US 11,885,622 B2
Interferometer with a looped or straight optical fiber
Eric Ducloux, Saint-Germain-en-Laye (FR); Cédric Molucon, Saint-Germain-en-Laye (FR); and Hervè Lefevre, Saint-Germain-en-Laye (FR)
Assigned to EXAIL, Saint-Germain-en-Laye (FR)
Appl. No. 17/603,797
Filed by EXAIL, Saint-Germain-en-Laye (FR)
PCT Filed Apr. 14, 2020, PCT No. PCT/EP2020/060408
§ 371(c)(1), (2) Date Mar. 16, 2022,
PCT Pub. No. WO2020/212314, PCT Pub. Date Oct. 22, 2020.
Claims priority of application No. 1904009 (FR), filed on Apr. 15, 2019.
Prior Publication US 2023/0160697 A1, May 25, 2023
Int. Cl. G01C 19/72 (2006.01); G01R 15/24 (2006.01)
CPC G01C 19/727 (2013.01) [G01R 15/246 (2013.01)] 19 Claims
OG exemplary drawing
 
1. A fiber-optic loop, or respectively in-line, interferometer comprising:
a light source adapted to generate a source beam,
a polarizer and a coil splitter arranged to split the source beam into a first single-mode wave and a second single-mode wave, the first single-mode wave and the second single-mode wave having a same polarization state, or respectively orthogonal polarization states,
a digital processor and a digital-analog converter adapted to apply a modulation electric voltage Vm(t) to a phase modulator adapted to induce a same phase shift Φm(t) on the first single-mode wave and the second single-mode wave,
an optical fiber coil adapted to receive and propagate the first single-mode wave along a first optical path and the second single-mode wave along a second optical path, the first optical path and the second optical path being in reverse direction in the optical fiber coil, or respectively the first optical path and the second optical path comprising a first passage in the optical fiber coil, a reflection on a mirror and a second passage in the reverse direction in the optical fiber coil, the orthogonal polarization states being inverted upon reflection on the mirror, and to form after a propagation time difference Δτ a first output wave and a second output wave, respectively, having a modulated phase difference ΔΦm(t)=Φm(t)−Φm (t−Δτ), the optical fiber coil having an eigen frequency fp equal to the inverse of the double of the propagation time difference Δτ,
the coil splitter being adapted to recombine the first output wave and the second output wave and to form a temporally modulated interferometric beam,
a photosensor and an analog-digital converter adapted to detect a power P(t) of the interferometric beam as a function of time,
wherein the modulated phase difference ΔΦm(t) is equal to the sum of a first periodic phase difference ΔΦΠ (t) of level equal to ±Π, a second periodic phase difference ΔΦalpha (t) of level equal to ±alpha and a third periodic phase difference ΔΦbeta(t) of variable level between −beta and +beta, alpha and beta having predetermined different values, in such a way that the modulated phase difference ΔΦm(t) has a period of modulation T equal to an odd multiple (2M+1) of the double of the propagation time difference Δτ, where M is a natural integer, the modulated phase difference ΔΦm(t) having, per period of modulation T, at least eight modulation levels among the twelve following modulation levels: ΔΦa+=Π+alpha+beta; ΔΦa−=Π+alpha−beta; ΔΦa=Π+alpha; ΔΦb+=Π−alpha+beta; ΔΦb−=Π−alpha−beta; ΔΦb=Π−alpha; ΔΦc+=−Π+alpha+beta; ΔΦc−=−Π+alpha−beta; ΔΦc=−Π+alpha; ΔΦd+=−Π−alpha+beta; ΔΦd−=−Π−alpha−beta; ΔΦd=−Π−alpha; and this modulated phase difference being such that:
a. ΔΦm(t+T/2)=−ΔΦm(t)
b. at each time t comprised between 0 and T.