Conversion of phase modulation of light into intensity modulation by means of an external fiber-optic interferometer

A new method of detecting phase modulation, based on using an “external” optical waveguide interferometer, is considered. This “detection” is weakly dependent on the length, position, and external conditions of the propagation channel for the phase-modulated light and, in many cases may prove more efficient than conventional methods of constructing phasemodulated fiber-optic systems. Pis’ma Zh. Tekh. Fiz. 23, 9–16 (May 26, 1997)     

Parallel processing techniques for the speckle brightness phase aberration correction algorithm

The speckle brightness adaptive algorithm has previously been implemented in approximately real-time on low frequency, one-dimensional arrays. To increase the speed of this technique, a temporally parallel algorithm and a spatially parallel algorithm are described. Theoretical analyses, simulation results and experimental measurements are presented for these algorithms. Theoretical predictions indicate that these techniques increase the correction speed, but some decrease in the accuracy of the compensating phase estimate occurs. Simulation results indicate that these parallel algorithms perform well at removing the effects of phase aberration. Preliminary experimental measurements demonstrate the correction speed improvements achievable with these algorithms.     

Compensation for time fluctuations of phase modulation in a liquid-crystal-on-silicon display by process synchronization in laser materials processing

We demonstrate the adverse influence of temporal fluctuations of the phase modulation of a spatial light modulator (SLM) display device on nanosecond laser micromachining. We show that active cooling of the display reduces the amplitude of these fluctuations, and we demonstrate a process synchronization technique developed to compensate for these fluctuations when applying the SLM to laser materials processing. For alternative SLM devices developed specifically for laser wavefront control (which do not exhibit such flickering problems), we show that our process synchronization approach is also beneficial to avoid machining glitches when switching quickly between different phase profiles (and hence beam patterns).     

Measurement of phase objects by simple means

A printed fringe pattern is imaged by a CCD camera, whereas a phase object is placed in the ray path for imaging. The ray deflections distort the image of the pattern and are measured by evaluation of the image with the Fourier transform method.     

Moire technique by means of digital image processing

Moiré technique by means of projected fringes is a suitable method for full field measurements of out-of-plane deformations and object contouring. One disadvantage in industrial applications has been the photographic process with the involved time-consuming development of the photographic film. This paper presents a new method using a TV camera and a digital image processor whereby real-time measurements of deformations and comparison of object contours are possible. Also the principles and limitations of the projected moiré method are described.     

Imaging phase objects by means of thermocapillary self-action

Transparent phase objects have been visualized for the first time using laser radiation reflected from an absorbing liquid layer situated in the Fourier plane of an optical system operating as a nonlinear Zernike filter. The radiation beam power necessary for the system operation is below 500 μW.     

Elimination of mismatch errors by means of phase inverters

Conclusions The use of low-reflection phase inverters provides the possibility of sharply reducing mismatch errors in measurements in a mismatched waveguide channel. In this, the cumbersome operation of matching the oscillator and the receiving device for each operating frequency becomes superfluous.The described method can also be used for measurements in devices which cannot be matched in principle. Extremely weak emissions due to an inadequate screening of the channel or very weak coherent signals can be detected by means of a phase inverter.     

Parallel methods for preliminary image processing in nondestructive testing

We consider parallel methods for preliminary processing of grayscale images under nondestructive testing of materials and structures. By virtue of the proved theorem, we show that grayscale images belong to the class of ℜ-functions which can be found and allow deep parallelization. We propose a new approach to geometric transformations of images, which can be considered as a single operation of transformation of coordinates. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 5, pp. 107–112, September–October., 1997.     

基于4×DSP的并行图像处理系统

在简要分析了当代几种典型的并行处理系统结构后,提出使用4颗TI公司高端数字信号处理器-TMS320C6416构建一种新型的并行图像处理系统。该系统通过一个同步四口SRAM和PCI总线构成互连结构,兼有紧耦合并行系统和松耦合并行系统的优点。然后,在所设计的并行硬件平台上,通过理论计算和实际的图像处理算法给出了包括点对点通信开销、加速比等在内的并行系统性能指标。最后,针对系统的性能瓶颈,进一步给出了提高系统性能的一些建议。     

Parallel processing of quadratic boundary elements for axisymmetric elasto-static problems

The concern of this paper is on improving the computational efficiency of boundary element methods (BEM) through the development of parallel algorithms for use on massively parallel machines. The application is on the axisymmetric elasto-static problems with quadratic boundary elements. Different ways of parallel approaches are discussed and a parallel approach suited to the BEM numerical process is developed. Numerical results from both the parallel algorithm and a serial algorithm are given in the paper to illustrate the efficiency of the parallel approach.     

Non-coherent detectors for quadrature-multiplexed continuous phase modulation signals

Here, non-coherent detectors for quadrature-multiplexed continuous phase modulation (QM-CPM) signals are developed (Fonseka et al., 2008). QM-CPM signals are more spectrally efficient than CPM signals, and multiamplitude QM-CPM signals can be constructed that outperform QAM. The non-coherent detectors view a QM-CPM signal as having composite states that represent the information modulated both onto the in-phase and quadrature-phase carriers. Viterbi decoding is used to jointly detect the quadrature-multiplexed signal components. Optimal sequence-based quadrature-matched filter (QMF) detectors are presented for use with QM-CPM detection and a QM-MSK detector is developed in detail. Differential phase and envelope (DPE) detectors are also presented which require less computation and are able to outperform the QMF-type detectors when the unknown carrier phase varies (phase jitter, phase hits etc.) within the sequence length used in the sequence-based QMF detectors. In the absence of these phase fluctuation effects, as the sequence length used in the QMF detectors increases, the performance of the QMF detectors approaches the performance of optimal non-coherent detection. The DPE-type detectors perform within about 2.5 dB of optimal coherent detection.     

Chaotic phase synchronization studied by means of continuous wavelet transform

A new approach to introduction of the phase of a chaotic signal is developed based on the continuous wavelet transform. The proposed method is applied to the study of phase synchronization of two chaotic dynamical systems with ill-defined phases.     

Improved compensation of turbulence-induced amplitude and phase distortions by means of multiple near-field phase adjustments

An approach for compensation of turbulence-induced amplitude and phase distortions is described. Two deformable mirrors are placed optically conjugate to the collecting aperture and to a finite range from this aperture. Two control algorithms are presented. The first is a sequential generalized projection algorithm (SGPA) that is similar to the Gerchberg-Saxton phase retrieval algorithm. The second is a parallel generalized projection algorithm (PGPA) that introduces constraints that minimize the number of branch points in the control commands for the deformable mirrors. These approaches are compared with the approach of placing the second deformable mirror conjugate to the far field of the collecting aperture and using the Gerchberg-Saxton algorithm to determine the optimal mirror commands. Simulation results show that placing the second deformable mirror at a finite range can achieve near-unity Strehl ratio regardless of the strength of the scintillation induced by propagation through extended paths, while the maximum Strehl ratio of the far-field approach drops off with increasing scintillation. The feasibility of the solutions is evaluated by counting the branch points contained in the deformable mirror commands. There are large numbers of branch points contained in the control commands that are generated by the Gerchberg-Saxton SGPA-based algorithms, irrespective of where the second deformable mirror is located. However, the control commands generated by the PGPA with branch point constraints achieves excellent Strehl ratio and minimizes the number of branch points.     

Absolute-length determination of a long-baseline Fabry-Perot cavity by means of resonating modulation sidebands

A new method has been demonstrated for absolute-length measurements of a long-baseline Fabry-Perot cavity by use of phase-modulated light. This method is based on determination of a free spectral range (FSR) of the cavity from the frequency difference between a carrier and phase-modulation sidebands, both of which resonate in the cavity. Sensitive response of the Fabry-Perot cavity near resonant frequencies ensures accurate determination of the FSR and thus of the absolute length of the cavity. This method was applied to a 300-m Fabry-Perot cavity of the TAMA gravitational wave detector that is being developed at the National Astronomical Observatory, Tokyo. With a modulation frequency of ~12 MHz, we successfully determined the absolute cavity length with resolution of 1 mum (3 x 10(-9) in strain) and observed local ground strain variations of 6 x 10(-8).     

Mixed neural-conventional processing to differentiate airwaydiseases by means of functional noninvasive tests

This paper describes a processing technique that can be used to combine information from different medical analyses to discriminate between different pathologies that have similar symptoms. The paper is focused on the differentiation between asthma, bronchitis, and emphysema, using only functional noninvasive tests, but the proposed technique can be easily applied to other similar situations where different tests have to be used to identify a pathology. The technique is based on mixed neural-and-conventional processing that not only suggests the pathology, but also estimates the reliability of this suggestion     

Influence of nonlinearity of modulation conversion in measurements by means of laser interference refractometers

The mechanisms underlying the appearance of nonlinearity errors under the conditions of interference modulation in the circuits of laser interference refractometers are analyzed and simple methods of reducing these errors are discussed. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 29–33, August, 1999.