Coupled plasmonic waveguides: Near field transducers for HAMR

This paper presents a design for a near field transducer for heat assisted magnetic recording that utilizes evanescent coupling between a dielectric waveguide and a metallic “needle” of uniform triagular cross-section. This design allows for complete coupling of power from an illuminating single mode dielectric waveguide into the plasmonic mode of the metallic needle. Coupling from the plasmonic waveguide into the medium is computed to be localized (40 nm FWHM) with 2.5% efficiency inside the FWHM (8% overall). A single mode dielectric waveguide illumination structure like that needed for the needle´s functioning is demonstrated using a curved focusing grating and a thin film waveguide. Illumination efficiencies of better than 5% are shown with room for the required increases.