Lasing Demonstrated in Tiny Cavities Made with Photonic Crystals

We have been so successful in engineering semiconductors to manipulate electrons that we are naturally interested in similar ways of controlling photons. One promising means is to create structures with periodic variations in the index of refraction—such as a hexagonal array of air holes penetrating a thin gallium arsenide film. As lightwaves scatter within the periodic dielectric structure, destructive interference cancels out light of certain wavelengths, thereby forming a photonic bandgap similar to the bandgap for electron waves in semiconductors. Photons whose energies lie within the bandgap cannot propagate through the structure. This exclusionary property can be used to advantage to create a low‐loss cavity: Simply put a defect into a periodic structure and you have a region within which the otherwise forbidden wavelengths can be locally trapped. in a similar fashion, a line of defects can serve as a waveguide. Researchers have been studying such bandgap structures, also called photonic crystals, in the hopes of harnessing their potential to control photons.