Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides

Nanophotonic waveguides and components are promising for use in the large-scale integration of photonic circuits.Coupling light between nanophotonic waveguides and a single-mode fiber is an important problem and many different solutions have been proposed and demonstrated in recent years.In this paper, we discuss a grating coupler approach.Grating couplers can be placed anywhere on a circuit and can easily be integrated.We have experimentally demonstrated >30% coupling efficiency with a 1 dB bandwidth of 40 nm on standard wafers.Theoretically, the coupling efficiency can be improved to >90% using an optimized grating design and layer stack.The fabrication of the couplers in silicon-on-insulator and in indium phosphide membranes is also discussed.