基于波前编码技术的眼底成像系统

提出了一种混合光学-数字眼底成像系统,该系统不需要探测和补偿不同人眼带来的像差的动态变化,即可获取高分辨率的视网膜图像。该系统在出瞳位置放置一块三次相位掩膜板对眼底图像进行编码,然后采用维纳滤波算法复原获取清晰图像。利用基于光学成像的二维卷积模型对该系统进行了仿真实验,结果表明,针对不同个体的人眼像差,三次相位板可以使系统的点扩散函数在一定范围内保持一致,从而校正包含离焦、彗差、像散、三叶草在内的人眼像差,获得清晰的眼底图像。该系统的设计简化了传统眼底相机的复杂光学结构,是一种便携式结构。     

LCOS人眼像差校正仪的系统控制实现

建立了一套基于LCOS校正器的人眼像差自适应校正系统,并为该系统编写了一套完整的控制软件。该系统采用哈特曼波前探测器进行波面探测,将探测所得波前畸变经过PC计算处理后转化为灰度图,再通过PC把灰度图发送给LCOS上进行波面校正,通过校正人眼像差的方式来提高系统成像质量。经过实测,系统波前误差得到大幅度降低。实测表明,该系统的控制软件算法可以实现低阶大像差情况下人眼视网膜高分辨率成像。     

离轴反射式人眼视网膜成像自适应光学系统设计

为了实现活体人眼视网膜的高分辨率成像,设计了一套视网膜成像液晶自适应光学系统来校正人眼的动态变化像差。基于开环双波段模式,分别采用夏克-哈特曼波前传感器(SHWS)和基于硅基板上的液晶空间光调制器(LCOS-SLM)来探测和校正人眼以及系统的波前像差;且分别采用近红外波段(790nm)的超发光二极管和可见光波段(570nm)的激光器作为波前探测和校正成像光源。系统采用离轴反射式结构来提高光能利用率,减小色差。用ZEMAX对系统性能进行了分析,证明设计的系统能够达到衍射极限,MTF@30lp/mm为0.4(对应视网膜上4μm),MTF@50lp/mm为0.16(对应视网膜上2.5μm)。和闭环折射式系统相比,能量利用率提高1倍以上,且杂光和色差干扰小,成像对比度好。     

大视场液晶自适应视网膜成像系统

设计了大视场眼底自适应成像系统,用于扩大现有视网膜自适应成像系统的视场。对人眼等晕角视场下的自适应像差校正成像进行分析,确定了波前探测与成像校正两个过程对视场的不同要求。在共光源像差探测及成像光学系统中,采用切变视场光阑的方式先后在波前探测和自适应校正成像过程中进行小-大视场切换,避免了大视场中眼波像差探测失真问题,使成像区域由200 μm扩展到500 μm。利用人眼等晕角大视场使眼底液晶自适应成像系统在不降低成像质量的前提下将成像区域扩展了2.5倍,大幅提升了该自适应成像系统在临床上应用的可行性。     

349单元自适应光学波前处理器

为了满足大型地基高分辨率成像望远镜对自适应光学系统校正频率和成像质量的要求,本文设计了一套349单元自适应光学波前处理系统,该系统在349单元变形镜自适应光学系统上实现了1 500Hz的波前校正频率。设计了以控制计算机、FPGA波前斜率处理器、GPU矩阵乘法处理器以及模块化数模转换机箱等作为主要部件的实时波前处理器,报道了349单元变形镜自适应光学系统对动态像差的闭环校正结果,实验中对模拟大气相干长度r_0为6cm,格林伍德频率为160Hz的大气湍流实现有效校正,自适应光学系统闭环后,波前像差的1 000帧平均均方根值由1.07λ(中心波长600nm,后同)下降至0.11λ。本文设计的349单元变形镜自适应光学系统能够在1 500Hz的波前校正频率下有较高的成像质量,波前处理延时优于235μs。功率谱分析结果表明自适应光学系统对100Hz以下的波前畸变具有明显的校正效果。     

利用激光全息技术校正大口径光学成像系统像差

基于光学全息原理,分析了激光全息技术校正光学成像系统像差的机理和方法,建立了全息记录实验系统,用于校正口径500 mm、低质量球面反射镜光学系统对有限远物体成像时的像差。采用原光路再现的方法,通过比较像差校正前后的干涉图样和成像结果,验证了该校正方法的可行性。实验结果表明,校正后该系统剩余波像差约为λ/8。     

超大视场头盔显示光学系统设计

设计了大视场头盔显示器的目视光学系统,用于满足头盔显示器对大视场、小畸变、高分辨率以及轻量化的苛刻要求.采用4×3阵列式排列、视场角为33°×24°的12组高质量成像目镜系统拼接成单眼目视光学系统来实现系统的大视场设计.为了使系统轻量化,每个单元目镜只采用一片透镜;透镜一面采用二元光学衍射面,利用其特殊色散特性校正目镜系统色差;另一面采用非球面,用于校正目镜光学系统的初、高级单色像差.其图像源为高亮度、高分辨率的OLED微显示器.设计结果显示:单目目视光学系统水平视场达到120°,垂直视场为60°,角分辨率为43 pixel/(°);单个目镜系统传递函数在40 lp/mm处,轴上视场高于0.62,全视场高于0.1;系统畸变小于3％;系统的双目视场为160°×60°,双目重叠视场为80°×60°.该设计实现了超大视场,满足头盔显示光学系统的成像要求.     

小孔径成像系统衍射退化图像恢复

针对小孔径成像系统图像的衍射退化,本文介绍了一种基于凸集投影法(POCS)的超分辨率图像复原技术,这是一种将各种先验约束引入到计算中以降低噪声和奇异性解的迭代算法,该算法可以很好的保持高分辨率图像的边缘和细节信息.使用衍射退化图像恢复技术的小孔径成像系统在航空航天相机、天文望远镜、受光源、镜头或能量大小限制的特殊光学成像系统等场合有广泛的应用前景.     

桌面97单元自适应光学系统性能测试

构建了一套桌面自适应光学系统性能测试系统,用以验证97单元自适应光学系统的校正能力。该测试系统主要由光源、快速控制反射镜、变形镜、Shack-Hartmann波前传感器、高速波前处理器、扰动相位屏等部件组成,分别利用干涉仪和Shack-Hartmann波前传感器的数据控制变形镜进行光路的展平校正,得到了系统的静态校正精度。然后,测试了精密跟踪系统的校正能力。最后,利用扰动相位屏模拟不同的大气扰动条件,以成像相机图像的斯特列尔比(SR)为指标,在不同目标亮度下测试了自适应光学系统的动态校正能力。测试结果显示:该97单元自适应光学系统的静态波像差校正精度的RMS接近λ/20;两种控制模式下精密跟踪系统的误差抑制带宽分别达到了15 Hz和39 Hz;系统在强湍流情况下,动态校正后的成像分辨率基本优于3倍衍射极限。由此表明,97单元自适应光学系统能够有效地校正像差,提高成像分辨率。     

相位差异散斑法图像复原技术

为了克服大气湍流和光学成像系统像差引起的波前相位畸变,提出利用相位差异散斑法同时采集焦面和离焦面通道的单帧短曝光图像来估算波前相位畸变.结合夏克哈特曼波前探测器设计了针对扩展目标的相位差异散斑法高分辨率成像和相位估计对比实验,通过定量移动高精密平移台获得焦面和离焦面图像,并将解算的波前面形与夏克哈特曼波前探测器实测的波...     

Dispersion, aberration and deconvolution in multi-wavelength fluorescence images

The wavelength dependence of the incoherent point spread function in a wide-field microscope was investigated experimentally. Dispersion in the sample and optics can lead to significant changes in the point spread function as wavelength is varied over the range commonly used in fluorescence microscopy. For a given sample, optical conditions can generally be optimized to produce a point spread function largely free of spherical aberration at a given wavelength. Unfortunately, deviations in wavelength from this value will result in spherically aberrated point spread functions. Therefore, when multiple fluorophores are used to localize different components in the same sample, the image of the distribution of at least one of the fluorophores will be spherically aberrated. This aberration causes a loss of intensity and resolution, thereby complicating the localization and analysis of multiple components in a multi-wavelength image. We show that optimal resolution can be restored to a spherically aberrated image by constrained, iterative deconvolution, as long as the spherical aberration in the point spread function used for deconvolution matches the aberration in the image reasonably well. The success of this method is essentially independent of the initial degree of spherical aberration in the image. Deconvolution of many biological images can be achieved by collecting a small library of spherically aberrated and unaberrated point spread functions, and then choosing a point spread function appropriate for deconvolving each image. The co-localization and relative intensities of multiple components can then be accurately studied in a multi-wavelength image.     

Aberration correction for confocal imaging in refractive-index-mismatched media

A major limitation to the use of confocal microscopes to image thick biological tissue lies in the dramatic reduction in both signal level and resolution when focusing deep into a refractive-index-mismatched specimen. This limitation may be overcome by measuring the wavefront aberration and pre-shaping the input beam so as to cancel the effects of aberration. We consider the images of planar and point objects in brightfield, single-photon fluorescence and two-photon fluorescence imaging. In all cases, the specimens are imaged using an oil-immersion objective through various thicknesses of water. The question of finite-sized pinhole is addressed and it is found, in general, that it is sufficient to correct only the first two or three orders of spherical aberration to restore adequate image signal level and optical resolution, at imaging depths of up to 50-100 wavelengths.     

Shack-Hartmann wave front measurements in cortical tissue for deconvolution of large three-dimensional mosaic transmitted light brightfield micrographs

We present a novel approach for deconvolution of 3D image stacks of cortical tissue taken by mosaic/optical‐sectioning technology, using a transmitted light brightfield microscope. Mosaic/optical‐sectioning offers the possibility of imaging large volumes (e.g. from cortical sections) on a millimetre scale at sub‐micrometre resolution. However, a blurred contribution from out‐of‐focus light results in an image quality that usually prohibits 3D quantitative analysis. Such quantitative analysis is only possible after deblurring by deconvolution. The resulting image quality is strongly dependent on how accurate the point spread function used for deconvolution resembles the properties of the imaging system. Since direct measurement of the true point spread function is laborious and modelled point spread functions usually deviate from measured ones, we present a method of optimizing the microscope until it meets almost ideal imaging conditions. These conditions are validated by measuring the aberration function of the microscope and tissue using a Shack‐Hartmann sensor. The analysis shows that cortical tissue from rat brains embedded in Mowiol and imaged by an oil‐immersion objective can be regarded as having a homogeneous index of refraction. In addition, the amount of spherical aberration that is caused by the optics or the specimen is relatively low. Consequently the image formation is simplified to refraction between the embedding and immersion medium and to 3D diffraction at the finite entrance pupil of the objective. The resulting model point spread function is applied to the image stacks by linear or iterative deconvolution algorithms. For the presented dataset of large 3D images the linear approach proves to be superior. The linear deconvolution yields a significant improvement in signal‐to‐noise ratio and resolution. This novel approach allows a quantitative analysis of the cortical image stacks such as the reconstruction of biocytin‐stained neuronal dendrites and axons.     

改进的天文斑点图像高清晰重建方法

由于受大气湍流的影响,利用地基光学望远镜获取的天文目标图像会发生严重的模糊或降质。解决这一问题的主要途径之一就是斑点成像技术,该方法利用短曝光"冻结"大气,获取天文目标的斑点图再经后处理重建高清晰图像。本文将动态支持域约束的思想与广义极大似然估计重建算法相结合,提出一种改进的基于广义极大似然原理的天文图像高清晰重建算法。该算法创新性地提出了动态支持域约束的思想,在代价函数中增加了非线性滤波项,它可以对上一次的迭代结果进行非线性处理,根据阈值自动调整目标的支持域,使支持域随着迭代次数的增加实现动态调整,克服了已有算法在整个迭代过程中支持域不变的缺点,使得该算法也可对扩展目标实现高清晰重建。实验结果表明,该算法不仅对点源天文星体短曝光图像实现了高清晰重建,而且将模拟扩展目标图像重建结果的峰值信噪比提高10%以上,对自适应光学长曝光图像也有较好的恢复效果。     

Specimen-induced distortions in light microscopy

Specimen‐induced aberrations affect the imaging properties in optical 3D microscopy, especially when high numerical aperture lenses are used. Studies on aberrations are often properly concerned with the degradation of image quality such as compromised resolution or reduced signal intensity. Apart from these, aberration effects can also introduce geometric image distortions. The effects, discussed here are particularly strong when thick biological specimens are investigated. Using a high numerical aperture interferometer, we measured wavefront aberrations in transmission mode and quantified geometric distortions associated with specimen‐induced aberrations. This assessment for a range of biological specimens allows estimation of the accuracy of spatial measurements. The results show that high‐resolution spatial measurements can be significantly compromised by specimen‐induced aberrations.     

基于实时波前信息的图像复原

提出了一种基于PIX总线的千单元可扩展波前探测图像恢复技术.采用波前探测与图像恢复相结合的方式来克服大气扰动和系统像差对图像分辨率的影响,满足大型地基望远镜高分辨率成像的需求.首先利用波前探测的方法得到波前相位畸变量,再由此恢复退化图像.其核心部件-波前处理器则采用波前处理主板和可扩展的波前处理子板相结合的方式来满足不同光学系统对波前处理规模的需求,波前空间采样散可扩展至千单元数量级.系统在室内进行了激光光源图像恢复实验,使激光光源的能量集中度提高50％左右;在室外对恒星和0.6″的双星图像进行了恢复,其半高全宽下降了约80％.系统采用大规模现场可编程门阵列(FPGA)作为波前处理的核心器件,实现了波前探测的实时处理和透过大气成像的退化图像的高分辨率图像恢复.     

利用相位差异技术恢复宽带白光图像

研究了用于扩展目标成像的相位差异技术。该技术利用焦面和离焦面上的两幅图像之间的相位差异来估算波前相位畸变,同时对采集的图像进行恢复。设计了白光目标成像实验系统,用宽带白光作光源,在实验室搭建实验平台,模拟无穷远处目标和波前相位畸变。采用直角梯形分光棱镜将光路分为两个通道,在一台相机上同时采集两个通道像面上的图像,消除了相机不同产生的差异,极大地抑制了噪声对图像恢复的影响,分光后系统抗两个通道独立的高斯白噪声的能力为10%。实验结果显示恢复后的图像分辨率提高了19%,表明该技术是适合光电成像系统的图像恢复技术。