Photonic crystal lasers and loss compensation in metamaterials

Incorporation of gain in photonic crystals and metamaterials can be utilized for different purposes. In particular, here we examine how the lasing threshold of a two dimensional photonic crystal (2D PC) containing a four-level gain medium is modified, as a result of the interplay between the group velocity and the modal reflectivity at the interface between the cavity and the exterior. The idea is demonstrated via selfconsistent calculations based on a finite-difference time-domain method. The simulations are in good agreement with theoretical predictions. Using a four-level gain system, we also study light amplification of arrays of metallic split-ring resonators with a gain layer underneath. We find that, while the differential transmittance δT/T is positive for the gain substrate alone, δT/T can be negative for split-ring resonators on the top of the gain substrate, which is not expected. These simulations, which demonstrate reduction of the resonator damping, agree with pump-probe experiments and can help to design new experiments to compensate for the losses of metamaterials.