Encapsulated and coated photonic crystal fibre sensor for temperature measurements up to 1000°C

Abstract

Fibre optic sensors for high temperature applications have significant advantages over their non-optical counterparts, because they are passive and immune to electromagnetic interference, can be multiplexed, have higher sensitivity, better accuracy, etc. The development of such sensors has emerged owing to their large number of industrial and R&D applications. Such applications range from weld control and monitoring to turbine engine testing. Space vehicles, high power lasers, fire alarm systems, monitoring of furnace operation or volcanic events also require reliable sensors with stability at ultra high temperature (up to 1000 °C). Sensors made from conventional Ge-doped optical fibres may survive under such harsh conditions. However, their optical properties are compromised because of the out-diffusion of Ge into the fibre cladding at high temperature. Fabry-Perot [1] and modal interferometer [2] in photonic crystal fibre (PCF) have been proposed to overcome the drawbacks of Ge-doped fibre sensors for high temperatures. The inconvenience of PCF based devices is their fragility, especially at high operating temperatures. A proper packaging that protects the fibre sensing head and at the same time maintains its optical performance is thus required, this being the aim of our work here presented.