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A protection circuit for laser diodes that operate below 2.1VDC (i.e. typical IR and NIR lasers). Note the polarity and that this will not work for 405nm laser diodes.
A standard protection circuit consists of three fast signal diodes in series to short any voltage above 2.1VDC (three 0.7V diode drops). The reversed diode protects against reverse voltages and the RC filter network provides noise reduction at the input to the laser diode.