High Temperature Measurement Up to 1100 $^{\circ} \hbox{C}$ Using a Polarization-Maintaining Photonic Crystal Fiber

A reflective fiber-optic interferometer for ultra-high temperature measurement is proposed and experimentally demonstrated. The device consists of a short piece of polarization-maintaining photonic crystal fiber (PM-PCF) spliced with a lead-in single mode fiber (SMF) without any offset. The hollow holes within the PM-PCF are partly collapsed due to the directional arc-heating splicing and excite two linearly polarized (LP) modes over the downstream PM-PCF. These two LP-modes are reflected at the end face of PM-PCF and backward recoupled into the lead-in SMF through the collapsed region. A superimposed interference pattern is obtained as the result of interference of the polarized modes. The proposed interferometer is demonstrated for ultra-high temperature measurement up to 1100 °C with a sensitivity of 12.3 pm/°C over repeated measurements. Meanwhile, isochronally thermal annealing has been studied to address the effect of residual stress in the sensing probe and the feasibility of further improving temperature measurement range of the device.