In this paper, we theoretically analyze the emission of guided polaritons accompanying spontaneous recombination in a semiconductor quantum dot coupled to metallic nanowire. This study is aimed to shed light on the interaction between optically excited quantum emitters and metallic nanowaveguides beyond the validity of dipole approximation. To the best of our knowledge, this is the first time the geometry of quantum emitter and spatial inhomogeneity of the electric field constituting the fundamental polariton mode are fully taken into account. Even though we performed the analysis for disk-like quantum dot, all the conclusions are quite general and remain valid for any emitter with nanometer dimensions. Particularly, we found that the strong inhomogeneity of the electric field near the nanowire surface results in a variety of dipole-forbidden transitions in the quantum dot energy s ctra. It was also unambiguously shown that there is a certain nanowire radius that gives maximum emission efficiency into the fundamental polariton mode. Since the dipole approximation breaks for nanowires with small radii and relatively big nanoemitters, the above features need to be considered in the engineering of plasmonic devices for nanophotonic networks.

We theoretically demonstrate that, for a given diameter of the core-pumped metal-dielectric nanowire, there is an optimum thickness of the metallic cladding that provides the maximum propagation length of the lowest-order surface plasmon polariton (SPP) modes. If the nanowire is fabricated with the optimum cladding thickness, the lowest pumping power is required to fully compensate for the SPP propagation losses. We also show that a strong confinement of SPPs within the nanowire can be achieved, but at the expense of either high optical gains or large nanowire diameters. For example, a gain of 565 cm(-1) would suffice to make up for the decay of SPPs in a 250-nm-thick silver-GaAs nanowire; the confinement of optical power within such nanowires exceeds 90%, which makes them ideal interconnects for nanophotonic circuitry.

We theoretically investigate composite cylindrical nanowires for the waveguiding of the lowest-order surface plasmon-polariton (SPP) mode. We find that the confinement of the SPP fields in a metallic nanowire can be significantly improved by a dielectric cladding and show that by adjusting the thickness of the optically-pumped cladding, the gain required to compensate for the losses can be minimized. If this structure is coated with an additional metal layer to form a metal-dielectric-metal (MDM) nanowire, we show that the field can be predominantly confined within the dielectric layer, to have amplitudes of three orders of magnitude higher than those in the metallic regions. We also show that the propagation lengths of SPPs can be maximized by the proper selection of the geometrical parameters. We further demonstrate that the mode is strongly confined in subwavelength scale, e.g., ∼λ(0)(2)/1220 for a 60-nm-thick nanowire, where λ(0) is the wavelength in vacuum. We also find that regardless of the size of nanowire, it is possible to carry over 98.5% of the mode energy within the nanowire. In addition, we demonstrate that by appropriate choice of the material thicknesses, the losses of an MDM nanowire can be compensated by a considerably low level of optical gain in the dielectric region. For example, the losses of a 260-nm-thick Ag-ZnO-Ag nanowire can be entirely compensated by a gain of ∼ 400 cm(-1). Our results will be useful for the optimum design of nanowires as interconnects for high-density nanophotonic circuit integration.

We theoretically investigate planar heterostructures for subwavelength guiding of surface plasmon modes and optimize their design to enhance the waveguiding efficiency. We show that by appropriately selecting the thicknesses of metallic and dielectric layers of a two-layer waveguide, one can compensate the intrinsic damping of the mode by having minimal optical gain in the dielectric region. We also reveal that mode confinement can be significantly improved by the use of an additional metal layer adjacent to the dielectric, to form a metaldielectric-metal (MDM) structure. By varying the layer thicknesses in the MDM waveguide, we demonstrate that the propagation length of the plasmonic mode can be maximized. We further show that the losses may be suppressed by minimal gain in the dielectric region by the careful choice of geometrical parameters. We note that the associated gain levels are relatively small; for example, the losses in a 300 nm thick Ag-ZnO-Ag waveguide can be compensated by a gain of ∼225 cm −1 . Our results may prove useful for the realization of efficient optical interconnects in high-density nanophotonic circuity.

We theoretically analyze guided modes in optically active and passive double-slot plasmonic waveguides. We show that for one of the two different mode symmetries supported by the waveguide, a most productive guiding condition can be realized by adjusting the thicknesses of the layers to optimal values. We also derive approximate analytic expressions to calculate the optimal geometrical parameters of the waveguide. Interestingly, our analysis shows that the propagation losses associated with the inverse mode symmetry of the double-slot waveguide are comparatively low, regardless of the dimensions of the waveguide. We further show that the propagation losses become the smallest in the limiting case of a single-slot (metal-dielectric-metal (MDM)) waveguide. For both double-and single-slot waveguides, we show that the gain required to overcome the losses can be reduced by choosing a dielectric with a low refractive index. We also derive accurate analytical expressions to readily estimate the critical gain and modal gain of the waveguides.