Phase-coded aperture for optical imaging

For the optical spectrum region, we describe a novel phase-coded aperture imaging system that can be used in a computational imaging camera. The optical design includes a phase-only screen followed by a detector array. A specific diffraction pattern forms at the detector array when the wavefront from a point source object passes through the phase screen. Since diffraction effects cannot be ignored in the optical regime, an iterative phase retrieval method is used to calculate the phase coded screen. Correlation type processing can be applied for the image recovery. Computer simulation results are presented to illustrate the excellent imaging performance of this camera.     

Common-path interferometer with a tri-window

A common-path interferometer is proposed with a tri-window. It is built using a 4f optical system with Ronchi ruling as a spatial filter. The input rectangular aperture is formed by three windows; the central window supports a phase object, and the other two are used for reference beams. Using an appropriate grating period relative to input aperture size, an interferogram containing three patterns can be obtained in the output plane. The object phase can then be reconstructed from the three patterns using just one interferogram. The experiments are carried out to demonstrate the feasibility and reliability of the proposed scheme.     

相干点源照明时消球差光学系统的像场结构

利用矢量傅里叶变换和稳相法获得了相干点源位于光轴上任意位置时，消球差光学系统像场结构的积分表达式，详细研究了使用线偏振光照明时像平面上大物方孔径角对像场结构的影响.模拟计算表明，在像空间垂直于光轴的平面上，如果物方孔径角较大，磁场分布绕光轴旋转90°后不再与电场分布相同，电场能量密度、磁能量密度和玻印亭矢量分布的等高线始终近似为椭圆，并且物方孔径角是导致玻印亭矢量分布失去圆对称性的主要因素.同时当使用小像方孔径角时，电场能量密度分布形状的长轴方向垂直于物空间电场的振动方向；随着像方孔径角逐渐增大，电场能量密度分布形状的长轴方向将逐渐变为与物空间电场的振动方向相同.这些结论完全不同于以前理论所预测的结果. 关键词： 成像系统 像场结构 矢量傅里叶变换 稳相法     

Measurements of the velocity gradient using a laser Doppler phenomenon

This paper reports on a method for measuring the velocity gradient using a laser Doppler phenomenon. The velocity gradient is determined from the velocity difference between two different points of the probing object and is actually obtained from the optical heterodyning of two differently Doppler-shifted scattered light fields from two points of the object having different velocities. The properties of output beat signals are theoretically investigated from their spectral broadening including the effect of the detecting aperture. The preliminary experiment was performed by using a rotating glass disk whose velocity is different from its center to the outside. The experimental results shows the usefulness of the present method for measurements of the velocity gradient.     

Shaping the beam profile of a partially coherent beam by a phase aperture

By use of a tensor method, an analytical formula for a partially coherent Gaussian Schell-model (GSM) beam truncated by a circular phase aperture propagating through a paraxial ABCD optical system is derived. The propagation properties of a GSM beam truncated by a circular phase aperture in free space are studied numerically. It is found that the circular phase aperture can be used to shape the beam profile of a GSM beam and generate partially coherent dark hollow or flat-topped beam, which is useful in many applications, e.g., optical trapping, free-space optical communication, and material thermal processing. The propagation factor of a GSM beam truncated by a circular phase aperture is also analyzed.     

经光阑衍射的平顶涡旋光束位相奇点的演化特性

推导出了平顶涡旋光束通过有光阑ABCD光学系统的传输解析式,并以光阑透镜和矩形光阑系统为例,与平顶光束比较研究了截断参量、相对离轴距离和光束阶数对衍射场中位相奇点演化特性的影响.数值计算表明,平顶涡旋光束通过上述光学系统均存在位相奇点,即使源处涡旋被光阑阻拦时,衍射场中也会出现位相奇点;而平顶光束通过光阑透镜系统存在刃型位错,随着截断参量增大,会发生刃型位错的演化和湮灭现象,且平顶光束通过矩形光阑系统没有发现位相奇点.     

经光阑衍射的平顶涡旋光束位相奇点的演化特性

推导出了平顶涡旋光束通过有光阑ABCD光学系统的传输解析式,并以光阑透镜和矩形光阑系统为例,与平顶光束比较研究了截断参量、相对离轴距离和光束阶数对衍射场中位相奇点演化特性的影响.数值计算表明,平顶涡旋光束通过上述光学系统均存在位相奇点,即使源处涡旋被光阑阻拦时,衍射场中也会出现位相奇点;而平顶光束通过光阑透镜系统存在刃型位错,随着截断参量增大,会发生刃型位错的演化和湮灭现象,且平顶光束通过矩形光阑系统没有发现位相奇点.     

Optical phase control for MMW sparse aperture upconversion imaging

The random phase errors of the optical carriers are discussed and controlled for passive millimeter-wave sparse aperture （PMMW SA） upconversion imaging. A two-channel model is set up for analyzing charac- teristics of the phase errors, and an active optical control technique based on stochastic parallel gradient decent algorithm （SPGD controller） is proposed to calibrate the phase errors. To demonstrate the feasi- bility of the SPGD controller, simulations are performed and an experimental system with a two-channel fiber array is set up. Simulation and experiment results show that the SPGD controller can effectively and rapidly compensate the phase errors of the optical carrier, and the accuracy of the phase control is sufficient for imagine svstems.     

基于模拟退火的相位展开方法

二维相位展开技术被广泛应用于光学精密测量、自适应光学、合成孔径雷达、图像处理等领域中。提出了一种基于模拟退火的相位展开方法。此方法对主值相位图采用局部平面近似，用模拟退火算法求出最优化平面参量，从而得到去除噪声和2π相位跳变的真实相位图。计算机模拟和实验结果均证明，此方法能有效地去除相位图中的噪声，实现带噪声的主值相位图的相位展开，可靠地重建被测物体的表面形貌。详细介绍了这一方法的原理及实验结果。     

Single-shot and lensless complex-amplitude imaging with incoherent light based on machine learning

We present a single-shot incoherent light imaging method for simultaneously observing both amplitude and phase without any imaging optics, based on machine learning. In the proposed method, an object with a complex-amplitude field is illuminated with incoherent light and is captured by an image sensor with or without a coded aperture. The complex-amplitude field of the object is reconstructed from a single captured image using a state-of-the-art deep convolutional neural network, which is trained with a large number of input and output pairs. In experimental demonstrations, the proposed method was verified with a handwritten character database, and the effect of a coded aperture printed on an overhead projector film in the reconstruction was examined. Our method has advantages over conventional wavefront sensing techniques using incoherent light, namely simplification of the optical hardware and improved measurement speed. This study shows the importance and practical impact of machine learning techniques in various fields of optical sensing.     

Two-dimensional synthetic aperture imaging in the optical domain

In scan-mode synthetic aperture imaging radar, spatial resolution in a range is given by a frequency-swept waveform, whereas resolution in the orthogonal direction is derived from the record of phase as the beam footprint executes linear motion over the object. We demonstrate here what is to our knowledge the first two-dimensional imaging that uses exactly this process in the optical domain for a 1 cm x 1 cm object with 90 mumx170 mum resolution.     

Crystal optics as guard apertures for coherent x-ray diffraction imaging

A crucial issue in coherent x-ray diffraction imaging experiments is how to increase the signal-to-noise ratio when measuring relatively weak diffraction intensities from a nonperiodic object. A novel crystal guard aperture is described that makes use of a pair of multiple-bounce crystal optics to eliminate unwanted parasitic scattering background. This background is often produced by upstream optical elements such as a coherent-beam defining aperture. Recent experimental observation and theoretical analysis confirm the effectiveness of the crystal guard aperture method with coherence-preserved wave propagation through the crystal guard aperture and dramatically reduced scattering background in coherent x-ray diffraction images.     

Synthetic aperture fourier holographic optical microscopy

We report a new synthetic aperture optical microscopy in which high-resolution, wide-field amplitude and phase images are synthesized from a set of Fourier holograms. Each hologram records a region of the complex two-dimensional spatial frequency spectrum of an object, determined by the illumination field's spatial and spectral properties and the collection angle and solid angle. We demonstrate synthetic microscopic imaging in which spatial frequencies that are well outside the modulation transfer function of the collection optical system are recorded while maintaining the long working distance and wide field of view.     

Object plane detection and phase-amplitude imaging based on transport of intensity equation

By using transport of intensity equation (TIE), phase distribution of an object is retrieved from through-focus intensity images. This technique allows simple and robust phase imaging compared with an interferometric approach. However, it is hard to measure phase distribution when a dynamic object moves in the direction of an optical axis. To clear this problem, autofocusing TIE which is based on local statistics is proposed. The proposed technique achieves the detection of the object plane and the retrieval of a focused object phase distribution simultaneously. In this approach, an object plane is determined by the focusing techniques based on local statistics such as variance, gradient, and Laplacian of amplitude distribution, after phase distribution in an image sensor plane is retrieved by the TIE. The performance of these three statistics is evaluated in numerical and optical experiments, and a suitable focus value is determined for precise phase imaging.     

Complex Pupil Masks for Aberrated Imaging of Closely Spaced Objects

Current approach demonstrates the suppression of optical side-lobes and the contraction of the main lobe in the composite image of two object points of the optical system under the influence of defocusing effect when an asymmetric phase edges are imposed over the apodized circular aperture. The resolution of two point sources having different intensity ratio is discussed in terms of the modified Sparrow criterion, functions of the degree of coherence of the illumination, the intensity difference and the degree of asymmetric phase masking. Here we have introduced and explored the effects of focus aberration (defect-of-focus) on the two-point resolution of the optical systems. Results on the aberrated composite image of closely spaced objects with amplitude mask and asymmetric phase masks forms a significant contribution in astronomical and microscopic observations.     

Comparative study of different Schlieren diffracting elements

This paper presents an analysis of diffraction effects taking place at different Schlieren diffracting elements. Two types of diffraction effects are prominent in the Schlieren schemes. One is diffraction of direct light (source image) at the Schlieren element, which limits the sensitivity and resolution of Schlieren systems. The second type is the diffraction of light deflected from the test object at the Schlieren-diffracting element. This second type of diffraction degrades the quality of Schlieren results. Experimental results showing the effect of diffraction of light deflected from the test object at a phase knife-edge, corner of a square phase aperture and an optical fiber tip as Schlieren diffracting elements have been presented and discussed.      

Improving the power coupling efficiency in a relay mirror system using a multiple laser array

We propose a new relay mirror system configuration in which the transmitting telescope is composed of an array of tightly tiled sub-apertures. By controlling the piston-type optical phase in each aperture using the stochastic parallel gradient descent (SPGD) algorithm, it is shown that the intensity distribution can be shaped at the receiving plane and that the power coupling efficiency can be improved.     

光学头光束孔径匹配

光学头是光盘存储器的核心部件，光学头光束孔径匹配是光学头设计的一个至关重要的问题。必须合理地确定光源的光束口径与光盘物镜孔径比值，才能保证其光能量耦合效率，并获得较小的光斑尺寸和合理的焦深。本文以衍射光学为基础，详尽地分析了光束孔径匹配对光能耦合效率、光斑尺寸、物镜焦深的影响。     

光学综合孔径成像技术实验研究

根据光学综合孔径成像系统的成像质量与点扩散函数和光学传递函数的关系,以G o lay-3阵列结构为例,从空间域和频率域对光学综合孔径成像技术进行理论仿真和实验研究。在空间域从理论上分析光学综合孔径成像系统的点扩散函数,对复杂目标的成像通过目标函数与点扩散函数的卷积求得,点扩散函数决定了成像质量。通过数值仿真和模拟实验取得了点扩散函数强度分布图,两者分布规律一致证明理论分析正确。在频率域研究光学综合孔径调制传递函数,理论仿真和实验取得的调制传递函数表明,空间域和频率域内光学综合孔径成像技术的理论分析与实验结果具有较好的一致性。