Development of a Miniature, Semi-Distributed Sapphire Fiber Optic Thermometer for Harsh and High Temperature Environments

Abstract

Fiber optic temperature sensing has become a well-defined field in the past few decades [1] through the use of Fiber Bragg Gratings, Fabry-Perot interferometry, and pyrometry, to list several techniques in use today. The use of fiber optics offers significant advantages over electronic sensing in terms of size and insensitivity to harsh conditions such as extreme temperatures and corrosive environments. The availability of optical sapphire materials, including fibers, has allowed the creation of fiber optic sensing elements able to continuously operate at temperatures of 1600"C [2] or more, thus outstripping the abilities of many commonly used thermocouples (excluding platinum types R, S, and B) [3] which will also exhibit a sensitivity to electromagnetic fields.

In addition to the aforementioned benefits, fiber optic sensing techniques provide a great deal of accuracy in temperature measurement over the entire working range of the sensor.

The work documented in this thesis consists of efforts to minimize the overall footprint of a sapphire based extrinsic Fabry-Perot interferometry (EFPI) temperature sensing element, as well as strides made in multiplexing the same element and reducing the error potential from cross sensitivity of the thermometer with applied strain. This work has been variously funded by Pratt & Whitney and the Department of Energy.