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Recently, various researches on optical recording based on near-field optical principles have been conducted for higher data storage density. However, there is a problem of the trade-off between signal output and spatial resolution, especially when an aperture-type near-field optical head is utilized for high speed data-readout. In order to solve this problem, we propose a novel near-field optical head, the planar aperture-mounted head with a minute scatterer, and analyze its read-out performance through the three-dimensional finite-difference time-domain (3D-FDTD) method. Our simulations reveal that the Silver scatterer placed at the center of the planar aperture strongly enhances optical energy due to the local surface plasmon excitation, and that this head has the potential to realize high resolution and high signal output simultaneously.
One of the most important parameters related to the near-field readout principle is aperture-to-media spacing (effective spacing). We proposed a near-field optical head with a protruding aperture that can reduce the effective spacing beyond the mechanical limit of the flying height and localize the near-field on the medium. Using nanostep lithography, we fabricated the protruding aperture, whose extension is 20 nm with 5 nm accuracy, so that the effective spacing is successfully reduced to 50 nm on a 3.2×3.6 mm flying head. We demonstrated signal readout with a 150 nm-long line-and-space pattern in chromium with the head. The flying height was estimated to be 75 nm, so that the effective spacing was 54 nm. The circumferential speed was 2.7 m/s and the signal frequency was 9.1 MHz. We also propose a promising structure for an optical head of higher density.
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