(FOG) senses changes in orientation using the Sagnac effect, thus performing the function of a mechanical gyroscope. However its principle of operation is instead based on the interference of light which has passed through a coil of optical fibre which can be as long as 5 km.Two beams from a laser are injected into the same fibre but in opposite directions. Due to the Sagnac effect, the beam travelling against the rotation experiences a slightly shorter path delay than the other beam. The resulting differential phase shift is measured through interferometry, thus translating one component of the angular velocity into a shift of the interference pattern which is measured photometrically.
Applications:
FOGs are used in Fibre optic gyrocompasses.
FOGs are used in the inertial navigation systems of some guided missiles.
FOGs can be a navigation aid in remotely operated vehiclesFibre Optic Gyroscope and autonomous underwater vehicles.
FOGs are used in surveying.
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