Dual fiber optic gyroscope

Claim 2

A Sagnac ring rotation sensor that includes a length of optical fiber formed in a sensing loop and an optical signal source for providing light to the sensing loop, characterised by a polarization maintaining module arranged to receive signals from the optical signal source, the polarization maintaining module including: means for providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam; and means for modulating a predetermined polarization component; 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.

Claim 3

The rotation sensor of claim 1 wherein the means for providing an unpolarized optical clockwise beam and an unpolarized counterclockwise beam include: 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 that passes light polarized along a first polarization axis and attenuates other polarizations, the first polarization axis being oriented at a 45° angle to the principal axes of the first polarization maintaining optical fiber; an optical coupler that couples 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 the counterclockwise beam and light remaining in first polarization maintaining optical fiber forming the clockwise beam; a third length of polarization maintaining optical fiber; and 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° to the principal axes of second polarization maintaining fiber.

Claim 4

The rotation sensor of claim 2 wherein the means for modulating a predetermined polarization component includes: a phase modulator 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; 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.

Claim 5

The rotation sensor of claim 2, 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.

Claim 6

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

Claim 9

The method of claim 6 including the steps of: 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 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° 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° 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.

Claim 10

The method of claim 7, further including the steps of: 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.

Claim 11

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

Claim 12

The method of claim of claim 9, 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.

Claim 13

The method of claim of claim 6 including the step of forming the sensing loop to comprise ordinary single mode, non-polarization maintaining fiber.