KEYWORDS: Servomechanisms, Signal processing, Signal detection, Optical tracking, Sensors, Clocks, Stereolithography, Detection and tracking algorithms, Photodetectors, Modulation transfer functions
Differential phase detection (DPD) is the most popular tracking error detection method for read-only optical discs (ROM
discs). However, DPD tracking-error signals deteriorate for high-density discs such as over 30-GB Blu-ray discs (BDs)
where zero-cross detection becomes inaccurate. To solve this problem, we propose a new zero-cross-detection-free DPD
(ZF-DPD) method by applying the least-mean-square (LMS) algorithm adaptive equalizer. We experimentally confirmed
its effectiveness for a high-density (33.3 GB/layer) four-layer BD-ROM disc.
KEYWORDS: Optical discs, Optical storage, Tolerancing, Signal processing, Signal to noise ratio, Reflectivity, Clocks, Multilayers, Data storage, Reliability
High-density multilayer optical disc storage was investigated by employing advanced signal processing methods such as adaptive equalization and adaptive partial-response maximum-likelihood (PRML) detection. Preliminary experiments, recording on single-layer and dual-layer Blu-ray discs (BD), indicate storage capability of 33.3 GB/layer with adaptive 5-tap PRML. A new signal qualification method, sequenced amplitude margin quasi-error estimation (SAMQES), was introduced for high-density multilayer recording, and possibility toward a total storage capacity of 200 GB was examined by using a six-layer BD-Recordable disc. Despite coherent interlayer crosstalk and lower signal-to-noise ratio, SAMQES showed moderate increase from those in single-layer recording.
KEYWORDS: Optical recording, Signal processing, Deep ultraviolet, Objectives, Tolerancing, Indium gallium nitride, Signal to noise ratio, Amplifiers, Semiconductor lasers
The possibility of high-density groove-only recording was investigated by using a high-numerical-aperture lens unit and an InGaN semiconductor laser. Wobbled grooves of 20 nm in depth were formed through a deep-UV disk mastering process and replicated by injection molding onto a polycarbonate disk substrate. This shallow wobbled groove structure improves a signal-to-noise ratio (SNR) and also enables an address in pre-grooves (ADIP). In the experiment, signals were recorded either in or on the grooves, and the achievable areal recording density was carefully examined in each case, comparing with a previous land-and-groove disk configuration. The authors' results indicate that the signal recording on the grooves, which correspond to the structured area located closer to the objective lens, brings higher track density than that in the grooves. A bit size of 120 X 320 nm, an areal density of 16.8 Gbit/in2, was verified at the data transfer rate of 35 Mbps on a phase-change disk of SbTe-based eutectic composition. This bit density can realize a storage capacity of 23.3 GB on a f 120 mm disk. Further investigation on higher areal density was also examined with an additional signal processing.
KEYWORDS: Near field, Electrodes, Gallium nitride, Semiconductor lasers, Servomechanisms, Objectives, Near field optics, Modulation transfer functions, Polishing, Surface finishing
We developed a 1.5-Numerical-Aperture optical setup using a GaN blue-violet laser diode. We used a 1.0 mm-diameter super-hemispherical solid immersion lens, and optimized a phase-change disk structure including the cover layer by the method of MTF simulation. The disk surface was polished by tape burnishing technique. An eye-pattern of (1-7)-coded data at the linear density of 80 nm/bit was demonstrated on the phase-change disk below a 50 nm gap height, which was realized through our air-gap servo mechanism.
Recently, solid immersion lenses (SILs) have yielded a great interest in near-field optical data storage. However, convincing data on areal recording density have yet to be reported. The difficulty is attributed to the fact that an air-bearing slider needs to be kept optically contacted and also that a tiny SIL is vulnerable to aberrations caused by an air gap between a lens and a disk. The air-bearing system cannot easily achieve the condition above because its linear velocity changes the air gap. We have developed a new SIL device mounted on an actuator, which allows the air gap to be varied arbitrarily and enables optical contact independent of disk rotation. The obtained eyepattern of (l,7)-coded data on a phase-change disk demonstrates near-field recording over 1.2- numerical-aperture (NA).
Both over 20 GB of capacity and higher data transfer rate more than 25 Mbps are required for the optical data storage in the era of digital broadcasting to record high-definition digital video stream.
KEYWORDS: Tolerancing, Optical discs, Second-harmonic generation, Digital video discs, Video, Transmission electron microscopy, Modulators, Digital video recorders, Light sources, Wavefronts
Using a two-element objective lens, over 0.9 NA lens and long WD lens are demonstrated. Using a thin cover layer, problems for skew margin and thickness tolerance are solved. Using a red LD, a 0.85 NA lens and a 0.1 mm cover PC disk, 8 GB rewritable disk system has been developed. Using a blue-green LD and an SHG blue laser, promising results are demonstrated for 12 GB and 17 GB of capacity.
A solid immersion lens (SIL) attached to a conventional objective could multiply the effective numerical aperture of an optical pick-up by a factor of refractive index n. A truncated hemispherical SIL (n equals 1.5) mounted on a slider, which was designed to follow the movement of the objective, kept good contact between the SIL and a disk substrate with a slight amount of air gap. Our simple configuration enabled the use of this method in an unsealed environment and extended the spatial cut-off frequency by 1.5 times. In addition, the combination with a second-harmonic generation green laser yielded high areal density optical data storage, six times that of current CD systems.
Some time ago we described a new type of near-field imaging system using the solid immersion lens. In this paper we shall discuss how this type of lens can be employed in optical storage systems to increase the bit density, along with the research that has been carried out at Stanford in cooperation with Sony Corporation and IBM, Almaden to reach this goal. 12 ()j aimis to work with both CD ROMs and magneto-optical storage.
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