High pressure sensing using fiber Bragg gratings written in birefringent side hole fiber

Pressure measurements are made by measuring Bragg grating peak splitting caused by transverse strain differences in the core of a single mode side hole fiber. The side holes and not the fiber exterior are pressurized, demonstrating the ability to use the side holes as a pressure conduit so that pressure measurements can be made in a thermally and mechanically stable environment. Geometrical and residual stress-based birefringence stemming from partial side hole collapse during the drawing process allows measurements to be made near atmospheric pressures. Peak fitting techniques are used to determine peak separation to sub-pm levels despite substantial peak overlap.