Editing Ring laser gyroscope (section)

==Fibre optic gyroscope==
A related device is the [[fibre optic gyroscope]] which also operates on the basis of the Sagnac effect, but in which the ring is not a part of the laser. Rather, an external laser injects counter-propagating beams into an [[optical fiber]] ring, where rotation causes a relative phase shift between those beams when interfered after their pass through the fiber ring. The phase shift is proportional to the rate of rotation. This is less sensitive in a single traverse of the ring than the RLG, in which the externally observed phase shift is proportional to the accumulated rotation itself, not its derivative. However, the sensitivity of the fiber optic gyro is enhanced by having a long optical fiber, coiled  for compactness, in which the Sagnac effect is multiplied according to the number of turns.