Vectorial modeling of near-field imaging with uncoated fiber probes:   Transfer function and resolving power
  Using exact three-dimensional vectorial simulations of radiation coupling into uncoated dielectric fiber probes, we calculate amplitude transfer functions for conical single-mode fiber tips at the light wavelength of 633 nm. The coupling efficiency of glass fiber tips is determined in a wide range of spatial frequencies of the incident radiation for opening angles varying from 30 to 120 degrees. The resolution in near-field imaging with these tips is considered for field distributions limited in both direct and spatial-frequency space. The characteristics of the transfer functions describing the relation between probed optical fields and near-field images are analyzed in detail. The importance of utilizing a perfectly sharp tip is also examined. 
Niels Gregersen, Bjarne Tromborg and Sergey I. Bozhevolnyi