Liquid Crystal Based Tunable Fiber Polarizer for Pressure Sensing

We propose a photoelastic pressure sensor using a liquid crystal (LC) tunable fiber polarizer. The polarizer contains an etched single mode fiber sealed in a LC cell. A low index LC is used as a tunable birefringent cladding of the fiber. Any electric-field induced LC director reorientation thus may affect the fiber´s light-guiding characteristics. Different polarization states experience different LC cladding indices. The transmittance contrast between x- and y-polarized modes reaches 31.9 dB, which is sensitive enough to monitor any polarization state change in the fiber. A pressure sensor with the sensitivity of 0.25 rad/N is thus demonstrated. The corresponding stress-optic coefficient of the fiber is measured at 1550 nm telecomm band. Advantages and applications of the LC tuning and sensing technologies are discussed.