Strain-insensitive high-sensitivity temperature sensing based on multimode interference in a square-core fiber

A strain-insensitive high-sensitivity temperature sensor based on multimode interference in a specialty fiber with a square core is developed and experimentally investigated. A 25 cm long square-core fiber is used as a multimode fiber (MMF) of a single-mode-multimode-single-mode structure and the temperature dependence of its transmitted spectrum is measured while the strain is applied continually from 0 to 500 μϵ with steps of 100 μϵ. The mean temperature sensitivity is -22.35 pm °C-1, which is ∼3.5 times higher than that of a standard MMF, and it is almost independent of strain with a small standard deviation of 0.44 pm °C-1.