Tradeoffs between threshold and directionality in microdisk laser design

A reasonable tradeoff between low threshold and high directionality of light emission is one of the main goals in the design of semiconductor microcavity lasers. Here, smoothing of the disk rim and pumping only a ring-shaped area lower the threshold power, however, neither has an effect on the directionality. Departure from a circular shape improves directionality however usually spoils the thresholds and the same occurs when loading microdisks with optical fibers or building photonic molecules from microdisk "photonic atoms". A search for configurations, which are provide both lower thresholds and better directionalities of the lasing modes, calls for detailed cold-cavity simulations with accurate numerical techniques.