“…Most of these optical sensors measure the variations of optical properties as a result of a change in the refractive index of a gas or a liquid. Various structures have been investigated as optical sensors such as fiber Bragg gratings (Fang et al, 2010), step-index fibers and photonic crystal fibers (Lee et al, 2011;Udd and Spillman, 2011), fiber-assisted surface plasmon resonances (Ma et al, 2009), and photonic crystals (Liu and Salemink, 2012;Jágerská et al, 2010;Kang et al, 2010;Bougriou et al, 2013). Recently, optical resonance in photonic crystals has received increased attention for refractive index sensing applications.…”