figure to the right shows another approach commonly employed to protect a laser diode from
ESD. In this approach a multi-layer varistor is placed in parallel with
the laser diode. A multi-layer varistor is a device whose resistance
changes, decreasing nonlinearly, with increases in voltage that appear
across the terminals.
Although some multi-layer varistors claim to have response times in the
range, their breakdown voltage (the voltage at which the varistor
transitions from high resistance to low resistance) is typically well in
excess of the 2.2-volt lasing threshold, or 2.0-volt maximum reverse-bias
voltage of a typical low-power laser diode. A multi-layer varistor whose
breakdown voltage is below 3.6 volts is not known to us at Lasorb.
Therefore, this approach is not believed to be completely effective in
preventing a low-power, fast-response laser diode from being damaged by
ESD polarity terminology used on this
The term “positive-ESD” is used to
mean electrostatic discharge (ESD) whose voltage polarity would tend
to forward-bias a laser diode. “Negative-ESD,” means ESD whose
voltage polarity would tend to reverse-bias a laser diode.