Optimization of the operational bandwidth in air-core photonic bandgap fibers for IR transmission

We determine the optimal inner glass ring thickness in infrared air-core photonic bandgap, fibers (PBGFs) with 19-cell and 7-cell cores. For PBGFs with a 19-cell core, we find that an inner ring thickness of 0.04 Lambda, where Lambda is pitch, yields the widest operational bandwidth. which is nearly 6%. The operational bandwidth increases as the refractive index decreases from 2.8 to 2.0. For PBGFs with a 7-cell core, one needs to draw fiber with a ring thickness of less than 0.03 Lambda to achieve a comparable operational bandwidth. (C) 2008 Elsevier B.V. All rights reserved.