Mach-Zehnder Interferometer for In-Situ Non-Contact Temperature Monitoring During Thermal Processing of an Optical Fibre

A Mach-Zehnder interferometer is formed in the transverse plane of an optical fibre. This is exploited to monitor the temperature of any given optical fibre in real time, without any predesigned temperature sensing elements engineered into the fibre and without a need to access the fibre ends. The interferometer is formed by the refraction at the air-glass interface and the subsequent internal reflections within the fibre. The temperature response of the fibre is then measured by quadrature phase shift detection of the interference pattern. For context, this is compared to finite element modelling and a previously studied Fabry-Pérot interferometer configuration. The temperature of an optical fibre was measured from room temperature up to 1174 ^\circC with an error of \pm 2.6\% for the Mach-Zehnder type interferometer. The measurement techniques presented offer a useful tool for precise temperature measurement for applications such as fibre post-processing.