Electrically Sensing Characteristics of the Sagnac Interferometer Embedded with a Liquid Crystal-Infiltrated Photonic Crystal Fiber

The electrically sensing characteristics of a liquid-crystal-infiltrated polarization-maintaining photonic crystal fiber have been studied. The small holes on the end face of the fiber collapse and two large holes remain open by controlling discharging-time, -current and -position of a fiber splicer, then liquid crystal is selectively infiltrated into the two large holes which can not only save liquid crystal, but also make the welding between the liquid-crystal-infiltrated polarization-maintaining photonic crystal fiber and single-mode fiber much easier. A new method to weld the two fibers is proposed by filling and volatilizing ethanol to make liquid crystal a few millimeters away from the end face which can improve the sensing system stability and prevent the discharge of a fiber splicer from destroying LC molecules. A Sagnac interferometer is set up by embedding the liquid-crystal-infiltrated polarization-maintaining photonic crystal fiber in a fiber loop and then its electroresponse characteristics are studied. The refractive-index distribution of the liquid-crystal-infiltrated polarization-maintaining photonic crystal fiber varies with electric voltage due to the variable index of liquid crystal which makes it possible to detect voltage. Three voltage ranges are discussed by the different dips and the sensitivity is improved with voltage increasing. The high sensitivity is up to 3.49 nm/V with the tuning range of 7 nm as voltage changes from 149.67 to 151.61 V. The Sagnac interferometer embedded with a liquid-crystal-infiltrated polarization-maintaining photonic crystal fiber can be utilized as a voltage sensor, electro-optical modulator or filter.