An optical isolator is a passive magneto-optic device that only allows light to travel in one direction. Isolators are

used to protect a source from back reflections or signals that may occur after the isolator. Back reflections can

damage a laser source or cause it to mode hop,amplitude modulate, or frequency shift.

In high-power applications, back reflections can cause instabilities and power spikes.Optical isolators are also

known as optoisolators, optocouplers and photocouplers.