Sagnac-ring fiber-optic interferometric system with Rayleigh length spaced polarizer

1. A fiber-optic interferometric system comprising:

a light source adapted to emit a source beam at a wavelength λ 0 in vacuum;

a fiber optic coil forming a ring optical path;

a coil splitter adapted to spatially separate the source beam into a first split beam and a second split beam, so that the first split beam and the second split beam travel through the fiber optic coil in opposite directions, the coil splitter being adapted to recombine said first split beam and second split beam after propagation in opposite directions in the fiber optic coil, so as to form an interferometric beam;

a receiver splitter adapted to guide the interferometric beam towards a photodetector;

polarization filtering means,

wherein the polarization filtering means comprise:

a first waveguide polarizer,

at least one other thin-plate polarizer having a physical thickness e and a refractive index n, and

at least one section of optical waveguide,

the first polarizer and the at least one polarizer being juxtaposed in series in the optical path between the receiver splitter and the fiber optic coil,

the at least one other thin-plate polarizer being interposed between, on the one hand, a first waveguide end of the first polarizer and, on the other hand, a second waveguide end of said optical waveguide section, the physical distance d between the first waveguide end of the first polarizer and the second waveguide end of said optical waveguide section being lower than or equal to twice the Rayleigh length, i.e.:

d

≤

2

×

π

⁢

⁢

w

0

2

λ

m

,

where

λ

m

=

λ

0

n

represents the wavelength of the beam in a medium of index n, w 0 represents the radius of a single-mode beam at 1/e in amplitude in said waveguides of said optical waveguide section and of the first waveguide polarizer, and

the physical thickness e of the at least one other thin-plate polarizer being lower than or equal to the physical distance d.

2. The fiber-optic interferometric system according to claim 1 , wherein the at least one other thin-plate polarizer has a physical thickness e lower than or equal to

π

⁢

⁢

w

0

2

λ

m

and wherein the physical distance d is lower than or equal to

π

⁢

⁢

w

0

2

λ

m

.

3. The fiber-optic interferometric system according to claim 1 , wherein the at least one other thin-plate polarizer has a physical thickness e lower than or equal to

π

⁢

⁢

w

0

2

2

×

λ

m

and wherein the physical distance d is lower than or equal to

π

⁢

⁢

w

0

2

2

×

λ

m

.

4. The fiber-optic interferometric system according to claim 1 , wherein the at least one other thin-plate polarizer has a physical thickness e lower than or equal to 50 microns.

5. The fiber-optic interferometric system according to claim 4 , wherein the at least one other thin-plate polarizer is formed of a thin plate of polarizing glass.

6. The fiber-optic interferometric system according to claim 4 , wherein the first waveguide polarizer is a fiber-optic polarizer.

7. The fiber-optic interferometric system according to claim 4 , wherein the first waveguide polarizer is formed by proton exchange on a lithium niobate substrate.

8. The fiber-optic interferometric system according to claim 7 , comprising an integrated optical circuit on a lithium niobate substrate, the integrated optical circuit comprising the first waveguide polarizer, the coil splitter and an optical phase modulator.

9. The fiber-optic interferometric system according to claim 4 , wherein said at least one section of optical waveguide comprises a section of single-mode optical fiber connected to the fiber optic coil.

10. The fiber-optic interferometric system according to claim 9 , wherein said section of optical waveguide is a section of polarizing fiber.

11. The fiber-optic interferometric system according to claim 1 , wherein the at least one other thin-plate polarizer is formed of a thin plate of polarizing glass.

12. The fiber-optic interferometric system according to claim 1 , wherein the first waveguide polarizer is a fiber-optic polarizer.

13. The fiber-optic interferometric system according to claim 1 , wherein the first waveguide polarizer is formed by proton exchange on a lithium niobate substrate.

14. The fiber-optic interferometric system according to claim 13 , comprising an integrated optical circuit on a lithium niobate substrate, the integrated optical circuit comprising the first waveguide polarizer, the coil splitter and an optical phase modulator.

15. The fiber-optic interferometric system according to claim 1 , wherein said at least one section of optical waveguide, said at least one other thin-plate polarizer and the first waveguide end of the first polarizer are arranged on the optical path of the source beam between the coil splitter and the receiver splitter.

16. The fiber-optic interferometric system according to claim 1 , wherein said at least one section of optical waveguide comprises a section of single-mode optical fiber connected to the receiving splitter.

17. The fiber-optic interferometric system according to claim 1 , wherein said at least one section of optical waveguide, said at least one other thin-plate polarizer and the first waveguide end of the first polarizer are arranged on the optical path of the first split beam and/or of the second split beam, between the coil splitter and the fiber optic coil.

18. The fiber-optic interferometric system according to claim 1 , wherein said at least one section of optical waveguide comprises a section of single-mode optical fiber connected to the fiber optic coil.

19. The fiber-optic interferometric system according to claim 1 , wherein the first polarizer and the at least one other thin-plate polarizer are linear polarizers having polarization axes aligned relative to each other.

20. The fiber-optic interferometric system according to claim 1 , wherein said section of optical waveguide is a section of polarizing fiber.