Resonant optical gyroscope with dual broadband light source

Abstract

A gyroscope includes first and second light sources emitting first and second light beams having a broadband spectrum, and a waveguide arrangement in communication with the light sources. A resonator is in communication with the waveguide arrangement to receive the beam. A first circulator is coupled to the waveguide arrangement between the first light source and the resonator. A second circulator is coupled to the waveguide arrangement between the second light source and the resonator. A first rate detector is in communication with the resonator through a first circulator, and a second rate detector is in communication with the resonator through a second circulator. The rate detector generates a rate measurement based on a resonant frequency offset of a beam detected in the resonator caused by rotation of the gyroscope. The output of the second rate detector is used to calculate a rotation rate that corrects for errors due to time-varying path length variations in the resonator.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under FA9453-20-C-0013 awarded by the Air Force Research Laboratory. The Government has certain rights in this invention. Background Art

[0003] Resonant optical gyroscopes often require narrow linewidth lasers for rate interrogation. One or more narrow linewidth lasers can be used to lock the cavity resonance in the gyroscope. The rotation rate is determined by comparing the resonance offset between the clockwise (CW) and counterclockwise (CCW) beam directions. However, such gyroscope systems are expensive and complex. In addition, the system bias performance is limited by the Kerr effect. The Kerr effect is formed by the different phase shifts between the counter-propagating beams caused by self-phase modulation (SPM) and cross-phase modulation (XPM), and is more prominent for narrow linewidth lasers.

[0004] The Kerr effect becomes even more important for integrated photonic gyroscopes. Due to their small scale factor, integrated photonic gyroscopes have very high finesse to reduce the cavity linewidth and increase the gyroscope sensitivity. Therefore, the intracavity intensity in an integrated photonic gyroscope is much higher than that in a conventional resonant fiber gyroscope (RFOG).

[0005] In addition, existing approaches for resonant optical gyroscopes rely on narrow linewidth lasers and resonant locking collars for rate detection, which are complex and expensive. Although broadband-based RFOGs can significantly reduce system complexity and cost, these systems have inherent non-reciprocity. Summary of the invention

[0006] The gyroscope includes a first light source configured to emit a first light beam having a broadband spectrum and a second light source configured to emit a second light beam having a broadband spectrum. A first waveguide arrangement is optically connected to the first light source and the second light source. An optical resonator having a first side and an opposite second side is optically connected to the first waveguide arrangement on the first side. The optical resonator is configured to receive the first light beam and the second light beam through the first waveguide arrangement. The second waveguide arrangement is optically connected to the optical resonator on its second side. A first phase modulator is optically connected to the optical resonator through the second waveguide arrangement, and a first reflector is optically coupled to the first phase modulator. A second phase modulator is optically connected to the optical resonator through the second waveguide arrangement, and a second reflector is optically coupled to the second phase modulator. A first optical circulator is optically coupled to the first waveguide arrangement between the first light source and the first side of the optical resonator. A second optical circulator is optically coupled to the first waveguide arrangement between the second light source and the first side of the optical resonator. A first rate detector is optically connected to the optical resonator through the first optical circulator, and a second rate detector is optically connected to the optical resonator through the second optical circulator. The first rate detector and the second rate detector are operable to generate respective first and second rate measurements based on a resonant frequency shift of a beam detected in the optical resonator caused by rotation of the gyroscope. The outputs of the first and second rate detectors are used to calculate a rotation rate that corrects for errors due to time-varying path length changes in the optical resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The features of the present invention will become apparent to those skilled in the art through the following description with reference to the accompanying drawings. Understanding that the drawings illustrate only typical embodiments and are not therefore to be considered as limiting the scope of the invention, the invention will be described with additional specificity and detail using the accompanying drawings, in which:

[0008] Figure 1 is a schematic diagram of a resonant optical gyroscope according to one embodiment; and

[0009] Figure 2 is a schematic diagram of a resonant optical gyroscope according to another embodiment. DETAILED DESCRIPTION

[0010] In the following specific embodiments, the embodiments are fully described to enable those skilled in the art to practice the present invention. It should be understood that other embodiments may be utilized without departing from the scope of the present invention. Therefore, the following detailed description should not be considered to have a limiting meaning.

[0011] Various implementations of a resonant optical gyroscope with dual broadband light sources are described herein.

[0012] The present method reduces non-reciprocity in a resonant optical gyroscope by using a dual light source system. This system can be implemented in a resonant fiber optical gyroscope (RFOG) or a waveguide resonant optical gyroscope such as an integrated photonic gyroscope.

[0013] Intensity-based resonant optical gyroscopes using broadband light sources can significantly reduce the Kerr effect. These gyroscopes measure the resonant shift between the CW and CCW beams due to rotation by comparing the intensity difference between the CW and CCW beam transmissions. For example, in such systems, light is first emitted in the resonator in the CW direction, and then the transmitted beam is reflected and emitted back into the resonator in the CCW direction. Because the CW and CCW resonance peaks are separated due to the Sagnac effect, the double-pass beam intensity varies with the rotation rate. However, because the light passing between the CW and CCW directions is not truly reciprocal in such time-varying systems, the so-called "bias errors due to time-varying resonator path lengths", such systems have reciprocity problems. These errors are essentially time-varying changes in the resonator path length, which is common to these light waves within the ring resonator if clockwise and counterclockwise resonant light waves are introduced into the ring resonator at the same time. However, in such a single light source architecture, the CW and CCW light waves are introduced at different times, causing the otherwise common path length to be changed to an observed differential path length for the CW and CCW beams. This differential path length manifests itself as the difference in the resonant frequency experienced between the broadband light wave component propagating in the CW direction and the broadband light wave component propagating in the CCW direction. This gives a relative error due to rotation rate, or rotation rate bias error (hereinafter referred to as "bias 共同 ”, which has the same units as the rotation rate) causes the gyroscope output to be indistinguishable from the gyroscope output.

[0014] If the gyro is stationary, the CW and CCW beam transmissions overlap each other and there is no additional transmission loss due to the double pass through the resonator. If the gyro is rotating, the CW and CCW resonances are separated. Therefore, the reflected CW beam is attenuated in the direction of CCW transmission. The additional intensity reduction is proportional to the rotation rate. Since the CCW and CW beams pass through the gyro resonator at different times, any changes in the gyro cavity within the time delay will introduce bias errors.

[0015] In the present method, the use of dual light sources solves the above-mentioned reciprocity problem. Each light source can measure the rotation rate separately. The two light sources are configured to measure the rotation rate with opposite signs. The CW beam from one light source and the CCW beam from the other light source pass through the resonator at the same time. Although the output signal from most bias errors is common, the output signal component from the rotation rate is not - it has opposite signs between the two light sources. Therefore, the bias error can be eliminated by common error subtraction while maintaining the desired signal from the rotation rate.

[0016] There are different ways to measure the rate using dual detectors for corresponding dual light sources to avoid interference between the signals generated by the two light sources and the backscattering, which is also generated by the signal light wave traveling in the resonator. In one approach, a pair of phase modulators are used to modulate the CW and CCW beams at different frequencies, respectively. In another approach, a fast switching scheme can be used to turn the dual light sources on and off so that the rate measurements are separated in time. In another approach, the dual light sources are configured to emit beams with different wavelengths, and optical filters are used to separate the different wavelengths from each other.

[0017] Additional details regarding the present method are described below and with reference to the accompanying figures.

[0018] Figure 1 is a schematic diagram of a resonant optical gyroscope 100 according to one embodiment. The gyroscope 100 generally includes: a first light source 102, the first light source configured to emit a first light beam having a broadband spectrum; a second light source 104, the second light source configured to emit a second light beam having a broadband spectrum; and an optical resonator 110, the optical resonator being in optical communication with the first and second light sources 102, 104. The optical resonator 110 is in optical communication with the first and second light sources 102, 104 and various other optical components through an optical path, the optical path including an optical fiber, a planar waveguide, or a combination thereof.

[0019] In some embodiments, the first and second light sources 102, 104 may be amplified spontaneous emission (ASE) devices, such as rare earth doped fiber amplifiers or superluminescent diode (SLD) devices, configured to emit a light beam having a broadband spectrum. For example, the optical resonator 110 may be implemented as a fiber ring resonator or a planar waveguide ring resonator. The various optical components of the gyroscope 100 may be connected by optical fibers or may be integrated on a single photonic chip using planar waveguides.

[0020] like Figure 1As shown in FIG. 1 , a first waveguide arrangement 112 is optically coupled to the first and second light sources 102, 104 and the optical resonator 110. The first waveguide arrangement 112 is configured to propagate a first light beam from the first light source 102 in a first direction and counter-propagate a second light beam from the second light source 104 in an opposite second direction. The first waveguide arrangement 112 may be implemented with optical fibers, planar waveguides, or a combination thereof.

[0021] The first optical circulator 114 is optically coupled to the first waveguide arrangement 112 between an output of the first light source 102 and a first coupler region 122 on a first side of the optical resonator 110. The second optical circulator 116 is optically coupled to the first waveguide arrangement 112 between an output of the second light source 104 and the first coupler region 122. A first rate detector 118 is in optical communication with the optical resonator 110 through the first optical circulator 114. A second rate detector 120 is in optical communication with the optical resonator 110 through the second optical circulator 116. The first and second rate detectors 118, 120 are operable to generate respective first and second rate measurements based on a resonant frequency shift of a beam detected in the optical resonator 110 caused by a rotation of the gyroscope 100.

[0022] In one specific implementation, the first waveguide arrangement 112 includes a first input waveguide 113 optically coupled between an output of the first light source 102 and a first port of a first optical circulator 114, and a second input waveguide 115 optically coupled between an output of the second light source 104 and a first port of a second optical circulator 116. A first bus waveguide 117 is optically coupled between a second port of the first optical circulator 114 and a second port of the second optical circulator 116. The first bus waveguide 117 is also optically coupled to the optical resonator 110 at a first coupler region 122. A first output waveguide 119 is optically coupled between a third port of the first optical circulator 114 and an input of a first rate detector 118. A second output waveguide 121 is optically coupled between a third port of the second optical circulator 116 and an input of a second rate detector 120.

[0023] In addition, a second waveguide arrangement 130 is optically coupled to the optical resonator 110 at a second coupler region 124 on an opposite second side of the optical resonator 110. A first phase modulator 140 is in optical communication with the optical resonator 110 through the second waveguide arrangement 130. A first reflector 142 is optically coupled to the first phase modulator 140. The first reflector 142 is in optical communication with the optical resonator 110 through the second waveguide arrangement 130 and the first phase modulator 140. A second phase modulator 144 is also in optical communication with the optical resonator 110 through the second waveguide arrangement 130. A second reflector 146 is optically coupled to the second phase modulator 144. The second reflector 146 is in optical communication with the optical resonator 110 through the second waveguide arrangement 130 and the second phase modulator 144. For example, the first and second reflectors 142, 146 may be Bragg gratings, loop mirrors, or edge high reflective (HR) coatings on waveguide edges.

[0024] The first intensity detector 150 is optically coupled to the second waveguide arrangement 130, and the second intensity detector 152 is also optically coupled to the second waveguide arrangement 130. As described further below, the first and second intensity detectors 150, 152 are configured to monitor the power of beams reflected from the first and second reflectors 142, 146, respectively.

[0025] In one specific implementation, the second waveguide arrangement 130 includes a second bus waveguide 132 that is optically coupled between the first phase modulator 140 and the second phase modulator 144. The second bus waveguide 132 is optically coupled to the optical resonator 110 at the second coupler region 124. The first connecting waveguide 133 is optically coupled between the first phase modulator 140 and the first reflector 142. The second connecting waveguide 134 is optically coupled between the second phase modulator 144 and the second reflector 146. The second bus waveguide 132 is also optically coupled to the first coupling waveguide 135 through the first polarization coupler 136. The first coupling waveguide 135 is optically coupled to the input of the first intensity detector 150. The first coupling waveguide 135 is also optically coupled to the first beam stop 139. The second bus waveguide 132 is also optically coupled to the second coupling waveguide 137 through the second polarization coupler 138. The second coupling waveguide 137 is optically coupled to the input of the second intensity detector 152. The second coupling waveguide 137 is also optically coupled to a second beam stop 141 .

[0026] In some embodiments, the first low frequency phase modulator 160 and the second low frequency phase modulator 162 can be optically coupled to the second waveguide arrangement 130. For example, the first low frequency phase modulator 160 can be optically coupled to the second bus waveguide 132 between the first phase modulator 140 and the first polarization coupler 136. The second low frequency phase modulator 162 can be optically coupled to the second bus waveguide 132 between the second phase modulator 144 and the second polarization coupler 138. The first low frequency phase modulator and the second low frequency phase modulator 160, 162 are configured to scramble the phase in order to reduce the bias caused by parasitic interference (e.g., due to unwanted back reflection light). In some embodiments, a micro heater can be used as a low frequency phase modulator 160, 162 to provide low frequency phase modulation.

[0027] During operation of the gyroscope 100, the first light source 102 emits a first light beam guided by the first input waveguide 113 in a first direction to a first port of the first optical circulator 114. The first light beam is guided from the second port of the first optical circulator 114 into the first bus waveguide 117. A portion of the first light beam in the first bus waveguide 117 is optically coupled into the optical resonator 110 and propagates in a counterclockwise (CCW) direction as a CCW beam. A beam portion of the CCW beam in the optical resonator 110 is optically coupled into the second bus waveguide 132 at the second coupler region 124. The beam portion is guided by the second bus waveguide 132 to the first phase modulator 140, which provides phase modulation or frequency shift to the beam portion. The first phase modulator 140 transmits the beam portion to the first reflector 142 through the first connecting waveguide 133. The first reflector 142 reflects the beam portion as a first reflected beam back to the first phase modulator 140 through the first connecting waveguide 133 and enters the second bus waveguide 132 .

[0028] A portion of the first reflected beam is optically coupled into the optical resonator 110 as a CW beam in the CW direction at the second coupler region 124. Another portion of the first reflected beam in the second bus waveguide 132 is tapped into the first coupling waveguide 135 through the first polarization coupler 136 and directed to the first intensity detector 150, which monitors the power of the first reflected beam.

[0029] The CW beam circulating in the optical resonator 110 is coupled from the optical resonator 110 into the first bus waveguide 117 at the first coupler region 122 and guided to the first optical circulator 114. The CW beam is output from the third port of the first optical circulator 114 into the first output waveguide 119, which guides the CW beam to the first rate detector 118 for further processing.

[0030] In addition, the second light source 104 emits a second light beam guided by the second input waveguide 115 to the first port of the second optical circulator 116 in the second direction. The second light beam is guided from the second port of the second optical circulator 116 into the first bus waveguide 117. A portion of the second light beam in the first bus waveguide 117 is optically coupled into the optical resonator 110 and propagates in the clockwise (CW) direction as a CW beam. A beam portion of the CW beam in the optical resonator 110 is optically coupled into the second bus waveguide 132 at the second coupler region 124. The beam portion is guided by the second bus waveguide 132 to the second phase modulator 144, which provides phase modulation or frequency shift for the beam portion. The second phase modulator 144 transmits the beam portion to the second reflector 146 through the second connecting waveguide 134. The second reflector 146 reflects the beam portion back to the second phase modulator 144 through the second connecting waveguide 134 as a second reflected beam and enters the second bus waveguide 132.

[0031] A portion of the second reflected beam is optically coupled into the optical resonator 110 as a CCW beam in the CCW direction at the second coupler region 124. Another portion of the second reflected beam in the second bus waveguide 132 is tapped into the second coupling waveguide 137 through the second polarization coupler 138 and directed to the second intensity detector 152, which monitors the power of the second reflected beam.

[0032] The CCW beam circulating in the optical resonator 110 is coupled from the optical resonator 110 into the first bus waveguide 117 at the first coupler region 122 and guided to the second optical circulator 116. The CCW beam is output from the third port of the second optical circulator 116 into the second output waveguide 121, which guides the CCW beam to the second rate detector 120 for further processing.

[0033] After the CW and CCW beams have passed through the optical resonator 110, each of the CW and CCW beams acquires a phase shift due to the resonator delay. Due to the Sagnac effect, the CW and CCW beams have different phase shifts. The rotation of the gyroscope 100 causes a resonant frequency shift between the CW and CCW beams output by the optical resonator 110, which is detected by the first and second rate detectors 118, 120. The rate calculation unit can be used to calculate a rotation rate for the gyroscope 100 based on the signals received from the first and second rate detectors 118, 120. The outputs of the first and second rate detectors 118, 120 can be used to calculate a rotation rate that corrects for errors caused by time-varying path length changes in the optical resonator 110, as further described below.

[0034] Each of the first and second light sources 102, 104 can be used to measure the rotation rate separately. The first and second light sources 102, 104 are configured to measure rotation rates with opposite signs. For example, a CW beam from one light source and a CCW beam from another light source pass through the optical resonator 110 at the same time. In addition to the rotation rates with opposite signs between the signals generated by the two light sources, most bias errors caused by time-varying resonator path length changes (due to temperature, strain, vibration, etc.) are common. Therefore, the bias errors can be eliminated by common error subtraction.

[0035] In order to measure the total rate of the gyroscope 100 using the first rate detector and the second rate detector 118, 120, it is necessary to avoid interference between the desired output signal generated by the first light source and the back reflected light generated in the second light source. Similarly, it is also necessary to avoid interference between the desired output signal generated by the second light source and the back reflected light generated in the first light source. In one method of avoiding such interference, the CW and CCW beams are modulated at different frequencies using a first phase modulator 140 and a second phase modulator 144, respectively. For example, the first CCW beam can be modulated by the first phase modulator 140 at a first frequency, and the first CW beam can be modulated by the second phase modulator 144 at a second frequency, wherein the second frequency is different from the first frequency. For example, the first frequency can be about 23kHz, and the second frequency can be about 17kHz. In this example, the indicated rate for the signal generated only by the first light source is the demodulated output of the rate detector 118, which is demodulated at a first frequency (e.g., about 23kHz) using a demodulator (not shown). In this example, the indicative rate for the signal generated by only the second light source is the demodulated output of the rate detector 120, which is demodulated at the second frequency (eg, approximately 17 kHz) using a demodulator (not shown).

[0036] To recover the rotation rate magnitude and direction, the following method can be used. The demodulated signal (Vdem) from the rate detector 118 118 ) is linearly proportional to the rotation rate Ω and has a positive slope. The demodulated signal (Vdem 118 ) is proportional to the rotation rate, while its sign indicates the direction of rotation of the signal from the first light source. This can be expressed as Vdem 118 =(Bias 共同 +Ω) / k, where k is the scaling factor. The demodulated signal (Vdem) from the rate detector 120 120 ) is linearly proportional to the rotation rate Ω and has a negative slope. The demodulated signal (Vdem 120) is proportional to the rotation rate, while its sign indicates the rotation direction of the signal from the second light source. Because the first light source 102 and the second light source 104 transmit into the resonator in opposite directions, the signs of their rate measurements are flipped. 118 In contrast, the demodulated signal from rate detector 120 measures the same common offset, but the sign of the rate offset is flipped. This can be expressed as Vdem 120 =(Bias 共同 -Ω) / k. The rotation rate can be calculated by k*(Vdem 118 -Vdem 120 ) / 2, where k is the scaling factor. The common bias noise can be calculated by (Vdem 118 +Vdem 120 ) / 2. This calculation is used for open loop operation, where the demodulated signal is used as the rate output. However, a similar approach is also used for closed loop operation.

[0037] For closed-loop operation, the demodulated signal is used as an error signal to adjust the frequency of each return beam to keep them in resonance. Therefore, the frequency of the feedback signal (f 102 ,f 104 ) indicates the average resonant frequency shift between the CW and CCW portions of each source signal. Similar to open-loop operation, the rate for closed-loop operation can be calculated by subtracting the rate measurements from the two relative sources: 速率 =SF*(f 102 -f 104 ) / 2, where SF is the scaling factor. The frequency of the return beam can be adjusted using a sawtooth waveform applied to each phase modulator, ie the well-known chirp repeater technique; or an acousto-optic frequency shifter can be applied.

[0038] In another method of avoiding interference between the first rate detector and the second rate detector 118, 120, a fast switching scheme can be used to turn the light source on and off so that the first rate measurement is separated from the second rate measurement in time. For example, the first and second light sources 102, 104 can be configured to be turned on and off at different times, respectively, so that the rate measurements generated from the first and second rate detectors 118, 120 are separated in time (e.g., less than about 1 ms).

[0039] In another approach, a broadband light source is configured to emit light waves having different wavelengths, and optical filters are used to separate the different wavelengths from each other. Figure 2 is a schematic diagram of a resonant optical gyroscope 200 using this method according to another embodiment.

[0040] The gyroscope 200 generally includes a first broadband light source 202, a second broadband light source 204, and an optical resonator 210. The optical resonator 210 is optically connected to the first broadband light source and the second broadband light source 202, 204 and various other optical components through an optical path, which includes an optical fiber, a planar waveguide, or a combination thereof. The various optical components of the gyroscope 200 can be connected by optical fibers or can be integrated on a single photonic chip using a planar waveguide.

[0041] For example, the optical resonator 210 may be implemented as a fiber ring resonator or a planar waveguide ring resonator. In one embodiment, the optical resonator 210 may include an optical polarizer 211 to suppress polarization bias errors.

[0042] The first broadband light source 202 is configured to emit a first light beam at a first wavelength spectrum, and the second broadband light source 204 is configured to emit a second light beam at a second wavelength spectrum, which is different from the first wavelength spectrum. In some embodiments, the first broadband light source and the second broadband light source 202, 204 can be ASE devices, such as SLD devices, which are configured to emit a light beam with a broadband spectrum.

[0043] like Figure 2 As shown in FIG. 1 , a first waveguide arrangement 212 is optically coupled to the first and second broadband light sources 202, 204 and the optical resonator 210. The first waveguide arrangement 212 is configured to propagate a first light beam from the first broadband light source 202 in a first direction and counter-propagate a second light beam from the second broadband light source 204 in an opposite second direction. The first waveguide arrangement 212 may be implemented with optical fibers, planar waveguides, or a combination thereof.

[0044] The first optical circulator 214 is optically coupled to the first waveguide arrangement 212 and is in optical communication with the first broadband light source 202. The second optical circulator 216 is optically coupled to the first waveguide arrangement 212 and is in optical communication with the second broadband light source 204.

[0045] The first optical filter 218 is optically coupled to the first waveguide arrangement 212 between the first optical circulator 214 and a first coupler region 222 on a first side of the optical resonator 210. The second optical filter 220 is optically coupled to the first waveguide arrangement 212 between the second optical circulator 216 and the first coupler region 222. As further described below, the second optical filter 220 is configured to filter out a first light beam from the first broadband light source 202 at a first wavelength spectrum, and the first optical filter 218 is configured to filter out a second light beam from the second broadband light source 204 at a second wavelength spectrum.

[0046] The first rate detector 223 is in optical communication with the optical resonator 210 through the first optical circulator 214 and the first optical filter 218. The second rate detector 225 is in optical communication with the optical resonator 210 through the second optical circulator 216 and the second optical filter 220.

[0047] In one specific implementation, the first waveguide arrangement 212 includes a first input waveguide 213 optically coupled between the first broadband light source 202 and a first port of the first optical circulator 214, and a second input waveguide 215 optically coupled between the second broadband light source 204 and a first port of the second optical circulator 216. A first bus waveguide 217 is optically coupled between a first optical filter 218 and a second optical filter 220. The first bus waveguide 217 is also optically coupled to the optical resonator 210 at a first coupler region 222. A first connecting waveguide 219 is optically coupled between a second port of the first optical circulator 214 and the first optical filter 218. A second connecting waveguide 221 is optically coupled between a second port of the second optical circulator 216 and the second optical filter 220. A first output waveguide 224 is optically coupled between a third port of the first optical circulator 214 and a first rate detector 223. A second output waveguide 226 is optically coupled between a third port of the second optical circulator 216 and a second rate detector 225.

[0048] In addition, a second waveguide arrangement 230 is optically coupled to the optical resonator 210 at a second coupler region 228 on a second side of the optical resonator 210. A first phase modulator 240 is in optical communication with the optical resonator 210 through the second waveguide arrangement 230. A first reflector 242 is optically coupled to the first phase modulator 240. The first reflector 242 is in optical communication with the optical resonator 210 through the second waveguide arrangement 230 and the first phase modulator 240. A second phase modulator 244 is also in optical communication with the optical resonator 210 through the second waveguide arrangement 230. A second reflector 246 is optically coupled to the second phase modulator 244. The second reflector 246 is in optical communication with the optical resonator 210 through the second waveguide arrangement 230 and the second phase modulator 244. For example, the first and second reflectors 242, 246 may be Bragg gratings, loop mirrors, or edge HR coatings on waveguide edges.

[0049] The first intensity detector 250 is optically coupled to the second waveguide arrangement 230, and the second intensity detector 252 is also optically coupled to the second waveguide arrangement 230. As described further below, the first and second intensity detectors 250, 252 are configured to monitor the power of beams reflected from the first and second reflectors 242 and 246, respectively.

[0050] In one specific implementation, the second waveguide arrangement 230 includes a second bus waveguide 232 that is optically coupled between the first phase modulator 240 and the second phase modulator 244. The second bus waveguide 232 is optically coupled to the optical resonator 210 at the second coupler region 228. The first connector waveguide 233 is optically coupled between the first phase modulator 240 and the first reflector 242. The second connector waveguide 234 is optically coupled between the second phase modulator 244 and the second reflector 246. The second bus waveguide 232 is also optically coupled to the first coupling waveguide 235 through the first polarization coupler 236. The first coupling waveguide 235 is optically coupled to the first intensity detector 250. The first coupling waveguide 235 is also optically coupled to the first beam stop 239. The second bus waveguide 232 is also optically coupled to the second coupling waveguide 237 through the second polarization coupler 238. The second coupling waveguide 237 is optically coupled to the second intensity detector 252. The second coupling waveguide 237 is also optically coupled to a second beam stop 241 .

[0051] In some embodiments, the first low frequency phase modulator 260 and the second low frequency phase modulator 262 are optically coupled to the second waveguide arrangement 230. For example, the first low frequency phase modulator 260 can be optically coupled to the second bus waveguide 232 between the first phase modulator 240 and the first polarization coupler 236. The second low frequency phase modulator 262 can be optically coupled to the second bus waveguide 232 between the second phase modulator 244 and the second polarization coupler 238. The first and second low frequency phase modulators 260, 262 are configured to scramble the phase in order to reduce the bias due to parasitic interference.

[0052] During operation of the gyroscope 200, the first broadband light source 202 emits a first light beam guided by the first input waveguide 213 to the first port of the first optical circulator 214. The first light beam is guided from the second port of the first optical circulator 214 to the first connecting waveguide 219, the first optical filter 218, and the first bus waveguide 217. A portion of the first light beam in the first bus waveguide 217 is optically coupled into the optical resonator 210 and propagates in the CCW direction as a first CCW beam. A beam portion of the CCW beam in the optical resonator 210 is optically coupled into the second bus waveguide 232 at the second coupler region 228. The beam portion is guided by the second bus waveguide 232 to the first phase modulator 240, which provides phase modulation or frequency shift for the beam portion. The first phase modulator 240 transmits the beam portion to the first reflector 242 through the first connector waveguide 233. The first reflector 242 reflects the beam portion as a first reflected beam back to the first phase modulator 240 through the first connector waveguide 233 and into the second bus waveguide 232 .

[0053] A portion of the first reflected beam is optically coupled into the optical resonator 210 in the CW direction at the second coupler region 228 as a second CW beam. Another portion of the first reflected beam in the second bus waveguide 232 is tapped into the first coupling waveguide 235 by the first polarization coupler 236 and directed to the first intensity detector 250, which monitors the power of the first reflected beam. Some of this remaining portion of the first reflected beam in the second bus waveguide 232 may be tapped into the second coupling waveguide 237 by the second polarization coupler 238 and directed to the second beam stop 241.

[0054] The CW beam circulating in the optical resonator 210 is coupled from the optical resonator 210 into the first bus waveguide 217 at the first coupler region 222 and is guided to the first optical circulator 214 through the first optical filter 218. The CW beam is output from the third port of the first optical circulator 214 into the first output waveguide 224, which guides the CW beam to the first rate detector 223 for further processing.

[0055] In addition, the second broadband light source 204 emits a second light beam guided by the second input waveguide 215 to the first port of the second optical circulator 216. The second light beam is guided from the second port of the second optical circulator 216 to the second connecting waveguide 221, the second optical filter 220, and the first bus waveguide 217. A portion of the second light beam in the first bus waveguide 217 is optically coupled into the optical resonator 210 and propagates in the CW direction as a first CW beam. A beam portion of the first CW beam in the optical resonator 210 is optically coupled into the second bus waveguide 232 at the second coupler region 228. The beam portion is guided by the second bus waveguide 232 to the second phase modulator 244, which provides phase modulation or frequency shift for the beam portion. The second phase modulator 244 transmits the beam portion to the second reflector 246 through the second connector waveguide 234. The second reflector 246 reflects the beam portion as a second reflected beam back to the second phase modulator 244 through the second connector waveguide 234 and into the second bus waveguide 232 .

[0056] A portion of the second reflected beam is optically coupled into the optical resonator 210 in the CCW direction at the second coupler region 228 as a second CCW beam. Another portion of the second reflected beam in the second bus waveguide 232 is tapped into the second coupling waveguide 237 by the second polarization coupler 238 and directed to the second intensity detector 252, which monitors the power of the second reflected beam. Some of this remaining portion of the second reflected beam in the second bus waveguide 232 may be tapped into the first coupling waveguide 235 by the first polarization coupler 236 and directed to the first beam stop 239.

[0057] The CCW beam circulating in the optical resonator 210 is coupled from the optical resonator 210 into the first bus waveguide 217 at the first coupler region 222 and is guided to the second optical circulator 216 through the second optical filter 220. The CCW beam is output from the third port of the second optical circulator 216 into the second output waveguide 226, which guides the CCW beam to the second rate detector 225 for further processing.

[0058] Interference between the outputs of the first rate detector and the second rate detector 223 and 225 is avoided by using the first optical filter and the second optical filter 218 and 220. For example, the second optical filter 220 is configured to filter out the first light beam at a first wavelength from the first broadband light source 202. The first optical filter 218 is configured to filter out the second light beam at a different second wavelength from the second broadband light source 204. The optical filter 218 is a bandpass optical filter that allows only light from the first broadband light source 202 to pass through, while blocking light from the second broadband light source 204. The optical filter 220 is a bandpass optical filter that allows only light from the second broadband light source 204 to pass through, while blocking light from the first broadband light source 202.

[0059] The rotation of the gyroscope 200 causes a resonant frequency shift between the CW and CCW beams output by the optical resonator 210. The resonant frequency shift results in a decrease in optical power after a round trip detected by the first and second rate detectors 223, 225. The rate calculation unit may be used to calculate a rotation rate for the gyroscope 200 based on signals received from the first and second rate detectors 223, 225. The outputs of the first and second rate detectors 223, 225 may be used to calculate a rotation rate that corrects for errors due to time-varying path length changes in the optical resonator 210.

[0060] Each of the first broadband light source and the second broadband light source 202, 204 can be used to measure the rotation rate separately. The first broadband light source and the second broadband light source 202, 204 are configured to measure the rotation rate with opposite signs. For example, a CW beam from one light source and a CCW beam from another light source pass through the optical resonator 210 at the same time. It is common for most bias errors to occur while maintaining sensitivity to the rotation rate, which has opposite signs between the two light sources. Therefore, the bias error can be eliminated by common error subtraction.

[0061] Exemplary embodiments

[0062] Embodiment 1 includes a gyroscope, the gyroscope comprising: a first light source and a second light source, the first light source being configured to emit a first light beam having a broadband spectrum, the second light source being configured to emit a second light beam having a broadband spectrum; a first waveguide arrangement, the first waveguide arrangement being optically connected to the first light source and the second light source; an optical resonator, the optical resonator having a first side and an opposite second side, the optical resonator being optically connected to the first waveguide arrangement on the first side, the optical resonator being configured to receive the first light beam and the second light beam through the first waveguide arrangement; a second waveguide arrangement, the second waveguide arrangement being optically connected to the optical resonator on its second side; a first phase modulator and a first reflector, the first phase modulator being optically connected to the optical resonator through the second waveguide arrangement, the first reflector being optically coupled to the first phase modulator; a second phase modulator and a second reflector, the second phase modulator being optically connected to the optical resonator through the second waveguide arrangement, the second reflector being optically coupled to the first phase modulator a first optical circulator optically coupled to the first waveguide arrangement between the first light source and the first side of the optical resonator, and a second optical circulator optically coupled to the first waveguide arrangement between the second light source and the first side of the optical resonator; and a first rate detector and a second rate detector, the first rate detector being in optical communication with the optical resonator through the first optical circulator, and the second rate detector being in optical communication with the optical resonator through the second optical circulator; wherein the first rate detector and the second rate detector are operable to generate respective first and second rate measurements based on a resonant frequency shift of a beam detected in the optical resonator caused by rotation of the gyroscope; and wherein outputs of the first and second rate detectors are used to calculate a rotation rate that corrects for errors due to time-varying path length changes in the optical resonator.

[0063] Embodiment 2 includes the gyroscope of embodiment 1, wherein a portion of the first light beam is optically coupled from the first waveguide arrangement into the optical resonator and propagates in a counterclockwise (CCW) direction as a first CCW beam, and a portion of the second light beam is optically coupled from the first waveguide arrangement into the optical resonator and propagates in a clockwise (CW) direction as a first CW beam.

[0064] Embodiment 3 includes the gyroscope described in Embodiment 2, wherein: the first CCW beam is coupled from the optical resonator into the second waveguide arrangement and is guided to the first phase modulator and the first reflector, the first phase modulator and the first reflector respectively modulate the CCW beam and reflect the CCW beam back along the second waveguide arrangement as a first reflected beam, the second waveguide arrangement optically couples the first reflected beam into the optical resonator to propagate in a CW direction in the optical resonator as a second CW beam; and the CW beam is coupled from the optical resonator into the second waveguide arrangement and is guided to the second phase modulator and the second reflector, the second phase modulator and the second reflector respectively modulate the CW beam and reflect the CCW beam back along the second waveguide arrangement as a second reflected beam, the second waveguide arrangement optically couples the second reflected beam into the optical resonator to propagate in a CCW direction in the optical resonator as a second CCW beam.

[0065] Embodiment 4 includes the gyroscope of Embodiment 3, wherein: the second CW beam is coupled from the optical resonator and directed by the first optical circulator to the first rate detector; and the second CCW beam is coupled from the optical resonator and directed by the second optical circulator to the second rate detector.

[0066] Embodiment 5 includes the gyroscope described in Embodiment 4, wherein the gyroscope further includes: a first intensity detector, which is optically connected to the second waveguide arrangement via a first polarization coupler; and a second intensity detector, which is optically connected to the second waveguide arrangement via a second polarization coupler.

[0067] Embodiment 6 includes the gyroscope described in Embodiment 5, wherein: a portion of the first reflected beam is directed by the first polarization coupler to the first intensity detector, wherein the first intensity detector monitors the power of the first reflected beam; and a portion of the second reflected beam is directed by the second polarization coupler to the second intensity detector, wherein the second intensity detector monitors the power of the second reflected beam.

[0068] Embodiment 7 includes the gyroscope described in Embodiment 6, and the gyroscope also includes: a first low-frequency phase modulator, which is optically coupled to the second waveguide arrangement between the first phase modulator and the first polarization coupler; and a second low-frequency phase modulator, which is optically coupled to the second waveguide arrangement between the second phase modulator and the second polarization coupler.

[0069] Embodiment 8 includes the gyroscope described in any one of Embodiments 4 to 7, wherein: the first CCW beam is modulated by the first phase modulator at a first frequency; and the first CW beam is modulated by the second phase modulator at a second frequency, wherein the second frequency is different from the first frequency.

[0070] Embodiment 9 includes the gyroscope of any one of Embodiments 4 to 7, wherein the first light source and the second light source are configured to be turned on and off at different times, respectively, so that the first rate measurement value and the second rate measurement value from the first rate detector and the second rate detector are separated in time.

[0071] Embodiment 10 includes the gyroscope of any one of Embodiments 4 to 7, the gyroscope further comprising: a first optical filter optically coupled to the first waveguide arrangement between the first optical circulator and the first side of the optical resonator; and a second optical filter optically coupled to the first waveguide arrangement between the second optical circulator and the first side of the optical resonator; wherein the second optical filter is configured to filter out a beam having a first wavelength, and the first optical filter is configured to filter out a beam having a second wavelength, the second wavelength being different from the first wavelength.

[0072] Embodiment 11 includes the gyroscope of Embodiment 10, wherein the first light source is configured to emit the first light beam at the first wavelength, and the second light source is configured to emit the second light beam at the second wavelength.

[0073] Embodiment 12 includes the gyroscope of any one of Embodiments 1 to 11, wherein the first light source and the second light source include amplified spontaneous emission devices or superluminescent diodes.

[0074] Embodiment 13 includes the method of any one of Embodiments 1 to 12, wherein the optical resonator comprises a waveguide ring resonator.

[0075] Embodiment 14 includes the method of any one of Embodiments 1 to 12, wherein the optical resonator comprises a fiber ring resonator.

[0076] Embodiment 15 includes the method of any one of Embodiments 1 to 12, wherein the optical resonator comprises a planar waveguide ring resonator.

[0077] Embodiment 16 includes the gyroscope of any one of Embodiments 5 to 15, wherein the first waveguide arrangement comprises: a first input waveguide, the first input waveguide optically coupled between the first light source and the first port of the first optical circulator; a second input waveguide, the second input waveguide optically coupled between the second light source and the first port of the second optical circulator; a first bus waveguide, the first bus waveguide optically coupled between the second port of the first optical circulator and the second port of the second optical circulator, wherein the first bus waveguide is optically coupled to the optical resonator at a first coupler region; a first output waveguide, the first output waveguide optically coupled between the third port of the first optical circulator and the first rate detector; and a second output waveguide optically coupled between the third port of the second optical circulator and the second rate detector.

[0078] Embodiment 17 includes the gyroscope of embodiment 16, wherein the second waveguide arrangement includes: a second bus waveguide, the second bus waveguide being optically coupled between the first phase modulator and the second phase modulator, wherein the second bus waveguide is optically coupled to the optical resonator at a second coupler region; a first connecting waveguide, the first connecting waveguide being optically coupled between the first phase modulator and the first reflector; a second connecting waveguide, the second connecting waveguide being optically coupled between the second phase modulator and the second reflector; a first coupling waveguide, the first coupling waveguide being optically coupled to the second bus waveguide through the first polarization coupler, wherein the first coupling waveguide is optically coupled to the first intensity detector; and a second coupling waveguide, the second coupling waveguide being optically coupled to the second bus waveguide through the second polarization coupler, wherein the second coupling waveguide is optically coupled to the second intensity detector.

[0079] Embodiment 18 includes a gyroscope, the gyroscope comprising: a first light source and a second light source, the first light source being configured to emit a first light beam having a broadband spectrum, the second light source being configured to emit a second light beam having a broadband spectrum; a first waveguide arrangement, the first waveguide arrangement being optically connected to the first light source and the second light source; an optical resonator having a first side and an opposite second side, the optical resonator being optically connected to the first waveguide arrangement on the first side, the optical resonator being configured to receive the first light beam and the second light beam through the first waveguide arrangement; a second waveguide arrangement, the second waveguide arrangement being optically connected to the optical resonator on its second side; a first phase modulator and a first reflector, the first phase modulator being in optical communication with the optical resonator through the second waveguide arrangement, the first reflector being optically coupled to the first phase modulator; a second phase modulator and a second reflector, the second phase modulator being in optical communication with the optical resonator through the second waveguide arrangement, the second reflector being optically coupled to the second phase modulator; a first intensity detector and a second intensity detector, the first intensity detector being in optical communication with the second waveguide arrangement through a first polarization coupler, the second intensity detector being optically connected to the second waveguide arrangement through a second polarization coupler; a first optical circulator and a second optical circulator, the first optical circulator being optically coupled to the first waveguide arrangement between the first light source and the first side of the optical resonator, the second optical circulator being optically coupled to the first waveguide arrangement between the second light source and the first side of the optical resonator; and a first rate detector and a second rate detector, the first rate detector being in optical communication with the optical resonator through the first optical circulator, the second rate detector being optically connected to the optical resonator through the second optical circulator; wherein a portion of the first light beam is optically coupled from the first waveguide arrangement into the optical resonator and is transmitted as a first CCW beam in a counterclockwise (CCW) direction propagates along the second waveguide arrangement, and a portion of the second light beam is optically coupled from the first waveguide arrangement into the optical resonator and propagates in a clockwise (CW) direction as a first CW beam; wherein the first CCW beam is coupled from the optical resonator into the second waveguide arrangement and is directed to the first phase modulator and the first reflector, the first phase modulator and the first reflector respectively modulating the CCW beam and reflecting the CCW beam back along the second waveguide arrangement as a first reflected beam, the second waveguide arrangement optically coupling the first reflected beam into the optical resonator to propagate in the CW direction in the optical resonator as a second CW beam;wherein the first CW beam is coupled from the optical resonator into the second waveguide arrangement and guided to the second phase modulator and the second reflector, the second phase modulator and the second reflector respectively modulate the CW beam and reflect the CCW beam back along the second waveguide arrangement as a second reflected beam, the second waveguide arrangement optically couples the second reflected beam into the optical resonator to propagate in the CCW direction in the optical resonator as a second CCW beam; wherein the first phase modulator is configured to modulate the first CCW beam at a first frequency, and the second phase modulator is configured to modulate the first CW beam at a second frequency, the second frequency being different from the first a frequency; wherein the second CW beam is coupled from the optical resonator and directed by the first optical circulator to the first rate detector, and the second CCW beam is coupled from the optical resonator and directed by the second optical circulator to the second rate detector; wherein the first rate detector and the second rate detector are operable to generate respective first and second rate measurements based on a resonant frequency shift of the beam detected in the optical resonator caused by rotation of the gyroscope; wherein the outputs of the first and second rate detectors are used to calculate a rotation rate that corrects for errors due to time-varying path length changes in the optical resonator.;

[0080] Embodiment 19 includes the gyroscope described in Embodiment 18, wherein: a portion of the first reflected beam is directed by the first polarization coupler to the first intensity detector, wherein the first intensity detector monitors the power of the first reflected beam; and a portion of the second reflected beam is directed by the second polarization coupler to the second intensity detector, wherein the second intensity detector monitors the power of the second reflected beam.

[0081] Embodiment 20 includes the gyroscope described in any one of Embodiments 18 to 19, wherein the gyroscope further includes: a first low-frequency phase modulator, which is optically coupled to the second waveguide arrangement between the first phase modulator and the first polarization coupler; and a second low-frequency phase modulator, which is optically coupled to the second waveguide arrangement between the second phase modulator and the second polarization coupler.

[0082] In light of the foregoing, it should be understood that although specific embodiments are described herein for the purpose of illustration, various modifications may be made without departing from the scope of the present disclosure. Therefore, the embodiments described are to be considered in all respects as merely illustrative and not restrictive. In addition, all changes within the meaning and scope of the equivalents of the claims are intended to be encompassed within their scope.

Claims

1. A gyroscope, comprising: a first light source configured to emit a first light beam having a broadband spectrum and a second light source configured to emit a second light beam having a broadband spectrum; a first waveguide arrangement in optical communication with the first light source and the second light source; an optical resonator having a first side and an opposing second side, the optical resonator being in optical communication with the first waveguide arrangement on the first side, the optical resonator being configured to receive the first and second optical beams through the first waveguide arrangement; a second waveguide arrangement arranged in optical communication with the optical resonator on the second side thereof; a first phase modulator and a first reflector, the first phase modulator being in optical communication with the optical resonator via the second waveguide arrangement, the first reflector being optically coupled to the first phase modulator; a second phase modulator and a second reflector, the second phase modulator being in optical communication with the optical resonator via the second waveguide arrangement, the second reflector being optically coupled to the second phase modulator; a first optical circulator optically coupled to the first waveguide arrangement between the first light source and the first side of the optical resonator and a second optical circulator optically coupled to the first waveguide arrangement between the second light source and the first side of the optical resonator; as well as a first rate detector and a second rate detector, the first rate detector being in optical communication with the optical resonator via the first optical circulator, the second rate detector being in optical communication with the optical resonator via the second optical circulator; wherein the first rate detector and the second rate detector are operable to generate respective first and second rate measurements based on a resonant frequency shift of a beam detected in the optical resonator caused by a rotation of the gyroscope; The outputs of the first rate detector and the second rate detector are used to calculate a rotation rate that corrects for errors due to time-varying path length changes in the optical resonator.

2. The gyroscope according to claim 1, wherein: a portion of the first optical beam is optically coupled from the first waveguide arrangement into the optical resonator and propagates in a counterclockwise (CCW) direction as a first CCW beam, and a portion of the second optical beam is optically coupled from the first waveguide arrangement into the optical resonator and propagates in a clockwise (CW) direction as a first CW beam; the first CCW beam is coupled from the optical resonator into the second waveguide arrangement and directed to the first phase modulator and the first reflector, the first phase modulator and the first reflector respectively modulating the CCW beam and reflecting the CCW beam back along the second waveguide arrangement as a first reflected beam, the second waveguide arrangement optically coupling the first reflected beam into the optical resonator to propagate in a CW direction in the optical resonator as a second CW beam; the CW beam is coupled from the optical resonator into the second waveguide arrangement and directed to the second phase modulator and the second reflector, the second phase modulator and the second reflector respectively modulating the CW beam and reflecting the CCW beam back along the second waveguide arrangement as a second reflected beam, the second waveguide arrangement optically coupling the second reflected beam into the optical resonator to propagate in the CCW direction in the optical resonator as a second CCW beam; The second CW beam is coupled from the optical resonator and directed by the first optical circulator to the first rate detector; and The second CCW beam is coupled from the optical resonator and directed by the second optical circulator to the second rate detector.

3. The gyroscope according to claim 2, wherein: The first CCW beam is modulated by the first phase modulator at a first frequency, and the first CW beam is modulated by the second phase modulator at a second frequency, wherein the second frequency is different from the first frequency; or The first light source and the second light source are configured to be turned on and off at different times, respectively, so that the first rate measurement and the second rate measurement from the first rate detector and the second rate detector are separated in time; or The gyroscope further comprises: a first optical filter optically coupled to the first waveguide arrangement between the first optical circulator and the first side of the optical resonator; and a second optical filter optically coupled to the first waveguide arrangement between the second optical circulator and the first side of the optical resonator; The second optical filter is configured to filter out a beam having a first wavelength, and the first optical filter is configured to filter out a beam having a second wavelength, the second wavelength being different from the first wavelength.

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