Figure 3 . Sensitivity, fabrication complications, losses, and footprint comparison of plasmonic WGs with dielectric or hybrid plasmonic WGs.
The main benefit of the plasmonic WGs is that the operational wavelength of light does not influence its size. This makes it possible to create plasmonic WGs with lengths on the order of several tens of nanometers, something that is not feasible with dielectric WGs. Additionally, exceptionally strong light confinement and effective interaction with nanomaterials that have various special properties become conceivable. A three-dimensional plasmonic mode converter is necessary since such WGs cannot readily be included in optical integrated circuits. The plasmonic WG is made up of a MIM WG, a Si-wire WG, and a plasmonic mode converter section. On an SOI substrate, the silicon ridge WG, and the silicon section of the plasmonic mode converter are constructed, followed by the formation of the metal components using electron beam lithography and evaporation. This set of procedures makes use of standard methods for fabricating nanostructures and is hence compatible with those applied to other silicon photonic devices. For device integration, this makes it possible to integrate with other optical components on the same substrate. For a MIM WG with a core size of 50 nm × 20 nm, a plasmonic mode converter with an air gap width of 40 nm has been developed as shown in Figure 4 (a). The E-field distribution in the whole plasmonic device and at different segments of the WG is presented in Figure 4 (b).