基于面阵 CCD 的航空相机摄影高度自动测量及调焦

目的：实现航空像机摄影高度自动测量和调焦，方法：用小波变换提取面阵CCD图象边缘，用图像特征参数确定成像范围内同一目标在不同CCD面上像的位置和高度。结果：分析了从众多目标中提取目标点的特征参数的方法。给出了设计系统的硬件框图。结论：该方法使爱人旬机调焦自成体系。     

Interferometer for optical coherence tomography

We describe a new interferometer setup for optical coherence tomography (OCT). The interferometer is based on a fiber arrangement similar to Young's two-pinhole interference experiment with spatial coherent and temporal incoherent light. Depth gating is achieved detection of the interference signal on a linear CCD array. Therefore no reference optical delay scanning is needed. The interference signal, the modulation of the signal, the axial resolution, and the depth range are derived theoretically and compared with experiments. The dynamic range of the setup is compared with OCT sensors in the time domain. To our knowledge, the first images of porcine brain and heart tissue and human skin are presented.     

Real-time tricolor phase measuring profilometry based on CCD sensitivity calibration

A real-time tricolor phase measuring profilometry (RTPMP) based on charge coupled device (CCD) sensitivity calibration is proposed. Only one colour fringe pattern whose red (R), green (G) and blue (B) components are, respectively, coded as three sinusoidal phase-shifting gratings with an equivalent shifting phase of 2π/3 is needed and sent to an appointed flash memory on a specialized digital light projector (SDLP). A specialized time-division multiplexing timing sequence actively controls the SDLP to project the fringe patterns in R, G and B channels sequentially onto the measured object in one over seventy-two of a second and meanwhile actively controls a high frame rate monochrome CCD camera to capture the corresponding deformed patterns synchronously with the SDLP. So the sufficient information for reconstructing the three-dimensional (3D) shape in one over twenty-four of a second is obtained. Due to the different spectral sensitivity of the CCD camera to RGB lights, the captured deformed patterns from R, G and B channels cannot share the same peak and valley, which will lead to lower accuracy or even failing to reconstruct the 3D shape. So a deformed pattern amending method based on CCD sensitivity calibration is developed to guarantee the accurate 3D reconstruction. The experimental results verify the feasibility of the proposed RTPMP method. The proposed RTPMP method can obtain the 3D shape at over the video frame rate of 24 frames per second, avoid the colour crosstalk completely and be effective for measuring real-time changing object.     

Comparative study of various endoscopes for pulsed digital holographic interferometry

A comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5-600 micros). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult.     

Microlens characterization by digital holographic microscopy with physical spherical phase compensation

Microlenses have been characterized by a digital holographic microscopy system, which is immune to the inherent wavefront aberration. The digital holographic microscopy system takes advantage of fiber optics and uses the light emitted directly from a single-mode fiber as the recording reference wave. By using such a reference beam, which is quasi-identical to the object beam, the inherent wavefront aberration of the digital holographic microscope is removed. The alignment of the optical setup can be optimized with the help of numerical reconstruction software to give the system phase with the off-axis tilt removed. There is one, and only one, reference fiber point position to give a reference wavefront that is quasi-identical to the object wavefront where the system is free of wavefront aberration and directly gives the quantitative phase of the test object without the need for complicated numerical compensation.     

基于时延估计的海底线阵阵形估计方法研究

阵形估计是水听器阵列应用中的关键问题,基于时延估计的阵形估计方法比基于传感器测量和基于匹配场处理的方法具有更强的适应性和较高的精度。针对浅海水听器阵列中水平长线阵存在的纵向相关振荡现象引起的不能简单以某一阵元为基准求相对时延的问题,充分利用了阵元信号的高相关性,提出了基于子阵时延的阵形估计方法,针对子阵间时延估计误差向阵端累积的问题,该方法以时延估计的克拉美罗界为依据提出了合理的子阵方式,在一定程度上减小了误差传递。对已有海试数据阵形估计处理的结果表明,相对于单源固定间距方法和未分子阵的双源时延估计方法,基于子阵时延的阵形估计方法满足阵元间距的约束,有较好的空间谱特性,减小了阵形估计误差,对长水听器阵列的应用及阵形估计具有较大应用价值。     

Pulsed digital holographic interferometry with 694- and 347-nm wavelengths

A method for deformation analysis and shape measurement based on digital holography is presented. Two wavelengths, 694 and 347 nm, are used. The object is illuminated with the two wavelengths at the same time, and digital holograms are recorded on a CCD chip. The information corresponding to the two wavelengths is separated in the Fourier domain, and the phase corresponding to the wave fronts is calculated. By recording holograms with two different wavelengths at the same time, we can get measurements of deformations or shape with different sensitivities. Experimental results are presented.     

Surface profiling of a transparent object by use of phase-shifting Talbot interferometry

Talbot interferometry is used to study the surface profile of a transparent object. Periodic patterns are produced by illuminating a grating with a collimated laser beam. The object is placed on the self-image plane of the grating. The deformed grating image, which interferes with another grating, results in the Talbot interferometric fringes. The fringe pattern is recorded on a CCD camera for subsequent analysis, and the phase variation is achieved by a linear translation stage. In this application two specimens are tested to demonstrate the validity of the method; one is a transparent object with a spherical shape with a height of less than 350 microm, and the other is a transparent object with an uneven surface of 50-microm average height. The experimental results are compared with the test results obtained with the mechanical stylus method.     

一种新型的OFDM智能天线

根据自适应天线阵列理论，结合给定的参考波束的误差，引入虚拟干扰的概念，对目标波束图形状进行调整，提出一种新的可以应用于任意类型天线阵列的波束综舍算法．应用提出的新算法，在主辩和旁瓣位置都可以对波束进行有效的调节．最终获得阵列的最优权矢量，能够最小化目标波束图与参考波束图间的差异．理论分析与仿真结果表明，与现有的同类算法相比，该算法能更有效地获得与参考波束基本相符的波束．应用于OFDM智能天线系统时，对不同子载波频率上信号进行单独处理，利用该算法进行波束综合，能够在整个有效频段，使所有子载波上获得基本一致的阵列输出．     

Simultaneous measurement of out-of-plane displacement and slope using a multiaperture DSPI system and fast Fourier transform

The simultaneous quantitative measurement of out-of-plane displacement and slope using the fast Fourier transform method with a single three-aperture digital speckle pattern interferometry (DSPI) arrangement is demonstrated. The method coherently combines two sheared object waves with a smooth reference wave at the CCD placed at the image plane of an imaging lens with a three-aperture mask placed in front of it. The apertures also introduce multiple spatial carrier fringes within the speckle. A fast Fourier transform of the image generates seven distinct diffraction halos in the spectrum. By selecting the appropriate halos, one can directly obtain two independent out-of-plane displacement phase maps and a slope phase map from the two speckle images, one before and the second after loading the object. It is also demonstrated that by subtracting the out-of-plane displacement phase maps one can generate the same slope phase map. Experimental results are presented for a circular diaphragm clamped along the edges and loaded at the center.     

Digital speckle techniques for measuring light deflection profiles of inhomogeneous phase objects

Digital speckle pattern photography is applied to the measurement of light deflection profiles of inhomogeneous transparent objects by transmission of a He-Ne laser speckle field through the object. The speckles are recorded with a CCD camera, and the local displacements are evaluated by comparison of the deflected speckle field with the undeflected field by a digital cross-correlation technique. In this way a complete two-dimensional deflection field can be obtained from a single pair of CCD records. The basic technique and two experimental setups suitable for objects with a size larger than that of the CCD chip are described. These novel techniques are applied to determine profiles of the refractive index of a free-burning arc in air. In addition, a cinematographic setup is described, which allows the investigation of transient objects by means of a video tape recorder.     

Sensitivity enhancement of grating interferometer based two-dimensional sensor arrays using two-wavelength readout

Diffraction gratings integrated with microelectromechanical systems (MEMS) sensors offer displacement measurements with subnanometer sensitivity. However, the sensitivity of the interferometric readout may drop significantly based on the gap between the grating and the reference surface. A two-wavelength (2-λ) readout method was previously tested using a single MEMS sensor for illustrating increased displacement measurement capability. This work demonstrates sensitivity enhancement on a sensor array with large scale parallelization (~20,000 sensors). The statistical representation, which is developed to model sensitivity enhancement within a grating based sensor array, is supported by experimental results using a thermal sensor array. In the experiments, two lasers at different wavelengths (633 and 650 nm) illuminate the thermal sensor array from the backside, time-sequentially. The diffracted first order light from the array is imaged onto a single CCD camera. The target scene is reconstructed by observing the change in the first diffracted order diffraction intensity for both wavelengths. Merging of the data from two measurements with two lasers was performed by taking the larger of the two CCD measurements with respect to the reference image for each sensor. ~30% increase in the average sensitivity was demonstrated for a 160×120 pixel IR sensor array. Proposed architecture is also applicable to a variety of sensing applications, such as parallel biosensing and atomic force microscopy, for improved displacement measurements and enhanced sensitivity.     

大型平台变形量实时监测的光电测量方法

本文介绍了一种用于大型平台变形量实时监测的光电测量方法.该方法将线阵CCD作为高度标尺置于各待测位置,利用一字线激光器作为面光源使各不同位置的线阵CCD同时接受同一光束信号,将各线阵CCD收到的高度位置信息采用线性坐标变换为与某一基线(面)重合坐标的标高输出值,并将各种不同载荷条件或不同时刻的高度值数据进行比较,从而得到实时的平台各点相对变形量,该方法在实际应用中取得了较好的效果.     

Experimental investigation of computed tomography sound velocity reconstruction using incomplete data

An approach for reconstructing the sound velocity distribution in the breast was previously proposed and verified by simulations, and the present study investigated the approach experimentally. The experimental setup comprised a 5-MHz, 128-channel linear array, a programmable digital array system, a phantom containing objects with differing physical properties, and a computer. The array system was used to collect channel data for simultaneous B-mode image formation and limited-angle tomographic sound velocity reconstruction. The phantom was constructed from materials mimicking the following tissues in the breast: glandular tissue, fat, cysts, high-attenuation tumors, and irregular tumors. The sound velocities in these materials matched those in the corresponding real tissues. The imaging setup is similar to that of x-ray mammography, in which a linear array is placed at the top of the breast and a metal plate is placed at the bottom for reflecting sound waves. Thus, both B-mode images and the sound velocity distribution can be acquired using the same setup. An algorithm based on a convex programming formulation was used to reconstruct the sound velocity images. By scanning the phantom at different positions, nine cases were evaluated. In each of the nine cases, the image object comprised a background (glandular tissue) and one or three regions of interest (fat, tumor, or cyst). The sound velocity was accurately estimated in the nine cases evaluated, with sound velocity errors being less than 5 m/s in 8 of 11 regions of interest. Thus, obtaining the sound velocity distribution is feasible with a B-mode imaging setup using linear arrays. Knowledge of the sound velocity distribution in the breast can be used to complement B-mode imaging and to enhance the detection of breast cancer.     

Spectral light extinction to characterize fast fog formation

Two supplementary methods for time-dependent droplet sizing, both based on the spectral dependence of light extinction, are applied to an adiabatically expanding vapor in which droplets are formed as a result of heterogeneous condensation. First, by measuring the extinction coefficients at three different wavelengths, we obtain time-dependent values of the modal radius, the size variance, and the droplet number density, with a typical time resolution of 1 μs. The shape of the size-distribution function is investigated by a second method. Using a white-light source in combination with a spectrometer and a CCD array, we obtain the full visible light attenuation spectrum with a time resolution of 1.5 ms. By applying an inversion technique based on trial size distributions, we find that the zeroth-order log-normal distribution describes the fog adequately. Both methods yield the same droplet growth curves and droplet number densities.     

Submicrometer optical tomography by multiple-wavelength digital holographic microscopy

We present a method for submicrometer tomographic imaging using multiple wavelengths in digital holographic microscopy. This method is based on the recording, at different wavelengths equally separated in the k domain, in off-axis geometry, of the interference between a reference wave and an object wave reflected by a microscopic specimen and magnified by a microscope objective. A CCD camera records the holograms consecutively, which are then numerically reconstructed following the convolution formulation to obtain each corresponding complex object wavefront. Their relative phases are adjusted to be equal in a given plane of interest and the resulting complex wavefronts are summed. The result of this operation is a constructive addition of complex waves in the selected plane and destructive addition in the others. Tomography is thus obtained by the attenuation of the amplitude out of the plane of interest. Numerical variation of the plane of interest enables one to scan the object in depth. For the presented simulations and experiments, 20 wavelengths are used in the 480-700 nm range. The result is a sectioning of the object in slices 725 nm thick.     

Two-dimensional imaging without scanning by multifocal multiphoton microscopy

We describe multifocal multiphoton microscopy giving images without laser scanning. A multitude of 8 x 8 laser beams is focused into a sample yielding two-photon excitation in a plane. The focal spots are arranged in a rectangular array with close spacing between individual points (approximately 0.5 microm). The fluorescence emission from the sample is recorded with a CCD camera, but, owing to the close distance between the beams, they can no longer be regarded as individual points but rather as an illumination of the plane that is covered by the array of focal points. The axial sectioning capability is comparable with an ordinary single-beam two-photon microscope. Interference between the beams that could compromise the axial sectioning capability does not occur in our setup owing to small temporal delays between the individual beams. The axial sectioning capability of the setup is discussed in detail by means of the step response in which the foci are scanned axially into a uniformly fluorescent medium.     

Short-coherence digital microscopy by use of a lensless holographic imaging system

An optical system based on short-coherence digital holography suitable for three-dimensional (3D) microscopic investigations is described. The light source is a short-coherence laser, and the holograms are recorded on a CCD sensor. The interference (hologram) occurs only when the path lengths of the reference and the object beam are matched within the coherence length of the laser. The image of the part of the sample that matches the reference beam is reconstructed by numerical evaluation of the hologram. The advantages of the method are high numerical aperture (this means high spatial resolution), detection of the 3D shape, and a lensless imaging system. Experimental results are presented.     

Spatial filtering in digital holographic microscopy

Abstract

An optical system based on digital holography suitable for microscopic investigations is described. A lensless digital hologram of the object under test is recorded on a CCD faceplate. The reference point source and the object are equidistant from the CCD. The point source for the illumination of the transparent microscopic object is located in another plane some millimetres behind the object. For digital reconstruction of the wavefronts the Sommerfeld propagation relation is used. The particular recording arrangement allows one to perform spatial filtering. Examples of amplitude filtering are presented.