Coupling of silicon nanophotonic circuits to optical fibers

Silicon-based nanophotonic waveguides and components fabricated in silicon-on-insulator technology build a platform for high density photonic integrated circuits, where active III-V devices can be incorporated using evanescent field coupling. These circuits can be fabricated with standard CMOS technology processing, allowing for low cost mass production in applications such as optical networks, computer interconnects and sensing. Connecting of these integrated structures to the real world of optical fibers appears is an important problem to be solved. In this paper we discuss some solutions and present some of fabricated devices including a grating coupler-polarization splitter with over 50% efficiency for both polarizations and a nonuniform grating coupler with 68% efficiency for single polarization. To the best of our knowledge, they are the highest coupling efficiencies obtained by regular SOI grating couplers for both, single polarization and polarization splitting.