In electronics, an optical isolator is a device that uses a short optical transmission path to transfer a signal between elements of a circuit while keeping them electrically isolated -- since the signal goes from an electrical signal to an optical signal back to an electrical signal, electrical contact along the path is broken. In one simple design, an electrical signal at one end triggers an LED, which in turn triggers a photosensor that produces an electrical signal at the other end.

The optical path may be air or a dielectric waveguide. The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, e.g., on a circuit board; in this case, the module is often called an optoisolator or opto-isolator.

In optics, the term optical isolator is also used for a purely optical device also known as a Faraday isolator.

Parts of this article adapted from Federal Standard 1037C