A simple approach, based on coupled mode theory, to study PhC lasers

PhC lasers have attracted large interest as efficient light-sources in on-chip and chip-to-chip interconnections. They allow for scaling the active volume while maintaining the high cavity Q-factor, thus exhibiting low threshold current and operating energy [1,2]. Methods for studying these laser cavities are typically based on FDTD simulations, which are often time-consuming and do not allow to catch the most relevant physics of these devices. We propose here an alternative and simple approach to analyze active PhC waveguides and lasers. Our approach is based on coupled-mode theory, which has proved to be an effective tool to study lasers with periodic gain and/or refractive index perturbation, as standard DFB lasers. We apply this method to PhC line-defect waveguides and lasers with a small complex refractive index perturbation (to account for gain and refractive index variation) with respect to a reference, unpumped PhC line-defect waveguide [3]. The optical electric field of the TE-like guided mode is expanded as sum of the forward- and backward-propagating Bloch modes of the passive waveguide; the equation governing the evolution ψ+,-(z) of the Bloch modes along the perturbed waveguide are: [Equation Present].