Dual fiber optic gyroscope - Patent Review 4997282

Claims

What is claimed is:

1. A Sagnac ring rotation sensor, comprising:

a length of a first polarization maintaining optical fiber having a pair of principal axes;

means for providing an optical signal to the first polarization maintaining optical fiber, the optical signal having a first linear polarization component parallel to one of the principal axes of the first polarization maintaining optical fiber and a second linear polarization component parallel to the other principal axis;

a first polarizer coupled to the first polarization maintaining fiber for passing light polarized along a first polarization axis and attenuating other polarizations, the first polarization axis being oriented at a 45.degree. angle to the principal axes of the first polarization maintaining optical fiber;

a length of a second polarization maintaining fiber optically coupled to the first polarization maintaining optical fiber, the second polarization maintaining fiber having principal axes that are parallel to the principal axes of the first polarization maintaining optical fiber, light coupled into the second polarization maintaining fiber forming a counterclockwise beam and light remaining in first polarization maintaining optical fiber forming a clockwise beam;

a third length of polarization maintaining optical fiber;

an optical waveguide positioned to guide signals between the second polarization maintaining fiber and the third polarization maintaining fiber, the optical waveguide having principal axes oriented at an angle of 45.degree. to the principal axes of second polarization maintaining fiber;

means for modulating the phase of light having a predetermined polarization in the optical waveguide;

first polarizing means for polarizing the counterclockwise beam in the optical waveguide such that signals incident upon the phase modulator from the second polarization maintaining fiber have the predetermined polarization;

a loop of optical fiber connected between the optical waveguide and the first polarization maintaining optical fiber to provide a sensing coil for the clockwise beam and the counterclockwise beam; and

second polarizing means for polarizing the counterclockwise beam in the optical waveguide such that signals incident upon the phase modulator from the sensing coil have the predetermined polarization.

2. The rotation sensor of claim 1, wherein the optical waveguide is formed in a substrate of lithium niobate.

3. The rotation sensor of claim 2 wherein the first and second polarizing means and the phase modulator are mounted on the lithium niobate substrate adjacent the optical waveguide with the phase modulator being between the first and second polarizing means.

4. The rotation sensor of claim 1 wherein the sensing loop comprises ordinary single mode, non-polarization maintaining fiber.

5. A Sagnac ring rotation sensor, comprising:

an optical signal source;

a polarization maintaining module arranged to receive optical signals from the optical signal source, the polarization maintaining module including:

an integrated optics waveguide;

means for providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam in the integrated optics waveguide; and

means for modulating a single polarization component in the integrated optics waveguide;

a coil of non-polarization maintaining optical fiber forming a sensing coil connected to the means for providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam; and

means for detecting interference between the clockwise beam and the counterclockwise beam to measure rotation of the coil.

6. The rotation sensor of claim 1, wherein the optical waveguide is formed in a substrate of lithium niobate, the first and second polarizing means and the phase modulator being mounted on the lithium niobate substrate adjacent the optical waveguide with the phase modulator being between the first and second polarizing means.

7. The rotation sensor of claim 5 wherein the sensing loop comprises ordinary single mode, non-polarization maintaining fiber.

8. A method for forming a Sagnac ring rotation sensor, comprising the steps of:

introducing an optical signal into a first length of polarization maintaining optical fiber, the optical signal having a first linear polarization component parallel to one of the principal axes of the first polarization maintaining optical fiber and a second linear polarization component parallel to the other principal axis;

placing a first polarizer that passes light polarized along a first polarization axis and attenuates other polarizations adjacent the first length of polarization maintaining optical fiber;

orienting the first polarization axis at a 45.degree. angle to the principal axes of the first polarization maintaining optical fiber;

coupling optical signals between the first polarization maintaining optical fiber and a length of a second polarization maintaining fiber, the second polarization maintaining fiber having principal axes that are parallel to the principal axes of the first polarization maintaining optical fiber, light coupled into the second polarization maintaining fiber forming a counterclockwise beam and light remaining in first polarization maintaining optical fiber forming a clockwise beam;

coupling signals from the first polarization maintaining fiber into an optical waveguide having principal axes oriented at an angle of 45.degree. to the principal axes of second polarization maintaining fiber;

coupling signals from the optical waveguide into a third length of polarization maintaining optical fiber; and

modulating the phase of light having a predetermined polarization in the optical waveguide;

polarizing the counterclockwise beam in the optical waveguide such that signals incident upon the phase modulator from the second polarization maintaining fiber have the predetermined polarization;

connecting a loop of optical fiber between the optical waveguide and the first polarization maintaining optical fiber to provide a sensing coil for the clockwise beam and the counterclockwise beam; and

polarizing the counterclockwise beam in the optical waveguide such that signals incident upon the phase modulator from the sensing coil have the predetermined polarization.

9. The method of claim 8, including the step of forming the optical waveguide in a substrate of lithium niobate.

10. The method of claim 8, further including the steps of mounting the first and second polarizing means and the phase modulator on the lithium niobate substrate adjacent the optical waveguide with the phase modulator being between the first and second polarizing means.

11. The method of claim 8 including the step of forming the sensing loop to comprise ordinary single mode, non-polarization maintaining fiber.

12. A method of forming a Sagnac ring rotation sensor, comprising the steps of:

providing an optical signal source;

forming a polarization maintaining module to include an integrated optics waveguide;

introducing signals from the optical signal source into the integrated optics waveguide;

providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam output from the integrated optics waveguide; and

means for modulating a single polarization component of light in the integrated optics waveguide;

connecting a coil of non-polarization maintaining optical fiber as a sensing coil to the integrated optics waveguide to receive the polarized optical clockwise beam and the unpolarized counterclockwise beam; and

detecting interference between the clockwise beam and the counterclockwise beam to measure rotation of the coil.

13. A method of forming a Sagnac ring rotation sensor, comprising the steps of:

providing an optical signal source;

introducing signals from the optical signal source into a polarization maintaining module;

providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam output from the polarization maintaining module;

modulating a predetermined polarization component of light in the polarization maintaining module;

connecting a coil of non-polarization maintaining optical fiber as a sensing coil to the polarization maintaining module to receive the unpolarized optical clockwise beam and the unpolarized counterclockwise beam;

detecting interference between the clockwise beam and the counterclockwise beam to measure rotation of the coil;

forming the polarization maintaining module to include a length of a first polarization maintaining optical fiber having a pair of principal axes;

providing an optical signal to the first polarization maintaining optical fiber, the optical signal having a first linear polarization component parallel to one of the principal axes of the first polarization maintaining optical fiber and a second linear polarization component parallel to the other principal axis;

placing a first polarizer that passes light polarized alon