Efficient Integrated Light-Delivery System Design for HAMR: Maximal Optical Coupling for Transducer and Nanowaveguide

Light-delivery system for heat-assisted magnetic recording consists of laser, waveguide, and plasmonic near-field transducer (NFT). The overall efficiency of light-delivery system is determined by the efficiency of optical power transfer from waveguide to media via the plasmonic NFT and coupling of light from laser to waveguide. In this paper, we present an overall efficiency optimization of the light-delivery system, including the waveguide-NFT-media coupling efficiency by improving the waveguide mode-plasmon mode conversion and waveguide-media-stack impedance matching and laser-to-waveguide coupling efficiency using multi-layer graded refractive-index (GRIN) cladding layer. We show that a high refractive-index waveguide improves waveguide mode-to-asymmetric plasmon mode conversion and also improves characteristic impedance matching with the media stack resulting in a maximal optical power transfer efficiency of 11.5% between the waveguide and the media via a taper-based NFT. The multi-layer GRIN cladding structure acts as a collimating lens with a high numerical aperture, which can achieve laser-to-waveguide coupling efficiency of 90% in our numerical example. Therefore, the overall optimization shows that the efficiency of light-delivery system can reach 9%-10%.