Resonant optical gyroscope with a broadband light source and RIN reduction techniques
A gyroscope comprises a source emitting a broadband beam, and a first waveguide arrangement that splits the beam into CCW and CW beams. First and second phase modulators are coupled to the waveguide arrangement and provide phase modulations or frequency shifts to the CCW and CW beams. An optical resonator is in communication with the phase modulators such that the CCW and CW beams are optically coupled into the resonator. A second waveguide arrangement receives the CCW and CW beams transmitted from the resonator. First and second RIN detectors are coupled to the second waveguide arrangement and respectively receive the CCW and CW beams. A rate detector receives the CCW and CW beams. A rate calculation unit receives intensity noise signals from the RIN detectors, and rate and intensity noise signals from the rate detector. The rate calculation unit performs a RIN subtraction technique to reduce intensity noise limited ARW.
1 . A gyroscope comprising:
a light source configured to emit a light beam with a broadband spectrum;
a first waveguide arrangement in optical communication with the light source, the first waveguide arrangement configured to split the light beam into a counterclockwise (CCW) beam and a clockwise (CW) beam;
a first phase modulator optically coupled to the first waveguide arrangement, the first phase modulator configured to receive the CCW beam and provide a phase modulation or frequency shift to the CCW beam;
a second phase modulator optically coupled to the first waveguide arrangement, the second phase modulator configured to receive the CW beam and provide a phase modulation or frequency shift to the CW beam;
an optical resonator in optical communication with the first phase modulator and the second phase modulator through the first waveguide arrangement, wherein the CCW beam is optically coupled into the optical resonator and propagates in a CCW direction in the optical resonator, and the CW beam is optically coupled into the optical resonator and propagates in a CW direction in the optical resonator;
a second waveguide arrangement optically coupled to the optical resonator, the second waveguide arrangement configured to receive the CCW beam and the CW beam transmitted from the optical resonator;
a first relative intensity noise (RIN) detector optically coupled to the second waveguide arrangement and configured to receive the CCW beam;
a second RIN detector optically coupled to the second waveguide arrangement and configured to receive the CW beam;
a rate detector optically coupled to the second waveguide arrangement, the rate detector configured to receive combined portions of the CCW and CW beams from the second waveguide arrangement; and
a rate calculation unit configured to receive a first intensity noise signal from the first RIN detector and a second intensity noise signal from the second RIN detector, the rate calculation unit further configured to receive a rate and intensity noise signal from the rate detector;
wherein the rate calculation unit is operative to perform a RIN subtraction technique to reduce intensity noise limited Angle Random Walk (ARW), and to calculate a rotation rate signal for the gyroscope.
2 . The gyroscope of claim 1 , wherein in the RIN subtraction technique, the intensity noise signal is subtracted from the rate using intensity signals at a demodulation frequency provided by the first and second intensity noise signals from the first and second RIN detectors.
3 . The gyroscope of claim 1 , wherein the rate detector is operative to detect a Sagnac phase shift between the CW and CCW beams in the optical resonator caused by rotation of the gyroscope.
4 . The gyroscope of claim 1 , wherein the light source comprises an amplified spontaneous emission device, an Erbium-doped fiber amplifier, a superluminescent diode, or two or more superluminescent diodes having different center wavelengths.
5 . The gyroscope of claim 1 , wherein the optical resonator comprises a waveguide ring resonator.
6 . The gyroscope of claim 1 , wherein the optical resonator comprises a fiber ring resonator.
7 . The gyroscope of claim 1 , wherein the optical resonator comprises a planar waveguide ring resonator.
8 . The gyroscope of claim 1 , further comprising:
a first optical isolator optically coupled to the first waveguide arrangement between the first phase modulator and the optical resonator; and
a second optical isolator optically coupled to the first waveguide arrangement between the second phase modulator and the optical resonator.
9 . The gyroscope of claim 8 , wherein the first waveguide arrangement comprises:
a first waveguide optically coupled between the light source and the first phase modulator;
a second waveguide optically coupled between the light source and the second phase modulator;
a third waveguide optically coupled between the first phase modulator and the first optical isolator;
a fourth waveguide optically coupled between the second phase modulator and the second optical isolator; and
a first coupling waveguide optically coupled to the optical resonator at a first coupling region on a first side of the optical resonator;
wherein the first optical isolator and the second optical isolator are in optical communication with the optical resonator through the first coupling waveguide.
10 . The gyroscope of claim 9 , wherein the second waveguide arrangement comprises:
a second coupling waveguide optically coupled to the optical resonator at a second coupling region on a second side of the optical resonator;
wherein the second coupling waveguide is split into a first waveguide branch and a second waveguide branch at a third coupling region, and split into a third waveguide branch and a fourth waveguide branch at a fourth coupling region;
wherein the CW and CCW beams are transmitted from the optical resonator at the second coupling region, which rejects any light that does not overlap with resonance peaks of the optical resonator.
11 . The gyroscope of claim 10 , wherein:
the first RIN detector is in optical communication with the optical resonator through the second coupling waveguide and the first waveguide branch;
the second RIN detector is in optical communication with the optical resonator through the second coupling waveguide and the third waveguide branch; and
the rate detector is in optical communication with the optical resonator through the second coupling waveguide, the second waveguide branch, and the fourth waveguide branch;
wherein the second waveguide branch and the fourth waveguide branch are coupled together at an input port of the rate detector.
12 . The gyroscope of claim 1 , further comprising an optical isolator optically coupled between the light source and the first waveguide arrangement.
13 . The gyroscope of claim 12 , wherein the first waveguide arrangement comprises:
a first waveguide optically coupled between the optical isolator and the first phase modulator;
a second waveguide optically coupled between the optical isolator and the second phase modulator; and
a first coupling waveguide optically coupled to the optical resonator at a first coupling region on a first side of the optical resonator;
wherein the first phase modulator and the second phase modulator are in optical communication with the optical resonator through the first coupling waveguide.
14 . The gyroscope of claim 13 , wherein the second waveguide arrangement comprises:
a second coupling waveguide optically coupled to the optical resonator at a second coupling region on a second side of the optical resonator;
wherein the second coupling waveguide is split into a first waveguide branch and a second waveguide branch at a third coupling region, and split into a third waveguide branch and a fourth waveguide branch at a fourth coupling region.
15 . The gyroscope of claim 14 , wherein:
the first RIN detector is in optical communication with the optical resonator through the second coupling waveguide and the first waveguide branch;
the second RIN detector is in optical communication with the optical resonator through the second coupling waveguide and the third waveguide branch; and
the rate detector is in optical communication with the optical resonator through the second coupling waveguide, the second waveguide branch, and the fourth waveguide branch;
wherein the second waveguide branch and the fourth waveguide branch are coupled together at an input port of the rate detector.