Polymeric waveguides are fabricated by $O_2$-reactive ion etching. NOA73(UV curable epoxy) and PMMA are used for the waveguide core layer and the cladding layer, respectively. The dependence of waveguide mode profiles and insertion losses on the fabrication parameters is investigated. A numerical simulation of multimode propagation in the planar structure is performed to study multimode interference effects. Based on these results, 1×2 and 1×4 optical splitters are fabricated. Advantages of these splitters are small size and large fabrication tolerances. The mode profiles of fabricated waveguides are observed and the power splitting ratios of fabricated splitters are measured. The power splitting ratio of 1×2 optical splitter is 1 : 0.921 and that of 1×4 optical splitter is 1: 0.675 : 0.820 : 0.677.
