Plasmonic inverse rib waveguiding for tight confinement and smooth interface definition

A plasmonic inverse rib optical waveguide geometry is proposed and investigated, inspired by the recent CdS-nanorod-on-silver plasmonic laser. The proposed technology is suitable for large scale fabrication. It only uses a single wet resist development and several coatings onto a flat metal surface to define the waveguide geometry. It thus relieves the need to etch or lift-off a noble metal. High-index sol-gel inverse ribs are privileged candidates for the tightest confinement. We investigate and explain the guidance mostly for the case of Au and the wavelengths around λ=633 nm. We get spot sizes down to ∼25×60 nm2. We notably describe how easily the tight confinement is granted and the reasons why only a single critical step defines the modal geometry. We finally detail how the classical building-blocks of integrated optics such as distributed reflectors and couplers can be made within the very same approach and integrated into devices for which losses are described.