Ultracompact refractive index sensor based on microcavity in the sandwiched photonic crystal waveguide structure

A refractive index (RI) sensor based on the two-dimensional photonic crystal is presented. The sensor is formed by a point-defect resonant cavity in the sandwiched waveguide structure. The transmission spectrums of the sensor with different ambient refractive indices ranging from n = 1.0 to n = 1.6 are calculated. The calculation results show that a change in ambient RI of Δn = 0.001 is apparent, the sensitivity of the sensor (Δλ/Δn) is achieved with 330 nm/RIU (when lattice constant a = 440 nm), where RIU means the refractive index unit; and the transmission efficiency in the RI range of 1.0-1.6 can reach about 40% to 70%, that make the detection of spectrum easy and feasible. The properties of the sensor are analyzed and calculated using the plane-wave expansion (PWE) method and simulated using the finite-difference time-domain (FDTD) method.