Double photonic band gap hollow-core photonic crystal fiber

Drawing on recent advances in understanding the origin of the photonic band gap observed in hollow core photonic crystal fibers, we apply the photonic tight binding model to a high air filling fraction fiber. By studying the interdependent effect of the apex, strut and air-hole resonators present in the photonic crystal cladding, we demonstrate that it is possible for a second photonic band gap windows to extend significantly below the air-line, whilst the general properties of the fundamental band gap remains relatively unaffected. We fabricate several hollow core fibers with extremely thin struts relative to the apex size. All fibers exhibit two strong transmission windows that bridge the benchmark laser wavelengths of 1064nm and 1550nm. These results pave the way to extend the guidance capability of low-loss hollow core fibers.