Liquid Crystal Optical Fibers for Sensing Applications

Abstract

Photonic crystal fibers (PCF) have been demonstrated for various novel sensing for which conventional optical fiber sensors either fail to provide a solution or have low sensitivity issues. A combination of liquid crystal (LC) materials with their tunable optical properties and PCFs with their air-hole microstructure provide the unique advantage to fabricate all-fiber tunable photonic devices. crystal infiltrated photonic crystal fibers (LCPCF) have been demonstrated for various tunable photonic devices such as filters, switches, polarizers, in-line fiber attenuators, polarization controllers etc. Fiber optic based electric field (e-field) and voltage sensors have been demonstrated using conventional fibers and fiber sensors such as fiber bragg gratings for in electric power industry. Due to the natural immunity of the fibers to electromagnetic fields, external transducers or actuators have to be used to induce e-field sensitivity resulting in sensors with low sensitivity. On LC infiltration PCF propagation properties become sensitive to external parameters such as electric fields. The inherent sensitivity of the LCPCF structure and the large e-field induced birefringence of the LC allows to fabricate all-fiber e-field sensor probes with high sensitivity and large measurable e-field range. The book chapter on Liquid crystal photonic crystal fiber for sensing applications focuses on the use of LCPCFs for electric field sensing. The book chapter will discuss miniature e-field probes with capability to detect and measure all the parameters of an unknown e-field such as amplitude, frequency and direction. The work presented in this book chapter includes authors' original contribution in this area. With a brief mention of the tunable properties of liquid crystals and the electric field sensing mechanism of LCPCFs, the book chapter will present details on fabrication and characterization of various LCPCF e-field probes. The capability of the e-field probe to simultaneously measure e-field intensity and frequency will be presented. The chapter will discuss a polarimetric e-field sensing scheme combined with LC infiltration length control to fabricate sensor probes customized for measurement in a particular e-field range. A true all-fiber directional e-electric field sensor using LCPCF will be discussed. The chapter will provide an insight into the future research and application areas of LCPCF such as an all-fiber sensor for both electric and magnetic fields. Fiber optic sensors with capability to simultaneously measure both electric current and voltage for practical in electric power industry and smart grids will also be discussed briefly.