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

Patent metadata

Field	Value
Publication number	US-9823076-B2
Application number	US-201415023747-A
Country	US
Kind code	B2
Filing date	Sep 23, 2014
Priority date	Sep 24, 2013
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

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

The invention claimed is:

1. A multi-axis fiber optic interferometric system, including:
a shared light source adapted to emit a source beam having a constant intensity as a function of time;
a plurality of N optical-fiber coils, each coil forming a ring optical path about an axis;
a first optical coupler-separator adapted to spatially separate the source beam into a first split beam and a second split beam;
shared phase modulator adapted to apply a time-modulated phase shift, having a period of modulation T m , between the first and the second split beams and to form a first phase modulated beam and a second phase modulated beam;
a shared photodetector; and
a shared signal-processing system;
wherein:
the shared phase modulator applying simultaneously at the entry of the N coils a rectangular-wave phase modulation consisting of a rising front at instant t=0 and a falling front in between instants t=0 and T m at each period of modulation T m ;
the N optical-fiber coils are connected in parallel, so as to inject simultaneously a fraction of the first phase modulated beam at a first end of each coil and a fraction of the second phase modulated beam at a second end of each coil, said N optical-fiber coils having respective transit times T 1 , T2, . . . TN for modulated waves that are all different from each other;
the first optical coupler-separator being adapted to recombine said fractions of the first phase modulated beam and said fractions of the second phase 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, the interferometric signal detected comprising at least 2*N components, the 2*N components having time positions triggered by the position of rising fronts and/or falling fronts in the interferometric signal detected during a same period of modulation T m .

2. The multi-axis fiber optic interferometric system according to claim 1 , further comprising:
a second optical coupler-separator arranged between the shared light source and the shared photodetector;
third optical coupler-separator arranged on the optical path of the first phase modulated beam between the phase modulator and the first ends of each of the N optical-fiber coils;
fourth optical coupler-separator arranged on the optical path of the second phase modulated beam between the phase modulator and the second ends of each of the N optical-fiber coils;
the third optical coupler-separator and the fourth optical coupler-separator each having at least one entry and N exits so as to transmit simultaneously and in parallel a fraction of the first phase modulated beam at the first end of each of the N optical-fiber coils and a fraction of the second phase modulated beam at the second end of each of the N optical-fiber coils and so that said fractions of the first phase modulated beam and said fractions of the second phase modulated beam propagate in opposite directions in each of said coils.

3. The multi-axis fiber optic interferometric system according to claim 1 , 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 , T2, . . . 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.

4. The fiber optic interferometric system according to claim 2 , further including a planar integrated optical circuit including:
a. the first optical coupler-separator;
b. the shared phase modulator; and
c. the third and fourth optical coupler-separator.

5. The fiber optic interferometric system according to claim 4 , wherein the first optical coupler-separator includes a Y junction.

6. The fiber optic interferometric system according to claim 1 , including a digital-to-analog converter adapted to apply a modulation voltage to the shared phase modulator so as to generate a phase shift modulated at a modulation frequency f m .

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

8. The fiber optic interferometric system according to claim 1 , 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 .

9. 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 for modulated waves that are all different from each other, the method comprising the following steps:
spatial separation of a source beam having a constant intensity as a function of time into a first split beam and a second split beam;
simultaneous application at the entry of the N coils of a rectangular wave time-modulated phase shift having a period of modulation T m between the first split beam and the second split beam to form a first phase modulated beam and a second phase modulated beam, the rectangular wave time-modulated phase shift consisting of a rising front at instant t=0 and a falling front in between instants t=0 and T m at each period of modulation T m ;
spatial separation of the first phase modulated beam into N fractions of the first phase modulated beam and spatial separation of the second phase modulated beam into N fractions of the second phase modulated beam;
simultaneous and parallel injection on the plurality of optical-fiber coils, respectively, of a fraction of the first phase modulated beam at the first end of each optical-fiber coil and of a fraction of the second phase modulated beam at the second end of said optical-fiber coil, so that each of said fractions of the first phase modulated beam and each of said fractions of the second phase 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 phase modulated beam having each travelled through one optical-fiber coil to form a first recombined beam;
optical recombination of the N fractions of second phase 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;
detection and recording of at least 2*N components of the interferometric electronic signal during a same period of modulation T m at a series of at least 2*N instants triggered by the position of rising fronts and/or falling fronts in the interferometric signal detected as a function of the respective transit times T 1 , T 2 , . . . TN 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 optica

Assignees

• Ixblue

Inventors

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

Classifications

• G01C19/728 Primary

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

• G01C19/721

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

• G02B6/29347

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