A method is provided for determining a laser threshold of a laser diode,
which is operated by a drive circuit as a function of a first signal in a
first feedback and a second signal in a second feedback, the first
feedback being supplied via an optical coupling of an optical output
signal of the laser diode. The method is characterized in that the second
feedback is supplied by an electrical signal picked up between the drive
circuit and the laser diode, the electrical signal is compared with an
adjustable activation threshold, only a portion of the electrical signal
that exceeds the adjustable activation threshold is transmitted to the
drive circuit in such a way that the second feedback is active only when
such a portion occurs, the adjustable activation threshold is changed in
such a way that the activity state of the second feedback changes, and
the laser threshold of the laser diode is determined as a function of the
value of the adjustable activation threshold during a change in the
activity state of the second feedback. Furthermore, a drive circuit is
presented which carries out the method.