Two-dimensional mode size transformation by Δn-controlled polymer waveguides

We report a new type of polymer waveguide for two-dimensional (2-D) mode size transformation in which Delta n (refractive index difference between core and cladding) is properly controlled along the waveguide suds while the core cross section is kept uniform, The beam diameter in the Delta n-controlled waveguide where the core diameter is 3.7 mu m and Delta n changes from 0.0027 to 0.0009 toward one end in the 5 mm-gradient Delta n region, is about twice as large as that in a normal waveguide where Delta n is 0.0027, The optical loss accompanied by mode size transformation is calculated to be less than 2.5% based on beam propagation methods (BPM's).