Browse Prior Art Database

Calibration of Optimal Focus for Read/Write of Optical Media

IP.com Disclosure Number: IPCOM000114354D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Jaquette, GA: AUTHOR [+2]

Abstract

A method for calibrating the optimal focus offset for Read/Write operations on optical media is disclosed. The optimal focus offset value is calculated from the uncorrected byte (or bit) error rate measured at a number of focus offsets. The inability to servo may also constrain the operational range. This detailed calibration can be performed at manufacture and stored to some involatile memory in the drive for use as the focus offset value or as an input to a calculation which determines the focus offset to be used.

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Calibration of Optimal Focus for Read/Write of Optical Media

      A method for calibrating the optimal focus offset for
Read/Write operations on optical media is disclosed.  The optimal
focus offset value is calculated from the uncorrected byte (or bit)
error rate measured at a number of focus offsets.  The inability to
servo may also constrain the operational range.  This detailed
calibration can be performed at manufacture and stored to some
involatile memory in the drive for use as the focus offset value or
as an input to a calculation which determines the focus offset to be
used.

      Optimization is performed relative to the uncorrected byte (or
bit) error rate.  The focus offset is optimized by measuring the soft
(uncorrected) Byte Error Rate (BER).  During the BER measurement,
servo errors are monitored.  The index of quality used is BER unless
an unacceptable rate of servo errors is experienced, in which case
this will limit the operational range of the focus offset.  BER
measurements are made at a number of focus offsets.  Data analysis is
performed to calculate two focus offsets, above and below optimal, at
which the BER has degraded to a given rate less than the nominal
rate.  The approximate midpoint between these two focus offset values
is then used as the best focus offset value.

      As can be seen in the Figure, the BER will begin to degrade the
farther the drive is from optimum focus.  The dashed line shows the
servo error rate. ...