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Holographically Generated High Resolution Track Servo Pattern for Optical or Capacitive Readout

IP.com Disclosure Number: IPCOM000047459D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Werlich, HW: AUTHOR [+2]

Abstract

As the track density of magnetic and optical storage devices increases, some kind of track servoing - be it of the magnetic, optical, or capacitive type - will become imperative. Proposed here is an optical approach capable of producing extremely fine servo patterns on small or large diameter disks. The pattern is a system of concentric, parallel lines (tracks/grooves/bands) with a spacing as small as N0.5 mm (20 m inch). It can be generated either by direct holographic exposure of a thin film of photoresist on a storage disk, or by contact - printing through a holographically generated mask (however, the latter method appears useful only for relatively coarse patterns).

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Holographically Generated High Resolution Track Servo Pattern for Optical or Capacitive Readout

As the track density of magnetic and optical storage devices increases, some kind of track servoing - be it of the magnetic, optical, or capacitive type - will become imperative. Proposed here is an optical approach capable of producing extremely fine servo patterns on small or large diameter disks. The pattern is a system of concentric, parallel lines (tracks/grooves/bands) with a spacing as small as N0.5 mm (20 m inch). It can be generated either by direct holographic exposure of a thin film of photoresist on a storage disk, or by contact - printing through a holographically generated mask (however, the latter method appears useful only for relatively coarse patterns). After exposure and development of the resist, the pattern can be used as is or be transferred onto the disk substrate by chemical etching, ion milling, metallization, or oxidation of the disk surface. It is conceivable that these servo lines would be located beneath the magnetic coating for optical readout (i.e., by a GaAs diode), or for capacitive readout, or in bands separate from data tracks. Emphasized here is the holographic generation of large-diameter, extremely fine-spaced, concentric servo tracks which can be generated with high precision only by holographic techniques. A hologram is the interference pattern that results from the superposition of two mutually coherent laser beams. In the simplest case where two plane waves are superposed, the resulting interference pattern is a system of straight, pa...