Photon plasmon coupling in nanocomposite plasmonic waveguides

The propagation of Surface Plasmon Polaritons (SPP) presents high interest nowadays because its hybrid nature in between electromagnetic and surface charge waves that allows exotic properties like subwavelength confinement, strong near electric field or high sensitivity to the environment. Particularly, waveguides based on SPPs can reduce the dimensions and power consumption of devices and circuitry in integrated optics. However, there is an important limitation in the propagation of SPPs because the signal suffers significant absorption losses in the metal. This attenuation can be overcome by using gain materials adjacent to the metal or by combining plasmonic and dielectric waveguides that exhibit reduced propagation losses. In this work nanocomposites made by the dispersion of colloidal CdSe quantum dots (QDs) in a polymer matrix are proposed to be designed together with plasmonic waveguides. These nanocomposites are useful because they join the properties of the QDs (room temperature emission and tunable wavelength) with the technological feasibility of polymers (thin film deposition by simple methods and patterning by e-beam or UV lithography). Indeed, a QD-PMMA film can act as the active core of a dielectric waveguide when it is deposited on a SiO₂/Si substrate and, if the nanocomposite is adjacent to a metal layer or stripe, the photoluminescence of the CdSe QDs can be coupled to SPPs through the interface. In fact, we demonstrate the compensation of the SPP propagation length by using such a nanocomposite in the waveguide by providing gain to the SPP or by allowing the propagation of hybrid dielectric-plasmonic modes.