Improved coupling efficiency using /spl Delta/n-controlled polymer waveguides with two-dimensional spot-size transformation

A new type of polymer waveguide for two-dimensional spot-size transformation is described. For this waveguide, while the core cross section in the waveguide is uniform, the /spl Delta/n is properly controlled along the direction of propagation such that the penetration of guided light beyond the core-cladding interface is controlled and spot-size is expanded two dimensionally at one end of the waveguide.