Bandgap Properties Modulated by a Single Ring of Filled Air Holes in a Hybrid-PBGF

We present a numerical study on a hybrid-cladding photonic bandgap fiber (hybrid-PBGF), in which the guided mode is confined to the core by two sets of bandgaps formed by the outer periodic air holes and an inner single ring of air holes filled some material with a higher index than air, respectively. The bandgap characteristics of the hybrid-PBGF, depending on the structural parameters of the single ring, are simulated by the multipole method. The results show that the bandwidth and position of the bandgaps can be easily modulated by the single ring parameters. By the combination of two sets of bandgaps, a broader bandgap than that in conventional PBGFs can be obtained.