A fibre optic modulator comprises an optical fibre 2 and a waveguide 10 of active material. The waveguide 10 is dimensioned such that any mode of the waveguide has a propogation constant which is separated from the propogation constant of the optical fibre mode by an amount equal to or greater than .lambda./L...http://www.google.fr/patents/US4722583?utm_source=gb-gplus-shareBrevet US4722583 - Modulators
