Ring laser gyroscope

A ring laser gyroscope uses interference of laser light within a bulk optic ring to detect changes in orientation and spin. It is an application of a Sagnac interferometer. Unlike a mechanical gyroscope, the device does not resist changes to its orientation (or at least, these effects are extremely tiny because photons are so light). Primary applications include navigation systems on commercial airliners, ships and spacecraft, where Ring Laser gyroscopes are often referred to as Inertial Reference System. In these applications, it has replaced its mechanical counterpart, the Inertial guidance system.