Pushing the Limit of High-Q Mode of a Single Subwavelength Dielectric Nanocavity

TL;DR

This paper introduces a universal leaky mode engineering approach to achieve high-Q resonant modes in single subwavelength dielectric nanocavities, significantly surpassing previous Q-factor limits and confirmed experimentally.

Contribution

The authors develop a new method based on quasi-bound states in the continuum to find high-Q modes in nonspherical dielectric nanocavities, avoiding heavy computations.

Findings

Q-factor up to 2.3×10^4 in silicon nanowires

64 times higher Q-factor than previous reports in nanodisks

Experimental demonstration of high-Q modes with Q=380

Abstract

High index dielectric nanostructure supports different types of resonant modes. However, it is very challenging to achieve high-Q factor in a single subwavelength dielectric nanoresonator due to non-hermtian property of the open system. Here, we present a universal approach of finding out a series of high-Q resonant modes in a single nonspherical dielectric nanocavity by exploring quasi-bound state in the continuum. Unlike conventional method relying on heavy computation (ie, frequency scanning by FDTD), our approach is built upon leaky 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 Q-factor can be up to 2.3*10^4 for square subwavelength nanowire (NW) (n=4), which is 64 times larger than the highest Q-factor (Q=360) reported so far in single subwavelength nanodisk. Such high-Q modes can be attributed to suppressed radiation in the corresponding eigenchannels and simultaneously quenched electric(magnetic) at momentum space. As a proof of concept, we experimentally demonstrate the emergence of the high-Q resonant modes (Q=380) in the scattering spectrum of a single silicon subwavelength nanowire.