Broadband optical coupling between microstructured fibers and photonic band gap circuits: Two-dimensional paradigms

We demonstrate high efficiency, broadband coupling between photonic crystal waveguides and photonic crystal fibers PCFs using simple two-dimensional design models. We demonstrate an effective largebandwidth small-footprint beam collimator for light exiting a two-dimensional subwavelength scale photonic crystal waveguide consisting of an air core. This collimator relies on destructive interference between diffracted light from the mouth of the waveguide and the light emitted by surface resonators. We demonstrate efficient coupling between air-core photonic crystal waveguides and various two-dimensional models of photonic crystal fibers. A hollow-core photonic crystal fiber, described by an air defect with a Bragg stack cladding on either side, 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 attached by spokes to the PCF cladding, is modeled by a slab waveguide. In this latter case, we demonstrate coupling efficiency better than 94% over a bandwidth of 17%, with peak transmittance exceeding 99%. Combining collimation at the photonic crystal exit port and a nonadiabatic taper in a small-mode-area PCF, we obtain over 98% coupling efficiency over a bandwidth of 135 nm centered at a wavelength of 1.5 m. These results provide valuable paradigms for efficient transfer of optical information between photonic band gap PBG microcircuits and PCF-enabled telecommunication networks.