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Browse Prior Art Database

Optical Fiber Head for Sample Servoing on Magnetic Disk

IP.com Disclosure Number: IPCOM000110395D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 3 page(s) / 143K

Publishing Venue

IBM

Related People

Shieh, HPD: AUTHOR [+2]

Abstract

Disclosed is a device using optical fiber to convey optical beams onto magnetic disk to perform fine tracking. With improved active servoing and wider tracking bandwidth, areal density of current magnetic recording can be further increased.

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

Optical Fiber Head for Sample Servoing on Magnetic Disk

       Disclosed is a device using optical fiber to convey
optical beams onto magnetic disk to perform fine tracking.  With
improved active servoing and wider tracking bandwidth, areal density
of current magnetic recording can be further increased.

      Present magnetic recording density is limited mainly by track
density, typically a few KTPI, an order of magnitude less than that
of typical optical recording.  The limitation is mainly due to the
current tracking scheme - an open loop servo and limited bandwidth,
which does not perform adequately with track spacing of less than 10
mm.  To increase  track density further, a more elaborate servo
scheme is desirable.  One feasible technique is to use a closed-loop
servoing where a servo signal is derived from embedded marks on
disks.  As a result, the R/W heads can follow the data on the disks
with minimum off-tracking.  An optical beam on a slider used to
follow pits embedded on magnetic disks and thus position the R/W head
to a position precisely on the data track was proposed (*).  The
optical beam, generated by a diode laser mounted side by side with
the R/W magnetic head on the slider, was demonstrated by Hitachi to
achieve recording density of 2 Gbit/in2.  Mounting a diode laser on a
slider not only changes the flying dynamics of a slider, but also
greatly increases the number of electrical connections to/from the
head.

      In this disclosure, we propose using an optical fiber to convey
an optical beam to and from head/slider for the servo purpose.
Optical fiber is mechanically strong, flexible and light weight.
Therefore, the drawback of using a diode laser can be minimized, but
closed-loop tracking and greatly increased track density can also be
achieved.

      A collimated laser beam (few mW in CW mode) is directed onto a
magnetic disk as a means of servoing.  An optical fiber conveys the
laser beam from a diode laser onto the magnetic disk onto where &mu.m
size pits are embossed, as shown schematically in Fig. 1.  The
reflected beam intensity is modulated by the disk topography - the
presence and absence of pits on the data track.  As the R/W head and
the fiber head may fly as close as 50 to 100 nm to the disk,
near-field image of the reflected beam is fed back into the fiber and
subsequently detected by a photodetector.  The servo signal is
derived from the unbalancing of the photodetector's signal.

      A single mode optical fiber with a core d...