Optimizing the design of planar heterostructures for plasmonic waveguiding

Abstract

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.

Plasmonic finite-thickness metal–semiconductor–metal waveguide as ultra-compact modulator

“…A metal-insulator-metal (MIM) waveguide does not exhibit cutoff even at very small core thickness and as the result allows unprecedented thin layouts of tens of nanometers [22][23][24]. Planar MIM plasmonic waveguides with thin metal claddings were studied and optimized for various purposes [25][26][27][28][29]. They possess several symmetric and asymmetric modes as well as metalclad and quasi-bound ones, depending on the frequency range [25].…”

Unveiling ultrasharp scattering–switching signatures of layered gold–dielectric–gold nanospheres

“…These exotic signatures in the scattering profile may be restored if we are able to mitigate the metallic losses by introducing some gain in the middle dielectric layer (layer 2). It is common to integrate gain medium (e.g., organic die molecules or semiconductor nanostructure, such as quantum dots and quantum wells) in the dielectric material to compensate for losses occurring at constituent metal layers in metal-dielectric layered metamaterials and nanostructures [41][42][43][44]. We adopt a similar approach for an MDM nanosphere, in which the material of layer 2 is assumed to have a complex dielectric permittivity, expressed as ε 2 ε 0 2 iε 00 2 , where negative ε 00 2 indicates dielectric material with some gain.…”

Analytical study of optimal design and gain parameters of double-slot plasmonic waveguides

“…Consider the planar plasmonic waveguide shown in figure 1, which consists of two dielectric layers separated by a metal layer, and bounded by metal regions that are sufficiently thick to be treated as infinitely extending. The propagation constant β of the transverse magnetic mode supported by the waveguide, which characterizes the guiding wavelength and the decay of SPPs having frequency ω, can be found by the dispersion equation [11] tanh(α m h) = −…”

“…Guiding optical modes in nanostructures has been a hot topic among many research groups over the past few decades due to its revolutionary applications in areas such as bio-sensing [1], scanning near-field optical microscopy [2,3], ultra-fast optical computing, and realization of plasmonic-circuit elements such as couplers, switches, and interconnects [4][5][6][7][8]. Optical energy may be transported in subwavelength scale by the form of plasmons in metal-dielectric structures [9,10], which can be of different geometries, e.g., planar waveguides [11,12], waveguides with square [13] and triangular [14] cross sections, cylindrical waveguides [15][16][17][18], gap waveguides [19,20] and coupled nanoparticles [21][22][23]. The major drawback of plasmonic waveguides from the viewpoint of their applications at optical and telecommunication frequencies is the inherent losses of their metal constituents.…”

“…However, owing to practical limitations, such as the temperature of operation and material properties of the gain medium, it is not possible to increase the pump power as desired in practice. Hence, it is essential that the waveguide is optimally designed in such a way that the required gain is minimal [11,16,27].…”