Browse Prior Art Database

Spatial Filtering for Storage Technology

IP.com Disclosure Number: IPCOM000101389D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 124K

Publishing Venue

IBM

Related People

Johnson, M: AUTHOR

Abstract

Two or more different types of information (for example, servo and timing) may be stored together in a single optical pattern on an information storage disk and then optically separated with spatial filtering using appropriate masks.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Spatial Filtering for Storage Technology

       Two or more different types of information (for example,
servo and timing) may be stored together in a single optical pattern
on an information storage disk and then optically separated with
spatial filtering using appropriate masks.

      Several data storage technologies require the recording and
reading of fine optical patterns.  For example, in magnetic disk
storage it is of interest to detect complex optical patterns on the
disk surface for delineation of magnetic tracks, sector information,
clock timing recovery, and servoing.  This will introduce the concept
of optical processing and, in particular, spatial filtering to this
technology.

      Consider the detection and recognition of optical servo
information on a rotating disk.  One simple but representative
pattern consists of arrays of inclined servo stripes overlaid with
radial timing bars (Fig. 1).  The phase relationship between the
timing bars and the inclined pattern crossings is a representation of
the radial position of the detector.  However, using only a single
detector and conventional electronic circuitry, it is very difficult
to separate the bar and skew patterns.  For example, a phase-locked
loop would not be able to discriminate between the two types of
signals.  The problem is endemic because the electrical spectra of
the timing and servo signals become mixed.  This is not true,
however, for the optical signals.  Optical spatial filtering allows
simple and effective separation of the two.

      A small area of the pattern is imaged (Fig. 2) via a
beamsplitter onto two separate detectors.  The central region of the
optical system contains the shift-invariant spatial frequency
spectrum of the pattern, which may be filtered through the use of a
suitable mask.  In the case shown, a single, one-dimensi...