Coupled mode analysis of the photonic crystal waveguide

Starting from an intuitive picture of photons bouncing back and forth within a slab of a uniform medium surrounded by photonic crystal (PC) layers, we develop a coupled mode formalism for the analysis of a PC waveguide. The modal solution in the core is given by counter-propagating waves while the cladding field is derived from a modified coupled mode formalism. This coupled mode approach is used to analyze the dispersion and loss of the PC waveguide. Although coupled mode theory is usually applied to structures with a small index contrast perturbation, we find that our coupled mode formalism with an empirical coupling constant can be used to model a large index contrast PC waveguide. A single constant is used to analyze the dispersion and the loss of a two dimensional PC waveguide, a GaAs substrate with air holes. Our results are corroborated with a two dimensional finite-difference time-domain (FDTD) simulation and we find good quantitative agreement between the coupled mode theory and the FDTD analysis.