Optical Properties of High-Delta Air-Silica Microstructure Optical Fibers

We analyze the waveguide properties of microstructure optical fibers consisting of a silica core surrounded by a single ring of large air holes. Although the fibers may support numerous transverse spatial modes, coupling between these modes even in the presence of large perturbations is prevented for small core dimensions due to a large wave-vector mismatch between the lowest-order modes. The result is an optical fiber that can appear single-mode with propagation properties that can only be achieved in multimode waveguides.