Polarization-insensitive terahertz third-harmonic generation from degenerate pairs of mirror-coupled super-BICs

Author:

Sun Guangcheng1ORCID,Wang Yue1ORCID,Xie Rongbo2ORCID,Zhao Xiaoguang2ORCID

Affiliation:

1. Key Laboratory of Ultrafast Photoelectric Technology and Terahertz Science in Shaanxi, Xi'an University of Technology 1 , Xi'an 710054, China

2. Department of Precision Instrument, Tsinghua University 2 , Beijing 100084, China

Abstract

Resonant nanostructures have emerged as versatile photonic platforms for boosting optical nonlinear responses on a subwavelength scale for their ability to confine intense electromagnetic fields while relaxing the phase-matching requirements. Recent significant advances in this field are associated with the utilization of non-radiative eigenmodes above the light cone, termed bound states in the continuum (BICs), which provide a unique mechanism for light trapping to realize excitation of ultrahigh quality (Q) factor resonances. Nevertheless, the current studies on BICs predominantly focus on symmetry-protected BICs (SP-BICs), whose excitation requires symmetry breaking, and Q factors are limited by fabrication imperfections. Here, we demonstrate a simple and feasible scheme for creating degenerate pairs of mirror-coupled super-BICs by harnessing magnetic dipole resonances coupled to their mirror images in adjacent metal films. Unlike trivial SP-BICs, mirror-coupled BICs showcases the huge enhancement of Q factors and are resilient against fabrication imperfections. By combining mirror-coupled resonance with the engineered radiative loss, we obtain a perfect absorber with near-unity absorption and ultra-narrow bandwidth at a critical coupling condition. Finally, we numerically demonstrate the terahertz (THz) regime, polarization-insensitive highly efficient third-harmonic generation benefiting from the maximum field enhancement localized within the perfect absorber. Our work not only paves the way toward unlocking the full potential of BIC resonance but also promise valuable insights for developing efficient THz optoelectronic devices and metadevices across a wide range of fields.

Funder

National Nature Science Foundation of China

Key Core Technology Research Project for Strategic Industry Chains of Xi'an Science and Technology Bureau

Key Research and Development Projects of Shaanxi Province

Youth Innovation Team of Shaanxi Universities

Publisher

AIP Publishing

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