All-Fiber high temperature and refractive index sensor based on three microspheres array Michelson interferometer

An all-fiber high temperature and refractive index (RI) sensor based on the Michelson interferometer is proposed and experimentally demonstrated. The sensor probe was composed of a three microspheres array (TMSA) which introduces higher-order cladding mode and a section of silica cavity. The microspheres were pre-fusion by fiber fusion splicers, and the silica cavity was a section of single mode fiber (SMF) cascaded to the TMSA about 2.7 cm. To ensure the cleanliness of the Fresnel surface reflection, the TMSA was successfully encapsulated by microtubule which splicing by tiny arc discharge. Furthermore, the effects of the mode order for excitation on RI sensitivity were analyzed in detail from experimental and theoretical. Temperature and RI sensitivity can be measured by monitoring the dip wavelength shift. Temperature sensing presents redshifts, which maximum temperature sensitivity is 115.3 pm/degrees C, and RI sensing presents blueshifts, which sensitivity is -56.63 nm/RIU. In addition, such a compact size, low cost, easy fabrication, and a highly sensitive sensor may widen the application value.