Browse Prior Art Database

Read Instability for the Magneto-Optical Media

IP.com Disclosure Number: IPCOM000121074D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 110K

Publishing Venue

IBM

Related People

Belleson, JG: AUTHOR [+2]

Abstract

This article discusses the problem and the solutions associated with the multiple erase/write cycles for MO media in the drive. All ANSI and ISO erasable MO media have the sector and track configuration, as shown in Fig. 1. Each track contains many sectors and each sector has header areas called ID. The ID area contains the track and sector number and it is embossed and non-erasable. The ID area is called the ROM portion of the sector. The area following the ID is the erasable zone for that sector and it is used for customer data. This area is called MO or the data portion of the sector. The read laser beam is modulated with a high frequency modulator (HFM) to reduce laser feedback noise. The depth of modulation is set around 200% for the given read power.

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Read Instability for the Magneto-Optical Media

      This article discusses the problem and the solutions
associated with the multiple erase/write cycles for MO media in the
drive.  All ANSI and ISO erasable MO media have the sector and track
configuration, as shown in Fig. 1.  Each track contains many sectors
and each sector has header areas called ID.  The ID area contains the
track and sector number and it is embossed and non-erasable.  The ID
area is called the ROM portion of the sector.  The area following the
ID is the erasable zone for that sector and it is used for customer
data.  This area is called MO or the data portion of the sector.  The
read laser beam is modulated with a high frequency modulator (HFM) to
reduce laser feedback noise. The depth of modulation is set around
200% for the given read power.  Both depth of modulation and read
power are functions of the media velocity, temperature and optical
drive design.  Both the ID and MO data are read at the same read
power in Fig. 1.

      To update sector n in Fig. 1, an optical controller has to
successfully read two sectors ahead, (n-2) and (n-1). This allows the
controller to turn on a Bias magnet so that the Bias field reaches
its maximum strength by the time the head is positioned on the
desired sector, n.  This time delay is associated with the time
constant of the coil and its driver.  Once the ID on sector n is
read, then the HFM is turned OFF and laser power switches to erase
level in GAP 1 between the ID and the data.  In GAP 2, laser power
is switched to read level and HFM is turned ON again.  Also, the Bias
magnet is turned OFF at this time.  But, the Bias field will be
present on sectors n+1 and n+2 due to the time constants of the coil.
On the next revolution, the Bias magnet is turned ON at n-2 sector,
but at the opposite direction for the write operation.  The laser
switches to write power with HFM OFF in GAP 1.  In GAP 2, the laser
switches back to the read mode at 1.5 mW, and HFM turns ON and the
Bias magnet is turned OFF.

      Every time sector n is updated, sectors n-1 and n+1 are also
subject to a high Bias field at 1.5 mW laser power. Experimental data
on several vendor media has shown that the repetitive erase and write
operation on sector n will cause damage and eventually e...