干涉仪自适应抗振的空间移相术

根据时域移相算法的概念,提出了一种空间移相术,它能够检测因外界振动导致条纹抖动而引起的干涉图样的空间相位变化.运用这种技术在TwymanGreen移相式干涉仪中建立了一套自适应抗振系统,它可以实时测量振动引起的相位变化大小,并通过反馈器件PZT实时校正干涉条纹的相位,使得干涉条纹稳定以保证光学测量的正常进行,与此同时PZT还作为移相器件.     

基于干涉条纹跟踪实现纳米级位移测量的方法研究

设计了一套干涉条纹图像实时采集处理系统。在分析迈克尔逊干涉条纹特征表象的基础上 ,给出了通过跟踪干涉条纹的移动量测量被测对象纳米级位移量的理论公式 ;提出了干涉条纹特征点的提取与跟踪算法 :分段线性变换、方形窗口中值滤波和门限化边缘提取 ,给出了基于统计学原理的通过计算多条干涉条纹移动量获得被测对象纳米级位移量的计算公式。实验结果表明了该方法的有效性和实用性     

乌氏干涉测量的信息读取

针对乌氏干涉仪条纹信号调整难、用肉眼读数难等问题,提出将He-Ne激光作为乌氏干涉仪光源的设计,得到了高质量的干涉条纹信号,并采用光电转换方法将条纹移动信号转变为电信号实现了微位移的高精度测量。设计了光电信号检测电路,利用双门限整形电路标定出整形方波,克服了干涉信号在设定比较值附近抖动引起误处理的缺点;提出了辨向细分电路,在1路干涉条纹信号下,提取了具有正交性的2路电子信号,实现了干涉条纹的移动辨向与信号细分。按此方案设计并搭建了一套激光干涉检测实验装置,用2个计量差值为5μm的标准量块,对激光干涉检测装置进行了标定,在电路为4细分的情况下,该装置测量分辨率达79 nm;解决了乌氏干涉仪自动读数的问题,提高了乌氏干涉仪的测量精度和准确性。     

Interference fringe detection system for distance measuring interferometer

A novel photodetection system for a homodyne distance measuring interferometer by means of fringe counting method is presented. The system is based on applying compact size integrated photodetector operating with fringe pattern having fixed, finite period. 13-element integrated photodiode arranged in novel signal processing scheme receives interference fringes movement. Additional lens is used to adjust the fringe period to photoelements’ distances. Due to the proposed configuration of the photoelement's signal processing and the applied lens the system has reduced sensitivity to interference fringe period errors caused by the angular misalignment of interfering beams. The theoretical analysis and experimental verification of the system metrological feasibilities are presented. Comparison of performance of examples of standard and novel detection systems is shown finally.     

Real-time surface shape measurement by an active interferometer

We have succeeded in video rate analysis of fringes stabilized by an active interferometer placed outside optical benches. The interferometer uses the closed loop control of injection current of a laser diode to compensate for fringe movement that is detected by a spatial filtering detector. A video image of the locked fringes with tilt is supplied to the real-time fringe analyzer that delivers unwrapped phase distribution from the three phase shifted fringes generated by the electronic moiré method. For a concave mirror of 130 mm diameter placed on a wooden desk we observed the repeatability of λ/60 for P-V surface error of λ/5.     

A new formula for fringe localization in holographic interferometry

Holographic interferometry generally involves the interference of two or more speckle fields reflected from or transmitted through a diffused object. The visibility of the resulting fringes depends on the degree of coherence of the interfering speckle fields. Through a statistical analysis it is found that the degree of coherence of speckle fields is essentially a function of the relative speckle displacement and average speckle size. The analysis leads to a new physical model for holographic interferometry. With this model the problem of fringe formation and localization may be analyzed and formulated in terms of speckle movement. A new formula for ideal fringe localization is then derived from the analysis. Furthermore, a localization factor V_c, i.e. the visibility of the holographic fringes, is introduced to analyze the partial fringe localization in holographic interferometry, which is of practical interest to most researchers.     

The discovery of nanometer fringes in laser self-mixing interference

We demonstrate the influences of optical feedback from an external mirror with high reflectivity in a He-Ne laser on self-mixing interference fringes and laser polarization states. When the external mirror is tilted to a certain level, the stable and uniform nanometer resolution fringes are generated. The fringe density is 40 times than that of the conventional self-mixing interference or two beam interference, and has still potential to be improved. Each self-mixing interference fringe corresponds to λ/80 displacement of the external mirror, i.e. 7.91 nm displacement of the external mirror. Moreover, when the movement direction of the external mirror is changed, the polarization flipping between two eigenstates will happen. The potential applications of the results are also discussed.     

光子多普勒速度测量系统的数据处理方法

光子多普勒速度测量（Photonic Doppler Velocimetry,PDV）系统是一种新型的激光测速系统,可广泛用于冲击波、爆轰波以及其他短时高速运动的测量。数据处理是PDV测速技术重要的组成部分,旨在从含有大量噪声的测量数据中获得靶面等运动体的速度信息。在分析PDV系统测速原理的基础上,讨论了激光冲击强化实验PDV数据中噪声的来源和特点,解释了条纹法的去噪原理,并针对小波变换的去噪问题,提出了一些新的处理方法。分别采用条纹法,短时傅里叶变换和小波变换法对激光冲击强化实验中的PDV数据进行了处理,从误差、处理的实时性和通用性等角度对三种方法进行了比较,并说明了小波变换法特别适合激光冲击强化实验PDV测速数据的处理。     

Détermination de la forme de la section d'une fibre optique non gainée à l'aide de l'analyse harmonique de son diagramme de rayonnement

Résumé Dans cet article, on étudie le diagramme de diffusion vers l'avant d'une fibre optique d'indice uniforme éclairée par un faisceau laser perpendiculaire à son axe lorsqu'elle tourne sur elle-même. On montre qu'il existe une relation linéaire entre les coefficients des développements en série de Fourier des fonctions représentant le déplacement angulaire d'une frange brillante et le contour de la section. Le mesure du déplacement d'une seule frange permet de connaître avec une excellente approximation la forme de la section.

---

In this paper, the movement of the forward scattering pattern of an unclad fibre illuminated by a laser beam perpendicular to its axis is studied when the fibre is rotated. The existence of a linear relation between the coefficients of the Fourier series which represent the angular shift of a bright fringe and the fibre cross-section is shown. Thus it is possible to know to an excellent approximation the shape of the cross-section by monitoring the fringe movement.

     

A fringe carrier technique for unambiguous determination of fringe orders in shearography

Shearography is an interferometric method which measures displacement derivatives. This paper presents a technique which eliminates the ambiguity in shearographic fringe interpretation. The technique is based on generating a carrier fringe pattern. Introduction of the carrier fringes results in the formation of a fringe pattern which has monotonically increasing fringe orders, thus allowing fringe orders to be determined in a straightforward manner and without ambiguity. The phase change due to deformation alone is then obtained by simply subtracting the known undeformed carrier fringe orders from the deformed carrier fringe orders. Elimination of fringe ambiguity has paved a way for automatic data acquisition in shearography.     

Fringe skeletonizing using an improved derivative sign binary method

A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach.     

Signal processing method of phase correction for laser heterodyne interferometry

A novel signal processing method of movement direction identification and phase correction is presented for laser heterodyne interferometry. Based on the reference signal, four intervals with phase difference of 90° each other are set up. The real-time movement direction identification and the integer fringe counting are realized by detecting the times that the rising-edge of the measurement signal crosses the intervals. The phase correction approach is proposed in detail to solve the fraction phase compensation when the initial phase difference is not equal to the zero phase difference. Three experiments of the stability test, the nanometer and micrometer displacement tests on bi-directional movement were performed to demonstrate the usefulness and feasibility of the presented signal processing method.     

Laser Doppler anemometry and the acousto-optic effect

This paper deals with the effect of phase variations along the paths of the laser beams due to refractive index changes caused by the acousto-optic effect, when an LDA system is used to measure sound waves. Theoretical and experimental results will be discussed. A theoretical expression will be developed for the movement of the fringes in terms of the angle of the sound wave, the wavenumber and the distance of propagation of the laser beams. Results will show that as the wavenumber increases, the angle at which the maximum amplitude of the fringe movement occurs tends away from π/2 to the laser beam bisector, and towards the angle of the laser beams. It will also be shown that the phase modulations detected experimentally are in reasonable agreement with those predicted theoretically.     

基于调制方向提取载波散斑条纹中心线的方法

条纹中心线法是一种重要的电子散斑干涉条纹解调方法,其前提条件是获得高准确度的条纹中心线.本文在分析载波电子散斑干涉条纹自身特征的基础上,提出了一种基于载波条纹调制方向提取条纹中心线的方法.该方法首先通过同态滤波有效滤除高频乘性散斑噪音,提取出载波条纹;然后应用基于调制方向提取中心线算法确定载波条纹灰度极值点并做二值化处理;再采用基于中心线拟合或者基于条纹间距的边沿中心线补偿法,获得完整的条纹中心线图.实验结果表明:该方法简单、可靠,能快速、准确地提取出连续的中心线.     

基于调制方向提取载波散斑条纹中心线的方法

条纹中心线法是一种重要的电子散斑干涉条纹解调方法,其前提条件是获得高准确度的条纹中心线.本文在分析载波电子散斑干涉条纹自身特征的基础上,提出了一种基于载波条纹调制方向提取条纹中心线的方法.该方法首先通过同态滤波有效滤除高频乘性散斑噪音,提取出载波条纹;然后应用基于调制方向提取中心线算法确定载波条纹灰度极值点并做二值化处理;再采用基于中心线拟合或者基于条纹间距的边沿中心线补偿法,获得完整的条纹中心线图.实验结果表明:该方法简单、可靠,能快速、准确地提取出连续的中心线.     

Anisotropic partial differential equation noise-reduction algorithm based on fringe feature for ESPI

Noise reduction is one of the most exciting problems in electronic speckle pattern interferometry. We present a new anisotropic partial differential equation noise-reduction algorithm based on fringe orientation for interferometric fringe patterns. The proposed equation performs diffusion along the two directions of fringe gradient and isophote line, which are extracted accurately according to fringe feature. By restriction of diffusion in the gradient direction of fringe patterns, this method can provide optimal results in denoising but does not destroy fringe edges. The experimental results show that this technique is more capable of significantly improving the quality of the fringe patterns than the classical anisotropic diffusion equation proposed by Perona and Malik. Based on our filtered fringe patterns, the phase map obtained by phase-shifting technique can be extracted more accurately. It is an effective pre-processing method for electronic speckle pattern interferometry.     

基于适度光反馈自混合干涉技术的振动测量

光反馈自混合干涉技术是一种新浮现的有别于传统双光束干涉的一类新的测试技术。为了在适度光反馈下进行振动的精密测量,提出了一种基于适度光反馈自混合干涉技术的振动测量方法。经对光反馈自混合干涉信号条纹分析,发现通过选定合适的光反馈水平及激光器线宽展宽因数,可以得到锯齿干涉条纹。这种干涉信号不仅包含振动幅度信息也包含振动方向信息。该振动测量方法利用锯齿干涉条纹的特点,首先通过条纹记数实现大范围振幅粗测,具有半波长位移分辨力;然后基于适度光反馈下小数条纹的特点,给出了小于半波长位移测量的线性表达式,从而实现位移的精测。仿真计算表明,该方法可以实现大量程高分辨力振动位移测量,在叠加20 dB的噪声下,振幅测量相对误差平均为0.5%。     

Study on an automatic processing technique of the circle interference fringe for fine interferometry

The fringe center method (FCM) is an important digital processing technique of fringe patterns analysis for interferometry. In this paper, an improved automatic processing technique based on FCM was presented, which correlated the processing link and the looped feature of the circle fringe pattern. It also integrated several techniques including noise removal, the fringe thinning, the fringe patching, assignment of the fringe orders and wavefront reconstruction and can be executed orderly and automatically. Based on the new the algorithms of the fringe patching and assignment of the fringe orders, the fringe feature information was extracted automatically and the interference wavefront was reconstructed by Zernike polynomial fitting method. With the automatic processing technique, the circle interference fringe of the fine polished aluminum disks surface captured by the Twyman-Green interferometer was processed, and the surface profile and the parameters of the disk were obtained automatically. The experiments show that the improved automatic processing technique was more accurate and fast in measurement than the conventional one. It was convenient to use it in in-situ industry inspection.     

A review of phase unwrapping techniques in fringe analysis

There has been an increasing interest in the automation of fringe analysis over the last decade. In recent years a number of researchers have addressed the problem of automatic phase unwrapping in fringe analysis. The advent of phase stepping and the development of FFT techniques has moved the emphasis in automated techniques away from fringe tracking and towards fringe counting or scanning approaches, but a major difficulty with such scanning techniques has been their susceptibility to noise. However, several alternative noise-immune phase unwrapping strategies have been proposed, but these approaches have not addressed the problems caused by large scale discontinuities such as those produced by aliasing. Other methods have been developed which confront this last difficulty. This paper gives an overview of the phase unwrapping problem and describes fringe tracking, fringe scanning, noise-immune and region processing techniques that have been developed in the search for the fully automated solution.     

Automatic fringe analysis for moiré topography

Two digital systems are developed for the automatic measurement of 3-D shapes using moiré techniques—an automatic 3-D shape measuring system using the scanning moiré method and an interactive fringe analysing system for moiré fringe photographs. In the automatic 3-D shape measuring system, a deformed grating is scanned and sampled with an electronic image scanning device so that moiré fringes are generated in a computer. This technique of electronic fringe generation eliminates ambiguity with regard to the sign of the moiré fringes. The interactive fringe analyser provides a flexible and versatile tool for moiré fringe analysis. Medical applications of these analysing systems are discussed.