Fibre optic modulators using active multimode waveguide overlays

The evanescent field coupling between a singlemode optical fibre, side polished close to the core and a high index, multimode, planar waveguide overlay has been investigated as a means of realising inline modulators without interruption of the fibre. Oils of known refractive index and thin layers of polished lithium niobate have been used in the role of the overlay and an electro-optic inline intensity modulator based on the latter has been realised and tested. The results demonstrate the technical feasibility of fabricating rugged, low loss solid state devices offering performances which are realistic in terms of applications.