Precision phase-shifting applied to fibre Bragg gratings

A simple method of displacing a holographic interferogram within a waveguide based on translation along a slightly tilted fringe pattern of the optical interferogram is presented. By way of example, phase-shifted fibre gratings are produced this way. The spatial resolution in fringe shift is separated from the physical spatial displacement of the optical elements and determined primarily by the fringe tilt angle. This relaxes the tolerances in optical components required and can potentially enable spatial displacements as small as 1 nm/μm to be realised.