Modal Analysis of Path Length Sensitivity in Superposition Architectures for Coherent Laser Beam Combining

An analytical model is developed to describe the modal behavior of a class of coherent beam combining resonators based on laser beam superposition. This model is used to explore the interplay between modal discrimination and tolerance to gain element path length changes. Under certain conditions, the sensitivity to the random phase fluctuations of the individual gain elements can be substantially reduced.     

Longitudinal spatial inhomogeneities in high-power semiconductorlasers

We study the spatial distribution of the temperature, gain, and carrier density along the longitudinal direction of a semiconductor laser cavity. In high-power laser diodes, the use of asymmetrical facet reflectivities creates a spatially nonuniform photon intensity profile and results in inhomogeneous temperature and carrier distributions along the active stripe. These profiles are determined from direct measurements of blackbody radiation and the spontaneous emission from the laser cavity. The temperature of the active stripe is observed to be significantly higher than that of the heat sink during lasing, and the effect of temperature on the modal gain spectrum is analyzed. We demonstrate that the local carrier density and optical gain within a laser are not pinned beyond threshold. A spatially inhomogeneous gain profile is possible in laser cavities as long as the threshold condition that the averaged round-trip gain equals the total losses is maintained. A theoretical model is presented which explains the observed experimental data     

Modeling, fabrication, and characterization of large aperture two-dimensional antiguided vertical-cavity surface-emitting laser arrays

We have investigated the modal behavior of two-dimensional (up to 400 elements) active-photonic-lattice-based antiguided vertical-cavity surface-emitting laser (VCSEL) arrays by both modeling and device characterization. A two-dimensional (2-D) model based on the effective index method has been constructed to analyze 2-D resonance and calculate array mode frequencies in rectangular geometry arrays. A more comprehensive three-dimensional bi-directional beam propagation code has also been developed to theoretically describe 2-D antiguided arrays with the VCSEL structure in the primary wave propagation direction. Gain spatial hole burning (GSHB) effects above laser threshold are applied to find conditions favorable for in-phase mode lasing and high intermodal discrimination. Three rectangular geometry array structures based on different interelement loss mechanisms have been designed and fabricated. Both far-field and spectral characterization were conducted on the devices to make detailed comparison with theoretical results. We found that introducing higher loss within the interelement region can allow the in-phase mode to exhibit the lowest threshold gain for a wide range of interelement widths around the in-phase resonance condition. A detailed spectral study of 5/spl times/5 arrays with the highest interelement loss design has demonstrated suppression of competing guided array modes and higher order leaky array modes at drive currents up to 10 times threshold.     

Ce3+:LiCaAlF6 crystal for high-gain orhigh-peak-power amplification of ultraviolet femtosecond pulses and newpotential ultraviolet gain medium: Ce3+:LiSr0.8Ca0.2AlF6

To develop high-peak-power ultrashort pulse laser systems in the ultraviolet region, a large Ce³⁺:LiCaAlF₆ (Ce:LiCAF) crystal, a tunable ultraviolet laser medium with large saturation fluence and broad gain spectrum width, was grown successfully with a diameter of more than 70 mm. To demonstrate high small signal gain, a four-pass confocal amplifier with 60 dB gain and 54 μJ output energy was constructed. Chirped pulse amplification (CPA) in the ultraviolet region was demonstrated using Ce:LiCAF for higher energy extraction. A modified bow-tie-style four-pass amplifier pumped by 100-mJ 266-nm 10-Hz pulses from a Q-switched Nd:YAG laser had 370-times gain and delivered 6-mJ 290-nm pulses. After dispersion compensation, the output pulses can be compressed down to 115 fs. This is the first ultraviolet, all-solid-state high-peak-power CPA laser system using ultraviolet gain media, and this demonstration shows further scalability of the Ce:LiCAF CPA system. Additionally, a new gain medium, Ce³⁺ :LiSr_0.8Ca_0.2AlF₆, with longer fluorescence lifetime and sufficient gain spectrum width over 18 nm was grown to upgrade this system as a candidate for a final power amplifier gain module     

一种新型无电解电容Buck-Boost正反激LED驱动电路的研究

提出了一种无电解电容Buck-Boost正反激LED驱动电路,该电路继承了传统驱动电路中将漏感能量回馈至输入端的优点。由于传统拓扑在无电解电容并增大输出功率的条件下存在输出电压纹波较大的缺点,在研究现有LED照明驱动的基础上,将正反激电路成功应用于传统驱动电路中的DC/DC级。变压器原边和副边均有电容作为中间级储能元件,变压器工作在正反激模态,提高了变压器的功率密度,同时变压器副边存在续流电感,大幅度降低了输出电压纹波率。详细分析了变换器稳态工作特性;最后,研制一台30 W的实验样机,测试结果表明了该设计的合理性和可行性。     

Advantages of modal decomposition for efficient scaling of parallel FDTD computations

When a scheme such as FDTD is used to perform full‐wave electromagnetic simulation of electrically large objects, it can result in excessive computation times. Parallel processing is one means to reduce the computation time. A shortcoming of the parallel approach is the communication overhead that is responsible for reduced speedup efficiency but inevitable at every time step. An alternative to reduce the communication is to look at FDTD from the modal analysis point of view. With modal analysis we can gain some very useful insights into the operation of the algorithm, which we pay for with a relatively expensive setup time. We consider parallelizing the modal analysis algorithm with transient and steady‐state excitation scenarios. Copyright © 2011 John Wiley & Sons, Ltd.     

一种提高SiC MOSFET在高开关速率下栅极电压稳定性的驱动电路

高开关速率且栅极电压稳定的驱动是SiC MOSFET高频工作、进而实现功率变换系统小型化和轻量化的关键技术之一.针对如何在高开关速率下稳定驱动SiC MOSFET,并实现可靠的短路保护,根据栅源电压干扰的传导特点,基于辅助器件的跨导增益构建负反馈控制回路,提出一种SiC MOSFET栅极驱动,进而研究揭示该驱动的短路保...     

车用永磁同步电机的电磁噪声分析与抑制

电机模态的准确分析是实现电机低噪声驱动设计的重要环节。当电机模态频率与对应阶次径向电磁力波频率接近时,会产生共振。以一台6极36槽的70 kW商务车主驱动永磁同步电机(PMSM)为研究对象,对比分析转子开辅助槽和针对一阶齿谐波的转子分段斜极方法对电磁力波的影响。采用转子开辅助槽和转子分段斜极的优化方法后,0阶12倍频径向电磁力波幅值可减小79%。建立电机三维有限元模态仿真模型,分析电机结构部件对模态的影响,结合常用车载驱动电机的安装固定方式对外壳进行约束,分析不同约束方式下电机的模态特性。结果表明,在峰值功率8 000 r/min的工况下,优化设计方案下的0阶12倍频的径向电磁力波幅值较大,但由于频率为4 800 Hz,远离电机模态的固有频率,因此不会发生共振,降低了电磁噪声。     

AC Drives in Traction Applications

DC motors and drives have previously been the choice for traction applications. The desire to use an induction motor in similar applications has been unfulfilled due to the absence of a suitable ac drive controller that could fully exploit the economical, rugged, and simple ac induction motor. AC drives using vector-control techniques are available to gain the high-performance operation in precise-torque and four-quadrant applications. This paper describes the use of such a drive for locomotion of large coal-handling equipment.     

Temperature dependent efficiency and modulation characteristics ofAl-free 980-nm laser diodes

Temperature dependent efficiency and modulation characteristics of strained quantum-well (QW) InGaAs-InGaAsP-InGaP 980-nm laser diodes of various designs are analyzed using self consistent carrier transport analysis including stimulated emission. The decrease of the differential efficiency of 980-nm laser diodes with temperature is found to be caused by an increased modal loss attributed to the free carrier (electron and hole) absorption. The obtained results agree well with experimentally observed increase of internal loss at higher temperatures. Modulation characteristics are determined mainly by drift-diffusion in separate confinement region along with processes of carrier capture and escape in QWs. At high temperatures modulation bandwidth is reduced because of the decrease in differential gain. Graded index separate confinement heterostructure and multi-QW lasers show superior efficiency and modulation behavior at high temperatures     

Characterization of semiconductor laser gain media by the segmented contact method

In this paper, we describe methods for analysis of edge-emitted amplified spontaneous emission spectra measured as a function of the pumped stripe length. We show that both the modal gain and the unamplified spontaneous emission spectra can be extracted from the data, and we describe a means of calibrating the spontaneous emission in real units, without requiring the carrier populations to be described by Fermi functions. The gain and emission spectra can be determined for transverse electric and transverse magnetic polarizations and by summing the recombination currents for each polarization the total radiative current can be measured. This enables the overall internal radiative quantum efficiency to be calculated. Once the calibration factor is known the internal stimulated recombination rate at the facet can also be estimated. The experiment can be configured to give a measurement of the passive modal absorption of the gain medium. The internal optical mode loss can be determined from the long-wavelength region of the gain spectrum or the modal absorption spectrum. In summary, we show that measurements of amplified spontaneous emission spectra provide a full characterization of the gain medium.     

Dynamics of the discharge-pumped vacuum ultraviolet Kr/sub 2//sup */ laser

A numerical simulation code has been developed to investigate the dynamics of the discharge-pumped vacuum ultraviolet Kr/sub 2//sup */ laser. Dynamics of spectral narrowing of the laser emission down to 0.2-nm full-width at half-maximum (FWHM) was well reproduced. Small signal gain behavior as a function of the applied voltage was predicted to have a gain coefficient of 0.08 cm/sup -1/ at the applied voltage of 32 kV, which was more than twice as large as the experimentally observed maximum gain value (0.035 cm/sup -1/). The code predicted that the laser output energy could become more than 1 mJ at the applied voltage at the Kr gas pressure of 10 atm.     

四梁耦合振子式超声波电动机的研制与实验

对四梁耦合振子式超声波电动机的驱动机理进行了研究,设计并制作了四梁耦合振子式的新型结构电机,并进行了实验测试。实验结果表明,该类型电机不但结构简单紧凑,而且具有良好的输出性能,如反应速度快、控制特性好,低速大转矩等,设计达到了预期效果。该研究对模态转换型新型超声波电动机的研发有实际意义和参考价值。     

Assessment of the continuous wavelet transform in the modal parameters estimation of 2MM and 3MM systems

In this paper, our interest is in the identification of a special class of electromechanical systems: a motor‐drive system using the continuous wavelet transform method. This new modal analysis technique is evaluated in terms of its accuracy in the estimation of the modal parameters, its ability in distinguishing and separating several modes, its resistance to noisy conditions, and its usability with different excitations types. For this investigation, two models of elastic drive systems are considered: the two‐mass model and the three‐mass model. Simulation results of the study are presented, and the effectiveness of the developed identification method is discussed. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

洗衣机机箱模态试验研究

本文将现代测试手段和模态分析技术相结合,应用试验模态分析方法对某全自动滚筒洗衣机机箱进行了模态试验,得到其固有频率、模态振型等模态参数。测试结果分析表明,该机箱左右两侧面及其后面存在较为严重的振动问题,并对此提出相应的改进措施。     

永磁直线同步电动机非正弦磁场数学模型研究

电机传动系统大都采用变频器供电,输出的是非正弦电压和电流,因此产生非正弦磁场,永磁直线同步电动机也如此。初步建立了永磁直线同步电动机时空三维非正弦电磁场的数学模型。模型在空间上采用体电流密度等效初、次级激励场源,充分解决了直线电动机的结构开断、边端效应等问题;在时间上考虑了非正弦供电的情况,最后用傅里叶变换对该模型进行解析计算,其计算结果和实验结果吻合。     

Influence of temperature and optical confinement on threshold current of an InGaAs/InP quantum wire laser

In this paper, we investigate the influence of the temperature on gain and threshold current density of a V-groove quantum wire InGaAs/InP laser. The calculation shows that room-temperature operation can be achieved if the optical confinement is large enough (0.26% in our case), while its slight improvement above this limit (around 0.4%) can provide a significant reduction of the threshold current (more than 70%) and an improved temperature stability of the laser.     

激光拼焊板在汽车车门上的应用

针对激光拼焊板的优越性能,以某轿车的前车门为例,采用数值模拟的方法,从自由模态、扭转刚度、垂向刚度等方面对比研究了激光拼焊板和普通加强板结构的性能差别,为激光拼焊板的进一步应用推广提供参考。结果表明:采用激光拼焊板结构可以减少零部件数量,并能显著提高车门的垂向刚度。     

行波超声波电机非参数辨识模型

超声波电机的输出特性与驱动频率呈非线性关系。同时在驱动频率切换期间,振动的初始状态对转速变化过程也会产生影响。行波超声波电机(traveling-wave ultrasonic motor, TUSM)动态过程与切换频率前后值的选取及频率变化方向有关。将TUSM频率阶跃响应过程近似线性化,利用系统辨识中的非参数建模方法,建立在特定切换频率条件下的二阶线性模型。在TUSM工作范围内,辨识若干组不同切换频率条件下的近似二阶线性模型,将这些模型的参数进行二维或三维拟合,得到了一个关于TUSM传递函数的多输入多输出模型。利用60 mm行波超声波电机作为研究实例,实验与仿真结果表明,模型计算值与实测值接近,表明建模方法可行。     

Recent progress in high-power blue-violet lasers

The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm/sup 2/. This is thought to be due to the large transparency current density Jt and the large optical internal loss /spl alpha//sub i/. Recently, the internal loss was successfully reduced to 13.6 cm/sup -1/ by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70/spl deg/C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use.