Metal-insulator-insulator-metal plasmonic waveguides and devices
Metal-insulator-metal (MIM) plasmonic waveguides have been proposed for highly integrated subwavelength structures. In this work, waveguiding and coupling of surface plasmon polaritons (SPPs) within finite planar MIM plasmonic waveguides are examined both theoretically and experimentally. Gain (dye-doped polymer)-assisted MIM waveguides and terahertz quantum cascade laser MIM waveguides are numerically analyzed. The numerical analysis of finite planar MIM waveguides using the transfer matrix formalism reveals both bound and leaky SP modes: three lowest energy bound modes and the highest energy mode consisting of non-radiative (bound) and radiative (leaky) portions separated by a spectral gap at the light line. The leaky regime is further divided into antenna and reactive mode regions. Spatial dispersion effect on the SH mode yields a reduced wave vector in its dispersion curve and an increased propagation loss. The MIM radiative SPPs are probed using attenuated total reflection in the Kretschmann configuration and using free space coupling. Both single- and double-sided leaky waves are analyzed. The leaky wave dispersion relation and its antenna mode radiation pattern are determined through both angle- and wavelength-dependent reflectance of TM polarized free space incident light. The inclusion of a dye-doped polymer into realistic finite MIM plasmonic waveguides is analyzed. The propagation of three bound SP modes, each within respective optimized symmetric glass-Ag-Rh6G/PMMA-Ag-glass waveguides, is calculated for core material exhibiting optical gain at 594 nm. The critical gain coefficients for lossless propagation of these three bound SP modes are determined. Only lossless propagation of the SH mode is predicted. For MIM structure with gain in adjacent medium in ATR geometry, the reflectance and energy flux distribution at resonance conditions versus gain coefficients are examined. The waveguide loss, confinement factor and threshold gain for terahertz quantum cascade laser SP waveguides are modeled from 2 - 7 THz. The effects of plasma layer thickness, plasma doping and substrate thickness and the effects of active region thickness are investigated for semi-insulating surface-plasmon and metal-metal waveguides, respectively. A surface emitting quantum cascade laser SP leaky waveguide are proposed, with emission properties controlled by varying plasma layer thickness.
Polaritons, Surface plasmon resonance, Plasma waveguides
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