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Browse Prior Art Database

Arbitrary Mark Length Laser Power Modulator for Optical Recording

IP.com Disclosure Number: IPCOM000111922D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Belser, KA: AUTHOR

Abstract

This is a method for controlling the application of laser power to a magneto optical disk to make Pulse Width Modulation (PWM) marks wherein the number of bits per revolution is the same at every radius when the disk spins at a constant angular velocity.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 60% of the total text.

Arbitrary Mark Length Laser Power Modulator for Optical Recording

      This is a method for controlling the application of laser power
to a magneto optical disk to make Pulse Width Modulation (PWM) marks
wherein the number of bits per revolution is the same at every radius
when the disk spins at a constant angular velocity.

      PWM marks on the media will be defined by a beginning and an
ending circular mark, each made by a short laser power pulse.  The
mark length is L = V*T + W, where V is the media velocity, T is the
time between the first and last mark exposure, and W is the width of
the circular mark when pulses with a short laser power pulse.  When
the mark length L is read back by the same Gaussian spot, the time
separation of the PWM mark edges is D = L/V = T + W/V.  This means
that T, which is the write process parameter, must be derived from D
by subtracting W/V.  The length D represents encoded run length
information.

      The region between the beginning and end of the mark are filled
in with a series of circular marks that are just tangent except for
the last mark which is overlapped.  These interior marks are
separated by an exposure time of W/V.  The key to this writing method
is the formation of an asynchronous "spot width" clock with period
W/V and whose phase is adjusted by asynchronous starting to
correspond to the leading edge of the data.  A long mark is made by
short pulses of laser power every clock period starting at the
desi...