Fiber Optic Gyro Please click the link below for even more information on this animation. This gyro uses the Sagnac effect to detect inertial rotations. Inertial rotations can be defined as rotations with respect to the relatively fixed stars of the universe. The Sagnac effect is the behavior during rotation of two oppositely traveling light beams that are confined to a closed path. In this case the enclosure is a coil of optical fiber. When the enclosure rotates the apparent speed of the beam propagating in the direction of rotation is reduced and that of the beam propagating in the opposite direction is increased. This results in the light anti-nodes (energy density maxima) shifting with respect to the fiber enclosure. The shift of the anti-nodes can be detected by a detector array that is placed parallel to the fiber. If we have a broad band source, at most locations, the intensity difference (contrast) between nodes and anti-nodes will be very small and it will be hard to detect their movement. However, even with a broadband source, there well be two locations, one at the input/output of the coil and the other just opposite this location (at the midpoint of the coil) where the node/anti-nodes will have high contrast. I show these as black anti-nodes. When the device rotates at a constant rotation rate, these anti-nodes move a bit to a new location along the fiber enclosure and we can detect this motion with a detector array a shown. I show the detector array at the input/output position of the FOG but it could just as well be located opposite this position at the midpoint of the coil. I show only a single loop of fiber but a practical FOG will have very many fiber coil turns in order to increase the anti-node motion. Also I have chosen to have the rotation platform rotate in a sinsusoidal time dependence so that it is easy to see the movement of the black anti-nodes which provide the signal for the detector and therefore define the rotation rate. Click for Info Rotation Speed