光网络中视频业务传输的节点排队机制

对服务质量(QoS)中的队列机制进行了重点的分析, 并对先进先出(FIFO)以及具有优先级(PQ)的两种队列机制的特点进行了详细的比较。具有优先级(PQ)队列可以降低高优先级业务的平均排队时延, 但却无法保证时延抖动的要求。提出了基于具有优先级队列机制的改进方案。仿真结果表明, 新的排队机制有效得解决了具有优先级(PQ)排队机制中无法保证高优先级(视频)业务传输中的时延抖动问题, 当初始时延分布差别很大的数据包在经过节点排队调度之后, 时延抖动有了明显改善。     

Optimizing amplifier spacing to improve performance in RZ-rectangular pulse based 10 Gb/s single channel dispersion managed optical communication system

In this paper, we optimize the inter-amplifier spacing in combination with duty cycle of RZ data format and EDFAs power so that link length of system can be maximized. The results for EDFA amplifier placement in 10 Gbps single channel dispersion managed optical communication system have been presented. By increasing the length of standard single mode fiber of dispersion 16 ps/nm/km in proportion to the increase in length of compensating fiber of dispersion −80 ps/nm/km, the pre-, post- and symmetrical-dispersion compensation schemes of the system have been compared. Further, schemes are observed at 8, 10 and 12 dBm values of EDFA power in the link with different duty cycle values of RZ optical pulse in the range of 0.2-0.8 with step size of 0.2 in relation to amplifier spacing to get lower value of bit error rate and timing jitter. The graphical results obtained show strong relationship among duty cycle of RZ optical pulse, EDFA power and, dispersion compensation scheme.     

Role of metastable states in circumventing laser pulse jitters in multi-step laser excitation experiments

The role of metastable states in circumventing laser pulse jitters in multi-step laser excitation of high-lying Rydberg and autoionizing states is discussed. A case study is presented where step-wise excitation of 3d4d ³G_3,4,5 states of Ca is achieved despite a large jitter between the laser pulses.     

Design of cascading two stages of high gain harmonic generation scheme based on Shanghai deep ultraviolet free electron laser

Cascading stages of high gain harmonic generation free electron laser (FEL) seem to be a feasible way to generate short wavelength radiation. With help of the analytical estimates, we design a two-stage cascading scheme to achieve 131nm DUV radiation on the basis of the Shanghai deep ultraviolet free electron laser test facility. Detailed studies on the FEL performance, the stability and the sensitivity of the output power to parameter variation have been achieved by GENESIS1.3, and design of the lattice structure is presented.     

Beam transport design for a 1 MeV prototype dielectric wall accelerator

The beam transport design of a novel proton dielectric wall accelerator is introduced in this paper. The protons will be accelerated from 40 keV to nearly 1 MeV under an accelerating gradient that is as high as 20 MV/m. A consideration of the beam line as well as the transport simulation is presented. The influences of the injection timing jitter and the accelerating pulse timing jitter are also discussed.     

GW级纳秒脉冲源激光触发同步实验

结合GW级纳秒脉冲源建立了实验平台,研究了激光触发开关的延迟时间及其抖动与激光能量、工作电压、激光波长、透镜焦距等参数的关系。结果表明:开关延迟与抖动随激光脉冲能量的上升、工作电压的上升而逐渐减小;采用紫外光得到的开关延迟与抖动小于相同条件下红外光得到的结果;在高气压小间隙开关条件下,采用小的透镜焦距可以得到更小的开关延迟与抖动。开关在自击穿电压220 kV、欠压比为80%、采用7 mJ,266 nm 波长激光时的抖动为0.3 ns,在此条件下进行了两台脉冲源的同步实验,得到其同步偏差85%置信率小于0.3 ns。     

纳秒级Trigatron开关触发特性

设计了一种Trigatron开关,以Tesla型GW级纳秒脉冲源为实验平台,实验研究了不同电压极性组合、触发电压、触发间隙、触发极直径和触发脉冲宽度对开关触发特性的影响。实验研究结果表明:开关电压极性组合、触发电压、触发间隙对开关触发特性影响较大,在各欠压比条件下差异均十分明显,触发极直径和触发脉冲宽度对开关的触发特性影响较小。根据实验结果优化了开关结构和工作参数,获得的开关抖动最低可达0.1 ns。     

触发电压对±100 kV多级多通道开关性能的影响

 研制了一种用于快脉冲直线型脉冲变压器的±100 kV多级多通道火花开关,研究了触发电压极性、幅值对多级多通道火花开关触发性能的影响,分析了不同触发电压下开关各部分延时及抖动。研究结果表明：触发电压的极性对双极性多级多通道火花开关触发性能影响较小;开关的触发放电延时和抖动随着触发电压的增大而减小。进一步分析了多级多通道火花开关的触发击穿模式以及影响开关击穿延时和抖动的主要因素,提出了减小开关触发击穿延时及抖动的技术途径。     

一维激光阵列相干合束远场特性的研究

利用傅里叶光学方法,获得了相干合束远场光强的解析表达式,数值模拟和实验研究了一维锁相二极管激光阵列的相干合束远场特性。研究表明:随着参与合束的发光单元数目的增加,尖峰变锐;同相模的光能集中在更小的立体角内,使得相干合束的亮度增加;异相模的光束能量较为分散,其峰值光强有所降低。系统抖动引起远场峰值光强的降低,破坏了远场的对称性和光束质量。相干合束发光单元数目越多,系统抖动对远场的影响便可以忽略。     

Reduction in timing jitter by chirp selection for externally modulated return to zero optical soliton pulse at 10 Gb/s

We investigate the chirp selection of externally modulated RZ soliton pulse at 10 Gb/s for fiber optical communication systems for the reduction in timing jitter. We have chosen single arm Mach-Zehnder amplitude modulator with sin² electrical shaped input-output (P-V) characteristic and its chirp range has been varied in the range of −5 to 5. The timing jitter, Q factor and bit error rate (BER) generated for the chirp range has been studied for various fiber lengths and post compensation has been demonstrated to reduce the timing jitter. The number of fixed output amplifiers after every 60 km span is varied from 2 to 10 and corresponding accumulated ASE noise has been studied to manage timing jitter and BER in permissible range, i.e. 5 ps and 10⁻⁹, respectively. It is observed that when two fiber spans are taken then the compensating fiber length for the system is less than 20 km for each case of the chirp considered. For 10 fiber spans, the compensating fiber length increases in the range 60-90 km depending upon the value of chirp taken. Finally it is shown that the chirp value of external modulator should be set to either 0 or −1 for externally modulated RZ soliton pulse in 10 Gb/s optical communication system which makes the system more insensitive to the timing jitter and the selection of dispersion compensating fiber length.