A nanomaterial sensor based on tapered photonic crystal nanometer-scale cavity in a microdisk

In this paper, we introduce an optical nano-cavity-based sensor comprising tapered air-holes in a circular path with a central radius close to the perimeter of an optical disk resonator. For more confinement and tuning of the whispering gallery modes (WGMs), the air-holes are interconnected by shallow-etched thin slots (SETSs) at a certain radius. In this way, we gained a combination of an optical microcavity disk resonator, a curved row of photonic crystal (PhC), and the SETSs joining the air-holes. The proposed structure benefits from the high-quality (Q) factor WGMs of the disk, the photonic bandgap of PhC, and a nanometer-scale circular slot region for sensing biomaterials. Improved sensitivity, as well as ease of fabrication, can be attained in this combined structure. The high-intensity electromagnetic (EM) fields penetrated in the very small volume nanocavity/slot region provide conditions for the interaction of EM fields with biomaterials in order to enable a lable-free sensing method. The combined slotted-PhC-microdisk resonator structure exhibits sensitivity as high as ~ 99 nm/RIU, and a modal volume as small as ~ 0.055(λ/n)3.