Directional optical waveguide coupler and power tap arrangement

Claim 1

A directional optical waveguide coupler and power tap capable of coupling core-guided modes propagating in a first direction out of a transmission optical waveguide and avoiding loss of core-guided modes which may be propagating in a second direction, the transmission optical waveguide including a core surrounded by a layer of cladding material having a refractive index which is less than the refractive index of the core material, the directional coupler and power tap comprising a second optical waveguide comprising a core having a given refractive index surrounded by a layer of cladding material having a refractive index which is less than the refractive index of said second waveguide core material, the core of said second waveguide having a cross-sectional area which is significantly smaller than the cross-sectional area of the core of the transmission waveguide, and one end of said second waveguide being abutted with an end of the transmission waveguide in a manner to permit a significant amount of the core-guided modes propagating in the first direction in the transmission waveguide to be coupled into the cladding layer of said second waveguide at said abutting point and to permit core-guided modes introduced at the other end of said second waveguide and propagating in a second direction in said second waveguide to be coupled primarily into the core of the transmission waveguide at said abutting point, and means disposed at a first intermediate position along the peripheral surface of said second optical waveguide capable of coupling out of the cladding layer of said second waveguide the cladding modes coupled therein primarily from the core of said transmission waveguide for subsequent conversion to a representative electrical signal.