Ultrahigh-bandwidth, on-chip all-optical pulse erasure using the χ(3) process in a nonlinear chalcogenide waveguide

We demonstrate on-chip all-optical pulse erasure based on four-wave mixing and cross-phase modulation in a dispersion engineered chalcogenide (As(2)S(3)) rib waveguide. We achieve an erasure efficiency of ~15 dB for picosecond pulses in good agreement with numerical simulations using the nonlinear Schr?dinger equation. The combined effect of the high instantaneous optical nonlinearity (γ = 9900 (W km)(-1)) and small group-velocity dispersion (D = 29 ps/nm km), which reduces pulse walk-off, will enable all-optical pulse erasure for ultrafast signal processing.     

Formation and erasure of population difference gratings in the coherent interaction of a resonant medium with extremely short optical pulses

In the regime of coherent interaction of short optical pulses with a resonant medium, which is implemented with a pulse duration shorter than the relaxation times in the medium, the formation of population gratings can occur without overlapping the pulses therein. In this case, there are new possibilities for controlling optical pulses, which are especially pronounced for extremely short pulses. It is shown that, with the proper choice of the parameters of a sequence of extremely short optical pulses, not only the formation of population gratings, but also their erasure are possible. It is demonstrated that this effect can be used for the creation of an ultrahigh-speed optical deflector.     

基于PPLN波导中倍频与差频效应的全光波长转换

对准相位匹配的铌酸锂光波导中基于倍频与差频级联二阶非线性效应的全光波长转换进行了研究.在建立理论模型的基础上,分别对单脉冲以及序列光脉冲的波长转换过程进行了数值模拟,并对转换过程中的走离现象以及脉冲延迟进行了分析.模拟结果表明信号光与抽运光脉冲非同步输入的情况下可以克服走离效应的影响,得到更好的转换效率.另外,在抽运时钟脉冲的驱动下,输入的40 Gb/s的NRZ信号光可以转换为RZ转换光,且波形较好.     

Intraband effects on ultrafast pulse propagation in semiconductor optical amplifier

High bit-rate (>10 Gb/s) signals are composed of very short pulses and propagation of such pulses through a semiconductor optical amplifier (SOA) requires consideration of intraband phenomena. Due to the intraband effects, the propagating pulse sees a fast recovering nonlinear gain which introduces less distortion in the pulse shape and spectrum of the output pulse but introduces a positive chirping at the trailing edge of the pulse.     

Regenerative 40 Gbit/s wavelength converter based on similariton generation

We present an all-optical regeneration technique based on spectral filtering of self-similar parabolic pulses (similaritons). In particular, we demonstrate numerically and experimentally that ghost pulses, which occur in the zero bit slots of telecommunication pulse trains, can be effectively suppressed. These results are obtained with a 40 Gbit/s pulse train.     

基于FPGA的脉冲信号发生器的设计

介绍了一种基于FPGA的脉冲信号发生器的设计方法与电路。该仪器可以产生周期在1m s秒到1000 s之间的方波信号,并且信号的占空比可以以千分之一周期的步进进行调节,输出模式可以分成连续模式和单次手动触发模式。输出脉冲f/T的精确度<0.02%,输出脉冲f/T的稳定性<±0.01%。在电路上采用了现场可编程逻辑门阵列(FPGA)来构建,不仅简化了电路,而且提高了精度,降低了功耗和成本。     

Ablation and analysis of small cell populations and single cells by consecutive laser pulses

Laser ablation of single cells through a sharpened optical fiber is used for the detection of metabolites by laser ablation electrospray ionization (LAESI) mass spectrometry (MS). Ablation of the same Allium cepa epidermal cell by consecutive pulses indicates the rupture of the cell wall by the second shot. Intracellular sucrose heterogeneity is detected by subsequent laser pulses pointing to rupturing the vacuolar membrane by the third exposure. Ion production by bursts of laser pulses shows that the drying of ruptured A. cepa cells occurs in ∼50 s at low pulse rates (10 pulses/s bursts) and significantly faster at high pulse rates (100 pulses/s bursts). These results point to the competing role of cytoplasm ejection and evaporative drying in diminishing the LAESI-MS signal in ∼50 s or 100 laser pulses, whichever occurs first.     

Behavioral studies of the auditory discrimination of paired pulses with identical pulse spacings by a dolphin

For a bottlenose dolphin, the thresholds of discrimination of paired pulses with pulse spacings of 50–1000 μs and different peak values of the second pulse in the test pair are investigated. It is shown that the pair discrimination thresholds depend on both the absolute level of pulses and the ratio between the pulse levels in the standard pair. As the pulse delay in a pair increases, the thresholds monotonically decrease. A possibility of the paired pulse discrimination by the total energy of pulses in a pair is considered for the case of pulse delays both within the critical interval (300 μs) and beyond it.     

13μs,200ns和2ns脉冲电场对酵母菌杀灭效果分析

研究了脉冲宽度对高压脉冲下细胞膜和细胞器膜跨膜电压的影响及细胞膜能量的变化,以及13μs,200ns和2ns脉冲对酿酒酵母(CICC31180)杀灭作用时脉冲数的影响。结果表明,随着脉冲数增加,13μs,200ns和2ns脉冲对啤酒酵母的灭杀效果均增强。在13μs脉宽,14kV电压和50个脉冲数下,酵母达到最小存活率-4.3个对数;在200ns脉宽,40kV电压和500个脉冲数下,酵母达到存活率-2.6个对数;在2ns脉宽,200kV电压和500个脉冲数下,酵母达到存活率-2.8个对数。三种脉冲对酵母菌杀灭的存活率对数与脉冲数的关系表现不是线性的,脉冲数增加到一定程度,存活率下降变缓。在同等灭杀效果-2.0个对数下,2ns脉冲比13μs脉冲在同轴电极中损耗的能量更少。     

基于数字调制技术的核磁共振射频脉冲发生器

在核磁共振（NMR）领域,射频脉冲信号的质量、形状对NMR性能及应用有着重要影响.本文基于现场可编程门阵列（FPGA）和直接数字频率合成（DDS）芯片AD9910设计了一种硬件结构更为简单的NMR射频脉冲发生器,实现了射频脉冲各项参数的数字化调制.其频率、相位、振幅的控制精度分别达到了32位、16位和14位,脉冲调制的时间精度为0.01 μs,可灵活生成持续时间不小于0.1 μs、载波频率不高于400 MHz的各类软脉冲和硬脉冲.同时,针对脉冲序列的特点建立了"脉冲+延时"的基础模型,提出了一种通用性更强的列表式脉冲序列控制方案,精简了对上级控制单元的控制需求.此外,对射频脉冲信号的频谱特性进行了理论分析,并采用Hanning窗对软脉冲的包络波形进行了优化处理,仿真和实验结果表明,Hanning窗可以有效抑制软脉冲的频谱泄漏问题.     

啁啾脉冲堆积用于光脉冲整形

报道了一种利用100 ps啁啾脉冲堆积产生2．2 ns任意整形脉冲的脉冲整形系统。采用掺Yb~(3 )光纤锁模振荡器得到稳定的锁模光脉冲序列,将该锁模脉冲通过啁啾光纤光栅展宽并通过1 nm带宽的高斯形光谱滤波器滤波,得到标准的100 ps高斯形啁啾脉冲序列,将此脉冲选单经过光纤延迟线组成的32路脉冲堆积器,得到了精度为32 bit的重复频率为1 Hz的2．2 ns任意整形光脉冲。研究了堆积脉冲的特性,分析了宽带啁啾堆积整形脉冲的光谱时间扫描特性对激光驱动惯性约束聚变打靶束匀滑的优化作用。实验测得了该系统输出的2．2 ns整形光脉冲具有小于50 ps的上升沿,与100 ps啁啾脉冲的时间抖动小于4 ps。     

基于绝热孤子压缩效应的小基座孤子脉冲研究

高重复频率超短光脉冲产生技术是高速光时分复用(OTDM)系统的关键技术之一,而一般的超短脉冲源直接产生的脉冲往往不够窄,因此必须对光脉冲进行压缩后才能满足高速光通信系统的要求。采用360 m长的色散渐减光纤(DDF),成功将从再生锁模光纤激光器(RMLFL)输出的中心波长1546 nm、重复频率10 GHz、脉宽分别为5.40 ps和4.60 ps的光脉冲,绝热压缩为脉宽为1.93 ps和1.71 ps的小基座孤子脉冲,压缩因子分别为2.80和2.69。利用这种绝热孤子压缩方法得到的光脉冲质量较好,可以用于160 Gb/s的光时分复用系统。     

Ultrahigh laser pulse energy and power generation at 10 kHz

This Letter presents results from a new master-oscillator, power-amplifier pulse-burst laser system demonstrating ultrahigh pulse energies greater than 2.0 J/pulse at 1064?nm with interpulse separations of 100?μs (10?kHz) for burst durations of 100 pulses. Each pulse generates peak powers exceeding 130?MW and an average power of approximately 20?kW is generated over a 100-pulse-burst. Pulse energies decrease by less than 10% over a 100 sequential pulses, demonstrating negligible "droop" over long-duration pulse trains. Second-harmonic generation of 532?nm with conversion efficiency greater than 50% is demonstrated for 100-pulse-burst durations.     

Generation of multiple pulses with extremely short pulse repetitioninterval

A new type of multipulse generator is proposed for the generation of high power pulses with an extremely short interpulse repetition interval. In this system, an air-core step-up transformer is used with a magnetic switch and a pulse forming line, which is charged in the double-resonance mode. Numerical simulations of this system have shown that 600 kV, 56 ns pulses, matched to a 20 Ω impedance can be produced with a minimum pulse separation of 2.7 μs. A small system was constructed to demonstrate the production of double pulses experimentally. The system contains two first stage capacitors of 150 nF each, a 1:15 air-core step-up transformer, a magnetic switch using cobalt based material, a second stage capacitor of 1.6 nF, and an 80 Ω load. Double-pulses 100 ns wide, peak voltages of 85 kV (first pulse) and 90 kV (second pulse) have been successfully generated with an interval of 3.75 μs between pulses, when the first stage capacitors were charged to 14 kV (for the first pulse) and 17 kV (for the second pulse)     

Significance of prechirping on long-haul path-averaged soliton impulse in re-circulating loop at 10 and 20 Gb/s with TOD

In this paper, we have investigated the performance of first- and second-order path-averaged soliton long-haul transmission link including the impact of third-order dispersion (TOD) at varied chirp. Here, the varied chirp is considered keeping in view the inadvertent frequency chirp imposed on all practical sources of short optical pulses. The propagation of strongly chirped pulses in loss-managed long-haul path-averaged soliton transmission network has been shown. The investigations reveal that in first-order (N=1) path-averaged soliton transmission link at 10 and 20 Gb/s, SPM effect on the rising and falling edges of a pulse results in spectral broadening for all values of induced chirp. On the contrary, spectral narrowing of the pulses is observed in second-order negatively chirped path-averaged soliton pulses. The effect of the nonlinearity changes from narrowing to broadening of pulses if the sign of the initial chirp is changed to positive. The results ascertain that the system is capable of transmitting a pulse up to the distance of 24,500 km at bit rates of 10 and 20 Gb/s. Investigations have been carried out by varying the chirp factor in the range −1 to 1 and −1 to 0.4] for 10 and 20 Gb/s, respectively, to demonstrate the robustness of the long-haul soliton link. The observations establish that the pulse width (full-width at half-maximum (FWHM)) remains within the optimal range even at the transmission distance of 24,500 km without and at discrete values of the chirp factor.     

Gbit/s rate bipolar pulse modulation of semiconductor injection lasers

Using a bipolar drive current pulse shape and very low threshold (9 mA) lasers, zero-background pseudorandom optical pulses were generated and detected at a rate of up to 4 Gbit/s without a pattern effect. The drive current pulse consists of a forward pulse followed by a reverse pulse, each of 70 ps duration and about 400 mA amplitude. No DC bias was applied, which is a necessary condition for pattern-effect-free modulation.     

测量行波管电子注的法拉第筒的热分析

利用ANSYS软件对测量行波管电子注截面的法拉第筒探头进行了热分析研究.分析了在单脉冲情况下,测量各种直径的不同脉冲功率密度的电子注、不同脉冲宽度对法拉第筒温度的影响,研究了测量不同功率密度的电子注可以使用的脉冲宽度.结果表明,仅法拉第筒上的注斑区域温度迅速上升,温度梯度较大,其它部分温度基本不变,为保证法拉第筒能够持...     

Description of sounds recorded from Longman's beaked whale, Indopacetus pacificus

Sounds from Longman's beaked whale, Indopacetus pacificus, were recorded during shipboard surveys of cetaceans surrounding the Hawaiian Islands archipelago; this represents the first known recording of this species. Sounds included echolocation clicks and burst pulses. Echolocation clicks were grouped into three categories, a 15 kHz click (n?=?106), a 25 kHz click (n?=?136), and a 25 kHz pulse with a frequency-modulated upsweep (n?=?70). The 15 and 25 kHz clicks were relatively short (181 and 144 ms, respectively); the longer 25 kHz upswept pulse was 288 ms. Burst pulses were long (0.5 s) click trains with approximately 240 clicks/s.     

在固体透明材料中利用级联四波混频方法获得宽带多色飞秒激光脉冲的研究

飞秒激光光谱学实验研究的深入与拓展对飞秒激光脉冲的要求也越来越高.比如多色抽运探测实验需要同时用到多个不同频率的超短飞秒激光脉冲.本文设计了一个更加简单紧凑的实验装置,对两束不同中心频率的入射光引入相反啁啾,在厚度为0.5 mm的CaF2晶体中利用级联四波混频获得了光谱半高全宽近100nm,支持傅里叶转换极限脉宽小于10 fs的多色飞秒激光脉冲.这一结果将为拓展飞秒激光光谱学研究和应用发挥重要作用.