Ultrasensitive refractive index sensor based on parallel-connected dual Fabry-Perot interferometers with Vernier effect

Abstract A kind of ultrasensitive refractive index sensor based on parallel-connected dual Fabry-Perot interferometers (FPIs) with Vernier effect is proposed and demonstrated. The open and closed cavity FPIs are used as the sensing and reference units, respectively. The Vernier effect is realized by superimposing the reflective comb spectra of the dual FPIs, which have slightly different free spectral ranges. The open groove of the open cavity FPI provides a convenient, efficient and economical method for filling in or draining out the cavity. The stability, repeatability and temperature response of the structures are investigated. Experimental results indicate that the proposed sensing structure features high sensitivity, good stability, quick and accurate measurement.