Fiber Optic Gyroscope Research Articles

Magnetic error suppression in Polarization-Maintaining fiber optic gyro system with orthogonal polarization states

In this paper, a polarization-maintaining fiber optical gyro (PMFOG) based on orthogonal polarization states is constructed. The clockwise light and counterclockwise light in the PMFOG pass through the same fiber coil with X/Y polarization and Y/X polarization respectively. Theory and experiments have shown that this system not only doubles the sensitivity of the PMFOG at the same length, but also suppresses the magnetic error obviously compared with the single-polarization PMFOG. The Poincare sphere model is established in the PMFOG with orthogonal polarization states under the radial magnetic field, which intuitively shows that magnetic error is opposite in the orthogonal polarization state, and can offset through each other. The radial magnetic error is suppressed from 0.112°/h/Gs to 0.011°/h/Gs, and the suppression reaches 10.07 dB. Meanwhile, the axial magnetic error is suppressed from 0.183°/h/Gs to 0.092°/h/Gs, achieving a suppression effect of 2.9 dB. The results of this research are of great significance to the miniaturization, the improvement of signal-to-noise ratio, and the optimization of environmental adaptability in fiber optic gyroscope.

Error analysis of dual-polarization fiber optic gyroscope under the magnetic field-variable temperature field

A dual-polarization fiber optic gyroscope system is built to systematically analyze the nonreciprocal errors of the system under the magnetic field-variable temperature field. Under the magnetic field-variable temperature field, the nonreciprocal errors are caused by magnetic-thermal coupling birefringence nonreciprocal error, linear birefringence nonreciprocal error and Shupe effect error. The nonreciprocal errors of dual-polarization fiber optic gyroscope system are related to temperature and temperature gradient. In X and Y polarization states, the signs of magnetic-thermal coupling birefringence nonreciprocal error and linear birefringence nonreciprocal error are opposite, and these two errors can be suppressed in the dual-polarization system. But the Shupe effect errors are the same in X and Y polarization states, which can not be suppressed in the dual-polarization system. The experimental results are consistent with the theoretical analysis, which verifies the correctness of the nonreciprocal error model under the magnetic field-variable temperature field. The research results provide a theoretical and experimental basis for the study of the environmental adaptability of the fiber optic gyroscope and other common-path fiber sensing systems based on dual-polarization.

Suppressing backscattering noise of a resonant fiber optic gyroscope using coherent detection.

This paper provides a novel, to the best of our knowledge, method for suppressing backscattering noise of a resonant fiber optic gyroscope (RFOG) with a coherent detection technique. The light from the fiber ring resonator is mixed with a reference beam rather than being demodulated directly in traditional configurations, generating a coherent signal with a radio frequency. The central frequencies of the two reference lights used for the clockwise and counterclockwise waves are different to avoid the effect of backscattered waves. Besides, a common phase modulation is applied on the two counter-propagating waves to eliminate the parasitic effect due to the residual amplitude modulation in the phase modulator. Two demodulation schemes for the rotation rate detection from the coherent signals are then proposed and demonstrated, with performance on noise suppression tested. One is the beat-frequency demodulation, and the other is the self-mixing demodulation technique. The influence of backscattering intensity is reduced from 270°/h to 3°/h and 0.05°/h with the two demodulation techniques, respectively, showing a full suppression of backscattering noise.

Heading-sensitive azimuth error analysis and scheme modification for the multi-position alignment of a fiber-optic gyro strapdown inertial navigation system.

As two-position is the most widely used scheme of multi-position alignment, azimuth error analysis regarding the whole alignment procedure as an entity is explicitly discussed. A formula to calculate an equivalent north accelerometer bias drift rate is developed. The effecting extent of each inertial measurement error is also theoretically deduced and validated through simulation. It is pointed out that the main error sources causing heading-sensitive azimuth error are accelerometer triad non-orthogonality and lever arm error. In a Kalman filter alignment algorithm, affected by the equivalent accelerometer bias change rate, extra azimuth error emerges from the mistake estimation of fiber-optic gyroscope drift. A three-sequence scheme and a reciprocating slow-rotation scheme are proposed to achieve the most inertial measurement error self-compensation. Theoretical error comparison and a turntable four-orientation alignment test show the superiority of the reciprocating slow-rotation scheme over the other two schemes. The heading-sensitive azimuth alignment error is reduced from 0.2268° to better than 0.0015° through scheme modification.

Telemetry system based on fiber-optic gyroscopes

The article presents a telemetry system for monitoring the bit trajectory during well drilling. Fiber-optic closed-loop gyroscopes are the main sensitive element in the telemetry system. The gyroscopes allow determining the azimuth and zenith angles of the well with a high accuracy exceeding most magnetometers. There is no need to use the expensive non-magnetic steels in the body of the telemetry system and non-magnetic drill pipes in the drill string. Fiber-optic closed-loop gyroscopes allow using the telemetry system when drilling near the casing of adjacent wells and magnetized rocks. An inertial navigation system is installed in the developed telemetry system as a measuring unit containing three angular velocity sensors and three accelerometers mounted rigidly. The sequence and results of simulation of a hydraulic link for data transmission from the bottom of the well to the top are described. Pilot tests of the telemetry system were carried out at well No. 450 of the Tatsuksinskoye field. The obtained values of the spatial intensity of the borehole curvature in depth are close in values to the directional survey data for the borehole. The trajectory obtained during the lift is close to the trajectory gathered from directional survey data.

Features of vacuum impregnation of optical fiber

The article discusses the features of impregnation of the fiber contour during the manufacture of a sensitive coil of a fiber-optic gyroscope. The technological process of impregnation has been developed. The results are analyzed, further directions of work are proposed.

Theoretical and experimental studies on non-reciprocity error induced by varying temperatures in polarization-maintaining fiber optical gyro with orthogonal-polarization states

In this study, a polarization-maintaining fiber optical gyro (PMFOG) with orthogonal-polarization states is constructed, and the non-reciprocity error induced by varying temperatures has been studied. Compared with the traditional optical gyro system based on single-polarization, theory and experiments have shown that the non-reciprocity error induced by varying temperatures is more evident in the PMFOG with orthogonal-polarization states. It is approximately five times larger than that of the traditional PMFOG. To decrease the non-reciprocity error induced by varying temperatures, we proposed an innovative structure in this study, which enhances the symmetry of the light path without the addition of redundant optical devices. The clockwise and counterclockwise light beams experience the same change of refractive index along the fast and slow axes of the fiber, and the non-reciprocity error induced by varying temperatures can be reduced to zero when the whole gyro is heated up nearly uniformly. This research, which overcomes a design limitation in PMFOGs with orthogonal-polarization states, is significant for the miniaturization and optimization of the environmental adaptability of fiber optic gyroscopes.

Evaluation and Suppression of the Effect of Laser Frequency Noise on Resonant Fiber Optic Gyroscope

This article provides a novel method to analyze and calculate the effect of laser frequency noise on a resonant fiber optic gyroscope (RFOG). The output signal of the fiber ring resonator is expressed as the sum of various harmonic responses. It is found that the laser frequency noise at certain noise frequency would be demodulated together with the rotation-induced frequency signal, and thus deteriorating the gyro output stability. A theoretical model is then setup. The effect of laser frequency noise on the RFOG based on the separate modulation-demodulation technique is numerically evaluated and the effectiveness of the reciprocal modulation-demodulation technique is verified both theoretically and experimentally. The measured angular random walk of the reciprocal RFOG improves as the detected light power at the photodetector increases, which indicates that the measured angular random walk reaches the theoretical shot-noise limited sensitivity in the RFOG. The best value is 0.0021 °/√h when the light power arrived at the photodetector is 69 μW.

A New Fusion Fault Diagnosis Method for Fiber Optic Gyroscopes.

The fiber optic gyroscope (FOG) is a high precision inertial navigation device, and it is necessary to ensure its reliability for effective use. However, the extracted fault features are easily distorted due to the interference of vibrations when the FOG is in operation. In order to minimize the influence of vibrations to the greatest extent, a fusion diagnosis method was proposed in this paper. It extracted features from fault data with Fast Fourier Transform (FFT) and wavelet packet decomposition (WPD), and built a strong diagnostic classifier with a sparse auto encoder (SAE) and a neural network (NN). Then, a fusion neural network model was established based on the diagnostic output probabilities of the two primary classifiers, which improved the diagnostic accuracy and the anti-vibration capability. Then, five fault types of the FOG under random vibration conditions were established. Fault data sets were collected and generated for experimental comparison with other methods. The results showed that the proposed fusion fault diagnosis method could perform effective and robust fault diagnosis for the FOG under vibration conditions with a high diagnostic accuracy.

An anti‐vibration‐shock inertial matching measurement method for hull deformation

In order to establish a unified spatial reference for the whole ship, inertial matching measurement of hull deformation is widely used because of its continuity and concealment. However, the vibration-shock signal of shipborne equipment often brings short-time output disturbance to the user-side fibre gyroscope unit (FGU), and the disturbance will bring great challenges to the accuracy and convergence of inertial matching measurement. To solve these problems, the authors put forward a new algorithm named as attitude quaternion matching method-improved double factor adaptive Kalman filter-parameter adaptive Kalman filter (AQM-IDFAKF-PAKF). (1) The AQM established the FGU attitude as observation to build the basic model for hull deformation inertial matching method. (2) The authors introduced IDFAKF to track the trend of dynamic hull deformation in vibration interference by using historical data. (3) After judging the anti-vibration-shock calculation stop node, PAKF was utilised to adaptively adjust the parameters of hull deformation matching after vibration-shock, so as to quickly calculate the static hull deformation angle after shock interference. Numerical simulation results illustrated that the AQM-IDFAKF-PAKF can quickly converge the calculation of hull deformation angle with a small steady-state error under the condition of vibration-shock signal interference.

Temperature drift compensation of fiber strapdown inertial navigation system based on GSA-SVR

The fiber strapdown inertial navigation system (INS) has been widely utilized in aircraft, autonomous driving, robotics, and other fields due to the rapid growth of fiber technology. The core components of INS, the fiber optic gyroscope (FOG) and quartz flexible accelerometer (QFA), are prone to affected by the environmental temperature variation. The traditional temperature drift compensation method requires a considerable time to calibrate each inertial sensor individually. But after the six inertial sensors are integrated, the temperature environment inside the INS will become more complex. As a result, this device-level method has an unsatisfactory effect in the practical application of INS. Furthermore, the traditional method ignores the fact that the temperature drift characteristics of FOG are not the same at different working states. To solve the above problems, we propose a novel temperature drift compensation method of INS based on gravitational search algorithm (GSA) tuning support vector regression (SVR). The startup state and stable working state are modeled independently based on the FOG's features. Without adding additional thermometers to the inertial sensors, the temperature field is constructed by making full use of the information provided by the built-in thermometer of six inertial sensors. The experimental results verify the effectiveness of our method during different working states. And compared with the traditional polynomial fitting method, our method has better performance in the navigation experiment, the navigation accuracy increased by more than 50%.

Influence of temperature on detectable minimum rotation rate in i-FOGs using Er-doped SFSs

Abstract In this study, an interferometric fiber optic gyroscope (I-FOG) model exploiting the double-pass backward (DPB) erbium-doped superfluorescent fiber source (SFS) with both thin-film filter (TFF) and fiber bragg grating (FBG) reflectors has been constructed and the effects of temperature variations on mean wavelength and detectable minimum rotation rate (DMRR) have been theoretically analyzed. the simulations corresponding with the relations between these parameters for temperature variations in the range of −60 °C to + 90 °C, have been performed using Matlab 2021b. DMRR variations have been found as 6.01 ppm/K and 3.83 ppm/K for the system with TFF, whilst they are 15.31 ppm/K and 1.58 ppm/K for the system with FBG.

Non-centrosymmetric solid core photonic crystal fiber for suppressing parasitic twist in fiber sensing coil

During the fabrication of fiber sensing coils, the parasitic twist of fibers would lead to the undesired elliptical birefringence in the fiber, which is the main cause of magnetically induced bias error for fiber optic gyroscope(FOG). For the purpose of suppressing the parasitic twist in the fiber coil, a polarization-maintaining solid core photonic crystal fiber (PCF) with non-centrosymmetric distribution of bending stiffness is proposed and investigated. The proposed PCF would bend towards a particular direction under the external forces, resulting in the consistency of birefringent axes arrangement, thus suppressing the nonreciprocal errors induced by both radial and axial components of the magentic field simultaneously. Dependence study of the fiber bending stiffness distribution on several key parameters is provided. The optical properties are also explored and compared with the previously studied PCF. Fiber coils fabricated with the proposed PCF are promising in reducing the magnetical sensitivity of FOG, thus making it possible for FOG to get rid of the thick magnetic shield, which is significant for the miniaturization of FOG.

Auxiliary arbitrary waveform generator for fiber optic gyroscope

Phase modulation of laser radiation using an auxiliary generator makes it possible to improve the accuracy characteristics of fiber-optic gyroscopes. The authors propose a method for generating a phase modulation signal implemented on the basis of a parallel architecture with the possibility of dynamically changing the signal parameters. A prototype of a compact embedded generator for generating signals with frequencies up to 2.5 GHz is presented. The generator is implemented on a field-programmable gate array, which ensured a compact design and made it possible to include it in the design of a fiber-optic gyroscope. The dynamic change of the generated signal is carried out using a personal computer using the developed specialized software that allows generating arbitrary waveforms. For the developed generator, the spectra of a sinusoidal signal and white noise are presented.

Wavelength-dependence reduction of the scale factor for tactical-grade fiber optic gyroscopes.

Fiber optic gyroscopes (FOGs) suffer from the scale-factor inaccuracy induced by the wavelength instability of the broadband source, which remains a bottleneck both in theory and in practical application. In this work, we propose a simple but effective technique for reducing the wavelength dependence of the scale factor by employing the size of the digital-ramp register as the actuator in the closed-loop scheme for nulling the ramp-reset-induced errors, instead of the conventionally-used feedback-chain gain. Experiments show that, for the tactical-grade FOG equipped with the super-luminescent diode (SLD) operating under temperatures from -40 °C to +60 °C, the proposed technique reduces the compensated scale-factor inaccuracy to 282 ppm, with respect to 2065ppm in the conventional case. This technique relaxes the stringent requirements on the wavelength stability of SLDs, which contributes to the large-scale production and application of tactical-grade FOGs.

Resonant fiber optic gyroscope using a reciprocal modulation and double demodulation technique.

A resonant fiber optic gyroscope (RFOG) using a reciprocal modulation and double demodulation technique based on a single laser source is proposed and demonstrated. The effect of the residual amplitude modulation of the phase modulator is well suppressed thanks to the reciprocal modulation and demodulation. On this basis, the backscattering noise is also eliminated by the double demodulation process. The long-term bias stability of the RFOG is successfully improved to 0.2°/h for a test time of 45 hours.

Faraday drift suppression based on dispersion compensation factor and broadband source parameters in a differential fiber optic gyroscope

We present an investigation of bias drift caused by the Faraday effect in differential fiber optic gyroscope (DFOG) based on dispersion compensation factor and broadband source (BS) parameters. The theoretical model of bias drift is established and the influence of dispersion compensation factor and BSs on the bias drift is revealed. The DFOG prototype is designed by optimizing the dispersion compensation factor and two BSs parameters. Then, the bias drifts caused by the Faraday effect in the DFOG and the traditional single-source fiber optic gyroscope (SFOG) are tested and compared. The bias drift caused by the axial magnetic field in the DFOG is about 0.0072 deg/h for 1Gs, which is about 1/22 of the SFOG. The bias drift caused by the radial magnetic field is about −0.0059 deg / h for 1Gs, which is about 1/16 of the SFOG. A discovery is that the bias drift caused by the Faraday effect in DFOG can be suppressed by optimizing the dispersion compensation factor and the two BSs parameters.

Investigation of radiation-induced active band attenuation in erbium-doped fiber and the radiation-resistant low noise broadband source design

We comprehensively investigate the radiation-induced active band attenuation (RIABA) characteristic of erbium (Er)-doped fiber. It is experimentally shown that the RIABA gradually alleviated with radiation dose increasing and the absorption/luminescence characteristics of Er3 + appear to be unaffected by irradiation ray. By employing the intrinsic luminescence spectrum of Er3 + as the original output spectrum, a radiation-resistant low noise broadband source with specially customized Er-doped photonic crystal fiber and multiple radiation-resistant methods is proposed. Under 50 krad irradiation dose, it demonstrates mean-wavelength stability of 26.4 ppm and the output power attenuation of <0.1 dB. Throughout the irradiation, the 3 dB bandwidth of the output spectrum is >40 nm. The broadband source proposed exhibits excellently comprehensive performances in the radiation environment and is quite feasible for strategic high-accuracy interferometric fiber-optic gyroscopes.

A method for temperature error compensation in fiber-optic gyroscope based on machine learning

This work presents a machine-learning based method for temperature error compensation of fiber optic gyroscope (FOG). Alternative to existing methods for constructing samples by single data point, a novel method of constructing samples by sequence is proposed, which fully considers the hysteresis and delay of temperature error. Moreover, temperature experiments with three distinct temperature trends, i.e., heating, holding and cooling, are conducted. Following the construction of training and test sets, the relevant training and test processes are completed using SVR algorithm. According to the degree of approximation in predicted value relative to the real value and the degree of improvement in gyro stability, the effects of various sample construction methods on the corresponding error compensation are analyzed. Considering the root mean square error (RMSE), mean absolute value error (MAE) and improvement-factor of FOG zero-bias stability as measurement indicators, this work proposes to construct samples by sequence with temperature trend feature-extraction, which effectively improves the overall accuracy of gyroscope. Allan variance is also utilized to verify the effectiveness of our proposed method. Lastly, this study also provides a theoretical guidance and reference for temperature error compensation in other types of sensors.

White-light-driven resonant fiber-optic gyro based on round trip filtering scheme.

As the second generation of the fiber-optic gyro (FOG), a resonant FOG (RFOG) appears as a very viable candidate for a miniaturized optical gyro. However, due to the impediment of laser-induced parasitic noise and system complexity, the actual performance of the RFOG is well below expectations. This paper proposes a novel, to the best of our knowledge, RFOG which is driven by broadband white light rather than a narrow linewidth laser. The fiber-optic ring resonator (FRR) works as a filter, and the rotation under detection is read out from the round trip loss of the FRR. The parasitic noise is effectively avoided due to the low coherence light, and the measuring resolution can be thus improved. In the experiment, a bias instability of 0.012 ∘/h is demonstrated with a 100-m fiber coil and a very simple structure. The proposed method would be a big step forward for making the RFOG practical with high performance and low cost.