# US 7,746,476 B2 · Fiber optic gyroscope

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- Number: US 7,746,476 B2
- Document ID: US7746476B2
- Status: Granted
- Kind: B2
- Application number: 11/776,452
- Filed: 2007-07-11
- Published: 2009-01-15
- Granted: 2010-06-29
- Earliest claimed: 2007-07-11
- Assignees: Emcore Corporation
- Inventors: Joseph R. Demers; Ka Kha Wong; Ronald T. Logan, Jr.
- Web page: https://patentgrep.com/patent/US7746476B2

## CPC

- G01C 19/728: {Assemblies for measuring along different axes, e.g. triads}
- G01C 19/725: {using nxn optical couplers, e.g. 3x3 couplers}
- 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 gyroscope including an optical circulator in the path of said first and second beams for providing polarized first and second beams of identical polarization. A phase modulator couples the first and second beams to the first and second end respectively of the fiber loop, and couples for receiving the return first and second beams from the second and first ends respectively of the fiber loop. First and second photodiodes are coupled to the optical circulator for receiving the optical signal from the first and second return beams.

## Claims

### Claim 1

A fiber optic gyroscope comprising:
a non-coherent light source for producing a beam of light;
a first beam splitter in the path of said beam to produce first and second beams;
an optical circulator in the path of said first and second beams for providing polarized third and fourth beams respectively, with polarization orthogonal to each other;
a second beam splitter in the path of said third beam for producing fifth and sixth beams;
first and second planar optical fiber loops each having a first end and a second end;
a phase modulator coupling said fifth and sixth beams to said first and said second ends of said first and second optical fiber loops respectively, and receiving the return fifth and sixth beams from said second and said first ends respectively of said fiber loops; and
first and second photodiodes coupled to said optical circulator for receiving the optical signal from said fifth and sixth return beams.

### Claim 2 (depends on 1)

A gyroscope as defined in claim 1, wherein said first beam splitter is a four-way silicon splitter.

### Claim 3 (depends on 1)

A gyroscope as defined in claim 1, wherein said optical circulator includes a polarizing beam splitter.

### Claim 4 (depends on 3)

A gyroscope as defined in claim 3, wherein said optical circulator further comprises a Faraday rotator coupled to an output of the polarizing beam splitter.

### Claim 5 (depends on 4)

A gyroscope as defined in claim 4, wherein said polarizing beam splitter directs the P polarization of the initial beam of light from the incoherent source onto a power monitoring photodiode.

### Claim 6 (depends on 5)

A gyroscope as defined in claim 5, wherein said polarizing beam splitter directs the S polarization of the initial beam of light from the incoherent source through and into the Faraday rotator.

### Claim 7 (depends on 4)

A gyroscope as defined in claim 4, wherein said polarizing beam splitter directs the return light of P polarization to said first and second photodiodes.

### Claim 8 (depends on 3)

A gyroscope as defined in claim 3, wherein said optical circulator includes a Faraday rotator, and wherein the polarizing beam splitter couples the light of S polarization to the Faraday rotator.

### Claim 9 (depends on 4)

A gyroscope as defined in claim 4, further comprising a monitor photodiode coupled to the polarizing beam splitter for monitoring the light of P polarization from the light source.

### Claim 10 (depends on 1)

A gyroscope as defined in claim 1, wherein said first and second photodiodes are assembled on a 1×4 photodiode array.

### Claim 11 (depends on 1)

A gyroscope as defined in claim 1, wherein said second beam splitter is embedded in a lithium niobate FOG chip.

### Claim 12 (depends on 7)

A gyroscope as defined in claim 7, wherein said polarizing beam splitter directs the return light of P polarization from the optical fiber loop to said 1×4 photodiode array.

### Claim 13 (depends on 3)

A gyroscope as defined in claim 3, further comprising a 1×4 V-groove assembly and a phase modulator for coupling the Faraday rotator with the optical fiber loop.

### Claim 14 (depends on 9)

A gyroscope as defined in claim 9, further comprising a lens array coupling the Faraday rotator with the 1×4 fiber V-groove assembly.

### Claim 15

A fiber optic gyroscope comprising:
a light source for producing a beam of light;
an optical circulator in the path of said beam for providing polarized primary and secondary beams of perpendicular polarization;
a beam splitter in the path of one of said polarized beams to produce at least first, second, and third beams;
at least first, second, and third planar fiber loops each lying in a plane orthogonal to one another, and each having a first end and a second end;
an optical interface coupling said first, second, and third beams to said first ends of each respective fiber loop, and for receiving the return first, second, and third beams from said second ends of each respective fiber loop; and
a photodiode array coupled to said optical interface for receiving the optical signal from said first, second, and third return beams.

### Claim 16 (depends on 15)

A gyroscope as defined in claim 15, wherein said beam splitter is a four-way silicon splitter.

### Claim 17 (depends on 15)

A gyroscope as defined in claim 15, wherein said optical circulator includes a Faraday rotator.

### Claim 18 (depends on 15)

A gyroscope as defined in claim 15, wherein said optical circulator includes a polarizing beam splitter.

### Claim 19 (depends on 15)

A gyroscope as defined in claim 15, further comprising a fourth planar fiber loop lying in a plane different from the planes of said first, second and third planar fiber loops.