Tapered Length Dependence of Pressure Sensitivity in Polarimetric Fiber Pressure Sensor Based on Tapered High Birefringence Fiber

Here we investigated the tapered length dependence of the pressure sensitivity in a temperatureindependent polarimetric fiber-optic pressure sensor (FPS) based on tapered high birefringence fiber (HBF) and a fiber Bragg grating (FBG) for three different tapered lengths of 200, 300, and 400 μm. The investigation on the tapered length dependence was also done for three different types of HBF including one panda type fiber (PM-1550XP) and two bow-tie type fibers (HB1250T and HB1500). The polarimetric FPS was constructed by incorporating a polarization-diversified loop structure composed of a polarization beam splitter, polarization controllers, and a sensor head comprised of a 10.0-cm-long tapered HBF segment and a 1.8-cm-long FBG. The tapered HBF was used as a birefringence element to create polarization interference (PI). A pressure-induced change in the HBF birefringence leads to the wavelength shift of the PI spectrum. The FBG, which is sensitive to an ambient temperature change but nearly insensitive to a pressure change, was utilized to compensate for the temperature cross-sensitivity of the tapered HBF. From the investigation, the pressure sensitivity of the tapered HBF was found out to be proportional to the tapered length irrespective of the fiber type. Moreover, for the same tapered length, HB1500 showed the largest pressure sensitivity. In consequence, the maximum pressure sensitivity of approximately-35.46 nm/MPa could be obtained using bow-tie type HBF (HB1500) with a tapered length of 400 μm. Its adjusted R
²
value representing the sensor linearity was measured as ~0.9973 in an applied pressure measurement range of 0-0.5 MPa.