Planar chiral metasurfaces with maximal and tunable chiroptical response driven by bound states in the continuum

• Main Authors: Tan, Shi, Deng, Zi-Lan, Geng, Guangzhou, Zeng, Xianzhi, Zeng, Yixuan, Hu, Guangwei, Overvig, Adam, Li, Junjie, Qiu, Cheng-Wei, Alù, Andrea, Kivshar, Yuri S., Li, Xiangping
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2023
• Subjects: Engineering::Electrical and electronic engineering; Birefringence; Chemical Interaction
• Online Access: https://hdl.handle.net/10356/170855
• Institution: Nanyang Technological University

Optical metasurfaces with high quality factors (Q-factors) of chiral resonances can boost substantially light-matter interaction for various applications of chiral response in ultrathin, active, and nonlinear metadevices. However, current approaches lack the flexibility to enhance and tune the chirality and Q-factor simultaneously. Here, we suggest a design of chiral metasurface supporting bound state in the continuum (BIC) and demonstrate experimentally chiroptical responses with ultra-high Q-factors and near-perfect circular dichroism (CD = 0.93) at optical frequencies. We employ the symmetry-reduced meta-atoms with high birefringence supporting winding elliptical eigenstate polarizations with opposite helicity. It provides a convenient way for achieving the maximal planar chirality tuned by either breaking in-plane structure symmetry or changing illumination angle. Beyond linear CD, we also achieved strong near-field enhancement CD and near-unitary nonlinear CD in the same planar chiral metasurface design with circular eigen-polarization. Sharply resonant chirality realized in planar metasurfaces promises various practical applications including chiral lasers and chiral nonlinear filters.