INTEGRATED PHOTONICS GYROSCOPE WITH COMMON INTENSITY MODULATION

A photonics gyroscope comprises a laser and a common intensity modulation unit that outputs an intensity modulated beam, split into a CCW beam having a first power level and a CW beam having a second power level. A first phase modulator (PA) receives the CCW beam, and a second PA receives the CW beam. A variable optical attenuator (VOA) is coupled to the first or second PA. The CCW beam is coupled into a resonator and the CW beam is coupled into the resonator. A first detector receives the CCW beam and a second detector receives the CW beam from the resonator. A CCW control loop locks the CCW beam, and a CW control loop locks the CW beam, to resonance peaks. The VOA receives a feedback loop signal to aid in balancing power levels between CCW and CW beams to eliminate a rate signal at an intensity modulation frequency.

BACKGROUND

The Kerr effect is a fundamental bias error source in optical gyroscopes, such as the resonator fiber optic gyroscope (RFOG). The Kerr effect is caused by the different phase shifts in the self-phase modulation (SPM) and cross-phase modulation (XPM) phenomenon. The SPM, due to the copropagating clockwise (CW) beam generates less phase shift than the XPM due to the counter-propagating counter-clockwise (CCW) beam in the RFOG. Therefore, if the CW and CCW beams encounter differential power fluctuations, the RFOG will have a non-reciprocal phase shift and cause bias error.

The Kerr bias becomes more significant in integrated photonics gyroscopes. Due to the small scale factor, the integrated photonics gyroscopes have very high finesses to reduce the cavity linewidth and increase the gyroscope sensitivity. Therefore, the intracavity intensity is much higher than the intensity in traditional resonant fiber optical gyroscopes.

Prior methods rely on passive intensity stabilization to reduce the Kerr effect. The CW and CCW intensity need to be controlled to levels of about 1 parts-per-million (ppm) to minimize the power fluctuation between the CW and CCW directions. While such methods are sufficient for traditional fiber optical gyroscopes, integrated photonics gyroscopes have a much higher Kerr effect. Thus, the intensity control needs to reach levels of about 10 parts-per-billion (ppb) for navigation grade performance, which is very challenging for integrated photonics gyroscopes.

SUMMARY

A photonics gyroscope comprises a laser device configured to emit an optical signal; a common intensity modulation unit configured to receive the optical signal from the laser device and produce an intensity modulated optical signal, wherein the intensity modulated optical signal is output from the common intensity modulation unit and split into a counter-clockwise (CCW) intensity modulated optical signal having a first power level, and a clockwise (CW) intensity modulated optical signal having a second power level; a first phase modulator optically coupled to the common intensity modulation unit, the first phase modulator configured to receive the CCW intensity modulated optical signal and produce a CCW phase modulated optical signal; a second phase modulator optically coupled to the common intensity modulation unit, the second phase modulator configured to receive the CW intensity modulated optical signal and produce a CW phase modulated optical signal; a variable optical attenuator optically coupled to the first phase modulator or optically coupled to the second phase modulator, the variable optical attenuator configured to receive the CCW phase modulated optical signal or the CW phase modulated optical signal. An optical resonator is in optical communication with the variable optical attenuator, wherein the CCW phase modulated optical signal is optically coupled into the optical resonator and propagates in a CCW direction in the optical resonator, and the CW phase modulated optical signal is optically coupled into the optical resonator and propagates in a CW direction in the optical resonator. A first optical detector is in optical communication with the optical resonator and is configured to receive the CCW phase modulated optical signal from the optical resonator, and a second optical detector is in optical communication with the optical resonator and is configured to receive the CW phase modulated optical signal from the optical resonator. A CCW control loop is operatively coupled between an output of the first optical detector and an input of the first phase modulator, the CCW control loop configured to lock the CCW phase modulated optical signal to a CCW resonance peak. A CW control loop is operatively coupled between an output of the second optical detector and an input of the second phase modulator, the CW control loop configured to lock the CW phase modulated optical signal to a CW resonance peak. A rate calculation unit is configured to receive digital signals output from the CCW control loop and the CW control loop, the rate calculation unit operative to calculate a rotation rate signal for the photonics gyroscope. The variable optical attenuator is configured to receive a signal from a feedback loop to aid in adjusting the variable optical attenuator to balance the power levels between the CCW and CW phase modulated optical signals to eliminate the rate signal at an intensity modulation frequency. The feedback loop maintains the balance of the power levels between the CCW and CW phase modulated optical signals such that a Kerr effect bias error in the photonics gyroscope is reduced or eliminated.

DETAILED DESCRIPTION

In the following detailed description, embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that other embodiments may be utilized without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense.

An integrated photonics gyroscope, such as an integrated resonator optical gyroscope, which employs common intensity modulation, is described herein. The common intensity modulation introduces a bias error that can only be observed when the clockwise (CW) and counter-clockwise (CCW) beam power in the gyroscope is not balanced. In the present approach, power is balanced between the CW and CCW beams, which reduces or eliminates an error signal due to the intensity modulation and Kerr effect.

The present approach reduces or eliminates the Kerr bias error via an active feedback loop in the gyroscope. While the CW and CCW beams are modulated with the same intensity modulation amplitude, the unbalanced power between the CW and CCW beams will generate a bias error at the modulation frequency due to the Kerr effect. Balancing the power between a CW port a CCW port eliminates the error signal due to intensity modulation and the Kerr effect in the gyroscope.

Further details regarding the present approach are described as follows and with reference to the drawings.

FIG.1is a schematic illustration of an integrated photonics gyroscope100according to one embodiment, which is configured to reduce or eliminate Kerr effect bias sensitivity. The integrated photonics gyroscope100generally includes an optical resonator110, such as an on-chip waveguide ring resonator, which is in optical communication with a laser device112through an optical path having a plurality of optical components. The laser device112is configured to emit a single frequency optical signal, and can be located on the same photonics chip as optical resonator110. Alternatively, laser device112can be on another chip separate from the chip where optical resonator110is located. For example, laser device112can be on a chip that is edge-coupled with the chip having optical resonator110.

An output of laser device112is optically coupled to an input of a common intensity modulation unit114, which is configured to provide an intensity modulation to the optical signal emitted by laser device112. The intensity modulated optical signal output from common intensity modulation unit114is split between a first waveguide116and a second waveguide118. As described further hereafter, the intensity modulated optical signal is split into a counterclockwise (CCW) signal that is fed into first waveguide116, and a clockwise (CW) signal that is fed into second waveguide118. Both the CW and CCW signals have the same intensity modulation amplitude.

The first waveguide116is optically coupled to an input of a first phase modulator (PM)120. An output of first phase modulator120is optically coupled to an input of a first variable optical attenuator (VOA)122. The second waveguide118is optically coupled to an input of a second phase modulator124. An output of second phase modulator124is optically coupled to an input of a second variable optical attenuator126. An output of first variable optical attenuator122is in optical communication with optical resonator110through a first coupling waveguide128, which is optically coupled to optical resonator110at a first coupling region130on a first side of optical resonator110. An output of second variable optical attenuator126is also in optical communication with optical resonator110through first coupling waveguide128at first coupling region130.

A second coupling waveguide134is optically coupled to optical resonator110at a second coupling region132on a second side of optical resonator110. An input of a first optical detector140is in optical communication with optical resonator110through second coupling waveguide134. An input of a second optical detector142is also in optical communication with optical resonator110through second coupling waveguide134.

A CCW control loop150is operatively coupled between an output of first optical detector140and an input of first phase modulator120. The CCW control loop150is configured to lock the CCW signal to a CCW resonance peak. A CW control loop152is operatively coupled between an output of second optical detector142and an input of second phase modulator124. The CW control loop152is configured to lock the CW signal to a CW resonance peak.

A rate calculation unit160is configured to receive digital signals output from CCW control loop150and CW control loop152, and calculate a rotation rate signal for integrated photonics gyroscope100. Each of first variable optical attenuator122and second variable optical attenuator126is configured to receive the rate signal output from rate calculation unit160in a feedback loop. The first variable optical attenuator122and second variable optical attenuator126receive feedback loop signals to aid in their adjustment in order to balance the power levels between the CCW and CW signals, to eliminate the rate signal at an intensity modulation frequency.

During operation of integrated photonics gyroscope100, the single frequency optical signal from laser device112is directed to common intensity modulation unit114, which modulates the amplitude of the optical signal (e.g., about 1% modulation amplitude (power fluctuation)) to produce an intensity modulated optical signal that is output from common intensity modulation unit114. The intensity modulated optical signal is then split into a CCW signal that is fed into first waveguide116, and a CW signal that is fed into second waveguide118. At this point, the CCW signal has a first power level, and the CW signal has a second power level.

The CCW signal in first waveguide116is directed to first phase modulator120, which is operative to provide a phase modulation and serrodyne frequency shift to the CCW signal. A serrodyne phase modulated CCW signal is then directed from first phase modulator120to first variable optical attenuator122. The CW signal in second waveguide118is directed to second phase modulator124, which is operative to provide a phase modulation and serrodyne frequency shift to the CW signal. A serrodyne phase modulated CW signal is then directed from second phase modulator124to second variable optical attenuator122. The variable optical attenuators122,126are adjustable to balance the power of the serrodyne phase modulated CW and CCW signals, such that the power levels of the CW and CCW signals are substantially equal to each other, which removes a bias error signal at the intensity modulation frequency.

The serrodyne phase modulated CW signal is sent to optical resonator110through first coupling waveguide128, which couples the serrodyne phase modulated CW signal into optical resonator110at first coupling region130, such that the CW signal propagates in a CW direction in optical resonator110. The serrodyne phase modulated CCW signal is also sent to optical resonator110through first coupling waveguide128, which couples the serrodyne phase modulated CCW signal into optical resonator110at first coupling region130, such that the CCW signal propagates in a CCW direction in optical resonator110.

The CCW signal circulating in optical resonator110is coupled out of optical resonator110into second coupling waveguide134at second coupling region132. The first optical detector140receives the CCW signal from second coupling waveguide134, and converts the received CCW signal into a corresponding electrical signal, which is sent to CCW control loop150. The CW signal circulating in optical resonator110is coupled out of optical resonator110into second coupling waveguide134at second coupling region132. The second optical detector142receives the CW signal, and converts the received CW signal into a corresponding electrical signal, which is sent CW control loop152.

The CCW control loop150outputs a control signal that is directed to first phase modulator120to aid in providing the serrodyne modulation for the CCW signal. The serrodyne modulation shifts the CCW laser frequency to be on the cavity resonance in the CCW direction. The CW control loop152also outputs a control signal that is directed to second phase modulator124to aid in providing the serrodyne modulation to the CW signal. The serrodyne phase modulation shifts the CW laser frequency to be on the cavity resonance in the CW direction. The CCW control loop150and CW control loop152also output control signals (frequency shift) that are directed to rate calculation unit160for further processing to determine the rotation rate.

The rotation rate has a sine wave at the common intensity modulation frequency when the CW and CCW power levels are not balanced for unevenly distributed Kerr effects. A rate signal is sent from rate calculation unit160to each of variable optical attenuators122and126in a feedback loop to aid in adjusting variable optical attenuators122and126so as to balance the power levels of CW and CCW signals. This is turn reduces or eliminates the sine wave in the rotation rate, which reduces or eliminates an error signal due to the intensity modulation and the Kerr effect in integrated photonics gyroscope100.

The CW and CCW power balance is controlled by the feedback loop to a level such that bias at the modulation frequency is eliminated. Unlike standard alone intensity stabilization systems, the present feedback loop uses bias as an error signal and is not limited by the low frequency environmental noise.

FIG.2is a schematic illustration of an integrated photonics gyroscope200according to one embodiment, which is configured to reduce or eliminate Kerr effect bias sensitivity. The integrated photonics gyroscope200generally includes an optical resonator210, such as an on-chip waveguide ring resonator, which is in optical communication with a laser device212configured to emit a single frequency optical signal. The laser device212can be on-chip with optical resonator210, or alternatively, laser device212can be on another chip separate from the chip where optical resonator210is located.

An output of laser device212is optically coupled to an input of a common intensity modulation unit214, which is configured to provide an intensity modulation to the optical signal emitted by laser device212. The intensity modulated optical signal output from common intensity modulation unit214is split between a first waveguide216and a second waveguide218. The intensity modulated optical signal is split into a CCW signal that is fed into first waveguide216, and a CW signal that is fed into second waveguide218. Both the CW and CCW signals have the same intensity modulation amplitude.

The first waveguide216is optically coupled to an input of a first phase modulator220. An output of first phase modulator220is optically coupled to an input of a variable optical attenuator222. The second waveguide218is optically coupled to an input of a second phase modulator224. An output of variable optical attenuator222is in optical communication with optical resonator210through a first coupling waveguide228, which is optically coupled to optical resonator210at a first coupling region230on a first side of optical resonator210. An output of second phase modulator224is also in optical communication with optical resonator210through first coupling waveguide228at first coupling region230.

In an alternative embodiment, variable optical attenuator222can be moved to be coupled between an output of second phase modulator224and optical resonator210, such that the CW signal would be directed from second phase modulator224into the variable optical attenuator before being sent to optical resonator210.

A second coupling waveguide234is optically coupled to optical resonator210at a second coupling region232on a second side of optical resonator210. An input of a first optical detector240is in optical communication with optical resonator210through second coupling waveguide234. An input of a second optical detector242is also in optical communication with optical resonator210through second coupling waveguide234.

A CCW control loop250is operatively coupled between an output of first optical detector240and an input of first phase modulator220. A CW control loop252is operatively coupled between an output of second optical detector242and an input of second phase modulator224. A rate calculation unit260is configured to receive digital signals output from CCW control loop250and CW control loop252, and calculate a rotation rate signal for integrated photonics gyroscope200. The variable optical attenuator222is configured to receive the rate signal output from rate calculation unit260in a feedback loop.

During operation of integrated photonics gyroscope200, the single frequency optical signal from laser device212is directed to common intensity modulation unit214, which modulates the amplitude of the optical signal (e.g., about 1% modulation amplitude) to produce an intensity modulated optical signal that is output from common intensity modulation unit214. The intensity modulated optical signal is then split into a CCW signal that is fed into first waveguide216, and a CW signal that is fed into second waveguide218. At this point, the CCW signal has a first power level, and the CW signal has a second power level.

The CCW signal in first waveguide216is directed to first phase modulator220, which is operative to provide a phase modulation and serrodyne frequency shift to the CCW signal. A serrodyne phase modulated CCW signal is then directed from first phase modulator220to variable optical attenuator222. The CW signal in second waveguide218is directed to second phase modulator224, which is operative to provide a phase modulation and serrodyne frequency shift to the CW signal. The second phase modulator224outputs a serrodyne phase modulated CW signal The variable optical attenuator222is adjustable to balance the power of the serrodyne phase modulated CW and CCW signals, such that the power levels of the CW and CCW signals are substantially equal to each other, which removes a bias error signal at the intensity modulation frequency.

The serrodyne phase modulated CW signal output from second phase modulator224is directed to optical resonator210through first coupling waveguide228, which couples the serrodyne phase modulated CW signal into optical resonator210at first coupling region230. The CW signal then propagates in a CW direction in optical resonator210. The serrodyne phase modulated CCW signal is sent from variable optical attenuator222to optical resonator210through first coupling waveguide228, which couples the serrodyne phase modulated CCW signal into optical resonator210at first coupling region230. The CCW signal then propagates in a CCW direction in optical resonator210.

The CCW signal circulating in optical resonator210is coupled out of optical resonator210into second coupling waveguide234at second coupling region232. The first optical detector240receives the CCW signal from second coupling waveguide234, and converts the received CCW signal into a corresponding electrical signal, which is sent to CCW control loop250. The CW signal circulating in optical resonator210is coupled out of optical resonator210into second coupling waveguide234at second coupling region232. The second optical detector242receives the CW signal, and converts the received CW signal into a corresponding electrical signal, which is sent CW control loop252.

The CCW control loop250outputs a control signal that is directed to first phase modulator220to aid in providing the serrodyne phase modulation for the CCW signal. The CW control loop252also outputs a control signal that is directed to second phase modulator224to aid in providing the serrodyne phase modulation to the CW signal. The CCW control loop250and CW control loop252also output control signals that are directed to rate calculation unit260for further processing to determine the rotation rate.

The rotation rate has a sine wave at the common intensity modulation frequency when the CW and CCW power levels are not balanced for unevenly distributed Kerr effects. A rate signal is sent from rate calculation unit260to variable optical attenuator222in a feedback loop to aid in adjusting variable optical attenuator222so as to balance the power levels of the CW and CCW signals. This in turn reduces or eliminates the sine wave in the rotation rate, which reduces or eliminates an error signal due to the intensity modulation and the Kerr effect in integrated photonics gyroscope200.

The photonics gyroscopes described herein can be fabricated by utilizing one of several well-established integrated photonics fabrication processes. In these fabrication processes, photonic integrated circuits can be fabricated with a wafer-scale technology involving lithography, on substrates (i.e., chips) of silicon, silica, or a nonlinear crystal material such as lithium niobate.

In other implementations, the photonics gyroscopes described herein can be fabricated by using an ultra-low loss silicon nitride waveguide platform. The silicon nitride waveguide platform allows low-loss waveguides with a small bend radius to made, along with various types of photonic components.

FIG.3is flow diagram of a method300for reducing or eliminating a Kerr effect bias error in a photonics gyroscope, according to an exemplary implementation. The method300comprises adding a common intensity modulation to an optical signal emitted from a laser device to produce an intensity modulated optical signal (block310); and splitting the intensity modulated optical signal into a CCW intensity modulated optical signal having a first power level, and a CW intensity modulated optical signal having a second power level (block312). The common intensity modulation is used by method300to determine the difference between the first and second power levels. The method300further includes sending the CCW intensity modulated optical signal to a first phase modulator, which produces a CCW phase modulated and serrodyne frequency shifted optical signal (block314); sending the CW intensity modulated optical signal to a second phase modulator, which produces a CW phase modulated and serrodyne frequency shifted optical signal (block316); and passing the CCW phase modulated and serrodyne frequency shifted optical signal, or the CW phase modulated and serrodyne frequency shifted optical signal, through at least one variable optical attenuator (block318). For example, a variable optical attenuator can be optically coupled to the first phase modulator or the second phase modulator. Alternatively, a first variable optical attenuator can be optically coupled to the first phase modulator, and a second variable optical attenuator can be optically coupled to a second phase modulator.

The method300then introduces the CCW phase modulated and serrodyne frequency shifted optical signal into an optical resonator such that the CCW phase modulated and serrodyne frequency shifted optical signal propagates in a CCW direction in the optical resonator (block320); and introduces the CW phase modulated and serrodyne frequency shifted optical signal into the optical resonator such that the CW phase modulated and serrodyne frequency shifted optical signal propagates in a CW direction in the optical resonator (block322). The method300detects modulated rate signals output from the optical resonator at a frequency of the common intensity modulation (block324); and calculates a rotation rate signal based on locking control loops (block326). The method300adjusts the variable optical attenuator to balance the power levels between the CCW and CW phase modulated and serrodyne frequency shifted optical signals based on the rotation rate signal at the intensity modulation frequency (block328); and maintains the balance of the power levels between the CCW and CW phase modulated and serrodyne frequency shifted optical signals, such that a Kerr effect bias error is reduced or eliminated (block330).

The intensity adjusting signal can be sent to the variable optical attenuator in a feedback loop to aid in adjusting the variable optical attenuator to balance the power levels between the CCW and CW beams. The feedback loop also aids in maintaining the balance of the power levels between the CCW and CW beams, such that the power levels are substantially equal to each other.

FIG.4is a graphical representation of a serrodyne phase modulation that can be applied in the operation of the present photonics gyroscopes. As shown inFIG.4, the serrodyne phase modulation produces a sawtooth wave form of the phase with respect to time. This allows for tuning of the laser frequency, by shifting the frequency to match a resonant peak of the optical resonator, and for phase tuning of the CW and CCW beams in the photonics gyroscope. In addition, a sine wave phase modulation can be applied to the phase modulators and is used for resonance peak detection.

Example Embodiments

Example 1 includes a photonics gyroscope, comprising: a laser device configured to emit an optical signal; a common intensity modulation unit configured to receive the optical signal from the laser device and produce an intensity modulated optical signal, wherein the intensity modulated optical signal is output from the common intensity modulation unit and split into a counter-clockwise (CCW) intensity modulated optical signal having a first power level, and a clockwise (CW) intensity modulated optical signal having a second power level; a first phase modulator optically coupled to the common intensity modulation unit, the first phase modulator configured to receive the CCW intensity modulated optical signal and produce a CCW phase modulated optical signal; a second phase modulator optically coupled to the common intensity modulation unit, the second phase modulator configured to receive the CW intensity modulated optical signal and produce a CW phase modulated optical signal; a first variable optical attenuator optically coupled to the first phase modulator, or optically coupled to the second phase modulator, the first variable optical attenuator configured to receive the CCW phase modulated optical signal or the CW phase modulated optical signal; an optical resonator in optical communication with the first variable optical attenuator, wherein the CCW phase modulated optical signal is optically coupled into the optical resonator and propagates in a CCW direction in the optical resonator, and the CW phase modulated optical signal is optically coupled into the optical resonator and propagates in a CW direction in the optical resonator; a first optical detector in optical communication with the optical resonator, and configured to receive the CCW phase modulated optical signal from the optical resonator; a second optical detector in optical communication with the optical resonator and configured to receive the CW phase modulated optical signal from the optical resonator; a CCW control loop operatively coupled between an output of the first optical detector and an input of the first phase modulator, the CCW control loop configured to lock the CCW phase modulated optical signal to a CCW resonance peak; a CW control loop operatively coupled between an output of the second optical detector and an input of the second phase modulator, the CW control loop configured to lock the CW phase modulated optical signal to a CW resonance peak; and a rate calculation unit configured to receive digital signals output from the CCW control loop and the CW control loop, the rate calculation unit operative to calculate a rotation rate signal for the photonics gyroscope; wherein the first variable optical attenuator is configured to receive a signal from a feedback loop to aid in adjusting the first variable optical attenuator to balance the power levels between the CCW and CW phase modulated optical signals to eliminate the rate signal at an intensity modulation frequency; wherein the feedback loop maintains the balance of the power levels between the CCW and CW phase modulated optical signals such that a Kerr effect bias error in the photonics gyroscope is reduced or eliminated.

Example 2 includes the photonics gyroscope of Example 1, wherein the laser device is configured to emit the optical signal at a single frequency.

Example 3 includes the photonics gyroscope of any of Examples 1-2, wherein the intensity modulated optical signal from the common intensity modulation unit is split between a first input waveguide and a second input waveguide, such that the CCW intensity modulated optical signal is fed into the first input waveguide, and the CW intensity modulated optical signal is fed into the second input waveguide.

Example 4 includes the photonics gyroscope of Example 3, wherein the first input waveguide is optically coupled to an input of the first phase modulator, and the second input waveguide is optically coupled to an input of the second phase modulator.

Example 5 includes the photonics gyroscope of any of Examples 1-4, wherein the first phase modulator is configured to provide a serrodyne phase modulation to the CCW intensity modulated optical signal, and the second phase modulator is configured to provide a serrodyne phase modulation to the CW intensity modulated optical signal.

Example 6 includes the photonics gyroscope of Example 5, wherein an output of the first variable optical attenuator is in optical communication with the optical resonator through a first coupling waveguide, which is optically coupled to the optical resonator at an first coupling region on a first side of the optical resonator.

Example 7 includes the photonics gyroscope of Example 6, wherein an output of the second phase modulator is in optical communication with the optical resonator through the first coupling waveguide at the first coupling region.

Example 8 includes the photonics gyroscope of Example 7, wherein a second coupling waveguide is optically coupled to the optical resonator at a second coupling region on a second side of the optical resonator.

Example 9 includes the photonics gyroscope of Example 8, wherein an input of the first optical detector is in optical communication with the optical resonator through the second coupling waveguide, and an input of the second optical detector is in optical communication with the optical resonator through the second coupling waveguide.

Example 10 includes the photonics gyroscope of Example 9, wherein: the CCW phase modulated optical signal is coupled out of the optical resonator into the second coupling waveguide at the second coupling region, the first optical detector configured to receive the CCW phase modulated optical signal from the second coupling waveguide and convert the received signal into a corresponding electrical signal, which is sent to the CCW control loop; and the CW phase modulated optical signal is coupled out of the optical resonator into the second coupling waveguide at the second coupling region, the second optical detector configured to receive the CW phase modulated optical signal from the second coupling waveguide and convert the received signal into a corresponding electrical signal, which is sent to the CW control loop.

Example 11 includes the photonics gyroscope of Example 10, wherein: the CCW control loop is configured to output a control signal that is directed to the first phase modulator to aid in providing the serrodyne phase modulation for the CCW phase modulated optical signal; and the CW control loop is configured to output a control signal that is directed to the second phase modulator to aid in providing the serrodyne phase modulation to the CW phase modulated optical signal.

Example 12 includes the photonics gyroscope of any of Examples 10-11, wherein the CCW control loop and the CW control loop are configured to output control signals that are directed to the rate calculation unit for further processing to aid in the calculation of the rotation rate signal.

Example 13 includes the photonics gyroscope of any of Examples 1-12, further comprising a second variable optical attenuator optically coupled to the second phase modulator, wherein the first variable optical attenuator is optically coupled to the first phase modulator.

Example 14 includes the photonics gyroscope of Example 13, wherein the first variable optical attenuator is configured to receive the CCW phase modulated optical signal, and the second variable optical attenuator is configured to receive the CW phase modulated optical signal, wherein an output of the second variable optical attenuator is in optical communication with the optical resonator.

Example 15 includes the photonics gyroscope of any of Examples 1-14, wherein the common intensity modulation unit, the phase modulators, the first and second optical detectors, the variable optical attenuator, the control loops, and the rate calculation unit, are integrated on a single photonics chip with the optical resonator.

Example 16 includes the photonics gyroscope of Example 15, wherein the laser device is located on the photonics chip with the optical resonator.

Example 17 includes the photonics gyroscope of Example 15, wherein the laser device is located on a different chip than the photonics chip with the optical resonator.

Example 18 includes a method comprising: providing a photonics gyroscope comprising a laser device configured to emit an optical signal, and an optical resonator in optical communication with the laser device through an optical path having a plurality of optical components; adding a common intensity modulation to the optical signal emitted from the laser device to produce an intensity modulated optical signal; splitting the intensity modulated optical signal into a counter-clockwise (CCW) intensity modulated optical signal having a first power level, and a clockwise (CW) intensity modulated optical signal having a second power level; sending the CCW intensity modulated optical signal to a first phase modulator, which produces a CCW serrodyne phase modulated optical signal; sending the CW intensity modulated optical signal to a second phase modulator, which produces a CW serrodyne phase modulated optical signal; providing at least one variable optical attenuator optically coupled to the first phase modulator, optically coupled to the second phase modulator, or optically coupled to both the first and second phase modulators, the at least one variable optical attenuator configured to receive the CCW serrodyne phase modulated optical signal or the CW serrodyne phase modulated optical signal; introducing the CCW serrodyne phase modulated optical signal into the optical resonator such that the CCW serrodyne phase modulated optical signal propagates in a CCW direction in the optical resonator; introducing the CW serrodyne phase modulated optical signal into the optical resonator such that the CW serrodyne phase modulated optical signal propagates in a CW direction in the optical resonator; detecting modulated rate signals that are output from the optical resonator at a frequency of the common intensity modulation; calculating a rotation rate signal for the photonics gyroscope based on locking control loops; adjusting the at least one variable optical attenuator to balance the power levels between the CCW and CW serrodyne phase modulated optical signals based on the rotation rate signal; and maintaining the balance of the power levels between the CCW and CW serrodyne phase modulated optical signals, such that a Kerr effect bias error is reduced or eliminated.

Example 19 includes the method of Example 18, wherein the balance of the power levels between the CCW and CW serrodyne phase modulated optical signals is maintained such that the power levels are substantially equal to each other.

Example 20 includes the method of any of Examples 18-19, wherein: the rotation rate signal is sent to the at least one variable optical attenuator in a feedback loop to aid in adjusting the at least one variable optical attenuator to balance the power levels between the CCW and CW serrodyne phase modulated optical signals; and the feedback loop aids in maintaining the balance of the power levels between the CCW and CW serrodyne phase modulated optical signals.

From the foregoing, it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the scope of the disclosure. Thus, the described embodiments are to be considered in all respects only as illustrative and not restrictive. In addition, all changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.