Tomographic reconstruction of asymmetric soot structure from multi-angular scanning

A tomographic deconvolution technique using the Fourier transformation has been applied for the reconstruction of asymmetric soot structure. Local soot volume fraction distribution can be identified from line-of-sight integrated data using light extinction measurements with multi-angular scanning. A peak-following interpolation technique was adopted to effectively increase the number of scanning angles. The results showed that the peak-following interpolation has improved the accuracy of reconstruction compared to the arithmetic interpolation in determining the local soot volume fraction. The measurement from a laser-induced incandescence technique substantiated the validity of the reconstruction technique.     

Interpolation Method for Computer-Generated Holograms Using Random Phase Technique

An interpolation method for reconstructed images of computer-generated holograms (CGHs) enables one to synthesize CGHs with a large space bandwidth product (SBWP) from CGHs with a small SBWP. The phase information of objects is regarded as constant because the method is based on digital image processing techniques. Therefore, diffraction efficiency is low due to the saturation effect in the recording process. To improve the diffraction efficiency, a random phase technique is employed for the interpolation method to the CGH. Effects of the random phase in the reconstructed image are discussed in several interpolation types. The interpolation method is also applied to a kinoform. Some computer simulations and optical experiments are presented.     

Low optical insertion-loss and vacuum-pressure all-fiber acetylene cell based on hollow-core photonic crystal fiber

We report a novel and easy-to-implement hollow-core photonic crystal fiber cell fabrication technique based on helium diffusion through silica. The formed gas cells combine low optical insertion loss (1.8 dB) and vacuum acetylene pressure (microbar regime). The estimates of the final gas pressure, using both Voigt interpolation and electromagnetically induced transparency, show a good match with the initial fitting pressure.     

On the determination of elastic residual strain fields in rail wheels using moiré interferometry

Moiré interferometry was used to determine the residual strain fields in a rail wheel. Hoop, radial, and shear displacement fields were determined in a whole field manner using a novel four-beam moiré interferometer. Diffraction gratings of 150 lines/mm were employed on the specimen surface. A system of data interpolation utilizing a simple control sample scheme was developed for field environments where sample loading occurs away from the optical device. Agreement was found between the moiré technique and physical measurements of wheel contraction during sectioning. Marginal agreement was found with strain gage measurements.     

Improving motion estimation by accounting for local image distortion

Cardiac elastography is a useful diagnostic technique for detection of heart function abnormalities, based on analysis of echocardiograms. The analysis of the regional heart motion allows assessing the extent of myocardial ischemia and infarction. In this paper, a new two-stage algorithm for cardiac motion estimation is proposed, where the data is taken from a sequence of 2D echocardiograms. The method combines the advantages of block-matching and optical flow techniques. The first stage employs a standard block-matching algorithm (sum of absolute differences) to provide a displacement estimate with accuracy of up to one pixel. At the second stage, this estimate is corrected by estimating the parameters of a local image transform within a test window. The parameters of the image transform are estimated in the least-square sense. In order to account for typical heart motions, like contraction/expansion, translation and rotation, a local affine model is assumed within the test window. The accuracy of the new algorithm is evaluated using a sequence of 500 grayscale B-mode images, which are generated as distorted, but known copies of an original ROI, taken from a real echocardiogram. The accuracy of the motion estimation is expressed in terms of errors: maximum absolute error, root-mean-square error, average error and standard deviation. The errors of the proposed algorithm are compared with these of the known block-matching technique with cross-correlation and interpolation in the sub-pixel space. Statistical analysis of the errors shows that the proposed algorithm provides more accurate estimates of the heart motion than the cross-correlation technique with interpolation in the sub-pixel space.     

Improving motion estimation by accounting for local image distortion

Cardiac elastography is a useful diagnostic technique for detection of heart function abnormalities, based on analysis of echocardiograms. The analysis of the regional heart motion allows assessing the extent of myocardial ischemia and infarction. In this paper, a new two-stage algorithm for cardiac motion estimation is proposed, where the data is taken from a sequence of 2D echocardiograms. The method combines the advantages of block-matching and optical flow techniques. The first stage employs a standard block-matching algorithm (sum of absolute differences) to provide a displacement estimate with accuracy of up to one pixel. At the second stage, this estimate is corrected by estimating the parameters of a local image transform within a test window. The parameters of the image transform are estimated in the least-square sense. In order to account for typical heart motions, like contraction/expansion, translation and rotation, a local affine model is assumed within the test window. The accuracy of the new algorithm is evaluated using a sequence of 500 grayscale B-mode images, which are generated as distorted, but known copies of an original ROI, taken from a real echocardiogram. The accuracy of the motion estimation is expressed in terms of errors: maximum absolute error, root-mean-square error, average error and standard deviation. The errors of the proposed algorithm are compared with these of the known block-matching technique with cross-correlation and interpolation in the sub-pixel space. Statistical analysis of the errors shows that the proposed algorithm provides more accurate estimates of the heart motion than the cross-correlation technique with interpolation in the sub-pixel space.     

激光干涉任意转角测量信号的获得及误差补偿技术

采用信号处理的方法对激光干涉测角系统的特性进行线性化处理,需要产生两路正交信号。采用空间互相垂直的两套干涉系统获得信号难免会使系统复杂、调整困难,因此提出了一种插值处理方法,可以利用测量得到的一路信号获得线性输出信号。输出信号的非线性误差较处理前大大减小了,但是无法满足高精度测量的要求。还提出了针对误差产生的原因进行的误差补偿技术。实验结果表明,提出的方法可以实现任意转角的高精度测量,光程差的测量误差小于±0 2μm,对应的转角测量误差为0 63″。     

Inversion of visible optical extinction data for spheroid particle size distribution based on PCA

The problem of light scattering properties of spheroid particles is studied, and a general approach is presented for calculating the single particle light scattering of spheroids. In this approach, the extinction efficiency of spheroid particles can be calculated by combining the spline interpolation of T matrix method and ADA (anomalous diffraction approximation) theory. Furthermore, the retrieval of spheroid particle size distribution is performed in the dependent mode and a selection method about the optical extinction data is proposed based on PCA (principle component analysis) of first derivative corresponding to the raw optical extinction. By calculating the contribution rate of first derivative corresponding to the raw optical extinction, the optical extinction with more significant features can be selected as the inversion optical extinction data. In this way, the selected optical extinction has less information redundancy and higher capacity of resisting noise disturbance. Simulation experiments indicate that the spheroid particle size distributions obtained with the proposed method coincide fairly well with the given distributions, which provides a simple, reliable and efficient method to retrieve the spheroid particle size distribution using the optical extinction data.     

基于三次样条插值的光纤F-P传感器傅里叶变换解调研究

从傅里叶变换原理入手,对不插值傅里叶变换解调和高斯频谱插值方法的误差进行了分析.介绍了三次样条插值的原理,通过三次样条插值得到输出光强信号对光频率均匀采样光谱.从光纤F-P传感器的腔长由20 μm以0.02 μm步长匀速增加至120 μm的仿真分析得出,经过三次样条插值后再进行傅里叶变换解调的精度相对频率插值法更高.在此基础上,采用美国Ocean Optics公司生产的USB2000型光谱仪和Melles Griot公司的17MAX600型光纤对准微动台(精度达0.01 μm)搭建了实验系统并进行了对比实验.结果表明,基于三次样条插值的傅里叶变换解调方法误差在0.06 μm以内.     

一种新的截断线及标志点处缺失相位插补方法

在基于相位信息的三维面形测量中,为了得到正确的相位展开而引入的截断线和为了便于三维拼接而附加在物体表面的标志点都会造成其覆盖区域的相位缺失,需要进行人为地插补修复。一种新的缺失相位插补方法——八方向梯度估算法,通过计算待插补点周围八方向梯度和其八邻域内的相位平均值,可估算出缺失的相位。与其它常用缺失相位插补方法相比,该方法运算速度快、插补效果好,运算过程无需人为参与,便于计算机自动实现,尤其适合于插补倾斜相位面上的较大标志点,有助于提高相位重建质量和在此基础上的三维面形重建质量。     

光学元件表面频谱分布影响因素的分析方法

 精密光学系统对光学元件的表面频谱误差的分布提出了控制要求,在加工中如何检测和控制光学元件表面的频谱分布成为一个新的问题。利用功率谱密度对频率的定量化描述功能,对检测数据进行样条插值,在同一极坐标系下计算功率谱密度,求取功率谱密度比值信息,分析小磨具技术的加工工具性能、形状及其运动方式对光学元件表面的频率分布影响。指出在加工中合理地改变加工参数可以快速有效地控制元件表面频谱的分布特征。在670 mm大口径非球面镜加工中做了验证。     

Performance of laser-ultrasonic F-SAFT imaging

The resolution and signal-to-noise ratio of laser-ultrasonics to detect small and buried defects can be greatly enhanced by using the synthetic aperture focusing technique (SAFT). Originally developed in the time domain, SAFT can also be implemented in the frequency domain (F-SAFT) using the angular spectrum approach for a significant reduction in processing time. In this paper, an F-SAFT based data processing method especially adapted to laser-ultrasonic data is presented. This method allows for further significant improvements towards laser-ultrasonic imaging of small defects. It includes temporal deconvolution of the waveform data, control for an optimal aperture and frequency bandwidth as well as spatial interpolation of the subsurface images. All the above operations are well adapted to the frequency domain calculations and embedded in the F-SAFT data processing. Also, the aperture control and spatial interpolation allow a reduction of sampling requirements to further decrease both inspection and processing times. The above improvements are illustrated using laser-ultrasonic data taken from an aluminum sample with flat-bottom holes.     

Phase ripple correction: theory and application

Spectral phase ripple associated with novel dispersive devices can distort broadband optical signals. We present a digital postprocessing algorithm to correct for this distortion by exploiting the static deterministic nature of the ripple. This algorithm is demonstrated with empirical data for several systems employing chirped fiber Bragg gratings (CFBGs). We employ this technique in a photonic time-stretch system incorporating CFBGs, improving the signal fidelity by 9 dB. Simulations and experiments show that this algorithm, which can be reduced to a simple interpolation and matrix multiplication, also mitigates additive noise. We see that the act of distortion correction yields signal fidelity superior to that of an ideal dispersive element.     

A multirate scan conversion method

B-mode ultrasonic imaging requires that the acquired polar coordinate ultrasound data be converted to the Cartesian format used by digital monitors. Image quality depends on the interpolation algorithm used to this purpose. In this work a selective sampling technique, based on acquiring data at specific points of the scanned area together with a straightforward linear interpolation step, is proposed. Hardware complexity is avoided, because the interpolation task can be carried out by software in real time, concurrently with data acquisition. The performances of the proposed approach are analysed with regard to those provided by other algorithms and some implementation issues are addressed.     

一种用于光机热集成分析的新方法——干涉图插值法

Zernike多项式是光机热集成分析中实现光、机、热各分析软件之间数据传递的重要工具。许多光学元件表面形状并不满足Zernike多项式的正交性条件，使有限元分析不能精确拟合光学元件表面变形及变形产生的各项像差。讨论影响Zernike正交性的几个因素，详细介绍将有限元分析得到的光学表面变形数据导入光学分析软件的一种新方法——干涉图插值法。该方法避开Zernike多项式拟合，在去除镜面刚体位移后将镜面畸变精确地表示成干涉图数据，直接生成数据接口。     

Novel Technique for All-Optical Clock Extraction Using Fiber Bragg Gratings

We demonstrate a simple passive technique, using phase shifted fibre Bragg gratings, for extraction of optical clock signals from RZ optical data signals . The generation of an optical clock signal at 12.5 GHz from a 12.5 Gbs RZ optical data stream is experimentally demonstrated with simulation of optical clock extraction at 10 GHz fro m 40 Gbs OTDM data streams .     

扩散张量图像的插值方法综述

扩散张量成像能够通过获得组织内水分子的三维位移分布来研究脑部结构，是近年来医学成像技术的研究热点.在采集、转换以及处理张量的进程中，研究者需要进行插值处理来提高图像分辨率或改善可视化效果.如在人脑模板构建、脑白质纤维追踪以及配准等应用中，张量插值是一个具有重要作用的处理步骤.本文对现有的张量插值方法进行综述，首先介绍了插值方法的理论内容，阐明各张量插值方法中所解决的技术问题及存在的局限性，然后介绍了常用的插值方法的评估指标，再利用现有的典型插值方法分别对仿真数据和真实数据进行插值实验和结果分析，最后对张量插值方法的未来发展趋势提出建议.     

Swept source optical coherence tomography based on non-uniform discrete fourier transform

A high-speed high-sensitivity swept source optical coherence tomography （SSOCT） system using a high speed swept laser source is developed. Non-uniform discrete fourier transform （NDFT） method is introduced in the SSOCT system for data processing. Frequency calibration method based on a Mach-Zender interferometer （MZI） and conventional data interpolation method is also adopted in the system for comparison. Optical coherence tomography （OCT） images from SSOCT based on the NDFT method, the MZI method, and the interpolation method are illustrated. The axial resolution of the SSOCT based on the NDFT method is comparable to that of the SSOCT system using MZI calibration method and conventional data interpolation method. The SSOCT system based on the NDFT method can achieve higher signal intensity than that of the system based on the MZI calibration method and conventional data interpolation method because of the better utilization of the power of source.     

Accurate definition of correlation peak position by optical speckle-displacement correlation technique

An optical speckle-displacement correlator based on hybrid optical–digital joint transform correlator architecture with a digital first stage and an optical second stage has been used to determine the correlation peak position with subpixel accuracy, without the use of intricate interpolation algorithms. A thorough analysis and a calculation of the parameters of the second optical stage are performed in order to achieve the necessary magnification of the correlation peak, so as to obtain an accurate definition of the peak position. The experiment setup for the realization of the optical speckle-displacement technique was constructed with a digital Fourier processor as its basic component, making possible a joint power spectrum median and ring median binarization, and an optical Fourier processor. The results which were obtained demonstrate that a setup of this kind can produce sharp and narrow correlation peaks, and can provide the necessary magnification for finding the peak position with subpixel accuracy.     

增量式轴角编码器的电子细分及零位处理

使用单片机对增量式光电轴角编码器产生的叠栅条纹信号进行计数和电子细分,便可将轴的机械转动模拟量转换成数字量;加上固定参考零位后,可使编码器具有"记忆"功能,因此对如何解决零位技术问题做了详细分析说明,并给出了实际解决方案.