Ultra-thin gold films in optical devices
Kristján LEÓSSON
(Innovation Center Iceland, Arleynir 2-8, IS-112 Reykjavik, Iceland)
During the past decade, long-range surface plasmon polariton (LR-SPP) waveguide devices have been used to demonstrate multiple optical functionalities, including modulation, switching, plasmon amplification, biosensing, polarization-controlled routing and processing of quantum information. Typically, LR-SPP waveguides consist of nanometer-thin metal stripes embedded in a homogeneous dielectric environment. At telecommunications wavelengths, their mode size can be matched to that of conventional optical fibers. While LR-SPP waveguides are inherently lossy they have some properties not shared by conventional dielectric waveguides, such as the possibility to carry electrical current, an essentially two-dimensional waveguide core, single-polarization waveguiding, and large effective-index change with nanometer-scale variations in geometry. Furthermore, plasmonic waveguides based on ultra-thin metal films also support short-range surface plasmon polaritons that exhibit much stronger field confinement than conventional single-interface SPPs. Fabricating high-quality ultra-thin (below 10 nm) noble metal films on transparent substrates is not straightforward, and recent progress in fabrication techniques for obtaining high-quality ultra-thin gold films on glass substrates will also be discussed. In addition to reducing scattering losses in thin-film plasmonic waveguides, this also has implications for use of noble-metal films as transparent electrodes.
