Interferometric system with multiaxial optical fibre and method for processing an interferometric signal in such a system

Patent metadata

Field	Value
Publication number	US-2016231120-A1
Application number	US-201415023747-A
Country	US
Kind code	A1
Filing date	Sep 23, 2014
Priority date	Sep 24, 2013
Publication date	Aug 11, 2016
Grant date	—

Abstract

An interferometric system with multi-axis optical fiber and a method for processing an interferometric signal in such a system, the multi-axis interferometric system includes a light source ( 1 ); a plurality of N optical-fiber coils ( 11, 12 ), a first optical separation element ( 3 ) capable of splitting the source beam ( 100 ) into a first split beam ( 140 ) and a second split beam ( 240 ); shared phase-modulation element ( 4 ); a photodetector ( 2 ) and a signal-processing system ( 800 ). The N optical-fiber coils ( 11, 12 ) are connected in parallel, the coils having respective transit times T 1 , T 2 , . . . TN that all differ from one another, and the signal-processing system ( 800 ) is capable of processing the interferometric signal ( 720 ) detected by the shared photodetector ( 2 ) as a function of the respective transit times in the various coils.

First claim

1 - 15 . (canceled)

16 . A multi-axis fiber optic interferometric system, including:
a shared light source adapted to emit a source beam; a plurality of N optical-fiber coils, each coil forming a ring optical path about an axis; a first optical separation means adapted to spatially separate the source beam into a first split beam and a second split beam; shared phase modulation means adapted to apply a time-modulated phase shift between the first and the second split beams and to form a first modulated beam and a second modulated beam; a shared photodetector and a shared signal-processing system; wherein: the N optical-fiber coils are connected in parallel, so as to inject simultaneously a fraction of the first modulated beam at a first end of each coil and a fraction of the second modulated beam at a second end of each coil, said N optical-fiber coils having respective transit times T 1 , T 2 , . . . TN that are all different from each other; the first optical separation means are adapted to recombine said fractions of the first modulated beam and said fractions of the second modulated beam having travelled counter-propagatively through the N coils to form an interferometric beam; and the signal-processing system are adapted to process the interferometric signal detected by the photodetector as a function of the respective transit times T 1 , T 2 , . . . TN in the different coils.

17 . The multi-axis fiber optic interferometric system according to claim 16 , further comprising:
a second optical separation means arranged between the shared light source and the shared photodetector; third optical separation means arranged on the optical path of the first modulated beam between the phase modulation means and the first ends of each of the N optical-fiber coils; fourth optical separation means arranged on the optical path of the second modulated beam between the phase modulation means and the second ends of each of the N optical-fiber coils; the third optical separation means and the fourth optical separation means each having at least one entry and N exits so as to transmit simultaneously and in parallel a fraction of the first modulated beam at the first end of each of the N optical-fiber coils and a fraction of the second modulated beam at the second end of each of the N optical-fiber coils and so that said fractions of the first modulated beam and said fractions of the second modulated beam propagate in opposite directions in each of said coils.

18 . The multi-axis fiber optic interferometric system according to claim 16 , wherein the signal-processing system is adapted to record a series of 2*N components of the detected signal at instants determined as a function of the respective transit times T 1 , T 2 , . . . TN respectively associated with each of the N optical-fiber coils and to extract therefrom at least N measurements of Sagnac phase shift respectively associated with each of the N optical-fiber coils from said series of components.

19 . The fiber optic interferometric system according to claim 17 , further including a planar integrated optical circuit including:
a. the first optical separation means; b. the shared phase modulation means; and c. the third and fourth optical separation means.

20 . The fiber optic interferometric system according to claim 19 , wherein the first optical separation means includes a Y junction.

21 . The fiber optic interferometric system according to claim 16 , including a digital-to-analog converter adapted to apply a modulation voltage to the shared phase modulation means so as to generate a phase shift modulated at a modulation frequency f m .

22 . The fiber optic interferometric system according to claim 17 , wherein the third optical separation means and, respectively, the fourth optical separation means, comprise one or several 2×2 couplers arranged in series, a 1×N coupler or a 3×3 coupler.

23 . The fiber optic interferometric system according to claim 16 , wherein the transit times T 1 , T 2 and T 3 are defined as follows: T 1 ≦0.9×T 2 and 1.1×T 2 ≦T 3 .

24 . A method of interferometric measurement of a plurality of phase shifts in an interferometric system comprising N optical-fiber coils optically coupled in parallel to a shared source, a shared phase modulator and a shared detector, said N optical-fiber coils having respectively transit times T 1 , T 2 , . . . TN that are all different from each other, the method comprising the following steps:
spatial separation of a source beam into a first split beam and a second split beam; application of a time-modulated phase shift between the first split beam and the second split beam to form a first modulated beam and a second modulated beam; spatial separation of the first modulated beam into N fractions of the first modulated beam and spatial separation of the second modulated beam into N fractions of the second modulated beam; simultaneous and parallel injection on the plurality of optical-fiber coils, respectively, of a fraction of the first modulated beam at the first end of each optical-fiber coil and of a fraction of the second modulated beam at the second end of said optical-fiber coil, so that each of said fractions of the first modulated beam and each of said fractions of the second modulated beam travel respectively in counter-propagating directions through an optical-fiber coil with, respectively, a different transit time T 1 , T 2 , . . . TN for each of the N optical-fiber coils; optical recombination of the N fractions of first modulated beam having each travelled through one optical-fiber coil to form a first recombined beam; optical recombination of the N fractions of second modulated beam having each travelled through one optical-fiber coil to form a second recombined beam; recombination of the first recombined beam and of the second recombined beam to form an interferometric beam time modulated as a function of the respective transit times T 1 , T 2 , . . . TN in the different optical-fiber coils; detection of the interferometric beam and generation of an interferometric electronic signal; recording of at least 2*N components of the interferometric electronic signal at a series of at least 2*N instants as a function of the respective transit times T 1 , T 2 , . . . N in the optical-fiber coils; processing of the at least 2*N components of the interferometric electronic signal recorded at the preceding step to deduce therefrom a plurality of N measurements of Sagnac phase shift associated with each of the N optical-fiber coils, respectively.

25 . The method of interferometric measurement according to claim 24 , wherein the step of application of a time-modulated phase shift comprises a rectangular-wave modulation at a modulation frequency f m .

26 . The method of interferometric measurement according to claim 25 , wherein the modulation frequency f m is equal to the proper frequency f p of one of the optical-fiber coils, said coil having a transit time T i , and the proper frequency being defined as follows: f p =1/(2·Ti).

27 . The method of interferometric measurement according to claim 25 , wherein the modulation frequency f m is lower than the proper frequency of all the optical-fiber coils.

28 . The method of interferometric measurement according to claim 25 , wherein the modulation frequency f m is higher than the proper frequency of all the optical-fiber coils, the modulation frequency being lower than:

f
m

≤

1

Assignees

• Ixblue

Inventors

• Guattari Frederic
• Molucon Cedric
• Ferrand Sebastien
• Ducloux Eric

Classifications

• G01C19/721

  Details, e.g. optical or electronical details · CPC title

• G02B6/29347

  Loop interferometers, e.g. Sagnac, loop mirror · CPC title

• G01C19/728 Primary

  Assemblies for measuring along different axes, e.g. triads · CPC title