Fiber Optic Gyroscope Research Articles

All-Solid Single-Polarization Anti-Resonant Fiber Base on Anisotropic Glass

A single-polarization solid-core anti-resonant fiber is proposed, and the influence of the fiber core material anisotropy of the solid-core anti-resonant fiber on polarization characteristics is investigated using the finite element method. Single-polarization guidance is achieved by using the anisotropy of optical fiber materials, which also ensures high birefringence. The numerical simulation results indicate that there are two single-polarization intervals (1210–1440 nm and 1490–1560 nm), with a maximum bandwidth of up to 230 nm, when the confinement loss difference between the two orthogonal polarizations exceeds two orders of magnitude. Specifically, when the work wavelength is 1550 nm, a polarization extinction ratio (PER) of 108 is obtained by optimizing the structure parameters. Additionally, the y-polarization fundamental mode (YPFM) can be well confined in the fiber center with a low confinement loss of 0.04 dB/m, while the x-polarization fundamental mode (XPFM) has a huge confinement loss larger than 4.65 dB/m due to the coupling with the tube mode. The proposed single-polarization solid-core anti-resonant fiber has a huge potential in applications such as laser systems, fiber-optic gyroscopes, and optical fiber communications.

Suppression of effects of temperature variation by high-order frequency modulation in large fiber-optic gyroscopes

Temperature variation degrades the performance of fiber-optic gyroscopes. In terms of a noise mechanism, we report that thermal phase noise contributes to the dominant effect of temperature variation in large fiber-optic gyroscopes when the conventional Shupe effect is basically suppressed. High-order frequency modulation is introduced to reduce the corresponding effect of temperature variation. A time-varying temperature variation experiment has been carried out for verification. Compared with the conventional eigen frequency modulation, the temperature sensitivity is reduced by 32 times, which effectively enhances the temperature adaptability of the fiber-optic gyroscope.

Thermal noise suppression in large fiber-optic gyroscopes

Low-cost noise reduction in large FOGs increases sensitivity in gravitational wave detectors, universal time and seismic wave measurements.

An Optimal Estimation Approach for MEMS INS Performance Improvements Based on Single-FOG Monitoring

A new approach is proposed for MEMS INS performance improvement, which uses a Fiber Optic Gyro to monitor the triad of MEMS gyros and compensates the errors of the MEMS INS in real time by using an elaborated Kalman filter. A state space model of single-FOG monitored MEMS INS is developed, and the observability of the model is analyzed for the Kalman filter. Simulated and experimental tests are carried out to evaluate the effectiveness of the proposed approach. The test results show that this method can effectively reduce the errors of the MEMS gyros and dramatically improve the initial alignment and navigation performances of the MEMS INS.

Numerical Study of Two-Stage Temperature Control Strategy for High-Temperature Stability of Satellite-Borne Fiber Optic Gyroscope

Abstract Fiber optic gyroscopes (FOGs) are widely used in attitude control systems of spacecraft such as satellites and Mars rovers for their superior spatial adaptability. However, changes in ambient temperature can cause errors in the FOG and reduce its output accuracy. In this paper, a fuzzy two-stage temperature control strategy applied to a satellite-borne three-axis integrated fiber optic gyroscope (TAIFOG) is proposed. And the control rules of the fuzzy two-stage temperature controller are described in detail. A thermodynamic model that can quickly and accurately respond to the dynamic thermal characteristics of the satellite-borne TAIFOG is also constructed based on the lumped method. The effectiveness of the proposed fuzzy two-stage temperature control strategy in improving the temperature stability of the satellite-borne TAIFOG in orbit is verified through numerical studies. Numerical results show that this fuzzy two-stage active temperature control strategy can fundamentally improve the thermal state of the satellite-borne TAIFOG and ensure that its sensitive element fiber optic coils maintain high-temperature stability while the TAIFOG is in orbit. In addition, the startup time of TAIFOG is reduced to 308 s compared to the case without active temperature control, which is a reduction of 96.27%. This active temperature control strategy is well suited for engineering applications to improve FOG output accuracy.

Compact single-polarization coupler based on a dual-hollow-core anti-resonant fiber.

A compact single-polarization (SP) coupler based on a dual-hollow-core anti-resonant fiber (DHC-ARF) is proposed. By introducing a pair of thick-wall tubes into a ten-tube single-ring hollow-core anti-resonant fiber, the core is separated into two cores to form the DHC-ARF. More importantly, by introducing the thick-wall tubes, dielectric modes in the thick wall are excited to inhibit the mode-coupling of secondary eigen-state of polarization (ESOP) between two cores while the mode-coupling of the primary ESOP can be enhanced, and thus the coupling length (Lc) of the secondary ESOP is greatly increased and that of primary ESOP is reduced to several millimeters. Simulation results show that the Lc of the secondary ESOP is up to 5549.26 mm and one of the primary ESOP is only 3.12 mm at 1550 nm through optimizing fiber structure parameters. By using a 1.53-mm-long DHC-ARF, a compact SP coupler can be implemented with a polarization extinction ratio (PER) less than - 20 dB within the wavelength range from 1547 nm to 1551.4 nm, and the lowest PER of - 64.12 dB is achieved at 1550 nm. Its coupling ratio (CR) is stable within 50 ± 2% in the wavelength range from 1547.6 nm to 1551.4 nm. The novel compact SP coupler provides a reference for developing HCF-based polarization-dependent components for use in the high-precision miniaturized resonant fiber optic gyroscope.

Improvement of the Temperature Stability of the Erbium-Doped Superfluorescent Fiber Source by Tuning the Reflectivity of the Fiber End

A novel and simple way of improving the mean wavelength temperature stability of the erbium-doped superfluorescent source is described and demonstrated. We show that by introducing small reflectivity feedback at the unpumped fiber end in the backward-pump superfluorescent source configuration, we can affect an overall temperature dependency of the mean wavelength of the output spectrum. The reflectivity adjustment can be made by an angled fiber cleave, varying the reflectivity between 0 to 4 %, or by a fusion arc, allowing its finer adjustment. With this approach, we were able to arbitrarily adjust the mean wavelength temperature trend from −4.38 to 5.23 ppm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C. Furthermore, an optimal reflectivity was attained, providing almost zero trend and reducing the total mean wavelength variation to 130 ppm over the temperature range of −40 to +100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, which is a 5.7-fold and 4.4-fold improvement compared to 0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> and a standard 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> fiber cleave angle, respectively. By avoiding any filtering components, a wide bandwidth of 37.8 nm and a power efficiency of 22% was reached. Since the proposed configuration does not include any extra components compared to the basic backward-pump configuration, it can be a viable solution for cost-efficient applications, such as, e.g., medium-grade fiber-optic gyroscopes. A benefit for these gyroscopes is the tunability of the source wavelength temperature dependency which can conveniently compensate the gyro coil temperature sensitivity.

Research on Magnetic-Induced Error of Small-Sized Fiber Optic Gyro Fiber Coil in Space Environment

Spacecraft is severely limited in weight and volume, resulting in a small bending radius of the fiber coil used by IFOG (Interference Fiber Optic Gyroscope). The fiber coil has such a size that the influence of bending on fiber birefringence cannot be ignored. In this paper, we research magnetic-induced errors of small-sized IFOG working in low orbit space. Firstly, we use the Jones matrix to analyze the effects of radial magnetic field and axial magnetic field on IFOG. Secondly, we establish a three-dimensional model for the radial magnetic-induced errors and magnetic-induced errors of minor radius fiber coil. Using the finite element method, we analyze the magnetic-induced error between different levels of the fiber coil. Combined with the birefringence distribution of the minor radius fiber coil, an accurate three-dimensional magnetic-induced error model is established. Thirdly, in the experiment, we design the magnetic-induced error test platform that includes the Fluke standard current source, transconductance amplifier, and Helmholtz coil. The experimental results show that, compared with the traditional calculation method, the three-dimensional magnetic-induced error model reduces the RMSE (Root Mean Square Error) of the radial magnetic field by 56.9% and the RMSE of the axial magnetic field by 35.7%, respectively.

Model-Rebuilt Disturbance Observer of a Tracking System Based on Acceleration Fusion for Laser Power Transmission

When using laser energy to power long-distance and fast-moving targets, it requires a fast-response and high-precision acquisition, pointing and tracking (APT) system. A fast-steering mirror (FSM) system was used in this paper to track the solar cell array as laser power receiver. The disturbance suppression performance is a key indicator for the FSM stabilization. Generally, a fiber-optic gyroscope (FOG) is employed in the high-sampling-rate velocity loop to enhance the anti-interference ability. However, with the expansion of miniaturized applications, a relatively large, heavy, and high-power FOG is hard to be installed on the small mirror. With this case, this paper used a small-size and high-bandwidth MEMS linear accelerometer in the acceleration loop, substituting the gyroscope. However, the drift and high-frequency noise of the MEMS accelerometer in low frequency will cause APT disturbance. Therefore, an acceleration fusion method with a modified complementary filter was proposed to blend signals of the charge-coupled device and the accelerometers. The fused virtual acceleration can eliminate drift and reduce noise in low frequency and was eventually used in the model-rebuilt disturbance observer loop. At last, the measured results show that the disturbance suppression performance is improved using the presented method, and low-price and small-size MEMS accelerometer can be applied in the APT system.

Compensation of scale factor nonlinear error introduced by harmonic distortion for open-loop fiber optic gyroscopes.

The scale factor (SF) of a gyroscope is the ratio of the detection output rotational rate and the input, and is expected to be a constant. However, for open-loop interferometric fiber optic gyroscopes (IFOGs) with sinusoidal modulation, harmonic amplitudes are inevitably affected by detection defects, such as nonuniform frequency response of the photodetector or unequal gain of amplification circuits. As a result, harmonic distortion leads to SF nonlinearity, which seriously hinders the accuracy of high-precision gyroscopes. In this Letter, the theoretical form of the SF error introduced by harmonic distortion of open-loop gyroscopes is analyzed, and an effective and simple compensation method is proposed. Instead of traversing the whole dynamic range, the proposed method simplifies the calibration pretest, where only a section of the dynamic range needs to be tested. Experimental results on an open-loop IFOG prototype show that, with our proposed method, the SF nonlinear error is suppressed to 2.5 ppm within the range -300 to +300∘/s, which is 33 times less than that before compensation.

Temperature field analysis and structure redesign of fiber optic gyroscope

Taking the fiber ring of the core device of the fiber optic gyro as the research object, the temperature field simulation analysis of the fiber gyroscope was carried out by ANSYS finite element analysis software, and the structural optimization of the fiber gyroscope was carried out, which effectively improved the temperature field distribution uniformity of the fiber optic ring and reduced the overall thermal equilibrium temperature and time when the fiber gyro reached stability.

A time asynchronous parameters calibration method of high-precision FOG-IMU based on a single-axis continuous rotation scheme

There is a time asynchronous problem with the output signals between each inertial sensor in an actual high-precision fiber optic gyro inertial measurement unit (FOG-IMU), which reduces the velocity update accuracy of the strap-down inertial navigation system in the actual applications. Firstly, the velocity error formulas are derived in the coordinate navigation system considering three time asynchronous errors between the three-axis accelerometers and gyros. Then an error-state Kalman filter is designed with respect to the time asynchronous parameters measurement model in angular dynamic environments. Afterward, a single-axis continuous rotation scheme is developed to calibrate the time asynchronous parameters. In particular, a simple observability analysis model is proposed to verify the rationality of the calibration scheme. Furthermore, the time asynchronous parameters are calculated effectively based on the proposed indirect calibration scheme. Finally, the proposed method is verified effectively through simulations and turntable experiments, which can significantly reduce the measurement errors of high-precision FOG-IMU. As a result, compared with the traditional three-parameter direct calibration method, the eastward and northward velocity errors are reduced by 7.01% and 2.48%, respectively.

Position and Attitude Determination in Urban Canyon with Tightly Coupled Sensor Fusion and a Prediction-Based GNSS Cycle Slip Detection Using Low-Cost Instruments.

We present a position and attitude estimation algorithm of moving platforms based on the tightly coupled sensor fusion of low-cost multi baseline GNSS, inertial, magnetic and barometric observations obtained by low-cost sensors and affordable dual-frequency GNSS receivers. The sensor fusion algorithm is realized by an Extended Kalman Filter and estimates the states including GNSS receiver inter-channel biases, integer ambiguities and non-GNSS receiver biases. Tightly coupled sensor fusion increases the reliability of the position and attitude solution in challenging environments such as urban canyons by utilizing the inertial observations in case of GNSS outage. Moreover, GNSS observations can be efficiently used to mitigate IMU sensor drifts. Standard GNSS cycle slips detection methods, such as the application of triple differences or linear combinations such as Melbourne-Wübbena combination and the phase ionospheric residual extended TurboEdit method. However, these techniques are not well suited for the localization in quickly changing environments such as urban canyons. We present a new method of tightly coupled sensor fusion supported by a prediction based cycle slip detection technique, applied to a GNSS setup using three antennas leading to multiple moving baselines on the platform. Thus, not only the GNSS signal properties but also the dynamics of the moving platform are considered in the cycle slip detection. The developed algorithm is tested in an open-sky validation measurement and two sets of measurement in an urban canyon area. The sensor fusion algorithm processes the data sets using the proposed prediction-based cycle slip method, the loss-of-lock indicator-based, and for comparison, the Melbourne-Wübbena and the TurboEdit cycle slip detection methods are also included. The obtained position and attitude estimation results are compared to the internal solution of raw data source GNSS receivers and to the observations of a high-accuracy GNSS/INS unit including a fiber optic gyro. The validation test confirms the proper cycle slip detection in an ideal environment. The more challenging urban canyon test results show the reliability and the accuracy of the proposed method. In the case of the second urban canyon test, the proposed method improved the integer ambiguity resolution success rate by 19% and these results show the lowest horizontal and vertical coordinate distortion in comparison of the linear combination and the loss-of-lock-based cycle slip methods.

A novel temperature-compensation method based on correlation analysis for multi-FOG INS

Aimed at improving the bias stability of Fiber-Optic Gyroscope (FOG)-based inertial navigation systems in environments of various ambient temperatures, a novel temperature-compensation method based on a correlation analysis of the same batch of FOGs is proposed. The empirical mode decomposition method was employed to filter the high-frequency noises of the FOGs. Then, the correlation information of the multiple FOGs was used to analyze the feasibility of the method. Eventually, the same residual error of the FOGs was compensated via the simple piecewise linear models. The experimental results indicate that excellent compensation effects for both high- and low-accuracy FOGs are achieved using the proposed method. Specifically, the accuracies of high-accuracy FOGs are improved by approximately 33.9%, 20%, and 31.2%, while those of low-accuracy FOGs are improved by approximately 39.1%, 20.8%, and 26.1%. The method exhibits the merits of simplicity, validity, and stability, and thus is expected to be widely used in engineering applications.

Real-Time Compensation for SLD Light-Power Fluctuation in an Interferometric Fiber-Optic Gyroscope.

An interferometric fiber-optic gyroscope (IFOG) demodulates a rotation signal via interferometric light intensity. However, the working environments of IFOGs typically involve great uncertainty. Fluctuations in temperature, air pressure, electromagnetic field, and the power system all cause the power of the superluminescent diode (SLD) light source to fluctuate as well. In this invited paper, we studied the effects of SLD power fluctuation on the dynamic and static performance characteristics of a gyro system through the use of a light-power feedback loop. Fluctuations of 0.5 mA, 1 mA, and 5 mA in the SLD source entering the IFOG caused zero-bias stability to be 69, 135, and 679 times worse. We established an effective method to monitor power fluctuations of SLD light sources and to compensate for their effects without increasing hardware complexity or system cost. In brief, we established a real-time power-sensing and -compensating system. Experimental results showed that for every 0.1 mA increase in the fluctuation amplitude of the driving current, the zero-bias stability became 4 to 7 times worse, which could be reduced about 95% through the use of SLD power compensation.

Simultaneous Suppression of Thermal Phase Noise and Relative Intensity Noise in a Fiber-Optic Gyroscope

The short-term sensitivity of a several-kilometers long fiber-optic gyroscope (FOG) is limited mainly by thermal phase noise (TPN) and relative intensity noise (RIN). Increasing the phase modulation frequency decreases the TPN but not the RIN since it behaves as white noise. Here, we propose and experimentally demonstrate that the angular random walk (ARW) can be effectively decreased by suppressing RIN at the modulation frequency and its third-order harmonic using direct feedback to the drive current of a superluminescent diode (SLD). Our simultaneous suppression of TPN and RIN yields an ARW of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {\text {deg}}/\sqrt {{\text {h}}}$ </tex-math></inline-formula> and a bias instability of 33 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {\text {deg}}/{\text {h}}$ </tex-math></inline-formula> using a fiber coil with a length of 5 km and an effective area of 280 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text {m}}^{{{2}}}$ </tex-math></inline-formula> for a measurement time of 40 h.

Research on the Single-Double Interval Closed-Loop Method of Resonant Fiber Optic Gyro

Resonant fiber optic gyro (RFOG) is a type of inertial sensor with great application potential. Its closed-loop signal detection methods include single closed-loop, double closed-loop and other methods to ensure high system stability and high-precision signal output. In view of the respective advantages of single and double closed-loop systems, a single-double interval closed-loop scheme for RFOG is proposed in this letter. By introducing the threshold trigger mechanism, the advantages of low control signal noise of the single closed-loop system and large dynamic range of the double closed-loop system are fully combined. In addition, in order to improve the linearity of the demodulation curve, a linear fitting method is applied to the system. The experiment shows that the short-term and long-term stability of the system have been improved effectively.

A Dual-Axis Rotation Scheme for Redundant Rotational Inertial Navigation System

A redundant rotational inertial navigation system (RRINS) comprises a redundant inertial measurement unit (RIMU) and a turntable for improving reliability and navigation accuracy. Because of the multi-sensor configuration, the RIMU has a more complex error model compared with the traditional orthogonal inertial measurement unit (IMU). Therefore, the RIMU-based rotation scheme cannot simply replicate the traditional IMU-based rotation scheme. In this study, a dual-axis rotation scheme for RIMU characteristics is proposed. First, the error model of the RIMU was established, and the error compensation of RIMU caused by rotation was analyzed. Second, the principles of rotation axis switching and reciprocating rotation were summarized, and a dual-axis rotation scheme was designed by these principles. Finally, the rotation scheme was applied to an RRINS prototype consisting of RIMU (four fiber optic gyroscopes + four quartz accelerometers) and a dual-axis turntable, and then simulations and experiments were performed. The results of the simulations and experiments show that the positioning accuracy of RRINS can be obviously improved by using the proposed rotation scheme.

Digital Control and Demodulation Algorithm for Compact Open-Loop Fiber-Optic Gyroscope.

With the advantages of small size, low cost, and moderate accuracy, an open-loop fiber-optic gyroscope (FOG) has a wide range of applications around control and automation. For the most cost-sensitive applications, a simple and stable digital algorithm with a reduced control-circuit volume and cost is highly desirable to realize high-precision control of a FOG. In this work, a new algorithm for an open-loop FOG is proposed based on the discrete multi-point demodulation in the sinusoidal modulation period. Utilizing this algorithm, stable control and angular velocity calculation of a gyro are realized with effectively suppressed gyro error. The use of this algorithm greatly reduces the requirements for processing power and simplifies the gyro circuit. Based on this algorithm, a digital FOG with a volume of only 25 × 20 × 40 mm3 achieves a bias instability of less than 0.15°/h, an angle random walk (ARW) of less than 0.015°/√h, a start-up time of less than 1 s, and a 3 dB bandwidth beyond 160 Hz. This low-cost, compact, and high-performance gyro is sufficient to satisfy the requirements of applications in the navigation and control fields such as unmanned driving.

Modifying the coherence of vertical-cavity surface-emitting lasers using chaotic cavities

Vertical-cavity surface-emitting lasers (VCSELs) have been widely adopted in a variety of applications in recent years, with even more applications currently under research and development as a result of the emergence of visible-light VCSELs. Most of these applications make use of the ease of fabrication of large two-dimensional arrays of lasers, a feature unique to VCSELs that makes them scalable and versatile. However, applications that rely on the uniformity of the emitted beam in the transverse plane, such as illumination, projection, holography, and displays, suffer from the coherence artifacts (speckles) that reduce the quality of the formed images when coherent lasers are used. In this work, we show that, by using a chaotic-cavity D-shaped mesa, the coherence of broad-area VCSELs can be substantially reduced (the number of mutually incoherent modes is almost doubled, and the spectral full width at half-maximum is increased from ∼ 1.1 n m to ∼ 4.5 n m ), and the maximum achievable optical power is increased by up to 60%. The simplicity of implementing the reported design, which requires no additional fabrication steps, makes it a promising solution for applications that would benefit from the lower speckle density of the emitted light as well as those that rely on lower temporal coherence, such as time-domain optical coherence tomography and fiber-optic gyroscopes.