Tunable optical narrowband filter using a gain-coupled phase-shift-controlled distributed feedback laser

In this paper, we have proposed and analyzed a new tunable optical narrowband filter using gain-coupled phase-shift-controlled distributed feedback (GC-PSC-DFB) laser diode. Coupled-mode equations are solved by using the transfer matrix method (TMM). The GC-PSC-DFB filters offer a stable single-mode bandpass output, similar to that obtained with phase-shifted index-coupled structures. However, GC structures do not suffer from the severe longitudinal spatial hole burning (SHB) that occurs in high-coupling quarter-wave-shifted DFB filters. This SHB can cause multimoded behavior for high-input signal power. Various filter parameters such as wavelength tuning range, side-mode suppression ratio (SMSR), and channel gain deviation have been investigated and discussed. Our results show that the GC DFB structures offer a wider tuning range of 23.3 /spl Aring/ compared with the similar index-coupled DFB structures with nearly steady bandwidth of 12 GHz, while maintaining 41.8-dB constant gain.     

测量接收机系统中的混频器设计

目前,几乎所有的射频/微波(RF/Microwave)电路系统均采用混频器实现变频.本文详细介绍了混频器的设计,该混频器实现了低电压3 V、低功耗、高1 dB压缩点、低噪声系数以及很强镜像抑制机制的功能,并解决了交调失真的问题.     

AMOLED灰阶补偿算法研究

为了解决一种小型AMOLED显示屏由灰阶丢失导致的图像变形问题,提出了一种AMOLED灰阶补偿算法。首先测试不同亮度下AMOLED显示灰阶时亮度变化的数据,然后依据测试数据建立亮度变化与灰阶丢失的映射关系,最后使用非线性灰阶压缩的方法对输入图像进行变换,补偿灰阶丢失引起的图像失真。通过软件仿真和硬件测试表明,该算法可以有效地补偿由于AMOLED亮度变化而无法正常显示的灰阶的问题,使图像能够正常显示。因此该算法可以保证小型AMOLED显示屏在不同亮度下工作时能够正常显示灰阶。     

Polyharmonic distortion modeling

For more than a quarter of a century, microwave engineers have had the benefit of a foundation of mutually interacting components of measurement, modeling, and simulation to design and test linear components and systems. S-parameters are perhaps the most successful behavioral models ever. They have the powerful property that the S-parameters of individual components are sufficient to determine the S-parameters of any combination of those components. S-parameters of a component are sufficient to predict its response to any signal, provided only that the signal is of sufficiently small amplitude. We have presented the PHD modeling approach. It is a black-box frequency-domain model that provides a foundation for measurement, modeling, and simulation of driven nonlinear systems. The PHD model is very accurate for a wide variety of nonlinear characteristics, including compression, AM-PM, harmonics, load-pull, and time-domain waveforms. The PHD model faithfully represents driven nonlinear systems with mismatches at both the fundamental and harmonics. This enables the accurate simulation of distortion through cascaded chains of nonlinear components, thus providing key new design verification capabilities for RF and microwave modules and subsystems.     

基于重复控制的逆变电源输出特性研究

本文提出了一种基于状态反馈控制和重复控制的新型逆变电源系统。系统利用状态反馈极点配置获得了逆变电源良好的动态特性,利用重复控制较好地抑制了非线性负载工况下的电压畸变。     

Optimal capacitor placement for power systems with nonlinear loads

The purpose of this paper is to derive a systematic procedure to decide the optimal location and size of compensation shunt capacitors for distribution systems with harmonic distortion. A set of indices determined by the sensitivity of voltage variation, real power loss and harmonic distortion to the reactive power source is used to decide the optimal location of the shunt capacitors. The problem is formulated as a nonlinear programming of the minimization of real power loss and capacitor cost under the constraints of voltage limits and total harmonic distortion. A practical power system is selected for computer simulation to test the efficiency of the proposed method. It is found that both the system loss and harmonic distortion can be reduced very effectively by this method.     

Stable single-mode operation of distributed feedback lasers with wirelike active regions

A stable single-mode operation mechanism in distributed feedback (DFB) lasers with wirelike active regions was theoretically investigated by taking into account "gain matching" between standing wave profiles of each resonant mode and periodic active regions. As a result, it was clarified that the resonant modes at the longer wavelength side of the stopband have higher modal gain than those at the shorter wavelength side and that the oscillation takes place at the longer wavelength side resonant mode nearest to the stopband. The influence of the cleaved facet with respect to the grating phase was also analyzed. The measured spectral properties of buried heterostructure GaInAsP/InP DFB lasers consisting of wirelike active regions, such as a subthreshold gain spectrum and the lasing wavelength with respect to the stop band, agreed well with theoretical results. Finally, it was confirmed that a stable single-mode operation was preserved even after a room temperature continuous wave aging of 7300 h at bias current of around 10/spl times/ the threshold.     

基于重复控制400Hz逆变电源数字控制系统研究

针对400Hz逆变电源输出电压波形的畸变问题,采用了重复控制技术解决方案.并根据该控制自身存在的问题,引入了电压有效值外环和电容电流瞬时值内环控制.系统利用重复控制抑制非线性负载下的电压畸变,电流瞬时值反馈控制提高系统的动态响应性能,构成了新型多环控制系统.该控制系统的有效性已在三相6kVA逆变电源实验样机上得剑证实.实验结果表明,该方案可保证系统有较快的动态响应、较高的稳态精度和较小的输出电压谐波畸变率.     

Negative group delay and pulse compression in superluminal pulse propagation

We systematically study the pulse advance and pulse compression in light propagation through a transparent, anomalously dispersive medium. Using an Argand diagram, we show that pulse compression is the only form of pulse distortion, while other forms of pulse distortion can be eliminated. Experimentally, we implement a dual-band electronic amplifier to measure the negative pulse group delay and compression and confirm that they are related via a quadratic form.     

Ultrashort pulse-propagation effects in a semiconductor opticalamplifier: microscopic theory and experiment

We present microscopic modeling and experimental measurements of femtosecond-pulse interactions in a semiconductor optical amplifier. Two novel nonlinear propagation effects are demonstrated: pulse break-up in the gain regime and pulse compression in the transparency regime. These propagation phenomena highlight the microscopic origin and important role of adiabatic following in semiconductor optical amplifiers. Fundamental light-matter interactions are discussed in detail and possible applications are highlighted     

Femtosecond self- and cross-phase modulation in semiconductor laseramplifiers

We present detailed derivation of our new model for femtosecond pulse amplification in semiconductor laser amplifiers. The various dynamic nonlinear terms of gain compression and associated self-phase modulation are derived semiphenomenologically, and are discussed physically. Included are the effects of carrier depletion, carrier heating and spectral hole-burning, as well as linear and two photon absorption and the instantaneous nonlinear index. Additionally, we account for dynamically changing gain curvature and slope. We apply the theory to strong signal cross-phase-cross-gain modulation experiments with ~500 fs pulses in a broad area GaAs amplifier and show that the model accurately describes the observed complex phenomena. We also present experimental results on single beam strong signal amplification in two different quantum-well amplifiers using 150-200 fs duration pulses. For such pulse lengths, carrier heating becomes an integrating nonlinearity and its self-phase modulation is similar to that due to carrier depletion. Additionally, since the pulse spectrum is broad, the gain slope and curvature shift and narrow it. The resultant spectral distortions are very different than observed (and modeled) earlier for the ~500 fs pulses. The model is again able to correctly describe the evolution of these ultrashort pulses, indicating that it remains valid, even though pulse durations approach the intraband relaxation time     

Single-mode distributed feedback and microlasers based on quantum-dot gain material

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-/spl mu/m single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20/spl deg/C up to 214/spl deg/C with threshold currents < 15 mA (1-mm cavity length). Utilizing the low-bandgap absorption of quantum-dot material miniaturized monolithically integrable edge-emitting lasers could be realized by deeply etched Bragg mirrors with cavity lengths down to 12 /spl mu/m. A minimum threshold current of 1.2 mA and a continuous-wave (CW) output power of >1 mW was obtained for 30-/spl mu/m cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-/spl mu/m emitting 400-/spl mu/m-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80/spl deg/C with sidemode suppression ratios exceeding 40 dB.     

Laser diodes with integrated spot-size transformer as low-costoptical transmitter elements for telecommunications

We have realized laser diodes with integrated spot-size transformer to achieve a high-coupling efficiency to a standard single-mode fiber (SMF) without microoptical elements. A coupling loss of about 1 dB has been achieved with tolerances of 12 μm in both vertical and horizontal direction. We have fabricated both distributed-feedback (DFB) and Fabry-Perot (FP)-type lasers. In the case of the FP lasers the longitudinal single-mode emission was stabilized by means of an external fiber Bragg-grating which was directly butt-coupled to the laser. We have experimentally and theoretically investigated the optical and electrical properties of the devices using a transmission line model     

自适应补偿器永磁同步电机积分型连续滑模控制

考虑参数不确定、齿槽转矩、谐波反电动势及电压源逆变器非线性畸变等非理想因素,为提高永磁同步电机驱动系统对参数不确定及非线性扰动下的鲁棒性、高动态特性,提出一种带自适应扰动补测器的积分型连续滑模控制策略。连续滑模控制器无抖振且保证了闭环系统在参数不确定和扰动下的有界。滑模面上的自适应扰动补偿器一方面降低了滑模控制器增益,另一方面保证了系统渐进收敛。最后,通过仿真分析验证了所提控制策略的有效性和优越性。     

分布式反馈激光器温度监测系统设计

为了保持分布式反馈激光器(DFB)工作时温度的恒定,提高输出激光的功率稳定度与波长稳定度,提出了一种模糊比例积分微分(PID)算法与遗传算法结合的温度处理优化算法,并根据DFB激光器内部温度传感器的非线性特性,设计了具有线性化处理功能的温度采集电路;采用正/反相功率放大电路,设计了半导体制冷器(TEC)双向驱动电路,实现了DFB激光器温度信息的采集、处理以及反馈调节的闭环监测系统。经MATLAB软件仿真,优化后的PID算法经15 ms到达设定温度值,最大波动幅度约为1.1,波动次数为1次;经系统测试,采用优化后的PID算法作为温度处理算法能够将DFB激光器工作时温度波动范围限制在±0.5℃之间并且使其输出激光的功率稳定度和波长稳定度分别达到了±0.1 mW和±0.5 nm。     

A 0.8‐V supply bulk‐driven operational transconductance amplifier and Gm‐C filter in 0.18 µm CMOS process

A low voltage bulk‐driven operational transconductance amplifier (OTA) and its application to implement a tunable Gm‐C filter are presented. The linearity of the proposed OTA is achieved by nonlinear terms cancelation technique, using two paralleled differential topologies with opposite signs in the third‐order harmonic distortion term of the differential output current. The proposed OTA uses 0.8 V supply voltage and consumes 31.2 μW. The proposed OTA shows a total harmonic distortion of better than ?40 dB over the tuning range of the transconductance, by applying 800 mV_ppd sine wave input signal with 1 MHz frequency. The OTA has been used to implement a third‐order low‐pass Gm‐C filter, which can be used for wireless sensor network applications. The filter can operate as the channel select filter and variable gain amplifier, simultaneously. The gain of the filter can be tuned from ?1 to 23 dB, which results in power consumptions of 187.2 to 450.6 μW, respectively. The proposed OTA and filter have been simulated in a 0.18 µm CMOS technology. Simulations of process corners and temperature variations are also included in the paper. Copyright © 2014 John Wiley & Sons, Ltd.     

Multi criteria simultaneous planning of passive filters and distributed generation simultaneously in distribution system considering nonlinear loads with adaptive bacterial foraging optimization approach

This paper presents adaptive bacterial foraging optimization (ABFO) algorithm to optimize the planning of passive power filters (PPFs) and distributed generations (DGs) in distribution system with presence of heavy nonlinear load simultaneously. The amount of nonlinear load is assumed to be serious which enforced the system planner to utilize the PPFS. Also the power loss minimization, reliability and voltage profile improvement, and other benefits encouraged the planner to employ the DGs.Some of DG technologies, such as wind generators and solar cells are based on power electronic devices and inverter implementation. Connection of this type of DGs to system produces harmonic. Therefore the utilization of PPFs among existent capacitor busses for harmonic compensation is inevitable. The objective is to minimize the power loss, the total harmonic distortion (THD) and the investment cost of PPFs and DGs simultaneously. Constraints include the voltage limits and the limit candidate buses for PPFs and DGs installation. The harmonic levels of system are obtained by current injections method and the load flow is solved by the iterative method of power sum, which is suitable for the accuracy requirements of this type of study. It is shown that through an economical planning of PPFs and DGs, the total voltage harmonic distortion and active power loss could be minimized simultaneously.     

InGaAs-GaAs quantum-dot lasers

Quantum-dot (QD) lasers provide superior lasing characteristics compared to quantum-well (QW) and QW wire lasers due to their delta like density of states. Record threshold current densities of 40 A·cm ^-2 at 77 K and of 62 A·cm^-2 at 300 K are obtained while a characteristic temperature of 385 K is maintained up to 300 K. The internal quantum efficiency approaches values of ~80 %. Currently, operating QD lasers show broad-gain spectra with full-width at half-maximum (FWHM) up to ~50 meV, ultrahigh material gain of ~10⁵ cm^-1, differential gain of ~10^-13 cm² and strong nonlinear gain effects with a gain compression coefficient of ~10^-16 cm³. The modulation bandwidth is limited by nonlinear gain effects but can be increased by careful choice of the energy difference between QD and barrier states. The linewidth enhancement factor is ~0.5. The InGaAs-GaAs QD emission can be tuned between 0.95 μm and 1.37 μm at 300 K