Fiber loop ring-down refractive index sensor based on high-Q photonic crystal cavity

A miniature refractive index sensor formed by a high quality (Q-) photonic crystal (PhC) cavity based fiber loop ring-down (FLRD) was demonstrated. To the best of our knowledge, this technology has not been reported. The ring-down time would be changed with the transmittance of PhC cavity, which is related to the refractive index of the infiltrated liquids. By using the finite-difference time-domain (FDTD) method, the system sensitivity was simulated. Result showed that the sensitivity of this simple scheme could reach to 1.25ms per refractive index unit (RIU) and the detection limit below 8×10^-6RIU was achieved. Moreover, the proposed structure has the potential to build on-chip device for in-situ measurement with high sensitivity and high precision.