Opt. Eng. 51, 054001 (2012)

Coupled-mode theory is a useful technique for determining the behaviour of electromagnetic fields in waveguides and other photonic structures, but is mainly used for developing analytical solutions to steady-state problems. In recent years, however, several groups have discussed time-dependent coupled-mode equations that can help to analyse Fano resonances in optical resonators and the temporal response of resonant grating effects. Vladislav Shteeman and Amos Hardy in Israel have now applied time-dependent coupled-mode theory to a 90° bend, a micro-interferometer with a based on a 5 × 5 array of waveguide cores, and a beamsplitter based on a 8 × 5 array of waveguide cores. They determined how optical pulses cause temporal variations in the refractive indices in the cores of each waveguide. The theory does not yet take into account backwards waves and is applicable only for small perturbations in the dielectric constants, which limits the effects that can be considered at this stage. The researchers claim that the solutions to their equations, although generally numerical, can be computed two orders of magnitude faster than traditional techniques such as finite-difference time-domain solutions to the Maxwell equations.