Cross-sensitivity effect in temperature-compensated sensors based on highly birefringent fibers

We analyzed the influence of the measurand-temperature cross-sensitivity effect on temperature stability in fiber-optic cross-spliced sensors that employ highly birefringent fibers. We show that the ratio of the measurand-temperature cross-sensitivity coefficient to the measurand first-order sensitivity determines the physical limit for temperature stability in cross-spliced sensors. Employing polarimetric as well as white-light interferometric methods, we experimentally determine a hydrostatic pressure-temperature cross-sensitivity coefficient in York bow-tie 800 fiber. From this we estimate the achievable limit for temperature stability of cross-spliced pressure sensors under environmental temperature changes.     

单轴光纤陀螺光学结构的研究与实现

针对实际系统中的单轴干涉式光纤陀螺仪结构与稳定性问题,提出将Lyot消偏器引入到陀螺光学结构中,新结构在不改变原陀螺光路高精度特性的基础上,使系统输入极低偏振度的自然光,提高了单轴光纤陀螺的精度和稳定性.利用琼斯矩阵与干涉矩阵建立了单轴干涉式光纤陀螺的系统模型,对该陀螺的输出及零点偏移情况进行了仿真分析和实验研究.结果表明,该设计结构在提高了陀螺系统的精度与稳定性的同时,还在一定程度上降低了系统对光源偏振度的要求.     

New interferometric fiber-optic gyroscope with amplified optical feedback

A novel interferometric fiber-optic gyroscope with amplified optical feedback by an Er-doped fiber amplifier (EDFA) is proposed and theoretically investigated (the proposed gyroscope is named the feedback EDFA-FOG, FE-FOG in what follows). The FE-FOG functions like a resonant fiber-optic gyro (R-FOG) because of its multiple utilization of the Sagnac loop; however, it is completely different because a low-coherence light source is used. In addition, the gyro output signal is pulsed because the modulation frequency of the phase modulator placed in the Sagnac loop is selected to match the total round-trip time delay of the light, which includes the Sagnac-loop delay plus that of the feedback loop of the fiber amplifier. The sharpness of the output pulse can be adjusted by both the gain of an EDFA and the modulation depth of the phase modulator. When rotation occurs the peak position of the output pulse is shifted as a result of the Sagnac effect. The resolution of the rotation measurement depends on the sharpness of the output pulse. The techniques of both the open-loop and closed-loop methods are described in detail, which shows the great advantage of the proposed gyroscope over the to the conventional interferometric fiber-optical gyroscope (I-FOG).     

Revised minimum reciprocity configuration and actualization methodology of interferometric all-fiber-optic gyroscopes

We propose a revised minimum reciprocity configuration (MRC) of an interferometric all-fiber-optic gyroscope (all-fiber I-FOG), based on our design of a fused-taper polarization-maintaining fiber coupler. This MRC reduces the insertion loss and production cost of the optical path, yet maintains the principle of reciprocity. Experimental results show that this I-FOG with five optical components exhibits better performance than a conventional I-FOG with six optical components. Using the revised MRC, the angle random walk and the bias instability of an I-FOG are improved from 0.025 deg/√hr to 0.011 deg/√hr, and 0.48 deg/hr to 0.21 deg/hr, respectively.     

Analysis of sensing coil polarization properties' effect on performance of fiber optical gyroscope

The mechanism of fiber coil polarization properties' effect on the performance of a fiber optical gyroscope (FOG) is investigated with analysis of secondary wave trains' polarization evolution and interference in the fiber coil. Based on the optical model, the simulation demonstrates that the bias error varies nonlinearly with the fiber coil polarization crosstalk, and the experiment verifies the analysis and simulation result, so some measures are promoted to reduce the bias' dependence on the fiber coil's polarization properties, which is significant for improving environmental adaptability and long-term stability of the FOG.     

Sagnac环形电流互感器的原理与发展研究

高压变电站中用于电力系统电流测量的全光纤电流传感器由于具有传统电流互感器无法比拟的优点,具有广阔的应用前景.Sagnac环形电流互感器是在干涉式光纤陀螺结构上发展起来的一种互感器结构.由于基于Sagnac干涉仪技术的光纤陀螺的实用化,用此技术来实现Sagnac环形电流互感器的实用化成为电流互感器的热点.本文首先介绍了S...     

Optical design of interferometric telescopes with wide fields of view

The performance of wide-field multiple-aperture imaging systems is dominated by easily understood, low-order errors. Each aperture produces an individual image, each pair of apertures produces a set of fringes under a diffraction envelope, and the system bandwidth produces a coherence envelope. For wide-field imaging, each of these elements must be coincident in the image plane as the field angle changes. We explore the causes of image degradation, derive first-order rules for preserving image quality across field, and give an example design that enforces some of the rules to achieve a relatively wide-field interferometric imaging telescope.     

Dispersion and birefringence of irregularly microstructured fiber with an elliptic core

We have investigated the dispersion and birefringence of an irregularly microstructured fiber with an elliptic silica core and irregular airholes. The polarization-dependent output power through the fiber reveals two well-defined principal-axis modes despite the irregularity of airholes. The dispersion of the fiber is measured in the range of 680 to 1000 nm using the Mach-Zehnder interferometric technique with sub-10 fs laser pulses, which yield two zero dispersion wavelengths at 683 and 740 nm for the two principal modes, respectively. The birefringence measured using the wavelength scanning method is about 0.0055 at 800 nm. It is also demonstrated that this irregularly microstructured fiber with high birefringence and short zero dispersion wavelength is useful for the one-octave-spanning supercontinuum generation suitable for an f-2f interferometric system.     

Analysis of polarization properties of a mode-locked fiber laser gyroscope

We investigated the polarization characteristics of a mode-locked fiber laser gyroscope (MLPLG) formed with a Nd-doped fiber as an optical gain medium and a Sagnac loop mirror. The output pulse patterns and the polarization states were found to be determined by fiber birefringence in the different sections of the MLPLG. We describe the conditions for the MLPLG to operate with automatic reciprocity leading to the possibility of phase-error-free operation.     

数字闭环光纤陀螺输出滤波器设计

在数字闭环光纤陀螺中,数字输出信号由高抽样率的反馈信号抽取得到,为避免抽取过程中发生频域混迭,应加入输出滤波器对信号进行低通滤波。根据多抽样率数字信号理论,采用多级抽取滤波器的设计方法,为陀螺设计输出滤波器。和一级低通滤波器比较说明,所设计的三级抽取滤波器,运算量小、滤波效果好。测试结果表明,加入输出滤波器不改变陀螺静态特性,抑制了振动时引起的高频误差,提高了陀螺精度。     

单片机在光纤环绕制中的探索

讲述了光纤陀螺光纤环的电路及软件设计 ,具有自动控制光纤环参数的功能 ,可以实现预备环的全自动绕制和工作环的半自动绕制 ,自动调整步速 ,装置简单 ,运行稳定 ,成本低     

Phase-locked loop based on machine surface topography measurement using lensed fibers

We present the phase-locked loop (PLL)-based metrology concept using lensed fibers for on-machine surface topography measurement. The shape of a single-mode fiber at the endface was designed using an ABCD matrix method, and two designed lensed fibers-the ball type and the tapered type-were fabricated, and the performance was evaluated, respectively. As a result, the interferometric fringe was not found in the case of the ball lensed fiber, but the machined surface could be measured by utilization of autofocusing and intensity methods. On the other hand, a very clear Fizeau interferometric fringe was observed in the case of the tapered lensed fiber. Its performance was compared with the results of the capacitance sensor and a commercially available white-light interferometer. We confirmed that PLL-based surface profile measurement using the tapered and ball lensed fibers can be applied for on-machine surface topography measurement applications.     

光纤陀螺中偶次谐波引起零偏误差的分析

本文介绍了一种计算由偶次谐波引起光纤陀螺零偏误差仿真方法,根据计算光纤陀螺的零偏误差可以用贝塞耳函数和三角函数表示.在计算中我们发现光纤陀螺的零偏误差与调制信号中的偶次谐波和光纤中由于偏振现象引起的角度误差有关.当调制深度设置到3π/5附近时,零偏误差可以减少到最小.由于制信号中的偶次谐波是引起零偏误差的主要原因,我们使用频谱分析仪测量了调制信号中的偶次谐波.此外,我们还通过光纤陀螺的输出测量了光纤陀螺的零偏误差.通过仿真得到的光纤陀螺零偏误差结果得到了试验的验证.     

Modeling the interferometric radius measurement using Gaussian beam propagation

We model the interferometric radius measurement using Gaussian beam propagation to identify biases in the measurement due to using a simple geometric ray-trace model instead of the more complex Gaussian model. The radius measurement is based on using an interferometer to identify the test part's position when it is at two null locations, and the distance between the positions is an estimate of the part's radius. The null condition is observed when there is no difference in curvature between the reflected reference and the test wavefronts, and a Gaussian model will provide a first-order estimate of curvature changes due to wave propagation and therefore changes to the radius measurement. We show that the geometric ray assumption leads to radius biases (errors) that are a strong function of the test part radius and increase as the radius of the part decreases. We tested for a bias for both microscaled (<1 mm) and macroscaled parts. The bias is of the order of parts in 10(5) for micro-optics with radii a small fraction of a millimeter and much smaller for macroscaled optics. The amount of bias depends on the interferometer configuration (numerical aperture, etc.), the nominal radius of the test part, and the distances in the interferometer.     

Intermodal interferometer for strain and temperature sensing fabricated in birefringent boron doped microstructured fiber

We present a compact in-line fiber interferometric sensor fabricated in a boron doped two-mode highly birefringent microstructured fiber using a CO(2) laser. The intermodal interference arises at the fiber output due to coupling between the fundamental and the first order modes occurring at two fiber tapers distant by a few millimeters. The visibility of intermodal interference fringes is modulated by a polarimetric differential signal and varies in response to measurand changes. The proposed interferometer was tested for measurements of the strain and temperature, respectively, in the range of 20-700?°C and 0-17?mstrain. The sensitivity coefficients corresponding to fringe displacement and contrast variations are equal respectively for strain -2.51 nm/mstrain and -0.0256 1/mstrain and for temperature 16.7 pm/°C and 5.74×10(-5) 1/°C. This allows for simultaneous measurements of the two parameters by interrogation of the visibility and the displacement of interference fringes.     

光纤陀螺刻度因子的建模方法

针对低精度光纤陀螺(FOG)刻度因子线性度较差的问题,提出了采用径向基函数(RBF)神经网络对刻度因子进行建模的方法,以减小光纤陀螺输出误差。通过测量数据对 RBF 神经网络进行训练,获得神经网络参数,根据神经网络结构和参数可以得到非线性刻度因子的解析表达式,将其作为刻度因子的模型,来提高 FOG 的精度。同时将 RBF 神经网络对刻度因子进行建模的结果与传统的建模结果进行了比较,验证了采用 RBF 神经网络对低精度刻度因子建模是非常有效的。     

基于最小二乘平滑滤波与CEEMDAN的光纤陀螺信号处理研究

针对光纤陀螺在面板堆石坝面板挠度监测中易受到噪声干扰,难以准确提取反映结构变形特征信号的实际问题,提出一种基于最小二乘平滑滤波与CEEMDAN混合降噪的方法。该方法运用CEEMDAN将光纤陀螺实测信号进行分解,得到一系列IMF分量。分别对每一阶IMF分量进行傅里叶频谱分析得到幅值谱图和幅值的方差,根据幅值方差的大小判断噪声IMF分量与有用信号IMF分量的分界,结合最小二乘平滑滤波对噪声IMF分量进行降噪。最后将降噪后的IMF分量与有用信号IMF分量进行重构,得到降噪后的光纤陀螺信号。通过对仿真信号和水布垭面板堆石坝面板挠度监测的实测数据进行分析,该方法能有效滤除噪声信号,准确提取反映结构变形的特征信号,验证了该方法对实际工程中光纤陀螺测量信号降噪的可行性和适用性。     

Study of organized Ξ susceptibility in germanosilicate optical fibers

Poling has been achieved in a specially designed germanosilicate fiber. The Ξ⁽²⁾ susceptibility was detected and measured through refractive index changes measurements using an interferometric method within the fiber. Two methods for poling have been used: the thermally-assisted electrical method and the UV-assisted electrical method. Both the poling techniques and the results concerning the linear electro-optic effect are presented.     

对称复位调制技术在小型化光纤陀螺中的应用

2π复位调制是光纤陀螺全数字闭环处理技术的一个重要环节。由于小型化Y波导的半波电压提高,小型化光纤陀螺的调制信号达不到2π复位的要求。通过分析闭环复位的原理,提出了一种新的对称复位调制技术,成功实现了小型化光纤陀螺的复位调制闭环控制。     

Interferometric measurement of light scattering behavior in continuous SiO2 fiber in PMMA matrix composite

Possibility of an interferometric method was examined for evaluating local light scattering behaviors in light transmitting materials. Phase profiles of wavefronts through a continuous SiO₂ glass fiber–PMMA composite was measured by detecting transmitted light though the composite using the interferometric system with a pair of interferometers. Wavefront though the composite shows an anisotropic phase profile, and the phase delay originates from local light scattering due to refractive index difference at an interface between SiO₂ fiber and PMMA matrix. Measured wavefronts demonstrated that the interferometric method is effective tool for an evaluation of local light scattering.