Design and analysis of mid infrared temperature sensor based on chalcogenide glass photonic crystal fiber

Abstract

Owing to exceptional optical properties, wide transmission window, thermal stability, and high thermo optic coefficient, Ge-Sb-Se Photonic Crystal Fiber (PCF) can be a good candidate for mid infrared range (MIR) temperature sensing applications. On the other hand, Sagnac Interferometer (SI) is one of the popular interferometric sensing tools which is not yet utilized for designing mid infrared temperature sensor. In this thesis, a novel Sagnac Interferometer based Ge20Sb15Se65 glass PCF temperature sensor operating in the mid infrared region is theoretically analyzed. Two different design structures named as circular lattice and square lattice PCFs are designed in COMSOL Multiphysics 5.3 which exhibit high phase birefringence and zero group birefringence in the operating wavelength. The PCF cladding air holes are proposed to be filled with a highly temperature sensitive liquid chloroform to enhance the temperature sensitivity. Different optical properties of this proposed PCF are investigated in MIR range by using finite-element method (FEM). These highly phase birefringent PCFs are used as the temperature sensing fiber of the proposed SI based temperature sensor. The temperature sensing characteristics of five different infiltration technique of liquid is investigated theoretically and compared. Simulation results show that full infiltration performs better than no infiltration or partial infiltration. In the numerical analysis, for circular lattice PCF, two sensing dips with high linearity is achieved for full infiltration which shows sensitivity of −5.87 nm/°C and 8.59 nm/°C respectively when the temperature increases from 35 to 95 °C for the specific fiber length of 1.08 mm. It also shows ultrahigh sensitivity of 22 nm/°C if the detection range is reduced to 35 to 40 °C which can be very useful for human body temperature measurement. For square lattice PCF average sensitivity of −10.5 nm/°C and 12 nm/°C is achieved with high linearity for detection range of 20-60 °C for the 0.22 mm fiber length. The proposed highly sensitive temperature sensor has broad detection window which can be applied in fingerprint unlocking, MIR radiation detection in human body, biomedicine applications, and environmental temperature monitoring.