Waveguide coupling device including tapered waveguide with a particular tapered angle to reduce coupling loss

摘要

A waveguide device comprising a cladding layer having a refractive index n.sub.cl, a first waveguide having a refractive index n. sub.g (n. sub.g n.sub.cl) formed on said cladding layer, and a second waveguide having a refractive index n.sub.cp (n.sub.cp n.sub. g) formed on said first waveguide, wherein the sectional shape of said second waveguide has a tapered structure in which a layer thickness of said second waveguide reduces as the distance from the end face of the waveguide increases, and a tapering angle &THgr; in said tapered structure satisfies the following conditions:PP&THgr;. sub.a ={90°-arcsin (n.sub.eff /n.sub.cp)}/2 (1)PP. THETA. 2.0 &THgr;.sub.a (2)PPwherein n.sub.eff represents an effective refractive index of said first waveguide. This waveguide device has a high resistance against the deviation in the positions of the light exit face of an LD or an optical fiber and the light entrance face of a waveguide and thus enables an optical coupling at a high efficiency.