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 reported, with which coupling efficiency of waveguides with 4- and 8-μm core diameters was reduced by /spl ap/1.6 dB. The length needed for spot-size transformation was less than 1 mm along the direction of propagation. In this polymer waveguide, refractive index difference between core and cladding (/spl Delta/n) is properly controlled along the direction of propagation while the core cross section is kept uniform.