Non-interferometric optical gyroscope based on polarization sensing

Abstract

Techniques and devices for optical sensing of rotation based on measurements and sensing of optical polarization or changes in optical polarization due to rotation without using optical interferometry.

What is claimed is: 
     
         1 . An optical gyroscope device for sensing rotation based on sensing of optical polarization of light without relying on optical interferometry, comprising:
 an optical beam splitting device that splits an input optical beam with an input optical polarization into a first optical beam with a first optical polarization and a second optical beam with a second optical polarization that is orthogonal to the first optical polarization;   an optical loop coupled to receive the first and second optical beams from the optical beam splitting device so that the first optical beam propagates in the optical loop in a first loop direction and the second optical beam propagates in the optical loop in a second loop direction opposite to the first loop direction;   an optical input and output device coupled between the optical loop and the optical beam splitting device to direct light from the optical beam splitting device to the optical loop and to receive output light from the optical loop, wherein the optical input and output device and the optical loop are configured to combine light of the first and second optical beams at the optical input and output device without causing optical interference between the first and second optical beams, to produce a combined optical beam as an optical output of the optical loop for sensing a rotation of the optical loop based on a phase difference Acl) between the counter propagating first and second optical beams in the optical loop that is caused by the rotation and that is linearly proportional to a rotation rate of the rotation;   an optical detection module that converts the optical output of the optical loop into an electrical output; and   a processing circuit coupled to receive the electrical output from the optical detection module and operable to process the electrical output to obtain information on optical polarization of the optical output, wherein the information includes at least two different Stokes parameters s 2  and s 3  of the optical output representing a cosine function and a sine function of the phase difference Δϕ between the counter propagating first and second optical beams in the optical loop and the processing circuit is configured to process the Stokes parameters s 2  and s 3  to determine the rotation rate of the optical loop.   
     
     
         2 . The device as in  claim 1 , wherein the processing circuit is configured to:
 perform time derivatives of s 2  and s 3  to produce ds 2 /dt and ds 3 /dt;   multiply s 2  with ds 3 /dt, the time derivative of s 3 , to produce s 2 *ds 3 /dt;   multiply s 3  with ds 2 /dt, the time derivative of s 2 , to produce s 3 *ds 2 /dt;   subtract s 2 *ds 3 /dt and s 3 *ds 2 /dt to obtain a time derivative of the phase difference Δϕ between the counter propagating first and second optical beams in the optical loop that is caused by the rotation as d(Δϕ)/dt; and   integrate d(Δϕ)/dt over time to obtain the phase difference Δϕ.   
     
     
         3 . The device as in  claim 1 , wherein:
 the optical detection module is configured to:   split the optical output into first, second, third and fourth different optical beams of an equal power level;   include a 0-degree polarizer in the first optical beam and a first photodetector to receive output from the 0-degree polarizer to produce a first detector signal P 1 ;   include a 90-degree polarizer in the second optical beam and a second photodetector to receive output from the 90-degree polarizer to produce a second detector signal P 2 ;   include a 45-degree polarizer in the third optical beam and a third photodetector to receive output from the 45-degree polarizer to produce a third detector signal P 3 ; and   include a circular polarizer in the fourth optical beam and a fourth photodetector to receive output from the circulator polarizer to produce a fourth detector signal P 4 ;   the processing circuit is configured to process the first, second, third and fourth detector signals to obtain four Stokes parameters as:
     S   0   =P   1   +P   2 , 
     s   1 =cos( P   1   −P   2 )/ S   0 , 
     s   2 =cos(Δϕ)=(2 P   3   −S   0 )/ S   0 , and
 
     s   3 =sin(Δϕ)=(2 P   4   −S   0 )/ S   0 .
 
   
     
     
         4 . The device as in  claim 3 , wherein the circular polarizer includes a quarter wave plate followed by a linear polarizer. 
     
     
         5 . The device as in  claim 1 , wherein:
 the optical detection module is configured to:   split the optical output into a first analyzing beam and a second analyzing beam;   introduce approximately 90 degree phase to the phase difference Δϕ between the two counter propagating optical beams in the first analyzing beam;   split the first analyzing beam into a first polarization beam and a second polarization beam orthogonal in polarization to the first polarization beam;   detect the first polarization beam to produce a first detector signal V 1 ;   detect the second polarization beam to produce a second detector signal V 2 ;   split the second analyzing beam into a third polarization beam and a fourth polarization beam orthogonal to the first polarization beam;   detect the third polarization beam to produce a third detector signal V 3 ; and   detect the fourth polarization beam to produce a fourth detector signal V 4 ;   the processing circuit is configured to:   calculate Stokes parameter s 3  from sin(Δϕ) which is a function of V 1  and V 2 ;   calculate the Stokes parameter s 2  from cos(Δϕ) which is a function of V 3  and V 4 .   
     
     
         6 . The device as in  claim 1 , wherein:
 at least one of the first and second optical beams in the optical loop is modulated at a modulation frequency; and   the device further includes a lock-in amplifier in detecting the optical output to obtain information on optical polarization of the optical output to reduce detection noise.   
     
     
         7 . An optical gyroscope device for sensing rotation based on sensing of optical polarization of light without relying on optical interferometry, comprising:
 a polarization beam splitter that receives input light to produce a first optical beam with a first polarization and a second optical beam with a second polarization orthogonal in polarization to the first polarization;   a first optical collimator coupled between the polarization beam splitter and a first polarization maintaining fiber to couple the first optical beam into the first polarization maintaining fiber with the first polarization aligned with a polarization axis of the first polarization maintaining fiber;   a second optical collimator coupled between the polarization beam splitter and a second polarization maintaining fiber to couple the second optical beam into the second polarization maintaining fiber with the second polarization aligned with the polarization axis of the second polarization maintaining fiber;   an optical loop coupled to receive light from the first and second polarization maintaining fibers as two counter propagating optical beams in a common polarization in the optical loop, and to output light from the counter propagating optical beams in the optical loop as an optical output from the optical loop;   a polarization analyzer to receive the optical output from the optical loop to obtain different Stokes parameters including at least two Stokes parameters s 2 , and s 3  that represent, respectively, cosine and sine functions of a phase difference Δϕ between the two counter propagating beams in the optical loop induced by a rotation of the optical loop: cos(Δϕ) and sin(Δϕ); and   a processing circuit coupled to the polarization analyzer to receive the two Stokes parameters s 2 , and s 3  of the optical output beam and to process the received two Stokes parameters s 2 , and s 3  to obtain the phase difference Δϕ and a rotation rate of the optical loop from the phase difference Δϕ.   
     
     
         8 . The device as in claim of  7 , wherein the polarization beam splitter is oriented such that the first optical beam and the second optical beam have approximately the same optical power. 
     
     
         9 . The device as in claim of  7 , comprising a Faraday rotator with 45 degrees rotation angle located in an optical path of the input light before entering the polarization beam splitter. 
     
     
         10 . The device as in claim of  7 , comprising a quarter wave plate located in an optical path of the input light and oriented to have with an optical axis at 45 degrees from input polarization of the input light before entering the polarization beam splitter.