A Practical Temperature Sensor with High Sensitivity Utilizing a Fiber Loop Mirror with a Long-Period Grating in a Photonic Crystal Fiber

A practical sensor with high sensitivity for the temperature measurement by using a highly birefringent (HiBi) fiber loop mirror (FLM) concatenated with a long-period grating (LPG) written in a photonic crystal fiber (PCF) is proposed. Only HiBi-FLM acts as a sensor head, while the PCF-LPG serves as a temperature insensitive filter to provide wavelength dependent optical power transmission. A bandpass filter is used to provide a narrow band light source, thus only one of transmission peaks of the HiBi-FLM is located within a negative linear region of the LPG's transmission spectrum. By utilizing the stable filtering function of the PCF-LPG, the resonant wavelength variation of the FLM with temperature is transferred effectively to the intensity variation of the output light. The temperature applied on the FLM is deduced by a cheap optical power. As a result, the sensitivity of the sensor is about -0.4872 dB/°C. When an optical power meter with the resolution of 0.01 dB, a temperature resolution of 0.02°C is achieved.