Injection seeding. II. Ti:Al2O3 experiments

Experiments have been designed and performed to determine the effects on the seeding efficiency of injection seed energy and power, alignment, and spatial mode matching between single longitudinal mode seed lasers and a power oscillator. The absorption features of H₂ O have allowed the characterization of the seeding efficiency by selectively absorbing the laser output energy corresponding to the seed wavelength. This enabled the accurate measurement of the residual unseeded laser output energy. Both a pulsed and a continuous wave seed source were used for these experiments. This work compares the results of the experiments with a theory for injection seeding developed in the previous paper     

B-spline signal processing. I. Theory

The use of continuous B-spline representations for signal processing applications such as interpolation, differentiation, filtering, noise reduction, and data compressions is considered. The B-spline coefficients are obtained through a linear transformation, which unlike other commonly used transforms is space invariant and can be implemented efficiently by linear filtering. The same property also applies for the indirect B-spline transform as well as for the evaluation of approximating representations using smoothing or least squares splines. The filters associated with these operations are fully characterized by explicitly evaluating their transfer functions for B-splines of any order. Applications to differentiation, filtering, smoothing, and least-squares approximation are examined. The extension of such operators for higher-dimensional signals such as digital images is considered     

Millimeter-wave integrated-horn antennas. I. Theory

The far-field pattern and input impedance of a dipole-fed horn antenna in a ground plane are calculated using full-wave analysis. The solution is based on the numerical evaluation of the pertinent Green's function for the horn structure and the application of the method of moments. The convergence characteristics of the full-wave analysis method are investigated, along the the resonant properties of the strip-dipole and the corresponding behavior of the far-field patterns     

Injection locking of high-power pulsed lasers. I. Monochromaticinjection

The theory of injection locking is based on the realistic situation where the injected intensity is much larger than the spontaneous noise intensity and smaller than the saturation intensity. Wideband homogeneously broadened lasers with injection are analyzed in the small-signal regime, including diffraction effects. The relevant equation for the injection-driven field is an iterative equation solved in the time domain. Multimode behaviors can be predicted. Injection locking is the result of a competition between the injection- and noise-driven fields. The laser behaviour is fully characterized by locking curves in the 2-D space of the injection parameters and by locked mode distributions     

A nonlinear optimum-detection problem. I. Theory

An approximate log-likelihood ratio for detecting a deterministic signal in linear and nonlinear Gaussian noise is derived. The new aspect of this detection problem is the inclusion of a nonlinear form of Gaussian noise and a certain interaction between the signal and the linear noise, such as modulation of the signal by the noise. The derived log-likelihood ratio consists of a modified version of the classical correlation detector and a new processor where the latter is an order of magnitude smaller than the former. In the absence of the signal-noise interaction, the modification consists of subtracting the estimate of the nonlinear noise from the input (to the correlation detector); the nonlinear processor is a quadratic correlation processor where the correlation is not against the (transformed) signal but against the difference of two estimates of the nonlinear noise under the two hypotheses (signal-presence and signal-absence). Presence of the signal-noise interaction introduces further modification and complication on both processors     

傍轴黎曼几何光学·Ⅰ理论

利用微分几何方法研究光束传输。从三维黎曼流形的曲率出发，构造了一个复空间。它的流线能兼容几何光学与波动光学的信息。     

Theory of polarization spreading techniques. I

Presents an analysis of a series of techniques grouped under the denomination “polarization spreading”, the intent of which is that of making the performance of a coherent optical receiver insensitive to the polarization transformations occurring along the optical fiber, without resorting to polarization compensation or control. The principle on which Polarization spreading operates is that of spreading the signal power over different states of polarization, so that heterodyning of at least half of the optical incident bit energy is always ensured. The main results obtained concern a condition that guarantees the maximum heterodyned signal energy, some classes of spreading waveforms satisfying the above condition, the derivation of the structure and the performance of optimum receivers in Gaussian noise. The results encompass most of the binary optical coherent modulation schemes proposed and experimented, such as ASK, FSK and DPSK     

The fast discrete Radon transform. I. Theory

An inversion scheme for reconstruction of images from projections based on the slope-intercept form of the discrete Radon transform is presented. A seminal algorithm for the forward and the inverse transforms proposed by G. Beylkin (1987) demonstrated poor dispersion characteristics for steep slopes and could not invert transforms based on nonlinear slope variations. By formulating the computation of a discrete computation of the continuous Radon transform formula, the authors explicitly derive fast generalized inversion methods that overcome the original shortcomings. The generalized forward (FRT) and inverse (IFRT) algorithms proposed are fast, eliminate interpolation calculations, and convert directly between a raster scan grid and a rectangular/polar grid in one step     

Injection seeding for single-mode operation in an optically pumped high-power D2O laser

Spectrally narrow, pulsed outputs consisting of almost a single mode have been obtained from an optically-pumped high-power (200kW) D₂O laser by adopting the injection seeding method, where single-mode radiation (seed pulse) from a low-power, compact D₂O laser has been injected into the main D₂O laser. Spectrally narrow outputs with high power having spectral widths as narrow as 5 MHz have been obtained, when the seed pulses with frequency tuned to one longitudinal mode of the main D₂O laser have been injected at a time sufficiently before the lasing of the main laser took place. The experimental results have been compared with those of numerical simulation modified to include the injection field with varying injection times.     

Area-efficient architectures for the Viterbi algorithm. I. Theory

In the state-parallel implementation of the Viterbi algorithm, one add-compare-select (ACS) unit is devoted to each state in the treillis. A systematic approach to partitioning, scheduling, and mapping N trellis states to P ACSs, where N>P , is presented here. The area saving of this architecture comes from the reduced number of ACSs and interconnection wires. The design of the ACS, path metric storage, and routing network is discussed in detail. The proposed architecture creates internal parallelism due to the ACS sharing, which can be exploited to increase the throughput rate by pipelining. Consequently, the architecture offers a favorable (smaller) area-time product, compared to the state-parallel implementation     

Noise of the stretched pulse fiber laser. I. Theory

A perturbation formalism is developed for the passively mode-locked stretched pulse fiber ring laser analogous to that of the fiber ring soliton laser. It is applied to determine the amplitude fluctuations, carrier frequency noise, and the pulse to pulse jitter due to the amplifier spontaneous emission noise     

A versatile leaky-wave antenna based on stub-loaded rectangularwaveguide .I. Theory

A new leaky-wave antenna is presented that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. The article presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations     

Noise characterization of block-iterative reconstruction algorithms: I. Theory

Researchers have shown increasing interest in block-iterative image reconstruction algorithms due to the computational and modeling advantages they provide. Although their convergence properties have been well documented, little is known about how they behave in the presence of noise. In this work, we fully characterize the ensemble statistical properties of the rescaled block-iterative expectation-maximization (RBI-EM) reconstruction algorithm and the rescaled block-iterative simultaneous multiplicative algebraic reconstruction technique (RBI-SMART). Also included in the analysis are the special cases of RBI-EM, maximum-likelihood EM (ML-EM) and ordered-subset EM (OS-EM), and the special case of RBI-SMART, SMART. A theoretical formulation strategy similar to that previously outlined for ML-EM is followed for the RBI methods. The theoretical formulations in this paper rely on one approximation, namely, that the noise in the reconstructed image is small compared to the mean image. In a second paper, the approximation will be justified through Monte Carlo simulations covering a range of noise levels, iteration points, and subset orderings. The ensemble statistical parameters could then be used to evaluate objective measures of image quality.     

多晶硅发射区中的少数载流子注入理论

本文提出了一种新的多晶硅发射区少数载流子注入理论.考虑了晶粒间界厚度和其中的少数载流子复合,假设晶粒间界和晶粒具有不同的少数载流子迁移率和寿命.引入少数载流子迁移率和寿命随多晶硅厚度变化的函数,通过求解与单晶硅少数载流子注入形式上完全相同的连续性方程,不仅得到了前人关于晶粒间界对少数载流子具有阻碍和复合双重作用的结论,而且成功地区分了不同晶粒间界对降低注入饱和少数载流子电流贡献的大小.其中,第一个晶粒间界能够最有效地减少注入饱和少数载流子电流.与此同时,本文还得到了能够降低注入饱和少子电流百分之十以上的有效晶粒间界个数与晶粒/晶粒间界界面态密度和晶粒大小之间的关系.     

Rectangular modes and dyadic Green's functions in a rectangularchirowaveguide. I. Theory

An analytic solution of electromagnetic-wave propagation in a rectangular chirowaveguide is represented in this paper in terms of spectral-domain dyadic Green's functions (DGF's) in a general form. The method used here is a combination of a wavefield decomposition method and DGF eigenfunction expansion technique. This DGF decomposition method avoids having to use the modified and normalized vector wave functions, which are found difficult to satisfy the boundary conditions of chirowaveguides in which the reconciliation of Dirichlet and Neumann conditions is impossible. On the other hand, this method can be generalized to a chirowaveguide of arbitrary cross section and is found reducible to a nonchiral case. It is observed that in a similar fashion to the conventional rectangular waveguide, the duality between the electric and magnetic types of DGF's in the rectangular chirowaveguide does not exist. To show the reducibility of the generalized DGF's for bi-isotropic media, we summarized the procedure of utilizing the formulas and proved in detail that the form of the DGF's can be reduced to that for chiral media and achiral (isotropic) media. Exactly the same DGF's are obtainable for the isotropic media by reducing the general formulas. The electric and magnetic fields in the rectangular chirowaveguide due to a point dipole excitation oriented in the y-direction are derived. The detailed numerical analysis includes the novel features of the dispersion relations, the effects of chirality on the novel features of the rectangular chirowaveguides, some newly discovered features, and vector field plots and contour plots of higher order modes of electric and magnetic fields     

Linear time-variant transformations of generalized almost-cyclostationary signals .I. Theory and method

The problem of linear time-variant filtering is addressed in the fraction-of-time (FOT) probability framework. The adopted approach, which is an alternative to the classical stochastic one, provides a statistical characterization of the system in terms of time averages of functions of time rather than ensemble averages of stochastic processes. Thus, it is particularly useful when stochastic systems transform ergodic input signals into nonergodic output signals, as it happens with several channel models encountered in practice. The analysis is carried out with reference to the wide class of the generalized almost-cyclostationary signals, which includes, as,a special case, the class of almost-cyclostationary signals. In this paper, systems are classified as deterministic or random in the FOT probability framework. Moreover, the new concept of expectation in the FOT probability framework of the impulse-response function of a system is introduced. For the linear time-variant systems, the higher order system characterization in the time domain is provided in terms of the system temporal moment function, which is the kernel of the operator that transforms the additive sinewave components contained in the input lag product into the additive sinewave components contained in the output lag product. Moreover, the higher order characterization in the frequency domain is also provided, and input/output relationships are derived in terms of temporal and spectral moment and cumulant functions. Developments and examples of application of the theory introduced here are presented in part II of this two-part paper.     

Linear two-wire transmission line coupling to an externalelectromagnetic field. I. Theory

The telegrapher's equations have been derived electrodynamically for the transmission line of two linear parallel conductors separated by a dielectric layer and excited by an electromagnetic field. The line coupling to a plane electromagnetic wave is illustrated for an arbitrary orientation of Poynting's vector and various polarization angles. The results are compared with the ones of other papers. The role of the magnetic field, while exciting the line, is clarified. The equations obtained in the paper are solved analytically in the case of the line excitation source being an electromagnetic pulse of arbitrary form     

Electromagnetic scattering by multiple three-dimensional scatterersburied under multilayered media. I. Theory

A general procedure is developed for the analysis of electromagnetic (EM) scattering by multiple three-dimensional (3D) dielectric and/or conducting objects buried under one-dimensional (1D) multilayered media. In this first part of a two-part paper, general closed-form formulations for the electric fields excited by an arbitrarily oriented electric dipole under the layered media are first presented, from which electric-field integral equations for the buried dielectric objects, pure conducting objects, and their combinations are then obtained, and the scattered electric fields in the upper space are formulated. Finally, the physical significance of the above formulations is discussed. In the second part, numerical implementations for these integral equations and the scattered fields are investigated     

Microwave attenuation by realistically distorted raindrops: Part I.Theory

By using a new raindrop model developed earlier and applying the first-order perturbation-expansion technique, the effects of realistic and nonaxisymmetric distortion of varying raindrop shapes on microwave attenuation are re-investigated in this paper. Under the assumption of nonaxisymmetric raindrop scatterers, a system of general equations satisfied by the scattering and transmission coefficients of the electromagnetic (EM) fields are derived under the zeroth-order and the first order approximations. Both the horizontal and the vertical polarizations are discussed. The scattered and transmitted EM fields are obtained by means of expansion of spherical vector wave functions. Under the first-order perturbation approximation, the total cross section is calculated and discussed. Compared with the previous formulas presented for the axisymmetric raindrop scattering, the new results of total cross section obtained here consist of two additional terms resulting from the nonaxisymmetric distortion. These additional terms due to the raindrop's nonaxisymmetry are represented analytically and discussed numerically. Part II of this paper will present an application of the analysis to the specific microwave attenuation due to rain in the moderate climatic region and in Singapore's tropical region     

A noise-whitening approach to multiple access noise rejection .I.Theory and background

Minimum probability of bit error is difficult to achieve in a DS-CDMA receiver. Since multiple-access noise is the sum of many independent random processes, it is reasonable to approximate it by a Gaussian process of the same power spectral density. This leads to the criterion of maximizing signal-to-noise ratio (SNR). In this paper, receivers that maximize SNR in a particular DS-CDMA system model under various constraints are proposed and analyzed. The method proposed here does not require locking and despreading multiple arriving CDMA signals. The maximization of SNR is compared with the minimization of probability of error, when the receiver is constrained to operate bit-by-bit, in the absence of knowledge of the other users' spreading codes, timing, and phase