The authors demonstrate nearly lossless, broadband coupling of light between photonic band gap (PBG) circuits and photonic crystal fibers (PCFs) using two-dimensional design paradigms. A hollow-core PBG fiber yields a coupling efficiency of better than 94% over a bandwidth of 25% of the center frequency, with peak transmittance exceeding 98%. A small-mode-area PCF consisting of a subwavelength solid core with nonadiabatic taper, combined with a PBG beam collimator at the air-waveguide exit port, yields over 98% coupling efficiency over a bandwidth of 135 nm centered at a wavelength of 1.5 μm.
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