Maximizing the Plasmonic Near-Field Transducer Efficiency to Its Limit for HAMR

Plasmonic near-field transducer (NFT) facilitates optical power transfer into a nano-spot in the recording media for heat-assisted magnetic recording. Typically, impedance matching is a condition for maximum power transfer between a given source and load. Even for waveguide-NFT-media stack system, we verify that matching the impedances of waveguide and media-stack at NFT resonance maximizes power transfer. However, it is not a sufficient condition. Since, NFT guides the light into the media-stack as symmetric and asymmetric optical modes, higher conversion of dielectric mode into a mode that exhibits maximum coupling into the media is the second condition for maximizing the power transfer into the media. In this study, operating wavelength range, material refractive indices, and NFT geometrical parameters are considered in the design space for maximizing the efficiency of an exemplary taper-based NFT structure. We first estimate the maximum efficiency and compare with the benchmark efficiency of “ideal” version of the considered NFT to confirm that the obtained efficiency is maximum. At maximum efficiency point, we show that the impedance matching between waveguide and high-index media stack is enhanced and mode-conversion efficiency into asymmetric plasmon mode is also enhanced because of high-index contrast feeding waveguide and suitable operating wavelength range.