measuring device has optical fiber gyrometer, central navigation and inertial stabilization

The invention relates to a fiber optic measuring device of the type in which the variation in a measured parameter generates a phase difference between two waves in a Sagnac ring interferometer (2). Electronic means (7) comprise a processing system (9) delivering a signal depending on the measured parameter and electronic means (12) controlling the phase modulator (4). Electronic means (12) produces a control signal for the modulator determined in such a way that the difference in deltaPHIm stage it produces between the counter-propagative waves periodically takes the following four values: (CF DRAWING iN BOPI) where phi0 is a constant phase difference and dependent on a, a positive contante satisfying the condition: (CF DRAWING iN BOPI) is maintaining constant the gain of the modulation command chain by producing a signal depending on the said gain by exploiting the four values ​​x1, x2, x3, x4 delivered in response to a period of the modulation signal according to formula (x1 + x2) - (x3 + x4), said signal acting on the modulator so as to maintain the gain constant.