Evanescent Coupling Between Dielectric and Plasmonic Waveguides for HAMR Applications

Heat assisted magnetic recording (HAMR) is a possible solution to further increase hard drive recording density. In a HAMR system, an external light source is employed to locally heat up magnetic media. To achieve a realistic HAMR system, a near-field transducer (NFT) is necessary to focus optical fields down to 10-20 nm in size. Different approaches to excite NFTs have been investigated, including focusing of external light sources and coupling from dielectric waveguides. Here we demonstrate evanescent coupling between a series of single mode dielectric waveguides and adjacent plasmonic waveguides with relatively large cross section (200 nm×300 nm). We envision for these large plasmonic guides could then be used, in turn, to efficiently drive NFT's with smaller cross sectional area. A series of samples with various overlap length of the dielectric c and plasmonic waveguides demonstrates that coupling in these waveguides can be designed and understood using mode indices calculated from the eigenmodes of the waveguide cross sections. Coupling strength which oscillates with the length of the overlap section of the waveguides is shown according to standard coupled mode theory.