EFFECTS OF HIGH-TEMPERATURE AND PRESSURE ON SILICA OPTICAL-FIBER SENSORS

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