Taper control of radially-symmetric gradient-index waveguides in photopolymer

Optical waveguide adiabatic tapers enable low-loss connections between devices with dissimilar mode profiles. Common examples are semiconductor lasers, single-mode optical fibers and planar waveguides. Planar lithographic processes can easily create tapers in the plane but out-of-plane, symmetric tapers are difficult. Three-dimensional direct-write lithography into photopolymer naturally creates radially-symmetric waveguides when the motion is parallel to the optical axis of the writing focus, but absorption in the photopolymer inevitably attenuates the index with depth. We demonstrate that material absorption, translation speed and/or writing power can be used to control this taper, providing an inexpensive mode coupler for integrated optical systems.