Development of surface reconstruction algorithms for optical interferometric measurement

Optical interferometry is a powerful tool for measuring and characterizing areal surface topography in precision manufacturing. A variety of instruments based on optical interferometry have been developed to meet the measurement needs in various applications, but the existing techniques are simply not enough to meet the ever-increasing requirements in terms of accuracy, speed, robustness, and dynamic range, especially in on-line or on-machine conditions. This paper provides an in-depth perspective of surface topography reconstruction for optical interferometric measurements. Principles, configurations, and applications of typical optical interferometers with different capabilities and limitations are presented. Theoretical background and recent advances of fringe analysis algorithms, including coherence peak sensing and phase-shifting algorithm, are summarized. The new developments in measurement accuracy and repeatability, noise resistance, self-calibration ability, and computational efficiency are discussed. This paper also presents the new challenges that optical interferometry techniques are facing in surface topography measurement. To address these challenges, advanced techniques in image stitching, on-machine measurement, intelligent sampling, parallel computing, and deep learning are explored to improve the functional performance of optical interferometry in future manufacturing metrology.     

Lensed optical fiber sensors for on-line measurement of flow

This paper describes a system using lensed optical fiber sensors that are arranged in the form of two orthogonal projections. The sensors are placed around a process vessel for upstream and downstream measurements. The purpose of the system is for on-line monitoring of particles and droplets being conveyed by a fluid. The lenses were constructed using a custom heating fixture. The fixture enables the lenses to be constructed with similar radii resulting in identical characteristics with minimum differences in transmitted intensity and emission angle. By collimating radiation from two halogen bulbs, radiation can be obtained by the sensors with radiation intensity related to the nature of the media. Each sensor interrogates a finite section of the measurement section. Each sensor provides a view. Parallel sensors provide a projection. Signal processing is carried out on the measured data in the time and frequency domains to investigate the latent information present in the flow signals.     

Coherence function control of a multi-mode laser diode by the frequency modulation and its low coherence interferometric application

In this investigation, a frequency-modulated multi-mode laser diode (LD) is introduced as a light source of low coherence scanning interferometry (LCSI) and its applicability is verified with experiments. The frequency modulation of a multi-mode LD can improve the contrast of the coherence peak corresponding to zero OPD and overcome the ambiguity to find the exact coherence peak appeared in frequency modulated single-mode LD or a multi-mode LD. As the experimental results, the coherence function of a multi-mode LD was changed with the frequency modulation and the expected coherence peak was obviously determined. As the result, the coherence length was 200 μm. Also, the possibility to measure surface profile of a sample was experimentally confirmed with step height samples. Although the proposed technique cannot be guaranteed for high accuracy in the lack of the position accuracy of the scanning stage, it is suitable for the demand of spatially coherent measurements and high speed measurements adopting the sub-sampling technique because of its low cost, high available power and better spatial coherence than other white light sources.     

高精度保偏光纤拍长测试

基于光相干域偏光测试技术,提出了一种高精度的保偏光纤拍长测试方法,实现了不同结构、不同尺寸保偏光纤的拍长测试。阐述了光相干域偏光测试技术原理并推导出测量方程;以迈克尔逊干涉仪为基础建立了测试系统并采用调制解调技术实现了信号的高精度检测。实验结果表明,系统的测量精度为0.01 mm。在此系统上进行了测试精度和重复性研究并对不同结构和尺寸的八种保偏光纤进行了实际测量,拍长测量精度和重复性均优于0.01 mm。     

大口径空间光学遥感器的碳纤维复合材料精密支撑构件的结构稳定性研究

摘要：为了研究应用于大口径空间光学遥感器中由碳纤维复合材料（CFRP）制成的精密支撑构件的结构稳定性,设计并研制了连接在主、次镜间的CFRP连接筒。对该连接筒建立等效力学模型、计算相关参数和确定铺层的合理形式,运用有限元法对连接筒进行分析计算,通过试验验证连接筒的结构稳定性。首先,由给定的主、次镜间角度变化量计算出连接筒前端面的最大挠度,根据实际载荷情况建立等效力学模型,计算连接筒轴向弹性模量,结合复合材料层压板理论,确定碳纤维铺层的合理形式。然后,运用ANSYS软件对有限元模型进行分析,计算主、次镜间的角度变化量和支撑结构的模态分布。最后,通过量级逐增的力学试验,采用光学测量的方法测量主、次镜间角度变化量,验证CFRP连接筒的结构稳定性。试验结果表明：主、次镜间角度变化量小于10″,CFRP支撑构件一阶基频大于75Hz。CFRP支撑构件满足主、次镜间角度变化量要求,具有较好的结构稳定性。     

用于生物量浓度在线检测的光纤衰减全反射传感器

为了在生物膜滴滤塔降解有机废气过程中实现生物量浓度的测量,设计了光纤衰减全反射(ATR)生物量浓度传感器,给出了传感器组成原理、结构参数、光路分析及其理论解释。根据光波进入光密介质(Si晶体)与光疏介质(生物菌液)的分界面时所产生的隐失波现象,以及生物菌液对隐失波的散射和吸收引起接收光能量变化的物理机理,建立了一种新的生物量浓度测量方法。实验选用可见光源,在25℃恒温情况下对生物量浓度测量进行了实验研究。实验结果表明:测量结果的相对误差均值为2.217%,基本上满足生物量浓度在线测量要求。该传感器的设计原理和方法具有一定的普遍意义,可应用于制剂、制酒、生化等行业。     

Design of an optical measurement system for dynamic testing of electrospindles

Dynamic characterization of electrospindles is necessary to ensure long life, reliability and high-tech performance required in many industrial applications. Many diagnostic approaches have been developed with regard to fault detection and dynamic characterization of rotating machinery.     

提高光纤传感测量精度的方法研究

采用激光干涉原理实现了微位移光纤传感测量.通过对光学系统和光电检测系统的研究,总结出提高光纤传感测量精度的方法,文中对微弱光信号的相位调制,数字解理过程,给出了低噪声设计的理论依据,电路参数的选取原则和预放级设计的一般方法.系统微位移测试精度约0.05nm.     

辐射光纤高温计及其系统的研究

为解决特殊情况下的高温在线测量，研制了一种辐射光纤高温计。介绍了仪表的工作原理、光滤波及测试结果的处理。     

光纤连接器端面检测技术

介绍了光器件中的光纤连接器端面有关光学性能的测试 ,分析了显微成像法和干涉法等几种测量端面几何参数的测量方法 ,详细讨论了光纤连接器的几何量测试 ,并对图像分割、平滑去噪声、图像二值化、几何量计算以及像素定标等具体步骤做了分析     

水膜厚度光纤检测系统

针对海水泵滑靴副水膜厚度测量需求,利用反射强度调制型位移光纤传感器工作原理设计并实现了一种水膜厚度检测系统。设计了与海水泵结构相对应的光纤探头,其采用具有较好补偿功能的三圈同轴型光纤束结构消除了由光源强度、反射表面性质以及光纤光强损耗和弯曲损耗等因素带来的影响;开发了由光源模块、电源模块、光电转换模块、低通滤波模块、信号比值模块等组成的前置器用于信号调理。对开发的水膜厚度光纤检测系统进行了静态性能和动态性能测试实验,结果表明:该检测系统的测量精度可达微米级,测量系统的量程为1 000μm,灵敏度为3.45mV/μm,动态性能良好,满足了对海水泵水膜厚度的检测需求。     

表面微观轮廓的高分辨率光学测量方法

较全面地介绍了用于表面微观轮廓测量的几种高分辨率甚至可达亚纳米的光学测量方法及其最新进展.文中重点描述了以扫描共焦显微检测法、离焦误差检测法为代表的光触针法,以TOPO轮廓仪、Nomarski显微镜、外差干涉轮廓仪、双焦干涉轮廓仪和同轴干涉轮廓仪为代表的干涉测量法和以扫描近场光学显微镜及光子扫描隧道显微镜为代表的近场光学法三种适用于表面微观轮廓测量的光学测量方法,分别介绍了其工作原理、特性、发展现状及存在问题,通过对这些方法的对比和总结,阐述了表面微观轮廓纳米级光学测量的发展趋势.     

干涉型光纤语音传感器及语音降噪方法研究

近年来,光纤语音传感器已经引起科研界的广泛关注,如何提高语音探测质量是所有类型光纤语音传感器都面临一个关键问题。提出了一种新型小波包语音提取方法,用来提高光纤语音传感器语音探测质量。基于光纤干涉仪原理,搭建了光纤语音传感实验系统。实验结果表明,无论是与硬阈值处理方法还是与软阈值处理方法相比,新阈值处理方法都提高了信噪比。并且保证了语音信号的连续性,改善了语音质量。本方法可广泛应用于语音探测领域,特别是实时语音探测。     

Simultaneous distributed measurement of the strain and temperature for a four-point bending test using polarization-maintaining fiber Bragg grating interrogated by optical frequency domain reflectometry

We demonstrate a simultaneous distributed strain and temperature measurement technique with the spatial resolution of 1 mm using fiber Bragg gratings inscribed in a polarization-maintaining and absorption-reducing fiber (PANDA-FBGs) and optical frequency domain reflectometry (OFDR). We conduct four-point bending tests in an environmental chamber. Using high birefringent PANDA-FBGs that are manufactured specifically for the simultaneous measurements, the uniform temperature distributions and the typical strain distribution profiles of the four-point bending tests were successfully obtained. The measurement errors of strain were from −31 με to 19 με, and of temperature were from −0.9 °C to 1.3 °C. The spatial standard deviation was 7.5 με and 0.9 °C. We also discussed the effect of the residual strain of the sensor-bonding procedures and the data averaging.     

基于光纤法布里珀罗干涉的扭矩测量方法研究

在动态条件下,获取准确的传动轴扭矩测量数据是评估传动轴健康状况和运行状态的重要手段之一。传动轴扭矩测量经常伴随着震动、高温高湿以及强电磁等恶劣环境,考虑到电类传感器有漏电、电火花以及难以在强电磁干扰环境下工作等问题,本文提出了一种基于非本征光纤法布里珀罗干涉技术的扭矩测量方法。阐述了光纤传感器的工作原理,给出了传感器的安装方式,搭建了扭矩测量平台并对传感器的性能进行了实验验证。实验结果表明,传感器灵敏度为(0.224±0.06)μm/Nm,与理论具有很好的一致性。本文提出的测量方法在传动轴扭矩测量中具有测量动态范围大、测量精度高和实时快速的优势。     

Simultaneous measurement of strain and temperature using a hybrid local and distributed optical fiber sensing system

Structure multi-parameters measurement, such as strain, displacement, corrosion and temperature, is of the utmost importance for structural health monitoring. Meanwhile uncoupling method of temperature and strain has still a technical problem in structure sensing measurement. In this paper, we proposed a method for simultaneous measurement of strain and temperature using a hybrid local and distributed optical fiber sensing system. The principle of the method is investigated and then validated by the theoretical simulation experiments and tensile tests in laboratory. Furthermore, one experiment for internal force measurement of a smart stranded wire, under the interaction of temperature and strain, is also conducted in lab. The experimental results show that the strain and temperature can be well measured simultaneously by using one multi-signal optical fiber sensor.     

塑料光纤折射率计连续测量研究

本文对基于宏弯曲塑料光纤的折射率计的连续测量特性进行了研究.宏弯曲结构的曲率半径与光纤半径的比值决定了该折射率计的工作特性.由于聚合物材料具有一定的吸水性,导致该折射率计在连续工作时其结构参数发生改变.实验表明,浸没时间超过40 h,折射率计产生了7.3×10-5 RIU的测量偏差.这项研究指出,基于塑料光纤的液体传感器,在连续工作时必须对其吸水性问题加以考虑.     

Uniaxial fiber Bragg grating accelerometer system with temperature and cross axis insensitivity

In this paper we describe the implementation and test of an optical fiber based accelerometer with cross axis insensitivity. The accelerometer uses two matching fiber Bragg gratings which are also responsible by the demodulation of the wavelength encoded information. The accelerometer was tested in a reinforced concrete slab, of a 3-storey building located at the University of Aveiro, Portugal. A maximum error of 0.25% for the slab eigenfrequencies was obtained when compared with the values acquired by an electronic sensor.     

Digital image processing for nonperiodic objects and an on-line image processing system for high resolution electron microscopy

A digital image processing method for noise removal and image enhancement in nonperiodic structural images is described. The method for noise removal uses a reversible transform between an image and image autocorrelation function. The Laplacian filter is then employed for image enhancement. Furthermore, an on-line image processing system for highresolution TEM is presented.     

双Mach-Zehnder光纤干涉传感系统中的偏振衰落控制

针对偏振衰落现象导致信号关联的二义性使分布式双Mach-Zehnder光纤干涉传感系统难以实现高精度定位的问题,提出了一种控制偏振衰落的方法来保持系统检测信号的稳定性.利用系统的偏振模型分析了偏振衰落的来源,指出传感光纤偏振特性的不一致使系统检测信号对输入偏振态敏感是造成信号相关性恶化的根本原因,据此提出控制输入偏振态、搜索偏振态工作点的抗偏振衰落思想.在此基础上通过分析输入偏振态的两个参量对信号相关系数的作用进一步明确了偏振控制对算法的要求,并利用模拟退火算法进行了验证.现场实验表明,该算法可快速搜索偏振态工作点,持续稳定系统检测信号的相关性;结果证实了提出的偏振衰落控制方法可行且有效.