发表机构
Singapore University of Technology and Design (SUTD); Australian National University（新加坡科技设计大学; 澳大利亚国立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究了由立方非线性材料制成的薄膜超表面，通过准法向模展开和时间耦合模理论，证明非线性极化率张量主轴与超表面轴的相对旋转可诱导手性，产生高达99.5%的非线性圆二色性，为非线性手性光学开辟新途径。
AI 中文摘要
传统上，手性超表面依赖于结构或外在的对称性破缺，而非线性圆二色性通常被视为已经具有手性的线性响应的共振增强结果。本文表明，手性可以由原本非手性的共振超表面的非线性极化率诱导产生。研究了由立方非线性材料（如晶体硅）制成的正方形晶格中的圆形孔组成的薄膜超表面。在正入射下，该结构线性非手性，支持高Q准导共振，对左旋和右旋圆偏振光表现出相同的响应。利用准法向模展开和扩展到非线性 regime 的时间耦合模理论，证明了立方非线性极化率张量主轴与超表面轴之间的相对旋转会产生相反圆偏振的不等三阶谐波产生。根据螺旋相位匹配标准，阐述了在没有几何手性的情况下非线性圆二色性的结果，并讨论了为什么这种机制在具有二阶非线性的材料中对二次谐波产生是被禁止的。由此产生的非线性圆二色性达到99.5%，并简单地依赖于相对角度，当谐波频率的共振被额外激发时，从四重周期性切换到八重周期性。我们的结果将非线性诱导的手性确立为一种全新的手性光子响应途径，无需几何对称性破缺，为平面CMOS兼容超表面中的非线性手性光学开辟了机会。
英文摘要
Achieving near-unity nonlinear circular dichroism (CD) typically requires geometric symmetry breaking, making it challenging to combine helicity selectivity, resonant enhancement, and structural simplicity. We show that crystal orientation enables near-unity third-harmonic (TH) CD in highly symmetric resonant metasurfaces formed by a square lattice of circular holes in a cubic nonlinear material. Under circularly polarized excitation, strong near-field components of both helicities enabled by the rotational symmetry of the metasurface open two symmetry-allowed in-plane TH generation pathways. Crystal orientation controls their nonlinear coupling, selectively enabling destructive interference for one incident helicity. Our nonlinear temporal coupled-mode theory identifies the conditions for near-unity CD, reveals the distinct roles of pump and TH resonances, and explains the fourfold and eightfold crystal-orientation dependence. Across silicon, germanium, and diamond, we obtain resonantly enhanced TH CD exceeding 99% in the near-infrared, establishing crystal orientation as a design degree of freedom for nonlinear CD in highly symmetric metasurfaces.
