Abstract: A system for testing a wave guide arc detecting circuit for a microwave system is disclosed. Testing is accomplished by utilizing a pulsed laser source to generate pulses of optical energy which are used to simulate an electrical arc across the wave guide. The laser source is then positioned such that the pulsed output signal impinges upon the wave guide arc detector circuit to be tested. This is most advantageously accomplished by affixing the wave guide arc detector circuit to the wave guide in a fashion similar to normal operation. This enables the arc detecting circuit to view the end of the wave guide through the interior of the wave guide. The laser source is positioned such that the output pulse of the laser source impinges on the open end of the wave guide. The operational status of the wave guide arc detecting circuit is determined by measuring the elapsed time between the generation of the output pulse of the laser and the detection of the pulse by the arc detecting circuit being tested.