相干原子系统的失谐对脉冲调制的影响

研究了一对非共振脉冲在相干介质中的时空传播,着重考究了失谐对相干脉冲相位调制的影响。计算结果表明当脉冲在介质中稳定传播时,脉冲的最终振幅与双光子脉冲共振的情况下相同,只由介质的初始状态决定,与失谐无关。而失谐仅仅只对脉冲的相位进行调制。     

两种基于交叉相位调制的光脉冲压缩方案

基于交叉相位调制的时间透镜可实现精确的二次相位调制, 但是它在光脉冲压缩领域的应用受到了抽运光脉冲的峰值功率过高的限制. 对该峰值功率的表达式进行了推导, 提出使用带有正色散的传输介质来实现输出段色散, 从而降低了抽运光脉冲的峰值功率.并进一步指出, 可以将基于交叉相位调制的时间透镜应用于4f系统, 来实现光脉冲压缩, 从而更有效地降低了抽运光脉冲的峰值功率. 推导了该系统的抽运光脉冲的峰值功率和分辨率的表达式, 并进行了光脉冲压缩的仿真分析.研究结果表明, 在基于交叉相位调制的4f系统中, 可以利用峰值功率较低的抽运光脉冲产生飞秒量级超短光脉冲; 随着压缩系数的提高, 输出光脉冲的脉冲宽度主要受到4f系统分辨率的限制, 并对4f系统分辨率的提高进行了讨论.     

RF modulation studies on an S band pulse compressor

An S band SLED-type pulse compressor has been manufactured by the Institute of High Energy Physics,Beijing, trying to reach 100 MW maximum input power, which means the output peak power is about 500 MW at the phase reversal time. To improve the reliability at very high power, amplitude modulation and phase modulation with flat-top output are considered, and RF modulation studies on the S-band SLED are presented in this paper.Furthermore, a method is developed using the CST Microwave Studio transient solver to simulate the time response of the pulse compressor, which can verify the modulation theory. In addition, the experimental setup was constructed and the flat-top output obtained in low power tests. Both amplitude modulation and phase modulation methods can give flat-top output, and the average power gain for both methods is almost the same.     

直接相位调制产生周期性线性啁啾脉冲特性研究

提出一种利用周期性抛物线调制信号对光脉冲进行相位调制以获得周期性线性啁啾脉冲的方法, 并对其进行了数值模拟与实验研究. 数值模拟结果表明: 增益饱和效应、群速度色散以及同步误差对啁啾脉冲的时间-光谱特性影响较大; 自相位调制对啁啾脉冲的影响较小. 实验获得了0.52 nm带宽的周期性线性啁啾脉冲, 与模拟结果符合较好. 实验结果同时表明装置中存在较大的偏振模色散, 导致幅频效应较大, 后续的研究中需加入对此的考虑. 模拟及实验研究表明: 直接相位调制是一种新型的可方便地获得周期性线性啁啾脉冲的方法, 其在光谱色散平滑中具有潜在应用. 关键词： 直接相位调制 周期性线性啁啾脉冲 幅频效应     

利用交叉相位调制和四波混频制作的时间透镜的仿真分析

利用高非线性光纤中的交叉相位调制和四波混频分别在仿真中实现了时间透镜. 对基于交叉相位调制的时间透镜中的高非线性光纤中的非线性过程进行了仿真分析. 仿真结果表明, 该时间透镜的主要影响因素为色散、自相位调制与四波混频; 通过采用带有一定色散斜率的高非线性光纤可同时消除色散、自相位调制和四波混频的影响; 另外, 该高非线性光纤的色散零点最好选在信号脉冲和抽运脉冲波长的中心附近. 然后对基于四波混频的时间透镜的实现进行了仿真分析. 仿真结果表明, 该时间透镜的主要影响因素为色散、 自相位调制和其他的四波混频; 通过设定合适大小的信号脉冲和抽运脉冲的功率可消除自相位调制和其他的四波混频的影响; 另外, 通过在高非线性光纤中引入一定的色散可进一步提高信号脉冲和抽运脉冲的功率, 从而获得更高功率的输出脉冲. 最后对两种时间透镜系统做出了比较. 关键词： 光脉冲压缩 时间透镜 交叉相位调制 四波混频     

基于脉冲对的交叉相位调制脉冲压缩中离散效应的抑制

提出一种新的抑制离散效应的方法——非对称脉冲对法，并对采用该方法和采用非同步耦合法在基于脉冲对交叉相位调制对脉冲进行压缩过程中，对离散效应影响的抑制效果进行了研究.数值模拟的结果显示：对于峰值功率为10mW、半极大全宽度为5ps的高斯入射脉冲，采用非对称脉冲对法，可以获得压缩比为137、基座能量比为0122、峰值功率为116mW的压缩脉冲. 关键词： 交叉相位调制 离散效应 非同步耦合法 非对称脉冲对法     

Cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in dispersion compensated WDM transmission systems

The basic mechanism of cross-phase modulation induced phase fluctuations in optical RZ pulse propagating in a periodically dispersion compensated transmission line has been investigated. Ordinary differential equations have been derived using variational analysis to estimate the phase fluctuation and the analytical result is verified by numerical simulations based on split-step Fourier method. We therefore explore the impact of different dispersion compensation maps on phase fluctuation for 10 Gb/s and 40 Gb/s WDM transmission systems. The effects of initial pulse spacing between channels, channel spacing and residual dispersion on phase shift have been studied. We find that cross-phase modulation induced phase fluctuation can be mitigated by proper adjustment of channel spacing and/or residual dispersion.     

超短激光脉冲二倍频理论分析

采用快速傅里叶变换（FFT）算法和Rung-Kutta法对KDP晶体中超短激光脉冲二倍频过程作了研究。详细讨论了群速度失配、群速度色散和三阶非线性相位调制效应对倍频光脉冲波形、光谱及转换效率的影响。研究结果表明：在超短激光脉冲二倍频中，三阶非线性相位调制效应可使二倍频光脉冲形状发生畸变，光谱明显展宽且转换效率降低；当入射基频光功率密度大于100GW/cm2时，三阶非线性效应是影响倍频过程的主要因素。     

Rapid pulse shaping with homodyne detection for measuring nonlinear optical signals

We have designed a common-mode interferometric acousto-optic pulse shaper that is capable of shaping individual pulses differently from a mode-locked laser. The design enables the measurement of weak nonlinear optical signals such as two-photon absorption and self-phase modulation at megahertz rates. The experimental apparatus incorporates homodyne detection as a means of resolving the phase of the detected signals. The fast data acquisition rate and the ability to perform measurements in scattering media make this experimental apparatus amenable to imaging applications analogous to measurements of two-photon fluorescence using a mode-locked laser.     

双谐振拓扑高压脉冲电容器充电电源

脉冲电容的充电电源是脉冲功率技术中的关键设备,为研究更高精度的高压脉冲电容充电电源,基于一种较为新颖的双谐振拓扑结构,通过推导传递函数,分析了其电压和电流传输特性。根据双谐振电路存在两个谐振点的特性,提出基于双谐振变换器的充电电源充电方式,即充电阶段采用串联谐振工作模式,到高压保持阶段通过频率调制降低开关频率至接近第二谐振点,实现对脉冲电容自放电压降的动态补偿,从而保证高压充电电源充电精度的同时,极大地提高脉冲电容的高压稳定度。为验证所提出方式的可行性,基于Matlab/simulink搭建仿真模型,分别对串联谐振全桥变换器和双谐振全桥变换器两种拓扑结构进行仿真,实验结果验证了所提出双谐振拓扑的频率调制方式的可行性。     

特形脉冲调制中射频泄漏的影响及其补偿

模拟器件的非理想因素和电路分布参数等影响造成了特形脉冲调制时的射频泄漏;这些射频泄漏将对特形脉冲的激发轮廓产生缺陷.本文从特形脉冲的射频调制原理着手,分析了射频泄漏对选择激发轮廓的影响,并采用一种新的相位循环方法对它进行补偿.实验的结果表明这种补偿方法有一定的实用性.     

Direct time-response measurement of high-speed optical modulators based on stretched-pulse interferometry

A simple technique for the direct measurement of the complex temporal response of a high-speed electro-optic (EO) modulator is proposed. This technique recovers the amplitude and phase temporal profiles of an instantaneous modulation over the duration of a chirped pulse (obtained by linear dispersion) using Fourier-transform interferometry, and it exploits the time-to-frequency mapping induced by the pulse dispersion process. The method can be implemented by using either time- or frequency-domain interferometric detection, allowing the characterization of modulation bandwidths in the tens-of-gigahertz range. The concept is demonstrated by accurately measuring the complex temporal response of a 2.5 Gbps intensity EO modulator.     

色散对高能激光光纤前端FM-AM效应的影响

<正>弦相位调制脉冲可以满足高能激光驱动器对宽带和束匀滑的要求,在光纤系统中传输后,由于光纤中群速度色散的作用,将会产生强度调制,从而加剧光纤功率放大器中的非线性效应和光谱整形的难度.通过对2GHz,14·25GHz正弦相位调制脉冲经过不同光纤长度传输实验为例,结合光纤系统中色散对FM-AM效应影响的理论分析,发现2GHz相位调制脉冲的实验结果与模拟结果符合较好.     

基于频域相位共轭技术的交叉相位调制所致失真的复原

理论分析和讨论了基于频域相位共轭技术的交叉相位调制所致信号失真的复原和补偿机理，数值模拟了在交叉相位调制作用下，高斯脉冲在中距相位共轭光纤系统中的传输演化过程.结果表明，频域相位共轭技术能够抑制交叉相位调制对光纤系统中传输信号的损害，复原其所导致的信号失真，并能够同步补偿群速度色散和自相位调制非线性效应所导致的信号失真.合适的初始脉冲时延和初始脉冲啁啾有利于频域相位共轭技术对交叉相位调制所致信号失真的抑制. 关键词： 频域相位共轭 交叉相位调制 色散 自相位调制     

Measurement of cross-phase modulation in optical materials through the direct measurement of the optical phase change

We measure the cross-phase modulation (XPM) nonlinear indices of optical materials resulting from the interaction of an ultrashort pump pulse at 800 nm with a weak ultrashort probe pulse at 400 nm through the direct measurement of the optical phase change, using frequency-resolved optical gating. The materials studied include fused silica (SiO(2)) , borosilicate glass (BK-7), beta-BBO , and KD(*)P . This method results in a XPM nonlinear index that is in agreement with calculations based on nonlinear indices from previous self-phase modulation measurements.     

Highly sensitive, single-shot characterization for pulse widths from 0.4 to 85 ps using electro-optic shearing interferometry

Single-shot characterization using electro-optic shearing interferometry (EOSI) is shown for pulse widths ranging from their transform limit (0.4 ps) to 200x their limit (85 ps). In EOSI, the spectral phase is reconstructed by interfering two spectrally sheared replicas of the pulse under test, where the shear is produced by applying linear temporal-phase modulation. We present a new reconstruction algorithm for accurately characterizing chirped pulses, even if the pulse extends beyond the linear region of the phase modulation. Furthermore, since EOSI does not rely on nonlinear optical processes, it requires only 1 nJ pulse energies for all pulse widths, corresponding to a single-shot sensitivity 1000x higher than previously demonstrated.     

Generation of single intense short optical pulses by ultrafast molecular phase modulation

Pulses with durations below 4 fs have been generated using the method of ultrafast molecular phase modulation. A laser pulse shorter than the molecular vibrational or rotational period obtains spectral broadening during propagation along a hollow waveguide filled with previously impulsively excited Raman active gases. The induced time dependent phase, frequency, and frequency chirp are controllable by changing the delay between excitation and probe pulse within the molecular vibrational period.     

基于铌酸锂双折射晶体的皮秒拍瓦激光系统光谱整形

为补偿皮秒拍瓦激光系统中钕玻璃宽带放大引起的增益窄化,提出了一种基于铌酸锂双折射晶体的高能量光谱整形方法.在相同强度调制下,对比了BBO、铌酸锂和石英3种晶体,针对1053 nm激光,选用了高双折射率、大口径且不易潮解的铌酸锂作为整形晶体.理论分析了晶体厚度、倾斜角、面内旋转角对强度调制的影响,发现它们分别决定调制的带宽、中心波长及深度.并对整形过程中晶体引入的光谱相位进行了分析,发现各阶色散量随晶体厚度、倾斜角、面内旋转角变化的规律,因此可通过上述参数控制各阶色散量.在此基础上,开展了中心波长为1053 nm、带宽为10 nm、调制深度为80%的光谱整形实验和相位测量实验,实验与理论分析相一致.针对神光Ⅱ皮秒拍瓦激光系统,利用上述整形方案,国内首次实现了1700 J, 6 nm (FWHM)的高能宽带激光输出,有效补偿了增益窄化.研究结果对国内基于钕玻璃放大系统的宽频带激光装置的工程研制具有重要意义.     

Simple and highly sensitive optical pulse-characterization method based on electro-optic spectral signal differentiation

A very simple self-referenced, linear pulse-characterization technique based on spectral phase reconstruction by frequency-domain signal differentiation is introduced. This technique can be implemented using electro-optic intensity modulation of the pulse under test with a synchronized RF sinusoid. The pulse spectral phase profile can be accurately and unambiguously reconstructed from only two measured energy spectra, i.e., at the input and at the output of the modulator, using a direct analytic equation. The method is experimentally demonstrated by precisely characterizing microwatt-power picosecond pulses after linear dispersion through short sections (50-700 m) of conventional single-mode fiber.     

Interaction of counterpropagating few cycle light pulses in nonlinear dielectric media and radiation generation at combination frequencies in this process

The regularities of the interaction of counterpropagating optical pulses of only a few oscillations of the light field in nonlinear dielectric media are studied theoretically. The temporal structure of the pulse field, due to its interaction with the counterpropagating pulse, is shown to be varied such that the field zeros are the most shifted in time and its extreme values are not shifted. The center of mass of the spectral density is shifted to the short-wavelength region. The efficiency of these phenomena is determined by the energy of the counterpropagating pulse and does not depend on its duration and spectral composition. The possibility of wave generation at tripled and combination frequencies is demonstrated for the media whose size is less than the interaction region. The efficiency of this generation with respect to the phase mutual modulation is shown to be increasing with a decrease in the number of oscillations in colliding pulses.