  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%.
