Dynamic characteristics of R-FOG based on the triangle wave phase modulation technique

A resonator fiber optic gyro (R-FOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. Fiber ring resonator (FRR) is the core-sensing element in the R-FOG. Till now, the dynamic response of the FRR is studied, and it is found that the frequency of the resonance dip is shifted away from the resonance frequency when sweeping the laser frequency, and thus must affect the performance of the R-FOG. Therefore, dynamic characteristics analysis of the R-FOG, which usually works in the dynamic state, is in urgent need. This paper presents the expression for the dynamic demodulation curve of the R-FOG based on the triangle wave phase modulation technique. Through analysis and simulation, it is concluded that the frequency zero-deviation will be induced when the R-FOG is in dynamic state, and the gyro error caused by the frequency zero-deviation will increase as the product of the operating range and the bandwidth of the R-FOG.     

谐振式集成光学陀螺解调特性分析

基于激光器频率谱检测技术,沿着光的传输方向分析了光波在谐振式集成光学陀螺系统中的传播,结合输入信号特征,建立频域内的数学模型,通过数值仿真和实验得到了调频检测系统下的解调曲线。按照光的传输方向：激光器、声光晶体移频器、光波导环形谐振器、探测器,利用贝塞尔函数展开和光场耦合模理论分析了谐振式集成光学陀螺解调特性,及其调频调制检测系统解调输出信号与谐振频率偏差之间的关系。通过数值计算,分析了解调曲线的变化规律,得到了施加在激光器压电陶瓷驱动器上调制波形的最佳调制系数。在实验上搭建了激光器频率调制解调技术系统,得到了解调曲线。数值仿真和实验结果表明,当调制系数M=2时,线性工作区间斜率最大,解调曲线最好。实测形状与理论分析结果相符,从解调信号得到±2×10³ rad/s的陀螺动态范围。     

激光频率调制线型分析

在激光频率调制的理论分析中,一般采用正弦波调制、正弦波解调,而没有讨论调制和解调的其它情况。本文主要分析了Guass线型吸收的情况下,锯齿波调制、方波解调的一次、二次谐波相检结果和三角波调制、方波解调的一次、二次谐波相检结果,以及调制深度对信号谱形和信号强度的影响。我们发现,在锯齿波调制、方波解调情况下,一次、二次谐波谱形和正弦波调制情况区别很大;但在三角波调制、方波解调情况下,可以获得和正弦波调制、正弦波解市场相似的结论。另外,不同的调制深度对输出的调制谱形也有重要的影响。我们还用甲烷的可调谐 红外光调制吸收光谱实验验证了理论分析结果。最终得到结论：频率调制谱的信号谱形及信号强度与调制波形、解调波形和调制深度均有关系。     

三角波调制对谐振微光学陀螺偏置稳定性的影响

谐振式微光学陀螺是一种新型的惯性传感仪器,与传统的机械陀螺与其他光学陀螺相比具有很多理论上的优势。通过分析抑制载波和提高信噪比,深入地研究了三角波调制频率和幅度对谐振式微光学陀螺偏置稳定性的影响。通过理论计算和仿真分析,考虑得到更好的载波抑制效果,调制幅度应选为15.44 V;考虑提高信噪比,调制频率应设为1 MHz。搭建了谐振式微光学陀螺系统,实验测试结果与理论分析吻合较好。此外,采用优化的调制参数,陀螺的偏置稳定性由0.39 ()/s提高到0.18 ()/s(10 s积分时间)。研究结果表明:选择优化的调制三角波参数可以将陀螺偏置稳定性提高一倍,对于其他调制方案,如正弦波相位调制方案,同样可以通过分析载波抑制和信噪比优化调制参数,改善陀螺偏置稳定性。     

基于相位调制-解调的光纤激光相位噪声检测方法研究

在主动相位控制相干合成中,常用的光纤激光主动相位控制方法主要有外差法、多抖动法和随机并行梯度下降算法等. 基于多抖动法和外差法的原理,提出了一种新型的基于相位调制-解调的相位检测与控制方法. 该方法利用周期信号对参考光进行相位调制,将调制后的参考光与待检测信号光进行相干检测,通过对相干光强信号和相位调制信号的融合处理,实现相位噪声的检测和控制. 对该方法进行了数值模拟和实验研究. 实验结果表明,对于频率为2 kHz,噪声范围为[0,2π)的正弦噪声,相位检测精度优于λ/50,控制精度可达 关键词： 光纤激光 相干合成 相位噪声检测 调制-解调     

两重外腔的自混合干涉及其信号分析

提出了具有两重外腔的自混合干涉。根据半导体激光器的自混合干涉理论，研究了两重外腔自混合干涉模型，及其信号的调制和解调方法。该方法用一个附加的参考反射镜在半导体激光器(LD)和目标间形成两重外腔，参考外腔用于补偿光学频率涨落引入的相位误差。用快速傅立叶变换相位探测技术(FFT)分析自混合干涉信号。运用这些方法，可提高相位测量精度，在微光机电系统、光学工程和其他工程应用上有潜在的实用价值。     

改进式相位生成载波调制解调方法

在对调制方法、混频原理、调制深度取值等问题深入研究的基础上,为得到更高的抗干扰能力,结合相位生成载波调制解调技术与微分交叉相乘解调算法,引入除法运算,提出一种改进的相位生成载波解调算法,以抑制光强扰动对解调结果的影响,并与传统的微分交叉相乘解调算法在光源产生低频干扰时的解调效果对比,进行仿真实验.对比信号源分别为20 Hz与200 Hz时的解调效果,结果表明,在光源有1Hz低频扰动的情况下,在高频信号解调的结果中,改进的解调算法可以准确地实现对待测信号的解调,解调结果与传统方法相比具有更高的线性度.     

金属杆内疲劳裂纹与振动/超声相互作用及其定量表征

根据同步解调的原理,考察振动声调制检测输出信号中的调制成分,对金属杆内振动/超声在裂纹面上的相互作用进行了分析.制作了含有不同尺寸裂纹的铝杆试样,以扫频激励的方式得到合适的高频激励参数,分析输出信号中的调制信息,发现工件中的高频超声可分为两部分:一部分声波通过裂纹面,受到低频振动信号的调制,另一部分则保持不变。在此基础上对非线性调制模型进行了修正,并提出了一种用于裂纹检测的定量方法。与超声C扫描检测结果对比表明,此定量方法可用于估计金属杆中疲劳裂纹尺寸。      

Interaction of fatigue crack with vibration and ultrasound in metallic rod and its use for quantitative characterization

According to the principle of synchronous demodulation,the modulation information in the output signal of vibro-acoustic modulation test was investigated and the nonlinear interaction of sound and vibration with the crack interface in a metallic rod was analyzed.A swept signal excitation was used to obtain a proper high frequency parameter in the test of aluminum rod samples with different sizes of cracks and the modulation information in the output signal was analyzed.It was found that the ultrasound wave in the structure can be separated into two parts.One is the wave which passes through the crack interface modulated by the low frequency vibration,and other wave has no any changes.The nonlinear modulation model was modified and a quantitative method for crack detection was proposed.It is demonstrated by comparing with the ultrasonic C-scanning that this method can be used to estimate the fatigue crack size in the metallic rod.     

The Application of Digital Filtering to Phase Recovery when Surface Contouring using Fringe Projection Techniques

If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then the surface acts as a phase modulator, with the amount of modulation at any point depending upon the height of the surface at that point. In recent years considerable effort has been devoted to the problem of fringe demodulation, with prominence given to techniques using fringe-phase stepping and Fourier analysis. It has long been known that phase demodulation is possible using a system of filters, and the technique has been widely used in the related area of frequency demodulation in radio. In this paper the development of phase demodulation using a system of digital filters is considered. For the accurate recovery of image phase it is necessary for the filters to introduce zero phase shift, or to have a phase shift proportional to frequency. The design of the digital filters is considered and their performance is assessed using the signal from a real modulated fringe pattern and a simulated signal. It is shown that the demodulation technique works well, even with a poor signal-to-noise ratio. © 1997 Elsevier Science Ltd. All rights reserved.     

一种低成本的光纤陀螺信号处理方法

讨论了一种低成本的干涉型光纤陀螺的信号处理方法。应用了自动相位跟踪技术,重点解决了PZT的稳定性问题,提高了光纤陀螺的精度。在方案中,以正弦波信号作为相位偏置信号,相位解调运用了同步相关检测的方法。方案的优点是其低成本和易于实现,能够满足在一定条件下陆地导航和定位系统的需要。     

相敏式激光啁啾色散光谱技术在高吸收度情况下的应用

研究了相敏式激光啁啾色散光谱法在高吸收度情况下的应用.用窄频半导体激光器作为光源,利用一工作于载波抑制模式的铌酸锂电光强度调制器调制单频激光,在单频激光两侧产生两个边频分量,并通过两边频分量产生外差干涉信号.利用外差干涉的相位波动来测量甲烷气体位于1653.7 nm附近的折射率波动,通过气体折射率与吸收系数之间的Kramers-Kronig关系计算甲烷气体浓度.传统的波长调制光谱法受限于郎伯-比尔定律,在应用于高吸收度的情况时,存在灵敏度下降的问题,甚至出现随气体浓度上升输出信号反而下降的现象.实验结果显示,相同实验条件下,波长调制光谱法的线性测量范围为38.1—1500 ppm·m,线性测量的动态范围仅为16 d B;而相敏式激光啁啾色散光谱法在很大的吸收度范围内均具有线性输出,检出限低至47.3 ppm·m,线性测量范围上限为174825 ppm·m,具有超过35 d B的动态范围.     

光外差-塞曼调制磁旋转光谱技术的线型研究

光外差－塞曼调制磁旋光谱技术是一种高灵敏的吸收光谱技术。它同时对激光频率和样品的塞曼效应进行调制,然后通过双解调来提取微弱的光谱信号。文内导出了该信号的数学表达式,并对影响线型和灵敏度的多种物理参数进行了分析,获得了与实验相符合的结果。     

Resonance asymmetry phenomenon in waveguide-type optical ring resonator gyro

The intensity output of a silica waveguide ring resonator (WRR) was found to show an asymmetric resonance characteristic. To further analyze and better design the resonator micro optic gyro (RMOG) with a waveguide-type ring resonator, in-depth research of the characteristics of the resonance asymmetry is fully developed for the first time, to the best of our knowledge. Four possible sources of the resonance asymmetry are analyzed and their respective contributions are compared. These four error sources are differential normal mode losses in the coupler, the backscattering induced noises, the polarization fluctuations and the optical Kerr effect. The differential normal mode loss is suspected to be the major contributor to the observed resonance asymmetry in the fabricated silica WRR. Asymmetric resonance curve produces a large output bias error in the RMOG based on the phase modulation technique, which is related to the modulation frequency differences between the CW and CCW lightwaves. Theoretical analysis shows that replacing the reflector WRR with a transmitter one is helpful to eliminate the effect of the different normal mode losses in the coupler on the resonance asymmetry.     

基于三角波驱动法珀可调谐滤波器的光纤光栅解调偏差校正算法

为了校正解调系统在三角波上升行程和下降行程对光纤布拉格光栅(FBG)波长解调结果出现的偏差,提出一种采样点相对位置的校正算法。将三角波2个扫描行程的FBG波峰分别映射到相应的标准具原始数据中,再对2个映射波峰在标准具光谱中的相对位置偏差进行校正,达到减小解调偏差的目的。实验采用2支不同波长的FBG进行验证,结果显示,经过校正,FBG1将三角波上下扫描行程的解调偏差从12.053 pm减小到了0.476 pm,FBG2将该解调偏差从12.101 pm减小到了0.427 pm,2支传感器的解调偏差相比校正前分别减小了25.3倍和28.3倍。     

调制转移光谱光频率标准系统中电光参数的优化研究

根据窄带相位调制光在非线性吸收介质中的近简并四波混频的物理机理,分析了采用电光调制器实现调制转移光谱(MTS)技术的电磁场激励及其动态演化过程,建立了MTS中频率色散谱和吸收谱的理论模型. 研究结果表明:以分子吸收谱线色散谱信号作为频率误差鉴别信号时,系统调制频率取0.72倍谱线线宽附近可以得到最佳的色散信号强度;解调相位的变化对吸收谱的影响很大,但对色散谱而言,解调相位在90°附近的小范围波动对频率误差信号解调效果影响不大;调制度在0.5–1区域可以得到较好的综合稳频效果. 关键词： 光频率标准 调制转移光谱 频率稳定 电光参数优化     

载波频率漂移对相位生成载波解调结果的影响分析

从载波相位调制解调原理出发,理论分析了载波频率漂移对解调结果的影响.通过对解调公式的推导及分析,给出了频率漂移对解调结果影响的公式.结果表明,当混频基频信号的频率与载波频率存在微小频差时,解调结果将出现低频调制,严重影响解调效果;仿真及实验验证结果与理论分析完全吻合.     

Detuned Twin-Signal-Recycling for ultrahigh-precision interferometers

We propose a new interferometer technique for high-precision phase measurements such as those in gravitational wave detection. The technique utilizes a pair of optically coupled resonators that provide identical resonance conditions for the upper as well the lower phase modulation signal sidebands. This symmetry significantly reduces the noise spectral density in a wide frequency band compared with single-sideband recycling topologies of current and planned gravitational wave detectors. Furthermore, the application of squeezed states of light becomes less demanding.     

Exchanged ridge demodulation of time-scale manifold for enhanced fault diagnosis of rotating machinery

The vibration or acoustic signal from rotating machinery with localized fault usually behaves as the form of amplitude modulation (AM) and/or frequency modulation (FM). The demodulation techniques are conventional ways to reveal the fault characteristics from the analyzed signals. One of these techniques is the time-scale manifold (TSM) ridge demodulation method with the merits of good time–frequency localization and in-band noise suppression properties. However, due to the essential attribute of wavelet ridge, the survived in-band noise on the achieved TSM will still disturb the envelope extraction of fault-induced impulses. This paper presents an improved TSM ridge demodulation method, called exchanged ridge demodulation of TSM, by combining the benefits of the first two TSMs: the noise suppression of the first TSM and the noise separation of the second TSM. Specifically, the ridge on the second TSM can capture the fault-induced impulses precisely while avoiding the in-band noise smartly. By putting this ridge on the first TSM, the corresponding instantaneous amplitude (IA) waveform can represent the real envelope of pure faulty impulses. Moreover, an adaptive selection method for Morlet wavelet parameters is also proposed based on the smoothness index (SI) in the time-scale domain for an optimal time-scale representation of analyzed signal. The effectiveness of the proposed method is verified by means of a simulation study and applications to diagnosis of bearing defects and gear fault.     

激光调制参数对光纤环型谐振腔光谱特性影响

谐振光学环型腔作为光学陀螺的核心敏感单元,其光学调制谱和与之对应的鉴频曲线的特性成为提高光学陀螺系统检测灵敏度的关键。为了研究光学陀螺的调制和鉴频谱线特性,优化陀螺性能,设计并搭建了实验测试系统,光纤环形谐振腔采用分光比为50∶50、直径17 cm的保偏光纤,总长2.2 m。使用直流高压放大器扫描窄线宽激光器（线宽小于1 kHz）的压电转化模块,扫描频率和电压分别选取20 Hz和1 V,使用模拟比例积分电路进行锁频并反馈给激光器的压电转化模块,使激光器的输出频率跟踪谐振腔实时变化。研究分析了光纤环型谐振腔在两种情况下所对应的透射谱和鉴频曲线:第一种情况为调制电压分别为2 V和4 V,对应调制频率从100 kHz到4 MHz变化;第二种情况为当调制频率为900 kHz,调制电压从2 V到10 V变化。通过实验,得到了不同调制参数下光学陀螺谱线的谐振深度、半高全宽、线性带宽、动态范围、品质因数、标度因数以及对应的锁频精度七种物理量的详细变化情况,并进一步得到了静态测试条件下三种陀螺的最佳调制频率及与之所匹配的调制电压。为进一步研究激光调制对光纤环型谐振腔光谱的影响提供指导。