Closed-loop Fiber Optic Gyroscope Research Articles

Automatic Detection of Fiber Optic Gyroscope Intrinsic Frequency Based on Optimal Projection Approximation

To address the complexity and low detection accuracy issues in the intrinsic frequency detection process of fiber optic gyroscopes, a highly precise automatic measurement method based on optimal projection approximation is proposed. Building upon the digital closed-loop fiber optic gyroscope hardware circuit, this method generates a frequency-adjustable square wave with a 25% duty cycle through field-programmable gate array (FPGA) fractional division. Subsequently, it calculates the difference between the high and low levels of the sign bits of the modulated optical intensity signal sampled by the analog-to-digital converter (ADC). This yields an error signal related to the modulation frequency and intrinsic frequency. The modulation frequency is then approximated using the nearest projection of this error signal, thereby achieving automatic detection of the fiber optic gyroscope’s intrinsic frequency. The experimental results indicate that this method, requiring no external auxiliary equipment, enables rapid and highly accurate measurement of the intrinsic frequency of the fiber optic gyroscope. The measurement of intrinsic frequency takes approximately 300 milliseconds, achieving a measurement accuracy of up to 0.001 Hz.

Ripple free minimum beat control for digital closed-loop fiber optic gyroscopes

针对数字闭环光纤陀螺控制系统采样频率抖动引起的输出纹波现象，基于离散控制系统理论建立了四态方波调制下数字闭环光纤陀螺的理论模型。研究了控制系统的稳定条件、稳态误差和频率响应特性，提出了数字闭环光纤陀螺无纹波最小拍控制方案。通过实验与原有控制系统进行对比，结果表明，无纹波最小拍控制有效消除了数字闭环光纤陀螺控制系统中采样频率抖动引起的输出纹波现象，并有效提高了数字闭环光纤陀螺的精度，零偏稳定性提高约30%。

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.

Low-Drift Closed-Loop Fiber Optic Gyroscope of High Scale Factor Stability Driven by Laser With External Phase Modulation

In view of the poor scale factor stability of the interferometric fiber optic gyroscope (IFOG), it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of the broadband light source. As the linewidth of laser is narrow, the errors of coherent backscattering, polarization coupling, and Kerr effect are reintroduced which cause more noise and drift. This paper studies laser spectrum broadening based on external phase modulation of Gaussian white noise (GWN). The theoretical analysis and test results indicate that this method has a good effect on spectrum broadening and can be used to improve the performance of the laser-driven IFOG. In the established closed-loop IFOG, a four-state modulation (FSM) is adopted to avoid temperature instability of the multifunction integrated-optic chip (MIOC) and drift caused by the electronic circuit in demodulation. The experimental results show that the IFOG driven by broadened laser has the angular random walk noise of 0.003 8 °/√h and the drift of 0.017 °/h, which are 62% and 66% better than those without modulation respectively, of which the drift has reached the level of the broadband light source. Although the noise still needs further reduction, its scale factor stability is 0.38 ppm, which has an overwhelming advantage compared with the traditional IFOG.

Elimination of Crosstalk from Digital Closed-Loop Fiber Optic Gyroscopes via Polymorphic Modulation Method

Elimination of Crosstalk from Digital Closed-Loop Fiber Optic Gyroscopes via Polymorphic Modulation Method

Research on light source average wavelength and crystal oscillator frequency for reducing temperature error of the FOG scale factor

Based on the working principle of the digital closed-loop fiber optic gyroscope (FOG), a model for the influence of crystal oscillator frequency on scale factor (SF) temperature error is theoretically derived. Besides, the correlation between the two main light sources average wavelength and the SF temperature error is discussed. The experimental results show that both the crystal oscillator frequency and the light source average wavelength have a greater impact on the FOG SF temperature error. There is a cubic function relationship between crystal oscillator frequency and temperature, the temperature error of the SF is inversely proportional to the crystal oscillator frequency. Using a higher frequency temperature-compensated crystal oscillator, the frequency stability can be improved by two orders of magnitude, from 67.14 ppm to 0.22 ppm, the SF temperature error is also greatly reduced. The SF error is proportional to the relative change in wavelength, and the change caused by the temperature is of the same order of magnitude. Compared with the super luminescent diode (SLD) light source, the Erbium-doped fiber light source has higher average wavelength stability, the SF error caused by it is also smaller. The error can be reduced by 15 ppm and controlled at about 10 ppm after temperature compensation.

Research on the feedback control characteristics and parameter optimization of closed-loop fiber optic gyroscope

The feedback parameter of closed-loop fiber optic gyroscope (FOG) in various engineering applications is discussed. It has been proved that unreasonable feedback parameter will cause great interference and serious distortion to the output signal. Therefore, we build a concise feedback control mode and obtain optimal range of feedback parameter. For different input signals concerned which nearly include all of the application scenarios in practice, detailed simulations and experiments are completed. The results show that the feedback parameter should be small in static applications and moderate for high response requirements. What is more, it should be relatively small when used in low-bandwidth measurement fields to ensure the response performance of low frequency signal and suppress high frequency noise and vice versa. This work plays an important guiding role for related parameter setting in the feedback control system of sensors, especially for gyroscope.

Application study of ultra high frequency modulation of laser radiation for fiber-optic gyroscope noise reduction

Microwave photonics is implemented in many applications, including the area of inertial navigation systems based on high-precision fiber-optic gyroscopes. Microwave photonic technologies allow increasing the fiber-optic gyroscope accuracy. This paper investigates and evaluates the effect of ultra high frequency modulation of laser radiation on the closed-loop fiber-optic gyroscope output signal. Research results show that ultra high frequency modulation makes it possible to broaden spectrum width due to redistribution to modulation harmonics of the laser radiation. This approach allows to reduce the standard deviation of the laser-driven fiber-optic gyroscope output signal more than 2.5 times compared to using a laser-driven fiber-optic gyroscope without modulation. In order to achieve the noise level of a laser-driven fiber-optic gyroscope the same as the noise level of a fiber-optic gyroscope with a broadband source, it is necessary to use a broadband noise source with a constant power spectral density and higher output power. This study is useful for understanding how application of microwave photonic technologies can impact on the fiber-optic gyroscope output signal. The obtained results can be used for researchers in this area of study and can facilitate the rapid development of this field.

Research and Compensation of Frequency Response of LiNbO3 Phase Modulator for High-Performance Fiber-Optic Gyroscope

A lithium niobate (LN) phase modulator is widely spread because ofhigh electro-optic coefficients. Particularly, it is a highly required component for a closed-loop fiber-optic gyroscope (FOG) of navigation and tactical grade. However, low-frequency distortions of LN phase modulator frequency response can degrade the FOG performance. This paper deals with the research and compensation of frequency response of an LN phase modulator. It is a complex task to measure the response of the LN phase modulator in a FOG because of its Sagnac interferometer. Therefore, the special and novel modulation/demodulation algorithm is proposed. To the best of our knowledge and belief, the proposed method is the first published method that provides the measurement of the pulse response of a phase modulator as a part of a closed-loop FOG. The pulse response obtained in the proposed way allows getting appropriate high order transfer function of a phase modulator. For the first time to the best of our knowledge, the humidity dependence of the LN phase modulator frequency response is found. Influence of the phase modulator frequency response on FOG angular random walk, bias drift, and scale factor nonlinearity and instability is theoretically analyzed and mathematically simulated. The algorithmic method of the phase modulator response compensation is proposed and experimentally confirmed. The experimental results show that the proposed measurement technique of the phase modulator transfer function allows creating the compensating inverse filter that provides phase modulator response being close to flat. The application of the proposed method in the FOG operating mode allows reducing unwanted spikes to the noise level.

Low-Noise Closed-Loop FOG Driven by Two Broadband Sources

We propose and demonstrate experimentally a low-noise closed-loop fiber optic gyroscope (FOG) driven by two broadband sources simultaneously. The basic characteristic of built-up super broadband light source (SBLS) consisting of two superluminescent diodes (SLDs) with different wavelengths was designed and analyzed. The dispersion characteristic of half-wave voltage of multifunction integrated optical circuit (MIOC) was investigated theoretically and experimentally. The tested results agree well with the theoretical model and confirm that the customized MIOC can operate well over a large spectral bandwidth. An experimental FOG driven by the SBLS was built with a solid-core polarization maintaining photonic crystal fiber coil and the closed-loop operation was realized well. Its bias drift and scale factor were tested preliminarily, and high performance is achieved compared with the FOGs with a single SLD source.

Efficient Modulation and Processing Method for Closed-Loop Fiber Optic Gyroscope with Piezoelectric Modulator.

This paper presents a simple method for compensating the Sagnac phase shift in an interferometric fiber-optic gyroscope (I-FOG) with a piezoelectric modulator. The common advantages of I-FOGs with closed-loop compensation are linearized output characteristics and insensitivity to the light source power, including its time and thermal-induced fluctuations. Whereas closed-loop operation is normally achieved via ramp modulation requiring an electro-optic modulator, all-fiber architectures with a piezoelectric modulator are mostly limited to open loop. Nevertheless, such setups can more conveniently utilize a less expensive single-mode fiber with depolarized light and do not require any custom-made components. The proposed method allows us to combine the advantages of both approaches. Closed-loop compensation is ensured by adding further sinusoidal modulation to the common biasing modulation, such that the Sagnac phase shift is compensated solely at the sampling instants. We describe and experimentally demonstrate the proposed approach, utilizing a test setup to compare our closed-loop solution with open-loop operation. The results denote that the method provides a cost-efficient manner of performance improvement compared to the open-loop I-FOGs based on a piezoelectric modulator.

Effect of digital-to-analog converter glitch on the modulation and demodulation of a digital closed-loop fiber-optic gyroscope

Abstract Dead zone or bias error, which is induced by a glitch in the digital-to-analog converter (DAC) in a fiber-optic gyroscope (FOG) is proposed. The DAC glitch produces different forms of jamming signals and ultimately results in demodulation errors which depend on the modulation frequency and pass through zero at the proper frequency. The demodulation error is modelled as a piecewise function according to its characteristic, i.e., it appears to be a constant value when the staircase ramp ranges from 2n−2 to 2n−1 and remains zero when the staircase ramp outs of this range, where n is the bit length of the register. Simulations reveal that the staircase ramp oscillates, which leads to the dead zone when the equivalent angular velocity induced by the demodulation error is greater than the input angular velocity; otherwise, the staircase ramp resets with different slopes, which results in a bias error. We test the DAC glitch effect in a closed-loop FOG. The test results reveal that the dead zone induced by the demodulation error is consistent with that of the simulation results.

Digital Closed-loop Fiber Optic Gyroscopes Signal Processing System Based on DSP

Fiber optic gyroscopes (FOGs) have several advantages including higher reliability, long working lifetimes, quick start-up, and wide dynamic ranges. Therefore, it is of important significance for developing fiber optic gyroscopes. In this paper, a digital closed-loop FOG using digital signal processor (DSP) technique is presented. The practical design principle and signal processing technique are discussed. Test results show that the accuracy of prototype of the FOG is up to 5°/ℎ.

Method of suppression of impulse interferences in digital closed loop fiber optic gyro detected signal

Periodic impulse interferences in the detected signal of digital closed loop fiber optic gyro lead to a bias error. In this paper, three kinds of interference sources, D/A converter and phase modulator, light source, and system power supply, are discussed and verified by an open-loop testing approach. A method with an integration of a digital average algorithm and a soft-switching median filter is proposed to suppress the periodic impulse interferences in detected signal. Selection criterions of the parameters used in the method are discussed and verified through simulation. Some considerations for the practical realization of the method within FPGA are given. An experimental verification of the method is presented by applying it to three gyros corrupted by periodic impulse interferences. The results demonstrated that the bias error could be decreased by about 85% with the method proposed.

Digital Signal Processing Scheme for Open Loop and Closed Loop IFOG using MATLAB/SIMULINK

Objective: Interferometric Fiber optic gyroscope (IFOG) is an angular rate sensor which plays a crucial role in inertial navigation system. Measuring the angular rotation rate can be done in two approaches namely open loop&closed loop. Designing and implementation of these methods using a simulation tool provides faster&accurate results. This paper presents a novel Simulink model implementation of Open loop&Closed loop Fiber optic gyroscope for the measurement of rotation rate. Method/Analysis: The gyroscope with each optical component is treated as a black box having M input and N output ports that are represented mathematically with its transfer function by connecting output to its input. This methodology is very efficient for finding the calibration&phase difference between the co-rotating&counter rotating beams. Findings: There are two major contributions in this paper. Firstly, the physical model of open loop FOG is built in Simulink model&angular rate is measured. The signal processing scheme of modulation and demodulation techniques for finding the rotation rate can also be analyzed mathematically. In second, to improve the accuracy and stability the feedback loop is very important to improve the gyro performance which can also be analyzed with different rotation rates. Experimental setup shows that an improved result is obtained in determining the direction of rotation and accuracy of the proposed model.

Research on dead zone of closed-loop fiber optic gyroscope and optic power crosstalk error

Research on dead zone of closed-loop fiber optic gyroscope and optic power crosstalk error

Analysis of dead zone sources in a closed-loop fiber optic gyroscope.

Analysis of the dead zone is among the intensive studies in a closed-loop fiber optic gyroscope. In a dead zone, a gyroscope cannot detect any rotation and produces a zero bias. In this study, an analysis of dead zone sources is performed in simulation and experiments. In general, the problem is mainly due to electrical cross coupling and phase modulation drift. Electrical cross coupling is caused by interference between modulation voltage and the photodetector. The cross-coupled signal produces spurious gyro bias and leads to a dead zone if it is larger than the input rate. Phase modulation drift as another dead zone source is due to the electrode contamination, the piezoelectric effect of the LiNbO3 substrate, or to organic fouling. This modulation drift lasts for a short or long period of time like a lead-lag filter response and produces gyro bias error, noise spikes, or dead zone. For a more detailed analysis, the cross-coupling effect and modulation phase drift are modeled as a filter and are simulated in both the open-loop and closed-loop modes. The sources of dead zone are more clearly analyzed in the simulation and experimental results.

Suppression of Thermal Effect on Closed Loop Fiber Optic Gyroscope

Fiber Optic Gyroscope (FOG), an inertial sensor measures the angular rotation of an object based on the principle of Sagnac effect. FOG is subjected to various environmental disturbances such as temperature, vibration etc., when it is operated in real time. Temperature variation is the major factor that affects the gyro performance. In this paper, a novel compensation approach called temperature soaking method has been presented which makes the gyro insensitive to temperature. This method has been carried out for a 3-axis (Gx, Gy and Gz) FOG and its outputs (bias values) were taken at different temperature points. In order to reduce the bias drift of FOG output, this method uses linear curve fitting function to generate the bias error coefficients. The generated bias error coefficients are subtracted from the existing bias data, which in turn reduces the bias error. The bias values obtained for 3-axis gyro at temperature points from -20°C to +60°C before compensation is then compared with the bias values obtained for after compensation at same temperature points. Experimental results demonstrate that, after compensation the bias drift greatly reduced from 15 to 0°/hr approximately. This method effectively improves the stability and performance of a gyro and makes it to withstand to different environmental conditions which in turn increases the range of applications from military, navigation to space.

Improved hybrid filter for fiber optic gyroscope signal denoising based on EMD and forward linear prediction

Fiber optic gyroscope (FOG) has been widely applied in strapdown inertial navigation system (SINS) as an ideal component. However the slowly varying drift of FOG that often submerged in noise will degrade the precision of SINS over time. The main objective of this paper is to focus on eliminating noise and extracting the slowly varying drift using a newly proposed hybrid filter called EMD-G-FLP. The implementation of EMD-G-FLP mainly consists of two steps. First, improved empirical mode decomposition (EMD) method is used to decompose original drift. Then a prediction filtering method named G-FLP is adopted to denoise obtained intrinsic modes. EMD-G-FLP is compared with methods based on wavelet packet translation (WPT) and G-FLP, respectively, using signals detected from a closed-loop interferometric FOG. The deficiencies of WPT-based method are analyzed by employing static and dynamic FOG drift. Experimental results show that, G-FLP and EMD-G-FLP retain the slowly varying drift without distorting the trend. Furthermore, compared with G-FLP, EMD-G-FLP reduces the noises including quantization noise, random walk and bias instability by about 82%, 75% and 53%, respectively.

English

2 ABSTRACT: The Three Axes Closed Loop Fiber Optic Gyroscope Signal Processing Unit is expected to perform extraction of rotation rate information (Sagnac Phase) from the Sensor and computation of incremental angles, digitization of accelerometer outputs and computation of incremental velocities and Compensation of the sensor outputs over operating temperature range.