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Fabrication of Optical-Mode Converters for Efficient Fiber-to-Silicon-Waveguide Couplers

Optical-mode converters are needed to efficiently couple light from an optical fiber to a photonic circuit by matching and transforming the propagating modes. This work is based on a horizontally-tapered coupler, in which light from an optical fiber is coupled into a large polymer waveguide and then gradually transferred to a smaller silicon waveguide whose width increases with distance along the guide. Several devices were designed and fabricated to measure the efficiency of the coupler. E-beam exposure doses and writing strategies were optimized to create the tapered silicon waveguides. A fabrication process was developed to form the polymer waveguides without etching the underlying silicon, and a set of marks was created to achieve sub-micron alignment between the two waveguides. Fabrication results showed that the coupler successfully transfers light between the two waveguides and that there is low loss in the polymer. A more accurate characterization of the coupler's efficiency was delayed due to fabrication problems not related to the developed process. Thesis Supervisor: Henry I. Smith Title: Professor of Electrical Engineering