Low-loss Adiabatic Dielectric-Plasmonic Hybrid Waveguide for HAMR Applications

To achieve a feasible heat-assisted magnetic recording (HAMR) system, a near-field transducer (NFT) is necessary to focus the optical field to a lateral region measuring tens of nanometres in size. Coupling light effectively... [ view full abstract ]

To achieve a feasible heat-assisted magnetic recording (HAMR) system, a near-field transducer (NFT) is necessary to focus the optical field to a lateral region measuring tens of nanometres in size. Coupling light effectively into the NFT is a key challenge in the design of a HAMR system. In this work, we theoretically and experimentally investigate the properties of coupling between a slab Si₃N₄ waveguide and a long tapered Au plasmonic waveguide through an evanescent coupling mechanism. The most important insight is how to construct an adiabatic taper with a length on the order of 10 μm (two orders of magnitude longer than typical devices) that can efficiently extract the incident light from the waveguide core to the NFT while overcoming the ohmic losses incurred by increasing the optical path length. Our study shows that in the fully optimized system, a maximum coupling efficiency between the photonic mode and the plasmonic mode of ~77% is achieved with a 6 μm long taper. The system can be characterized in terms of the coupling length (the distance between constructive interference points) and the field intensity enhancement at the tip, which is estimated to be 16× for an NFT with a 50 × 50 nm² tip. All these factors, particularly the system’s ability to remove light from the dielectric waveguide to prevent optical interference in other parts of the system, make this a viable candidate for HAMR implementation.