KEYWORDS: Servomechanisms, Near field, Actuators, Polymers, Solids, Signal detection, Scanning probe lithography, Near field optics, Control systems, Tolerancing
We present our progress on the development of a single-wavelength near-field recording system with a blue-violet laser and a NA=1.45 Solid Immersion Lens in a conventional 3D actuator. We will introduce our near-field optical recorder and present good recording results achieved on discs with a 3 μm thick spin-coated protective polymer cover-layer using a channel bit length of 43.7 nm. Furthermore, we will show recent results on high-speed near-field readout, up to 3xBD speeds, through a cover-layer using feed-forward control in the air gap servo system.
Progress is reported on cover-layer incident Near-Field Recording. Very good recording results are obtained on a CuSi disc demonstrating excellent signal quality with modulation corresponding to the full effective numerical aperture of 1.45. Comparing the Near-Field system with Blu-ray Disc further shows that an extension to at least 4 data layers should be possible. In addition, a method for dynamic tilt control is presented. Controlling the tilt between the solid immersion lens and the disc surface improves the system robustness and relaxes media manufacturing tolerances for a roadmap towards 500 GB capacity on a single-sided, 4-layer disc which is protected by a polymer cover-layer.
We present read-out results of a 50 GB disk with a blue laser and a NA=1.9 Solid Immersion Lens in a conventional focus and tracking actuator. Furthermore, we show a light path and a disk design that enable cover-layer incident near field recording on dual-layer disks with a capacity of 300 GB on a double-sided disk.
KEYWORDS: Signal processing, Signal detection, Sensors, Optical tracking, Error analysis, Optical filters, Optical storage, Satellites, Signal to noise ratio, Detection and tracking algorithms
We report on the technical progress in increasing the recording density of optical storage systems by means of improved read-channel signal processing and write-channel optimisation.
The recording density increase is realized by employing PRML (Viterbi)
bit detection in combination with improved timing recovery and adaptive equalisation algorithms, and by using a signal quality characterisation scheme which enables a proper control of the write process in the considered range of storage densities. The Blu-ray Disc (BD) optical disc system employing blue-violet laser with the wavelength of 405nm, objective lens with numerical aperture of 0.85 and disc cover layer thickness of 0.1mm is used as an experimental platform in our present study. Multi-track experimental results for both single-layer read-only (BD-ROM) and single-layer rewritable (BD-RE) media are presented to show the feasibility of the increased-density BD.
A 10 μm free working distance recording head for blue, cover-layer incident MO recording has been developed with NA=0.95 and integrated high bandwidth MFM coil. ZF-MAMMOS recording experiments are described.
RF-MAMMOS is a promising technology to reach storgae densities around 100 Gb/in2. Using domain expansion (and collapse) driven by a small, external magnetic field, bits much smaller than the optical spot size can be read out with saturated signal levels. Because these bits are selected by the center of the thermal profile induced by the focused laser spot, it is essential that the readout conditions determining the size of this heated region, the copy window, are controlled very accurately. At the same time, the external field needs to be synchronized to the recorded data. This can be achieved by data dependent field switching: the external field starts in the expansion direction and is only modulated at the bit clock frequency when expansion for a mark is detected. In this way, each first peak of a mark run length contains complete timing information which is used as input for a phase locked loop (PLL). Based on this approach, a method is proposed to solve the readout margin problem. By applying a small, fixed modulation to the laser power or the external field at a frequency above the bandwidth of the PLL, we demonstrate that the induced timing modulation provides a suitable signal to actively control the size of the copy window. First experimental results confirm the feasibility of better than 1% power control accuracy, opening the way to robust readout at the highest densities.
We present a magneto-optical recording head designed for a 400 nm laser with a 0.85 numerical aperture doublet objective lens and a thin film Magnetic Field Modulation coil integrated in a flying slider.
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