High Performance Temperature Sensing of Single Mode-Multimode-Single Mode Fiber With Thermo-Optic Polymer as Cladding of Multimode Fiber Segment

We present a fiber sensing for temperature with two different mode interferences. The sensor consists of a single mode-multimode-single mode (SMS) fiber with a specifically designed and synthesized thermo-optic polymer cladding, forming a leaky mode fiber interferometer and a guided one at different temperatures. A maximum temperature sensitivity of 1.4 dB/°C below 61°C and of 15 nm/°C above 72°C have been achieved. The high temperature sensitivity is mainly attributed to the high thermo-optic coefficient of the polymer cladding. The phenomenon of the fiber temperature sensing around the transformation point can be observed and studied using the proposed fiber sample. It is found that the SMS fiber sensor is more sensitive to temperature for both of the mode interferences when the refractive index (RI) of the polymer is closer to that of the multimode fiber core, and the measurement range is relatively wide.