Design of a photonic crystal microcavity for biosensing

We have designed an air-bridged PhC microcavity with high sensitivity and a high quality factor. The structure parameters of the microcavity are optimized by three-dimensional finite-difference time-domain method. We compare the performance of a silicon-on-insulator PhC microcavity and an air-bridged PhC microcavity, and analyze the effect of the thickness of the slab and the radius of the defect hole on the performance of the air-bridged PhC microcavity. For a thinner slab and a larger defect hole, the sensitivity is higher while the quality factor is lower. For the air-bridged photonic crystal slab, the sensitivity can reach 320-nm/RIU (refractive index unit) while the quality factor keeps a relatively high value of 120 by selecting the proper slab thickness and the defect hole radius, respectively, when the refractive index is 1.33. This is meaningful for low-detection-limit biosensing. © 2011 Chinese Institute of Electronics.