Optical logic element and optical logic device

Details Optical logic element and optical logic device Optical logic element and optical logic device

1998-03-02

1999-12-21

Nguyen, Tan T.

Static information storage and retrieval

Radiant energy

Semiconductive

365215, G11C 1304

Patent

active

060057912

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention concerns an optical logic element. More particularly the present application a multistate, multistable optical logic element, and even more particularly a proximity-addressable optical logic element.


BACKGROUND OF THE INVENTION

In general the invention concerns a new class of optoelectronic devices which can store information and/or perform logic functions by means of an optical memory substance which is contained in individually addressable cells or elements. Each element is an independent unit and can be combined with similar elements to form larger assemblies, typically in the form of planar sheets or layers. The latter may be configured in tertiary structures, for example by stacking in order to form optical data memories and optical logic devices with a high performance-to-volume ratio.
Present-day digital optical data storage technologies has been developed in response to an ever-expanding need for data storage capacity in a compact format and they have been remarkably successful in providing solutions which combine a high areal data density with replaceability and/or portability.
The crucial step has been the use of small, efficient semiconductor lasers emitting coherent light which can be focused to near-diffraction-limited spots, thus providing a correspondingly accurate definition and dense arrangement of the information bits in the data carrying medium. In practical systems, cost and space limitations have logically resulted in a design in which the laser beam is scanned across the surface of a rotating disc, picking up a serial bit stream as it follows an optical guidance track under servo control.
Systems based on this generic design have now been refined to a point where the data density is close to the theoretical limit, and further improvements in order to match future demands cannot be met by incremental improvements as in the past.
One obvious limitation is the use of two-dimensional data storage format. Even though the area data density is high, physical bit positions are restricted to a planar surface on a rigid, self-supporting, surface of high mechanical quality, leading to a relatively unimpressive volumetric data density. Technical solutions have recently been published wherein data are stored in several planes at different depths below the surface of the disk. Discrimination between different layers is possible due to the very short depth of field associated with a precise focus and this principle is expected to be developed to encompass up to ten planes or layers (see e.g. E. K.(signature), "Stacking the decks for optical data storage", Optics and Photonics News, August 1994, p. 39). It appears, however, that the benefits reaped from multiple layers or levels are partially neutralized by cost issues as well as technical trade-offs between the number of layers on the one hand and the achievable areal data density in each layer on the other hand. Even when implemented according to the claims set forth, such technological solutions lack the potential for sustained long-term development and improvement.
In many instances limitations in access time and data transfer rates represent a much more serious drawback for rotating disk systems than do the above-mentioned limitations on data densities and capacities.
In applications where files on a disk have to be accessed quickly in random sequence, the laser focusing servo must rapidly move an optical assembly radially from one position on the disk to another. At the correct radial position, tracking must be resumed quickly, involving alignment in two dimensions, adjustment of the spinning speed, establishment of synchronization and finding and identifying the file header. These electromechanical procedures involve access times which are long, typically 200 ms or more. Efforts have been made to reduce the access time, e.g. by increasing the disk rotation speed in order to reduce the time taken for rotational alignment, and reduce the weight of the servo-controlled focusing and tracking components. Imp

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