Effects of high temperature and pressure on silica optical fiber sensors

We report on the effects of liquids at high temperature and pressure on silica optical fibers, sensors, and gratings. We propose that the diffusion of molecules into the silica and the resultant expansion of the network are responsible for observed fiber expansions of up to 0.2% and Bragg wavelength increases of 2 nm at 1525 nm. An amorphous carbon hermetic coating has shown a reduction of these effects by an order of magnitude at 300/spl deg/C. These results have strong implications for the deployment of fiber sensors in hostile environments such as oil wells.