Chip-scale inertial sensor and inertial measurement unit

1 . A chip-scale inertial sensor for detecting a rate of rotation of the inertial sensor about an axis, the inertial sensor comprising:

an optical vibratory gyroscope for detecting a first rate of rotation of the inertial sensor about the axis, the optical vibratory gyroscope configured to output a main signal corresponding to the first rate of rotation;

an optical Sagnac gyroscope for concurrently detecting a second rate of rotation of the inertial sensor about the axis, the optical Sagnac gyroscope configured to output a supplementary signal corresponding to the second rate of rotation; and

a microcontroller configured to:

receive one or more inputs based on the main signal and supplementary signal; and

determine, based on the one or more inputs, a corrected first rate of rotation of the inertial sensor about the axis.

2 . A chip-scale inertial sensor according to claim 1 , wherein the optical vibratory gyroscope and the optical Sagnac gyroscope receive light from the same light source.

3 . A chip-scale inertial sensor according to claim 2 , further comprising a beamsplitter to split the light from the light source for transmission into the optical vibratory gyroscope and the optical Sagnac gyroscope.

4 . A chip-scale inertial sensor according to claim 3 , further comprising a light source for transmitting light into the optical vibratory gyroscope and the optical Sagnac gyroscope.

5 . A chip-scale inertial sensor according to claim 4 , further comprising at least one detector to detect light transmitted from the optical vibratory gyroscope and the optical Sagnac gyroscope, the microcontroller to receive the one or more inputs from the at least one detector.

6 . A chip-scale inertial sensor according to claim 5 , wherein determining, based on the one or more inputs, a corrected first rate of rotation comprises comparing the first rate of rotation to the second rate of rotation and determining the corrected first rate of rotation based on the comparison.

7 . A chip-scale inertial sensor according to claim 6 ,

wherein comparing the first rate of rotation to the second rate of rotation comprises calculating the difference between the main signal and supplementary signal to determine the short and long term errors of the optical vibratory gyroscope and,

wherein determining the corrected first rate of rotation based on the comparison comprises correcting the main signal to remove the short and long term errors.

8 . A chip-scale inertial sensor according to claim 7 , wherein the errors are due to linear acceleration and/or long term drift of the inertial sensor.

9 . A chip-scale inertial sensor according to claim 8 ,

wherein comparing the first rate of rotation to the second rate of rotation comprises determining if the main signal is saturated, and

wherein, if the main signal is saturated, the corrected first rate of rotation is determined using the supplementary signal only.

10 . A chip-scale inertial sensor according to claim 9 , wherein the optical vibratory gyroscope and optical Sagnac gyroscope are fabricated on the same chip.

11 . A chip-scale inertial sensor according to claim 10 , wherein the microcontroller is further configured to output a feedback signal to actuate a test mass of the optical vibratory gyroscope to recalibrate the optical vibratory gyroscope based on the comparison.

12 . A chip-scale inertial sensor according to claim 11 , wherein the feedback signal is output to electrodes of the optical vibratory gyroscope to electrostatically actuate the test mass.

13 . A chip-scale inertial sensor according to claim 12 , wherein the optical Sagnac gyroscope comprises a coiled or spiralled waveguide structure to propagate light clockwise and counter clockwise, the rotation of the sensor causing changes in the optical path lengths of the light propagating clockwise and counter clockwise.

14 . A chip-scale inertial sensor according to claim 13 , wherein the coiled or spiralled waveguide structure is in the form of one of a coiled optical fiber, a coiled waveguide, a spiralled waveguide and a microdisk.

15 . A chip-scale inertial sensor according to claim 14 , wherein the diameter of the coiled or spiralled waveguide structure is in the order of millimetres or centimetres.

16 . A chip-scale inertial sensor according to claim 15 , wherein the microcontroller is to control the frequency of the light propagating clockwise and counter clockwise based on the supplementary signal output by the optical Sagnac gyroscope to reduce frequency changes of the light due to drifting.

17 . A chip-scale inertial sensor according to claim 16 , wherein the optical Sagnac gyroscope and optical vibratory gyroscope are made of silicon or silicon nitride.

18 . A chip-scale inertial sensor according to claim 17 , wherein the optical vibratory gyroscope comprises:

one or more microresonators, each microresonator supporting a corresponding optical resonance;

a micro-electro-mechanical inertial test mass suspended adjacent to and non-contiguous with the one or more microresonators, the test mass deflectable under the application of an inertial force;

one or more optical couplers for coupling light transmitted into the optical vibratory gyroscope into and out of a corresponding microresonator; and

one or more detectors for detecting light received from the one or more microresonators by the one or more optical couplers,

wherein a change in a spacing between the test mass and at least one microresonator causes a change in the optical resonance characteristics of that microresonator.

19 . A chip-scale inertial sensor according to claim 18 , wherein the optical vibratory gyroscope further comprises one or more electrodes for counteracting a deflection of the test mass with an electrostatic force; and

wherein the microcontroller is further configured to:

control the electrostatic force of the one or more electrodes to cause the test mass to vibrate at a fixed frequency in a first direction perpendicular to the axis such that the optical vibratory gyroscope can detect the first rate of rotation of the inertial sensor about the axis;

receive an electrical signal from the one or more detectors;

detect a change in the optical resonance characteristics of the one or more microresonators in response to a change in the spacing between the test mass and the one or more microresonators in a second direction perpendicular to the first direction at the fixed frequency; and

determine the first rate of rotation of the inertial sensor about the axis based on the change in optical resonance characteristics of the one or more microresonators.

20 . A chip-scale inertial sensor according to claim 19 , wherein the microcontroller is further configured to control the electrostatic force of the one or more electrodes to recalibrate the optical vibratory gyroscope based on the comparison.

21 . An inertial measurement unit comprising:

a plurality of chip-scale inertial sensors for detecting a rate of rotation about a respective axis, each inertial sensor comprising:

an optical vibratory gyroscope for detecting a first rate of rotation of the inertial sensor about the axis, the optical vibratory gyroscope configured to output a main signal corresponding to the first rate of rotation; and

an optical Sagnac gyroscope for concurrently detecting a second rate of rotation of the inertial sensor about the axis, the optical Sagnac gyroscope configured to output a supplementary signal corresponding to the second rate of rotation; and

a controller configured to, for each inertial sensor:

receive one or more inputs based on the main signal and supplementary signal of the inertial sensor; and

determine, based on the one or more inputs, a corrected first rate of rotation of the inertial sensor about the respective axis.

22 . An inertial measurement unit according to claim 21 , the inertial measurement unit comprising a first chip-scale inertial sensor for detecting rate of rotation of the first inertial sensor in a first axis, a second chip-scale inertial sensor for detecting rate of rotation of the second inertial sensor in a second axis perpendicular to the first axis and a third chip-scale inertial sensor for detecting rate of rotation of the third inertial sensor in a third axis perpendicular to the first axis and second axis,

wherein the controller is further configured to determine a total rate of rotation of the inertial measurement unit based on the corrected first rate of rotation determined for each inertial sensor.

23 . A chip comprising a chip-scale inertial sensor according to claim 22 .

24 . A method performed by a microcontroller for determining a rate of rotation of an inertial sensor about an axis, the method comprising:

receiving one or more inputs based on a main signal output from an optical vibratory gyroscope for detecting a first rate of rotation of the inertial sensor about the axis and a supplementary signal output from an optical Sagnac gyroscope for concurrently detecting a second rate of rotation of the inertial sensor about the axis; and

determining, based on the one or more inputs, a corrected first rate of rotation of the inertial sensor about the axis.

25 . A computer readable medium having instructions stored thereon which, when executed by one or more processors, cause the one or more processors to perform the method of claim 24 .