Resonator Micro-optic Gyro Research Articles

Broadband source-driven resonant micro-optic gyroscope based on a multi-turn waveguide-type ring resonator.

The resonant micro-optic gyroscope (RMOG) is one of the most promising candidates for chip-scale optoelectronic gyroscopes. A broadband source-driven RMOG based on a multi-turn waveguide-type ring resonator (WRR) has been proposed and demonstrated. The theoretical sensitivity is enhanced with the multi-turn structure, while the parasitic backscattering can be resolved by the use of the broadband source, thus greatly improving the long-term bias stability of the RMOG. We also reduce the relative intensity noise (RIN)-induced error of the broadband source at the gyro output by optimizing the number of loop turns of the WRR, and improve the angle random walk (ARW) by 4.8 dB compared with the case of a single-turn WRR. Finally, a bias stability of 1°/h is obtained with a 5-turn WRR of 4.05 cm diameter, achieving the tactical-grade resolution. To the best of our knowledge this is the best result reported to date for an RMOG of similar size.

Residual amplitude modulation induced error in resonant micro-optic gyroscope

A universal expression is proposed for evaluating the residual amplitude modulation (RAM) in a phase modulator. The different effects of the interference and linear terms of the RAM on the resonant micro-optic gyroscope (RMOG) are analyzed. It is found that the effect of RAM depends on the magnitude of RAM itself and the phase component. A theoretical model is then developed to calculate the RAM induced bias error in the RMOG. Finally, a technique for suppression of RAM is proposed and demonstrated, and the bias error of the separate-phase-modulation RMOG is successfully eliminated.

Design and Optimization of a Resonant Micro-Optic Gyroscope Based on a Transmissive Silica Waveguide Resonator

In order to optimize the performance of a resonant micro-optic gyroscope, a well-designed transmissive structure, which was obtained by optimizing the transmission coefficient of a coupler was used as the core component of a planar waveguide optical gyroscope. By analyzing the relationship between the resonator’s transmission coefficient and the gyroscope’s scale factor, the optical waveguide resonator sensing element with optimal parameters for the resonant micro-optic gyroscope was obtained. A scale factor of 1.34 mV/°/s was achieved using an open-loop system, and a bias stability of 183.7 °/h over a one-hour test was successfully demonstrated.

Polarization error in resonant micro-optic gyroscope with different waveguide-type ring resonator structures.

The waveguide-type ring resonator (WRR) is the key rotation-sensing element in a resonant micro-optic gyroscope (RMOG). A universal model used to analyze both the polarization characteristics of the WRR and corresponding temperature-related polarization error in the RMOG is presented. It indicates that the polarization problem stems from the excitation of two polarization states within the WRR. Unequal variations of incident lights on the cavity in the two directions can cause bias errors at the RMOG output. With the application of different silica WRRs to the RMOG, the polarization errors are tested and verify the theoretical results. Finally, a segment of tilted waveguide gratings with Brewster's angle is fabricated on the silica waveguide within the cavity. The measured polarization extinction ratio of the output light from the WRR is as high as 35.2 dB. The corresponding temperature dependence of the polarization error is theoretically reduced to 0.0019 (°/s)/°C, which indicates that temperature control is sufficient for a tactical grade RMOG.

Resonant micro optic gyroscope equipped with multi-turn waveguide ring resonator

Waveguide ring resonator (WRR) is beneficial to the miniaturization and integration of the resonant micro optic gyroscope (RMOG). The shot-noise-limited sensitivity of the RMOG equipped with the multi-turn WRR is derived. The simulation results show that when the crossing loss or the waveguide propagation loss is higher than 0.07 dB/crossing or 1.2 dB/m, the WRR of multi-turn structure does no good to the sensitivity of the RMOG. Two configurations of the WRR are introduced and tested. According to the measured waveguide propagation loss and crossing loss, the optimal angular random walk (ARW) is obtained when the RMOG equipped with a WRR of 2 or 3 turns. The ARW of the RMOG equipped with a 3-turn WRR is measured at different laser output power which agrees well with the theoretical value.

Measured radiation effects on InGaAsP/InP ring resonators for space applications.

Photonic ring resonators can be considered building blocks of new concept satellite payloads for implementing several functions, such as filtering and sensing. In particular, the use of a high Q-factor ring resonator as sensing element into a Resonant Micro Optic Gyroscope (RMOG), provides a remarkable improvement of the performance with respect to the competitive technologies. To qualify a ring resonator for Space applications, the radiation effects on it in the Space must be carefully evaluated. Here, we investigate the effects of gamma radiation on a high Q InGaAsP/InP ring resonator, for the first time, to our knowledge. The ring resonator under study has a footprint of about 530 mm2 and it is based on a InGaAsP/InP rib waveguide, with a width of 2 µm and a thickness of 0.3 µm, formed on a 0.7 µm thick slab layer on an InP substrate 625 µm thick. For a total dose of about 320 krad Co60 gamma irradiation, a mean variation of about 13% and 4% was measured for Q and extinction ratio (ER), respectively, with respect to the values before irradiation (Q = 1.36 × 106, ER = 6.24 dB). Furthermore, the resonance peak red-shifts with a linear behaviour was observed increasing the total dose of the absorbed radiation, with a maximum resonance detuning of about 810 pm. These non-significant effects of a quite high gamma radiation dose confirm the potential of high-Q InP-based ring resonators into Space systems or subsystems.

Synchronous in-phase and quadrature demodulation technique for resonant micro-optic gyroscope.

The phase modulation and demodulation technique is widely used in resonant optical gyroscopes to accurately detect resonance frequencies, which directly affect gyro sensitivity. In order to overcome the influences of the system phase fluctuations, an in-phase and quadrature (IQ) demodulation technique is introduced for a resonant micro-optic gyroscope (RMOG). The phase fluctuations in the RMOG are measured, and their influence on the demodulation slope at the resonance point is compared between the traditional sinusoidal demodulation and the IQ demodulation both theoretically and experimentally. It can be concluded that the output of the proposed IQ demodulation is not affected by any phase fluctuations. The demodulation slope is always at its maximum value, thus improving the signal-to-noise ratio of the detection system. By using the IQ demodulation technique, a random walk coefficient of 0.5°/√h is carried out. A long-term bias stability of 9°/h is successfully observed, which is improved by a factor of 1.6 compared with that obtained using the traditional phase-sensitive sinusoidal demodulation technique.

Resolution improvement for digital closed loop resonator micro-optic gyro based on tunable resonator

In the resonator micro-optic gyro (RMOG) frequency locking loop, digital-to-analog converter quantization error leads to low-accuracy laser tuning, causing frequency locking and rotation sensing dead zones. This paper proposes a planar waveguide resonator (PWR) frequency locking scheme with a piezoelectric (PZT) ring to tune the PWR resonant frequency to track and lock to the laser frequency. The proposed scheme achieved PZT-PWR Q = 4 × 107 and frequency tuning coefficient = 1.124 MHz / V. Direct comparison on an RMOG device experimentally verified the proposed scheme reduced frequency locking noise to 0.25 deg / s and improved gyro resolution from 1 to <0.05 deg / s.

Backreflections in resonant micro-optic gyroscope

Backreflection noise is one kind of main optical error in the resonant micro-optic gyroscope (RMOG). Resonance characteristics of backreflection noise in a RMOG is analyzed theoretically. Part of the backreflection noise can not be eliminated by using the traditional phase modulation techniques. This part of backreflection brings a nonzero bias to the output of RMOG due to the asymmetry of resonance curve. Degradation of gyro’s linearity is induced because this part’s transfer curve has two notches with separation proportional to the Sagnac phase shift when the RMOG is rotating. It’s recommended to set the length of straight waveguide to be half the ring length.

Single-polarization fiber-pigtailed high-finesse silica waveguide ring resonator for a resonant micro-optic gyroscope.

A new record for high-finesse silica waveguide ring resonators (WRRs), to the best of our knowledge, is demonstrated experimentally. The achieved finesse and resonant depths of the silica WRR with a length of 7.9cm and a diameter of 2.5cm are 196.7% and 98%, respectively. In addition, the silica WRR chip is coupled with single-polarization fiber to improve the polarization extinction ratio (PER) and, thus, to reduce the polarization error. With the application of this high-finesse and high-PER WRR to the resonant micro-optic gyroscope (RMOG), a bias stability of 0.004°/s is observed over a 1h timeframe. To the best of our knowledge, this is the first RMOG reported in the open literature that can sense the earth's rotation rate (15°/h).

Under-Coupling Whispering Gallery Mode Resonator Applied to Resonant Micro-Optic Gyroscope.

As an important sensing element, the whispering gallery mode resonator (WGMR) parameters seriously affect the resonant micro-optic gyroscope (RMOG) performance. This work proposes an under-coupling resonator to improve the resonator’s Q value and to optimize the coupling coefficient to maximize the RMOG’s sensitivity. GeO2-doped silica waveguide-type resonators with different coupling coefficients were simulated, designed, fabricated and tested. An under-coupling ring resonator with a quality factor of 10 million is reported. The RMOG system was built based on this resonator and the scale factor was tested on a uniaxial high-precision rotating platform. Experimental results show that this resonator could improve the RMOG sensitivity by five times.

Resonant micro-optic gyro using a short and high-finesse fiber ring resonator.

A novel hybrid integrated scheme is proposed for a high-performance resonant micro-optic gyro (RMOG), which requires a low-loss micro-ring resonator for mass production. A new record for the RMOG is established experimentally with a short fiber ring resonator and an integrated signal detecting and processing circuit. The finesse of the short fiber ring resonator with a length of 60 cm and a diameter of 4.77 cm is as high as 202, and the theoretical sensitivity of the RMOG is better than 0.3°/h assuming the average optical intensity at the photodetector is 1 mW. The 60 cm long spliceless micro-ring resonator is experimentally proved to be sufficient for a tactical-grade RMOG. An angle random walk coefficient of 0.64°/√h and a typical bias stability below 9.6°/h for the integration time of 50 s are successfully demonstrated using an innovative open-loop approach for an operation time of 1600 s.

Transfer function of optical waveguide ring resonator in frequency domain for micro-optic gyro

Resonator micro optic gyro (R-MOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. Optical waveguide ring resonator is the core-sensing element in R-MOG. According to the feature of the input signal, we established the transfer function of a Si-based ring resonator model in frequency domain for R-MOG with the coupled-mode theory. According to using the derived transfer function in the frequency domain, we analyzed the demodulation characteristics of R-MOG using Bessel function expansion based on laser frequency modulation spectrum technique. And we analyzed the relationship between the frequency modulation demodulation output signal and the resonant frequency deviation and obtained the best modulation coefficient applied in laser PZT drive. When the modulation coefficient M=2, the maximum linear interval slope, the demodulation curve is the best.

Test and Analysis of the Optical Kerr-Effect in Resonant Micro-Optic Gyros

As one kind of the main optical error sources in the resonant micro-optic gyro (RMOG), the optical Kerr-effect brings a nonzero bias to the output of the RMOG. The optical Kerr-effect induced bias error is proportional to the difference between the clockwise (CW) and counterclockwise (CCW) light-intensities input to the resonator. A new method for testing the optical Kerr-effect induced bias error in the RMOG is proposed and demonstrated. A square-wave intensity-modulated optical signal with a symmetrical duty ratio of 50% is achieved by an acousto-optic modulator (AOM), thus making the input-intensity mismatch between the CW and CCW lightwaves change periodically. In this way, we obtain the optical Kerr-effect induced bias errors that vary periodically in accordance with the variation of the square-wave signal. The experimental results show a good agreement with the theoretical value. Moreover, the testing result of the closed-loop RMOG is consistent with the open-loop one. The above method is insusceptible to other noise, such as the backscattering-induced noise and the polarization fluctuation.

Reduction of optical Kerr-effect induced error in a resonant micro-optic gyro by light-intensity feedback technique.

As a type of main optical error source in the resonant micro-optic gyro (RMOG), the optical Kerr-effect brings a nonzero bias to the output of the RMOG. The light-intensity fluctuations are interpreted as the cause. To eliminate the drifts due to the optical Kerr-effect, the intensities of the clockwise (CW) and counterclockwise (CCW) lightwaves circulating in the resonator should be equal at all times. Through theoretical analysis and experimental investigation, a linear relationship between the second-harmonic demodulated signal and the light-intensity input to the resonator is demonstrated for the sinusoidally phase modulated RMOG. Both our numerical simulation and experimental verification are carried out, which, for the first time to the best of our knowledge, demonstrate that the second-harmonic demodulated signal can be used as a feedback error signal to reduce both the input-intensity mismatch between the CW and CCW lightwaves and their intensity fluctuations. By applying the light-intensity feedback loop to the closed-loop RMOG, the light-intensity fluctuations are reduced to 2.7×10⁻⁵, down from 5.86%. As a result, the optical-Kerr effect induced error is effectively reduced.

Reduction of backreflection noise in resonator micro-optic gyro by integer period sampling

In resonator micro-optic gyros (RMOGs), the interference between the backreflection light beam of one pathway and the signal light beam of the other pathway deteriorates the gyro output waveforms, resulting in severe reduction in the gyro's accuracy. In this paper, an integer period sampling (IPS) method is introduced to minimize the sampling error caused by backreflection in RMOG for the first time to our knowledge. The experimental results show that both the bias repeatability and the short-term bias stability become better when the IPS condition is satisfied. A bias stability of 0.41°/s over one hour with an integration time of 10 s has been realized in a RMOG that employs a silica waveguide ring resonator.

Y-Type Branch Waveguide Used in Resonant Micro-Optic Gyro

Resonant Micro-Optic Gyro (RMOG) is a kind of optical sensors measuring angular velocity via Sagnac Effect, which yields different central resonant frequency between the clockwise (CW) and counterclockwise (CCW) light path of a ring-resonator when rotating. In this paper, Y-type branch waveguide is put forward to replace K-type coupler in RMOG to reduce the influence of splitting ratio asymmetry due to fabrication errors and temperature drift. Y-type branch waveguide based on silicon-on-silica is designed and analyzed. Simulation results show that Y-type branch waveguide performs better fabrication tolerance than K-type coupler, which reduces the nonlinear Kerr-Effect induced noise excited by power nonuniformity of the counter-propagating beams, therefore the detection sensitivity of RMOG can be improved.

Research on Mean Filtering Algorithm in Resonant Micro-Optic Gyro Signal Processing Based on Labview

As one of the new optical sensing devices, Resonant Micro-optic Gyro (RMOG) measures the rotation rate due to the resonance frequency difference based on the optical Sagnac effect. In order to reduce the influence of the light path and circuit noise and the output edge pulse signal, the mean filtering algorithm based on Labview is put forward to improve the gyros performance. The mean filtering algorithm is simulated and realized with Labview, which approves that the algorithm is effective in noise restraining. The test of RMOG demonstrates that the zero bias stability is 1.4 °/s during 1 hour with 10-second smoothing.

Analysis of Intensity Variation of Laser in Resonator Micro-Optic Gyro

The paper describes the basic principle and structure of the resonator micro-optic gyro (RMOG), the influence of intensity variation of laser is analyzed for the first time. The relationship between the light intensity input the integrated optical resonator (IOR) and the slope at working range is simulated and analyzed by the optical field overlapping method. The amplitudes of the output square waveforms with different zero biases are simulated and analyzed. The experimental setup is constructed and tested, the test result shows that in order to reach the limited ultimate sensitivity of 15.5 deg/h, it is necessary to restrict the zero bias within 8.1 deg/s under open-loop output scheme.

Current modulation technique used in resonator micro-optic gyro

Resonator micro-optic gyro (RMOG) is a promising candidate for the next generation inertial rotation sensor based on the Sagnac effect. A current modulation technique used in an external cavity laser diode is proposed to construct the gyroscope system for the first time. The resonance curves before and after eliminating accompanying amplitude modulation are theoretically analyzed, calculated, and simulated; the demodulation curves with different modulation currents are formulated theoretically; and the optimum modulation current corresponding to the maximum sensitivity is obtained. The experiment results from the established RMOG experimental setup demonstrate that a bias stability of 2.7 deg/s (10 s integrated time) over 600 s, and dynamic range of ±500 deg/s are demonstrated in an RMOG with a silica optical waveguide ring resonator having a ring length of 12.8 cm.