Real-time heterodyne speckle pattern interferometry using the correlation image sensor

A real-time method for heterodyne speckle pattern interferometry using the correlation image sensor (CIS) is proposed. The CIS demodulates the interference phase of heterodyned speckle wavefronts pixelwise at an ordinary video frame rate. The proposed method neither suffers loss of spatial resolution nor requires a high frame rate. Interferometers for out-of-plane and in-plane deformation are developed with a 200 × 200 pixel CIS camera. Experimental results confirm that the proposed method realizes real-time imaging of a rough-surfaced object under deformation. The average standard deviations of demodulated phase-difference images for the out-of-plane and in-plane interferometers are 0.33 and 0.13 rad, respectively.     

Measurement of ultrasonic pressure by heterodyne interferometry with a fiber-tip sensor

A fiber-optic measurement system is described that allows ultrasound to be detected in fluids. It is based on a heterodyne interferometer, and the sensing element consists of a metal-coated fiber tip. The heterodyne technique permits direct acquisition of the sound pressure. The required ac photodetection is carried out with wide bandwidth, and the system provides high temporal and spatial resolution. For optimum performance the system parameters are matched to the sound-wave properties of the current application with the aid of theoretical and numerical calculations. The fiber-optic sensor system was applied to two problems of ultrasonic exposimetry in which the favorable features of the measurement technique were exploited. Shock waves from an electromagnetic lithotripter were investigated by use of the wide bandwidth of the system, and the subharmonic in an ultrasonic cleaner was detected, which indicates cavitation.     

Isochromatics demodulation from a single image using the regularized phase tracking technique

Abstract

In this work we propose a robust fringe demodulation technique applied to the analysis of a single isochromatics fringe pattern produced in photoelasticity. The method used is a regularized phase tracking algorithm with a new sequential scanning technique specifically adapted for the characteristics of the isochromatic fringe patterns: possible apparition of closed fringes, large dynamic range in its spatial frequency content and low noise. The performance of the method is discussed and experimental results are presented.     

Efficiency of capturing a phase image using cone-beam x-ray Talbot interferometry

We assesses the efficiency of x-ray Talbot interferometry (XTI), a technique based on the Talbot effect for measuring a wavefront gradient, in terms of how quickly it can capture a high-quality phase image with a large signal-to-noise ratio for a given incident photon number. Photon statistics cause errors in the phase of the moiré fringes and impose a detection limit on the wavefront gradient. The relation between the incident photon number and the detection limit is determined, and a figure of merit of XTI for a monochromatic cone beam is then defined. The dependence of the figure of merit on optical system parameters, such as grating pitch and position, is then discussed. The effects of varying the pattern height and linewidth of the second grating are shown for rectangular and trapezoidal teeth. Finally, we show how to design a practical cone-beam Talbot interferometer for certain boundary conditions.     

Comparative study of autodyne and heterodyne laser interferometry for imaging

For given laser output power, object under investigation, and photodiode noise level, we have theoretically compared the signal-to-noise ratios of a heterodyne scanning imager based on a Michelson interferometer and of an autodyne setup based on the laser optical feedback imaging (LOFI) technique. In both cases, the image is obtained point by point. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity (i.e., directly on the detector), while in the autodyne configuration, the wave beating takes place inside the laser cavity and therefore is indirectly detected. In the autodyne configuration, where the laser relaxation oscillations play a leading role, we have compared one-dimensional scans obtained by numerical simulations with different lasers' dynamical parameters. Finally, we have determined the best laser for LOFI applications and the experimental conditions for which the LOFI detection setup (autodyne interferometer) is competitive compared to a heterodyne interferometer.     

High-sensitivity small-angle sensor based on surface plasmon resonance technology and heterodyne interferometry

A high-sensitivity small-angle sensor based on surface plasmon resonance technology and heterodyne interferometry is proposed that uses a new technique with two right-angle prisms. Interestingly, the technique provides a novel method for designing small-angle sensors with high sensitivity and high resolution. Its theoretical resolution can reach 1.2x10(-7) rad over the measurement range of -0.15 degrees < or =theta< or =0.15 degrees . The method has some merits, e.g., a simple optical setup, easy operation, high resolution, high sensitivity, and rapid measurement. Its feasibility is demonstrated.     

Hybrid retinal image registration using phase correlation

Abstract

This paper deals with registration of retinal images, which were taken by high-resolution digital colour fundus cameras. The proposed method describes successful application of phase correlation method. It combines several basic steps — global correction of shift, rotation and scaling, detection of landmarks, their correspondences and finally image registration using second-order polynomial model. The method is tested on two sets of images. The first set contains images from the diabetic patients where many retinal pathologies can disturb the registration process. The second set contains images from healthy subjects, which were acquired by different illumination conditions. The method was evaluated using four different criteria - tree objective and one subjective. These criteria are also compared. The achieved registration accuracy of the landmarks position error is 1·13 and 0·93 pixels for respective image sets. Finally, the simple scheme for retinal pathology visualisation of registered fundus pairs is presented.     

基于相位解调的光纤MEMS压力传感器

提出了一种新的压力传感器,该传感器基于Fabry-Perot腔干涉和相位解调理论测量压力。设计用MEMS技术以及普通的光通讯接插件制作出工艺简单,分辨率高的光纤MEMS压力传感器。阐述了传感器的工作原理,分析了硅膜的厚度对传感器性能的影响以及FP腔的长度对反射光信号的影响。研究了基于相位解调法的傅里叶变换方法,傅里叶解调法受光源强度波动的影响较小,解调精度高。实验结果表明改传感器在[0-3]MPa测量范围内,线性好,灵敏度可达到3.50 m/MPa（腔长改变/压力）。     

幅值和相位解调的行星架裂纹故障特征提取

在介绍行星架裂纹故障对行星齿轮箱振动信号影响的基础上,结合同步平均、振动分离和窄带解调技术,提出一种基于幅值、相位解调的行星架裂纹故障特征提取方法。该方法对原始振动信号进行角域同步平均,消除转速波动、行星轮等其他旋转部件的影响;通过振动分离技术重构信号,并对重构信号进行同步平均得到行星架振动分离信号;通过窄带解调获得行星架的幅值和相位特征。通过观察幅值和相位的变化,提取行星架裂纹故障特征。行星齿轮箱故障实测信号分析结果表明该方法可有效提取行星架裂纹故障特征。     

Quantitative phase imaging using four interferograms with special phase shifts by dual-wavelength in-line phase-shifting interferometry

A new approach of quantitative phase imaging using four interferograms with special phase shifts in dual-wavelength in-line phase-shifting interferometry is presented. In this method, positive negative 2π phase shifts are employed to easily separate the incoherent addition of two single-wavelength interferograms by combining the phase-shifting technique with the subtraction procedure, then the quantitative phase at one of both wavelengths can be achieved based on two intensities without the corresponding dc terms by the use of the character of the trigonometric function. The quantitative phase of the other wavelength can be retrieved from two dc-term suppressed intensities obtained by employing the two-step phase-shifting technique or the filtering technique in the frequency domain. The proposed method is illustrated with theory, and its effectiveness is demonstrated by simulation experiments of the spherical cap and the HeLa cell, respectively.     

In-plane dynamic speckle interferometry: comparison between a combined speckle interferometry/speckle correlation and an update of the reference image

A common problem during study of, for instance, tensile tests with interferometers is that the sample moves too much so that the speckles decorrelate and no phase information is obtained. Two ways to overcome this problem are compared: a combination of speckle interferometry and speckle correlation and a method in which the reference image is updated during the experiment. The comparison shows that both techniques can be used to measure the deformation of an object even if it is exposed to rigid body motions. Both techniques are applied to measurements of microscale deformation fields of an adhesive joint in a carbon-fiber epoxy composite.     

Coherent imaging with two-dimensional focal-plane arrays: design and applications

Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images.     

Homodyne and heterodyne signal processing assisted phase resolved optical technique for latent fingerprint imaging: a theoretical study

A general theory for phase-resolved fingerprint imaging and background suppression based on laser-induced fluorescence is developed and presented in this paper. Novel approaches of incorporating an even-step phase shifting method with a homodyne-assisted phase-resolved method as well as the camera exposure control approach for the heterodyne-assisted phase-resolved method are proposed, theoretically formulated and discussed. Theoretical results imply that the fluorescence from latent fingerprints can be extracted effectively, irrespective of whether its lifetime is longer than that of the background or not. Furthermore, it is shown that there exists an optimum modulation frequency, which is dependent on the fluorescence lifetimes of both the background and the fingerprint, to obtain a fingerprint image with better contrast.     

Real-time volume imaging using a crossed electrode array

This paper describes a unique crossed electrode array for real-time volume ultrasound imaging. By placing orthogonal linear array electrode patterns on the opposite sides of a hemispherically shaped composite transducer substrate, a 2D array can be fabricated using a small fraction of the elements required for a traditional 2D array. The performance of the array is investigated using a computer simulation of the radiation pattern. We show that by using a 288-element crossed electrode pattern it is possible to collect large field of view volume images (60deg times 60degsector) at real-time frame rates (>20 volume images/s), with image contrast and resolution comparable to what can be obtained using a conventional 128-element linear phased array.