亚波长铌酸锂薄膜导模共振结构设计及二次谐波转化效率优化

Subwavelength lithium niobate film guided mode resonance structure design and second harmonic conversion efficiency optimization

基于亚波长铌酸锂薄膜刻蚀导模共振超表面结构,理论模拟了超表面结构的光学响应特性,探讨了刻蚀微纳结构的周期、填充因子和刻蚀深度等参量对透射光谱的影响,同时研究了不同偏振态和入射角度的光源对光谱线宽的作用;利用非对称的光栅结构设计,使连续谱中的束缚态(bound states in the continuum,BIC)衰退为高Q值(>10000)的准BIC模式;利用束缚态的局域场增强效应,将亚波长铌酸锂薄膜的二次谐波转化效率提升了5个数量级.模拟结果表明,当入射基频波的峰值功率密度在约1 GW/cm2量级时,可实现紫外波段二次谐波高效转化,即单次穿过亚波长铌酸锂薄膜后,出射的紫外波段二次谐波转化效率高达10–3量级.这为提升微纳结构、光学表界面体系的非线性响应特性提供了思路和设计方案.

The optical response characteristics of a subwavelength lithium niobate film guided-mode resonance metasurface were investigated via simulations.The influences of parameters such as the period,filling factor and etching depth of the etched micro–nano structure on the transmission spectrum were examined,and the effects of light sources with different polarization states and incidence angles on the spectral linewidth were imvestigated.Because of the asymmetric grating structure design,the bound states in the continuum(BIC)decay into a quasi-BIC mode with a high Q value(>10000),and the second harmonic conversion efficiency of the subwavelength lithium niobate film increases by five orders of magnitude as a result of the local field enhancement effect of the bound state.The simulation results show that a high-efficiency conversion of the second harmonic can be realized in the ultraviolet band when the peak power density of the incident fundamental wave is on the order of~1 GW/cm2,that is,the ultraviolet second harmonic conversion efficiency emitted after a single pass through the subwavelength lithium niobate film is up to 10–3 orders of magnitude.This study affords ideas and design schemes for improving the nonlinear response characteristics of a micro–nano structure and optical table interface system.