Importance

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Abstract

The invention relates to a fibre optic measuring device of the type in which the change 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). The electronic means (12) produce a control signal for the modulator determined in such a way that the phase difference .delta..PHI..sub.m which it produces between the counter-propagating waves periodically takes the following four successive values: ##EQU1## where .PHI..sub.o is a constant phase shift and it depends on a, and a is a positive constant satisfying the condition: cos .PHI..sub.o =cos a.PHI..sub.o. The gain of the channel for controlling the modulation is kept constant 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 the expression (x1+x3)-(x2+x4), the said signal acting on the modulator in such a way as to keep the gain constant.

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First Claim