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Calibration of Laser Differential Efficiency Shift for WORM Media

IP.com Disclosure Number: IPCOM000114279D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Jaquette, GA: AUTHOR [+4]

Abstract

A method of calibrating and storing the shift in differential efficiency of a laser is disclosed. The optics of a multi-purpose optical drive allows for light to be reflected back into the laser cavity creating an external cavity. Because of this, the differential efficiency of the laser shifts as the spot created by the optical beam is brought into focus. This shift can vary over a population of lasers and is dependent on the efficiency of the optical feedback path and the character of the light reflected from the optical media. Thus, if the differential efficiency of the laser is characterized out of focus, it is necessary to apply a correction factor to determine the proper current for writing when in focus to correct for the shift in differential efficiency.

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Calibration of Laser Differential Efficiency Shift for WORM Media

      A method of calibrating and storing the shift in differential
efficiency of a laser is disclosed.  The optics of a multi-purpose
optical drive allows for light to be reflected back into the laser
cavity creating an external cavity.  Because of this, the
differential efficiency of the laser shifts as the spot created by
the optical beam is brought into focus.  This shift can vary over a
population of lasers and is dependent on the efficiency of the
optical feedback path and the character of the light reflected from
the optical media.  Thus, if the differential efficiency of the laser
is characterized out of focus, it is necessary to apply a correction
factor to determine the proper current for writing when in focus to
correct for the shift in differential efficiency.  Because the ideal
correction factor may vary from drive to drive, it may be necessary
to calibrate this at manufacture and store this correction factor in
involatile memory so that it can be applied anytime during the
products life.  The Figure illustrates one possible set of laser
differential efficiencies.  In this case the solid line is the out of
focus power-current (P-I) curve and the dashed line represents the in
focus P-I curve.  It can be seen that whereas the proper current to
pulse the laser to some write power Pw when starting from some base
power P1 is I1 in the out-of-focus case, the proper current is
different, I2, for the in-focus case.  The required currents differ
by a scaling factor which is the differential efficiency shift of the
laser.

      A calibration of the differential efficiency of a laser...