Efficient power coupling to waveguides in high index contrast systems

Abstract

Future integrated optical circuits will hold, on a single chip, several optical components that communicate via high index contrast waveguides. Silicon nitride (SixNy) and silicon oxynitride (SixOyNz) waveguides with silicon oxide cladding can be used to guide light on a chip because they have small dimensions, low scattering loss, and can be fabricated with silicon-based technology. With more components on a chip, we need to develop novel technologies to seamlessly route the optical signal from one waveguide to multiple waveguides simultaneously, or from the optical fiber to a waveguide. This thesis presents the design and fabrication of two such devices. The first is a compact multimode interference coupler, also called multi-mode interferometer (MMI), which can equally distribute the optical power from one input waveguide to multiple output waveguides. The prototypes were fabricated for silicon-rich SixNy waveguides with 1 input and 4 or 8 output ports. The second device is a compact fiber-to-waveguide coupler, which can efficiently confine the light from an optical fiber to a sub-micron waveguide.

(cont.) The prototypes were fabricated for SixOyNz waveguide of index 1.70. The advantages of these couplers are their very compact size, high efficiencies, and their fabrication process can be adapted by mainstream silicon-based manufacturing technology. In addition, their designs are very robust and can be applied for efficient coupling into any high index contrast dielectric waveguide.