Spectral and Modal Tuning of Surface Plasmons in Symmetric Nanocomposite–Metal Configurations

This study presents a detailed investigation into the dispersion and confinement characteristics of surface plasmon polaritons (SPPs) in a symmetric waveguide architecture composed of nanocomposite–metal–nanocomposite (NMC–M–NMC) layers. The nanocomposite claddings incorporate metallic nanoparticles, enabling the simultaneous excitation of propagating surface plasmon modes and localized plasmon resonances. This coupling mechanism leads to superior field confinement and an extended modal wavevector range compared to conventional metal–insulator–metal (MIM) waveguides. The resulting structure supports both long-range SPP (LRSP) and short-range SPP (SRSP) modes, each exhibiting distinct advantages: LRSP modes offer reduced propagation losses and longer transmission distances, while SRSP modes exhibit tight spatial confinement around the metallic core. A key feature of the proposed system is its tunability, achieved by varying the nanoparticle characteristics—such as radius, volume fraction, and interparticle spacing—as well as the thickness of the central metal layer. This flexibility allows dynamic control over the effective wavelength and intensity distribution of the plasmonic modes, making the structure highly adaptable to a wide range of optical design requirements. To further elucidate the material influence on SPP behavior, comparative simulations are performed using two representative nanocomposite systems: silver–silica and gold–alumina. These comparisons reveal material-specific differences in mode dispersion and confinement, thereby providing valuable guidance for material selection in plasmonic device engineering. The demonstrated ability to manipulate SPP propagation and confinement through structural and material parameters underscores the potential of the NMC–M–NMC configuration in advanced photonic applications. In particular, this platform shows strong promise for integration into nanophotonic circuits, plasmonic sensors, optical modulators, and subwavelength light guiding components within next-generation optoelectronic systems.

Graphical Abstract