Modal characteristics of nano-sized air-capillary-core optical fibers

A novel optical fiber design, based on hollow-core optical fibers [1, 2], with an air-capillary at the center is presented to attain a large mode area maintaining single-mode behavior at 1064 nm and low bending-loss (<;0.1dB/m) of the fundamental mode. We carried out fully-vectorial analysis of Maxwell´s equations yielding a wavelength dependent core index that can be controlled by varying air-capillary radius. Numerical simulations using the fully-vectorial analysis demonstrate close agreement with the results computed from finite element method. We have shown that an effective mode area >; 150 μm² can be achieved even at large relative index difference (Δ = 0.14%) between the doped-core and the cladding at a standard core-radius of 5 μm. We also address how to further increase effective mode area without requiring a very low relative index difference [3, 4], making it more amenable to fabrication techniques, and also investigated dispersion and bend-loss characteristics.