Description of near– and far–field light emitted from a metal–coated tapered fiber tip

We present an analytical calculation of near- and far-field radiation emitted from a metal-coated tapered fiber probe. From FDTD simulations made in Cartesian coordinates we find that charge distribution on a tip is rim localized and its density is a bipolar periodic and continuous function. Similar angular charge density distributions may result from random irregularities of tip surfaces created in the fabrication process. Thus forward emission from a tip can be described as emission of quasi-dipoles and multi-quasi-dipoles. Analytically calculated characteristics are in agreement with our FDTD simulations and previous measurements of Obermüller and Karrai.