Cavity confinement in defect-based honeycomb photonic crystals and the design of waveguide–cavity Fano-coupler for dielectric loss sensing

Abstract

Honeycomb photonic crystal (PhCs) also known as photonic graphene exhibits salient features such as common complete photonic bandgap, topological states, and degrees of freedom to manipulate local density of states for efficient light–matter interactions. In this work, we report the cavity confinement offered by the six different point defect geometries of honeycomb PhCs. It is found that the reported point defect geometries are capable of supporting high confinement with low effective mode area of the order of 10−4 m2. To make use of this cavity confinement, a Fano-coupler is designed based on waveguide–cavity (WG-C) interactions in honeycomb PhC. The transmission/reflection profiles of a WG-C geometry shows typical Fano resonances with the quality factor of the order of 104. Comparing square and triangular PhCs, honeycomb WG-C shows a relatively stable Fano-lineshape resonance for a variation in imaginary part of the dielectric permittivity (ɛr′′) of an unknown dielectric material loaded at the center of the cavity from 0 to 0.01. The proposed WG-C Fano-coupler is suitable for dielectric loss sensing over a conventional cavity perturbation method, in which Fano resonance is sustained with Q factor variation of 25,805 to 2431 for ɛr′′ variation from 0 to 0.01, respectively. Due to the nature of PhC cavity decay dynamics, two different linear sensitive regimes with the dielectric loss sensitivity of 96.901/ɛr′′ (for ɛr′′=0 to 0.005) and 26.911/ɛr′′ (for ɛr′′=0.005 to 0.01) are observed. We anticipate that the cavity confinement and Fano-interactions reported in honeycomb PhCs might be useful not only to explore sensing elements but also for unraveling light–matter interactions in cavity quantum electrodynamics, quantum optics and lasing systems.