Transmissive Refractive Index Sensing Based on Frequency-Sensitive Responses of Two-Dimensional Photonic Crystals

In this paper, we propose a new scheme of refractive index (RI) sensing, which utilizes frequency-sensitive responses of 2-D photonic crystals. Specifically, the 2-D photonics crystals consist of dielectric rods arranged in rectangular lattice and support frequency-sensitive supercollimation (SC). Small changes in ambient RI are sensed by measuring transmission rate of a narrow spectral source. This RI sensing scheme exploits the sensitive dispersion properties around the SC frequency: Both reflection and beam diffraction are enhanced in response to a slight increase of ambient RI. Operation and performance of the transmissive RI sensing are demonstrated by finite-difference time-domain (FDTD) simulations. The major advantage of our design is that all the essential components can be compactly integrated, which makes it attractive for a number of applications, such as hand-held equipment and distributed sensor networks.