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Browse Prior Art Database

Single Power Monitor for Dual-Beam Laser Array

IP.com Disclosure Number: IPCOM000106567D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Dewey, AG: AUTHOR [+2]

Abstract

Disclosed is a system for independent control of the power level of both elements of a two-laser array, such as is used in a DRAW (Direct Read After Write) optical head, using a single monitor photodiode.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Single Power Monitor for Dual-Beam Laser Array

      Disclosed is a system for independent control of the power
level of both elements of a two-laser array, such as is used in a
DRAW (Direct Read After Write) optical head, using a single monitor
photodiode.

      In the case of a single laser, the power is monitored by a
large-area photo-diode which is only coarsely aligned, but monitoring
the power of a two-laser array would require the beams to be focused
(and hence separated) onto a two-element detector with accurate
alignment.  The system shown in the Figure accomplishes power control
of both elements of the laser array with the same simple optics, and
single photodetector, as used in a single-laser head, by employing a
sampled-servo control loop.

      In a DRAW head, the verify (V) laser is normally only on during
writing.  The read-write (R/W) laser is controlled during reading (of
data or of the sector headers), at which time switch 10 is closed and
the output form the photodetector is PR.  To control the V laser, it
is turned on periodically when the drive is reading (either data or
sector headers) and the output of the photodetector is PR + PV.
Switch 10 is opened, switch 20 is closed and the output of
differential amplifier 30 is PR + PV minus the previously-held value
of PR from sample/hold circuit 40.