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mode, we has near Figure evanesce by simul single-mo roughly 1 undercut fiber taper allo tal mode to in cut geometry from radiating detailing the o the PCWG is s acterize the ta swept-wavelen me. (b) Illus-ocess and the f lectivities r1,2ws the evanescent tail of its fundamen-teract with the PCWG, and the under-of the PCWG prevents the fiber taper into the PC substrate. A schematic ptical path within the fiber taper and hown in Fig. 1(b). To spectrally char-per–PCWG coupler, an external-cavity gth source with a wavelength range of Fig. 1. (a) Schematic of the coupling sche tration of the contradirectional coupling pr feedback within the PCWG caused by the re of the waveguide terminations.show in this Letter that this coupling scheme-unity eff iciency. 1(a) shows an illustration of the fiber taper nt coupling scheme. A fiber taper, formed taneously heating and stretching a standard de fiber until it has a minimum diameter of mm, is positioned above and parallel to an planar PCWG. The small diameter of theEfficient input and o to a photonic c