Optical frequency splitter using Bragg diffraction directional couplers

摘要

The zero-dB fused optical fibre coupler comprises two fibres (1,2) with their cores (4) and GeO2-doped sheaths (5) combined over the coupling region (6), in the centre of which a Bragg grating (3) of relatively short length is produced by photo-refractive effect. The radial distribution of dopant in the fibre sheaths may allow for the different field distribution of LP01 and LP11 waves so that the effective variation of refractive index is the same for both modes, and polarisation dependence is reduced.