Theory of distributed mixing and amplification in a superconductingquasi-particle nonlinear transmission line

An analysis is presented for the behavior of the superconducting quasi-particle nonlinear transmission line driven by a high-frequency local oscillator (LO). The theory developed includes a large-signal nonlinear analysis, a small-signal analysis, and a noise analysis. This model is used to simulate the conversion loss and noise temperature of distributed quasi-particle mixers based on the nonlinear transmission line. The numerical results are compared to an experimental mixer at 460 GHz. The theory also predicts that the nonlinear transmission line will provide parametric amplification when the idler frequency is inductively tuned. This new phenomenon may present new opportunities to low-noise receiver systems at submillimeter wavelengths     

Steepness of a loaded exponentially tapered distributed RC notch filter

An exponentially tapered distributed RC notch filter loaded by a source and a load resistor is shown to have maximum notch steepness for a finite taper degree.     

Impedance transformation using a hyperbolic cosine-squared tapered transmission line

A closed-form equation for the impedance transformation of an arbitrarily complex load, using a hyperbolic cosine-squared tapered transmission line, is presented. Design charts are also given. A numerical example is considered and results indicate a tremendous reduction in size, in comparison to other forms of lines, when hyperbolic cosine-squared lines are employed to match a large complex impedance to a real 50 Ω impedance.     

An exponentially tapered transmission line antenna

The analysis and design of an exponentially tapered transmission line antenna is presented. The exponentially tapered transmission line is designed to operate such that it has radiator characteristics at high frequency and serves as a matching section at low frequency. The NEC-2 is used to model the antenna at frequencies ranging from 500 MHz to 1 GHz to obtain the input impedance and the desired radiation pattern     

Theory of a distributed feedback laser

This paper treats distributed feedback laser operation in which a classical electromagnetic field obeying Maxwell's equations interacts with an active medium according to the laws of quantum mechanics. The theory describes arbitrarily intense two-mode operation of fundamental and higher modes in both index and gain grating configurations. Spacial hole burning and finite atomic linewidth are included in the analysis and are shown to give marked changes in some laser intensity profiles.     

The design, fabrication, and evaluation of a silicon junction field-effect photodetector

A new device for photodetection is introduced in this study that is capable of responsivities comparable to devices operating in the charge-storage mode. Since the physical process involved corresponds to a photodiode in series with a high value of resistance, the device operates in real time and hence avoids the problems of switching encountered in the charge-storage mode at low light levels. The device utilizes this physical process in a new technique that significantly reduces the required surface area. Although the junction field-effect transistor (FET) serves as the prototype for the device, considerations for improving the magnitude of the output response and its linearity along with the responsivity-bandwidth product lead to a device having a very low transconductance_{m}and a large cutoff voltage VGC. Field-effect photodetectors fabricated in accordance with the principles developed for optimum photodetection are evaluated. Epitaxial silicon of conventional doping was used in the fabrication. The devices are found to exhibit the photodetecting characteristics expected from theoretical considerations. A simple two-lump approximation of the distributed gate-channel interface is found to adequately describe the frequency response of the devices. In contrast to the area-independent responsivity of the charge-storage mode, it is shown that the responsivity of the field-effect photodetector is proportional to the square of the device surface area. Depending upon the illumination level and the deviation from linearity that is tolerable, this area dependence presents one of the fundamental drawbacks of the field-effect photodetector for applition in dense arrays.     

Exponentially tapered transmission line model of the arterialsystem

The arterial systemic tree is intricate and complex due to its numerous branches, nonuniform cross section and elasticity, and the rich harmonic composition of its pressure- and flow-pulses. To deal with this complexity, the modeling of the arterial system based on the technique of nonuniform transmission lines was undertaken. The main advantages of the technique are that it maintains a satisfactory response over a wide range of frequencies and that it analyzes the impedance and local reflection factor of various segments. The model, which utilizes far fewer parameters than previous models, supplies important information about reflections at bifurcations and impedance matching at the termination line     

Effect of shunt capacitance on tapered distributed RC network characteristics

The effect of stray shunt capacitance on the characteristics of distributed RC networks, particularly in MOS integrated form, is considered. It is shown that the expected superiority of the tapered network over the uniform network in giving lower attenuation for a given phase shift is unlikely to be physically realisable because of the greater sensitivity of the former to the effect of stray shunt capacitance.     

An efficient synthesis technique of tapered transmission line withloss and dispersion

A synthesis technique of lossy and dispersive tapered transmission line is presented that extends lossless cases suggested by Klopfenstein and others. A special optimization process based on the Fourier transform pair and generalized Taylor's procedure is performed to extract the exact null points of lobe-like frequency response in terms of the input reflection coefficient of lossy-tapered line in which the loss may be frequency dependent and distance dependent. The theory is verified by evaluation of a synthesized microstrip taper profile in the lossy case and is expected to be helpful for design of tapered line in the high-frequency microwave integrated circuits (MICs) with loss     

Theory of a wide-band distributed gyrotron traveling-wave amplifier

We present the concept of an ultra-wide-band distributed gyrotron traveling-wave amplifier for millimeter and submillimeter waves. The radius of the waveguide in the interaction region is increased along the axis, while the strength of the dc magnetic field is decreased in such a way that the wave cutoff frequency is kept nearly equal to the electron cyclotron frequency. The basic principle of operation, peak gain, and saturated efficiency are analyzed. It is shown that instantaneous bandwidth over at least two octaves is theoretical possible. Technological requirements for achieving such an amplifier are assessed, including proposed structures for distributed input wave coupling.     

Properties and design theory of ultrafast GaAsmetal-semiconductor-metal photodetector with symmetrical Schottkycontacts

A GaAs metal-semiconductor-metal photodetector fabricated in a symmetrical and interdigital Schottky contact structure on a semi-insulating GaAs substrate is discussed. The device exhibits a high-speed response and a very low dark current, even with a moderate size (200 μm²). Ultrafast responsivity is due to the high drift velocity of the photoelectrons and low capacitance. A design theory for optimum performance which includes a compromise between the circuit time constant and the transit time is described     

Short-cavity distributed Bragg reflector laser with an integrated tapered output waveguide

A distributed Bragg reflector strained-layer multiple-quantum-well laser at 1.5- mu m wavelength with an integrated tapered waveguide beam expander is discussed. The far-field FWHMs in the lateral and vertical directions are 10 and 15 degrees , respectively. A quantum efficiency of 17% out the tapered facet was measured with a corresponding threshold current of 28 mA. The alignment tolerances for coupling into a cleaved single-mode fiber are 9.5 and 7.5 mu m FWHM in the lateral and vertical directions, respectively. A 3-dB improvement for single-mode fiber coupling using a SELFOC lens was obtained.<>     

薄膜光探测器绑定点的几何设计与仿真分析

目前,光器件在硅基衬底上的集成是光电领域的研究热点。将基于表面张力的流体自组装技术应用于薄膜金属-半导体-金属（MSM）光探测器的集成上,其集成效果的优劣与器件绑定点的几何形状有关。为了有效预测薄膜MSM光探测器绑定点的间距和形状对集成效果的影响,利用MATLAB对其集成过程中表面自由能的分布状况进行了仿真分析。首先,在介绍薄膜MSM光探测器的基础上,对其集成过程建立了平移和旋转仿真模型。然后,根据表面自由能与匹配度的线性关系,分别仿真出了不同间距和形状的绑定点在集成过程中匹配度的分布状况图。通过分析匹配度的斜率以及正确装配状态和误装配状态之间的关系,预测两端绑定点间距较长、绑定点形状为梯形时集成效果较好。最后,考虑到薄膜光电器件有可能需要区分正负极的情况,将其两端绑定点设计成不对称形状并进行仿真分析,尽量避免集成过程中出现正负极反接的状态。     

Solar-cell design based on a distributed diode analysis

The front surface of a p-n junction solar cell has resistive losses associated with the diffused layer, the metal-semiconductor contact, and the grid structure. These losses are analyzed by considering the spatially distributed nature of the p-n junction and the grid conductors. This distributed diode analysis is especially useful for solar cells operated under concentrated sunlight conditions. The results show the dependence of the V-I characteristics and the maximum power output per unit cell on the ratio of the diffused layer resistance to the junction dynamic resistance. This ratio can assist the designer in establishing proper grid structure geometries and should tpically be less than 0.1 if the power output per unit cell is to be within 3 percent of that for the lossless case. Experimental measurements are reported which confirm the theoretical calculations. An analysis of the grid conductor losses associated with multiple-connected unit cells shows the disastrous effect that the grid header resistance can have on the performance of a solar cell. The results indicate that the use of a tapered header conductor to decrease the metal coverage may actually worsen cell performance.     

基于桥接T型光电探测器阵列的功率合成研究与设计

针对行波探测器阵列(TWDA)仅提高了光电探测器 的输出功率而输出带宽未得到改善的问题,本文提出了一种区别 于TWDA的基于桥接T型光电探测器阵列新结构。本设计采用基于constant-R结构的桥接T型 结构代替TWDA中的传统 constant-K结构的方法,从而形成人工传输线结构。即耦合微带线提供串连电感和所需要 的互感 ,电容并联于其中一条微带 线上,再将单个光电二极管嵌入到此人工传输线上,构成单个阵列单元,再按照阵列式结构 将这些阵列单元有效级联起来构 成桥接T型光电探测器阵列。仿真结果表明,所提出的桥接T型光电探测器阵列能够使多个光 电探测器功率合成的同时提高 工作带宽,虽然桥接T型光电探测器阵列合成功率相比于传统TWDA合成功率有稍许减少,但 在工作带宽上却提高了2倍, 减少的稍许合成功率可以通过增加级联数目加以补偿。     

A unified design methodology for CMOS tapered buffers

In this paper, the various disparate approaches to CMOS tapered buffer design are unified into an integrated design methodology. Circuit speed, power dissipation, physical area, and system reliability are the four performance criteria of concern in tapered buffers, and each places a separate, often conflicting, constraint on the design of a tapered buffer. Enhanced short-channel tapered buffer design equations are presented for propagation delay and power dissipation, as well as a new split-capacitor model of hot-carrier reliability of tapered buffers and a two-component physical area model. Each performance criterion is individually investigated and analyzed with respect to the number of stages and tapering factor, and the interaction of the four criteria is examined to develop both a qualitative and a quantitative understanding of the various design tradeoffs. The creation of process dependent look-up tables for optimal buffer design is described, and a methodology to apply these look-up tables to application-specific tapered buffers for both unconstrained and constrained systems is developed     

The design of antenna arrays with tapered sidelobe heights

Arrays for many radar and sonar applications have customarily been designed for equal sidelobe levels. This is, perhaps, as much due to the convenience of the analytical Dolph-Chebyshev technique as to any specific requirement. Using a simple adaptation of a previously reported numerical technique for symmetrical arrays, designs can be obtained whose directional response has a specified taper on the envelope containing the sidelobes. The method is applicable to both sum and difference patterns for both line and planar arrays. However, there seems to be little to be gained by this procedure except in the case when the outer sideiobes are to be more severely controlled.     

Single frequency 1550-nm AlGaInAs-InP tapered high-power laser witha distributed Bragg reflector

A strained-layer multiple-quantum-well tapered laser with single-frequency operation near 1550 nm and with 20-dB sidemode suppression, for continuous-wave power levels up to 0.6 W is reported. At a power level of 0.5 W, 80% of the power from this device remains in the central lobe of the far-field. Increased lateral mode stabilization was observed in devices having both a Gaussian-patterned contact and a distributed Bragg reflector (DBR) compared to those without a DBR. An increase by a factor of five in the power level obtainable, with at least 80% of that power in the central lobe of the far-field pattern, was obtained using the DBR reflector     

组合锥型光纤SERS探针的理论设计与优化

对组合锥型光纤表面增强拉曼（SERS）探针的结构参数进行了设计与优化。通过建立描述消逝波激发组合锥光纤探针表面纳米颗粒的激发光衰减系数模型,结合激发光经渐变锥段的全反射传输、探针平直段与激发光纤间的模式匹配原理,给出了组合锥型光纤SERS探针的结构参数设计与优化方法。利用该设计与优化方法,在给定的光纤和纳米颗粒结构以及周围环境和激发光功率下,进行了光纤SERS探针结构参数的模拟设计。