Selective formation of gradient-index profiles inside a planar polymer substrate by a lithographic technique

A fabricating technique that is capable of easy pattern formation for gradient-index polymer optical devices is proposed. Monomers with low refractive indices are diffused into a gel that contains barium ion patterned by a lithographic technique, and then the diffusion profile is fixed by thermal polymerization. The gradient-index profiles can be selectively formed in the ultraviolet- (UV-) irradiated regions by utilizing the difference in diffusion rate of monomers between regions in the same substrate. The optical properties and shapes of the gradient-index profiles are determined by the diffusion behavior of the monomers into the UV-irradiated regions. A lens array, consisting of two equivalent gradient-index lenses distributed uniformly in the substrate, and a low-loss Y-branched waveguide are fabricated by this technique, and their optical properties are demonstrated.