Optical Sensor Based on Vernier-Cascade of Ring Resonator and Echelle Diffraction Grating

An optical sensor based on the Vernier-cascade of a ring resonator and an echelle diffraction grating (EDG) demultiplexer is proposed and analyzed. Due to the difference between the free spectral range of the ring and the channel spacing of the EDG demultiplexer, the refractive index change of the analyte fluid on the ring can be detected by the power distribution among the channels of the EDG. By combining a coarse measurement and a fine measurement, a refractive index sensitivity in the order of 10^-6 RIU can be achieved. An optical sensor system can be realized by using a low-cost broadband light source and a detector array.