Transverse characterization of tapered photonic crystal fibers

We demonstrate the tapering of photonic crystal fibers to create an all-silica two-dimensional photonic crystal with a submicron pitch and holes smaller than 200 nm. We characterize the fundamental partial band gaps of this structure as a function of the taper diameter by probing the fiber in the transverse geometry along both symmetry axes. In tapering the fiber, we are able to shift the fundamental partial gap from the midinfrared to 1100 nm, corresponding to a reduction in diameter by 2.5 times. A complete description of the tapering process is provided. We produced a number of tapers that either maintained the cross-sectional aspect ratio or collapse the holes relative to the photonic crystal structure. From these, we show that the strength of the band gap can be continuously varied by collapsing the holes. For tapers which maintain the cross-sectional aspect ratio, we show that there is a good correlation between the experiment and the band-structure calculations. (C) 2004 American Institute of Physics.