Design and optimization of tapered structure of near-field fiber probe   based on FDTD simulation
  The finite-difference time-domain method was employed to simulate light propagation in tapered near-field fiber probes with small metal aperture. By conducting large-volume simulations, including tapered metal-cladding waveguide and connected optical fiber waveguide, we illustrated the coupling between these guiding modes as well as the electric field distribution in the vicinity of the aperture. The high collection efficiency of a double-tapered probe was reproduced and was ascribed to the shortening of the cutoff region and the efficient coupling to the guiding mode of the optical fiber. The dependence of the efficiency on the tapered structure parameters was also examined. 
Hiroaki Nakamura, Tetsuya Sato, Hirotomo Kambe, Keiji Sawada, and   Toshiharu Saiki