Simultaneous Determination of the Amplitude-Phase Structure of an Optical Signal and a Transfer Function with the Influence of the Medium Given by a Modulation Function

We consider a solution to the phase problem in optics as applied to registering and analyzing amplitude-phase structures of 1) d optical fields that form or transfer images and 2) transfer or spread functions of the medium where optically inhomogeneous fields propagate or those of the systems forming fields and producing distortions. The influence of the medium is characterized by the modulation function and is described by the operation of multiplication. In order to measure the amplitude and phase field characteristics and transfer or spread functions, we use an original development of the modulation-spectral method proposed earlier by the authors. There are two variants of optical schemes considered. They include identical parts designed to form the light field to be processed. Using the first optical system, one forms the spectrum of spatial frequencies and introduces the first additional space modulation in the plane of spatial frequencies. The second optical system is placed in the same plane to form the image of the investigated field in the input plane of the developing scheme after passing the transmitting medium. In the first variant, the second part of the scheme contains at the input the third optical system forming the spatial spectrum in the registration plane. At the input of this scheme, the second additional spatial modulation is introduced. In the second variant, the third optical system forms the image of the developing scheme input plane in the registration plane. The second additional spatial modulator is placed in the spatial frequency plane of the third optical system. In the output, in both cases four independent two-dimensional intensity distributions are registered, which allow one to solve the formulated problem.     

Measurement of the amplitude and phase structures of an optical field and the transfer function for describing the effect of a medium in the form of a modulating function

The phase problem in optics is solved as applied to the detection and analysis of the amplitude and phase structures of two-dimensional optical fields forming or transmitting an image and the amplitude and phase structures of the transfer or instrumental functions of either the media containing optical inhomogeneities or the systems forming fields and involving instrumental distortions. The effect of the medium is characterized by a modulating function and described by a multiplication operation. Two variants of the optical scheme are considered. In each variant, the spatial-frequency spectrum is formed by the first optical system and the first spatial modulation is introduced in the spatial-frequency plane. The second optical system is arranged in the same plane. This system images the field under investigation into the plane located at the exit of the transmitting medium. In the first variant of the optical scheme, the second spatial modulation is introduced in the same plane. The third optical system forms a spatial-frequency spectrum in the detection plane. In the second variant of the scheme, an image of the plane positioned at the exit of the probing medium is formed in the detection plane by the third optical system. The second spatial modulation is introduced in the spatial-frequency plane of the third optical system. In both variants, four independent two-dimensional intensity distributions that make it possible to solve the problem posed are detected at the exit.     

Modulation-spectral method for analyzing the amplitude-phase structure of optical inhomogeneities of objects

An original solution to the phase problem in optics is considered as applied to the problems of recording and analysis of the amplitude-phase structure of optical fields used for studying fine structures and inhomogeneities in steady-state objects producing effects to fractions of the wavelength period. The problem is solved by probing objects using radiation with a known structure. Intensity distributions of the probing field are detected at the exit from the object by using the modulation-spectral method directly for the spatial frequency spectrum and for the spatial frequency spectrum subjected to additional modulation formed in a special way, which is realized in the plane under study and provides visualization of the phase information contained in the light field in some form. The intensity distributions obtained make it possible to calculate the two-dimensional amplitude-phase structure of the field analyzed and, hence, the fine structure of the optical inhomogeneities of the object analyzed for the chosen probing direction. For steady-state objects, probing in a number of directions is possible. Information on the bulk structure of the inhomogeneities under study can be obtained by using the information available on the symmetry of the object. Two variants of action of the medium on probing radiation are considered. In the first one, the action is related to spatial field modulation (described by the multiplication operation); in the second one, the action leads to redistribution of radiation in the plane studied (described by the convolution operation).     

Coherent imaging of extended objects

When used with coherent light, optical imaging systems are inherently unable to reproduce both the amplitude and the phase of a two-dimensional field distribution. This is because their impulse response function varies slowly from point to point, a property known as non-isoplanatism. For sufficiently small objects, this usually results in a phase distortion and has no impact on the measured intensity. Here, we show that the intensity distribution can be dramatically distorted when extended objects are imaged. We illustrate the problem using two simple examples: the pinhole camera and the thin lens. The effects predicted by our theoretical analysis are confirmed by experimental observations.     

幅值和相位配准技术及其在光学相干层析血流成像中的应用

频域光学相干层析系统中扫描机构定位精度、 机械抖动及样品移动会造成A扫描信号幅值和相位发生波动, 影响生物组织成像质量. 利用最小灰度差匹配、Lorentzian曲线极值拟合和谱域光程差补偿等方法对A 扫描信号进行幅值配准. 通过对A扫描信号相位分布特征的匹配实现相位差检测与配准. 通过求已配准的A 扫描复信号之差, 消除静态组织对血流成像的影响. 进行了人眼扫描实验, 有效提取了视网膜三维血流图像. 实验结果表明, 提出的幅值及相位配准方法大大减小了系统扫描精度、人眼跳动等因素对生物组织在体成像质量的影响. 快速、精确的相位配准方法也可广泛应用在多普勒OCT、相位显微等与相位分辨有关的光学成像领域. 关键词： 频域光学相干层析 配准 血流成像 相位分布特征     

Testing and Analysis of the Structure of Transmitting Media or Objects with Registration of the Field Structure in the Image Plane

A solution to the phase problem in optics is considered within the context of the registration and analysis of the amplitude–phase structure of optical nonuniformities in stationary transmitting media or in investigated objects. To solve the problem, the object or the medium is tested by radiation with a known structure. For a certain selected direction of testing, the structural change due to the interaction with the object is registered. To obtain information on the amplitudes and phases of the testing light field, an original development of the modulationspectral method put forward by the authors is used. To solve the problem, the intensity distribution is detected in the image plane both for an unmodulated field and for that subjected to an additional twodimensional modulation specially formed in the plane of spatial frequencies. The modulation should provide a visualization of the phase information contained in the light field. The intensity distributions obtained make it possible to determine the twodimensional structure of the testing field at the output of the medium or the object. In the proposed variant of the method, the testing field should not be affected in the investigated plane. The interpretation of the results is easier, since it is the image that is registered. The two intensity distributions can be registered simultaneously, provided the light beam is divided into two channels after the optical system. It is significant that the method requires no iteration procedures in solving the problem. This allows one to expect speedingup of the processing of the information and analyzing it in almost real time. Two variants of optical schemes are considered in the paper. The first one deals with media or objects with a modulation effect described by multiplication by a complex function characterizing the effect. In the second case, the effect of the object leads to redistribution of the radiation in the investigated plane and is described by the operation of convolution of the testing signal and the function characterizing the effect.     

飞秒激光在锥形镀膜探针传输中相位奇异的研究

利用数值模拟的方法对飞秒激光脉冲中光波振荡一个周期内不同时刻的光场进行了计算、比较, 获得了输出端平面内各空间点处光场的最大值及达到最大值时对应的时间, 得到了探针近场的振幅和相位分布. 在研究振幅分布的过程中发现, 在探针输出端的有些区域振幅始终为零, 即在光波振荡的一个周期内这些区域始终为相位奇异点; 通过分析相位分布得到了相位奇异随时间的演化及相位奇异的特点.     

Analysis of the amplitude and phase structure of transmitting media with probing field registration in the image plane

The problem of obtaining information on the amplitude and phase internal structure of a medium in which radiation propagates is considered. The information is extracted by probing the medium; the information on the amplitude and phase distribution of the probing field behind the transmitting medium in the plane of image formation is analyzed. A modified version of the modulation-spectral method proposed earlier by the authors is applied. In this version, there is no need to act on the probing field in the plane under investigation. The interpretation of results is simplified since the image is registered. Two versions of the schematic solution are analyzed. The first version corresponds to the experimental scheme intended for media that produce a modulating action on radiation and is described by multiplication by a complex function characterizing the action. The second version corresponds to the case when the action of the medium leads to a redistribution of radiation and can be presented by the convolution of the probing signal and the function describing the action.     

基于Talbot效应的可调位相差二维六角位相阵列器的理论研究和数值模拟

系统研究了基于Talbot效应的光栅阵列器,利用数值模拟方法开展了阵列器的理论研究,对二维振幅型与固定位相差型阵列器进行了分析,通过外加电场调制位相差可以很好的解决二维振幅型与固定位相差型阵列器后z处光强分布不可调节和工作易受温度影响的问题.推导了外加电场调制位相差位相型阵列器实现均匀光强分布的理论模型,并验证了Paturz等人的实验结果,为此种新型阵列器的研究提供了基础.     

How to Determine the Amplitude-Phase Structure of a 2D Optical Field and a 2D Complex Transfer Function, with the Effect of the Medium Described by Convolution

We consider the solution to the phase problem in optics in application to registration and analysis of the amplitude–phase structure of twodimensional optical fields that form or transmit images, as well as the amplitude–phase structure of transfer and spread functions of media, in which light propagates, or those of systems that form fields or images. The idea of our method is to introduce two additional modulators that visualize phase information. We consider two variants of optical schemes designed for analyzing the amplitudephase characteristics of twodimensional optical fields as well as twodimensional complex transfer and spread functions. These schemes are special because the twodimensional structure of the fields is transmitted at a distance in a disturbing medium or system and four independent twodimensional intensity distributions are to be registered in the course of processing the twodimensional fields. To solve the problem, the first additional modulation preceding the transmitting medium is introduced in the scheme. Then the spectrum of spatial frequencies is formed by the optical system. The second additional spatial modulation is applied either in the optical system plane (the first variant of the scheme) or in the plane of spatial frequencies formed by the optical system (the second variant). A separate optical system is used for registration in the plane of spatial frequencies in the first variant of the scheme and in the image plane in the second variant. The intensity distributions obtained make it possible to solve the problem.     

A novel phase-sensitive scanning near-field optical microscope

Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton(SPP) devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field optical microscope(SNOM) with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.     

Application of acousto-optic interaction for holographic conversion of light fields

This paper represents a survey of research on the problem of acousto-optic conversion of optical images. This method of conversion permits us to retain all information that is contained in both amplitude and phase spatial modulation of a light wave. Particular attention is given to acousto-optic visualization of phase objects and registration of optical wavefronts. Information possibilities of the acousto-optic method are illustrated by numerical calculations as well as by some experiments recently performed in this area.     

畴腐蚀掺镁铌酸锂可调阵列光分束器的研究

研究了不同畴腐蚀深度的掺镁铌酸锂二维六角可调阵列光分束器的分数Talbot效应.对不同Talbot分数β和不同畴腐蚀深度的阵列光分束器Talbot衍射像进行了数值模拟理论研究.模拟结果表明,Talbot分数β可以改变Talbot衍射像的周期及结构分布,而畴腐蚀深度可有效调制衍射像的光强分布.在理论研究的基础上,设计并制备了具有不同畴腐蚀深度的掺镁铌酸锂二维六角阵列光分束器,对其在不同Talbot分数β条件下的分数Talbot效应进行了通光实验研究,实现了畴腐蚀阵列光分束器对近场Talbot衍射光强分布的调制,实验结果与理论研究结果一致.     

基于随机分数傅里叶变换的双图像加密算法

利用光学随机分数傅里叶变换设计了一种双图像加密算法,并给出了相应的光学实现.加密算法中,将两幅原始图像分别作为加密系统输入复函数的振幅和位相分布函数,利用随机分数傅里叶变换进行加密,所得复函数的振幅即为加密图像,而位相部分是变换的输出相位,随机位相作为加密算法的密码.在数值模拟中,二值文本图像和灰度图像分别被作为原始图像用于加密结果分析和加密安全测试,结果表明该加密算法具有很好的安全性.     

一种基于角谱理论的改进型相位恢复迭代算法

进行星间激光通信的光学发射天线光束整形器设计时, 首要解决的问题是根据输入光场及理想的输出光场, 确定整形器的相位分布, 其核心就是相位恢复. 基于角谱传播理论, 在传统 Gerchberg-Saxton (G-S)迭代算法的基础上, 提出了一种幅度梯度加成迭代算法, 给出了算法的详细流程与分析. 与G-S相比, 新算法利用迭代过程, 构建光场幅度反馈回路, 利用梯度搜索最佳迭代路径, 两者的联合作用加速其迭代收敛进程. 数值仿真表明, 新算法的单位迭代次数所引起迭代误差下降的速度是G-S算法的1.7倍, 其收敛速度明显优于G-S算法; 对不同的随机初始相位, 新算法都能进行有效迭代, 表现出适应性强, 且收敛一致性好的优点. 幅度梯度加成迭代算法为复杂光场的高效相位恢复提供了一种新思路, 为设计各种衍射光学元件提供了技术支持. 关键词： 相位恢复 迭代算法 角谱理论 光通信     

基于正交调制的偏振光谱成像系统研究

为了同时获取目标的全偏振二维图像信息和其光谱信息,设计了一种基于正交调制的偏振光谱成像系统。该系统由光学接收模块、相位调制器、Wollaston棱镜、Savart偏光镜、检偏器以及成像模块组成。其可以将原始光信号分解成两束相互正交的偏振光,并且分别成像在CCD焦平面的上下两部分上,从而构成两幅偏振图像。两组图像的叠加可以将干涉条纹的数据相互抵消,从而获得目标的纯图像信息,两组图像的相减可以将目标灰度图像相互抵消,从而获得目标的纯干涉条纹。通过理论分析与计算得到了光强分布函数和光谱变化形式。实验在稳定的光源环境中采用高对比度目标与背景板,完成了全偏振图像的实时采集。经相位校正和切趾处理改善了干涉图像的畸变,又通过去低频滤波和阈值滤波抑制了图像中背景噪声的影响,从而实现了对目标图像的提取及偏振光谱的复原。该系统具有稳定性高、光谱分辨率可调、信噪比高、可识别能力强等特点,对在复杂背景中提取目标图像、光谱及偏振态信息具有重要意义。     

高斯光束经表面有缺陷的厚非线性介质的传输特性

光学元件上存在的缺陷会对传输光束产生局域振幅和位相调制. 基于衍射理论模型和分步傅里叶算法,模拟分析了高斯光束经过表面有缺陷的非线性介质的传输过程中于介质内及从介质出射后在自由空气的传输特性, 并详细研究了在厚介质前表面有缺陷的情况下,介质中和自由空气中的光强分布演化规律. 研究表明,介质厚度越长、介质的非线性折射率越大,光束整体聚焦越厉害, 聚焦点离介质后表面越近.光束受调制点的位置离中心越近,光束分裂成丝产生的局部光强越大, 且介质表面存在缺陷将使通过的光束在介质后表面处产生一个很大的光强, 相位调制型缺陷产生的这一光强点比振幅调制型缺陷产生的光强点更强.