# US 9,518,826 B2 · Interferometric measurement system with optical fibre and inertial guidance or navigation system including such an interferometric measurement system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,518,826 B2 - Document ID: US9518826B2 - Status: Granted - Kind: B2 - Application number: 14/400,852 - Filed: 2013-05-15 - Published: 2015-05-14 - Granted: 2016-12-13 - Earliest claimed: 2012-05-16 - Assignees: Ixblue - Applicants: Frederic Guattari; Cedric Molucon; Eric Ducloux - Inventors: Frederic Guattari; Cedric Molucon; Eric Ducloux - Web page: https://patentgrep.com/patent/US9518826B2 ## CPC - G01C 19/721: {Details, e.g. optical or electronical details} - G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S) ## Abstract A fiber optic interferometric measurement system includes a light source; first and second optical transmission elements; first and second Sagnac-ring interferometers, respectively, including first and second fiber optic coils, and, respectively, having lengths L1 and L2; and first and second individual integrated optical circuits, respectively, connected to the first and second optical transmission elements, and to the two ends of the first and second optic coils, respectively. The interferometric system includes a multiple integrated optical circuit integrating, on a single substrate, the first and second individual integrated optical circuits, and the difference Δl between the optical length of the first optical transmission elements and the optical length of the second optical transmission elements is higher than the maximum of ΔNb1×L1 and ΔNB2×L2, in which ΔNb1 and ΔNb2, respectively, are the group birefringence index difference of the first and second fiber optic coils, respectively. ## Claims ### Claim 1 A fiber-optic interferometric measurement system including: a broad-spectrum light source adapted to emit a source light beam; a beam splitter adapted to receive the source light beam and to form a first split source beam and a second split source beam; first optical transmission means of optical length l1 adapted to transmit the first split source beam and second optical transmission means of optical length l2 adapted to transmit the second split source beam; a first Sagnac ring interferometer including a first fiber-optic coil and a first individual integrated optical circuit connected on the one hand to the first optical transmission means and on the other hand to the two ends of the first fiber-optic coil, the first fiber-optic coil having a length L1 and a group birefringence index difference ΔNb1; a first detector adapted to detect a first interferometric signal formed by the propagation of the first split source beam in the first Sagnac ring interferometer; a second Sagnac ring interferometer comprising a second fiber-optic coil and a second individual integrated optical circuit connected to the second optical transmission means and to the two ends of the second fiber-optic coil, the second fiber-optic coil having a length L2 and a group birefringence index difference ΔNb2; a second detector adapted to detect a second interferometric signal formed by the propagation of the second split source beam in the second Sagnac ring interferometer; and a multiple integrated optical circuit integrating on a same substrate the first individual integrated optical circuit and the second individual integrated optical circuit, wherein the difference Δl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is higher than the maximum of ΔNb1×L1 and ΔNb2×L2. ### Claim 2 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, wherein the difference Δl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is higher than four times the value of the maximum of ΔNb1×L1 and ΔNb2×L2. ### Claim 3 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, wherein the first optical transmission means include an optical fiber and/or the second optical transmission means include an optical fiber. ### Claim 4 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, wherein the first and the second, fiber-optic coil include a polarisation-maintaining optical fiber having a group birefringence index difference ΔNb1, respectively ΔNb2, comprised between 10−4 and 10−3, and wherein the difference Δl between the optical length l1 of the first fiber-optic transmission means and the optical length l2 of the second fiber-optic transmission means is comprised between 10−4 and 10−3 multiplied by the maximum of L1 and L2. ### Claim 5 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the beam splitter and the first and second source-detector separators. ### Claim 6 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l2 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the multiple integrated circuit and the first and second source-detector separators. ### Claim 7 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, further including third optical transmission means of optical length l3 adapted to transmit a third split source beam, a third Sagnac ring interferometer including a third fiber-optic coil and a third individual integrated optical circuit connected to the third optical transmission means and to the two ends of the third fiber-optic coil, the third fiber-optic coil having a length L3 and a group birefringence index difference ΔNb3, wherein the multiple integrated optical circuit integrates on the same substrate the first individual integrated optical circuit, the second individual integrated optical circuit and the third individual integrated optical circuit and wherein the difference of optical length between any two of the first, second and third optical transmission means is higher than the maximum of ΔNb1×L1, ΔNb2 ×L2 and ΔNb3 ×L3. ### Claim 8 (depends on 7) The fiber-optic interferometric measurement system according to claim 7, wherein the optical length difference between any two of the first, second and third optical transmission means is higher than four times the value of the maximum of ΔNb1×L1, ΔNb2×L2 and ΔNb3×L3. ### Claim 9 (depends on 1) The fiber-optic interferometric measurement system according to claim 1, wherein the broad-spectrum light source is chosen among a superluminescent diode and a rare-earth doped fiber source. ### Claim 10 (depends on 1) A gyroscopic measurement system including the fiber-optic interferometric measurement system according to claim 1, wherein the fiber-optic interferometric measurement system is configured to measure a rotation speed with respect to an axis perpendicular to a surface of the first fiber-optic coil and to measure another rotation speed with respect to another axis perpendicular to a surface of the second fiber-optic coil. ### Claim 11 (depends on 1) An inertial guidance or navigation system comprising the fiber-optic interferometric measurement system according to claim 1, wherein said inertial guidance or navigation system includes three fiber-optic Sagnac ring interferometers, having respectively a length Li with i=1, 2, 3 and a group index difference ΔNbi with i=1, 2, 3, wherein the three fiber-optic coils are configured to measure the rotations about three axes of a coordinate system in space, the axes of the three fiber-optic coils forming the axes of the coordinate system, and wherein the optical length difference between the broad-spectrum light source and any two of the three interferometers is higher than or equal to the maximum of ΔNbi×Li for i=1, 2, 3. ### Claim 12 (depends on 2) The fiber-optic interferometric measurement system according to claim 2, wherein the first optical transmission means include an optical fiber and/or the second optical transmission means include an optical fiber. ### Claim 13 (depends on 2) The fiber-optic interferometric measurement system according to claim 2, wherein the first fiber-optic coil and the second fiber-optic coil include a polarisation-maintaining optical fiber having a group birefringence index difference ΔNb1, respectively ΔNb2, comprised between 10−4 and 10−3, and wherein the difference Δl between the optical length l1 of the first fiber-optic transmission means and the optical length l2 of the second fiber-optic transmission means is comprised between 10−4 and 10−3 multiplied by the maximum of L1 and L2. ### Claim 14 (depends on 3) The fiber-optic interferometric measurement system according to claim 3, wherein the first fiber-optic coil and the second, fiber-optic coil include a polarisation-maintaining optical fiber having a group birefringence index difference ΔNb1, respectively ΔNb2, comprised between 10−4 and 10−3, and wherein the difference Δl between the optical length l1 of the first fiber-optic transmission means and the optical length l2 of the second fiber-optic transmission means is comprised between 10−4 and 10−3 multiplied by the maximum of L1 and L2. ### Claim 15 (depends on 2) The fiber-optic interferometric measurement system according to claim 2, further including a first source-detector separator and a second, source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l2 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the beam splitter and the first and second source-detector separators. ### Claim 16 (depends on 3) The fiber-optic interferometric measurement system according to claim 3, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l2 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the beam splitter and the first and second source-detector separators. ### Claim 17 (depends on 4) The fiber-optic interferometric measurement system according to claim 4, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the beam splitter and the first and second source-detector separators. ### Claim 18 (depends on 2) The fiber-optic interferometric measurement system according to claim 2, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the difference Δl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the multiple integrated circuit and the first and second source-detector separators. ### Claim 19 (depends on 3) The fiber-optic interferometric measurement system according to claim 3, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the differenceΔl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the multiple integrated circuit and the first and second source-detector separators. ### Claim 20 (depends on 4) The fiber-optic interferometric measurement system according to claim 4, further including a first source-detector separator and a second source-detector separator arranged between the beam splitter and the multiple integrated circuit, wherein the differenceΔl between the optical length l1 of the first optical transmission means and the optical length l2 of the second optical transmission means is located between the multiple integrated circuit and the first and second source-detector separators.