Ultrasensitive Temperature Sensor Based on a Fiber Fabry–Pérot Interferometer Created in a Mercury-Filled Silica Tube

We demonstrate an ultrasensitive temperature sensor based on a unique fiber Fabry-Pérot interferometer (FPI) that was created by means of splicing a mercury-filled silica tube with a single-mode fiber. The air cavity of the fiber FPI was formed by the surface of the mercury column and the endface of the single-mode fiber. Moreover, the mercury-based fiber FPI exhibits an ultrahigh temperature-sensitivity of up to -41.9 nm/°C, which is about one order of magnitude higher than that of the ordinary FPI-based fiber-tip sensors reported so far. Hence, such a mercury-based fiber FPI temperature sensor could be used for highly sensitive ambient temperature sensing applications.