Interferometric measurement device comprising a filtering interferometer

1. An interferometric measurement device including:

a broad-spectrum spontaneous emission light source,

a measurement interferometer comprising a modulator, and receiving, as an input, a light signal of input light power P in and delivering, as an output, a modulated light signal of output light power P out , said modulated light signal being modulated by said modulator at a modulation frequency f m , said modulated light signal depending on a physical parameter to be measured and being proportional to said input light power P in , and

an optical radiation detector, receiving the modulated light signal exiting from said measurement interferometer and delivering a modulated electrical signal ( 3 A) proportional to said output light power P out ,

said interferometric measurement device including a filtering interferometer insensitive to said physical parameter to be measured placed between said light source and said measurement interferometer or between said measurement interferometer and said optical radiation detector,

said filtering interferometer having a filtering interferometer input and a filtering interferometer output,

said filtering interferometer being:

i) a two-wave interferometer configured so that exactly two split light signals, propagated over two respective arms of the filtering interferometer, are being superimposed and interfering with each other to form a filtered light signal transmitted on the output of the filtering interferometer, the filtering interferometer having a free spectral range ISL, expressed in frequency, equal to an inverse of a difference between two respective propagation times of said interfering light signals over said two arms, or

ii) a multiple-wave resonant interferometer comprising a resonator, wherein more than two light signals propagated through said resonator are being superimposed and interfering with each other to form a filtered light signal transmitted on the output of the filtering interferometer, the filtering interferometer having a free spectral range ISL, expressed in frequency, equal to an inverse of a propagation time of said interfering light signals over a resonator passage,

said filtering interferometer having a finesse F, and a filtering interferometer response equal to a ratio between a light power outputted by the filtering interferometer and a source light power at the filtering interferometer input, said response presenting, as a function of an optical frequency of a transmitted light, peaks and troughs, said peaks being periodically separated in frequency by the filtering interferometer free spectral range ISL, each of said troughs being located, in frequency, between two said successive peaks, said peaks presenting a full width at half maximum equal to the filtering interferometer free spectral range ISL divided by its finesse F,

wherein said filtering interferometer has:

i) in a case the filtering interferometer is a two-wave interferometer, a length-difference between said arms, or

ii) in a case the filtering interferometer is a multiple-wave resonant interferometer, a resonator one-passage length,

such that the free spectral range ISL of the filtering interferometer defines a frequency interval centred about an optimum frequency f optim equal to (2k+1) ISL/2, k being a natural number, and of width Δf equal to [0.9−(3/2F)] ISL, that comprises the modulation frequency f m of the modulated light signal at the output of the measurement interferometer.

2. The interferometric measurement device according to claim 1 , wherein said filtering interferometer is configured in dual-passage mode.

3. The interferometric measurement device according to claim 2 , wherein said filtering interferometer comprises a fiber-optic interferometer.

4. The interferometric measurement device according to claim 2 , wherein said measurement interferometer comprises a fiber-optic SAGNAC ring interferometer.

5. The interferometric measurement device according to claim 1 , wherein said filtering interferometer comprises a fiber-optic interferometer.

6. The interferometric measurement device according to claim 5 , wherein said fiber-optic filtering interferometer comprises a polarization-maintaining optical fiber.

7. The interferometric measurement device according to claim 5 , wherein said measurement interferometer comprises a fiber-optic SAGNAC ring interferometer, and a length of the optical fiber of the filtering interferometer is slightly higher than a length of the optical fiber of the S AGNAC ring interferometer.

8. The interferometric measurement device according to claim 1 , said filtering interferometer being said multiple-wave resonant interferometer, wherein the resonator of the filtering interferometer comprises a ring resonator and two optical couplers whose ratios T/C of transmission coefficient T to coupling coefficient C are comprised between 70/30 and 95/5.

9. The interferometric measurement device according to claim 8 , wherein the ring resonator has a null surface.

10. The interferometric measurement device according to claim 1 , wherein, when said filtering interferometer is placed between said light source and said measurement interferometer, said interferometric measurement device includes a doped-fiber optical amplifier placed between said filtering interferometer and said measurement interferometer.

11. The interferometric measurement device according to claim 1 , wherein said measurement interferometer comprises a fiber-optic SAGNAC ring interferometer.

12. A fiber optic gyrometer including the interferometric measurement device according to claim 11 .

13. A fiber optic gyrometer including the interferometric measurement device according to claim 1 .

14. The interferometric measurement device according to claim 1 , wherein,

said filtering interferometer is said two-wave interferometer configured so that the exactly two split light signals, propagated over the two respective arms of the filtering interferometer, are being superimposed and interfering with each other to form the filtered light signal transmitted on the output of the filtering interferometer, the filtering interferometer having the free spectral range ISL, expressed in frequency, equal to the inverse of the difference between two respective propagation times of said interfering light signals over said two arms, and

the length-difference between said arms such that the free spectral range ISL of the filtering interferometer defines the frequency interval centred about the optimum frequency f optim equal to (2k+1) ISL/2, and of the width Δf equal to [0.9−(3/2F)] ISL, that comprises the modulation frequency f m of the modulated light signal at the output of the measurement interferometer.

15. The interferometric measurement device according to claim 1 , wherein,

said filtering interferometer is said multiple-wave resonant interferometer comprising a resonator, wherein the more than two light signals propagated through said resonator are being superimposed and interfering with each other to form the filtered light signal transmitted on the output of the filtering interferometer, the filtering interferometer having the free spectral range ISL, expressed in frequency, equal to the inverse of the propagation time of said interfering light signals over the resonator passage, and

the resonator one-passage length such that the free spectral range ISL of the filtering interferometer defines the frequency interval centred about the optimum frequency f optim equal to (2k+1) ISL/2, and of the width Δf equal to [0.9−(3/2F)] ISL, that comprises the modulation frequency f m of the modulated light signal at the output of the measurement interferometer.

16. The interferometric measurement device according to claim 1 , wherein,

said filtering interferometer comprises a fiber-optic interferometer,

said measurement interferometer comprises a fiber-optic SAGNAC ring interferometer, and

a length of the optical fiber of the filtering interferometer is between 2% and 5% longer than a length of the optical fiber of the SAGNAC ring interferometer.