Browse Prior Art Database

Laser Power Correction Algorithm

IP.com Disclosure Number: IPCOM000112024D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Demura, M: AUTHOR [+3]

Abstract

In an optical storage drive means for maintaining a known laser power level at the optical media is required. Uncertainly in knowledge of the power levels at the optical media can result in degradation of customer data, suboptimal writing of customer data and a shorter laser life. Fig. 1 shows the typical method employed in current art to control the laser power. Light from a laser diode is first collimated and then diverted into a beamsplitter which transmits most of the light out toward the media. Light not transmitted at the beamsplitter is reflected toward a power servo photodetector. Current from this photodetector is fed into a power servo circuit which supplies the necessary laser driver current to maintain a constant photodetector current.

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Laser Power Correction Algorithm

      In an optical storage drive means for maintaining a known laser
power level at the optical media is required.  Uncertainly in
knowledge of the power levels at the optical media can result in
degradation of customer data, suboptimal writing of customer data and
a shorter laser life.  Fig. 1 shows the typical method employed in
current art to control the laser power.  Light from a laser diode is
first collimated and then diverted into a beamsplitter which
transmits most of the light out toward the media.  Light not
transmitted at the beamsplitter is reflected toward a power servo
photodetector.  Current from this photodetector is fed into a power
servo circuit which supplies the necessary laser driver current to
maintain a constant photodetector current.  By maintaining a constant
photocurrent, the power at the detector is held constant, implying
the power at the media is held constant as well.  At time of
manufacture, a power meter is placed in lieu of the optical media.
The gain of the power servo loop is adjusted until the desired power
is achieved.

      This method works well as long as the ratio of beamsplitter
reflection to transmission remains unchanged.  However, it is well
known that under changes in humidity and temperature, this
beamsplitter ratio will change.  Using the current art described
above results in an unknown and undesirable change in power at the
optical media.

      Disclosed is a method for maintaining a known power level at
the optical media even under conditions where the characteristics of
the beamsplitter change.  Fig. 2 displays the typical inner workings
of laser diodes used...