Method and power-assisted optic-fiber measuring device and gyro

1. Optical-fibre measuring device in which the variation of a measured parameter generates a phase difference between two waves, including:

a wide-spectrum light source with a light power P,

a Sagnac ring interferometer, preferably single-mode, in which propagate two counter-propagating waves, the wave propagation time between the separation and recombination thereof being τ,

a detector receiving a light flux from the interferometer and converting it into an electrical signal representing the total phase difference δφ t between the counter-propagating waves,

an optical phase modulator generating a phase difference δφ m =δφ b +δφ cr , including a biasing component δφ b and a feedback component δφ cr ,

electronic means receiving the electrical signal from the detector and providing a first signal S 1 function of the measured parameter,

said first signal function of the measured parameter producing an optical phase modulator first control signal V cr , determined so that the phase difference δφ cr produced thereby between the counter-propagating waves offsets the phase difference δφ p introduced by the measured parameter,

said electronic means including a demodulator contributing to provide the first signal function of the measured parameter,

said electronic means providing a second signal S 2 function of the light power P of the light source,

characterized in that the optical phase modulator generates a disturbance component δφ cp adding to the phase difference δφ m =δφ b +δφ cr .

2. The optical-fibre measuring device according to claim 1 , characterized in that the biasing component δφ b is generated by an optical phase modulator second control signal V b , determined so that the phase difference δφ b produced thereby between the counter-propagating waves takes at least six states (δφ 1 , δφ 2 , . . . ) defined by α 0 and ε 0 , with 0≦ε 0 <α 0 ≦π and such that:

δφ 1 =α 0 −ε 0 δφ 4 =−(α 0 −ε 0 )

δφ 2 =α 0 δφ 5 =−α 0

δφ 3 =2π−α 0 δφ 6 =−(2π−α 0 )

and in that the electronic means produce a second signal S 2 function of the power P of the light flux measured by the detector using the six values x 1 , x 2 , x 3 , x 4 , x 5 et x 6 provided in response to a period of the control signal according to the formula (x 1 +x 4 )−(x 2 +x 5 ).

3. Gyrometer characterized in that it complies with the measuring device according to claim 1 , the measured parameter being the rotation speed of the interferometer.

4. The optical-fibre measuring device according to claim 1 , characterized in that the electronic means include a closed-loop feedback circuit comprising electronic means for servo-controlling the light power P of the light source.

5. The optical-fibre measuring device according to claim 4 , characterized in that it comprises an amplifier to amplify the electrical signal produced by the detector and an analog-digital converter digitizing the amplified electrical signal, said amplifier and converter being placed between said detector and said electronic means.

6. The optical-fibre measuring device according to claim 4 , characterized in that the electronic means comprise a biasing modulator producing an optical phase modulator second control signal V b to generate said biasing component δφ b .

7. The optical-fibre measuring device according to claim 4 , characterized in that the electronic means comprise:

a regulator placed after said demodulator, the regulator being a first integrator,

a second integrator placed after said first integrator,

a disturbance source introducing a frequency disturbance f cp generating an optical phase modulator third control signal V cp , said third control signal V cp producing a phase difference δφ cp between the counter-propagating waves and adding to the first control signal V cr ,

said disturbance being injected through a disturbance injection circuit immediately before or after the regulator.

8. The optical-fibre measuring device according to claim 1 , characterized in that it comprises an amplifier to amplify the electrical signal produced by the detector and an analog-digital converter digitizing the amplified electrical signal, said amplifier and converter being placed between said detector and said electronic means.

9. The optical-fibre measuring device according to claim 8 , characterized in that the electronic means comprise a biasing modulator producing an optical phase modulator second control signal V b to generate said biasing component δφ b .

10. The optical-fibre measuring device according to claim 8 , characterized in that the electronic means comprise:

a regulator placed after said demodulator, the regulator being a first integrator,

a second integrator placed after said first integrator,

a disturbance source introducing a frequency disturbance f cp generating an optical phase modulator third control signal V cp , said third control signal V cp producing a phase difference δφ cp between the counter-propagating waves and adding to the first control signal V cr ,

said disturbance being injected through a disturbance injection circuit immediately before or after the regulator.

11. The optical-fibre measuring device according to claim 1 , characterized in that the electronic means comprise a biasing modulator producing an optical phase modulator second control signal V b to generate said biasing component δφ b .

12. The optical-fibre measuring device according to claim 11 , characterized in that:

the electronic means comprise an adder comprising two inputs and one output,

the first input of the adder receiving said optical phase modulator first control signal V cr and the other input thereof receiving said optical phase modulator second control signal V b ,

and said device comprising a digital-analog converter receiving the output signal of the adder and controlling the optical phase modulator.

13. The optical-fibre measuring device according to claim 11 , characterized in that the electronic means comprise:

a regulator placed after said demodulator, the regulator being a first integrator,

a second integrator placed after said first integrator,

a disturbance source introducing a frequency disturbance f cp generating an optical phase modulator third control signal V cp , said third control signal V cp producing a phase difference δφ cp between the counter-propagating waves and adding to the first control signal V cr ,

said disturbance being injected through a disturbance injection circuit immediately before or after the regulator.

14. The optical-fibre measuring device according to claim 12 , characterized in that the electronic means comprise:

a regulator placed after said demodulator, the regulator being a first integrator,

a second integrator placed after said first integrator,

a disturbance source introducing a frequency disturbance f cp generating an optical phase modulator third control signal V cp , said third control signal V cp producing a phase difference δφ cp between the counter-propagating waves and adding to the first control signal V cr ,

said disturbance being injected through a disturbance injection circuit immediately before or after the regulator.

15. The optical-fibre measuring device according to claim 1 , characterized in that the electronic means comprise:

a regulator placed after said demodulator, the regulator being a first integrator,

a second integrator placed after said first integrator,

a disturbance source introducing a frequency disturbance f cp generating an optical phase modulator third control signal V cp , said third control signal V cp producing a phase difference δφ cp between the counter-propagating waves and adding to the first control signal V cr ,

said disturbance being injected through a disturbance injection circuit immediately before or after the regulator.

16. The optical-fibre measuring device according to claim 15 , characterized in that the disturbance has a zero-mean value.

17. The optical-fibre measuring device according to claim 15 , characterized in that the disturbance is aperiodic.

18. The optical-fibre measuring device according to claim 15 , characterized in that the frequency f cp of the disturbance is greater than the frequency of the measured parameter signal.

19. The optical-fibre measuring device according to claim 15 , characterized in that the disturbance signal includes pseudo-random ramps.

20. Method for measuring a parameter whose variation generates a phase difference between two waves, in which:

two counter-propagating waves emitted by a wide-spectrum light source with a light power P are propagated in a preferably single-mode Sagnac ring interferometer, the wave propagation time between the separation and recombination thereof being τ,

the light flux outputted from the interferometer is detected and converted into an electrical signal representing the total phase difference δφ t between the counter-propagating waves,

a phase difference δφ m =δφ b +δφ cr between the counter-propagating waves is generated, said phase difference δφ m including a biasing component δφ b and a feedback component δφ cr ,

an electrical signal outputted from the detector is sent to electronic means and said electronic means determine a first signal S 1 function of the measured parameter,

said first signal function of the measured parameter producing an optical phase modulator first control signal V cr , determined so that the phase difference δφ cr produced thereby between the counter-propagating waves offsets the phase difference δφ p introduced by the measured parameter,

said electronic means determine a second signal S 2 function of the light power P of the light source from the electrical signal outputted from the detector,

characterized in that the optical phase modulator generates a disturbance component δφ cp adding to the phase difference δφ m =δφ b +δφ cr .