Resolution and contrast enhancement in optical sub-traction microscopy with annular aperture

A method for improving lateral resolution and reducing imaging distortion of optical subtraction microscopy is proposed. First, an azimuthally polarized (AP) light is modulated by an annular aperture. Then, an image with higher lateral resolu-tion is obtained by subtracting an image obtained by an annular AP beam from an image obtained by a radially polarized beam. The simulation results demonstrate that compared with the case without the annular aperture, negative side-lobes in the effective point spread function are effectively suppressed, and the imaging quality of subtraction microscopy is obvi-ously enhanced.     

Scattering of electromagnetic waves by an anisotropic plasma-coated conducting cylinder

This paper considers the scattering of electromagnetic waves by an infinitely long anisotropic plasma-coated conducting cylinder. The source is assumed to be a magnetic current filament which gives rise to an incident magnetic field with only an axial component. Complete expressions for the scattered electric and magnetic fields are obtained. Scattering by an anisotropic plasma column and that by an isotropic plasma-coated conducting cylinder are special cases of the present problem.     

Fringe integral equation method for a truncated grounded dielectricslab

The problem of scattering by a semi-infinite grounded dielectric slab illuminated by an arbitrary incident TM_z polarized electric field is studied by solving a new set of “fringe” integral equations (F-IEs), whose functional unknowns are physically associated to the wave diffraction processes occurring at the truncation. The F-IEs are obtained by subtracting from the surface/surface integral equations pertinent to the truncated slab, an auxiliary set of equations obtained for the canonical problem of an infinite grounded slab illuminated by the same source. The F-IEs are solved by the method of moments by using a set of subdomain basis functions close to the truncation and semi-infinite domain basis functions far from it. These latter functions are properly shaped to reproduce the asymptotic behavior of the diffracted waves, which is obtained by physical inspection. The present solution is applied to the case of an electric line source located at the air-dielectric interface of the slab. Numerical results are compared with those calculated by a physical optics approach and by an alternative solution, in which the integral equation is constructed from the field continuity through an aperture orthogonal to the slab. The applications of the solution to an array of line currents are also presented and discussed     

Polarization characteristics of the radiation field from anaperture in an impedance surface

The radiation field from an aperture in an impedance surface is studied by using a newly proposed expression of an equivalent magnetic current. Simple relations between the polarization and the surface impedance are derived concerning two subjects: the currents on a reflector illuminated by an aperture in an impedance surface and the cross polarization of the aperture     

Finite element analysis of axisymmetric radomes

A two-step technique for the analysis of axisymmetric radomes is presented. Initially, an axisymmetric finite-element approach is employed, together with an absorbing boundary condition for mesh truncation, to determine the near fields scattered by an empty radome illuminated by a distant source. Next, the reciprocity theorem is invoked to determine the far-field pattern of an antenna encased by the radome, by computing the interaction between the current distribution on the antenna and the near-field data determined in the first step. The details of the formulation are presented along with numerical results for two different arrays enclosed by radomes of varying permittivities     

Generation of Gaussian signals from summed m-sequences

The amplitude distribution is considered of a signal obtained by summing M consecutively delayed versions of an m-sequence generated by an r-stage shift register, particularly for the case M > r. It is shown, how, for M > r, best approximation to a Gaussian distribution can be obtained by choice of an m-sequence having an appropriate characteristic polynomial.     

Advanced LOS path-loss model in microcellular mobile communications

This paper proposes an advanced line-of-sight path-loss model incorporating characteristics of an actual urban environment. Accurate results are obtained by using a two-path model with shadowing caused by obstacles that would appear in an actual urban environment and rising reflection area caused by vehicular traffic. By applying the model in an urban environment, microcellular path loss can be predicted from ultra-high-frequency to microwave bands     

空间光学系统无热化设计

在空间光学系统无热化设计时,需要考虑机械结构的热性能对系统热稳定性的贡献,满足系统总光焦度和消热差、消色差要求,解出各光学组元的光焦度,再在保持光焦度不变条件下进行像差平衡。本文以成像光谱仪为例,对反射系统进行了热分析,对折射系统介绍了无热化设计的原理和方法,并给出了设计结果。     

Nonlinear Devices Acting as SNR Amplifiers for a Harmonic Signal in Noise

A harmonic signal corrupted by an additive white noise is processed by an arbitrary memoryless nonlinear device. The transformation of the signal-to-noise ratio (SNR) by the nonlinearity is explicitly computed and analyzed for Gaussian and non-Gaussian noise. Simple nonlinearities, easily implementable as electronic circuits, are shown capable of producing an amplification of the SNR. Such an amplification is not obtainable with linear filters, whatever their complexity or high order, but becomes easily accessible with simple nonlinear devices.     

Hybrid opto-mechanical gyroscope with injection-interferometerreadout

A hybrid micromachined-optoelectronic mechanical system (MOEMS) gyroscope is proposed. It consists of an electrically excited micro-mechanical resonator and an optical readout performed by a laser diode operating as an injection interferometer. An analysis of the system, validated by preliminary experimental results, indicates an attainable performance of 1 deg/h√Hz     

Note Regarding the Propagation of Electromagnetic Fields Through Slots in Cylinders

A coaxial line is terminated at each end in an impedance. Excitation is provided by an incident plane polarized field that propagates through a small aperture in the sheath of the cable. The writers begin with the theory of diffraction by small holes presented by other investigators, and develop an exact theory for load current calculation.     

On compensating nonlinear distortions of an OFDM system using anefficient adaptive predistorter

This paper presents an efficient adaptive predistortion technique compensating for nonlinear distortions caused by a high-power amplifier (HPA) cascaded with a linear filter in an OFDM system. In the proposed approach, the memoryless HPA, preceded by a linear filter with memory in OFDM systems, is modeled by the Wiener system, which is then precompensated by the proposed adaptive predistorter with a minimum number of filter taps. It is confirmed by computer simulation that the proposed approach produces a faster convergence speed than the previous adaptive predistortion technique, and provides a small output backoff as low as 5.5 dB for an OFDM system employing an HPA with a linear filter     

一种基于相位调制器的40 GHz OFDM-ROF系统实验研究

实验研究了一种基于相位调制器(PM)并级联强度调制器(IM)实现40 GHz毫米波传输正交频分复用(OFDM)信号的光纤无线通信(ROF)系统。在中心站,采用20 GHz的射频(RF)信号驱动PM,调节驱动信号的强度,使输出的信号经光纤布拉格光栅(FBG)滤除中心载波后再送入IM。2.5 Gbit/s的OFDM信号直接调制在光毫米波上,经过50 km标准的单模光纤(SSMF)传输到基站。在基站,光调制信号经光电转换器(PD)转换成电调制信号,再与RF信号混频,恢复出基带OFDM信号。实验结果表明,在无色散补偿、误码率(BER)为10-3的条件下,下行链路中2.5 Gbit/s的OFDM信号经光纤传输50 km后,其功率代价小于1 dB,而且信号的星座图依然较好。     

Efficient, low parasitics 1.3 μm InGaAsP electroabsorptionwaveguide modulators on semi-insulating substrate

The high-speed operation of waveguide modulators is limited by the RC time constant, where the capacitance is primarily due to the parasitics. As part of an effort to reduce the parasitic capacitance, the authors have demonstrated a 1.3 μm InGaAsP electroabsorption waveguide modulator on semi-insulating InP substrate. A parasitic capacitance smaller than 10 fF was achieved by fabricating the bonding pad on an isolated mesa and by making use of an air bridge. For a 400 μm long waveguide modulator, an operating voltage as small as 2 V at an on-off ratio of 10 dB was obtained by optimizing InGaAsP bandgap for the operating laser wavelength. The device consists of a five-layer structure on semi-insulating substrate grown by liquid-phase epitaxy. These layers are undoped-InP buffer layer, undoped-InGaAsP waveguide layer, undoped-InP spacer layer, p-InP cladding layer, and p-InGaAsP contact layer     

Laser mode locking with addition of nonlinear index

A nonlinear index medium introduced into a passively or actively mode-locked system can lead to shorter pulses. The bandwidth limitation by gain dispersion is partially overcome by spectral broadening via the nonlinear index medium. We have found that the pulse shortening in an actively mode-locked system is limited to roughly a factor of 2 by the onset of an instability which occurs when an excessive amount of nonlinear medium is added. The instability appears as an oscillation in the pulse shape and energy. The study suggests that active mode locking of Nd YAG lasers could be improved by such means. It is also likely that the colliding pulse mode-locked system is affected by nonlinear index processes. We have found a pulse shortening of roughly the same magnitude as in the actively mode-locked system, again limited by the onset of instability.     

Analysis of magnetic stimulation of a concentric axon in a nervebundle

The authors present an analysis of magnetic stimulation of an axon located at the center of a nerve bundle. A three-dimensional axisymmetric volume conductor model is used to determine the transmembrane potential response along an axon due to induced electric fields produced by a toroidal coil. The authors evaluate four such models of an axon located in: (1) an isotropic nerve bundle with no perineurium, (2) an anisotropic nerve bundle without a perineurium, (3) an isotropic nerve bundle surrounded by a perineurium, and (4) an anisotropic nerve bundle surrounded by a perineurium. The transmembrane polarization computed along an axon for the above four models is compared to that for an axon located in an infinite homogenous medium. These calculations indicate that a nerve bundle with no sheath has little effect on the transmembrane potential. However, the presence of a perineurium around the nerve bundle and anisotropy in the bundle significantly affects the shape of the transmembrane response. Therefore, during magnetic stimulation, nerve bundle anisotropy and the presence of perineurium must be taken into account for calculation of stimulus intensities for threshold excitation     

Scattering of plane waves by an anisotropic dielectric half-plane

Scattering of plane waves by a semi-infinite anisotropic thin dielectric layer is investigated, which can be considered as an example for electromagnetic energy absorbing materials. A pair of second-order boundary conditions is used to simulate an anisotropic thin dielectric layer as an infinitesimally thin sheet. Formulation is based on the Fourier integral transform technique, which reduces the scattering problem to two decoupled scalar Wiener-Hopf equations. Diffracted, reflected, and transmitted field terms are evaluated by using the Wiener-Hopf solutions that is obtained by the standard method. The uniqueness of the solution is satisfied by imposing an edge constraint in addition to the classical edge condition     

A new method of nonstationary time series analysis based oninhomogeneous AR equation

We propose a new model for nonstationary time series analysis. The model is of a noise-contaminated signal of an AR system excited by a sequence of an input signal represented in terms of orthogonal functions. We also propose an algorithm that enables us to estimate parameters of the AR part and the input signal simultaneously. The models are finally evaluated by testing the recovery of an output signal. Examples of data analysis of the synthetic time series are shown for the ease in which the input signal is represented by a sequence of wavelets     

Electronically tunable external-cavity semiconductor laser

The authors have demonstrated electronic tunability of 35 nm in an external cavity GaAs semiconductor laser by using an acousto-optic (AO) tunable filter and an AO modulator inside the cavity. Tuning is accomplished by varying only the drive frequency of the AO devices     

基于图切割的拉普拉斯金字塔图像融合算法

针对在图像拼接中普通的拉普拉斯金字塔融合算法容易丢失细节的缺点,以及由于运动物体造成的融合鬼影现象,本文提出了一种基于图切割的拉普拉斯金字塔融合算法。首先,引入图切割技术,寻找最优缝合线,确定一种自适应融合区,以消除运动物体造成的融合鬼影;其次,利用源图像完整细节对重构误差进行补偿,提出一种基于包含水平方向在内多个方向的加权融合方法,将源图像和拉普拉斯金字塔融合图像按照这种融合规则进行融合。实验结果表明,与经典拉普拉斯融合方法对比,在客观指标上,本文方法的图像均值平均提高了0.326,标准差(SD)平均提高了1.109,信息熵平均提高了0.041,图像清晰度平均提高了0.289;在主观效果上,本文方法无明显拼接痕迹和融合鬼影,较好保留了图像细节,提高了融合质量,全景图拼接更加真实,改善了整体的视觉效果。