Low Temperature Sensor Based on Etched LPFG with Different Materials Coating

A low temperature sensor based on etched Long Period Fiber Grating LPFG is proposed and demonstrated. A chemically etched LPFG sensor coated with (Indium In, Aluminum Al, Silver Ag, Palladium Pd and Titanium Ti) embedded within a build low temperature setup. The sensor investigation was carried out under temperature range of 20℃ to -150℃; and the resonance wavelength shift was collected with different cooling rates of (10, 15, 20, 25℃/min) in order to investigate the effect of cooling rates on the sensor performance. However, the experimental results show that 10 mm LPFG sensor with grating period of 400 µm offer temperature sensitivity of 1.5 times, 2 times, 2.5 times, 3 times and 3.5 times higher than bare LPFG for Ti-coated LPFG, Pd-coated LPFG, Ag-coated LPFG, Al-coated LPFG and In-coated LPFG respectively. The maximum measuring error is less than ±0.5℃, which confirms the effectively using of LPFG sensor in cryogenic application. Moreover, the overall resonance wavelength shifts are 1.213 nm, 1.532 nm, 1.935 nm, 2.015 nm, 2.397 nm and 2.671 for bare LPFG, Ti-coated LPFG, Pd-coated LPFG, Ag-coated LPFG, Al-coated LPFG and In-coated LPFG sensors respectively. According to the cooling rates, the results illustrate that as cooling rate increase, the sensor sensitivity decrease due to the sensor response. For more investigations, simulation work is carried out using MATLAB and the sensor shows a good agreement results between experimental and simulation measurements. It is worth to mention that the main findings will essentially contribute to choose suitable materials for coating LPFG for low temperature sensing purposes and will increase the existing knowledge about optical fiber sensor applications.