High sensitivity temperature and pressure sensor based on cascaded Fabry-Perot and Sagnac interferometers

Abstract

A sensor was proposed and experimentally demonstrated to improve temperature and pressure sensitivity by the Vernier effect. The sensor is composed of a cascaded Fabry-Perot interferometer (FPI) and a Sagnac interferometer (SI), which has almost the same free spectral range (FSR) forming the Vernier effect. The SI is a fiber-loop consisting of a segment of polarization maintaining fiber (PMF). The FPI consists of a section of quartz capillary inserted between two sections of single mode fiber. A micro-channel is drilled in the quartz capillary using a femtosecond laser to circulate air inside and outside the Fabry-Perot (F-P) cavity. SI and FPI in the sensor structure are selectively sensitive to temperature and pressure. In temperature sensing, the SI acts as the sensor and FPI as the reference, whereas in pressure measurements, the FPI is the sensing unit and SI the reference unit. Thus, in Vernier effect sensing, they perform the functions of reference or sensing units to each other. The sensor provides high sensitivity for both temperature and pressure. Experimental results show that the temperature sensitivity is ∼23.14 nm/°C, which is ∼13.4 times higher for the single SI sensor (–1.73 nm/°C), and the pressure sensitivity is ∼49.2 nm/MPa, which is ∼12.2 times higher than for the single FPI sensor (4.02 nm/MPa). The sensor has a simple structure, easy preparation, and high sensitivity of both temperature and gas pressure, and has widespread prospective application.