Integral equation analysis of scattering by a spherical microparticle coupled to a subwavelength-diameter wire waveguide.

A rigorous integral equation analysis of the coupling between a fiber waveguide and an adjacent spherical particle is developed. The solution is obtained by applying the entire-domain Galerkin technique, based on Mie-type spherical wave expansion of the field in the sphere and the use of dyadic Green's function of the fiber waveguide. The conversion between cylindrical and spherical wave functions is done through classic analytical formulas. The analysis is applied to numerically investigate transmission through silica wires of subwavelength diameter in the presence of particles of comparable size. The results show the possibility of sensing microparticles through the reduction of transmitted power, which is maximum for certain critical values of the fiber diameter.