Optical Transducers for Near Field Recording

TLDR

Near‑field optical transducers that focus light below the diffraction limit must be positioned close to a recording medium, and such sub‑20‑nm apertures and antennas are promising for optical or heat‑assisted magnetic data storage. The study uses gold transducers with a minimum size of 20 nm positioned 7.5 nm from the medium. Optimized simple apertures couple about 1.5 % of incident power into sub‑50‑nm spots, and more sophisticated designs can increase this efficiency by at least three‑fold.

Abstract

Optical transducers that concentrate optical energy in the near field to dimensions much smaller than the standard diffraction limit are often classified as apertures or antennas. For near field recording the transducer must obviously operate with a recording medium in its immediate vicinity which can strongly interact with the transducer. Transducers composed of gold and with a minimum dimension of 20 nm are spaced 7.5 nm from the medium in this study. Even simple apertures when optimized are able to couple ∼1.5% of the incident power into optical spots with a full width at half maximum diameter of less than 50 nm or a tenth of a wavelength. More sophisticated apertures and antennas can improve this coupling efficiency by a factor of three or more, although not by orders of magnitude. Such transducers may have applications in optical or heat assisted magnetic data storage.