Study of power transients in EDFA with gain stabilisation by alaser effect

Power transients at the output of amplifiers with gain stabilisation by a laser effect when switching on/off input channels, are theoretically studied using a simulation model and compared with experimental results     

Effective suppression of signal-wavelength dependent transients in a pump-controlled L-band EDFA

Typical pump-controlled L-band erbium-doped fiber amplifiers (EDFAs) in a feed-forward scheme give significant transients due to gain difference on wavelength of input signal when only a few channels are left. The fiber Bragg grating added pump-controlled L-band EDFA eliminates the wavelength dependent gain difference and transients.     

EDFA gain transients: experimental demonstration of a low cost electronic control

Er-doped fibre amplifier (EDFA) gain transients are dynamic performance-degrading effects that need to be effectively suppressed in next-generation reconfigurable optical networks. In this paper, we experimentally assess the feasibility of an electronic dynamic gain control based on low-cost optoelectronic components, showing that a linearized electrical circuit and a control bandwidth smaller than 1 MHz can achieve the same performance as the commonly proposed all-optical feedback solutions.     

Protecting computer systems against power transients

The sources of electrical transients, broadly interpreted as occurrences of any disturbance, either on the power line or the computer system's data line, are reviewed. Common transients are overvoltages due to lightning strikes, transients caused by switching sequences in the power system, and undervoltages which could be caused by a nearby start-up of heavy loads or by distant faults. The impact of transients on small stand-alone and on distributed computer systems is examined. Growing concern among computer users that power-line surges, in particular, may damage equipment or cause loss of data has created a market for surge suppressors. Some guidelines are provided for choosing a protective device for both types of systems mentioned above. Potential negative side effects are indicated     

EFDA泵浦源半导体激光器驱动电源的设计

设计了一种EFDA泵浦源半导体激光器的驱动电源,采用由PC机和单片机构成的上下位机的控制结构,具有恒定功率和恒定电流两种控制模式.该驱动电源具有激光器保护电路,电流精度和光功率控制精度分别为0.15％和0.2％.     

Bit error rate reduction by power shaping in WDM networks with EDFAs

The trend in multi-wavelength optical networks is toward dynamic route and wavelength assignment to support burst-switching or packet switching. Where erbium-doped optical amplifiers (EDFAs) are used for multi-wavelength amplifications, the time interval between traffic blocks can be long enough to induce EDFA optical power transients created by abrupt changes in the average input power to the EDFAs and can adversely affect the performance of the network. To mitigate the effects of EDFA optical power transients on optical networks, a method based on power shaping where heads and tails are joined to the beginning and end of a traffic block is proposed. A head (tail) gradually increases (decreases) the channel power by employing a pseudo-random bit sequence in which the probability of a “1” (“0”) increases from 0 to 0.5. This paper reports experimental results showing that EDFA optical power transients can be significantly reduced with adequate shaping periods. The effects of alternative shaping profiles are examined, and for a linear shaping profile, experiments show that the drop transient deviation is reduced by 0.5 dB while the add transient deviation is reduced by 0.71 dB. We show by lab experiments that the bit error rate induced by wavelength add-drop transients in a chain of EDFAs in an emulated fiber network can be reduced by 25% using power shaping techniques. Power shaping is an economical means of suppressing EDFA optical power transients compared to other physical layer approaches that require the addition of specialized components and can be applied to EDFAs as well as other solid-state and Raman optical amplifiers.     

System analysis of power transients in advanced WDM networks

This paper considers dynamical transient effects in the physical layer of an optical circuit-switched wavelength-division-multiplexed network. These transients of the average transmission power have millisecond time scales. Instead of studying detailed nonlinear dynamics of the network elements, such as optical line amplifiers, a linearized model of the dynamics around a given steady state is considered. System-level analysis in this paper uses modern control theory methods and handles nonlinearity as uncertainty. The analysis translates requirements on the network performance into the requirements to the network elements. These requirements involve a few gross measures of performance for network elements and do not depend on the circuit switching state. One such performance measure is the worst amplification gain for all harmonic disturbances of the average transmission power. Another is cross-coupling of the wavelength channel power variations. The derived requirements guarantee system-level performance for all network configurations and can be used for specifying optical components and subsystems.     

混合RFA/EDFA与EDFA的QoS性能比较

介绍了采用EDFA系统与采用混合RFA/EDFA系统的两种WDM网络,在放大器正常放大、遭受大功率信号攻击、遭受大功率噪声攻击三种环境下进行研究,通过理论分析和仿真试验得出,在系统QoS性能方面,采用混合RFA/EDFA的系统优于只采用EDFA的系统。     

Low-frequency transients and impedance in the power mainsconsidering line loading

Protection against the transients originated by the connection or disconnection of loads in the power mains is of fundamental importance for the electric energy quality. The knowledge of the parameters of the disturbances and of the characteristics of the mains lines is essential for the mitigation of the unwanted phenomena and for the design of protection measures. This paper offers a lumped-constant analysis of the influence of the network loads on the transient waveshapes, and on the impedance seen when looking into the mains. The complex problem involving two loads and two line sections is reduced to a simplified model permitting analytical treatment with the consequent possibility of prediction and of extraction of the important features. The simplifying assumptions are (1) the line losses are low, and (2) the distance between the loads involved in the transient is short with respect to the total line length. The approximation limits are pointed out and the experimental validation demonstrates excellent agreement. Only the more significant case involving capacitive loading of the line is worked out in detail. Other cases of interest also involving resistive-inductive loading have been treated and are delineated in summary     

利用Optisystem仿真研究EDFA增益的影响因素

利用Optisystem软件建立EDFA系统,对EDFA增益的影响因素进行了分析.通过系统仿真分析,根据影响EDFA增益的因素,确定影响EDFA增益的最佳因素参数,验证了EDFA仿真系统的正确性和设计方案的可行性,更加准确地得到最佳优化设计方案.     

Wavelength and power dependence of injected C-band laser on pumpconversion efficiency of L-band EDFA

The effect of wavelength and power of an injected C-band laser on the pump conversion efficiency of a L-band erbium-doped fiber amplifier was studied via numerical simulation and experiment. In the studied C-band wavelength range of 1530-1560 nm, for higher injected power with longer wavelength, the backward output amplified spontaneous emission power is compressed more; but the residual laser power is greater due to the smaller emission coefficient at longer wavelength. Thus there is a best choice for injection wavelength and power. With an injection of -2 dBm at 1550 nm, 4.3 and 2.5 dB of gain enhancement for -12 and -2.6 dBm input at 1586 nm were achieved, respectively     

Hybrid identification of nuclear power plant transients with artificial neural networks

Proper and rapid identification of malfunctions (transients) is of premier importance for the safe operation of nuclear power plants. Feedforward neural networks trained with the backpropagation (BP) algorithm are frequently applied to model simulated nuclear power plant malfunctions. The correct identification of unlabeled transients-or transients of the "don't-know" type have proven to be especially challenging. A novel hybrid neural network methodology is presented which also correctly classifies the unlabeled transients. From this analysis the importance for properly accommodating practical aspects such as the drift of electronics elements of a simulator, the digitization of simulated and actual plant signals, and the accumulating errors during numerical integration became obvious. Beside the feedforward neural networks trained with the BP algorithm, many other types of networks and codes were used for finding the best (sensitive and robust) algorithms. Various neural network based models were successfully applied to identify labeled and unlabeled malfunctions of the Hungarian Paks nuclear power plant simulator. The BP and probabilistic methods have been proven as the most robust against the misleading recognition of unlabeled malfunctions.     

强激光的时间整形和空间整形——利用双折射透镜组实现激光束的空间整形

本文使用琼斯矩阵方法对双折射透镜组空间整形系统的光强透射率分布和工作特性进行了分析,并讨论了工程设计中参数的选择以及加工误差带来的影响等有关问题.     

强激光的时间整形和空间整形——时空变换脉冲整形系统的工作特性

本专题论文分为两部分。在第一部分中,用傅里叶光学方法,对时空变换脉冲整形系统的工作特性和一些工程设计中的实际问题,作了深入的理论分析和数值计算。     

An EDFA gain control and power monitoring scheme for fault detection in WDM networks by employing a power-stabilized control channel

Schemes are proposed for the highly reliable gain control of erbium-doped fiber amplifiers (EDFAs) and for power monitoring to detect faults in wavelength-division-multiplexing (WDM) networks. These schemes employ one WDM channel (a control channel). The EDFA gain and output power levels are controlled by monitoring the control channel power that is automatically controlled and stabilized in the node. This prevents the uncontrolled EDFA operation that might result from any serious change in the control channel power. The use of a power stabilized control channel for power monitoring makes it possible to detect transmission system faults correctly because the monitoring of the control channel power is unaffected by the amplified spontaneous emission (ASE) generated in the EDFA. We also report experimental results on the dependence of the transient response of the EDFA gain and output power on the signal channel power and channel number input into the EDFA, when the power of the control channel changes due to problems with its light source. Numerical calculation of the gain transience explains the experimental results.     

Numerical analysis of slow current transients and power compression in GaAs FETs

Two-dimensional transient simulation of GaAs MESFETs is performed when the gate voltage and the drain voltage are both changed abruptly. Quasi-pulsed current-voltage (I-V) curves are derived from the transient characteristics. It is discussed how the slow current transients (lag phenomena) and the pulsed I-V curves are affected by the existence of substrate traps and surface states. It is shown that the so-called power compression could occur both due to substrate traps and due to surface states. Effects of impact ionization of carriers on these phenomena are also discussed. It is shown that the lag phenomena and the power compression are weakened when impact ionization of carriers becomes important, because generated holes may help the traps to change their ionized densities quickly.     

Beam shaping to suppress phase mismatch in high power second-harmonic generation

A deliberate pattern of distributing the radiation energy of a high power laser can minimize the steady-state thermal gradients in a nonlinear crystal, thus permitting a large increase of the average powers of such systems. The theory of the two main techniques of beam shaping-fanning and scanning-is developed. Results of several experiments based on this theory are given. Experimental techniques, including some not yet attempted, are discussed.     

高功率半导体激光器光束整形的设计和实现

为了使线阵半导体激光器光束能更好应用于激光远程无线电力传输,设计了基于光楔-曲面镜-棱镜组的线阵半导体激光束整形系统,采用数值计算方法,取得了系统中各元件的参量及理论整形效果。在此基础上加工出实物元件,搭建整形系统。实验中测得整形后的激光光斑尺寸为9.9cm×9.6cm,能量均匀度为68.9%,系统能量传输效率为71.3%,光束质量可满足接收端的光电池对激光空间均匀性的要求。最后分析了仿真系统与实验系统间产生差异的原因。结果表明,该系统可同时实现激光束阵列快轴和慢轴方向的扩束与准直,并能够调节输出光斑的形状及光强均匀度,且采用光学元件数量较少。光电池组件是激光无线电力传输过程的关键元件,该设计对激光转换效率的研究有较重要的实用价值。     

提高半导体激光二极管功率密度的光束整形方法

针对半导体激光二极管由束散角大（14~46）导致的激光功率密度在传播过程中不断衰减的问题,提出了一种提高激光功率密度的光束整形方法。首先以X型柱面平凸透镜和Y型柱面平凸透镜对激光二极管输出光束慢轴和快轴方向进行准直,然后通过一对平凸透镜组合进行扩束,进一步提高光束平行度,最后由单片平凸透镜将光束聚焦为高功率密度的光点。采用Light Tools软件仿真光路、优化光学元件参数,对光学元件进行实际选型后安装并调试光束整形系统。测试结果表明:半导体激光二极管输出光束的67%激光能量汇聚于直径1 mm圆内,激光功率密度优于30 W/cm2。     

Reference level free multichannel gain equalization and transientgain suppression of EDFA with differential ASE power monitoring

We demonstrate a novel means of gain flatness monitoring and control of a multichannel gain flattened erbium-doped fiber amplifier (EDEA), which does not require a gain dependent reference level for the feedback loop. Using the difference of amplified spontaneous emission/probe powers extracted from the edges of the gain-flattened bandwidth, gain flatness monitoring, equalization, and transient gain suppression can be achieved regardless of the steady-state gain value of an EDFA. This approach eliminates the need of elaborate measurements for the determination of control parameters for each application, making it possible to use the same circuitry for different amplifiers. Measurements show flatness control within 0.03 dB/10 nm, at the same time the suppression of time-dependent gain excursion to below 0.2 dB