Plasmonic/metallic passive waveguides and waveguide components for photonic dense integrated circuits: a feasibility study based on microwave engineering

To investigate the potential for dense integration of photonic components, we analyse passive plasmonic/metallic waveguides and waveguide components at optical frequencies by using mostly microwave engineering approaches. Four figures of performance are formulated that are utilised to compare the characteristics of four different slab waveguides with zero frequency cut-off modes. Three of these are metallic based whereas the fourth one, which also serves as a reference, is dielectric based with high index-contrast. It is found that all figures of performance cannot be optimised independently; in particular there is a trade-off between the waveguide Q-value and the transversal field confinement. Microwave methods are used to design several photonic transmission line components. The small Q-value of the metallic waveguides is the main disadvantage when using materials and telecom frequencies of today. Hence plasmonic waveguides do not offer full functionality for some important integrated components, being severe for frequency-selective applications. To achieve a dense integration, it is concluded that new materials are needed that offer Q-values several orders of magnitude higher than metals.