Tuneable edge enhancement filters for optical correlation

Difference of Gaussian (DOG) filters, a form of wavelet filter, are an extremely useful preprocessing tool for the enhancement of image edge data. The DOG filter is highly tuneable by control of the standard deviations of its constituent Gaussian distributions. These can be used in the frequency plane of optical correlators and implemented in the form of a static non-updateable filter. This article reports on a simple optical technique using photorefractive materials whereby a filter, updateable in real time and very similar to the DOG filter, is implemented by tuning the intensity of the hologram reference wave to give enhanced modulation in a selectable frequency band. This is called a tuneable photorefractive (TPR) filter. The results of the DOG and TPR filters are compared with those of the phase-only filter and classical matched spatial filter with respect to the criteria of signal-to-noise ratio, Horner efficiency and discrimination capability.     

Dynamic optical correlation using localized holography

A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 microm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.     

Least squares approach in wavenumber domain for sound field recording and reproduction using multiple parallel linear arrays

A novel signal processing method is proposed for sound field recording and reproduction using multiple parallel linear microphone and loudspeaker arrays. In sound field recording and reproduction, the problem is how to calculate the transfer filters that transform the signals recorded by microphones into the driving signals of the loudspeakers. The proposed method is based on the spatial Fourier transform in the horizontal angle combined with the least squares (LS) approach in the elevation angle. In the proposed method, the signals recorded by each linear microphone array and those that drive each loudspeaker array are decomposed into the wavenumber domain by the spatial Fourier transform in the horizontal direction. The transfer filters are then calculated by the LS approach in the wavenumber domain. As a result, the size of the matrix of each transfer function in the wavenumber domain is much smaller than that of the conventional LS approach in the temporal frequency domain (LSTF), and well-conditioned stable transfer filters can be obtained with low computational cost without regularization. Computer simulation results show that the proposed method reconstructed a sound field around the control points as accurately as the conventional LSTF.     

Characteristics of photopolymer holographic matched filters in a van der Lugt correlator

Parameters of van der Lugt holographic matched filters for phase and amplitude transparencies, including random phase masks, are studied. Conditions for recording such filters in a phase self-developing photopolymer are determined. A significant difference in the recording conditions for the holographic filters for amplitude transparencies and phase masks is demonstrated. The holographic filters for phase masks with a signal-to-noise ratio of 20–40 dB and η from 6 to 70% that are recorded in the photopolymerizable composition seem to be promising for optical pattern recognition.     

GPS signal acquisition via compressive multichannel sampling

In this paper, we propose an efficient acquisition scheme for GPS receivers. It is shown that GPS signals can be effectively sampled and detected using a bank of randomized correlators with much fewer chip-matched filters than those used in existing GPS signal acquisition algorithms. The latter use correlations with all possible shifted replicas of the satellite-specific C/A code and an exhaustive search for peaking signals over the delay-Doppler space. Our scheme is based on the recently proposed analog compressed sensing framework, and consists of a multichannel sampling structure with far fewer correlators.The compressive multichannel sampler outputs are linear combinations of a vector whose support tends to be sparse; by detecting its support one can identify the strongest satellite signals in the field of view and pinpoint the correct code-phase and Doppler shifts for finer resolution during tracking. The analysis in this paper demonstrates that GPS signals can be detected and acquired via the proposed structure at a lower cost in terms of number of correlations that need to be computed in the coarse acquisition phase, which in current GPS technology scales like the product of the number of all possible delays and Doppler shifts. In contrast, the required number of correlators in our compressive multichannel scheme scales as the number of satellites in the field of view of the device times the logarithm of number of delay-Doppler bins explored, as is typical for compressed sensing methods.     

三维超分辨光瞳滤波器的优化设计

利用matlab优化工具箱,采用非线性规划,对三区振幅型(透过率为1-0-1)和三区位相型(相位角为π-0-π)光瞳滤波器进行三维超分辨优化设计,建立了优化模型,经计算机多次迭代运算,改变斯特尔比s值,给出了优化结果.结果显示:所设计的滤波器较好地实现了横向和轴向三维超分辨,且轴向超分辨能力优于横向;相同斯特尔比下,位相型三维超分辨能力优于振幅型,并且这两种滤波器结构简单,容易实现.     

Diffraction correlators invariant to the shift of optical elements

Linear in intensity image processing systems based on the principles of diffraction optics are considered in the paper. Influence of optical element shifts on calculation accuracy in the systems is studied. It is shown that image processing in the diffraction intensity correlators (vignetting, partial coherence, etc. are not taken into account) is absolutely invariant to longitudinal shifts of a holographic filter and, to a great extent, invariant to longitudinal shifts of objectives. The experiments show that the correlators operate rather stable with the optical elements shifted within 10% from the focal lengths of the objectives used, which is higher by two orders than the analogous limits in the diffraction amplitude correlators.     

Designing optimal long-period fiber gratings with the overlapped Gaussian-apodization method for flattening EDFA gain spectra

A new and effective optimization approach to the inverse design problems of complex long-period fiber grating (LPG) filters was developed in the present study. The proposed synthesis method was based on the overlapped Gaussian-apodization method and the evolutionary optimization algorithm which can efficiently search for optimal solutions and simultaneously take into account various experimental requirements for the fabrication of the designed filters. To verify the effectiveness of the proposed method, a LPG filter for flattening EDFA gain spectra was designed. Compared to the existing results from discrete layer-peeling (DLP) inverse scattering algorithms, an LPG filter with adaptive grating lengths and much simpler, smoother, and less complicated coupling coefficient profiles for taking the practical fabrication conditions for gain flattening into account, was used in the proposed method. Simulation results confirm that optimal solutions of an LPG filter design are suitable for practical fabrication.     

Birefringence effects in estar base reconnaissance film in an optical correlator

Coherent optical correlators using Fourier transform matched filters are generally constructed using the interference between a transformed signal beam and an equipolarized collimated coherent reference beam. Polarization effects of any system elements must be accounted for in using such a correlator, or in any system using holographic techniques, particularly if analysers are used. Birefringence effects of estar base film, used almost exclusively in aerial reconnaissance work, have been examined by the authors when such film is placed in the signal path. Methods of compensation for such effects are suggested.     

Optical-digital processors for morphological and rank order filtering

Non-linear rank order and morphological filtering can be achieved in optical-digital processors. In these processors, all convolutions are performed in inherently parallel optical correlators. Arithmetic and logic operations are made digitally. Due to the threshold decomposition concept, grey scale images are sequentially treated slice by slice. The optical-digital method of local histogram calculation within both binary and weighted neighbourhoods allows local non-linear operations. We derive rank order and morphological filters from optically calculated convolutions. Several configurations of optical convolvers are discussed. Further improvements in the technology of spatial light modulators and encoded light sources are needed before these processors' practical uses will appear.     

Time Ordering and Counting Statistics

The basic quantum mechanical relation between fluctuations of transported charge and current correlators is discussed. It is found that, as a rule, the correlators are to be time-ordered in an unusual way. Instances where the difference with the conventional ordering matters are illustrated by means of a simple scattering model. We apply the results to resolve a discrepancy concerning the third cumulant of charge transport across a tunnel junction.     

The Application of Genetic Algorithm in E-Plane Waveguide Filter Design

Traditional optimization methods, such as Powell's method and the Simplex method, are generally very difficult to design high performance filters with the relative band-width less than 0.15% or more than 10%. In this paper, Genetic Algorithm (GA) is used to design filters that meet these requirements. Two special filters are designed in this paper with the relative band-width as 0.15% and 25%, respectively. The numerical results demonstrate that GA can be used to design filters of superior quality when compared to the filters designed by using Powell's method or Simplex method.     

Heavy quarkonia survival in potential model

We investigate the quarkonia correlators in QCD with no light quarks within a potential model with different screened potentials. Our results for the temperature dependence of the charmonium and bottomonium correlators are qualitatively consistent with existing and preliminary lattice results. We identify however, a much richer structure in the correlators than the one seen on the lattice.Arrival of the final proofs: 3 March 2005PACS: 11.15.Ha, 11.10.Wx, 12.38.Mh, 25.75.Nq     

Measurement of high-order current correlators

The feasibility of measuring high-order current correlators by means of a linear detector is analyzed. Two different types of measurements are considered: measurement of fluctuation power spectrum and measurement of unequal-time current correlators at fixed points in time. In both cases, formally exact expressions in terms of Keldysh time-ordered electron current operators are derived for the detector output. An explicit time ordering is found for the current correlators under the expectation operator used in measurements of high-order unequal-time current correlators. The situation when a detector measures current correlators at different points of a conductor is considered.     

Lower bound for electron spin entanglement from beam splitter current correlations

We determine a lower bound for the entanglement of formation of pairs of electron spins injected into a mesoscopic conductor. The bound can be expressed in terms of experimentally accessible quantities, the zero-frequency current correlators (shot noise power or cross correlators) after transmission through an electronic beam splitter and can be used to gain information about the entanglement from experiment. Spin relaxation (T1 processes) and decoherence (T2) during the ballistic coherent transmission of carriers are taken into account within Bloch theory. A variable inhomogeneous magnetic field gives rise to a useful lower bound for the entanglement of arbitrary states. The decrease in entanglement due to thermally mixed states is studied. Both the entanglement of the output of a source (entangler) and T(1,2) can be determined from current correlators.     

Quantum Harmonic Oscillator Systems with Disorder

We study many-body properties of quantum harmonic oscillator lattices with disorder. A sufficient condition for dynamical localization, expressed as a zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the eigenfunction correlators for an effective one-particle Hamiltonian. We show how state-of-the-art techniques for proving Anderson localization can be used to prove that these properties hold in a number of standard models. We also derive bounds on the static and dynamic correlation functions at both zero and positive temperature in terms of one-particle eigenfunction correlators. In particular, we show that static correlations decay exponentially fast if the corresponding effective one-particle Hamiltonian exhibits localization at low energies, regardless of whether there is a gap in the spectrum above the ground state or not. Our results apply to finite as well as to infinite oscillator systems. The eigenfunction correlators that appear are more general than those previously studied in the literature. In particular, we must allow for functions of the Hamiltonian that have a singularity at the bottom of the spectrum. We prove exponential bounds for such correlators for some of the standard models.     

Moments of heavy–light current correlators up to three loops

We consider moments of the non-diagonal vector, axial-vector, scalar and pseudo-scalar current correlators involving two different massive quark flavours up to three-loop accuracy. Expansions around the limits where one mass is zero and the equal-mass case are computed. These results are used to construct approximations valid for arbitrary mass values.     

Long-distance asymptotics of temperature correlators of the impenetrable Bose gas

The inverse scattering method is applied to the integrable nonlinear system describing temperature correlators of the impenetrable bosons in one space dimension. The corresponding matrix Riemann problems are constructed for two-point as well as for multi-point correlators. Long-distance asymptotics of two-point correlators is calculated.     

三区振幅型三维超分辨光瞳滤波器的优化设计

光瞳滤波器是光学成像系统实现超分辨的基本元件之一，多数三维超分辨滤波器因结构复杂而难于实现。用MATLAB优化工具箱，采用非线性规划，对三区振幅型（1-0—1型）光瞳滤波器进行了三维超分辨优化设计。建立了优化模型，并给出了优化实例。结果表明所设计的滤波器较好地实现了横向和轴向三维超分辨，且轴向超分辨能力优于横向。该滤波器结构简单，容易实现。