透射共轴式光声消化内窥成像系统

光声成像作为一种既能提供光学高对比度又能实现声学大成像深度的新兴医学影像技术,可通过对肿瘤滋养血管的三维成像,为癌症的早期诊断提供一种全新的高灵敏检测方法。本文针对消化道肿瘤的临床成像需求,提出了一种内部光激发、外部声探测的透射共轴式光声消化道内窥成像系统,并通过仿体与离体生物组织的成像实验,与现有的反射非共轴式光声内窥成像系统的成像性能进行了对比。实验结果表明,在仿体样品中,透射共轴式光声内窥成像系统的信噪比相对反射非共轴式系统最高提高了43.3 dB,成像深度增大了28.4%;而离体生物组织中,在10.7 mm深处,其信噪比也提高了9.7 dB。实验验证了本设计有效提高了光声信号的探测灵敏度,使该系统相较现有反射式系统具备更优的成像信噪比和成像深度,为光声消化道内窥技术推向临床提供了一种具有重要应用潜力的实施方法。     

一种新型的全光纤速度干涉仪实验研究

全光纤可测量任意反射面的速度干涉仪,对强动载下的界面运动速度测量具有重要意义.基于传统光纤速度干涉仪的特点,设计了一种新型全光纤速度测量系统.该系统不仅能消除延迟线圈的分布式相位调制噪声,还能得到高条纹对比度的干涉信号.采用偏振分束器替代耦合器,应用琼斯矩阵法分析推导了偏振分束器能够消除系统中的非相干光束原理.振动台表面速度测量的实验结果表明,该系统能得到89.1％条纹对比度的干涉信号,大幅提高系统信号噪声比,并且相比Levin结构的传统干涉仪能抑制延迟光纤线圈的相位噪声超过30 dB.     

压缩传感用于极弱光计数成像

为解决灵敏度达到单光子水平的面阵探测器件其单位像素上灵敏度有限和测量数多等问题,研制了具有极高灵敏度的成像系统来实现欠采样的极弱光成像探测。该成像系统基于光子计数成像技术和压缩感知理论,利用数字微镜器件(DMD)完成随机空间光调制,通过单光子点探测器收集光子,以计数形式记录下光强值。然后,利用算法重建出极弱光照明下的图像。文中设计了相关实验,研究了测量数、光强极弱程度和测量时间对成像质量的影响。最后,引入了图像质量评价标准和系统信噪比,分析对比了实验数据。结果表明,当测量数高于信号总维度的19.5%时,系统能完美成像,信噪比可低至2.843 8dB,DMD单位像素上的平均光子数可低于1.106count/s,成像的关键在于信号的波动大于噪声的波动。该成像系统基本满足了极弱光成像探测在光强、灵敏度和采样数等方面的要求。     

全孔径背向散射诊断光学系统

基于新的激光聚变驱动装置的需要,设计了全孔径背向散射诊断光学系统并介绍了光学设计中涉及的若干关键技术。采用低反射率的楔形反射镜衰减背向散射光能量,降低后继元件对光学薄膜损伤阈值的要求。通过缩束镜缩小光束口径,减小光学元件尺寸;同时采取折叠光路结构来缩小系统体积。对空间滤波器和光学滤片进行组合,屏蔽了打靶倍频光干扰及不同散射类型的相互串扰。采用光学白板对色散严重的背向散射光进行漫反射匀化,使光谱测量系统获得完整的光谱信息。最后,选取抛物面为空间分布成像目标面,通过分析空间分布成像光束的结构设计了成像镜头。设计的诊断光学系统具有散射时间测量、光谱测量、空间分布成像、能量测量等功能,光学测量模块尺寸为1.9m×0.9m×1.5m。该全孔径背向散射诊断光学系统在新的激光聚变驱动装置中具有潜在的应用价值。     

利用Monte Carlo模拟技术研究OCT图像对比度

建立了光在生物组织中传播的模型,利用MonteCarlo模拟技术快速计算和可移植性的优点,研究了OCT图像对比度与显微物镜数值孔径、焦距深度、时间门参数的关系,并给出它们的关系曲线.通过在所建立的模型基础上加入透镜透过率函数和光学传递函数,弥补了以往程序只能模拟光在生物组织中传播行为的缺点.该模型不仅可以分析生物组织图像与生物光学特性的关系,而且还可以指导OCT结构的完善和创新.模拟结果表明:在构建OCT时,参考臂与样品臂的这两个显微物镜的数值孔径越大,生物组织的采样深度越浅,处理信号的时间门宽度越小(但时间门宽度不能小于激光脉冲时间),混浊生物组织图像对比度越好.     

LiNbO3外调制器的10 Gbit/s光纤传输系统

建立了一个10 Gbit/s光纤传输系统平台,实现了10 G光信号无中继、无误码传输,系统采用了NRZ码、高性能的GaInAsP 多量子阱DFB激光器、LiNbO₃电光调制器。进行了系统的传输实验,得到了系统的各项指标参数,分析了影响系统传输质量的因素,研究了传输系统中的一些关键问题。无中继距离为84 km,采用了CWDM技术对信号进行复用。在误码率为10^-12时,接收机的最小接收光功率可达到-26.76 dBm。系统的功率代价为0.49 dB,没有出现误码率平台。实验还对发送光信号的消光比与接收机灵敏度之间的关系进行了研究,连续观察24 h无误码。     

空间差分干涉的光纤分布式水下声波测量

为了实现大范围的水下微弱声波探测,提出了一种基于后向瑞利散射空间差分干涉的光纤分布式声波检测(DAS)技术。声波振动引起单模传感光纤中后向瑞利散射光的变化,将含有声波信息的后向瑞利散射光注入到非平衡迈克尔逊干涉仪,调节干涉仪的臂长差实现不同长度的相邻空间段的后向瑞利散射光干涉,然后采用3×3耦合器解调技术解调出相位信息,实现声波信号的测量。实验搭建了一套基于DAS技术的水下声波测量系统,该系统不仅能够实时准确定位两个声波位置,还能还原声波的幅值、频率、相位等信息,并且实现了1kHz情况下的-148.8dB(re rad/μPa)水下声压相位灵敏度,100~1 500Hz频率的频响平坦度在1.2dB之内。实验结果证实DAS技术能够实时快速地实现多个声波信息的定量测量。     

动态线偏振光散射纳米颗粒粒度测量法的研究与分析

多重散射是传统动态光散射法测量纳米颗粒溶液浓度上限受到限制的主要原因。为此文中提出了动态线偏振光散射纳米颗粒粒度测量法,通过改变颗粒入射光和散射光的偏振状态,降低颗粒间多重散射的影响。现利用Mie散射理论分析了入射光与散射光偏振状态之间的关系,并通过实验方法探知偏振光在散射介质中的传输特性,揭示了在动态光散射中使用垂直偏振光作为入射光的实验依据。最后对动态线偏振光散射颗粒测量法和传统光子相关光谱测量法进行了实验及分析,通过两种方法的比较,验证了上述理论的正确性。     

非接触玻璃厚度测量系统

该文研究了一种基于迈克逊干涉仪原理的非接触玻璃厚度测量系统。利用样品前后表面反射回来的探测光与参考臂的反射光发生干涉产生弱干涉信号,并用信号处理模块对弱干涉信号光进行差分放大,再对其进行带通滤波、包络解调等,从而得到玻璃厚度。系统还利用了直线电机控制反射镜实现光程的变化,并对待测物纵向深度信息进行高速循环式探测,从而实现了对玻璃厚度的高速、高精度、循环式测量。该系统适用于平板玻璃、光学镜片等玻璃制品厚度的高精度测量。     

太赫兹光致力近场显微成像技术及应用研究

设计并搭建了太赫兹光致力显微成像系统(THz PiFM),首次在太赫兹波段实现了近场光力纳米显微成像测量。该系统基于原子力显微镜,利用探针对所受力的灵敏检测能力,通过探测探针与样品之间近场偶极相互作用产生的光场梯度力,实现无探测器的太赫兹近场显微成像。利用该系统,对可见光激发下的单层MoS₂晶粒进行了近场纳米显微成像表征,并分析了晶粒边缘近场光力信号增强的机制。研究结果表明,THz PiFM对二维材料中的载流子具有高灵敏的探测能力。与传统的太赫兹近场显微成像技术相比,THz PiFM无需太赫兹探测器,而且可获得更加优越的空间分辨率和成像信噪比,是一种低成本、高性能的新型太赫兹近场显微成像技术。     

A prototype two-detector confocal microscope for in vivo corneal imaging

Confocal microscopy through-focusing (CMTF) of the cornea produces a three-dimensional (3-D) display of corneal structure and intensity profiles that allow objective measurements of corneal sublayer thickness and relative assessment backscattering of light. In this study, a prototype confocal instrument was evaluated in which a photon counting photomultiplier tube (PMT) detector was added to provide faster and more quantitative measurements, while still maintaining the imaging capability of the microscope. To acquire images and measure backscattered light simultaneously, an uncoated pellicle beam splitter was incorporated into the light path of the confocal microscope. This beam splitter reflects 8% of the confocal signal to the PMT. The CMTF scans were performed on four rabbits using the prototype instrument. Corneal images and 3-D reconstructions acquired with and without the beam splitter in the light path appeared identical. Both the camera and PMT CMTF curves had easily identifiable peaks corresponding to the epithelium, basal lamina, and endothelium. No significant differences were found between PMT and camera CMTF measurements of epithelial, stromal, or corneal thickness (n = 12 scans). Furthermore, a high correlation was found between camera and PMT measurements (linear regression analysis, y = 0.999 x -0.4, r = 0.99, p < 0.001). The data suggest that by adding a pellicle beam splitter, CMTF intensity data can be acquired using a PMT. The PMT has a faster sampling rate and greater dynamic range than the camera and provides a count of the photons detected. Thus, the instrument has the potential for improving corneal pachymetry and back-scattering measurements while still providing high-resolution corneal images.     

复合式多点测量速度干涉仪光学系统设计

为满足爆炸冲击作用下物质界面的速度测量需求,设计了一种复合式多点测量的速度干涉仪。采用物方和像方双远心光路,将光纤阵列出射的照明激光定点投射到待测物面上,实现了针状滴注式照明,充分利用了照明激光能量,且保证了待测物面在运动过程中具有恒定的照度。成像系统像面采用末端为大芯径的锥形光纤接收信号光,既保证了物面运动过程中信号光与光纤的有效耦合,又保证了信号的单模输出,以便进入单模光纤马赫-曾德干涉仪进行差频干涉。采用具有微小楔角、沿直径方向镀矩形带状45°反射膜的反射镜,将照明光路与成像光路同轴,并校正了成像系统的大量像散。该干涉测量系统在物面运动10mm的行程中,物面滴注式照明照度保持恒定,像面光斑大小没有超出大芯径的光纤芯径。此光学系统能够满足爆炸冲击界面的大行程速度测量需求。     

高灵敏度获取SPR生物传感器的信息

获得高灵敏度的生物信息是SPR生物传感器扩展其应用的重要保证。它涉及生物传感芯片、光路、信号采集以及信号处理,其中生物传感芯片、信号获取和数据处理是实现高灵敏度获取的3个主要因素。本文通过对空间相位调制微阵列检测系统和微阵列光强检测系统的分析,得到了信号获取系统可以达到的灵敏度;同时,还分析了信号获取系统的传感单元对灵敏度的影响,提出了合理选择和设计信号获取系统的措施。研究结果表明,相位检测的灵敏度和分辨率要明显高于光强检测,光强检测的灵敏度能达到10^-4RIU,相位检测的灵敏度可达到10^-6RIU。     

太赫兹功率探测器高灵敏度调制解调系统设计

针对太赫兹被动成像系统前端功率探测器内部引入的低频噪声(1/f噪声)对成像精度的影响较为明显的问题,设计了一种高灵敏度调制解调系统来降低低频噪声对成像的干扰.通过控制外部信号源使功率探测器在正常工作与饱和状态之间快速切换,实现对目标信号的调制,从而将目标信号的频率调制到高于功率探测器引入的低频噪声频段以便将低频噪声滤除...     

膏药测量中双传感器补偿法失效现象的研究

介绍了膏药激光透射法测量系统及双传感器补偿法的测量原理。在测量系统中，为消除光源强度变化对测量精度的影响，采用分光镜将光源分为测量光和参考光，同时采用两个光电传感器接收信号并进行补偿。在实验中，这种双传感器补偿法并未达到预期效果。分析原因之后，指出光源偏振方向的随机变化，导致系统中分光镜分光比的随机变化，若保证光源偏振方向不变，分光比也不会因光源强度变化而变化，从而可达到补偿效果。为此，给出了解决方案及实验结果。结果表明：该解决方案是可行的，实验结果可以满足系统精度要求。     

基于距离选通的激光主动成像技术的研究

距离选通激光主动成像可在恶劣环境条件下有效克服大气后向散射和背景干扰,得到被观测目标的高对比度图像.详细分析了大气后向散射对主动成像系统的影响,阐述了距离选通成像技术高速门控成像的原理,并就构成距离选通激光主动成像系统的关键器件如光源、像增强CCD(ICCD)、接收光学系统提出了具体性能要求和选取中需遵循的依据,文章最...     

Motion of a Micro/Nanomanipulator using a Laser Beam Tracking System

This article presents a study of the control problem of a laser beam illuminating and focusing a micro-object subjected to dynamic disturbances using light intensity for feedback only. The main idea is to guide and track the beam with a hybrid micro/nanomanipulator, which is driven by a control signal generated by processing the beam intensity sensed by a four-quadrant photodiode sensitive detector (PSD). Since the pointing location of the beam depends on real-time control issues related to temperature variation, vibrations, output intensity control, and collimation of the light output, the 2-D beam location to the PSD measurement output must be estimated in real-time. To this aim, a Kalman filter (KF) algorithm is designed to predict the beam location to perform efficient tracking and following control approach. Hence, a robust master/slave control strategy of the dual-stage micro and nanomanipulator system is presented based on sensitivity function decoupling design methodology. The decoupled feedback controller is synthesized and implemented in a 6-DoF micro/nanomanipulator allowing few centimeters displacement range with a nanometer resolution. A relevant case study, related to laser-beam tracking for imaging purposes, validates experimentally the proposed framework.     

Aperture apodization on regular gratings with variable transmission in the zero diffraction order

A new principle of aperture apodization for imaging and transform optical systems with controlled splitting of the output light beam into spatially selected diffraction orders and deflection of all higher orders beyond the operating region is proposed and investigated. Implementation of the principle is based on the use of regular gratings whose transmission coefficient in the useful zero diffraction order changes slowly from cell to cell, and excess light is coupled to higher orders and is screened with a field stop. To test the proposed principle, we designed, experimentally fabricated, and investigated an optical refracting telescope equipped with an apodizing filter with a binary amplitude circular structure and having the intensity of the first spurious diffraction peak of the point spread function 10 times lower than that in the embodiment without filter.     

Mid-infrared optical coherence tomography

A time domain optical coherence tomography (OCT) system is described that uses mid-infrared light (6-8 microm). To the best of our knowledge, this is the first OCT system that operates in the mid-infrared spectral region. It has been designed to characterize bioengineered tissues in terms of their structure and biochemical composition. The system is based upon a free-space Michelson interferometer with a germanium beam splitter and a liquid nitrogen cooled HgCdTe detector. A key component of this work has been the development of a broadband quantum cascade laser source (InGaAs/AlInAs containing 11 different active regions of the three well vertical transition type) that emits continuously over the 6-8 microm wavelength range. This wavelength range corresponds to the so called "mid-infrared fingerprint region" which exhibits well-defined absorption bands that are specifically attributable to the absorbing molecules. Therefore, this technology provides an opportunity for optical coherence molecular imaging without the need for molecular contrast agents. Preliminary measurements are presented.