ABSTRACT
A graded index waveguide coupler has high efficiency, of 78%, but it has stringent alignment tolerances and complex fabrication processes; it is also polarization sensitive. A grating coupler is relatively easy to fabricate and integrate. It has a high alignment tolerance and needs no facet polishing. Light couplers are essential components of both optical interconnects and silicon photonics systems. This chapter introduces and compares the working principles and the properties of the different silicon couplers with each other. Among the reported silicon-on-insulator tapered or inverted tapered spot-size converters, different coupler solutions optimize either small footprint or high coupling efficiency or simple fabrication processes. However, the insertion efficiency is polarization sensitive. However, an epoxy adhesive was needed for bonding with a nanophotonic waveguide. Besides, the inverted prism coupler was polarization sensitive and close to the waveguide, which easily disturbs the waveguide structures.
