Formation of a refractive index grating

摘要

An apodised refractive index grating is recorded in a photosensitive optical fibre by forming first and second component interference patterns with different pitches, that are recorded in the grating such as to result in apodisation. The component patterns (16, 17) are spatially in phase in a central region and move progressively out of phase towards the ends of the patterns. The patterns may be recorded sequentially or concurrently. The fibre may be stretched one or cyclically.