Optical gyroscope with broadband comb interrogation

Abstract

Embodiments utilize an optical frequency comb generator coupled to an optical resonator of an optical gyroscope. The optical frequency comb generator generates an optical frequency comb having frequency peaks, each corresponding to a respective resonant frequency of the optical resonator. A control servo may be coupled to the optical frequency comb generator and control the optical frequency comb output of the optical frequency comb generator. During this process, the optical frequency comb remains tuned to the resonant frequency of the optical resonator during gyroscope operation.

Description

Background Art

[0001] Resonator fiber gyroscopes (RFOGs) typically utilize a narrow linewidth laser source to generate the optical signal necessary to determine rotation rate measurements. RFOGs typically operate by propagating an optical signal generated by a laser through an optical resonator in a counter-propagating direction. As the RFOG experiences rotation about its sensing axis, the laser directed into the optical resonator shifts in frequency to track the resonance of the resonator, which shifts in frequency due to the Sagnac effect; this frequency shift between the two output signals from the resonator can then be used to determine the rate of rotation experienced by the RFOG.

[0002] However, signals generated by narrow-linewidth lasers are more susceptible to the optical Kerr effect, a nonlinear optical phenomenon that modifies the refractive index of a waveguide depending on the intensity of the optical signal. Broadband light sources (i.e., wide-linewidth sources that produce optical signals with a broadband frequency range) can reduce the optical Kerr effect present in RFOGs, but also introduce additional problems: the broadband nature of the light source and the narrow resonance peak of the optical resonator can cause the output intensity of the optical signal to be significantly reduced after propagating through the optical resonator. As a result, the output signal may be too weak to be detected and processed by the circuit system, making it impossible to determine the rotation rate. Summary of the invention

[0003] The details of one or more embodiments are set forth in the following description. Features shown or described in conjunction with one exemplary embodiment may be combined with features of other embodiments. Thus, any of the various embodiments described herein may be combined to provide additional embodiments. If necessary, various aspects of the embodiments may be modified to adopt concepts from various patents, applications, and publications as identified herein to provide yet additional embodiments.

[0004] In one example, an optical gyroscope is disclosed. The optical gyroscope includes an optical resonator and an optical frequency comb generator coupled to the optical resonator. The optical frequency comb generator is configured to generate an optical frequency comb. The optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of the optical resonator. The optical resonator is configured to receive an optical signal from the optical frequency comb. The optical signal propagates in the optical resonator along a first direction. The optical gyroscope includes a reflective element coupled to the optical resonator. The reflective element is configured to reflect the optical signal after propagation along the first direction. The optical resonator is configured to receive the reflected optical signal. The reflected optical signal propagates in the optical resonator along a second direction opposite to the first direction. The optical gyroscope includes at least one processor coupled to the optical resonator. The at least one processor is configured to determine an intensity corresponding to the reflected optical signal after propagation along the second direction. The at least one processor is configured to determine a rotation rate based on the intensity corresponding to the reflected optical signal.

[0005] In another example, a method for operating an optical gyroscope is disclosed. The method includes generating an optical frequency comb from an optical frequency comb generator. The optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of an optical resonator of the optical gyroscope. The method includes coupling an optical signal from the optical frequency comb into the optical resonator. The optical signal propagates in the optical resonator along a first direction. The method includes reflecting the optical signal after propagating in the optical resonator along the first direction. The method includes coupling the reflected optical signal into the optical resonator. The reflected optical signal propagates in the optical resonator along a second direction opposite to the first direction. The method includes determining a change in intensity based on the optical signal and the reflected optical signal. The method includes determining a rotation rate based on the change in intensity.

[0006] In yet another example, a program product is disclosed. The program product includes a non-transitory processor-readable medium on which program instructions configured to be executed by at least one processor are embodied. The at least one processor is configured to receive a signal corresponding to an optical signal after propagating in an optical resonator of an optical gyroscope along a first direction by executing the program instructions. The at least one processor is configured to determine an intensity corresponding to the signal. The at least one processor is configured to determine a repetition rate of an optical frequency comb based on the intensity corresponding to the signal. The at least one processor is configured to send at least one control signal to an optical frequency comb generator. The at least one control signal is configured to modulate an optical frequency comb generated by the optical frequency comb generator with a repetition rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered to be limiting of the scope of the invention, the exemplary embodiments will be described with additional specificity and detail through use of the drawings, as briefly described below and as further described in the Detailed Description.

[0008] Figure 1 A block diagram of an exemplary optical gyroscope as described in one or more embodiments is depicted.

[0009] FIG. 2A to FIG. 2B Depicted are graphical representations of resonant peak shifts of optical signals generated with a broadband source and an optical frequency comb, respectively, as described in one or more embodiments.

[0010] Figure 3 A block diagram of an exemplary optical gyroscope as described in one or more embodiments is depicted.

[0011] Figure 4 A flow chart of an exemplary method for operating an optical gyroscope as described in one or more embodiments is depicted.

[0012] FIG. 5A to FIG. 5B Depicted is a flow chart of an exemplary method for controlling an optical frequency comb generator as described in one or more embodiments.

[0013] According to common practice, the various features described are not necessarily drawn to scale, emphasis instead being placed on specific features relevant to the exemplary embodiments. DETAILED DESCRIPTION

[0014] In the following detailed description, reference is made to the accompanying drawings which form a part thereof and in which specific illustrative embodiments are shown by way of illustration. However, it should be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the methods presented in the drawings and the specification should not be interpreted as limiting the order in which the various steps may be performed. Therefore, the following detailed description should not be considered to have a limiting meaning.

[0015] Figure 1 A block diagram of an exemplary optical gyroscope 100 for realizing the advantages of the present disclosure is depicted. Figure 1 The optical gyroscope 100 in the illustrated embodiment is implemented as a resonator fiber gyroscope (RFOG), wherein a fiber resonator 112 is used to resonate an optical signal propagating in the optical gyroscope. Other optical ring resonators may be used as sensing resonators. The components of the optical gyroscope 100 may be optically coupled via suitable light-guiding devices such as waveguides, mirrors, beam splitters, etc. The components of the optical gyroscope 100 are typically connected by optical waveguides for teaching purposes, but free-space optics may also be used where applicable.

[0016] exist Figure 1 In some embodiments, the optical gyroscope includes a broadband light source 102 coupled to an electro-optic modulator 106. In some embodiments, such as Figure 1 In the embodiment shown, the laser source 102 is split into two waveguides. One is coupled to a phase modulator 104 for Pound-Drever-Hall (PDH) modulation. The other is coupled to an electro-optic modulator 106 for generating an optical frequency comb. The laser source 102 is configured to generate a low phase noise laser output.

[0017] The electro-optic modulator 106 acts as an optical comb generator and is configured to generate an optical frequency comb based on the laser signal. Although the characteristics of broadband signals are generally known to those of ordinary skill in the art, as an example, the broadband frequency range of the optical signal may include multiple resonant frequency peaks corresponding to the resonant modes of the optical resonator 112 (see Figure 2A ). In some embodiments, the functions of the phase modulator 104 and the electro-optic modulator 106 are performed by an integrated modulator unit. The phase modulator 104 is configured to modulate the phase of the laser signal in conjunction with the Pound-Drever-Hall circuit 130, as described subsequently. The electro-optic modulator 106 then uses the applied electric field to generate sidebands of different frequencies, where each signal has an intensity peak at a different frequency. In this way, the electro-optic modulator 106 generates an optical frequency comb from a broadband source, where each signal represents a "tooth" in the comb.

[0018] A portion of the optical signal including the optical frequency comb is provided to a detector 108 (e.g., a photodiode). The detector 108 is configured to convert the optical signal into a corresponding electrical signal based on the intensity of the optical signal and provide the electrical signal to a relative intensity noise (RIN) servo 140. The RIN servo 140 includes a circuit system configured to adjust the intensity level of the optical frequency comb generated by the modulator 106. For example, the RIN servo 140 generates a feedback signal to the laser source 102 that adjusts the intensity of the broadband optical signal output from the laser source 102. When the intensity is above or below a set value, the RIN servo 140 controls the output of the laser source 102 to compensate for the change in the output intensity detected from the detector 108 so that the output intensity remains at a constant level. In this process, the RIN servo 140 acts as a feedback servo to adjust the intensity of the optical signal.

[0019] The portion of the optical signal not provided to the detector 108 propagates to the optical resonator 112 and is coupled to the optical resonator 112 by a suitable coupler ( Figure 1 When optical signals enter the optical resonator 112, they propagate around the resonator coil in a first direction. Figure 1In the illustrated embodiment, the optical signal propagates through the optical resonator 112 multiple times in a counterclockwise (CCW) direction. The optical resonator 112 is configured to pass an optical signal at a frequency at a resonant frequency mode of the resonator. Typically, the optical resonator 112 acts as an optical filter that passes light overlapping the resonant peak and blocks light that does not overlap the resonant peak. The frequency components of the optical signal wave from the laser that match the resonant frequency mode of the optical resonator 112 will resonate within the resonator and transmit through the resonator. In contrast, the frequency components of the optical signal that do not match the resonant frequency mode of the optical resonator 112 are reflected at the input coupler. Some broadband sources such as amplified spontaneous emission (ASE) sources have a wide range of frequency components, most of which do not correspond to the resonant mode of the resonator 112 and therefore will be reflected and then lost. Although the optical signal generated by a narrow linewidth laser can be tuned to match the resonant frequency of the optical resonator 112, such signals are more susceptible to the optical Kerr effect, resulting in rotation rate errors, which are called bias instability.

[0020] In some embodiments, the optical resonator 112 is configured as a "zero-dispersion" cavity, i.e., a resonator that compensates for material dispersion effects. For example, the waveguide dispersion effects of the optical resonator 112 can be tuned by its core-cladding geometry to shift the dispersion effects of the resonator outside its bandwidth, i.e., outside the frequency range of interest. Doing so can reduce power losses due to free spectral range (FSR) mismatch caused by material dispersion in the resonator.

[0021] A portion of the signal is reflected by the optical resonator 112 and received by the detector 110. The detector 110 is configured to convert the CCW optical signal into an electrical signal based on the power of the optical signal and provide the electrical signal to the Pound-Drever-Hall circuit 130. The PDH circuit 130 is configured to generate one or more control signals to the laser source 102. Specifically, the PDH circuit 130 is configured to generate an error signal that locks the output of the laser source 102 to the resonant frequency of the optical resonator 112. The carrier frequency signal undergoes PDH phase modulation from the phase modulator 104. When the gyroscope undergoes rotation, the resonant frequency of the optical resonator 112 will change. In order to compensate for the change in resonance, the PDH circuit 130 controls the frequency of the laser source 102 via the error signal so that the frequency of the laser source 102 follows the change in the resonant frequency of the optical resonator 112. For example, as Figure 2BAs shown, one of the teeth 210 (the carrier) is locked to a frequency corresponding to one of the CCW signal peaks 204 due to the error signal generated by the PDH circuit 130. If the CCW resonant frequency changes, the PDH error signal from the PDH circuit 130 detects the change in resonant frequency and forces the carrier frequency of the laser source 102 to adjust accordingly to maintain frequency lock.

[0022] After propagating in the optical resonator 112, the optical signal is coupled out of the resonator (e.g., by an optical coupler) and provided to a detector 114 or a phase modulator 116. The phase modulator 116 is configured to modulate the phase of the optical signal and generate a phase-modulated optical signal. The type of phase modulation may be controlled by the function generator 120. For example, the phase modulator 116 may apply a sinusoidal modulation signal to the received optical signal and generate a phase-modulated optical signal having a phase shift according to the sinusoidal modulation signal to improve the signal-to-noise ratio of the second pass through the optical resonator 112. Other types of modulation signals may be used.

[0023] The optical signal is reflected at the reflective element 117 and begins to propagate in the opposite direction toward the optical resonator 112. Figure 1 100, but in some embodiments, the reflective element may be a Bragg grating configured to reflect a broad spectrum of light. Most of the phase modulated optical signal is coupled back into the optical resonator 112 (may be close to 100%), but a small portion may not enter the resonator but propagate to the anti-reflection end 115. The anti-reflection end 115 is configured to prevent back reflection of the phase modulated optical signal, which, if allowed to reflect back into the optical gyroscope 100, may cause optical interference errors with the signal entering / leaving the resonator.

[0024] Upon reaching the optical resonator 112, the phase-modulated optical signal is coupled into the resonator and propagates in the resonator in a second direction opposite to the first direction. Figure 1 In the example shown, the phase modulated optical signal propagates in the optical resonator 112 in a clockwise (CW) direction. Due to the rotation, the resonant frequency of the optical resonator 112 in the CW mode may be offset from the resonant frequency in the CCW mode (see FIG. 2A to FIG. 2B ).

[0025] To perform rotation rate processing, the phase modulated optical signal is coupled out of the optical resonator 112 and detected by a detector 118. The detector 118 is configured to convert the phase modulated optical signal into an electrical format based on the intensity of the signal incident on the detector and provide the phase modulated signal to a mixer 119. In addition, a function generator 120 is configured to provide a demodulation signal to the mixer 119. The mixer 119 is configured to demodulate the phase modulated signal from the detector 118 based on the demodulation signal provided by the function generator 120. The demodulated signal is then provided to a processor 122 for determining the rotation rate. When the optical gyroscope 100 undergoes rotation, the resonant frequency of the optical resonator 112 shifts to a different frequency compared to the resonant frequency when the gyroscope is not experiencing rotation. Therefore, the intensity of the demodulated signal corresponds to the Sagnac frequency shift between the CW and CCW directions. Specifically, during rotation, there will be an intensity variation due to a frequency offset between the optical signal propagating through the resonator 112 in a first direction and the phase modulated optical signal propagating back through the resonator 112 in a second direction. The processor 122 is configured to determine the frequency offset between the CW and CCW signals from the intensity variation of the output provided from the mixer 119, and therefore determine the rate of rotation.

[0026] When a portion of the CCW optical signal is provided to the phase modulator 116 for modulation and ultimately propagation back into the optical resonator 112, another portion of the signal is detected at the detector 114. The detector 114 is coupled to the control servo 150 and is configured to generate an electrical signal proportional to the intensity of the optical signal incident on the detector. The control servo 150 includes control and processing circuitry and is configured to control the repetition rate F of the optical frequency comb generated by the electro-optical modulator 106. rep Feedback control is performed. The repetition rate represents the difference between consecutive resonant frequency peaks ("teeth") of the optical frequency comb, and is typically equally spaced in the frequency domain. As the repetition rate changes, the control servo device 150 controls the modulation applied by the electro-optic modulator 106, for example by sending a control signal that configures the modulator 106 to adjust the modulation frequency applied to the laser signal from the laser source 102. In the process, the electro-optic modulator 106 can adjust the teeth of the optical frequency comb.

[0027] FIG. 2A to FIG. 2B Illustration depicting the resonance peak shift between CW and CCW directions due to rotation and alignment with the optical frequency comb. Figure 2A plots the Sagnac frequency shift between the CW and CCW directions due to rotation, and Figure 2B Depicted is the alignment of an optical frequency comb with the resonant frequency modes of an optical resonator. FIG. 2A to FIG. 2BThe vertical axis in represents the intensity output of a signal in the optical gyroscope according to the signal frequency (horizontal axis). FIG. 2A to FIG. 2B They are shown for pedagogical purposes and are not necessarily drawn to scale.

[0028] refer to Figure 2A , the broadband laser signal 202 from the laser source 102 has a wide frequency range compared to the output signal from a narrow linewidth laser. The wide frequency range or spectrum of the broadband laser signal 202 may contain many resonant frequency modes of the optical resonator 112. In addition, the resonance peaks 204 and 206 correspond to signals propagating in the opposite direction in the optical resonator 112. For example, in Figure 1 In the configuration shown, signal peak 204 represents the transmission peak of the CCW optical signal frequency component that propagates first in the optical resonator 112, and signal peak 206 represents the transmission peak of the CW optical signal frequency component (reflected optical signal) that propagates subsequently in the optical resonator 112. Figure 1 As shown, the light first passes in the CCW direction, then is reflected and emitted back into the resonator 112 in the CW direction. Due to the frequency shift during rotation, the transmitted intensity of the CW signal will be less than the transmitted intensity of the CCW signal. The intensity difference can be expressed as Figure 2A This is represented as shown, where the intensity of the CCW signal is at level P1 and the power of the CW signal is at level P2, where the intensity difference is given by ΔP=P1−P2.

[0029] As previously described, the optical resonator 112 reflects light at frequencies other than the resonant frequency of the resonator mode, allowing only frequency components corresponding to the resonant frequency of the resonator to resonate. Each set of signal peaks corresponds to a different resonant mode of the optical resonator 112. When the gyroscope undergoes rotation, the resonant modes between the CW and CCW directions will shift in frequency relative to each other, thereby producing Figure 2A The two distinct signal peaks 204 and 206 of a given set are shown in FIG. Figure 2A 100 , but due to this frequency shift, the intensity of the returned phase modulated optical signal (e.g., CW signal) is reduced because the frequency component of the CW signal is no longer at the center of resonance relative to the CW resonance. Ultimately, utilizing the broadband spectrum 202 in the optical resonator 112 causes a significant portion of the input optical power to be lost via destructive interference even before the CW optical signal returns to the resonator 112, resulting in low optical efficiency. Additionally, due to shot noise limitations, the power loss may affect the accuracy of the rotation rate measurement determined by the optical gyroscope 100. Therefore, while a broadband source may provide advantages in RFOG rate sensing, it introduces the disadvantage of potential power loss in the resonator, and therefore a broadband source alone may not be suitable for intensity change detection.

[0030] Reference now Figure 2B , the present disclosure can compensate for the disadvantages of using broadband signals in resonator gyroscope operation while maintaining its advantages. The optical gyroscope 100 is configured to lock the output of the light source to the resonant frequency mode of the optical resonator 112, even when the optical gyroscope undergoes rotation about its sensing axis. Instead of providing the broadband signal directly through the optical resonator 112, an EO modulator (106) is used to generate an optical frequency comb 208 that is provided to the optical resonator 112. As shown in FIG. Figure 2B As shown, each tooth 210 of the optical frequency comb 208 is locked to a resonant frequency mode of the optical resonator 112. For example, in one embodiment, each tooth 210 is locked to the center frequency of the resonant peak 204 corresponding to a CCW signal in the optical resonator 112. This reduces the power loss associated with the light loss due to the destructive interference of the CCW signal, makes it easy to detect the intensity difference between the CCW and CW directions, and improves the optical power efficiency of the gyroscope. In addition, the angular random walk (ARW) of the optical gyroscope can be reduced by a square root of N, where N is the number of resonant peaks utilized.

[0031] In addition, the optical frequency comb 208 is controlled by the control servo 150 to maintain locking to the optical resonator 112. For example, during operation, the frequency difference between two consecutive CCW peaks may change, and the peaks 204 may be further apart. To compensate for the frequency spacing shift, the control servo 150 adjusts the repetition rate (the frequency spacing between two consecutive teeth 210) of the optical frequency comb 208 based on the intensity of the optical signal (e.g., CCW signal) leaving the optical resonator 112 incident on the detector 114. In response to the change in intensity, the control servo 150 is configured to adjust the repetition rate of the optical frequency comb 208 so that the OFC teeth remain locked to the signal peaks 204 of the CCW signal. In an example, when the frequency spacing between the signal peaks 204 increases so that each signal peak 204 is spaced farther apart, the control servo 150 configures the electro-optic modulator 106 to reduce the repetition rate (i.e., increase the frequency spacing of the teeth 210) to match the corresponding frequency spacing between the peaks 204. Similarly, as the frequency spacing between signal peaks 204 decreases so that each signal peak 204 is spaced closer together, control servo 150 configures electro-optic modulator 106 to increase the repetition rate (ie, decrease the frequency spacing of teeth 210). 载波 To achieve locking, the electro-optic modulator 106 locks the teeth 210 of the optical frequency comb 208 based on the error signal generated by the PDH circuit 130. In this way, the optical frequency comb 208 can be locked to the first passing resonant mode (e.g., CCW resonance peak) of the optical resonator 112 and maintain the lock even during rotation.

[0032] Figure 3A block diagram of an exemplary optical gyroscope 300 is depicted. Figure 3 The optical gyroscope 300 depicted in FIG. Figure 1 , except as described subsequently, its function is substantially similar. Specifically, the optical gyroscope 300 includes an optical frequency comb generator 306 coupled to the control servo device 150 and the optical resonator 112. The optical frequency comb generator 306 is configured to generate a frequency similar to that described with respect to Figure 1 2 . In some embodiments, the optical frequency comb generator is integrated into a single unit of the optical gyroscope 300. For example, the optical frequency comb generator 306 can be a Kerr comb generator. The optical frequency comb generator 306 can also include a laser source that is used as a pump source to generate the optical frequency comb. The control servo 150 adjusts the repetition rate of the optical frequency comb generated by the optical frequency comb generator 306 based on the strength of the signal detected at the detector 114. The PDH circuit 130 adjusts the carrier envelope frequency (f ceo ) to lock the teeth of the optical frequency comb generator 306 to the resonance peaks of the optical resonator 112. In addition, the RIN servo device 140 is configured to adjust the intensity of the optical frequency comb generated by the optical frequency comb generator 306 based on the intensity of the signal detected at the detector 108.

[0033] Figure 4 A flow chart of an exemplary method for operating an optical gyroscope is depicted. The method 400 may be performed via Figures 1 to 3 The present invention is implemented by the techniques described herein, but may also be implemented via other techniques. For ease of explanation, the blocks of the flowchart are arranged in a generally sequential manner; however, it should be understood that this arrangement is merely exemplary, and it should be recognized that the processing associated with the methods described herein (and the blocks shown in the figure) may occur in a different order (e.g., where at least some of the processing associated with the blocks is performed in parallel and / or in an event-driven manner).

[0034] The method 400 optionally includes generating a pump optical signal from a light source at block 402. For example, the pump optical signal may be generated by a single frequency output from the laser source 102. At block 404, the method 400 continues by generating an optical frequency comb, for example, from laser light from the laser source 102. The optical frequency comb may be generated by, for example, Figure 1 The electro-optic modulator depicted in FIG. 1 may be produced by Figure 3Thus, block 402 is optional, as in some embodiments, the optical frequency comb is generated without using a pump source such as the laser source 102. Each tooth of the optical frequency comb is arranged to be a resonant frequency mode of the optical resonator 112 along a first direction (e.g., CCW direction), so that the initial optical signal propagating into the optical resonator experiences less power loss.

[0035] Continuing to block 406, method 400 couples an optical signal from the optical frequency comb into an optical resonator along a first direction. Figure 1 and Figure 3 In the example shown, the first direction is a CCW direction, but in other examples, the first direction may be a CW direction. The function of block 406 may be performed by a first optical coupler that couples the optical signal into the optical resonator 112. The method 400 continues to block 408 by reflecting the optical signal after propagating in the optical resonator. This function may be performed by a reflective element such as a mirror or a Bragg grating. In some embodiments, a phase modulator coupled to the reflective element produces a phase modulated optical signal after leaving the optical resonator. For example, in Figure 1 In FIG. 1 , the CCW optical signal leaves the optical resonator 112 and is phase modulated by the phase modulator 116 to reduce the signal-to-noise ratio.

[0036] At box 410, method 400 continues by coupling the reflected optical signal into the optical resonator along a second direction. In some embodiments, the second direction is a CW direction opposite to the CCW direction in box 406. The reflected signal is then coupled out of the optical resonator after propagating one or more times along the second direction and is received by one or more processors. Then, at box 412, method 400 determines a change in intensity based on the reflected optical signal after propagating in the optical resonator along the second direction. The change in intensity is the power loss between the optical signal and the reflected optical signal due to the shift in the resonant frequency of the optical resonator. Then at box 414, method 400 determines the rotation rate based on the change in intensity. For example, a large change in intensity corresponds to a high rotation rate experienced by the optical gyroscope.

[0037] FIG. 5A to FIG. 5B Flowcharts of methods 500A-500B for controlling an optical frequency comb generator in an optical gyroscope are depicted. The functions performed in methods 500A-500B may be combined with each other and may be combined with Figures 1 to 3 The description of and the function of method 400 are combined. Method 500A to method 500B can be performed via Figure 1 and Figure 3 This is achieved by controlling the servo device 150.

[0038] Referring to method 500A, it includes determining an intensity corresponding to an optical signal in an optical gyroscope at block 502. The optical signal propagates in an optical resonator along a first direction and is coupled out of the resonator and received by the control servo 150. Figure 1 In some embodiments, the optical signal propagates in a CCW direction, is converted by the PD 114 into an electrical signal, and is provided to the control servo 150. At block 504, the method 500A continues by determining a repetition rate of the optical frequency comb generated by the optical frequency comb generator. The repetition rate is determined based on the strength of the optical signal, which may vary as the resonant frequency spacing of the optical resonator changes during gyroscope operation. In some embodiments, the method 500A determines the repetition rate based on a free spectral range between two adjacent resonant frequencies of the optical resonator. The free spectral range is determined by the optical signal when it first propagates through the optical resonator, Figure 1 In the embodiment shown, this is along the CCW direction.

[0039] The method 500A then continues to block 506 and controls an optical frequency comb generator that generates an optical frequency comb. For example, the method 500A may send at least one control signal to the optical frequency comb generator that modulates the optical frequency comb based on the repetition rate. This enables each tooth of the optical frequency comb to be locked to a corresponding one of the plurality of resonant frequencies of the optical resonator.

[0040] Referring now to method 500B, one embodiment of modulating an optical frequency comb generator as part of a control feedback loop is depicted. Method 500B includes determining an intensity corresponding to an optical signal after propagating through an optical resonator in a first direction. At block 510, method 500B determines whether the intensity corresponding to the optical signal falls within a tolerance level, such as a minimum allowed threshold intensity. If so, this indicates that the teeth of the optical frequency comb are sufficiently locked to the resonant frequency of the optical resonator. For example, if the tolerance level is implemented as a minimum allowed threshold intensity, an intensity above the minimum threshold indicates that high power efficiency is achieved for the first pass through the optical resonator via mode locking of the optical comb teeth. In this case, method 500B may return to block 508 and receive additional intensity measurements.

[0041] If the intensity corresponding to the optical signal at block 510 is not within the tolerance level, the method 500B proceeds to block 512 and determines an adjusted repetition rate of the optical frequency comb. For example, if the tolerance level is implemented as a minimum threshold, an intensity level below the threshold indicates that the teeth of the optical frequency comb are not sufficiently locked to the resonant frequency of the optical resonator and that the optical frequency comb needs to be adjusted. Therefore, at block 512, similar to block 504, an adjusted repetition rate is determined based on the intensity corresponding to the optical signal. Next, at block 514, the method 500B controls the optical frequency comb generator at the adjusted repetition rate, similar to that described for method 500A.

[0042] The methods and techniques described herein may be implemented at least in part in digital electronic circuits, or with a programmable processor (e.g., a special purpose processor or a general purpose processor such as a computer) firmware, software, or various combinations of each. Apparatus embodying these techniques may include appropriate input and output devices, a programmable processor, and a storage medium tangibly embodying program instructions for execution by the programmable processor. A process embodying these techniques may be performed in the following manner: a programmable processor executes an instruction program to perform a desired function by operating on input data and generating appropriate outputs. These techniques may be advantageously implemented in one or more programs executable on a programmable system, the programmable system comprising at least one programmable processor coupled to receive data and instructions from a data storage system, at least one input device, and at least one output device, and to transmit data and instructions to the data storage system, at least one input device, and at least one output device. Generally speaking, the processor will receive instructions and data from a read-only memory and / or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including (by way of example) semiconductor memory devices such as erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and flash memory devices; magnetic disks, such as internal hard disks and removable disks; and magneto-optical disks. Any of the foregoing may be supplemented by or incorporated in specially designed application-specific integrated circuits (ASICs).

[0043] Exemplary embodiments

[0044] Embodiment 1 includes an optical gyroscope comprising: an optical resonator; an optical frequency comb generator coupled to the optical resonator and configured to generate an optical frequency comb, wherein the optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of the optical resonator; wherein the optical resonator is configured to receive an optical signal from the optical frequency comb, wherein the optical signal propagates in the optical resonator along a first direction; a reflective element coupled to the optical resonator, wherein the reflective element is configured to reflect the optical signal after propagating in the first direction, wherein the optical resonator is configured to receive the reflected optical signal, wherein the reflected optical signal propagates in the optical resonator along a second direction opposite to the first direction; and at least one processor coupled to the optical resonator, wherein the at least one processor is configured to determine an intensity corresponding to the reflected optical signal after propagating in the second direction, wherein the at least one processor is configured to determine a rotation rate based on the intensity corresponding to the reflected optical signal.

[0045] Embodiment 2 includes the optical gyroscope of embodiment 1, wherein the optical frequency comb includes a plurality of frequency peaks, wherein each frequency peak overlaps with a respective resonant frequency of the optical resonator corresponding to an optical signal propagating along the first direction.

[0046] Embodiment 3 includes an optical gyroscope according to any one of Embodiments 1 to 2, the optical gyroscope comprising a control servo device coupled to the optical resonator, wherein the control servo device is configured to: receive an optical signal after propagation along the first direction, determine an intensity corresponding to the optical signal, and configure the optical frequency comb generator based on the intensity corresponding to the optical signal, wherein the optical frequency comb generator is configured to generate a modulated optical frequency comb in response to at least one control signal from the control servo device.

[0047] Embodiment 4 includes the optical gyroscope of embodiment 3, wherein the optical resonator is configured to have minimum frequency dispersion within a frequency range of the optical frequency comb.

[0048] Embodiment 5 includes the optical gyroscope according to any one of embodiments 1 to 4, the optical gyroscope comprising a laser source coupled to the optical frequency comb generator, wherein the laser source is configured to generate a pump signal, wherein the optical frequency comb generator is configured to generate an optical frequency comb from the pump signal.

[0049] Embodiment 6 includes the optical gyroscope of any one of embodiments 1 to 5, wherein the optical frequency comb generator includes an electro-optic modulator or a Kerr optical comb generator.

[0050] Embodiment 7 includes the optical gyroscope according to any one of Embodiments 1 to 6, the optical gyroscope comprising a Pound-Drever-Hall circuit, wherein the Pound-Drever-Hall circuit is configured to receive an optical signal from the optical resonator and generate an error signal based on the optical signal, wherein the error signal represents a carrier frequency indicative of one of the resonant frequencies of the optical resonator, wherein the error signal causes the optical frequency comb generator to lock a frequency peak of the optical frequency comb to the carrier frequency.

[0051] Embodiment 8 includes an optical gyroscope according to any one of Embodiments 1 to 7, wherein the optical gyroscope includes a relative intensity noise (RIN) servo device coupled to the optical frequency comb generator, wherein the RIN servo device is configured to receive an optical signal from the optical frequency comb generator and modulate the intensity of the optical frequency comb based on the intensity of the optical signal.

[0052] Embodiment 9 includes the optical gyroscope according to any one of embodiments 1 to 8, the optical gyroscope comprising a phase modulator coupled to the optical resonator and the reflective element, wherein the phase modulator is configured to generate a phase modulated optical signal from the reflected optical signal based on a phase modulation signal.

[0053] Embodiment 10 includes a method for operating an optical gyroscope, the method comprising: generating an optical frequency comb from an optical frequency comb generator, wherein the optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of an optical resonator of the optical gyroscope; coupling an optical signal from the optical frequency comb into the optical resonator, wherein the optical signal propagates in the optical resonator along a first direction; reflecting the optical signal after propagating in the optical resonator along the first direction; coupling the reflected optical signal into the optical resonator, wherein the reflected optical signal propagates in the optical resonator along a second direction opposite to the first direction; determining a change in intensity based on the optical signal and the reflected optical signal; and determining a rotation rate based on the change in intensity.

[0054] Embodiment 11 includes the method of embodiment 10, wherein the optical frequency comb comprises a plurality of frequency peaks, wherein each frequency peak overlaps with a respective resonant frequency of the optical resonator corresponding to an optical signal propagating along the first direction.

[0055] Embodiment 12 includes a method according to any one of Embodiments 10 to 11, the method comprising: receiving an optical signal after propagating in the optical resonator along the first direction, determining an intensity corresponding to the optical signal, and configuring the optical frequency comb generator based on the intensity corresponding to the optical signal, wherein the optical frequency comb generator is configured to generate a modulated optical frequency comb in response to at least one control signal.

[0056] Embodiment 13 includes the method of embodiment 12, comprising controlling a repetition rate of the optical frequency comb based on an intensity corresponding to the optical signal.

[0057] Embodiment 14 includes the method according to embodiment 13, the method comprising: determining a free spectral range based on an intensity corresponding to the optical signal; and setting a repetition rate of the optical frequency comb to the free spectral range.

[0058] Embodiment 15 includes a method according to any one of embodiments 10 to 14, the method comprising: generating a Pound-Drever-Hall (PDH) error signal based on an optical signal, wherein the error signal represents a carrier frequency indicative of one of the resonant frequencies of the optical resonator; and locking the teeth of the optical frequency comb to the carrier frequency.

[0059] Embodiment 16 includes the method of any one of Embodiments 10 to 15, comprising modulating the intensity of the optical frequency comb based on the intensity of an optical signal received from the optical frequency comb generator.

[0060] Embodiment 17 includes a program product, which includes a non-transitory processor-readable medium, on which program instructions configured to be executed by at least one processor are specifically embodied, wherein by executing the program instructions, the at least one processor is configured to: receive a signal corresponding to an optical signal after propagating in an optical resonator of an optical gyroscope along a first direction; determine an intensity corresponding to the signal; determine a repetition rate of an optical frequency comb based on the intensity corresponding to the signal; and send at least one control signal to an optical frequency comb generator, wherein the at least one control signal is configured to modulate the optical frequency comb generated by the optical frequency comb generator with the repetition rate.

[0061] Embodiment 18 includes the program product of embodiment 17, wherein the at least one processor is configured to: determine whether an intensity corresponding to the signal is within a tolerance level; and when the intensity is below the tolerance level, modulate the optical frequency comb generator.

[0062] Embodiment 19 includes the program product of any one of Embodiments 17 to 18, wherein the repetition rate corresponds to a frequency spacing between two adjacent resonant frequencies of the optical resonator, wherein the at least one processor is configured to set each frequency peak of the optical frequency comb to a corresponding one of a plurality of resonant frequencies.

[0063] Embodiment 20 includes the program product of embodiment 19, wherein the plurality of resonant frequencies corresponds to an optical signal from the optical frequency comb generator propagating through the optical resonator for the first time.

[0064] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that the present invention be limited only by the claims and the equivalents thereof.

Claims

1. An optical gyroscope, comprising: Optical resonators; an optical frequency comb generator coupled to the optical resonator and configured to generate an optical frequency comb, wherein the optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of the optical resonator; wherein the optical resonator is configured to receive an optical signal from the optical frequency comb, wherein the optical signal propagates in the optical resonator along a first direction; a reflective element coupled to the optical resonator, wherein the reflective element is configured to reflect the optical signal after propagating along the first direction, wherein the optical resonator is configured to receive a reflected optical signal, wherein the reflected optical signal propagates in the optical resonator in a second direction opposite to the first direction; as well as and at least one processor coupled to the optical resonator, wherein the at least one processor is configured to determine an intensity corresponding to a reflected optical signal after propagating in the second direction, wherein the at least one processor is configured to determine a rotation rate based on the intensity corresponding to the reflected optical signal. 2 . The optical gyroscope of claim 1 , wherein the optical resonator is configured to have minimum frequency dispersion within a frequency range of the optical frequency comb.

3. A method for operating an optical gyroscope, the method comprising: generating an optical frequency comb from an optical frequency comb generator, wherein the optical frequency comb is locked to at least one resonant frequency of a plurality of resonant frequencies of an optical resonator of the optical gyroscope; coupling an optical signal from the optical frequency comb into the optical resonator, wherein the optical signal propagates in the optical resonator along a first direction; reflecting the optical signal after propagating in the optical resonator along the first direction; coupling a reflected optical signal into the optical resonator, wherein the reflected optical signal propagates in the optical resonator in a second direction opposite to the first direction; determining a change in intensity based on the optical signal and the reflected optical signal; as well as A rotation rate is determined based on the change in intensity.

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