  The evanescent coupling from a photonic crystal resonator to a micron-thick
optical fiber is investigated in detail by using a 3D-FDTD method. Properly
designed photonic crystal cavity and taper structures are proposed, and optimal
operating conditions are found to enhance the coupling strength while
suppressing other cavity losses including the coupling to the slab propagating
mode and to the higher-order fiber mode. In simulation, the coupling into the
fundamental fiber mode is discriminated from other cavity losses by spatial and
parity filtering of the FDTD results. The coupling efficiency of more than 80%
into the fundamental fiber mode together with a total Q factor of 5,200 is
achieved for the fiber diameter of 1.0 um and the air gap of 200 nm between the
fiber and the cavity.
