Passive Phasing in a Coherent Laser Array

A coherent array of fiber lasers in a self-Fourier cavity is described and analyzed. With individual regenerative feedback added to each fiber laser, the integrated gain in each individual fiber is a function of its cold cavity phase shift (fiber length). This results in a gain-dependent phase shift due to the Kramers-Kronig relations, and has been shown to partially compensate for the random differences in fiber lengths often encountered in coherent fiber arrays. A coupled cavity analysis of the active gain elements and the passive external cavity is performed and a self-consistent fundamental supermode determined. The output phase distribution of the array is determined based on a random distribution in fiber lengths. The Strehl ratio of this phase distribution is calculated and compared to experimental data.     

Analysis and optimization of a novel biasing for constant‐gain CMOS open‐loop amplifiers

A replica biasing circuit is presented which allows open‐loop gain in CMOS amplifiers to be accurately set. The proposed solution is a new biasing which takes advantage of a triode‐biased transistor instead of the ΔV_GS approach which is the traditional one. The circuit can be applied to both RF and IF amplifiers which are based on resistive loads in order to achieve high‐frequency and/or low‐noise performance. A detailed analysis of second‐order effects is then given which emphasizes the effects due to mobility degradation, channel‐length modulation and threshold voltage mismatches. Simulated results show a good sensitivity to process variations. Copyright © 2001 John Wiley & Sons, Ltd.     

三相三柱变压器对偏磁电流的耐受特性研究

为了分析三相三柱电力变压器在高压直流输电系统大地回流作用下运行性能的变化情况,采用电路—磁路耦合的数值方法建立了包括变压器内部主要漏磁回路在内的该型式变压器详细模型,并利用该模型通过改变漏磁磁阻值重点讨论了漏磁回路对变压器耐受直流电流偏磁能力的影响。仿真分析结果表明,三相三柱变压器内部漏磁回路特性对变压器受直流电流偏磁作用的影响不可忽视。当漏磁磁阻减小至一定程度时,该种型式变压器仍然会受到直流偏磁电流的影响,因此在三相三柱变压器设计制造环节应对其漏磁回路加以充分考虑。     

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.     

Base coupled differential amplifier: a new topology for RF integrated LNA

A new topology of bipolar low noise amplifier (LNA) for RF applications, named base coupled differential (BCD), is presented. The proposed approach is compared by simulation against most classical topologies. The BCD configuration has the key advantage to join an integrated matching on a single‐ended input with a differential output. This is done by using down‐bond wiring, so that no integrated inductors are needed. The main advantages of this new topology are a drastic area reduction and an increased linearity range (or a reduced biasing current with the same linearity) together with a noise figure (NF) and voltage supply reduction. Particularly, the BCD LNA presented in this paper has been designed for 2.44GHz frequency operation. It is characterized by a NF of 1.93dB, a voltage gain (Av) of 19.5dB, an input impedance of 50Ωa third Input‐referred Intercept Point (IIP3) of ‐7.25dBm and a dissipated power (PD) equal to 19mW. Copyright © 2003 John Wiley & Sons, Ltd.     

Digitally‐assisted constant‐on‐time dynamic‐biasing technique for bandwidth and slew‐rate enhancement in ultra‐low‐power low‐dropout regulator

A digitally‐assisted constant‐on‐time dynamic‐biasing (COT‐DB) technique has been proposed to enable significant enhancement in dynamic performances, while the average current consumption can be kept to ultralow level. This dynamic‐biasing technique has a predefined magnitude and duration on biasing current boost, which is beneficial to estimate power budget in systems with finite energy source. The proposed technique has been applied to a low‐dropout regulator (LDO) to demonstrate the effectiveness. Experimental results show that significant improvements in settling times during load‐transients and line‐transients are as much as 880×, while the current consumption is only 1.02 μA. In fact, for the same dynamic performances, the average current consumption of LDO with COT‐DB technique can be as low as 0.39% of the LDO with heavy static biasing. The digitally‐assisted implementation of the technique also allows robust augmentation of the technique onto almost all analog systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Non-Markovian gain of strained-layer wurtzite GaN quantum-welllasers with many-body effects

A theoretical model for the optical gain of strained-layer wurtzite GaN quantum-well (QW) lasers is developed taking into account valence-band mixing, many-body effects and non-Markovian relaxation. The valence-band structure is calculated from a 6×6 multiband effective mass Hamiltonian for the wurtzite structure taking into account built-in strain due to lattice mismatch. The theoretical foundation for the optical processes is based on the time-convolutionless reduced-density operator formalism given in previous papers for an arbitrary driven system coupled to a stochastic reservoir. Many-body effects are taken into account within the time-dependent Hartree-Fock approximation and the optical gain with Coulomb (or excitonic) enhancement is derived by integrating the equation of motion for the interband polarization. It is predicted that the Coulomb enhancement of gain is pronounced with increasing magnitude of compressive strain in the QW     

Gain compression improvement on low‐power cascaded current reuse LNAs

Current reuse low‐noise‐amplifiers (CRLNAs) have been the norm to achieve high‐gain and low‐noise figure under low‐power budgets. However, conventional CRLNAs suffer from a severe lack of large‐signal linearity, especially in conventional cascaded CRLNAs. This main drawback is related with the typical biasing method imposed in the output stage. To prove our point, a large‐signal study is performed for a single stage common‐source in two distinct biasing situations: voltage biased and current biased. On the basis of the gathered results, a new CRLNA solution is proposed to relief the large‐signal bottleneck. The suggested design is analyzed in a 0.13 µm complementary metal–oxide–semiconductor (CMOS) standard process. Post‐layout simulations show 8 dB compression point improvement compared with the conventional CRLNA solution. The CRLNA draws a current of 650 μA from a 1.2 V supply. At 2.45 GHz, a power gain of 25.3 dB and a NF of 2.3 dB are achieved, while the IIP3 is ?9 dBm. Copyright © 2016 John Wiley & Sons, Ltd.     

The allowed varactor parameter tolerances for the electrical tunability of two microstrip parametric amplifiers

The variations in varactor parameters which can be compensated by the electrical re-tuning of two specific amplifiers have been studied using a digital computer. The designs of two different microstrip parametric amplifiers were at first optimized with respect to the bandwidth. Then after changing the varactor parameters, pumping and biasing conditions were optimized in order to attain maximum flat gain bandwidth within certain acceptable limits for gain and frequency. The results show that considerable variations can be compensated electrically.     

Planar photonic crystal coupled cavity waveguides

We present absolute transmission measurements of coupled cavity waveguides defined within planar photonic crystals. We investigate a range of cavity types and also vary the spacing between cavities. Modal analysis of the individual cavities reveals the symmetries that determine the coupling between adjacent cavities. Enhanced transmission is demonstrated by modifying the photonic crystal lattice. We highlight the need for correct impedance matching at the waveguide input in order to improve the transmission.     

高温燃烧微库仑法检测抗燃油氯含量的方法研究

介绍采用高温燃烧微库仑法检测抗燃油氯含量的原理,并进行了检测条件优化试验,得出转化率与主要影响因素如温度、增益、取样电阻、载气流速、氧气流速、偏压、进样量等的关系。在优化试验得出的最佳试验条件下对高温燃烧微库仑法进行了重复性测试和回收率测试,结果表明高温燃烧微库仑法检测抗燃油氯含量具有精密度和准确度高、分析速度快、干扰少、仪器设备费用少、维护工作量小等优点。     

Tapered-cavity surface-emitting distributed-Bragg-reflector semiconductor lasers: modeling and experiment

We report on the design and fabrication of tapered cavity grating coupled surface-emitting distributed Bragg reflector (DBR) lasers in the 980-nm regime. A curved second-order grating is used at the end of a tapered gain section to provide feedback as well as collimated surface out-coupling. A detailed numerical analysis shows that operation up to approximately twice the threshold is possible without significant degradation of the far field. Near diffraction-limited collimated surface-emitting output with moderate power of about 150 mW is obtained under continuous operation.     

转子-轴承耦合系统动力响应问题研究

应用有限元法，从流固全耦合角度建立了以速度、压力为求解对象的汽轮发电机组转子—轴承系统动力特性分析模型，研究了不平衡转子在轴承内定速旋转时的流固耦合问题，讨论了各种参数变化对流场和系统动力特性的影响。结合实例深入研究了耦合系统动力特性，指出耦合系统动力特性与单个子系统有一定差别，在高速、大偏心和大不平衡力作用下时较明显。     

一种高增益DC-DC变换器实验分析

针对传统Boost升压电路受到电路元件寄生参数的影响无法实现高升压比的问题,提出了一种基于三绕组双倍压单元的新型高增益直流变换器。变换器利用二极管、电容和耦合电感构成的双倍压单元扩大电压增益,并利用无源无损吸收电路来吸收漏感能量,抑制漏感带来的尖峰电压。通过对新型变换器工作的各个模态进行详细分析,推导了电压增益及元器件电压电流应力;实验表明该新型变换器能够有效提高电压增益、降低功率开关管的电压应力。     

Active Plasmonics: Surface Plasmon Interaction With Optical Emitters

The interaction between surface plasmons and optical emitters is fundamentally important for engineering applications, especially surface plasmon amplification and controlled spontaneous emission. We investigate these phenomena in an active planar metal-film system comprising InGaN/GaN quantum wells and a silver film. First, we present a detailed study of the propagation and amplification of surface plasmon polaritons (SPPs) at visible frequencies. In doing so, we propose a multiple quantum well structure and present quantum well gain coefficient calculations accounting for SPP polarization, line broadening due to exciton damping, and particularly, the effects of finite temperature. Second, we show that the emission of an optical emitter into various channels (surface plasmons, lossy surface waves, and free radiation) can be precisely controlled by strategically positioning the emitters. Together, these could provide a range of photonic devices (for example, surface plasmon amplifiers, nanolasers, nanoemitters, plasmonic cavities) and a foundation for the study of cavity quantum electrodynamics associated with surface plasmons.      

Novel Multiwavelength L-Band Brillouin–Erbium Fiber Laser Utilizing Double-Pass Brillouin Pump Preamplified Technique

We experimentally demonstrate successful operation of an enhanced multiwavelength L-band Brillouin-erbium fiber laser and analyze its performance under various operating conditions. This scheme utilizes double-pass amplification technique to preamplify the Brillouin pump (BP) power within the laser cavity before entering the single-mode fiber. Owing to this double-pass pre-amplification within the erbium gain medium, the proposed laser structure is able to operate at low pumping power and exhibits a low-threshold power of 15.9 mW. Moreover, the double-pass pre-amplification of BP is able to shift the unstable operation of the laser to a higher pump power, enabling us to generate high-power laser signals. We experimentally show that the proposed novel setup can produce up to 30 channels at 40 and 0.035 mW of 1480 nm pump and BP powers, respectively. An obvious suppressant for unstable self-lasing cavity modes because of the effect of homogenous saturation of the erbium-doped fiber gain due to the high intensity of BP is observed in the laser cavity configuration.     

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     

Effects of hot-carrier stress on the performance of CMOS low-noise amplifiers

The effects of direct current (dc) hot-carrier stress on the characteristics of NMOSFETs and a fully integrated low-noise amplifier (LNA) made of NMOSFETs in an 0.18-/spl mu/m complementary MOS (CMOS) technology are investigated. The increase in threshold voltage and decrease in mobility caused by hot carriers lead to a drop in the biasing current of the transistors. These effects lead to a decrease in the transconductance and an increase of the output conductance of the device. No measurable change in the parasitic gate-source and gate-drain capacitances in the devices under test were observed due to hot carriers. In the LNA, the important effects caused by hot carriers were a drop of the power gain and an increase of the noise figure. A slight increase in the input and output matching S/sub 11/ and S/sub 22/, respectively, after hot-carrier stress was observed. The linearity parameter IIP3 of the LNA improved after stress. This is believed to be due to the improvement of the linearity of the I-V characteristics of the transistors in the LNA at the particular operating point where the measurements were performed.     

Accuracy on emitted wavelengths in DFB laser arrays resulting fromthe longitudinal mode selection mechanism

We compare the merit of various longitudinal mode selection mechanism in distributed feedback laser for application as arrayed sources in the wavelength-division multiplexing context. Phase-shifted and complex-coupled laser arrays have been fabricated and characterized. We propose that the dispersion on the emitted wavelengths is strongly correlated to the field localization along the cavity. By comparison of the dispersion values measured within the laser arrays, we can conclude that the complex grating with gain is the best suitable mechanism for high wavelength accuracy and stability, due to the strong and distributed localization of the field in the gain sections of each period of the grating     

Modeling and design of a novel high-sensitivity electric field silicon-on-insulator sensor based on a whispering-gallery-mode resonator

In this paper, we present the modeling and design of a new approach to a miniaturized electric field sensor, based on a whispering-gallery-mode resonator coupled with a Fabry-Perot cavity in silicon-on-insulator technology. The sensing element consists of a metal oxide semiconductor capacitor, optimized to achieve high electrical sensitivity and low optical losses. The theoretical model of the whole sensor architecture includes the influence of all electrical and optical parameters, including thin oxide thickness, silicon and polysilicon doping concentration, optical losses due to propagation, absorption and scattering, wavelength and amplitude characteristics of the architecture, charge accumulation effects in the capacitor, and thermal effects. The very high sensitivity of this device, demonstrated by simulations, is due to the simultaneous influence of the two coupled resonators and the metal oxide semiconductor structure.