A Composite Sagnac Fiber Loop for Gas Pressure Sensing

A novel optical fiber sensor, based on a composed-type Sagnac loop for gas pressure sensing, has been introduced and experimentally validated. This sensor consists of a centimeter-scale twin-hole and dual-core fiber (THDCF) sandwiched by two segments of polarization-maintaining fibers (PMFs) via splicing. Given that the pure quartz PMF is insensitive to the variations in gas pressure, it is unsuitable for gas pressure sensing. To improve the sensitivity, a short piece of THDCF is added to the PMF-based Sagnac loop. Theoretical analysis has demonstrated that the presence of THDCF could significantly amplify the impact of air pressure on birefringence. Experimental results reveal that as the ambient gas pressure rises from 0 to 1.2 MPa, the interference spectrum exhibits an obvious red shift with a high sensitivity of 8.381 nm/MPa. The sensor’s reliability has undergone repeated verification by increasing and decreasing the pressure. Attributed to its simple structure, easy fabrication, low cost, and high sensitivity, the proposed sensor is particularly suited for development in harsh environments.