Operation of fibre optic gyroscope

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.

Beam splitting optics launches light from a laser diode into two waves propagating in the clockwise and anticlockwise directions through a coil consisting of many turns of optical fibre. The strength of the Sagnac effect is dependent on the effective area of the closed optical path: this is not simply the geometric area of the loop but is enhanced by the number of turns in the coil. The FOG was first proposed by Vali and Shorthill in 1976. Development of both the passive interferometer type of FOG, or IFOG, and a newer concept, the passive ring resonator FOG, or RFOG, is proceeding in many companies and establishments worldwide.

June 14, 2012

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