Polarization-Independent Enhancement of Third-Harmonic Generation Empowered by Doubly Degenerate Quasi-Bound States in the Continuum

Recent advancements in nonlinear nanophotonics are driven by the exploration of sharp resonances within high-index dielectric metasurfaces. In this work, we leverage doubly degenerate quasi-bound states in the continuum (quasi-BICs) to demonstrate the robust enhancement of third-harmonic generation (THG) in silicon metasurfaces. These quasi-BICs are governed by C4v symmetry and therefore can be equally excited with the pump light regardless of polarization. By tailoring the geometric parameters, we effectively control Q-factors and field confinement of quasi-BICs and thus regulate their resonantly enhanced THG process. A maximum THG conversion efficiency up to 1.03 × 10–5 is recorded under a pump intensity of…

• NN
  National Natural Science Foundation of China

  Awards: 12304420, 12264028, 12104105, 12364045, 12364049
• NS
  Natural Science Foundation of Jiangxi Province

  Awards: 20232BAB211025, 20242BAB25041, 20232BAB201040