Highly Sensitive and Tunable Fano-Like Rod-Type Silicon Photonic Crystal Refractive Index Sensor

Abstract

A highly sensitive and tunable 2D rod-type silicon photonic crystal cavity based biosensor configuration has been designed and numerically analyzed. The structure is optimized so that the light-matter interaction is maximized in the cavity region. Out-of-plane light confinement is achieved by sandwiching the rods between metal plates, and tuning is achieved by introducing an air-gap between on top of the rods and the metal plate. A single rod is positioned in the middle of the waveguide so that the cavity Q-factor is enhanced by obtaining a Fano-like resonance. The air-gap between the rods and the metal plate acts as a slot structure, confining E-field in that small region and simultaneously decreasing mode-volume while making the resonance characteristics highly dependent on the gap size. This creates the opportunity to tune the resonance characteristics by electrostatic actuation via applying voltage to the top and bottom metal plates. The proposed structure has a sensitivity value of 1039 nm/RIU, a mode volume of 0.214 ( $\lambda $ /n)3, flexible tuning capabilities, and is the first tunable 2D PhC rod-type refractive index sensor.