Noun
Sagnac effect (plural Sagnac effects)
A phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferometer. A beam of light is split and the two beams are made to follow the same path but in opposite directions. To act as a ring the trajectory must enclose an area. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference. The relative phases of the two exiting beams, and thus the position of the interference fringes, are shifted according to the angular velocity of the apparatus.
RLG A ring laser gyroscope relies on the Sagnac effect to measure rotation by measuring the shifting interference pattern of a split beam of light as it moves around the ring in opposite directions. Source: Internet
The Sagnac effect is the same principle used in FOG's as in RLG's HRG The hemispherical resonator gyroscope (HRG), also called wine-glass gyroscope or mushroom gyro, makes using a thin solid-state hemispherical shell, anchored by a thick stem. Source: Internet