Waveguide Optics for Coherent Optical Processing

The results of an effort to further improve thin-film waveguide Luneburg lenses for implementation of the optical Fourier transform as may be employed for real-time wideband RF spectrum analysis is delineated. Overlay Ta2O5 thin-film waveguide Luneburg lenses on Corning 7059 waveguide on thermally-grown SiO2 on a silicon substrate were demonstrated achieving the diffraction-limited results. The smallest beamwidth observed is 1.65 microns for an F/4 Luneburg lens design with side lobes below 17 dB decaying to approximately 30 dB. A numerical procedure was developed and applied to compute the performance of these lenses using waveguide thickness profile ray traces to determine the ray intercepts in the image plane to provide the wavefront phase error and to determine the resulting intensity diffraction pattern. The procedure allows for introduction of profile errors and provides data for F/1, F/2.5 and F/4.5 lenses. A method to synthesize the edge shape so as to obtain the 'true' lens thickness profile has been developed and applied, demonstrating diffraction-limited results. The effort included reduction of waveguide scattering, the creation of a spatial filter, improved reflectors by cleavage, and a waveguide fan-out array. (Author)