Pushing the limit of high-Q mode of a single dielectric nanocavity

Abstract

High-index dielectric resonators support different types of resonant modes. However, it is challenging to achieve a high-Q factor in a single dielectric nanocavity due to the non-Hermitian property of the open system. We present a universal approach of finding out a series of high-Q resonant modes in a single nonspherical dielectric cavity with a rectangular cross section by exploring the quasi bound-state-in-thecontinuum (QBIC). Unlike conventional methods relying on heavy brutal force computations (i.e., frequency scanning by the finite difference time domain method), our approach is built upon Mie mode engineering, through which many high-Q modes can be easily achieved by constructing avoid-crossing (or crossing) of the eigenvalue for pair-leaky modes. The calculated Q-factor of mode TE(5,7) can be up to Q theory ¼ 2.3 × 10 4 for a freestanding square nanowire (NW) (n ¼ 4), which is 64 times larger than the highest Q-factor (Q theory ≈ 360) reported so far in a single Si disk. Such high-Q modes can be attributed to suppressed radiation in the corresponding eigenchannels and simultaneously quenched electric (magnetic) field at momentum space. As a proof of concept, we experimentally demonstrate the emergence of the high-Q resonant modes [Q ≈ 211 for mode TE(3,4), Q ≈ 380 for mode TE(3,5), and Q ≈ 294 for mode TM(3,5)] in the scattering spectrum of a single silicon NW.

Strong Coupling of Exciton and High‐Q Mode in All‐Perovskite Metasurfaces

“…To maximize the coupling strength and Rabi splitting, high‐ Q modes ensuring large field confinement within the perovskite metasurface are always desired. As a peculiar resonant mode, [ 33 ] the bound state in the continuum (BIC) provides a perfect solution to resolve this issue. [ 34,35 ] BIC corresponds to a nonradiating resonant mode lying within the continuum spectrum.…”

Extraordinary fluorescence enhancement in metal-dielectric core-shell nanoparticles

“…1(c) and 2(c) provide conditions for extraordinary large F = 125 and F = 1850 for Au@TiO 2 and Au@Si core-shells, respectively. Our optimal configurations are obviously far away from the usual MEF range, because the Q-factors of the = 7-pole TE resonances are comparable to the highest Q-factors of purely dielectric structures of similar size [31], both being between the Q-factors of typical plasmonic structures (Q 10 2 [32]) and WGMs in large homogeneous silica spheres (Q ≥ 10 8 [33]).…”

Manipulating Optical Scattering of Quasi-BIC in Dielectric Metasurface with Off-Center Hole

“…Bound states in the continuum (BICs) are special nonradiating states with an infinite lifetime [ 48 , 49 , 50 , 51 , 52 ] that were first introduced in quantum systems in 1929 by von Neumann and Wigner [ 53 ]. In recent years, BICs are also widely found in all-dielectric metasurfaces [ 54 , 55 , 56 , 57 , 58 , 59 , 60 ].…”