Browse Prior Art Database

Solid-State Laser Output Waveshape Correction

IP.com Disclosure Number: IPCOM000099645D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 87K

Publishing Venue

IBM

Related People

Gibson, BD: AUTHOR

Abstract

Many laser printhead designs use solid-state lasers as their light sources and require high frequency current modulation to produce the desired pel information. Because of the very high frequency response of the solid-state laser diodes, the current waveforms driving them should be absent of noise and glitches. The lasers can be damaged if they are subjected to a current noise spike of significant amplitude. Gray level printing also requires accurate pulse amplitude. Electrically, the laser diode, once biased to its threshold, appears as a very low impedance device. This is a problem because the characteristic impedance of the cable connecting the driver to the laser is generally about an order of magnitude higher than the laser diode.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Solid-State Laser Output Waveshape Correction

       Many laser printhead designs use solid-state lasers as
their light sources and require high frequency current modulation to
produce the desired pel information.  Because of the very high
frequency response of the solid-state laser diodes, the current
waveforms driving them should be absent of noise and glitches.  The
lasers can be damaged if they are subjected to a current noise spike
of significant amplitude.  Gray level printing also requires accurate
pulse amplitude. Electrically, the laser diode, once biased to its
threshold, appears as a very low impedance device.  This is a problem
because the characteristic impedance of the cable connecting the
driver to the laser is generally about an order of magnitude higher
than the laser diode.  If the cable is not sufficiently short in
length, the initial current reaching the laser can be nearly twice
the intended value as shown by the equation:

      Current at the laser = 1 + (Zo - R) / (Zo + R)
or about 2 where R is the resistance of the laser and Zo is the
characteristic impedance of the cable.

      The current is reflected back and forth in the cable creating
noise at the laser output.

      As the current signals driving the laser are required to toggle
at higher frequencies, this problem becomes increasingly pronounced.

      The way this problem has been approached in the past is to make
the laser driver cable as short as possible.  This means getting the
driving electronics up very close to the laser itself.

      Terminating ...