High-Sensitivity Temperature Sensor Based on Microsphere Cavity in Super Larger Thermo-Optic Coefficient Germanium-core Fiber

A high-sensitivity temperature sensor based on an in-fiber germanium (Ge) microsphere Fabry-Perot (FP) cavity is presented. The lower melting point of the Ge core compared to that of a silica-based fiber is utilized to fabricate the microsphere at the fiber end as a FP cavity by splicing a Ge-core borosilicate-clad fiber to a single-mode fiber. The Ge-core borosilicate-clad fiber employed is fabricated using a molten core approach with the standard optical fiber draw tower. The large thermo-optic coefficient of semiconductor Ge microsphere cavity gives rise to high temperature sensitivity. Experimental results show that the temperature sensitivity of
_~
221 pm/°C can be achieved as the temperature changes from -40°C to +50°C. The proposed sensor also exhibits outstanding stability, with the measurement error and standard deviation within the range ±0.184°C and 0.0049-0.0155°C, respectively. The advantages of high sensitivity, outstanding stability and in-fiber cavity make the proposed sensor a potential candidate for temperature sensing applications.