Multicolor Lithography for High Efficiency, Low Insertion Loss NLO polymer Devices

摘要

Advances in using multicolor lithography to define waveguides in NLO polymer thin films are described in this report. These waveguides are defined by the refractive index gradients produced by optically photoprocessing the polymer films. This process, based on the spatial, temporal, and intensity distribution of laser radiation on the film, permits the 3-dimensional control of refractive index gradients within the films, allowing the fabrication of advanced waveguide structures. Experiments were done on three polymer films developed at USC. Measurements were made of the photoprocessing rates in these films and compared to a theory developed for photoprocessing in photoresist films. The thermal stability of photoprocessed films was investigated. Refractive index changes and optical attenuation in the photoprocessed regions were measured using prism coupling and ellipsometry. An optimal film was selected, and waveguide channels were photoprocessed in it through a mask. These channels were subsequently buried using flooding radiation without the mask. The film was then subjected to reactive ion etching over the channels, removing material at the surface. These experiments demonstrated the feasibility of using optical photoprocessing to create waveguide transitions from large waveguides matching optical fibers to small waveguides for minimizing the spacing of modulation electrodes.