Coupler for optical communication system

Claim 1

An optical coupler for interconnecting transmission lines in an optical communication system having at least three optical signal transmission lines each comprising at least one optical waveguide having a core of transparent material having a refractive index N1 surrounded by a layer of transparent cladding material having a refractive index N2 that is lower than N1, said coupler coupling the signal in any one of said optical transmission lines to all of the remaining optical signal transmission lines and comprising: a propagation medium of transparent material of refractive index N3, formed by at least three elongated frusto-conical shaped arms, each having an outer side surface and two planar end faces namely a major base and a minor base which are substantially perpendicular to the longitudinal axis thereof and a connecting medium for mutual optical interconnection of the said minor bases and for mechanical holding of said arms, said longitudinal axes meeting at a common point situated in the said connecting medium which is comprised between said minor bases, said arms being symmetrically disposed with respect to the said common point so that the angle between any pair of said axes is the same, said minor bases having diameters determined such that their respective light radiation pattern in the said connecting medium is substantially hemispherical for the numerical aperture A of the associated transmission line, the value A being equal to √N 1 2 - N 2 2 , layer means surrounding said propagation medium except said major bases for reflecting light that impinges upon the side surfaces thereof, and support means for connecting said transmission lines to said major bases respectively such that the optical waveguide of which a said transmission line is comprised terminate parallel to the corresponding longitudinal arm axis with waveguide end faces disposed in a plane substantially adjacent to the corresponding major base.