Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-04-26
2003-05-27
Psitos, Aristotelis M. (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
Reexamination Certificate
active
06570840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to digital optical recording and retrieval from data storage structures. More specifically it relates to three-dimensional mark, land and tracking guide configurations for improved Figure of Merit, and to methods and apparatus for production thereof.
2. Description of Prior Art
Information storage and retrieval employing a spinning disc upon which digital data (representing documents, software, music, images and other types of information) are recorded, and from which data are retrieved by means of one or more optical beams impinging on the surface of the disc (or a “daughter” disc produced from a disc master), is well known in the art. Likewise well known are other structures upon which digital data are optically recorded and from which the data are retrieved, including cylinders and cards. Optical recording on multi-layered data “wafers,” from which data are selectively extracted by scanning or other means essentially free of moving parts, can easily be anticipated in the relatively near future, as well as other sophisticated structures for ultra large-scale optical data storage and selective retrieval.
While each such type of structure might be separately addressed in this discussion, it is believed that the concepts discussed can be more clearly addressed with particular emphasis on essentially planar, disc-shaped structures, upon which data are recorded and from which data are retrieved while the discs are spinning about a central axis. From time to time, reference may be made to these other structures in connection with the invention disclosed herein, whose application and embodiments are by no means limited to discs.
A number of commonly employed disc-based optical data recording methods exist, each proceeding on a fundamentally different physical basis, and various implementation variations exist within each method. However, these optical disc recording methods have a number of features in common. For example, they all utilize a spinning, disc-shaped storage structure upon whose surface (or surfaces, or layers) one or more spiral data tracks are imposed. In some applications, there may be only one continuous track on the particular surface; in others there are a plurality of tracks, each occupying an annulus on that disc surface. Of course, in essentially rectangular optical recording structures, such as cards and data wafers, the tracks would likely constitute approximately parallel lines of data marks.
Each data track comprises a succession of a great number of microscopic marks interspersed by unmarked, or differently marked, areas commonly designated as “lands.” The track pitch (i.e., the radial distance between the longitudinal axes of adjacent, essentially circular track portions) is microscopic, as is the length and width of each of the marks. Accordingly, a data track on a disc surface may be thought of as a large number of closely spaced essentially circular pathways, each containing a great many data marks and intervening lands in succession. In some applications, a particular data track or track portion might not be completely circular, in the sense that it might occupy only an arc of a circle on the disc. However, in this discussion arcuate and circular data tracks or portions of tracks will be referred to interchangeably as being circular data tracks. Since the circumference of each of these essentially circular pathways is very great, in comparison to the dimensions of the marks and lands, a small succession of marks and intervening lands will appear to be a linear (i.e., straight line) sequence at the microscopic level. Accordingly, at the microscopic level, radially adjacent data tracks on the disc may be viewed as essentially parallel lines of data, each containing a longitudinal succession of linear marks and lands, although at the macroscopic level they are essentially concentric circular paths.
The disc is normally written (i.e., recorded) and read by rotating it rapidly on a motor-driven spindle. Tracking—maintenance of the radial position of the write beam and/or the read beam precisely in the center of the data track—is accomplished through a servo apparatus that compares at least a single pair of continuous readings. Each reading in the pair is taken on opposite sides of the longitudinal axis of the track. Based on these readings, the servo continuously adjusts the radial position of the beam to cause the readings on opposite sides of the track to be equal. This condition occurs when the beam is focused precisely upon the longitudinal axis of the track, i.e., when the two reading points are equidistant from the track axis. The sensing method will, of course, depend on the particular optical data recording method employed.
Tracking may be accomplished with a single beam—the read beam or the write beam, depending on which operation is being tracked. Here, the reflected beam is optically split into a data retrieval beam (or write monitoring beam, in direct-read-after-write—DRAW—applications) and a tracking beam. In CD and DVD-R applications, the reflected tracking beam component of essentially circular cross-section is divided into two equal semi-circles, the dividing line between them being parallel to the longitudinal track axis. The tracking sensor continuously compares the intensity of the two halves of that image, and a servomechanism adjusts the radial position of the beam to cause the sensed light in both halves to be equal. The latter condition indicates that the readings are being taken from the center of the track axis, i.e., that proper tracking is occurring.
Generally, the same sensor is employed for tracking and for data retrieval (or write monitoring). In single-beam (“push-pull” or “PP”) CD tracking, one of the two sensed components is subtracted from the other, and a zero difference (i.e., equal input from both sides) indicates proper tracking. Data retrieval (or write monitoring) is accomplished by adding the two halves.
In DVD-ROM applications, differential phase tracking is employed, in which the reflected light is divided into four quadrants and the phasing of each is compared to determine tracking condition.
Most CD playback devices employ triple-beam data retrieval tracking (although the “Red Book” only prescribes standards for single-beam, PP tracking). In triple-beam tracking, the read beam is split into three beams, the read beam itself, a first tracking beam directed one or more mark lengths ahead of it and offset ¼ of the track pitch (approximately ¾ mark width) to one side, and the second tracking beam directed one or more mark lengths behind the read beam and offset ¼ of the track pitch to the other side. Each of the two tracking beam reflections is individually sensed continuously for tracking, in the manner described above in respect to PP tracking.
Beam focusing is likewise accomplished through a suitable feedback mechanism. Beam focusing is commonly employed and well known in the art, and therefore need not be further described except as may be necessary to describe particular applications.
The specifics of optical data recording, retrieval and tracking depend on which type of optical data recording is being considered. Accordingly, to understand optical data recording and retrieval, and to further understand tracking—and the present invention—it is important first to consider the various optical data recording methods commonly in use, with particular attention to those aspects of data retrieval and tracking pertaining to the present invention and its various embodiments and applications.
The most commonly employed optical data recording methods fall into four categories.
In Magneto-Optic (“MO”) data recording, the general purpose is to store erasable data files on a disc for archival purposes, e.g., in computer hard drives. In MO recording, the disc's recording surface is comprised of one or more thin metallic-alloy layers having specific magneto-optic properties, which are sandwiched between thin dielectric and
Eberly Carlyle J.
Holmes John R.
Rilum John H.
Wilkinson Richard L.
Koundakjian Stephen J.
Optical Disc Corporation
Psitos Aristotelis M.
LandOfFree
Figure of merit in optical recording structures does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Figure of merit in optical recording structures, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Figure of merit in optical recording structures will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3049568