Guiding Properties of a Photonic Quasi-Crystal Fiber Based on the Thue–Morse Sequence

We present a novel microstructured optical fiber having a quasi-periodic distribution of air holes based on the Thue-Morse sequence. The transverse section of these fibers is basically a two-dimensional photonic quasi-crystal that can also provide complete photonic bandgaps without being a perfect periodic structure. Like in the conventional photonic crystal fibers, if the quasi-periodicity is broken by decreasing the size of some air holes or by introducing an extra air hole, the modified holes become defects that localize and guide light along the fiber. The guidance is attributed to the inhibition of transverse radiation produced by the photonic quasi-crystal cladding. Dispersion curves of guided modes for different structural parameters are calculated, along with the transverse intensity distribution of the fundamental mode. In particular, several specially designed Thue-Morse quasi-crystal fibers with nearly zero ultraflattened group-velocity dispersion are presented.