Optical Transducers for Near Field Recording

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.