Browse Prior Art Database

Read Laser Overpower Protection in the Optical Drives

IP.com Disclosure Number: IPCOM000119944D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Finkelstein, BI: AUTHOR [+3]

Abstract

This article describes a technique that will detect a high laser read power in the magneto-optical (MO) drives. A high laser read power could partially or completely inadvertently erase recorded data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 71% of the total text.

Read Laser Overpower Protection in the Optical Drives

      This article describes a technique that will detect a
high laser read power in the magneto-optical (MO) drives.  A high
laser read power could partially or completely inadvertently erase
recorded data.

      The optical read power is monitored by an auxiliary photodiode
and maintained at the desired value by the laser read power servo
loop (PSL).  A degradation in the PSL circuit or the auxiliary
photodiode, due to dust, alignment, etc., may raise the read power to
an unsafe level that could damage or inadvertently erase recorded
data.  The hardware read overpower protection circuit that uses the
same photodiode can not detect this type of overpower failure.
However, the proposed technique uses the read-back signal amplitude
from the calibration track to detect the overpower failure.

      The figure shows a simple flowchart for the write and the read
overpower check algorithm.  Known write calibration routine is
executed whenever a new MO media is inserted into the drive, before
seeking into the customer or user recording zone.  The write bias
field is left "ON" during the read cycle of the write calibration
algorithm.  A higher read laser power, in the presence of the bias
field, will more likely erase or partially erase the calibration
data. After the completion of the write calibration, the read-back
signal amplitude from the best written sector is measured once more,
and it is compared with...