Laser oscillation due to light slowed-down by excitons in photonic crystals

The polariton-mediated photonic crystal laser is theoretically investigated, which is made of a periodic structure containing excitonic and gain materials in its unit cell-this kind of structure can also be called a potaritonic crystal. The basic concept of this laser lies in exploiting the anomalous dispersion of the polaritonic crystal as the photonic environment in which light created by stimulated emission propagates. This crystal provides a stage for photons, which enables a significant enhancement of optical gain in the vicinity of its band edge. The gain enhancement is found to be caused by the increased confinement of light in the gain region and the slowing-down of light in the presence of excitons. This effect permits the laser to oscillate with a very low threshold and in the single mode. The threshold-gain values obtained axe found to be much lower than those for the Fabry Perot lasers and the Distributed-Feedback lasers. Moreover, exciton damping, which is undesirable for laser action, is shown to be decreased to a considerable degree by designing the polaritonic crystal structure appropriately. All these advantages of polaritonic, crystals stem from the fact that the radiation field is modulated significantly by adding excitons to conventional photonic crystals.