Low-threshold native-oxide confined narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers

Narrow-stripe folded-cavity surface-emitting InGaAs-GaAs lasers are demonstrated, AlAs native-oxide layers above and below waveguide region are employed for current and optical confinement to form narrow-stripe InGaAs-GaAs quantum-well lasers. A low-temperature (400/spl deg/C) selective wet-oxidation technique and an ion-beam-etching technique are used to fabricate insulator confined narrow-stripes and internal 45/spl deg/ deflectors, respectively. Continuous-wave threshold currents as low as 4.5 mA and 59% surface-emitting quantum efficiencies are achieved on the devices with 2-/spl mu/m-wide aperture and a 420-/spl mu/m-long cavity.     

The resolution of closely spaced signals

This paper presents a method for resolving signals closely spaced in parameter space in the sense that the parameters of the signals being measured (i.e., time of arrival, frequency, etc.) are close together. A maximum-likelihood method is used to resolveMsignals inK-dimensional space, whereMmay be unknown. The resulting procedure first generates aK-dimensional cross-ambiguity function and then passes this function through aK-dimensional linear filter. The procedure effectively reduces the problem from its original form of optimally searching for a maximum in the(M times K)-dimensional space to searching forMmaxima in theK-dimensional parameter space. The method is obviously sub-optimal; its advantage lies in the relatively simple form of the detection scheme.     

Radar separation of closely spaced targets

The capability of a hypothetical radar against attacks by closely spaced aircraft may be examined in geometric terms and the results can be plotted graphically. It is seen that a pulse Doppler type radar, which provides information about target velocity as well as range and angle, is essential in this kind of environment. When the targets are so closely spaced that all else fails, then separation or at least knowledge of the number of targets present is still possible if sufficient Doppler resolution is available to permit the measurement of the small changes in velocity that will be required for the aircraft to maintain formation.     

Output coupling for closely confined Pb1-xSnxTe double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-xSnxTe. For the TEOmode incident at the laser mirror and for thin optical guiding regions such that only the TEO, TE1, TMO, and TM1modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.     

Coupling between closely spaced back-to-back paraboloidal antennas

Using the geometrical theory of diffraction (GTD), a method of calculating the power coupling between closely spaced back-to-back paraboloidal antennas is presented. The method is illustrated by considering the coupling between two identical front-fed symmetric paraboloids, each of which is fed by a TE11mode circular waveguide.     

近距离放置双麦克风语音增强算法

介绍了一种基于近距离放置的双传声器波束形成和双通道能量差掩蔽相结合的语音增强算法.该算法简单,适合在DSP上实时实现,对特定方向上的语音具有很好的增强效果,能够应用于多种噪声环境.实验表明,即使在信噪比较低的情况下,该算法也有良好的表现.     

Capacity of MIMO systems with closely spaced antennas

Wide-band radio channel measurements at 5.2 GHz with four transmit and four receive antennas at variable element spacing are reported, aiming to evaluate the potential of compact antenna arrays at mobile terminals. We show that, for an element spacing d<0.5/spl middot//spl lambda/ (down to 0.2/spl middot//spl lambda/), the link capacity is not smaller than that for much larger d. This is explained by the observation that mutual coupling changes the radiation patterns of closely spaced antenna elements, individually. Compact multi-antenna terminals may thus become practical.     

Lowest mutual coupling between closely spaced loop antennas

The conditions for zeroing the mutual flux between two closely spaced coil antennas are examined. The analysis is expanded to examine the case of multiple linear antenna coils. Array antennas are used in many areas including magnetic resonance imaging (MRI). Theoretical and experimental results are presented and compared. Good agreement between theory and measurements has been confirmed. A two-dimensional receiving array antenna is proposed     

Alpha-particle-induced charge transfer between closely spaced memory cells

A detailed analysis of various mechanisms involved in α-particle-induced charge transfer between two trench-type DRAM cells is reported. An analytical model has been developed to describe the charge-transfer mechanisms. The charge-collection process consists of two phases. In the first phase, funneling is tile dominant mechanism, and the axial current is calculated based on the drift component. In the second phase, the structure behaves similarly to a bipolar transistor, and both the drift and diffusion components contribute to the charge transfer. A discussion of the dependence of the charge transfer on stored charge, cell separation, charge in the α-particle track, and the substrate doping concentration is presented.     

Radiation patterns and correlation of closely spaced linear antennas

A simple point source analysis is used to prove that, in theory, completely decorrelated reception can be achieved from two linear antennas with an arbitrarily small spacing. The conditions necessary to achieve this are consistent with two high gain (superdirective) beams in opposite directions. It is shown that the horizontal radiation patterns and correlation coefficient of arrays of vertically orientated linear antennas can be found via an exact relation to simple, point-source theory that includes the effects of mutual coupling. This theory leads to practically achievable optimum diversity designs at closer spacings than previously thought possible. The theory is illustrated for a dual antenna configuration and can be extended to multiple antennas.     

Channel tracking for RAKE receivers in closely spaced multipathenvironments

This paper deals with the problem of channel tracking for RAKE receivers in propagation environments characterized by closely spaced multipath components. After outlining why conventional single-path channel tracking algorithms fail in such scenarios, several new estimation algorithms are developed that are tailored to channels with closely spaced multipaths. This is achieved by removing or minimizing self-interference caused by multipath components. Other interfering users are treated as noise. Both timing tracking and phasor tracking and their interaction are covered in this paper. The derived algorithms are benchmarked against perfect channel knowledge on one hand and conventional tracking algorithms on the other hand, both in a UMTS test scenario. In moderate scenarios, the use of these new algorithms leads to performance improvements of up to 2 dB, in terms of signal-to-noise ratio (SNR) at moderate bit error rates, and even manages to track the channel in conditions where conventional tracking algorithms fail completely     

Interactions between closely coupled GaAs injection lasers

Interaction effects between injection lasers have been experimentally studied at 2°K and 77°K under pulse conditions in a single block configuration which permits close optical coupling between the lasers. This close coupling made previously reported effects an order of magnitude more prominent and revealed a new effect. The reduction of the threshold current of one laser by the influence of the coherent beam of a second laser by as much as a factor five has been observed. With respect to the quenching of one laser by a second laser, a quenching ratio (defined as the ratio of the quenched power to the quenching power) of 0.7 was obtained. A new effect observed was the reduction of the threshold current of one laser by the influence of the spontaneous emission from a second laser. A reduction of 10 per cent is typical for this effect. A qualitative discussion treating the two lasers as one optical cavity is given to incorporate these effects into one coherent picture. Logical device applications are also discussed.     

High-speed fibre optic links using 780 nm compact disc lasers

High-speed fibre optic data links with transmission speeds of up to 2 Gbit/s and distances of up to 2 km for 50 and 62.5 mu m core multimode fibres were demonstrated using low cost compact disc (CD) lasers and Si detectors operating at 780 nm. To the best of the authors' knowledge, this is the highest data rate yet demonstrated for CD lasers operating at a wavelength of 780 nm. This suggests that a low cost CD laser with multimode fibre and its simple receptacle package design may be more usable for the short-range nature of gigabit fibre optic link applications than has previously been considered to be practical.<>     

Simulation of wave scattering by a group of closely spaced bodies

The modified method of discrete sources is extended to 3D problems of scattering of electromagnetic waves by a group of impedance bodies of revolution. The approach proposed allows the development of efficient solution algorithms, including algorithms for the case where scatterers are spaced by very small distances. Numerical results are obtained for bodies of various configurations, and it is demonstrated that the results are highly accurate.     

Alpha-particle induced charge transfer between closely spaced trench capacitor memory cells

A detailed analysis of various mechanisms involved in alpha-particle induced charge transfer between two trench type dRAM cells is reported and an analytical model has been developed to represent the transfered charge. The results compare very favorably with detailed simulation results.     

Very low threshold graded-indexseparate-confinement-heterostructure strained InGaAsPsingle-quantum-well lasers

A low threshold current density of ~100 A/cm² has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well     

EMI-based classification of multiple closely spaced subsurface objects via independent component analysis

Previous work in subsurface object discrimination using electromagnetic induction data has shown that discrimination algorithms based on statistical signal processing techniques are effective for classifying data from objects that occur in isolation. However, for multiple closely spaced subsurface objects, the raw (unprocessed) measurement is a mixture of the responses from several objects and as such cannot be used directly to determine the identity of each of the individual objects. Thus, we propose to separate individual signatures from the mixture by posing the problem as a blind source separation (BSS) problem and effecting signature separation using independent component analysis. We propose to apply BSS to separate the mixed signatures and then follow the separation process with a Bayesian classifier. This approach is evaluated using both simulated data and data from unexploded ordnance items. The results show that this approach can be used to effectively classify multiple closely spaced objects.     

基于马氏随机场模型的空间近邻目标检测及量测划分

天基光学传感器对空间近邻目标的像平面跟踪过程中,传统方法在单帧恒虚警检测后进行量测划分,采用的虚警率过高可能引入较多的杂波点,过低则群目标在像平面的部分信息损失.在分析空间近邻目标在像平面特征的基础上,提出一种使用马氏随机场模型进行预检测处理然后以k-均值进行量测划分的方法,仿真结果表明,相比传统方法,基于马氏随机场模型的空间近邻目标检测及量测划分准确率更高,且在信噪比较低的情况下,性能改善明显.     

The generalized scattering matrix of closely spaced strip and slotlayers in waveguide

In this paper, a method-of-moments integral-equation formulation of a generalized scattering matrix (GSM) is presented for the full-wave analysis of interactive planar electric and magnetic discontinuities in waveguide. This was developed to efficiently handle a variety of waveguide-based strip-to-slot transitions, especially on thin substrates. This single matrix formulation replaces the problematic procedure of cascading individual GSM's of an electric (strip) layer, a thin substrate, and a magnetic (slot) layer