Bi-Functional Coated Tapered LPFG Sensor: Gas and Temperature Sensing

Abstract

A bi-functional coated tapered Long Period Fiber Grating LPFG as a gas and a temperature sensor is proposed. Obtains a sensor with a high sensitivity is still a matter of challenge. In this work, a taper LPFG is used for sensing purposes. Besides, in order to increase the sensor performance, numbers of Cr and Al layers are coated on the taper region. In this work, different concentrations of four gases Ar, NH3, CH4 and N2 are applied for temperature range (25℃ up to 80℃). however, the experimental results illustrate that the transmission loss is reduce which means a significant interaction between sensing medium and cladding mode is occurred successfully which leads to higher sensitivity. Nevertheless, from the main findings, the temperature sensitivities are 2.9 pm/℃, 4.9 pm/℃, 4.5 pm/℃ and 3.1 pm/℃ for 4% concentrations of Ar, NH3, CH4 and N2 respectively. In addition, the gases sensitives are 0.213 nm%-1, 0.41 nm%-1, 0.39 nm%-1, 0.201 nm%-1 with limit of detection LoD of 0.061%, 0.024%, 0.032% and 0.073% for Ar, NH3, CH4 and N2 respectively. Additionally, the sensor shows a good repeatability, recoverability and stability. In terms of stability, the sensor shows a stable value of wavelength shift under different values of gas concentration and temperatures which was estimated 1.55 µm. Besides, it shows a fast responsivity with 53 s and 60 s as response time and recovery time respectively. Interestingly, with less than 0.06 nm of standard deviation, the signal returned to its original resonance wavelength which confirms that this sensor has a good recoverability. From these results, a coated taper LPFG can be a promising candidate for medical and industrial applications.