Hollow ring defect in photonic crystal fibers for annulus mode profile

We propose new design parameters for index-guiding holey-fiber (IGHF) that can provide flexibility in defect and lattice design as well as adiabatic mode transformation capability. The new defect consists of the central air hole and germanosilicate-ring surrounding it. In this paper, utilizing layers of hollow structure as a defect, we introduce a new IGHFstructure and its optical properties are theoretically analyzed and experimentally demonstrated. The annulus mode intensity profile, effective mode area, chromatic dispersion properties and splicing loss for the single-layered and two-layered defect structure are investigated along with their dependence on the proposed defect parameters using plane wave expansion method and 3D full-vectorial Beam Propagation Method (BPM). Unlike conventional silica defect IGHF, the proposed structure showed an annulus mode profile in the fundamental mode, which can benefit from larger effective area to separate the fiber non-linearity from other unique optical properties of IGHFs. The proposed IGHF also showed low splice loss unlike previous conventional IGHFs with collapsed hole by arc since the newly introduced defect structure, germanosilicate-rings are remained as solid core with high index contrast D. With the new defect parameters we could achieve a large area annulus mode profile, low splice losses to standard fiber, 0.7dB at 1.55 m, and chromatic dispersion with low slope, 0.002ps/km.nm2.