Finisar Corporation, Sunnyvale, California, and COMSOL, Inc., Burlington, Massachusetts

Internal heating is a key issue for vertical cavity surface emitting lasers (VCSELs), a semiconductor micro laser diode that emits light in a cylindrical beam vertically from the surface of a fabricated wafer. They generally have higher thermal impedance than edge emitting lasers and are fairly efficient for optical devices, running at roughly 25% efficiency in contrast to light emitting diodes' (LEDs) typical 2% to 3%. For instance, they produce 10 mW of optical power from a 40-mW input; the remaining is dissipated as heat.