Optic Gyroscope Research Articles

Ultrahigh bandwidth measuring approach of an I-FOG based on axial magnetic sensitivity.

The bandwidth is one of the key indicators of the interferometric fiber optic gyroscope (I-FOG) in the application with high frequency jitter. The traditional bandwidth measurement equipment, such as the angular vibration table, can only provide angular vibrations of hundreds of hertz and cannot meet the measurement needs of a high bandwidth gyro. We propose an approach, with which a signal of several thousand hertz can be provided and can measure a high bandwidth of I-FOGs. The bandwidth measurement approach is based on the axial magnetic sensitivity. We present the measurement principle, derive the axial magnetic sensitivity expression of the fiber coil in I-FOGs, and demonstrate the bandwidth measuring system. With this system, the bandwidth of an I-FOG is measured and the experimental result shows that the bandwidth is ∼10 kHz. It is proved that this new, to the best of our knowledge, approach is capable of testing the bandwidth of the I-FOG at ultrahigh frequencies.

Polarization Stability of Spun Fiber Resonator for Resonant Fiber Optic Gyro

As an important inertial navigation sensor, resonant fiber optic gyro (RFOG) has become a research hotspot in recent years due to its advantages of light weight and high stability. The optical effects in the fiber ring resonator(FRR), such as scattering effects, polarization mode crosstalk, etc., are the bottleneck restricting the development of RFOG, and they are also the key problems that researchers are trying to solve. Aiming at the problem of polarization noise, this paper conducts in-depth theoretical and experimental research on polarization stability using spun fiber resonator for the first time. Compared with a common polarization-maintaining fiber (PMF) resonator of the same length, the results show that the RFOG using the spun fiber resonator has improved temperature stability compared to the conventional resonator structure. This research provides a new idea for the polarization noise suppression method of RFOG, and lays an important foundation for the practical application of spun fiber in RFOG.

Systematic Measurement of Temperature Errors of Positive and Negative FOG Scale Factors Using a Low-Precision Turntable

Measurement of temperature errors of fiber optic gyro (FOG) scale factor is important in FOG technology. In traditional methods, the measurement errors of FOG scale factors are greatly affected by the turntable’s orientation control errors. This article proposes a systematic method to measure the positive and negative FOG scale factor errors using a low-precision turntable. The relationship between the inertial navigation errors and the complete inertial measurement unit errors is revealed. A simplified tracking algorithm is devised to obtain the change rates of the velocity errors with lower computation. A measurement procedure is designed, with three groups of π and -π rotations around the east axis of the turntable at each temperature. Observation equations are derived to estimate the positive and negative FOG scale factor errors. Simulation and experimental results show that a low-precision turntable can accurately measure the FOG scale factor errors at each temperature. Furthermore, temperature errors of accelerometer biases, scale factors, and nonlinear scale factors can also be measured at the same time using the rotation sequences and formulas in this article without additional rotations.

Dual-polarization interferometric fiber optic gyroscope with Shupe effect compensation

Dual-polarization (DP) interferometric fiber optic gyroscope (IFOG) has been studied for over a decade, which has important applications in inertial navigation and rotational seismology. Currently, the Shupe effect is an important factor degrading the accuracy of the DP IFOG. Here, a dual-quadrupolar winding pattern is proposed to compensate for the Shupe effect. The finite-element simulation experiments verify that the phase shifts induced by the Shupe effect in two polarizations are almost reversed and well compensated. Static laboratory test results show that, in this configuration, the angle random walk is reduced 10-fold to 7.1×10−5 °/h, while the bias instability is reduced ninefold to 1.7×10−4 °/h. Moreover, a 3-h temperature variation experiment is carried out. The results show that, compared with the original output, the net rotation rate errors originating from the Shupe effect are effectively compensated and the temperature drift is reduced by 13 times. To summarize, the dual-quadrupolar-wound method is a valid approach to compensate for the Shupe effect, and the temperature adaptability of this DP configuration is greatly enhanced.

Coherent optical gyroscope on the basis of the bidirectional ultra-short pulse Erbium ring fiber laser

A gyroscopic effect has been studied in the bidirectional ultra-short pulse erbium-doped fiber ring laser hybridly mode-locked with a co-action of a Single-Walled Carbon Nanotube-based saturable absorber (SWCNT-SA) and Nonlinear Polarization Evolution introduced by means of the short-segment polarizing fiber. Owing to the Kerr nonlinearity contribution through self-phase modulation and self-steepening effects to the carrier-to-envelope phase slip of both clockwise (CW) and counterclockwise (CCW) solitons, wideband controllable tuning of a gyroscope bias point has been demonstrated by means of an appropriate adjustment of either intracavity polarization or pump power. Angular velocity detected ranges from 0.12 deg/s to 360 deg/s while the highest rotation sensitivity reaches 7 kHz/(deg/s) for 0.79 m2 single-coil ring gyroscope being in agreement with the calculated scale factor value. The gyroscope dead band with upper limit of ≈5.15 deg/s corresponding to the beat-note frequency of ≈15 kHz has been detected during clockwise rotation of the gyroscope. The highest gyroscope resolution of ≈0.01 deg/s=38 deg/h has been estimated on the basis of the bias point drift measurement.

Simulation Study on Digital Control Model of Fiber Optic Gyro SLD Light Source

Fiber Optic Gyroscope is an angular velocity sensitive device based on Sagnac effect. Super Luminescent Diode (SLD) is a widely used light source in fiber optic gyroscope, and its characteristics will directly affect the overall performance of gyroscope. In this paper, the working mechanism of SLD light source is studied, and the photoelectric characteristics of SLD light source and the influence of light source temperature and driving current on center wavelength are analyzed. According to the relationship between the central wavelength of the light source and the driving current and die temperature, a three-dimensional model of the central wavelength of the light source is obtained. In order to control the driving current and die temperature quickly and stably, the fuzzy PID control scheme of die temperature and incremental PID control scheme of driving current are studied and designed. Based on the three-dimensional model of the center wavelength of light source, the center wavelength of SLD light source is controlled stably and quickly.

Advanced Interferometric Fiber Optic Gyroscope for Inertial Sensing: A Review

As one of the most successful applications in optical fiber sensing, interferometric fiber optic gyroscope (IFOG) has become the ideal choice for inertial navigation systems, and has been widely used in the fields of aviation, aerospace, navigation, and land. Exploring the theoretical noise limit and improving the practical precision are the objectives of FOG investigations, and the advanced photonic crystal fibers offer powerful approaches and potential to achieve these goals. In this review, the progress of photonic crystal fibers in FOGs research and applications for angular velocity measurement have been reviewed, together with the advanced technologies for improving the FOG's precision and reducing its volume.

Radiation-Induced Magneto-Optic Fluctuations in Spaceborne Fiber-Optic Gyroscope

Radiation-induced magneto-optic fluctuations (RI-MOF) is a kind of environmental compounding effect of fiber optic gyroscope (FOG) in space application. Here, we suggested a model of RI-MOF and experimentally tested it in irradiated polarization-maintaining fibers (PMFs) and polarization-maintaining photonic crystal fibers (PM-PCFs). The test results reveal that the main sources of RI-MOF are the radiation-induced change of the Verdet constant and the modal birefringence. In a spacecraft with good thermal control conditions, an evaluation method based on the RI-MOF model can be summarized and implemented to suppress the environmental disturbance on the performance of FOG.

Hysteresis of lock-in range in a He-Ne ring laser gyroscope.

In this paper, a hysteresis of the lock-in range in a He-Ne ring laser gyroscope is theoretically analyzed. We propose a new model accounting an additional coupling of the counterpropagating waves due to their diffraction on the gratings induced in the cavity mirrors. Numerical simulations in the proposed model show the existence of broad hysteresis areas of a lock-in range. Dependence of hysteresis on the pump excess above the threshold has been studied.

Performance analysis of the fiber coils combining hybrid polarization-maintaining fiber designs and symmetrical winding patterns.

Research on the performance of polarization-maintaining fiber (PMF) for fiber coils is significant for the precision improvement of an interferometric fiber optic gyroscope (IFOG) working in harsh environments. In this paper, we firstly report analytical models of the fiber polarization theory and present two types of hybrid PMF structures by a collaboration of geometry and stress effects: a Panda-type horizontal-elliptical core PMF (Panda-type HE-PMF) based on a superposition of geometry and stress, and a Panda-type longitudinal-elliptical core PMF (Panda-type LE-PMF) with geometry offset stress effect, achieving enhanced and suppressed modal performance by adjusting geometric anisotropy of elliptical-core in different directions. Then, the influence mechanisms of the geometric birefringence on the modal performance of both PMFs as the variation of fiber structural parameters are investigated via numerical simulations to determine the target fiber designs. The other significant attribute, including effective mode area (Aeff), nonlinear coefficient (γ), and chromatic dispersion (D), and their tolerance to PMF parameter fluctuations are also evaluated. Finally, both target PMFs with structural optimization are practically fabricated and wound into four fiber coils with quadrupolar (QAD) and 16-polar symmetrical winding patterns, respectively. The polarization ability and thermal performance are further demonstrated by experiments conducted on both PMFs, wound fiber coils, and built IFOGs under static and dynamic environments (over a wide temperature range of -40 °C to 70 °C), and compared with a conventional PMF. The testing results suggest that designed HE-PMF coils both achieve high birefringence, static extinction ratio (ER) values of up to 30.80 dB and 31.93 dB, respectively, corresponding to an almost one-fold increase over conventional coils. Remarkably, the ER property of the HE-PMF coil by combining this HE-PMF design and a 16-polar winding pattern consistently remains above 29.5 dB with a minimal fluctuation in ER of only 3.0 dB across the entire variable temperature conditions. The bias stability of the IFOG assembled with this coil is strongly enhanced to 0.0019 °/h and 0.082 °/h under static and dynamic conditions, respectively, which is a significant improvement over conventional coils of 0.136 °/h. Also, the static angle random walk performance of the improved IFOG is reduced to 0.000624 °/√h. In contrast, the LE-PMF as a comparison is shown to limited polarization characteristics with a low birefringence and ER due to the suppression effect of the geometric birefringence, and the applied IFOG output also exhibits larger drift, indicating a poor thermal ability. Experimental results show great agreement with theoretical analysis and numerical simulations, confirming the validity of design principles. The advances in both designs are instructive for the engineering applications of PMFs for IFOGs and for improving the accuracy of fiber sensors.

Application and Development of Fiber Optic Gyroscope Inertial Navigation System in Underground Space

Fiber Optic Gyroscope Inertial Navigation System (FOG-INS) is a navigation system using fiber optic gyroscopes and accelerometers, which can offer high-precision position, velocity, and attitude information for carriers. FOG-INS is widely used in aerospace, marine ships, and vehicle navigation. In recent years, it has also played an important role in underground space. For example, in the deep earth, FOG-INS can be used in directional well drilling, which can enhance recovery in resource exploitation. While, in shallow earth, FOG-INS is a high-precision positioning technique that can guide construction in trenchless underground pipelaying. This article extensively reviews the application status and latest progress of FOG-INS in underground space from three aspects—FOG inclinometer, FOG drilling tool attitude measurement while drilling (MWD) unit, and FOG pipe-jacking guidance system. First, measurement principles and product technologies are introduced. Second, the research hot spots are summarized. Finally, the key technical issues and future trends for development are put forward. The findings of this work are useful for further research in the field of FOG-INS in underground space, which not only provides new ideas and directions for scientific research, but also offers guidance for subsequent engineering applications.

Rest-frame analysis of rotating metamaterials, gyroscopes, and century-old problems in number theory [Invited

We discuss the electrodynamics of slowly rotating metamaterials as observed in their rest frame of reference, using first order polarizability theory. A formulation governing the response of an arbitrary array of scatterers to excitation under rotation is provided and used to explore the rotation footprint properties, with applications to non-reciprocal dynamics, rotation sensors and optical gyroscopes. The metamaterial sensitivity to rotation is rigorously defined, and the associated physical mechanisms are exposed. These can be intimately related to two century-old problems in number theory: the no-three-in-line problem (N3IL), and the Heilbronn triangle problem. New arrays, base on Erdős solution to the former, are proposed and their sensitivity to rotation is explored. It is shown that structures inspired by Erdős solution may achieve rotation sensitivities that outperform that of the Sagnac loop gyroscope. The average and peak performances of ensembles of random arrays are also explored. The effect of signal noise on the rotation sensitivity is studied. It is shown that the additional degrees of freedom suggested by metamaterial approach to rotation sensing can be used to minimize the negative effect of signal noise on the smallest detectable rotation rate. Furthermore, we show that the systematic N3IL constructions inspired by Erdős encapsulates most of the significant factors leading to enhanced rotation-sensitive metamaterials.

Accurate measurement and enhancement of fiber coil symmetry.

The pure Shupe effect is substantially reduced in a fiber optic gyroscope (FOG) with symmetrical windings. However, the effect of the temperature-induced nonuniformity of the stress in the coil depends on the mean temperature derivative (T-dot). Research on precision winding technology has discovered that the symmetry of optical fiber rings affects the temperature performance of fiber optic gyroscopes. Optical fiber rings with good symmetry also have good temperature performance. This paper first establishes a temperature drift model of optical fiber rings that includes the Shupe effect and T-dot effect and then uses finite element simulation to analyze the drift error of optical fiber rings in a variable temperature environment. Analysis shows that this drift is caused by the variation and uneven distribution of the fiber length and the refractive index in the positive and negative winding of the optical fiber ring, which results in a residual phase difference that is directly related to the symmetry of the optical fiber ring. Simulation and analysis show that balancing the residual phase difference of the optical fiber ring can be achieved by cutting the length of the optical fiber ring at both ends. This paper uses optical frequency domain reflectometry (OFDR) technology to precisely test the symmetry of the optical fiber ring, ensuring accurate adjustment of the lengths at both ends of the optical fiber ring. Experimental tests on two gyroscopes have shown that the optical fiber ring with a smaller drift error can be obtained after testing and adjusting its length. The experimental data indicates that the bias stability of two laboratory gyros are increased by 23.6% and 18.1%, and the bias range are reduced by 22.4% and 30.0%.

Methods for Comprehensive Calibration of a Low-Frequency Angular Acceleration Rotary Table

The total harmonic distortion (THD) index and its calculation methods are presented to calibrate the sinusoidal motion of the low-frequency angular acceleration rotary table (LFAART) and make up the incomprehensive evaluation based on the angular acceleration amplitude and frequency error indexes. The THD is calculated from two measurement schemes: a unique scheme combining the optical shaft encoder and the laser triangulation sensor and a regular scheme using the fiber optical gyroscope (FOG). An improved reversing moments recognition method is presented to upgrade the accuracy of solving the angular motion amplitude based on optical shaft encoder output. The field experiment shows that the difference in the THD values achieved using the combining scheme and FOG is within 0.11% when the signal-to-noise ratio of the FOG signal is higher than 7.7 dB, indicating the accuracy of the proposed methods and the feasibility of taking THD as the index.

Autonomous Instrumental Error Correction for a Strapdown Inertial Navigation System

Microelectromechanical systems (MEMS)-based strapdown navigation systems offer advantages such as small size, low cost, and minimal power consumption. However, MEMS sensors are prone to significant low-frequency noise and poor bias repeatability, which can lead to navigational errors over time. These errors make them unsuitable for autonomous navigation applications, even with frequent recalibration. One way to solve this problem is the rotation modulation method. This approach is widely recognized but has only been successful with precise laser and fiber optic gyroscopes equipped with precise rotating platforms. This article focuses on the potential of adapting the rotation modulation method for the case of inexpensive MEMS sensors that can significantly improve navigation performance while maintaining the benefits of microelectromechanical technologies. Potential issues of implementation were discussed, and corresponding requirements were formulated. The proposed optimal computation scheme was verified during static tests of the developed inertial measurement unit (IMU). The rotation of the IMU is capable of harmonically modulating the quasi-static errors of inertial sensors, which are practically eliminated during the navigational algorithm processing estimation, which paves the way for a significant reduction of its navigation errors and increases its autonomous operation time. The static tests conducted in laboratory conditions confirmed the research method's high technical potential. It has been shown that the proposed method is effective for various spatial orientations of the rotational modulation axis. Installing an IMU on a non-steering car wheel allows for abandoning an artificial rotational motion source while preserving the proposed method's advantages. The proposed implementation's main limitation is that the IMU's output data update frequency becomes a multiple of the frequency of the modulating rotation. Accordingly, this frequency should be at least twice the maximum frequency of body manoeuvres to ensure their observability. Additionally, a critical issue is the compensation of the angular velocity of modulation from gyroscope readings. However, despite the mentioned considerations, such an implementation of IMU modulation by rotation still has enormous potential for application in terrestrial navigation.

Exceptional point based lattice gyroscopes

Ring laser gyroscopes (RLGs) based on non-Hermitian exceptional points (EPs) have garnered much recent interest due to their exceptional sensitivity. Such gyroscopes typically consist of two-ring laser resonators, one with loss and one with an equal amount of optical gain. The coupling strength between these ring resonators is a key parameter determining the sensitivity of EP-based RLGs. Here we explore how the exceptional sensitivity demonstrated in this coupled dimer may be further enhanced by adding more dimers in an array. Specifically, we propose two types of ring laser gyroscope lattice arrays, each composed of N coupled dimers arrayed serially or concentrically with periodic boundary conditions, that guide counter-propagating photons in a rotating frame. Using coupled mode theory, we show that these lattice gyroscopes exhibit an enhanced effective coupling rate between the gain and loss resonators at the EP, thereby producing greater sensitivity to the angular rotation rate than their constituent dimers. This work paves the way toward EP-based RLGs with the necessary sensitivity for GPS-free navigation.

Ring Laser Gyros: Improving Precision and Accuracy Through Soft-Core Processor-Based Active Current Balance Control Approach- Simulation and Implementation Results

In this article, we intend to demonstrate on digital active current control in ring laser gyros (RLG). The specific source errors that effect the performance of laser gyro is discussed. This work proposes a system of digital detection and control system to address deficiencies of the conventional analog circuits. The hardware framework is constructed using the Field Programmable Gate Array (FPGA) and the required analog interface, which incorporates driving and acquisition circuitry for the specific physics of gyros. The software flow is provided in full and uses the parallel PI (proportional-integral) control algorithms. The outcomes demonstrate that the precision of anode currents are accurately controlled within ±0.1µA along with cathode voltage, demonstrating that the performance of the digital system is superior to that of analog circuits, which will be very beneficial for the laser gyro application. The simulation results prove that the proposed approach has good result of balancing anode currents, meanwhile, it makes the sensor a good dynamic performance. In both anodes, the experimental findings are contrasted with balanced and unbalanced currents. The optimal constant current is obtained from the remarkable agreement between simulated and experimental results.

Modulation index detection and stabilization technique of phase modulator in resonant fiber optic gyro base on sampling demodulation

A new modulation index detection and stabilization technique (MIDST) based on sampling demodulation is proposed to reduce the influence of phase modulator (PM) thermal instability on resonant fiber optic gyro (RFOG). Firstly, the factors causing the PM thermal instability and the influence on RFOG are analyzed. Then, a phase modulation index detection technique is proposed to detect the fluctuation of modulation index without complicating the optical path configuration of RFOG. Finally, considering the temperature fluctuation, a modulation index stabilization loop based on auto disturbance rejection controller (ADRC) is designed to stabilize the phase modulation index. In experiments, modulation index can be detected in real time and accurately, and the fluctuation is reduced from 10% to 0.3% over 100 °C temperature range (−40 °C to ＋60 °C) with MIDST. The stability of scale factor and the suppression effect of backscattering noise could be improved effectively.

APPLICATION FEATURES OF GLASS-CERAMIC SO-115M IN MANUFACTURING OF OPTICAL PARTS FOR RING He-Ne-LASERS

The results of an investigations into the effect of filamentous striae with birefringence from 3 to 15 nm/cm in SO-115M glass-ceramic on the manufacturing quality of optical parts for ring lasers and the exact characteristics of laser gyroscopes based on them are presented. It is shown that the presence of striaes with stresses of no more than 15 nm/cm in SO-115M glass-ceramic does not depend on the speed of manufacturing the resonator optical circuit and the quality of its assembly. The presence of striaes in the output mirror additional backscattered of a ring laser may have the destination of lock-in zone. Correct adjustment of the output mirror allows to reduce scattering and reveal the growth of the lock-in zone in laser gyroscope. It is shown that the accuracy of the laser gyroscope improves by the quality mirror substrates, the geometry of the resonator body, and increases the accuracy of scattering inside the resonator.

Effective Frequency Lock-In Changes of a Ring Laser Gyroscope Due to Harmonic Components of Dithering Signal

The frequency lock-in phenomenon is the most important error factor that degrades the performance of a ring laser gyroscope by causing a non-linear output to the rotational angular velocity input. To solve the problem of frequency lock-in, a mechanical dithering technique has been proposed and most successfully and widely applied to date. In addition, in the case of dithering with a sinusoidal signal of a single-frequency component, the theoretical background is well established. However, in actual applications, it is almost impossible to implement a perfect single sinusoidal signal owing to various electrical and mechanical constraints. In general, although the occupied portion is smaller than the fundamental frequency component, the dithering signal inevitably includes harmonics. Therefore, it is essential to analyze the influence of the corresponding harmonic component to accurately predict the frequency lock-in characteristics of a ring laser gyroscope. In this study, it is assumed that the dithering signal has odd harmonics, and through numerical experiments, the frequency lock-in widths of the ring laser gyroscope according to the dithering amplitude change and the effectiveness of improving the related characteristics according to the application of random dithering are analyzed. The analysis confirmed that the resonance condition, including the higher harmonics of mechanical dithering, can be a major variable that determines the frequency lock-in characteristics of the ring laser gyroscope. To improve the relevant performance of the ring laser gyroscope, in-depth research from that point of view is necessary.