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Plasmonics Subwavelength Discrete Solitons Solitons are solitary wave packets that can maintain their shape and amplitude due to the delicate balance between nonlinearity and dispersion. Solitons have attracted wide research interest in many areas of science, such as solid state physics, Bose-Einstein condensates, and biology. In optics, discrete solitons in nonlinear lattice have been proposed and observed in dielectric waveguide arrays under self-focusing and self-defocusing nonlinearities. In these settings, the nonlinearity can balance the light tunneling between neighboring waveguides, giving rise to self-localization and stationary propagation. In all previous work, the soliton dimension and the periodicity of the system are much larger than the excitation wavelength. We present the first study of subwavelength discrete solitons in a plasmonic metamaterial: nanoscaled periodic structures consisting of metal and nonlinear dielectric slabs. The solitons supported by such media result from a balance between tunneling of surface plasmon modes and nonlinear self-trapping. The dynamics in such systems, arising from the threefold interplay between periodicity, nonlinearity, and surface plasmon polaritons, is substantially different from that in conventional nonlinear dielectric waveguide arrays. We expect these phenomena to inspire fundamental studies as well as potential applications of nonlinear metamaterials, particularly in subwavelength nonlinear optics.
Figure (a) The intensity of a nonlinear localized mode in metal-dielectric multilayers at the wavelength of 1.55 mm. The mode size is lower than the diffraction limit (about 530nm) of the system.The white and shaded regions represent the metal (28nm thick) and dielectric (60nm thick) slabs, respectively. (b) Nonlinear propagation of the mode over 40um in a lossless metal-dielectric multilayer, which shows stationary behavior. (c) Linear propagation in which the wave packet diffracts. Note an experimental observation of subwavelength discrete is feasible considering the actual material losses. Y. M. Liu, G. Bartal, D. A. Genov and X. Zhang, Phys. Rev. Lett. 99, 153901 (2007)
Plasmonic Waveguide Overview Nanoscale plasmonic devices can bridge the gap between the optical and electronic transition length scales. This provides a clear path toward realizing nano-LED and nanolaser systems with dimensions that are orders of magnitude smaller than those used in practice today. Nano-optical emitter research at XLab looks at two regimes of nano-scale optical light emitters: a semi-classical regime of spontaneously emitting and laser devices and a quantum regime at the single photon level. Plasmonic Component Design Much of our research in this area is made possible by a fundamentally new approach to surface plasmon optics. We have recently reported in Nature Photonics, a hybrid plasmonic waveguide. This is a composite of a high contrast semiconductor waveguide and a plasmon supporting metal-dielectric interface separated by a thin low permittivity dielectric gap. The coupling between the plasmonic and waveguide modes across the gap allows "capacitor-like" energy storage leading to a sub-wavelength sized mode. The hybrid plasmons of the structure have potentially favorable confinement and propagation characteristics, due to the involvement of the low loss dielectric waveguide.
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