Fibre optic mode coupling system uses fibre with grating inscribed in cladding to provide dissipation of selected optical mode in cladding

摘要

The system uses a grating of gradually varying mean index to provide coupling between fibres of different diameter. The optical fibre has a core and a cladding with a grating inscribed by irradiation, coupling at least one light mode with the cladding so that this mode is dissipated within the cladding. The mean index is gradually varied along the grating, at least in the region of the ends of the grating. The gradual variation of the mean index, or of the amplitude of modulation of the index for inscription in the grating, enables limitation of insertion losses for the filter which is formed by the grating.