Hybrid Surface Plasmon Polariton Modes of Subwavelength Nanowire Resonators

We perform Comsol simulations of two types of hybrid plasmonic resonator configurations, similar to those proposed for nanowire plasmonic laser in [1] and [2]. In both references the nanowire - based plasmonic resonators are studied,
which overall sizes are larger than the wavelength in vacuum. However, it is advantageous for the nanolaser to have subwavelength sizes at least in two dimensions. Therefore, we study the two configurations and the hybrid mode
behavior in the case, where resonator sizes are smaller than the half of the wavelength in vacuum.

First, we assume finite dimensions of the silver substrate and changing its geometrical parameters check how this change influences the effective refractive index and the field intensity inside the gap. Next, the field distributions for different types of modes supported by hybrid resonators are calculated. Finally, the parameters of a well-localized gap plasmon mode are studied depending on the vacuum wavelength. In order to directly compare resonators, where metal and semiconductor nanowires are employed, we consider the two resonators, both including silver slab and magnesium fluoride gap region, as is shown in figure. The two compared structures contain Ag and GaAs nanowires, respectively, on top of the gap medium.

We have found that the modes of the structure containing Ag nanowire have much smaller propagation lengths and Q-factors than those containing GaAs nanowire, which can lead to higher lasing threshold for an Ag nanowire resonator.

References

[1] R. F. Oulton, V. J. Sorger, T. Zentgraf, R.-M. Ma, C. Gladden, L. Dai, G. Bartal, X. Zhang, Plasmon lasers at deep subwavelength scale, Nature, 461: 629632, 2009
[2] K. J. Russell, T.-L. Liu, S. Cui, and E. L. Hu, Large spontaneous emission enhancement in plasmonic nanocavities, Nat. Photonics 6: 459462, 2012.

filonenko@mci.sdu.dk