Optical Fiber Refractometer Based on Etched-Stress Applying Parts PANDA Fiber

In this letter, an optical fiber refractometer fabricated by etched-stress applying parts (SAPs) PANDA fiber is proposed and experimentally demonstrated. The proposed structure depends on an in-fiber Mach-Zehnder interferometer (MZI), which is induced by the two orthogonal polarization modes of the fiber and the dip wavelength shifts as a function of the surrounding medium refractive index. In the sensor area, one of the axes is quickly etched to near the fiber core modifying the evanescent field, which results in increasing birefringence variation by the surrounding medium. The fiber has been chemically etched with the etched length of 5 cm. High sensitivity of 151 nm/RIU (refractive index unit) within the linear sensing range from 1.3401 to 1.3997 and a resolution of \(1.32 \times 10^{-4}\) RIU are obtained for the proposed liquid refractive index sensor.