共查询到20条相似文献,搜索用时 31 毫秒
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A method of producing an arbitrary complex field modulation by use of two pixels of an analog ferroelectric spatial light modulator (SLM) is demonstrated. The method uses the gray-scale modulation capabilities of a SLM to spatially encode the complex data on two pixels. A spatial filter is used to remove the carrier signal. This technique gives fast gray-level amplitude and phase modulation. 相似文献
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Angela Dudley Ruslan Vasilyeu Vladimir Belyi Nikolai Khilo Piotr Ropot Andrew Forbes 《Optics Communications》2012,285(1):5-12
In this work we investigate the structure of nondiffracting speckle fields, both experimentally and theoretically. We are able to produce very good agreement between the experimentally recorded and theoretically calculated fields by using complex amplitude modulation on a phase-only spatial light modulator to implement controlled ring-slit experiments for the generation of nondiffracting speckle fields. The structure of the nondiffracting speckle due to binary and continuous phase modulations for both a uniform and a normal distribution is investigated. We find that we are able to engineer whether the nondiffracting field will appear as speckle or a structured zero-order Bessel beam by adjusting the standard deviation in the distribution. Having the ability to control where in the spectrum, from fully-developed nondiffracting speckle to a symmetric zero-order Bessel beam, the nondiffracting field will exist can prove to be a useful resource in the non-destructive testing of materials. 相似文献
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Rafael Betancur John Restrepo Roman Castaneda 《Optics and Lasers in Engineering》2009,47(12):1340-1347
A novel technique for designing specific shapes of power distributions is presented. It bases on the modulation of the spatial coherence of the optical field in amplitude and phase. The modulating functions are synthesized from the phase-space diagram of the field, provided by the marginal power spectrum. Numerical results for the phase modulation of the complex degree of spatial coherence are presented. This beam shaping technique is suitable in applications that require specific shapes and sizes. 相似文献
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Magnetic Resonance Fingerprinting (MRF) reconstructs tissue maps based on a sequence of very highly undersampled images. In order to be able to perform MRF reconstruction, state-of-the-art MRF methods rely on priors such as the MR physics (Bloch equations) and might also use some additional low-rank or spatial regularization. However to our knowledge these three regularizations are not applied together in a joint reconstruction. The reason is that it is indeed challenging to incorporate effectively multiple regularizations in a single MRF optimization algorithm. As a result most of these methods are not robust to noise especially when the sequence length is short. In this paper, we propose a family of new methods where spatial and low-rank regularizations, in addition to the Bloch manifold regularization, are applied on the images. We show on digital phantom and NIST phantom scans, as well as volunteer scans that the proposed methods bring significant improvement in the quality of the estimated tissue maps. 相似文献
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A simple scheme is presented to steer the propagation of a spatial photovoltaic soliton in a photovoltaic crystal. The basic idea is to impose a sinusoidal phase modulation on the light beam before entering the crystal. It is found that the self-deflection, soliton-like propagation, annihilation and splitting of this spatial-phase-modulated (SPM) beam can be realized by choosing appropriate modulation parameters; besides, a SPM beam can produce a waveguide with strong stability to steer a non-phase-modulated beam. These unique properties would have potential applications in the optical switch, splitter, modulator, and waveguide, etc. 相似文献
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In this work, to achieve higher capacity, spatial modulation (SM) is utilized in a cooperative scheme in two different models of Cooperative SM, where SM is applied either at the source or the selected partner through an antenna array. A theoretical model of SM capacity is defined based on closed form lower and upper bound of the SM capacity. Based on the theoretical analysis of the channel capacity in both CSM systems the simplest and easier to implement selection criteria have been suggested to select a single partner to maximize CSM capacity. The CSM system in which SM is applied through the partner’s antenna array is providing significant enhancement over the other CSM model and cooperative multiple-input-multiple-output (CO-MIMO) networks based on multiple partners. Moreover, the system with a single randomly selected partner equipped with four antennas, behaves similarly as the best configuration of CO-MIMO based on the cooperation of four partners with the computational complexity linearly increases with the number of available partners to help. All of the theoretical findings are verified through simulation studies. 相似文献
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A spatial bifurcation (a transition from stationary to oscillatory regime) in a chain of unidirectionally coupled phase systems is studied. It is shown that complication of coupling terms can make this bifurcation spatially chaotic in contrast to the previously observed "regular" and "predictable" type. It is demonstrated that the found type of spatial bifurcation corresponds to a smooth (predictable) manifold in the parameter space, while its spatial location gets actually unpredictable being governed by regularities of chaotic behavior. We infer that complex collective dynamics may arise in networks with plain architecture and simple dynamics of individual elements if nontrivial coupling is realized. 相似文献
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J. Chen A. Hangauer R. Strzoda M.-C. Amann 《Applied physics. B, Lasers and optics》2008,90(2):243-247
An accurate wavelength modulation spectroscopy based method to measure the dynamics of the wavelength modulation behavior
of tunable diode lasers is introduced in this paper. This method requires only standard equipment and a simple mechanical
setup. Under the condition of a constant laser modulation current, the wavelength modulation amplitude can be determined by
analysis of the distance between the two zero crossings of the measured second harmonic spectrum of gas absorption. When
measuring at different modulation frequencies, the frequency response of the current-to-wavelength tuning coefficient can
be obtained. The use of a frequency analyzer instead of a lock-in amplifier to obtain the second harmonic spectrum has two
advantages: it provides a higher bandwidth and allows for very precise detection of the zero crossings because of the logarithmic
output. The results exhibit very good agreement with a reference measurement performed with a fast FTIR Spectrometer.
PACS 42.60.Fc; 42.62.Fi; 42.55.Fx 相似文献
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Linear diffraction gratings that provide strongly asymmetric diffraction without surface modulation are created and studied. The spatial phase shift of the refractive-index grating relative to the absorption grating is the origin of nonreciprocal behavior. 相似文献
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The recently introduced beam propagation method using complex Jacobi iteration adapted for modeling of non-paraxial beam propagation in nonlinear optical waveguides is presented in this paper. The beam propagation equation is based on our recently proposed modified Padé(1,1) approximant operator. The resulting approach is very efficient and well-suited for large structures with long propagation paths. 相似文献
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Based on the propagation X ray phase contrast imaging theory, a spatial domain constraint iterative phase retrieval method is described in detail. This algorithm limits the object spatial domain according to the actual sample size firstly, and modify the image plane data with the actual test data, then the iteration can be terminated until iteration precision or the number of iterations meet the preset requirements. Finally the numerical simulation is made to evaluate the rapid phase retrieval algorithm performance, and a real column fiber material experiment is carried out using a micro focus X ray phase contrast imaging experiment platform, the phase distribution image of the column fiber is calculated out by this algorithm. The results show that this phase retrieval algorithm is effective, and the method has a potential stability and accuracy for X ray phase contrast imaging technology. 相似文献
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S. Tomasiello 《Journal of sound and vibration》2003,265(3):507-525
An iterative method based on differential quadrature rules is proposed as a new unified frame of resolution for non-linear two-degree-of-freedom systems. Dynamical systems with Duffing-type non-linearity have been considered. Differential quadrature rules have been applied with a careful distribution of sampling points to reduce the governing equation of motion to two second-order non-linear, non-autonomous ordinary differential equations and to solve the time-domain problem. The time domain of the problem is discretized by means of time intervals, with the same distribution of sampling points used to discretize the space domain (which can be seen as a single interval). It will be shown that accurate solutions depend not only on the choice of the distribution of sampling points, but also on the length of the time interval one refers to in the computations. The numerical results, utilized to draw Poincaré maps, are successfully compared with those obtained using the Runge-Kutta method. 相似文献
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基于单曲面迭代计算的曲面透镜设计方法 总被引:1,自引:0,他引:1
为在平面上实现所需的照明,满足照明系统的要求,需要对光学系统进行二次设计。传统的设计方法往往用规则曲面指定透镜的一个表面,并以此为基础来设计另个一表面,这样会导致其表面形状复杂,不方便加工或装配。对此,提出了一种基于单曲面迭代计算的透镜曲面设计方法,即适当设计指定光线从透镜的一个表面到另一个表面的光路分布,再以此分别迭代计算透镜的各个表面。该设计方法采用两个自由曲面配合成曲面透镜,较以往的设计方法更加灵活、方便,设计得到的曲面镜头较以往更加简单光滑,便于加工和装配。结合一陈列灯镜头设计,给出了基于单曲面迭代计算的曲面透镜设计计算结果。 相似文献
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We apply the polar decomposition of the Mueller matrix describing a liquid-crystal-on-silicon display to identify the diattenuator, depolarizer, and retarder contributions as a function of the gray level. The retarder contribution is expressed in terms of the equivalent Jones matrix to apply previous techniques to evaluate the phase modulation. This allows searching for optimized polarization configurations for phase- or amplitude-only modulation responses. We present results for lambda=633 nm showing a phase-only modulation up to 2 pi rad and flat intensity modulation. 相似文献