Theory of Plasmonic Fabry-Perot Nanolasers

Abstract

Semiconductor plasmonic Fabry-Perot lasers at submicron and nanometer scales exhibit many characteristics distinct from those of their conventional counterparts at micron scale. The differences originate from their small sizes and the presence of plasma metal in the cavity. To design a laser of this type, these features have to be taken into account properly. In this paper, we provide a comprehensive approach to the design and performance evaluation of the plasmonic Fabry-Perot nanolasers. In particular, we show the proper procedure to obtain the key parameters for lasing action, which are usually neglected in the conventional semiconductor Fabry-Perot lasers but become important for nanolasers.

Advances in small lasers

“…Even higher optical gain, up to many thousands per cm for bulk semiconductors, has been inferred from recent experiments on metallic lasers and nanowire lasers 17,18,20,29,30 . Although these numbers have not been confirmed via direct amplification measurements, they are consistent with predictions of theoretical models for high carrier densities 21 and the low group velocity of light in small plasmonic waveguide lasers 18,20 . Particularly high gain has mostly been found for devices operated at low temperatures, however, even for room temperature electrically pumped lasers bulk material gain of ~940 cm -1 is inferred, albeit with a limited device lifetime due to the high injection currents 31 .…”

“…We have assumed that the phase and group velocity of light in the cavity are the same, also that  can be calculated from the overlap of the modal electric field energy with the gain medium, which is in general not true 21,22 . When  is taken as waveguide confinement, it can be greater than one 21,22 , making modal gain higher than material gain, though material gain required for threshold may not be reduced due to increased group index 21 n. However, when is taken as an energy confinement factor, it is always less than one 21 .…”

“…When  is taken as waveguide confinement, it can be greater than one 21,22 , making modal gain higher than material gain, though material gain required for threshold may not be reduced due to increased group index 21 n. However, when is taken as an energy confinement factor, it is always less than one 21 . The smallest lasers may not be based on a propagating mode, but one can still assign an energy confinement factor and a photon (or plasmon) lifetime, so many of the key parameters and concepts of the various classes of small lasers can be compared and explained via the simplified model.…”

“…They allow direct electrical pumping and provide high optical gain from a few hundred per cm for bulk semiconductors 21 to > 5×10 4 cm -1 in quantum dot structures 28 . Even higher optical gain, up to many thousands per cm for bulk semiconductors, has been inferred from recent experiments on metallic lasers and nanowire lasers 17,18,20,29,30 .…”

“…However, for more conventional applications such as communications, computing and light sources, metallic nanolasers require substantial improvement in the following: 1) Improved room temperature threshold current, currently on the order of a milliampere, whereas in theory much lower threshold currents are predicted 21,23 . 2) Significant lifetimes of the devices need to be demonstrated.…”