

作者及机构信息

杜芊,
陈溢杭

通信作者:陈溢杭,yhchen@scnu.edu.cn

基金项目:广东省自然科学基金(批准号: 2015A030311018, 2017A030313035)和广州市科技计划(批准号: 2019050001)资助的课题

Authors and contacts

Corresponding author:Chen Yi-Hang,yhchen@scnu.edu.cn

Funds:Project supported by the Natural Science Foundation of Guangdong Province, China (Grant Nos. 2015A030311018, 2017A030313035) and the Science and Technology Program of Guangzhou, China (Grant No. 2019050001)

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参考文献

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施引文献

下载: 全尺寸图片幻灯片

C₄_v	E	2C₄	C₂	2σ_v	2σ_d	C₂_v	E	C₂	σ_y	σ_x
A₁	1	1	1	1	1	A₁	1	1	1	1
B₁	1	–1	1	1	–1	A₁	1	1	1	1
A₂	1	1	1	–1	–1	A₂	1	1	–1	–1
B₂	1	–1	1	–1	1	A₂	1	1	–1	–1
E	2	0	–2	0	0	B₁	1	–1	1	–1
E	2	0	–2	0	0	B₂	1	–1	–1	1

下载: 导出CSV

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