Sapphire Fiber Based Sensing Technologies for High Temperature Applications
Sapphire fiber has been studied intensively for harsh environment sensing in the past two decades due to its supreme mechanical, physical and optical properties. It is by far the most reported and likely the best optical fiber based sensing technology for sensing applications in temperature beyond 1000°C.
Several sensing schemes have been proposed and studied to date including sapphire fiber extrinsic and intrinsic Fabry-Perot interferometers, fiber Bragg gratings and long period gratings inscribed in sapphire fibers. Lacking the cladding, sapphire fiber is highly multi-moded which renders sapphire fiber based sensor fabrication much more difficult than those based on silica fibers. Among all the reported work on sapphire fiber sensing, the vast majority is for single point temperature measurement.
In this work, different sensing schemes are proposed to enhance the capability of the sapphire fiber based sensing technology. For the single point sensing, a miniaturized sapphire fiber temperature sensor for embedded sensing applications was proposed and studied. The sensors are no more than 75 µm in diameter and are ideal for non-invasive embedded sensing applications. Unlike existing sapphire fiber sensors, the thin film sensors are batch-fabrication oriented and thus have a potential to permit mass production with low cost. In addition to single point sensors, multiplexed sapphire fiber sensing systems are investigated for the first time. Two multiplexed sensing solutions, named frequency-multiplexing and spatial-multiplexing, are proposed and studied to achieve multiplexed sensing based on sapphire fibers.