A hybrid finite-difference-time-domain/angular spectrum propagation modeling technique and a finite-difference thermal model are used to study near-field optical and two- photon absorption data storage systems. The electromagnetic model is used to analyze scattering effects in structures where scalar-based theory is not appropriate. The thermal model is used in a near-field magneto optic data storage system to calculate data mark sizes.
We report on a novel method for generating sub-micron lithographic patterns in photoresist through the use of a scanned sub-wavelength optical aperture. The aperture consists of the tip of a single-mode optical fiber that is drawn down to a diameter of 80 nm and coated with aluminum. The fiber tip is manipulated with a modified scanning tunneling microscope (STM) that brings the tip into proximity of a photoresist-coated substrate. The resolution is primarily a function of the aperture diameter and tip-to-sample separation. A linewidth of 200 nm has been achieved in preliminary experiments.
We describe a new type of microlens for data storage applications that has improved off-axis performance. The lens consists of a micro-Fresnel pattern on a curved substrate. The radius of the substrate is equal to the focal length of the lens. If the pattern and substrate are thin, the combination satisfies the Abbe sine condition. Therefore, the lens is free of coma. We analyze a 0.5 numerical aperture, 0.50 mm focal length lens in detail. A 0.16 numerical aperture lens was fabricated holographically, and results are presented.
We describe performance of a differential spot-size (wax-wane) focus servo. Cross talk from the tracks are analyzed in the single detector and differential focus circuits. Magnitude of the cross talk is reduced by a factor of three in the differential circuit. A false FES signal is present when the spot crosses sector marks at na angle.