Jacob B. Khurgin, Professor, ECE, Johns Hopkins University
Recently there has been a surge in activities devoted to development of the nano-scale semiconductor lasers. In particular, semiconductor lasers employing surface-plasmon polaritons in metal dielectric structures (“spasers”) with their promise of subwavelength operation have generated a lot of interest in the laser community. Yet it is not clear exactly how small semiconductor laser can be made without sacrificing performance.
In my talk I will review the recent experimental and theoretical results and present a theory that would clearly outline the fundamental limits of how small can the nano-laser actually be. First I will show that in order to go beyond diffraction limit one absolutely must use metallic structures with associated loss. Then I will show that the lasing threshold of the single mode metal-semiconductor nano-laser (spaser) is determined only by the photon absorption rate in the metal and exhibits very weak dependence on the composition, shape, size (as long as it is less than half-wavelength) and temperature of the gain medium. This threshold current is on the order of a few tens of micro-amperes for most semiconductor-metal combinations which leads to unattainably high threshold current densities for a substantially subwavelength in all three dimensions semiconductor laser (spaser). At the same time, lasers that are sub-waveelngth in only one dimensions, particularly in infrared and THz regions can be made operational.
I will also discuss the issues of coherence properties of nano-lasers, and their modulation speed and compare them with those of standard semiconductor lasers . I will also consider surface plasmon emitting diodes, (SPED’s), operating far below “spasing” threshold that may be a more viable option for the chip scale integrated nanophotonics.
About Jacob B. Khurgin:
Hosted by: Professor John Bowers