Browse Prior Art Database

Adaptive Optical Head for Embedded Servo

IP.com Disclosure Number: IPCOM000115685D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 127K

Publishing Venue

IBM

Related People

Yung, BH: AUTHOR

Abstract

The major show stopper for having higher track density (TPI) in a dedicated servo based DASD environment is the Track Mis-Registration (TMR) due to thermo-mechanical drift in the HDA assembly. Embedded servo would eliminate this problem. Embedded servo pattern can be generated magnetically or optically. This disclosure addresses issues involving optical servo. It requires an optical head to generate the Track Error Signal (TES) using servo pattern lay down through lithographic process (1). Traditional optical head is too bulky due to the size of the objective lens, its associated focus actuator and beam bender. This bulkiness may offset the competitiveness in the volumetric density due to inefficient Disk Per Inch (DPI) packaging. Rotary actuator based optical head has been demonstrated.

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Adaptive Optical Head for Embedded Servo

      The major show stopper for having higher track density (TPI) in
a dedicated servo based DASD environment is the Track
Mis-Registration (TMR) due to thermo-mechanical drift in the HDA
assembly.  Embedded servo would eliminate this problem.  Embedded
servo pattern can be generated magnetically or optically.  This
disclosure addresses issues involving optical servo.  It requires an
optical head to generate the Track Error Signal (TES) using servo
pattern lay down through lithographic process (1).  Traditional
optical head is too bulky due to the size of the objective lens, its
associated focus actuator and beam bender.  This bulkiness may offset
the competitiveness in the volumetric density due to inefficient Disk
Per Inch (DPI) packaging.  Rotary actuator based optical head has
been demonstrated.  However, to integrate the optical head with the
magnetic head using rotary actuator is a real challenge.  This
disclosure discloses a novel optical head design to generate the TES
and yet, mechanically adaptive to the magnetic head assembly to
maintain the DPI efficiency.  The technology is also applicable for
high density double sided flexible media recording.

      FLOPTICAL (2) technology combines Compact Disk (CD) optical
head with existing flexible disk drive technology.  This CD pickup
head is not suitable for high density DASD application due to its
bulkiness.

      A diode laser is positioned at a proper distance above a media
with surface relief track information, be it grooves and/or embossed
marks.  The laser is installed with its junction at a proper
orientation relative to the media such that the spot size (1/e2/) is
of proper ratio to the track pitch such that it yields satisfactory
TES.  To sense the diffracted light and hence generate the TES
signal, two Photodetectors (PD) are positioned across the track.  The
size of the detector determines the Numerical Aperture (NA) of the
detection system (Fig. 1).  This configuration permits small and
light-weight packaging such that it can be integrated with a magnetic
head without significantly affecting its aerodynamic performance.
Due to the low fly height and/or contact, the variation in fly height
has a minimum impact on the TES integrity.

      Typical laser diode has an active area of (hxw) 1x3 microns
(&mu.m) with its divergence angles (Theta-prp/Theta-prl) &theta.-
/&theta.|| on the order of 30 degrees/10 degrees.  As the diode
illuminates on the media, the elliptical spot sizes (in &mu.m) along
each of the semiaxis are:
               A = h + d x tan(&theta.-/2)
               B...