Parabolic Tapered Coupled Two Photonic Crystal Nanobeam Slot Cavities for High-FOM Biosensing

We describe the design and the characterization of high-Q coupled photonic crystal nanobeam cavities for biosensing with 3-D finite-difference time-domain simulation. The majority of optical field localizes in the slotted low-index area, which contributes to a strong light-matter interaction. By introducing a parabolic modulated radius tapering structure, a calculated high quality factor of 1.14 × 10
⁷
has been obtained. Successive infiltrations by liquids with different refractive indices yield a high bulk sensitivity of 415 nm/RIU. A high figure of merit of 4122 and the ultra-compact sensing part of 11.2 μm × 0.8 μm are obtained, which is potentially an ideal platform for lab-on-chip sensors array.