  A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit
is developed to simulate the whispering gallery modes of a microsphere in the
vicinity of a dipole source. This provides a guide for experiments that rely on
efficient coupling to the modes of microspheres. The resultant spectra are
compared to those of analytic models used in the field. In contrast to the
analytic models, the FDTD method is able to collect flux from a variety of
possible collection regions, such as a disk-shaped region. The customizability
of the technique allows one to consider a variety of mode excitation scenarios,
which are particularly useful for investigating novel properties of optical
resonators, and are valuable in assessing the viability of a resonator for
biosensing.
