High-Q and High-Sensitivity Photonic Crystal Cavity Sensor

We present the design, fabrication, and the characterization of a high-quality-factor (Q) and high-sensitivity photonic crystal (PhC) cavity sensor on the silicon-on-insulator platform. By optimizing the structure of the PhC cavity, most of the light can be distributed in the lower index region; thus, the sensitivity can be dramatically improved. The transmission spectrum of the PhC cavity sensor is measured by immersing the device into a sodium chloride (NaCl) solution of different mass concentrations. A Q factor of
$1.3 \times 10^{4}$
and a very high sensitivity of 428 nm/RIU have been experimentally demonstrated. Furthermore, the total size for the sensing part of the PhC cavity sensor is only
$14.5 \times 0.75\ \mu\hbox{m}^{2}$
.