Ultra-High Stability Chip-Scale Optical Gyroscope

Based on the development of high sensitivity, low cost, high integration and miniaturization demand of the resonant micro-optical gyro(R-MOG), and in order to achieve a resonant micro-optical-mechano-electrical integrative gyro having high sensitivity, a microsphere optical resonator key sensitive element for producting a cavity with high quality value (Q value) and large diameter in the field of integrated optical micro resonator is proposed, for making a resonant micro optical gyro. Microsphere optical resonator is made by means of water-hydrogen flame melting, and the SiO2 microspherical cavity is formed under the natural cooling and contraction surface tension. Microsphere optical resonator with its diameter D ranging from 300 μm to 2200 μm is fabricated by melting method with hydrogen flame as a heat source through controlling the hydrogen flame’s area by regulating the flow of hydrogen gas. The resonator serves as the key unit of the resonant optical gyro sensitive parts, its Q value and diameter D have direct effect on the performance of the resonant angular velocity sensor. Affect parameters on the performance of the microsphere optical resonator with different diameters is tested and processed to obtain the result. The corresponding relationship among Q value, DQ product, resonant micro-optical gyro’s sensitivity and microspherical cavity diameter D is analyzed, and the reason for them is given. With the increase of microspherical cavity diameter D, the Q value and DQ product reduce after rising first, while the gyro sensitivity goes to rise and fall. Based on the microsphere optical resonator DQ product optimization research, the resonant micro-optical gyro’s key sensitive unit with best parameters is obtained. When the microspherical cavity diameter D varies from 600 to 200 μm, the gyro sensitivity can meet the condition that δΩ D is 1260 μm, the Q value of microsphere optical resonator is 7.18×107 and the corresponding optimal limited sensitivity of the resonant micro-optical gyro is almost 10°/h, and this result adequately meets the requirement of business level gyro applications. This work can serve as an experimental foundation in the research of new type resonant micro optical gyro at chip level, high accuracy and low cost, and will also provide a technical reference for further study of high integrated and high precision resonant micro optical gyro.

We present a simple analysis of the design of a passive miniature resonant optical gyroscope. By combining the requirements on the angular random walk and the bias stability, we end up with simple expressions of the minimum diameter of the ring waveguide cavity and the maximum power that should be used to probe it. Using state-of-the-art performances of photonic integrated circuit and whispering gallery mode technologies in terms of propagation losses and mode size, we show that tactical grade gyroscope performances can be achieved with a diameter of a few cm provided the detrimental influence of Kerr effect is mitigated, using for instance an active control of the unbalance in the intensities. We further extend the analysis to medium performance gyroscope and give some hints on the efforts to be made to potentially demonstrate a miniature resonant optical gyroscope with this level of performance.

As a new inertial navigation device, the resonant optical gyroscope offers advantages that include high precision, device integration, impact resistance, and solid-state realization. This device will be widely used in future military and civil applications. Following consideration of the factors that affect accuracy improvement of resonant fiber optic gyroscopes, the relationships among the insertion loss, coupling coefficient, and unit length loss of the cavity fiber and the resonance depth, full width at half maximum, and fineness of the transmission spectrum line are analyzed. To improve the transmission spectrum’s resonance depth, the coupling coefficient should be controlled at 0.2 and the optical coupler insertion loss should be reduced as far as possible. Additionally, the laser linewidth effects on the transmission spectrum and the limit sensitivity are analyzed. It is found that if the laser linewidth of the resonant optical gyroscope is less than 100 kHz, it can meet the resonance depth requirements, thus, providing a technical reference for further research into integrated optical waveguide gyroscopes.

In the last decade, substantial progress has been made to improve the performance of optical gyroscopes for inertial navigation applications in terms of critical parameters such as bias stability, scale factor stability, and angular random walk (ARW). Specifically, resonant fiber optic gyroscopes (RFOGs) have emerged as a viable alternative to widely popular interferometric fiber optic gyroscopes (IFOGs). In a conventional RFOG, a single-wavelength laser source is used to generate counter-propagating waves in a ring resonator, for which the phase difference is measured in terms of the resonant frequency shift to obtain the rotation rate. However, the primary limitation of RFOG performance is the bias drift, which can be attributed to nonreciprocal effects such as Rayleigh backscattering, back-reflections, polarization instabilities, Kerr nonlinearity, and environmental fluctuations. In this paper, we review the challenges and opportunities of achieving performance enhancement in RFOGs.

The first- and second-order fractional-order proportional integral (FOPI) controllers based on the Al-Alaoui operator and the continued fraction expansion method are designed and applied to the closed-loop control system of a resonant optical gyro. The phase margin method is used to tune the control parameters. The characteristics of the unit step responses of the integer order proportional integral (IOPI) and the FOPI controllers are calculated and compared. Responses to perturbations at different positions of the closed-loop control system are simulated. Results show that for the resonant optical gyro, the FOPI closed-loop control system has much better unit-step-response performance and noise-resistance ability than the IOPI control system, which is important for improving the dynamic response characteristics and the robustness of the gyro’s feedback system and enhancing the detection ability of the gyro. Experiments on a resonant optical gyro experimental system also verify the advantages of the FOPI controller in step response and bias stability.

Resonant integrated optical gyroscopes (RIOGs) could integrate multiple devices onto a single chip, further reducing the size and weight of the gyroscope and opening it up to a broader spectrum of applications. This paper conducts in-depth research on resonant optical gyroscopes. A silicon on insulator (SOI) resonator ring with a Q value of 4.65×106 was designed based on the Hermite curve. A resonant micro-optical gyroscope (RMOG) was achieved using the resonator ring, traditional phase modulators, and detectors. The results show that the bias instability of the RMOG can reach 0.004°/s, and the gyroscope has the ability to detect angular velocities ranging from -600°/s to +600°/s. Furthermore, a RIOG was demonstrated by designing PIN modulators, detectors and a ring resonator on a single chip, significantly reducing the system floor space to 25 mm2, and the bias instability testing is 0.06°/s.

A new double closed-loop control system with mean-square exponential stability is firstly proposed to optimize the detection accuracy and dynamic response characteristic of the integrated optical resonance gyroscope (IORG). The influence mechanism of optical nonlinear effects on system detection sensitivity is investigated to optimize the demodulation gain, the maximum sensitivity and the linear work region of a gyro system. Especially, we analyze the effect of optical parameter fluctuation on the parameter uncertainty of system, and investigate the influence principle of laser locking-frequency noise on the closed-loop detection accuracy of angular velocity. The stochastic disturbance model of double closed-loop IORG is established that takes the unfavorable factors such as optical effect nonlinearity, disturbed disturbance, optical parameter fluctuation and unavoidable system noise into consideration. A robust control algorithm is also designed to guarantee the mean-square exponential stability of system with a prescribed H∞ performance in order to improve the detection accuracy and dynamic performance of IORG. The conducted experiment results demonstrate that the IORG has a dynamic response time less than 76us, a long-term bias stability 7.04°/h with an integration time of 10s over one-hour test, and the corresponding bias stability 1.841°/h based on Allan deviation, which validate the effectiveness and usefulness of the proposed detection scheme.

Bias stability is a critical performance parameter in navigation applications. We investigate the possibility of enhancing the bias stability in a navigation grade Resonant Fiber Optic Gyroscope (RFOG) through the use of dual frequency comb source. In a conventional RFOG, a single wavelength laser source is used to generate counter propagating waves in a ring resonator whose phase difference is measured to obtain the rotation rate. However, the primary limitation of the RFOG performance is the bias drift observed due to non-reciprocal effects such as Kerr nonlinearity, Rayleigh backscattering, and environmental fluctuations. To enhance the bias stability, we have investigated an alternative approach based on a frequency comb source. By using different set of frequencies (3, 5, 7, 9 etc) for the counter propagating waves, the above limitations can be mitigated since the uncertainty in the demodulated phase is diminished compared to a single frequency measurement leading to enhanced accuracy in the rotation rate determination. Using a theoretical model of the frequency comb-based RFOG, we have carried out simulations in Matlab and investigated the bias stability enhancement with respect to the number of comb lines used. Our simulation results shows that a bias stability of 0.01°/hr can be achieved using frequency comb source with 5 fundamental modes in ring resonator.

Nowadays interferometric fiber-optic gyroscopes (FOG, IFOG) are extensively used in strapdown INS, and in broad range of applications they have replaced their main competitor and predecessor - ring laser gyroscopes (RLG). To cover the new perspective applications with demands for low-cost and compact but precise inertial sensors, Optolink developed new products: most compact inertial measurement units IMU200 and IMU400. The aim of the current work was the development of pilot IMU200 devices and the estimation of the performance of IMU200 and IMU400 with direct measurements and also with SINS simulation methods. IMU200 SWaP properties are as follows: 75×75×60mm, <0.5kg, 1/3 l, ≤6W. The main IMU200 Gyro/Accelerometer accuracy parameters: Angle Random Walk (ARW) = 0.015°/√hour, Bias Instability (BI) = 0.02°/hour; Velocity Random Walk (VRW) = 40µg/√Hz, BI = 6µg. For IMU400, developed before IMU200, SWaP properties are: 80×95×62 mm, <0.7kg, ½ l, ≤7W. The main IMU400 accuracy parameters are: ARW = 0.007°/√hour, BI = 0.01°/h; Velocity Random Walk (VRW) = 40µg/√Hz, BI = 6µg. SINS expected performance (1σ, 10 min alignment time): for IMU200 heading 0.4°×sec(lat), for IMU400 ~ 0.2°×sec(lat).

The performance of passive fiber optic gyroscopes involving ring resonators is limited mainly by the loss and finesse of the cavity. In this work, we show performance enhancement of the recently studied resonant fiber optic gyroscope with a "reflector" using active loss compensation. Our gyroscope does not require expensive ultra-narrow linewidth lasers, expensive lock-in detection methods, or polarization-maintaining fibers, which are mandatory for all standard resonant fiber optic gyroscopes. The performance of this gyroscope shows four-fold enhancement in the $Q$Q factor $ (2.2 \times {10^8}) $(2.2×108), compared to an earlier experimental setup involving losses. Enhanced sensitivity to rotation is experimentally demonstrated using loss compensation as well as tuning the embedded reflector in the resonator. A shot-noise-limited sensitivity of 0.03 deg/h is possible with this experimental realization. This work demonstrates that our gyroscope can provide a cost-effective alternative, even in the navigational grade.

To suppress the high frequency noise in resonant micro optic gyroscope, this paper proposes a reduced sampling rate proportional-derivative control loop. Simulation results show that the loop bandwidth is broaden to 19.3 kHz.

Rayleigh backscattering noise, which is one of the reasons that limit the sensitivity, has been deemed as noise in traditional resonant optic gyroscopes. However Rayleigh backscattering noise is one of the incentives of mode splitting phenomenon in high-Q resonators. Regarding the change of the resonance frequency of the resonator caused by the scattering signal as a measurement, we can use mode splitting to measure temperature, size of nanoparticle, etc. Light is confined by total internal reflection in whispering gallery mode (WGM) optical resonators, which is characterized by high-Q factors and small mode volumes. With regards to this, we propose a sensing mechanism based on mode splitting in high-Q WGM optical resonators. It is possible for us to measure the angular velocity of carrier according to the changes in the resonant frequencies of the two splitting modes. We propose the Miniature resonant optic gyroscope based on mode splitting (MROG-MS) with WGM resonators in the paper. Considering the Sagnac effect, mode splitting in high quality optical micro-resonators, and the rotation-induced impact on backscattering process, we modify the equations of motion that describe mode splitting, derive the explicit expression of angular rate versus the splitting amount, and verify the sensing mechanism by the simulation based on COMSOL. Furthermore, after monitoring the transmission spectra at different number of scattering particles, the simulation shows that mode splitting phenomenon resulted by single particle is more suitable for angular velocity measurement.

Non-reciprocal biasing for performance enhancement of the resonant fiber gyroscope with ‘Reflector’ using In-line Faraday rotators: Design, analysis and characterization

Since the developments of lasers and the optical fibers in the 70s, the optical gyroscopes have been subject to an intensive research to improve both their resolution and stability performances. However the best optical gyroscopes currently on the market, the ring laser gyroscope and the interferometer fiber optic gyroscope are still macroscopic devices and cannot address specific applications where size and weight constraints are critical. One solution to overcome these limitations could be to use an integrated resonator as a sensitive part to build a fully Integrated Optical Resonant Gyroscope (IORG). To keep a high rotation sensitivity, which is usually degraded when downsizing this kind of optical sensors based on the Sagnac effect, the resonator has to exhibit a very high quality factor (Q): as detailed in equation (1) where the minimum rotation rate resolution for an IORG is given as a function of the resonator characteristics (Q and diameter D) and of the global system optical system characteristics (i.e. SNR and bandwidth B), the higher the Q×D product, the lower the resolution.

Three closed loop noise suppression method for resonant micro optical gyroscope