Dual Sagnac Interferometer-Based Fiber Microstructured Sensor With High Sensitivity

An ultra-compact fiber-optic microstructured sensor is fabricated and utilized for highly sensitive sensing. A straight single-mode fiber (SMF) and two SMF-based Sagnac interferometers are integrated together via three-core twisted microfiber. The propagating modes in both interferometers and high-order modes in the twisted microfiber interact with each other in the microfiber region, finally enhancing multi-mode interference and fiber-optic sensitivity. The twisted points in microfiber could increase the propagating modes and improve mode interference at the same time. By coating UV-glue film around twisted microfiber, sensing scope and sensitivity could be further improved, because of glue material with relatively large refractive index, high thermo-optic coefficient and humidity-sensitive characteristics. In sensing applications, four different environmental parameters are measured in sequence, which fiber-optic sensitivities are -142.4 pm/oC for temperature sensing, 57.2 pm/%RH for humidity sensing, -59.7 pm/με for strain sensing, and 0.108 dB/o for torsion sensing. It could be easily predicted that such compact fiber-optic microstructured sensor has broad sensing potentials and high sensitivity, which could be utilized in various sensing applications.