Photonic Crystal Fiber Loop Mirror-Based Chemical Vapor Sensor

A compact chemical vapor sensor based on a fiber loop mirror (FLM) inserted with a high-birefringent photonic crystal fiber (HiBi-PCF) is proposed and experimentally demonstrated. Because the resonant dips of the HiBi-PCF FLM are sensitive to the phase difference between two counter-propagating waves in the FLM, a highly sensitive chemical vapor can be achieved by measuring the resonant dip shifts when chemical vapor diffuses into the air holes of the HiBi-PCF. Experimental results show a high sensitivity of 15.5 pm/ppm for ethanol is obtained when a 5.1 cm long HiBi-PCF is used in the FLM. Three different mechanisms for the high sensitivity of the proposed sensor are discussed. A liquefaction model with a full-vector finite element method is proposed and is regarded as the main contribution.