Fiber Optic Gyroscope Research Articles

A method to improve the modulation depth servo accuracy of an integrated fiber-optic gyroscope using the Bouc-Wen model

The development of integrated fiber-optic gyroscopes using piezoelectric modulation (PEM) represents a significant advance in the field of fiber-optic gyroscopes. However, the hysteretic creep nonlinearity of Piezoe-lectric Transducer (PZT) affects the modulation depth monitoring and leads to a drift of its resonant frequency. The accuracy of the PEM's closed-loop feedback signal determines the open-loop gyroscope's accuracy. However, the hysteresis deteriorates the controller phase and the gain margin, inducing the fluctuation of the amplitude of each harmonic wave, which undoubtedly increases the difficulty of the closed-loop feedback control of the modulator. This paper proposes a method to quantify the high-frequency hysteresis nonlinearity of PZT, combining the advantages of feedforward compensation and feedback closed-loop. Feedforward compensation is used to reduce the hysteresis nonlinearity of PEM, reduce the interference of the nonlinear phase shift to zero drift, and increase the control accuracy of feedback control to PEM under temperature disturbance.

Seismic waves of the 10 December 2020 M6.6 Yilan earthquake observed by interferometric fiber-optic gyroscope

A newly developed cost-effective fiber-optic gyroscope (FOG) and an existing seismometer co-locating at the campus of National Central University (NCU) recorded seismic waves of a M6.6 Yilan earthquake and aftershock events occurring at around 24.74° N 122.03° E (88 km away from NCU) during 10–11 December 2020. Two nearest accessible broadband seismographs located in Hsinchu have also been employed as measurement references for facilitating the analysis of the detected seismic signals. Conventional seismometers usually detect the translational components of the seismic waves, while the FOG observes the rotational component. The recorded FOG data exhibit high-resolution details of the rotational component of shockwaves, which provides additional information of seismic waves. The shock waveforms of the translational and rotational components, analyzed under the conservation of the shock wave energy density received by FOG and seismograph, are found to be significantly correlated. The correlation coefficients of 60-s data are > 0.85 for the main shock and > 0.86 for the aftershock, while those of the 10-s peak periods are as high as 0.9064 and 0.8953, respectively. The highly correlated data imply that the energy registered by the two devices are equivalent. The optical interference-based rotation senor of the cost-effective FOG provides a high sensitivity of better than 3.6 deg/h and an extended dynamic sensing range as high as 55 dB with the fully sensing ability from pm 3.6 deg/h to pm 720,000 deg/h. The FOG seismometer sheds some light on building an earthquake six-degree-of-freedom observation array to have a bettering on the understanding of the seismicity.

On-board Dynamic Measuring of Long-wave Track Irregularity based on Visual Inertial Fusion

This paper studies an inspection method to measure the long-wave track irregularities using the signals of IMU (Inertial Measurement Unit) and Laser & Camera installed on a bogie, which is implemented in comprehensive inspection trains. To reduce the influence of random noise and vehicle vibration, the mechanical structure is optimized; the spatial-dependent change of the "two-point chord" on the track is observed by high-precision FOC (Fiber Optic Gyroscope) and laser camera components; the angular velocity measurement method is deduced. To eliminate high-frequency attenuation of the signal, a sensor fusion algorithm based on the concept of complementary filters is presented. The angular velocity-based method is also used to measure low spatial frequencies, while the acceleration-based method is used to measure high spatial frequencies. The measurement accuracy of the system is evaluated from two aspects: internal and external coincidence accuracy. The test shows that the repeatability accuracy of the system to alignment and profile of the wavelength of 200 m is 0.5 mm and 0.8 mm, respectively, and the trend item and the line design value maintain good consistency.

Results of Comparative Study of Light Sources for Fiber Optic Gyroscopes

Results of Comparative Study of Light Sources for Fiber Optic Gyroscopes

Thermomechanical analysis of the effects of homogeneous thermal field induced in the sensing coil of a fiber-optic gyroscope

A thermal field in the sensing coil of fiber-optic gyroscope gives rise to bias drift. The transient effect and the quasi-static effect are distinguished. The equations of this phenomenon developed in this article highlight the importance of knowing the strain field versus temperature along the optical fiber in the sensing coil. The influence of winding patterns on thermal bias is discussed using an analytical approach. To determine the strain field, a parameterized approach is proposed. An axisymmetric finite element model describing a double coated optical fiber is implemented. Thanks to this model, the thermo-mechanical behavior of the optical fiber coil is computed and explained in detail. Then, the computed strain field is validated with strain measurements by Rayleigh Optical Frequency Domain Reflectometry (Rayleigh-OFDR) for two different coils using two different optical fibers. The thermal bias drift for a spatial homogeneous thermal loading, referred to as Mohr effect in this paper, is computed. Finally, we point out that the contribution of radial and axial strains in the reference frame formed by the optical fiber coil is negligible compared to orthoradial strain on Mohr effect.

Study on FOG scale factor error calibration in start-up stage based on GWO-GRU

The fiber optic gyroscope (FOG) is the core component of the inertial system, which has been widely utilized in aviation, maritime, automotive, and other fields. The scale factor is one of the critical parameters to characterize the dynamic performance of the FOG. Due to the temperature sensitivity of the optoelectronic devices, the scale factor errors will be caused with the temperature change. The traditional compensation method usually compensates the output of the FOG in a stable working state. Without considering the difference between the characteristics of the FOG in the start-up stage and the stable working state, the compensation accuracy of the traditional method cannot meet the demand for quick start-up in application areas. According to the above analysis, a novel scale factor error compensation method based on the grey wolf optimization (GWO) and gated recurrent unit (GRU) neural network is proposed in this paper. Furthermore, a new experiment is designed to calibrate the scale factor error in the start-up stage, which can reduce the calibration time and ensure the calibration accuracy. The experimental results demonstrate the proposed method significantly improves the compensation accuracy compared with other methods, such as the multilayer perceptrons (MLPs) and the traditional GRU network.

Development of Three-Axis Fibre-Optic Seismograph for Direct and Autonomous Monitoring of Rotational Events with Perspective of Historical Review.

The paper presents historical perspective of fibre-optic seismographs designed and constructed at the Institute of Applied Physics at Military University of Technology, Poland based on the so-called minimum configuration of fibre-optic gyroscope. The briefly presented history, which originated in the 1998 by the system named GS-13P, laid solid foundations for the construction of a three-axis fibre-optic seismograph. The presented system meets all technical requirements of rotational seismology in terms of measurement parameters (measuring range from 10-8 rad/s to several rad/s and frequency from 0.01 Hz to 100 Hz) and utility features (mobility, autonomy, power independence, environmental stability). The presented device provides universal application both for research in engineering applications (high buildings, chimneys, wind towers) as well as in seismological research.

A Low-Drift Laser-Driven FOG Suitable for Trans-Pacific Inertial Navigation

We report a laser-driven fiber-optic gyroscope (FOG) with an angle random walk of 0.9 mdeg/√h, an Allan-deviation minimum of 4.9 mdeg/h, and an Allan-deviation maximum (or true drift) of 12.6 mdeg/h. This state-of-the-art performance was achieved by implementing an optical gate and a power-control feedback loop to suppress several sources of drift in the FOG, namely optical spikes that result from the square-wave biasing modulation, the nonlinear Kerr effect, drift in the detected power arising from spurious interferometers in the fiber circuit and laser-power fluctuations, and bias offset drift in the demodulation electronics. The measured output of this FOG was used to simulate 20 10-h trans-Pacific flights of an aircraft guided solely by inertial sensors. 95% of the flights landed within ±10 nmi of their intended destination. To our knowledge, this is the first report of a laser-driven FOG that meets the Federal Aviation Administration's Required Navigation Performance 10 criteria for aircraft navigation.

Integrated Interferometric Fiber Optic Gyroscope Employing a Photo-Electronic Chip

A novel integrated interferometric fiber optic gyroscope (I-FOG) employing photo-electronic chip and mini polarization maintaining photonic-crystal fiber (PM-PCF) coil is proposed. In the I-FOG, the front optical path, which includes a super-luminescent diode, lens group, a Y junction waveguide and a photodiode, is integrated in a photo-electronic chip employing spatial coupling methods. To minimize the fiber coil with large sensitive effect, a type of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60~\mu \text{m}/100~\mu \text{m}$ </tex-math></inline-formula> ultra-thin diameter PM-PCF is customized. Finally, with a 600-m-long PM-PCF coil of 26mm outer diameter, a high-accuracy integrated I-FOG is achieved. It experimentally demonstrates a bias stability of 0.05°/h at the integration time of 100 s, with an ARW of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0083^{\circ} /\text{h}^{\mathrm {1/2}}$ </tex-math></inline-formula> and a scale factor nonlinearity of 32ppm over the range of ±400°/s at room temperature. It also shows a bias stability of 0.11°/h at the integration time of 100 s over the temperature range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 30^{\circ} \text{C}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60^{\circ} \text{C}$ </tex-math></inline-formula> . Compared with conventional I-FOG with discrete photo-electric devices and PANDA polarization maintaining fiber (PMF), the integrated I-FOG proposed has great advantages in high accuracy and small volume, which is quite feasible for the application of tactical weapon, autonomous positioning and navigation platforms.

Analysis and compensation of residual gyro drifts on azimuth alignment accuracy in the RINS

The rotational inertial navigation system (INS) uses rotational alignment to improve azimuth alignment accuracy significantly. However, due to the existence of magnetic drifts in the fiber optic gyro, under the comprehensive influence of outside conditions, there will be residual drifts that cannot be averaged out along the body frame or the geographic frame, which will have a significant impact on azimuth alignment accuracy. An innovative and effective calibration compensation strategy is proposed by analyzing the generation mechanism of residual drifts and their influence on alignment accuracy, which can significantly improve azimuth alignment accuracy. With the aid of a high-precision total station, the experimental results of initial alignment in four directions show that the accuracy of azimuth alignment is improved from to by compensating residual drifts, which has significant theoretical significance and practical value in engineering applications for improving the overall performance of the INS.

Fiber re-circulating emulator for precise 504-km optical frequency combs transmission.

The propagation distance confines the development of precise time-frequency transmission using optical frequency combs due to the dispersion of the link. Here we disseminate a fiber re-circulating loop to emulate 504-km comb-based transmission. An optical filter in combination with a spool of dispersion compensation fiber is utilized to restrict the dispersion effect. The residual instability reached 4.0 × 10-14 at 1 s and 7.32 × 10-18 at 10,000 s over the 504-km link. The result indicated that this approach could meet the demand for long-haul clock transmission and comparison in the giant fiber-optic gyroscope to detect the seismic and gravitational potential.

Fiber-Optic Gyroscope Thermal Calibration through Two-Dimensional N-Order Polynomial for Landslide Displacement Monitoring

A fiber-optic gyroscope (FOG) with lower precision but higher cost advantage is typically selected according to working conditions and engineering budget. Thermal drift is the main factor affecting FOG precision. External thermal calibration methods by algorithms can effectively weaken the influence of thermal drift. This paper presents a thermal calibration method of a two-dimensional N-order polynomial (TDNP) and compares it with artificial neural network (ANN) methods to determine a software FOG thermal calibration method for landslide displacement monitoring. The TDNP thermal calibration coefficient matrix was established, and the thermal calibration capability of the TDNP method with different orders N was evaluated on the basis of error analysis. The ANN model with 1 to 18 hidden neural layers was established on the basis of LM, BR, and SCG algorithms to choose a suitable ANN. Finally, the mean absolute errors of FOG thermal calibration through the TDNP with different orders and the LM were compared. This method was applied in the Huangtupo landslide area, China. The results highlight that the TDNP method with order 5 had better performance and satisfied the requirements of landslide displacement monitoring. The research results can compensate for the lack of adaptability of the FOG thermal calibration method in landslide displacement monitoring.

Optimization of the annealed proton exchange method with controlled annealing for multifunctional integrated optical chip production.

The main objective of our study is to develop a new approach to the annealed proton exchange (APE) method for the fabrication of the multifunctional integrated optical chip (MIOC) used in fiber-optic gyro systems and to eliminate the loss of time and material, especially in mass production applications. In this work, self-polarized waveguides, which are the basic components of a MIOC device, were produced by the APE method and studied. With the developed method, controlled annealing trials have been carried out from a certain region on the LiNbO3 substrate used in waveguide production, and the annealing time specific to the annealing process was determined. By utilizing a special setup for the hot acid process, the proton exchange process was accomplished without a sudden temperature change of the substrate. Using prism coupling measurements of the fabricated waveguides, annealing times were determined to obtain index change values suitable for 45%-50% optical throughput. Mode profiles of devices with high optical throughput that were produced by the proposed method were measured, and it was seen that devices from different proton exchange runs had similar profiles. As a result, many undamaged substrates were fabricated, and their optical quality was found to be within the expected values.

An ultra-short coil fiber optic gyroscope

This paper presents a novel ultra-short coil fiber optic gyroscope structure. An experimental system based on the spatially non-reciprocal phase modulator is built to realize the fiber optic gyroscope (I-FOG) of a 5 m length fiber coil, and the experimental results are in good agreement with the theoretical analysis. This structure can fundamentally eliminate the limitation of modulation frequency by the transit time and reduces the complexity of the demodulation system. The theoretical analysis and experimental results both prove that the FOG has a simple modulation and demodulation process and fast response, greatly simplifying the demodulation and feedback circuit. The ultra-short coil fiber optic gyroscope realizes a novel phase modulation method, which provides an idea for the development of FOG shortened fiber coil towards miniaturization, integration and on-chip gyro, and is expected to play an important role in lowering costs and improving precision.

Highly birefringent polarization maintaining low-loss single-mode hollow-core antiresonant fiber

In this paper, a highly birefringent polarization maintaining low losses and a single mode antiresonant hollow core fiber is proposed and analyzed, that is able to exhibit better performances compared to the recent related structures. The usage of bi-thickness cladding tubes with additional high refractive index layers on our geometrically optimized structure improves birefringence nearly by one order: the highest birefringence is 4.7 × 10−4 at 1.51 µm and sustains &gt; 1 × 10−4 for a wide bandwidth of 100 nm with a larger core diameter of 26 µm. Elliptical nesting on our proposed structure lowers the confinement loss to 0.007 dB/m at 1.51 µm and maintains a loss of &lt; 1 dB/m for a wide range of 210 nm. A polarization extinction ratio of 300 and higher order mode extinction ratio of 63, for our fiber, ensure a single polarization and single mode operation at 1.51 µm. Moreover, the proposed fiber exhibits a bend robust performance with a very low bend loss of 0.009 dB/m at a small bend radius of 6 cm and sustains a bend loss of &lt; 0.01 dB/m from a bend radius of 4 cm and above. Hence, our presented fiber, containing the above excellent characteristics, may be fruitful for designing polarization-controlled devices (fiber optic sensors, fiber optic amplifiers, fiber optic gyroscope, etc.) in the field of optical communication.

1030 nm All-Fiber Closed-Loop Fiber Optic Gyroscope with High Sensitivity

Angle random walk (ARW) is a critical noise component of a typical gyroscope alongside with bias instability noise. ARW has dominant effects especially in short-term accuracy. The measurement uncertainty degrades with the deterioration in ARW resulting in the lowered overall gyroscope accuracy. Many inertial navigation applications such as satellite control and gyro-compassing require low ARW. For an interferometric fiber optic gyroscope, lowest detectable rotation is proportional to scale factor of sensor and inversely proportional to optical bandwidth of light source used in the gyroscope. In this study, using a novel pump laser control closed-loop method, gyroscope performance is able to significantly enhance including signal-to-noise ratio (SNR). Fiber optic gyroscope includes an Yb-doped amplified spontaneous emission (ASE) source with broad emission spectra of 15 nm bandwidth used as light source in order to improve gyroscope sensitivity. The final ARW performance is about 0.008°/√hr for a fiber coil of 150 m length.

A Fast North-Finding Algorithm on the Moving Pedestal Based on the Technology of Extended State Observer (ESO).

We propose a kind of fast and high-precision alignment algorithm based on the ESO technology. Firstly, in order to solve the problems of rapid, high-accuracy, and anti-interference alignment on the moving pedestal in the north-seeker, the ESO technology in control theory is introduced to improve the traditional Kalman fine-alignment model. This method includes two stages: the coarse alignment in the inertial frame and fine alignment based on the ESO technology. By utilizing the ESO technology, the convergence speed of the heading angle can be greatly accelerated. The advantages of this method are high-accuracy, fast-convergence, strong ability of anti-interference, and short time-cost (no need of KF recursive calculation). Then, the algorithm model, calculation process, and the setting initial-values of the filter are shown. Finally, taking the shipborne north-finder based on the FOG (fiber-optic gyroscope) as the investigated subject, the test on the moving ship is carried out. The results of first off-line simulation show that the misalignment angle of the heading angle of the proposed (traditional) method is ≤2.1′ (1.8′) after 5.5 (10) minutes of alignment. The results of second off-line simulation indicate that the misalignment angle of the heading angle of the proposed (traditional) method is ≤4.8′ (14.2′) after 5.5 (10) minutes of alignment. The simulations are based on the ship-running experimental data. The measurement precisions of Doppler velocity log (DVL) are different in these two experiments.

Application of additional high-frequency modulation to reduce influence of residual amplitude modulation LiNbO3 phase modulator on fiber optical gyroscope signal

Residual amplitude modulation in LiNbO3 phase modulator is one of the key factors that limit the accuracy of high-sensitive fiber-optical sensors. A fiber-optical gyroscope is an angular velocity sensor whose sensitivity is better than 0.001 °/h. Optical light intensity changes after phase modulator is a reason for wrong phase difference that introduces an error in the angular velocity signal. Most existing residual amplitude modulation suppression methods are based on reduction of back reflections between an optical fiber and integrated optical waveguide, absorbing groove to suppress or reduce reflection on the bottom face, and algorithmic compensation. In this paper, new approach to reduce residual amplitude modulation in LiNbO3 for fiber optical gyroscope application is presented. Method feature is an application of additional differential signal modulation with uniform amplitude distribution in the input signal voltage range of the phase modulator. The proposed method allows to suppress residual amplitude modulation of the multifunctional integrated optical circuit phase modulator more than 3 times using additional triangle signal modulation with the frequency f = 200.09 MHz and power P = 36 dBm. This method is suitable for improving fiber optical gyroscope accuracy. Moreover, it could be applied for any fiber-optic sensors based on LiNbO3 phase modulator. The paper will be of interest to specialists in the field of highly sensitive fiber optical sensors, fiber, and integrated optics.

Recent Advancements in Resonant Fiber Optic Gyro—A Review

The fiber optic gyro (FOG), which is currently one of the most widely used fiber optic sensors, has firmly occupied a considerable market share of inertial sensors and offers the benefits of high stability and easy integration. The resonant FOG, also known as the RFOG, is a sensor that identifies a rotation rate by employing the use of a fiber ring resonator. It possesses a higher application potential in terms of optical stability and system miniaturization because it is an FOG of the second generation. This review begins with an exploration of the RFOG principle and then moves on to concentrate on the two aspects of RFOG optical noises suppression and signal processing in order to examine the progression of RFOG in the most recent years. Several distinct types of RFOG schemes that have a high application potential are dissected individually; these are the types of schemes that are anticipated to become mainstream application schemes in the not-too-distant future. In the end, the prospect and research challenge of RFOG are presented to help researchers clarify research directions. This article presents an in-depth analysis of the current state of research regarding RFOG-related technologies and offers a forecast regarding the path that the inertial sensor will take in the foreseeable future.

Simulation and optimization of spectral parameters of resonant optical gyroscope

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.