Wavefront Processing Research Articles

Adapting wave-front algorithms to efficiently utilize systems with deep communication hierarchies

Large-scale systems increasingly exhibit a differential between intra-chip and inter-chip communication performance especially in hybrid systems using accelerators. Processor-cores on the same socket are able to communicate at lower latencies, and with higher bandwidths, than cores on different sockets either within the same node or between nodes. A key challenge is to efficiently use this communication hierarchy and hence optimize performance. We consider here the class of applications that contains wave-front processing. In these applications data can only be processed after their upstream neighbors have been processed. Similar dependencies result between processors in which communication is required to pass boundary data downstream and whose cost is typically impacted by the slowest communication channel in use. In this work we develop a novel hierarchical wave-front approach that reduces the use of slower communications in the hierarchy but at the cost of additional steps in the parallel computation and higher use of on-chip communications. This tradeoff is explored using a performance model. An implementation using the reverse-acceleration programming model on the petascale Roadrunner system demonstrates a 27% performance improvement at full system-scale on a kernel application. The approach is generally applicable to large-scale multi-core and accelerated systems where a differential in communication performance exists.

基于FPGA的自适应光学系统波前处理机

In accordance with the need of a larer ground-based high resolution imaging telescope for adaptive optical wave-front processing,an Adaptive Optical(AO) wave-front processing system with larger calculation and thousands of units was designed based on the Field Programming Gate Array(FPGA) and its operation scheme,implement processing and tested results were given.At the software,the FGPA was used to configure and control data and to realize the conversion and transmission of multi-channel D/A data synchronously.Meanwhile,the FPGA was taken as a key element to preprocess the image and calculate the wave-front gradient of a sub-aperture.With satisfied wave-front processing precisions,it shortens wave-front processing delay and improves the ability of wave-front processing.Results demonstrate that the system can achieve the wave-front processing in 2 000 frame/s.At the hardware,this system combined the wave-front processing host board and wave-front processing sub board to improve the output ability of the system.As each wave-front processing sub board can promote the output of 120 road and the maximum expansion capacity of the main board is 10,the system can reach the momentum of the output in 1 200 road.

可扩展式自适应光学系统波前处理器的硬件设计

For the need of lager ground-based high resolution EO imaging telescope adaptive optics wave-front processing,thousands of units AO wave-front processing system is required to design.In this paper,an extendible adaptive optics wave-front processor has been presented.This system uses wave-front processing host board and wave-front processing sub board,and can realize expansion according to the scale of adaptive system.Each wave-front processing sub board can promote the output of 120 roads,with the maximum expansion capacity of 10,the system can reach 2 000 frames/s sampling and processing frequency and promote the momentum of the output of 1 200 roads.This article gives a detailed design,implementation and test results.

The study of color digital holography free from the zero-order diffraction interruption

In the study of color digital holography, using the spherical wave as the reconstruction wave, the wave-front reconstruction with the angular spectrum diffraction formula is an effective approach. However, this method is usually accompanied by intense zero-order diffraction interruption. In this paper, based on the theoretical analysis, an important modification of the wave-front reconstruction process has been made. The color digital holography experiment result demonstrated that the quality of reconstructed color image has been improved remarkably with this modified method.

Nonlinear optics and liquid crystal light valve for laser beam control

The recent advances in solid state laser technology now permit to achieve high energy and efficiency sources for a wide range of applications extending from laser physics to material processing, biophotonics, remote sensing and coherent lidar systems. In particular the progress of fibre laser exploiting the double clading diode pumping structure are impressive: they are compact and emit single mode beams. However optical damage and nonlinear effects limit the output peak power emitted by a single mode fiber laser. Also limitations arise in bulk laser materials due to the thermal loading which induces strong wavefront distortions on the beams. We develop in this paper original concepts adapted to power-energy scaling of bulk or fibre lasers. The final objective is to emit high brightness and high energy beams whose quality is close to the diffraction limit. For this purpose we present new technics to be inspired from from Fourier optics and allowing the wavefront processing either through nonlinear interactions or with adaptive optical components such as electro optic phase modulators or liquid crystal light valves.

A novel method of high resolution imaging through random perturbation wave front

A novel method is proposed for eliminating the effect of the traditional optical aberration on high resolution imaging by random perturbation wave front and digital image processing. A random phase mask, whose phase spectrum fluctuation is accordant with Kolmogorov distribution, is positioned near the aperture stop of optical system, making the optical aberration image become random perturbation image, that is, the intermediate image. The blind deconvolution algorithm based on maximum-likelihood estimation technique is used to restore the intermediate image acquired by a digital detector. The effects of optical aberrations and the noise on the restoration image are explored. To demonstrate the validity of the method proposed, the computer simulation and laboratory experiments are carried out for the imaging of the optical system with primary aberration. The results have shown that the present method is well suited for effectively improving the imaging quality of the optical system with certain aberration, thus making the optical system resolution close to or reach the diffraction-limit of the optical system.

A wide-angle polymeric Y-junction using gradient-index (GRIN) zones

We propose a new class of Y-junctions based on wavefront processing to facilitate phase matching during branching. This is achieved by grading the lateral index profile of the waveguides. Simulations show that, at 85% power transmission, when compared to an all step-profile truncated-structural Y-branch (TSYB) that we proposed earlier, it widens the full branching angle by 1.5°. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 126–129, 1999.

Wave-front processing through integrated fiber optics

We process an optical wave front emanating from a monomode optical fiber by fusion splicing several small sections of step-index and graded-index multimode optical fibers. In this way a wave front of an optical wave can be engineered without its leaving the optical fiber. Results for several integrated coherent imaging delivery systems are presented.

Error detection in arrays via dependency graphs

This paper describes a methodology based on dependency graphs for doing concurrent run-time error detection in systolic arrays and wavefront processors. It combines the projection method of deriving systolic arrays from dependency graphs with the idea of input-triggered testing. We call the method ITRED, forInput-driven Time-Redundancy Error Detection. Tests are triggered by inserting special symbols in the input, and so the approach gives the user flexibility in trading off throughput for error coverage. Correctness of timing is proved at the dependency graph level. The method requires no extraPEs and little extra hardware. We propose several variations of the general approach and derive corresponding constraints on the modified dependency graphs that guarantee correctness. One variation performs run-time error correction using majority voting. Examples are given, including a dynamic programming algorithm, convolution, and matrix multiplication.

Microwave Imaging Techniques for Non-Destructive Testing of Materials

ABSTRACTRecent technological advances for microwave multiport sensors lead us to look for efficient wavefront processing techniques in order to improve image quality, in terms of spatial resolution and contrast. This paper reviews some of these techniques which can be used for Non-Destructive Testing purposes. Mutual advantages and limitations are analysed.

Microwave tomography: From theory to practical imaging systems

AbstractThis paper deals with numerical processing techniques and practical applications of active microwave imaging. Different wavefront processing are presented, from an immediate use of measured projections to more complex procedures. Both spectral approaches to diffraction tomography and spatial iterative methods for generalized imaging are considered using multi‐incidence of multifrequency techniques for 3D and/or 2D objects. The technology of the so‐called microwave camera is presented for the fast recording of the scattered field with arrays of probes involving one‐ or two‐dimensional sensors at a single frequency or in a broad‐frequency band. Three different systems are depicted: a single‐frequency linear sensor devoted to industrial applications (on‐line transverse control of conveyed products), a single‐frequency planar microwave camera for biomedical applications and research, and a broad‐frequency linear microwave camera for civil engineering applications (detection of the rebars in reinforced concrete strctures). Microwave images obtained experimentally with the three systems are presented on configurations of practical interest for each field of application.

The mapping of 2-D array processors to 1-D array processors

We consider the case of a 2-dimensional wavefront array processor where only one wavefront appears at any time. We show that in such a situation, this 2-dimensional wavefront processor can be mapped to a linear array processor if the wavefronts never backtrack. The mapping will not increase the number of registers in each processor element. Two examples, the spoken words recognition problem and the longest common subsequence problem, are given to demonstrate the feasibility of this method.

Experience with occam for simulating systolic and wavefront arrays

The use of occam as a simulation language for systolic and wavefront processor arrays is described. Partitioning problems which may arise are discussed and their implications for Transputer systems assessed. General principles for parallel simulation in occam are discussed, and occam is compared with other languages in this context.

Wavefront processing of radio-frequency wavefront data

A class of special-purpose processors is described. These processors are for use in holographic imaging systems that utilize electromagnetic waves with radio frequencies. The systems, which operate in very nearly real time, consist of arrays of receiving antennas with a receiver at each antenna. The received intensities control modulation in a second array of antennas that radiate waves generated by a coherent source at a frequency higher than the received waves. The processors are wavefront processors in two senses because they process received wavefronts and because the data flow resembles a wavefront. The processors are data driven so they require no clock, and they operate in parallel. Measurements with a prototype system are described, and a diffraction theory analysis of images is given. Extension to phase receivers and holograms are described, along with a discussion of visible image production in real time.

Efficient Solution of Load-Deflection Equations

Load deflection equation solution based on row operations, involving three passes of coefficient matrix, using wavefront processing and modified Gauss algorithm

Moiré-fringe multiplication by means of filtering and a wave-front reconstruction process

Two principal problems associated with the practical application of moire fringes are to obtain sufficient sensitivity for measuring small strains and to develop a simple and inexpensive technique for engraving lines on the surface of a model. This paper deals with simple solutions to both problems. It is shown that the maximum number of fringes that can be observed for a given model is independent of the gratings utilized and depend only on the geometry of the employed optical system. Examples of moire patterns corresponding to the equivalent of 6000 lines per inch and patterns of the derivatives of the displacements corresponding to the same number of lines illustrate the paper.