Application of wavelet package filtering in the de-noising of fiber optic gyroscopes

To reduce the drift error existing in the output signal of fiber optic gyroscopes （FOG）, a mathematical model of the FOG output signal is set up; the error characteristics of the FOG output signal are analyzed, and semi-soft threshold filtering is chosen based on the comparison of hard threshold and soft threshold filtering. The semi-soft threshold wavelet package filtering method is applied in the filtering of the FOG output signal. Experiments of the stationary and dynamic FOG output signals filtered with the wavelet package analysis are carried out in a lab environment, respectively. Experiments done with the real-time measured FOG signal show that the method of semi-soft threshold wavelet package filtering reduces the mean square error from 5 （°）/h to 1 （°）/h, so it is effective in eliminating the white noises and the fractal noises existing in the FOG. The novel method proposed here is proved valid in reducing the FOG drift error, satisfying the technical demands of high precision and realtime processing.

An Open-Loop Test of a Resonator Fiber Optic Gyro

The resonator fiber optic gyro （R-FOG） ,which utilizes a resonance frequency change due to the Sagnac effect,is a promising candidate for the next generation inertial rotation sensor. In this study, an open-loop R-FOG is set up using phase modulation spectroscopy. First,the demodulation curve is obtained using a lock-in amplifier. From the demodulation signal,a gyro dynamic range of ± 4.2rad/s is obtained. Then,using different phase modulation frequencies,the open-loop gyro output signal is measured when the gyro is rotated clockwise or counterclockwise. The bias drift as a function of time is also measured. The fluctuation of the output over 5s is about 0.02rad/s. The drift can be reduced by taking countermeasures against system noise.

Research on fiber optic gyro signal de-noising based on wavelet packet soft-threshold

Gyro＇s drift is not only the main drift error which influences gyro＇s precision but also the primary factor that affects gyro＇s reliability. Reducing zero drift and random drift is a key problem to the output of a gyro signal. A three-layer de-nosing threshold algorithm is proposed based on the wavelet decomposition to dispose the signal which is collected from a running fiber optic gyro （FOG）. The coefficients are obtained from the three-layer wavelet packet decomposition. By setting the high frequency part which is greater than wavelet packet threshold as zero, then reconstructing the nodes which have been filtered out noise and interruption, the soft threshold function is constructed by the coefficients of the third nodes. Compared wavelet packet de-noise with forced de-noising method, the proposed method is more effective. Simulation results show that the random drift compensation is enhanced by 13.1%, and reduces zero drift by 0.052 6°/h.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed- loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.

Phenomena of optic-bound effect on fibre optic gyro

The optic-bound effect on fibre optic gyro （FOG） precision is analysed theoretically, and formulas describing the change of FOG light power under the action of optic-bound effect are given. It is confirmed that optic-bound effect is a main instantaneous non-reciprocity effect of FOG in addition to the Sagnac effect and can lead to a dynamic error of FOG in practical environments. An approach to suppressing or eliminating the error due to the optic-bound effect is presented and verified experimentally. The result shows that the approach is valid and the precision of FOG is improved observably.

Resonator integrated optic gyro based on multilevel laser frequency lock-in technique

The resonator integrated optic gyros（RIOGs） based on the Sagnac effect have gained extensive attention in navigation and guidance systems due to their predominant advantages： high theoretical accuracy and simple integration. However, the problems of losing lock and low lock-in accuracy are the bottlenecks, which restrict the development of digital RIOGs. Therefore, a multilevel laser frequency lock-in technique has been proposed in this Letter to address these problems. The experimental results show that lock-in accuracy can be improved one order higher and without losing lock in a variable temperature environment. Then, a digital miniaturized RIOG prototype（18 cm × 18 cm × 20 cm） has been produced, and long-term（1 h） bias stability of 26.6 deg/h is successfully demonstrated.

Residual intensity modulation in resonator fiber optic gyros with sinusoidal wave phase modulation

We present how residual intensity modulation(RIM) affects the performance of a resonator fiber optic gyro(R-FOG) through a sinusoidal wave phase modulation technique. The expression for the R-FOG system's demodulation curve under RIM is obtained. Through numerical simulation with different RIM coefficients and modulation frequencies, we find that a zero deviation is induced by the RIM effect on the demodulation curve, and this zero deviation varies with the RIM coefficient and modulation frequency. The expression for the system error due to this zero deviation is derived. Simulation results show that the RIM-induced error varies with the RIM coefficient and modulation frequency. There also exists optimum values for the RIM coefficient and modulation frequency to totally eliminate the RIM-induced error, and the error increases as the RIM coefficient or modulation frequency deviates from its optimum value; however, in practical situations, these two parameters would not be exactly fixed but fluctuate from their respective optimum values, and a large system error is induced even if there exists a very small deviation of these two critical parameters from their optimum values. Simulation results indicate that the RIM-induced error should be considered when designing and evaluating an R-FOG system.

Optimization of the resonant frequency servo loop technique in the resonator micro optic gyro

Proportional integrator (PI) is always adopted in the resonant frequency servo loop in a resonator micro optic gyro (RMOG). The oscillation phenomenon is observed when adjusting the loop gain surpassing a threshold. This phenomenon limits system performance on step response speed and residual error. Based on the experiment system, a simulation model was set up. Further analysis shows that the threshold gain is related to the system loop filter setting and the loop delay. The traditional PI frequency servo loop technique in the RMOG system cannot keep up with the environment's disturbance quickly enough, which leads to a large residual error. A compensating method is proposed to optimize the tracking performance, solve the oscillation problem, and speed up the system response. Simulation and experiment results show that the compensated system is superior in performance. It has less residual error in the stable state and is 10 times quicker than the uncompensated system on the step response.

NUMERICAL MODEL OF THERMAL TRANSIENT EFFECT IN FIBER OPTIC GYRO

The sensitivity of the interferometric fiber optic gyro in the presence of time varying thermal gradients plays a key role in its performance. It is well known that this sensitivity is due to the difference of index changes between the points symmetrical with respect to the middle of the coil. In order to reduce this sensitivity, different winding patterns, such as quadrupolar winding, were introduced to keep the thermal environment of the symmetrical points. In this paper, a numerical model of the transient temperature distribution in the gyro was established. The temperature gradient of the coil was solved in conjugation with the nature convection heat transfer in the aperture between the coil and the case. Effects of the winding pattern and the design of its case were investigated to optimize the design of the interferometric fiber optic gyro.

Dynamic Free-Spectral-Range Measurement for Fiber Resonator Based on Digital-Heterodyne Optical Phase-Locked Loop

We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.

G波段二次谐波准光回旋行波管研究

为开展适用于太赫兹频段的大功率回旋放大器研究。对基于准光共焦波导的二次谐波准光回旋行波管进行了研究,理论与仿真结果表明,准光波导具有良好的模型选择性,利用器件的二次谐波工作,其基波与二次谐波的返波振荡可以得到很好的抑制。在理论与仿真研究基础上,设计了一只G波段的二次谐波准光回旋行波管,理论计算结果表明:在65 kV电子束电压、10 A电流、速度横纵比为1、磁场强度为4.19 T时,最大输出功率为90 kW,效率为13.8%,增益为34.8 dB。当输入功率10 W时,-3 dB带宽为2 GHz。

谐振式光学陀螺噪声抑制技术研究现状(特邀)

谐振式光学陀螺仪利用光学谐振腔在时空上对光波极强的局域增强效应,有望成为兼具高精度和小体积的光学陀螺。然而,谐振式陀螺转动产生的Sagnac效应相对微弱,容易受到陀螺系统内非互易性以及互易性噪声的干扰,成为其精度提升的瓶颈。在陀螺的小型化过程中这一问题更加凸显。因此,对谐振式光学陀螺仪进行噪声抑制显得尤为重要。本文详细综述了谐振式光学陀螺中非互易性和互易性两大类噪声的原理及其抑制方法,总结了该领域近来年的研究现状及未来挑战与发展趋势,为我国谐振式光学陀螺发展提供参考。

高精度惯性导航系统的技术预见

面对水下装备无人化/智能化的发展趋势,系统分析国内外知名惯性导航系统生产公司的产品,梳理水下装备的核心设备—惯性导航系统的发展趋势。基于工具检索国内外知名惯性导航系统公司的公开文献、专利以及产品手册等开源信息,提炼关键信息以及参数进行对比分析。目前,光纤陀螺惯性导航系统在国内已成为实现水下装备高精度定位的核心产品,基于谐振陀螺的惯性导航系统尚处于研发阶段。国际市场上,基于激光陀螺的惯性导航产品正逐渐被基于谐振陀螺和光纤陀螺的惯性产品替代。从法国赛峰和Exail这两家顶尖公司的产品指标看,谐振陀螺高精度惯性产品相比光纤陀螺高精度惯性产品而言,无论在体积还是在质量上都有较大优势,后续可能完全替代光纤陀螺系统成为市场主流。

ELM-AdaBoost模型在光纤陀螺温度误差补偿中的应用

针对光纤陀螺零偏与温度之间复杂的非线性关系,引入极限学习机(extreme learning machines,ELM)模型补偿光纤陀螺的零偏温度误差;针对单个ELM在预测准确性和稳定性不足及其对奇异样本敏感的问题,引入自适应增强算法(adaptive boosting,AdaBoost)建立ELM-AdaBoost预测模型改善光纤陀螺性能,分析光纤陀螺的温度误差机理及模型参数对预测精度的影响,给出ELM算法隐含层神经元个数及AdaBoost算法迭代次数的确定方法。仿真结果表明:基于ELM-AdaBoost预测模型的补偿效果优于多元线性回归模型和单个ELM神经网络模型,并具有良好的泛化性能和温度适用性,补偿后陀螺零偏均方根误差降低93%以上,显著改善了光纤陀螺零偏稳定性能。

基于光纤陀螺的工程结构形变检测精度分析

针对光纤陀螺形变检测系统在应用中遇到的形变精度难以评估和运行速度难以选择问题,对形变检测精度和光纤陀螺性能之间的关系进行了分析。从光纤陀螺的工程结构形变检测机理出发,基于光纤陀螺误差模型,分析了光纤陀螺零偏重复性误差和稳定性误差与形变检测误差的对应关系,在此基础上还仿真分析了检测系统的运行速度与检测精度的关系。仿真结果表明,当运行速度较快时,稳定性误差是影响检测精度的主要因素,当运行速度较低时,重复性误差是影响检测精度的主要因素,若采用中精度光纤陀螺,运行速度2 m/s时,可实现均方根为8.514μm的形变测量精度。研究成果可为光纤陀螺工程结构形变检测技术的工程应用提供理论指导。

采用激光光源线宽展宽的光纤陀螺标度因数性能提升技术

光纤陀螺中使用激光光源代替传统宽谱光源有利于提升性能和降低成本,但激光光源作为一种窄线宽的高相干光源,将其用于光纤陀螺又会引入瑞利散射、克尔效应和偏振交叉耦合等干扰,因此有必要对激光光源进行线宽展宽。首先对基于高斯白噪声外部相位调制的激光光源线宽展宽方法进行理论分析,建立光谱展宽卷积模型。其次采用延迟自相关测量方法验证了高斯白噪声外部相位调制对激光光源线宽的展宽效果。最后基于仿真分析结论,搭建了激光器线宽展宽光源装置,将激光光源的光谱展宽成线宽20 GHz的光谱,应用于光纤陀螺并验证了标度因数性能,为激光光源在光纤陀螺中的应用提供了理论基础,具有一定的工程应用价值。

基于暂态过程优化的谐振式光纤陀螺背向散射噪声抑制方法研究

针对谐振式光纤陀螺受背向散射噪声影响严重的问题,在优化三角波调制解调参数的基础上,提出了一种基于暂态过程优化的噪声抑制方法。该方法通过部分采样和均值滤波,在不改变陀螺光、电硬件配置的前提下,优化了三角波调制时存在的暂态过程现象,提高背向散射噪声的抑制比,改善解调曲线工作区的线性度。搭建样机并进行实验后,结果表明,基于暂态过程优化的噪声抑制方法能将暂态过程的占空比由64.3%降低至12.1%,解调后背向散射噪声的抑制比达到46.8%,且解调曲线工作区线性度达99.6%。可见,基于暂态过程优化的方法能有效提高谐振式光纤陀螺背向散射噪声的抑制能力,并改善解调曲线工作区的线性度。

光纤陀螺Shupe效应温度补偿模型研究

针对光纤陀螺温度补偿问题,以光纤陀螺Shupe效应原理为基础,仿真了变温温度场下光纤环温变情况。根据仿真模型的结果,试验多温度传感器采集光纤环不同位置温度数据,建立了多温度传感器补偿模型,分析了不同补偿模型之间的差异。并使用构造温度数据的方法,建立了构造温度补偿模型,验证了此模型在提升补偿精度与补偿适应性上的特点,为实际工程应用中提供了可行的补偿方法。

基于Cortex-M3的组合罗经显控软件的设计与实现

为解决传统光纤陀螺罗经系统价格昂贵的问题,利用低成本的光纤陀螺罗经和双天线卫星定位定向系统组成组合罗经的主罗经单元成为重要措施。组合罗经显控单元的主控芯片采用基于Cortex-M3的LPC1768,为了减少大量代码的编写、缩短软件开发周期,屏幕选用迪文串口屏,通过串口接收主罗经发来的报文,将船舶航向以罗盘图片的方式在屏幕上实时显示出来。同时,为了方便不同的用户使用,设计了3种显示模式:罗经模式、航向模式以及导航模式。经实船测试,该显控软件的设计可行且能够满足航行要求。

一种光纤速率陀螺组件系统误差的两级补偿方法

针对某型光纤速率陀螺组件系统误差复杂、补偿难的问题,提出了一种两级误差补偿方法,实现了系统全温综合误差的补偿。首先,通过理论分析得到了系统误差类型,包括:三轴陀螺不正交、刻度系数、模拟电路误差及刻度系数温度、模拟电路温度误差,并结合试验,分析验证了其误差特性。根据误差特性制定了两级补偿方法,并通过一级补偿了三轴陀螺不正交、刻度系数、模拟电路误差,在此基础上,通过二级补偿了刻度系数温度、模拟电路温度误差。试验表明,该补偿方法能将系统输出精度提高一个数量级,具有一定的工程应用价值。