Nonlinear inverse synthesis technique for optical links with lumped amplification

The nonlinear inverse synthesis (NIS) method, in which information is encoded directly onto the continuous part of the nonlinear signal spectrum, has been proposed recently as a promising digital signal processing technique for combating fiber nonlinearity impairments. However, because the NIS method is based on the integrability property of the lossless nonlinear Schrödinger equation, the original approach can only be applied directly to optical links with ideal distributed Raman amplification. In this paper, we propose and assess a modified scheme of the NIS method, which can be used effectively in standard optical links with lumped amplifiers, such as, erbium-doped fiber amplifiers (EDFAs). The proposed scheme takes into account the average effect of the fiber loss to obtain an integrable model (lossless path-averaged model) to which the NIS technique is applicable. We found that the error between lossless pathaveraged and lossy models increases linearly with transmission distance and input power (measured in dB). We numerically demonstrate the feasibility of the proposed NIS scheme in a burst mode with orthogonal frequency division multiplexing (OFDM) transmission scheme with advanced modulation formats (e.g., QPSK, 16QAM, and 64QAM), showing a performance improvement up to 3.5 dB; these results are comparable to those achievable with multi-step per span digital backpropagation.

The impact of pump phase-modulation and filtering on WDM signals in a fibre optical parametric amplifier

WDM signal degradation from pump phase-modulation in a one-pump 20dB net-gain fibre optical parametric amplifier is experimentally and numerically characterised for the first time using 10x59Gb/s QPSK signals.

Characterisation of cascaded Raman-assisted fibre optical parametric amplifiers using WDM QPSK signals

We report the first WDM numerical characterisation of crosstalk growth in cascaded Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPAs). A cascade of ten RA-FOPAs results in ∼13dB lower crosstalk than the equivalent cascade of conventional FOPAs.

Compact 120 TW Ti: sapphire laser system with a high gain final amplifier

A 120TW/36fs laser system based on Ti:sapphire chirped-pulse amplification (CPA) has been successfully established in our lab. The final four pass Ti:sapphire amplifier pumped by an energetic single-shot Nd:YAG-Nd:glass laser was designed and optimized. With 24J/8ns pump energy at 532 nm, 300 mJ/220 ps chirped pulse was amplified to 5.98 J in this amplifier, and a total saturated gain of similar to 20 was achieved. The focused intensity of compressed beam could reach to 10(20) W/cm(2) with the M-2 of similar to 2.0. (c) 2005 Elsevier Ltd. All rights reserved.

啁啾脉冲放大系统空间特性的优化分析

采用Franz-Nodvik模型，通过模拟计算，系统地分析了啁啾脉冲放大（CPA）过程中抽运光和信号光能量密度以及晶体参量对放大器输出能量和转换效率的影响。将理论模拟与实验结果进行比较，证明了理论分析的有效性。计算结果表明：在啁啾脉冲放大系统中，存在一个抽运光最佳能量密度。合理选择抽运光的能量密度可以有效提高系统的能量转换效率和稳定性，而且还可以大大降低系统对注入信号光能量的要求以及由于信号光能量抖动所造成的输出不稳定性。

用钛宝石再生放大器产生高重复率啁啾脉冲列

针对啁啾脉冲放大技术建成的钛宝石激光装置，提出一种获得高重复率激光脉冲列的方法．通过改变钛宝石再生放大器中泡克耳斯盒电光开关的传统工作模式，使得腔内放大的脉冲从某特定时刻起，每当在腔内往返一次就以一定的倒出比例（倒出率）倒出腔内脉冲能量的一部分，从而可以在有限的时间段内产生高重复率的啁啾激光脉冲列．基于Franz-Nodvik放大理论，建立了该高重复率再生放大器的理论模型，通过数值计算，系统地分析了初始增益、倒出时刻、倒出率对输出的脉冲序列的影响．在抽运功率为35mJ、倒出率为1／2的实验条件下，通过腔外

1kHz-0．1TW高效率钛宝石激光放大器

介绍了一种高重复频率掺钛蓝宝石飞秒激光多通高效率放大系统．在抽运功率为23W，入射功率为660mW时，获得7．2W的放大输出，放大效率达30％．经压缩器压缩后，获得单脉冲能量4．5mJ，脉冲宽度为38fs，重复频率为1kHz，峰值功率大于0．1TW的超短超强激光脉冲．

Spectral shaping of femtosecond pulses with a prism-waveguide coupler

We report a novel technique for spectral shaping of femtosecond pulses employing a prism-waveguide coupler (PWC). It is demonstrated that the PWC is capable of producing a frequency-dependent loss with greater attenuation at the peak of the spectrum profile of femtosecond pulses than in the wings, which is especially useful for compensation for gain narrowing in most chirped-pulse amplification laser systems.

有限尺寸光栅压缩器的优化设计

分析了超短超强激光系统中有限尺寸光栅压缩器设计的关键物理参数及约束条件,得到了压缩器优化的三项基本变量。给出了一种输出能量最大化的压缩器优化方法,进而确定了有限尺寸光栅压缩器的最大工作能力。针对传统的圆光束方案提出了改进的椭圆光束方案,增大了聚焦能量,减小了焦斑尺寸,提高了峰值聚焦功率密度。通过数值模拟对500 mm曝光口径介质膜光栅在圆光束和椭圆光束两种方案下的最大输出能力进行分析比较,指出单块光栅在椭圆光束方案下可以实现500 fs,500 J,1 PW的脉冲输出。

宽光束进入展宽器提高输出脉冲对比度分析

根据分析啁啾脉冲对比度模型,通过光线追迹法详细分析了展宽器对输出脉冲对比度的影响.发现当扩大进入展宽器的入射光束口径,从2mm扩大到40mm时,输出脉冲的对比度提高了近两个数量级;同时发现在相同条件下,当输入脉冲为双曲正割函数时,其输出脉冲的对比度明显好于输入脉冲为高斯脉冲和矩形脉冲的情形。

Offner展宽器曲面镜误差对输出脉冲对比度的影响

在ffner展宽器的设计研究中,对曲面镜曲率半径的误差研究非常重要,它直接影响输出脉冲的质量。因此有必要分析ffner展宽器中曲面镜曲率半径的误差对输出脉冲对比度的影响。参考ffner展宽器的光线追迹模型,建立了ffner展宽器中曲面镜曲率半径存在误差时的光线追迹模型;根据建立的模型,详细分析了曲面镜曲率半径的误差对输出脉冲质量的影响;发现在目前曲面镜曲率半径的加工误差在0.2%~0.5%的情况下,完全可以满足神光II拍瓦激光装置中对展宽器的要求;同时发现如果曲面镜曲率半径存在误差时,应该尽量使两曲面镜之间的距离保持为凹面反射镜曲率半径的一半,而不是使两曲面镜保持同心。

全电介质脉宽压缩光栅的研究进展

超短脉冲超高能量激光器作为研究光和物质相互作用以及惯性约束聚变的手段而得到了广泛的应用。综述了应用于啁啾脉冲放大(CPA)系统的脉冲压缩光栅(PCG)的发展概况；分析和评述了脉宽压缩光栅的设计原理和制作工艺，并给出了脉宽压缩光栅的发展展望。实践和理论证明采用多层膜介质衍射光栅是实现高性能脉宽压缩光栅的一种优良的设计方案。

用于掺钛蓝宝石激光系统的高反膜的激光损伤

用电子束蒸发制备了用于掺钛蓝宝石啁啾脉冲放大激光系统的TiO2/HfO2/SiO2高反膜，其带宽约为176nm（R>98%, λ0=800nm），激光损伤阈值（LIDT）为2.4 J/cm2。通过TiO2和HfO2单层膜的透过光谱计算了这两种材料的折射率和消光系数。高反膜的性能主要由高折射率材料决定：折射率越高，反射带越宽；消光系数越小，薄膜吸收越小，LIDT越高。最后，讨论了高反膜的激光损伤机制。

用于钕玻璃啁啾脉冲放大系统光谱整形的多层介质膜反射镜

在千焦拍瓦高功率啁啾脉冲放大系统设计中,为了尽量消除增益窄化和增益饱和效应的影响,同时尽可能提高高功率激光输出脉冲信噪比参数,激光脉冲时空和光谱的整形问题备受关注.提出一种光谱整形新方法,利用特定结构的多层介质膜反射镜,可实现对大能量高功率啁啾脉冲钕玻璃放大系统中啁啾脉冲的光谱整形.研究结果表明,只要合理选择多层介质膜系的结构参数,可有效地控制其反射率分布,且在保证反射相位基本不变的条件下其调制度可超过60%.针对钕玻璃1053nm波长设计而成的光谱整形反射镜,反射带宽可达到196nm,色分辨率约为0.1nm,在几十纳米波长范围所对应的相位偏差小于12mrad,相当于λ/524,能够满足"神光Ⅱ"千焦拍瓦改造的技术指标要求.