Finite-difference time-domain algorithm for quantifying light absorption in silicon nanowires

We introduce an accurate and fast finite-difference time-domain (FDTD) method for calculating light absorption in nanoscale optical systems. The dispersive FDTD update equations were derived from auxiliary differential equations (ADE), wherein dispersive media were fitted by various dispersion models including the Drude, Debye, Lorentz, and critical point models. Light absorption in the dispersive media was quantified by calculating polarization pole currents in the ADE. To verify this simulation method, the absorption spectrum of a 300 nm thick silicon film was calculated and compared to an analytic solution. In addition, the absorption cross-section of a single silicon nanowire with a diameter of 300 nm was calculated using monochromatic and broadband light sources. We believe that this reformatted FDTD method is a powerful tool for the design of novel nanophotonic components, including nanowire photovoltaic devices.