Label-free optical sensor by designing a high-Q photonic crystal ring-slot structure

We propose a label-free refractive index (RI) sensor based on a high-Q photonic crystal (PhC) ring-slot resonator. The proposed device consists of a ring-slot cavity, in which light is coupled input and output by using a PhC line defect waveguide (W1). By using two dimensional finite-difference time-domain (2D -FDTD) simulation, we show that a Q-factor as high as 107 is achieved when the width (w) of ring-slot equals to 0.20a and the radius of center air hole inner ring-slot equals to 0.34a. Even though the refractive index (RI) equals to 1.330 (water surroundings) at telecom wavelength range, Q of ~11477.3 can also be achieved when the width of ring-slot equals to 0.28a. The RI sensitivity (S) equals to 160 nm/RIU (refractive index unit) and the detect limit (DL) of 8.75×10−5 RIU is obtained. These suggest that the design is a promising candidate for label-free biosensing in medical diagnosis, life science and environmental monitoring.