Near-field characterization of glass microfibers on a low-index substrate

We characterize the propagation of infrared light inside a silica glass microfiber laid on a magnesium fluoride substrate, using both numerical simulations and near-field experiments. Propagation constants and cut-off diameter are computed by finite-element analysis, while near-field measurements reveal the evanescent tails of the modes. The microfibers display an excellent surface quality since very low scattering levels are measured, and the field distribution is in good agreement with simulations. Finally, dust scattering and coupling structure are investigated.