Numerical analysis of low-RI WGM resonators excited by a periodically arranged multilayer dielectric planar waveguide

In the applications of whispering gallery mode (WGM) resonators, especially those with low refractive indices (RIs), optical excitation is always a critical issue due to the lack of suitable and matching waveguide materials. The Bloch surface wave (BSW) can facilitate achieving an effective coupling, resulting from its field distribution extending a large portion of its mode energy around the external surface and its easy adjustment of the effective refractive index. In this paper, a BSW waveguide platform for adaptive excitation of spherical WGM resonators is proposed, designed, and numerically analyzed. The simulation results show that the WGM resonator stimulated by BSW exhibits a resonance depth (RD) as large as ∼98% and a high total quality factor Q_total∼3.13×10⁴ which is in the same order of magnitude as its intrinsic value Q_intrinsic of 5.8×10⁴. Moreover, less limited by its constitutive materials, this BSW-WGM platform is robust and especially suitable for fully integrated applications.