光学成像系统光学波前的高精度测试

基于扩展奈波尔-泽尼克理论,分析了不同出瞳振幅分布情况对光学系统焦面处光强分布的影响.针对光学成像系统出瞳振幅实际分布状态,提出了一种新的测试光学波前的方法,解决了相位恢复算法中出瞳振幅分布不均匀和快速傅里叶变换引入计算误差的问题.通过测评实验,对一光学系统进行了测试,获得的光学系统出瞳波前(PV)值为0.196 5λ...     

用于内窥镜的OCT成像技术

介绍OCT成像技术的基本原理,指出OCT系统设备选择和系统搭建过程中对成像的关键特性有重要影响的方面,并针对每个方面提供有助于提高OCT系统成像特性的建议。分时域、频域和功能OCT三部分进行讨论,简述每种OCT的成像原理,分析它们各自的特点,提出每一类OCT技术与内窥镜结合的结构简图。最后总结OCT技术与内窥镜结合的优势,指出与内窥镜相结合将有助于OCT技术在医学成像领域的进一步发展。     

Quasianamorphic optical imaging system with tomographic reconstruction for electron beam imaging

We have developed a quasianamorphic optical tomography system coupled to a streak camera to provide continuous recording of the electron beam profile of an intense, long-pulse induction accelerator. A tomographic reconstruction method based on a maximum-entropy algorithm is used to reconstruct the images. The system has simplified the calculation of beam moments, eliminated ambiguity due to beam motion, and contributed to accelerator tuning.     

An integrated measurement system for simultaneous functional magnetic resonance imaging and diffuse optical tomography in human brain mapping

An integrated measurement system is described for performing simultaneous functional magnetic resonance imaging (fMRI) and diffuse optical tomography (DOT) for human brain mapping experiments. The components of this system consist of an MRI-compatible multi-overlapping-channel optical probe, methods for co-registration of optical and fMRI measurements, and DOT reconstruction algorithms with structural and physiological constraints derived from the MRI data. The optical probe is fully MRI-compatible in the sense that it produces negligible MR image distortion and does not require any modification to the MRI scanner or data acquisition protocol. The probe can be attached to any part of the head without posing any limitation on optical data acquisition. Co-registration of images from fMRI and optical measurements was achieved by localizing the positions of the optical fibers using MRI markers. Human studies show successful implementation of the entire system.     

立体成像眼底相机光学系统设计

为了实现从不同角度同时拍摄同一眼底视网膜区域的图像,使采用双目立体视觉法进行眼底三维重建成为可能,设计了一种免散瞳立体成像眼底相机光学系统。该光学系统由成像系统和照明系统两部分组成,在成像系统中,使用Gullstrand-Le Grand眼模型来模拟正常人眼,运用体视显微镜成像原理进行分光设计;在照明系统中,通过设置黑点板的方式消除网膜物镜产生的杂散光,并加入环形光阑以避免角膜反射光的产生。设计结果表明,本立体成像眼底相机光学系统截止频率在95lp/mm处各视场的MTF值均大于0.2,成像系统畸变小于-3%,场曲值小于0.1mm,色差矫正良好,并且具有较强的调焦能力,能对-10~+5m~(-1)的人眼清晰成像。     

大尺寸光学元件在位动态干涉拼接测量系统

为了满足车间条件下大口径光学元件的高精度在位、在线检测的迫切需求,本文构建了一个适于一般环境下应用的动态干涉拼接测量实验系统。该系统由动态干涉仪、二维移动平台、控制系统及拼接软件等部分构成。应用该系统对200mm×300mm×20mm的光学元件在一般应用环境下进行了拼接测量实验,采用误差均化拼接算法进行拼接,并对拼接后的结果进行分析处理,比较拼接测量与全口径测量结果,PV值的相对误差为3.1%,RMS值的相对误差为1.6%,Power值的相对误差为2.1%。该系统为在车间环境下建立大口径光学元件在位检测建立了基础。     

Multipixel system for gigahertz frequency-domain optical imaging of finger joints

Frequency-domain optical imaging systems have shown great promise for characterizing blood oxygenation, hemodynamics, and other physiological parameters in human and animal tissues. However, most of the frequency domain systems presented so far operate with source modulation frequencies below 150 MHz. At these low frequencies, their ability to provide accurate data for small tissue geometries such as encountered in imaging of finger joints or rodents is limited. Here, we present a new system that can provide data up to 1 GHz using an intensity modulated charged coupled device camera. After data processing, the images show the two-dimensional distribution of amplitude and phase of the light modulation on the finger surface. The system performance was investigated and test measurements on optical tissue phantoms were taken to investigate whether higher frequencies yield better signal-to-noise ratios (SNRs). It could be shown that local changes in optical tissue properties, as they appear in the initial stages of rheumatoid arthritis in a finger joint, are detectable by simple image evaluation, with the range of modulation frequency around 500 MHz proving to yield the highest SNR.     

星载TDI CCD动态成像全物理仿真系统设计

基于高精度卫星姿态控制仿真三轴气浮台,研制了高精度卫星姿态控制仿真子系统,用于为地面TDI CCD动态成像仿真系统提供真实的仿真环境。根据TDI CCD实际成像原理,采用软件模拟替代实际线阵相机的TDI电荷转移迭加过程,研制了基于面阵CCD的星载TDI CCD动态成像仿真系统。利用该系统,实现了最高指向控制精度为0.1°,姿态稳定度为0.01(°)/s的卫星姿态控制仿真实验,模拟了积分时间为0.1 s的TDI CCD相机4~16级动态成像过程。研究了卫星姿态对TDI CCD相机拍照的影响,分析了实际航天高性能TDI CCD相机成像建模理论。像移速度匹配误差为0,姿态稳定度大于0.01(°)/s的实验显示了物理仿真与数学仿真结果与理论分析基本一致,不仅验证了该平台物理仿真方案的正确性,也初步验证了航天CCD成像建模理论的正确性。     

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.     

动态图像处理系统的设计与研究

利用CMOS图像传感器与DSP芯片构成一个高速动态成像系统。由DSP电路驱动CMOS芯片并通过片上AD变换后输出数字信号并即时进行处理。利用这个系统进行了单帧与连续帧的图像采样实验,获得了比较理想的结果。证明了采样频率越高,其对于运动物体的测量数据就越准确。整个系统结构简单,性能可靠,可以灵活地改变三种获取图像的模式,便于对图像信息进行数字化处理。     

Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography

All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at approximately 49 degrees to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually.     

空间成像与激光通信共口径光学系统设计

针对空间成像系统与激光通信天线同时需要大口径光学系统而使卫星载荷质量增大的问题,提出了一种成像光学系统与收发合一激光通信天线共口径工作的新型光学系统。从像差理论出发,给出了以主次反射镜为共用部分、成像和通信工作在不同视场的共口径光学系统初始结构设计方法。实际设计了共口径光学系统,该系统口径为600mm,次镜遮拦比为0.225,成像系统的传递函数在50lp/mm时大于0.47,接近衍射极限;发射分系统波像差远小于λ/20,发射激光的最小束散角可达4μrad,出射光斑质量良好;接收系统达到衍射极限,光斑远小于探测端面,满足探测要求。最后,进行了公差分析,给出了光学系统的装调方法。该设计通过共用主次镜减少了系统总质量和总体积,同时满足空间成像和激光通信系统的性能要求。     

Adaptive calibration of a capacitance tomography system for imaging water droplet distribution

A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10⁻¹⁷ F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.     

Digitally balanced detection for optical tomography

Analog balanced Photodetection has found extensive usage for sensing of a weak absorption signal buried in laser intensity noise. This paper proposes schemes for compact, affordable, and flexible digital implementation of the already established analog balanced detection, as part of a multichannel digital tomography system. Variants of digitally balanced detection (DBD) schemes, suitable for weak signals on a largely varying background or weakly varying envelopes of high frequency carrier waves, are introduced analytically and elaborated in terms of algorithmic and hardware flow. The DBD algorithms are implemented on a low-cost general purpose reconfigurable hardware (field-programmable gate array), utilizing less than half of its resources. The performance of the DBD schemes compare favorably with their analog counterpart: A common mode rejection ratio of 50 dB was observed over a bandwidth of 300 kHz, limited mainly by the host digital hardware. The close relationship between the DBD outputs and those of known analog balancing circuits is discussed in principle and shown experimentally in the example case of propane gas detection.     

推扫型TDI CCD光学遥感器动态成像研究

针对基于推扫技术的TDI CCD空间光学遥感器动态成像试验,研制了一套检测系统。在系统中,设计了模拟卫星推扫的双支承U型结构精密转台。搭载遥感器,以角速度0.555°/s在±5°的范围内转动时,转台稳速控制精度达到0.3%。设计了一种奈奎斯特频率靶标,在每组矩形垂直靶条间加入公差为a/n的等差级数间隔靶条,解决了遥感器推扫时CCD像元与垂直靶条像匹配不确定性问题,使配准简化,提高了测量结果的准确性。试验结果表明:遥感器获得了垂 直、水平及45°方向的0视场,±0.86视场奈奎斯特频率靶条像,验证了采用推扫技术的TDI CCD遥感器所具有的高品质。     

动态扫描拼接成像系统的多模控制

提出了凸轮驱动的线阵CCD像面动态扫描拼接方法以扩大遥感仪器的覆盖宽度,并对系统负载非平衡特性及其多模控制算法进行了分析.讨论了现有拼接方法的优缺点,进而引入凸轮驱动的动态扫描拼接方法.该方法采用电机和凸轮作执行机构,电机做匀速旋转运动,通过凸轮带动多个线阵CCD做往复直线运动,实现动态扫描拼接.为了提高CCD成像质量,从理论上对凸轮结构的特殊性、平台姿态角及相机方位角造成的系统负载非平衡特性进行了分析,结果表明:平台俯仰角对负载非平衡特性影响较小,可以忽略;当平台横滚角和相机位角之和非零时,负载力矩在凸轮升程段和回程段表现出不同的特性.针对凸轮升程段和回程段采用相同控制器时凸轮转速在两阶段存在转速降的情况,提出了变输入的多模控制方法,并进行了相关实验.结果表明:变输入的多模控制方法可有效消除凸轮转速在升程段和回程段存在的转速降,且在从动件匀速段的凸轮稳速精度达到0.48％.该方法简单、方便,易于工程实现.     

高动态调光成像系统畸变的自校正

针对基于数字微镜器件(DMD)的高动态成像系统在光学设计过程中由二次倾斜造成的畸变,建立了一套基于区域的系统畸变自校正模型。首先,根据像素级区域调光高动态系统中光路设计的特点,分析了畸变产生的原因。考虑不同种类畸变模型产生的原因及特点,结合系统自身的优势,建立了一种基于区域的畸变校正函数模型。为了解决在校正过程中某一点存在多次赋值或者未赋值的情况,采用逆推校正的方法逆向求解畸变参数,进行畸变校正。最后,利用数字微镜器件(DMD)自身投影标定模板的方法,实现了系统畸变的自校正设计。实验结果表明:校正后的系统像元误差为0.87pixel。与传统的畸变校正模型相比,该模型可以有效解决系统中的倾斜畸变、径向畸变以及偏心畸变,且畸变校正过程不依赖外部环境,校正过程快、可靠性高,满足了DMD高动态系统像素级调光的要求。     

扩散光层析技术及其应用

扩散光层析技术是新近发展的一种生物医学无损成像方法,可用于组织和血氧水平的可视化实时探测,对脑成像和肿瘤监测等具有重要意义。本文介绍该技术在实验方法和仪器等方面的进展,及在临床上获得的应用。     

基于嵌入式光学相干层析成像控制系统设计

为了实现低成本、小型化的光学相干层析成像（OCT）控制系统的设计,在分析了该系统的原理和控制信号的逻辑关系的基础上,创新地将快速扫描延迟线的振镜驱动信号,位相调制器的高频激励信号,电控位移台控制信号以及信号放大滤波电路等集成于一个嵌入式OCT控制系统中。测试结果表明,该OCT控制系统产生的各种控制信号能够满足OCT系统实际工作的要求。