PCF interferometer based temperature sensor with high sensitivity

In this work, the use of a photonic crystal fiber (PCF) with a highly Germanium (Ge) doped core is exploited as temperature sensor for the first time (to our knowledge). The PCF has an outer diameter of 125 μm and consists of a microstructured cladding with an average pitch and hole diameter of Λ=4.6 μm and d=1.0 μm, respectively. A short PCF stub (~2.0 mm) is used for the preparation of an interferometer. The PCF is spliced between single mode fibers (SMF), meaning that the PCF holes are fully collapsed in the splicing region while the Ge-doped core is still present. The splice parameters were changed to make a short collapse region of (200±30) μm. The first splice is used to excite the fundamental core mode and multiple higher order cladding modes by applying a core-to-core offset. The second splice acts as spatial filter to detect only the light which is guided in and near the core. The interferometer is heated up to 500°C and the total wavelength shift with the temperature variation found to be 74 pm/°C which is more than 5 times higher than a fiber Bragg grating at 1550 nm (13 pm/°C). The PCF interferometer preparation requires only a few steps, cleaving and splicing the fibers. The short length, the high thermal sensitivity and stability of the structure make the device attractive for many sensing applications including high temperature ranges.