All-fiber Mach-Zehnder interferometer using a tapered photonic crystal fiber for refractive index measurement

A compact and robust refractive index (RI) sensor based on a tapered photonic crystal fiber (PCF) Mach-Zehnder Interferometer (MZI) was proposed. It consists of a section of tapered PCF which is spliced between two single-mode fibers (SMF). A strong evanescent field was formed near the tapered region and made the susceptible to external RI variations. In addition, a PDMS detection cell is designed to increase the stability and robustness of the sensor. The interference between the core and the cladding modes of the PCF is utilized. Experimentally, the sensor exhibits highly RI sensitivity which is found to be 51.902nm/RIU within a range from 1.3411 to 1.3737. A resolution of 1.93×10^-5 RIU was achieved since the OSA has a resolution of 1pm. The proposed all-fiber RI sensor based on tapered PCF is attractive due to its compact size, low cost and immunity to electromagnetic interference beyond what conventional magnetic field sensors can offer.