Browse Prior Art Database

LEADING SPOT TRACKING TECHNIQUE FOR OPTICAL DISK SYSTEMS

IP.com Disclosure Number: IPCOM000025154D
Original Publication Date: 1983-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 83K

Publishing Venue

Xerox Disclosure Journal

Abstract

One of the more promising focusing/tracking techniques for use in optical disk memories is based on having a central read or read/write beam straddled by radially offset outrigger beams. For example, to implement such a "three spot" focusing/tracking technique, a laser beam may be split by a diffraction grating, thereby providing + and - first order outrigger beams to straddle a centralized zero order read or read/write beam. Typically, however, such an implementation causes one of the outrigger beams to lead the read or read/write beam and the other to lag. In memories using a pregrooved disk, this might introduce an unwanted offset or instability into the tracking system while data is being written on the disk because the data alters the optical properties of the disk to the lagging beam but not the leading beam.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 57% of the total text.

Page 1 of 2

XEROX DISCLOSURE JOURNAL

LEADING SPOT TRACKING TECHNIQUE FOR OPTICAL DISK SYSTEMS
Robert A. Sprague

Proposed Classification
U.Si CI. 369/44 Int. Cl. Gllb 7/00

One of the more promising focusing/tracking techniques for use in optical disk memories is based on having a central read or read/write beam straddled by radially offset outrigger beams. For example, to implement such a "three spot" focusing/tracking technique, a laser beam may be split by a diffraction grating, thereby providing + and - first order outrigger beams to straddle a centralized zero order read or read/write beam. Typically, however, such an implementation causes one of the outrigger beams to lead the read or read/write beam and the other to lag. In memories using a pregrooved disk, this might introduce an unwanted offset or instability into the tracking system while data is being written on the disk because the data alters the optical properties of the disk to the lagging beam but not the leading beam.

To avoid that problem, as shown in enlarged, fragmentary form in Figure 1, the spots 11 and 12 formed on a pregrooved medium 13 by the outrigger beams should both lead or lag the spot 14 formed by the read or read/write beam. To that end, a two frequency blazed or unblazed diffraction grating having a small angle between its frequencies may be used to split a laser beam into three diffraction beams with the desired spatial relationship. For example, a pair of replicated blazed single frequency gratings could be assembled in back-to...