Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backwards propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.