Generation of compact near-field energy for optical recording: Transducer efficiency and signal detection

A new theory of illumination is derived for near-field optical transducers, in which transmitted power is related to total power in the illuminating laser beam. Several transducers are compared, including simple holes in metallic films, a dielectric probe and solid immersion lens combination, and plasmon-enhanced holes. The ratio of transmitted power to incident power is a function of the illumination numerical aperture, due to the angular selectivity of the transducers. Also, a simplified collection theory is reviewed, which reveals that, when transducers are used for the collection of data signals in optical storage applications, a combination of the transducer and a solid immersion lens provides a large angular collection range, and hence a good contrast signal.