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Browse Prior Art Database

Detector Module for Magneto-Optic Head

IP.com Disclosure Number: IPCOM000116263D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Dewey, AG: AUTHOR

Abstract

Use of a three-beam Wollaston prism has allowed the design of a compact optical head for use in a magneto-optic data storage drive. The data and servo detectors are integrated on a single chip, and the servo signals are generated from the central beam using a quad detector and the astigmatic servo method. The outer two beams are also focused by the astigmatic lens onto the data detectors. This implies that the focused beam size on the data detectors is much larger than it would be if they were focused by a spherical lens. This requires larger data detectors with higher capacitance, which affects the electronic noise level of the data preamps.

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Detector Module for Magneto-Optic Head

      Use of a three-beam Wollaston prism has allowed the design of a
compact optical head for use in a magneto-optic data storage drive.
The data and servo detectors are integrated on a single chip, and the
servo signals are generated from the central beam using a quad
detector and the astigmatic servo method.  The outer two beams are
also focused by the astigmatic lens onto the data detectors.  This
implies that the focused beam size on the data detectors is much
larger than it would be if they were focused by a spherical lens.
This requires larger data detectors with higher capacitance, which
affects the electronic noise level of the data preamps.

      A modified head design is described in which the data beams are
focused by a spherical lens, which allows smaller data detectors and
which could increase the SNR of the head.  It uses the differential
Spot-Size-Measuring (SSM) servo method, but uses only a single Si
chip for the data, servo, and power monitor detectors.  The SSM
method is an improvement over the astigmatic servo method in that it
is relatively immune to pattern noise.

      Fig. 1 shows a possible configuration in which A is a cover
glass over a sealed module containing a miniature prism assembly B
and the Si detector array C.  The array is shown in Fig. 2 and
includes two data detectors, two 3-element detectors for the servo,
and a monitor detector to which the beam used for APC of the laser
may b...