Polarization-Controlled Strain Sensor Based on Helical Birefringence Fiber Loop Mirror

A polarization-controlled strain fiber sensorwith a low detection limit and high sensitivity is proposed and demonstrated using a helical birefringence fiber loop mirror (HBFLM). The HBFLM is consists of a micro-helix region, a macro-helix region, and a fiber ring mirror (FLM). The two standard single-mode fibers (SMFs) are pre-surrounded by each other and use hydrogen flame heating and stretching techniques to prepare the micro-helix region (MIHR). The pre- rotation turns of the MIHR determine the coupling length. The MIHR is influenced by a twisting force. The purpose of the macro-helix region (MAHR) is to regulate the x- and y-polarizationstates in the fiber (applying stress inducesdouble refraction). At the same time, the envelope of the transmission spectrum is modulated to ultimately control the strain sensor. The polarization control of the strain sensor is realized by using the principle of stress birefringence of the SMF. The reasons for the polarization control spectrum are analyzed theoretically. The strain and temperature characteristics were indicated in the experiment. Polarization-controlled strain sensors are expected to be used in high-precision and varying strain range measurements.