飞秒光脉冲在光子晶体光纤不同色散区产生超连续谱的数值分析

采用预测校正分步傅里叶方法数值模拟了飞秒光脉冲在光子晶体光纤中的非线性传输和超连续谱产生,分析了初始光脉冲的中心波长、峰值功率和光纤长度在光子晶体光纤正、反常色散区对超连续谱形状和带宽的影响。结果表明,当初始光脉冲的中心波长在光纤的反常色散区时,产生的超连续谱宽要远宽于正常色散区,但是光谱的平坦性较差;当光脉冲中心波长在靠近零色散波长的反常色散区且其他脉冲参数不变的情况下,存在一个产生宽且平坦的超连续谱的最佳峰值功率和最佳光纤长度。对于超连续谱系统的优化设计与实际应用具有参考意义。     

基于全正色散光子晶体光纤的超连续谱光源

利用预估校正分步傅里叶法数值求解非线性薛定谔方程, 模拟超短激光脉冲在全正色散光子晶体光纤中传输时的演化情况, 分析了不同脉宽和能量的脉冲对产生的超连续谱的影响. 结果表明: 无啁啾高斯脉冲在此全正色散光子晶体光纤中传输时, 始终保持单个脉冲特性, 提高脉冲峰值功率可进一步展宽获得的超连续谱.模拟结果同时表明, 利用中心波长为1060 nm, 脉宽和能量分别为50 fs, 15 nJ的脉冲抽运此光纤, 当传输12 cm 后便可获得具有较好的光谱连续性和光谱平坦度的超连续谱. 进一步模拟结果表明, 采用棱镜对对其进行脉冲压缩, 可获得脉宽约15 fs, 谱宽约700 nm的理想超连续谱光源. 关键词： 超连续谱 光子晶体光纤 全正色散     

光子晶体光纤中超连续谱产生的理论与实验研究

研究了光子晶体光纤中超连续激光光源的产生机理.利用非线性偏振旋转技术产生的中心波长为1 556.0 nm的飞秒光脉冲作为泵浦光源,在69 m长的高非线性光子晶体光纤中,得到了20 dB带宽约为140 nm的超连续谱;采用实验和数值模拟方法,研究了不同泵浦功率下超连续谱形成的过程.结果表明,在不同的泵浦功率下,超连续谱的形成机理不同,在各种非线性效应的共同作用下,泵浦光脉冲的峰值功率越高,得到超连续谱的带宽越宽,实验与数值模拟结果一致.另外,要想获得平坦的宽带超连续谱,必须选择合适的光纤长度.     

色散平坦渐减光纤中超连续谱的产生

对双正交偏振光脉冲在色散平坦渐减光纤中传输时超连续谱的产生进行了计算和分析。结果表明，由于交叉相位调制效应的作用，双光脉冲可以产生比单光脉冲明显展宽且更为平坦的超连续谱。对于双基孤子脉冲，可以得到-20dB谱宽达388nm的平坦宽带超连续谱，比单基孤子脉冲产生的超连续谱谱宽增加72nm，交叉相位调制效应对超连续谱的产生起到增强的效果。当输入脉冲的抽运功率较低时，交叉相位调制效应对超连续谱的产生的增强效果更为显著，它极大地提高了超连续谱的产生的效率。数值计算的结果还表明，与其他高阶非线性效应相比，拉曼自频率移效应对超连续谱产生的影响更为明显。     

光子晶体光纤产生的超连续谱(英文)

多波长光源在光通信系统中有着广泛的应用,本文提出一种基于超连续谱的多波长光源产生方案.超短脉冲经过光子晶体光纤,基于自相位调制、交叉相位调制、四波混频等非线性效应产生超连续谱,实验中对该超连续谱进行切割,得到多波长光源.仿真和分析发现:对输入脉冲的峰值功率、输入脉冲宽度和光纤长度等各个参数进行调整优化后,可以得到3dB带宽为73nm的超连续谱,且连续谱的指标可以满足超高速、超长距离、超大容量光通信系统对多波长光源的要求.     

色散渐减光纤中超连续谱产生的数值模拟及优化

从脉冲在光纤中传输所遵循的广义非线性薛定谔方程出发,通过数值模拟对色散渐减光纤产生超连续谱(SC)进行了研究.结果表明:色散渐减光纤的色散斜率k、色散参量D0、参量L0和R及脉冲的峰值功率、脉冲宽度对SC谱的产生有着极其重要影响;在色散渐减光纤产生超连续谱的过程中,三、四阶群速度色散甚至更高阶群速度色散对超连续谱的影响完全可以忽略,但高阶非线性效应对SC谱的产生影响很小;计算表明对光纤和脉冲的各参量进行优化选择后,可以获得宽而平坦的超连续谱.     

光子晶体光纤产生飞秒超连续谱的实验研究

研究了飞秒脉冲经过光子晶体光纤时超连续谱产生的物理机制。采用输出波长可调谐的钛宝石光参量放大器作为泵浦源,光纤光谱仪测量不同泵浦功率和不同泵浦波长条件下光子晶体光纤产生的超连续谱的光谱图,对进行了归一化处理后的不同泵浦功率和不同泵浦波长条件下的超连续谱进行对比,分析影响光子晶体光纤超连续谱差异的物理机制。实验结果表明,当泵浦波长不变时,随着入射泵浦脉冲平均功率的增大,波峰增多,谱宽也逐渐加宽并伴随着出现能量向短波方向集中的现象,泵浦功率到达一定强度时,超连续谱的宽度最后到达饱和,谱的包络趋于稳定;入射光功率稳定在300 mW时,超连续谱的宽度和形状皆受到泵浦波长影响,在760～840 nm范围内,泵浦波长越长,波峰数越多,泵浦脉冲波长离零色散点越近,光子晶体光纤产生的超连续谱谱宽会越宽,超连续谱的形状相对越平坦。     

色散平坦渐减光纤中非线性啁啾脉冲的传输及超连续谱的产生

基于非线性薛定谔方程,数值研究了色散平坦渐减光纤中非线性啁啾脉冲的传输及超连续谱的产生。研究结果表明,初始啁啾对脉冲传输及超连续谱产生的影响与泵浦条件和光纤参量的选取有很大关系。当色散平坦渐减光纤具有小的归一化二次色散系数时,适当的正啁啾能显著增强超连续谱的带宽,而负啁啾和太大的正啁啾抑制超连续谱的带宽。能增强超连续谱带宽的正啁啾有一个较宽的范围,但随着输入脉冲孤子阶数的降低,该范围将变窄。当色散平坦渐减光纤具有大的归一化二次色散系数同时输入脉冲为低阶孤子时,初始啁啾对超连续谱带宽的增强效果不明显,初始啁啾接近为0时可产生最宽的超连续谱。     

激光泵浦碲化物产生中红外超连续谱数值模拟

对2 m波段脉冲激光泵浦碲化物光子晶体光纤产生中红外超连续谱进行了数值研究。通过材料的拉曼增益谱间接求得了对应的拉曼响应函数;由光子晶体光纤的材料折射率和波导结构,通过COMSOL软件获得了碲化物光子晶体光纤中基模等效折射率,计算了相应的色散曲线和限制损耗 ;利用自适应的分步傅里叶算法,模拟了中心波长为1.96m、峰值功率为20 kW的50 fs脉冲光泵浦碲化物光子晶体光纤时超连续谱的产生,当光纤长度为6 cm时,产生的中红外超连续谱波长范围为1.0~4.5 m。     

纳米光纤的色散特性及其超连续谱产生

通过数值计算,分析了纳米光纤的色散特性,并比较了纳米光纤中不同直径和不同材料的色散特性.结果表明：二氧化硅纳米光纤有两个零色散波长,随光纤直径的增大,其色散曲线趋于平坦,零色散波长也随之发生改变;硅光纤只有一个零色散波长,且随着直径的增大,零色散波长向长波方向移动.采用广义非线性薛定谔方程来描述超短激光脉冲在纳米光纤中的传输演化过程,利用分步傅里叶方法求解方程.比较了超短脉冲在光纤不同色散区传输时,色散对超连续谱产生的影响以及脉冲波形的演化.在正常色散区,超连续谱谱宽很窄,而在零色散区和反常色散区则可产生 关键词： 色散 超连续谱产生 非线性光学 纳米光纤     

Supercontinuum generation based on nanofiber

Supercontinuum generation (SCG) using a femtosecond Ti:Sapphire laser as a pump source and a nanofiber as a nonlinear element is investigated by numerical modeling. Many parameters are taken into account involving input pulse duration, peak power and diameter of the nanofiber. The results show that the narrower the input pulse is, the easier the SCG could be observed. The relation between the spectrum broadening and the diameter of nanofiber is not a direct proportion. According to our simulation, the dimension of the nanofiber plays an important role in effecting the dispersion and then the generation of supercontinuum.     

飞秒脉冲在熔石英玻璃中超连续谱产生的研究

从非线性薛定谔方程出发,利用分步傅里叶方法,研究了时空耦合飞秒脉冲在熔石英玻璃中传输时,传输距离、入射激光脉冲峰值功率、衍射、色散和非线性等因素对超连续谱产生的影响。结果表明,飞秒脉冲在熔石英玻璃中传输时,超连续谱的产生主要分为两阶段：由材料的自聚焦等三阶非线性效应引起的脉冲压缩阶段及由自相位调制和材料群速度色散引起脉冲分裂阶段。当高峰值功率的飞秒脉冲在熔石英玻璃中传输时,材料的三阶非线性效应抑制衍射效应,引起脉冲压缩,从而产生子脉冲,由此引入新的频率成分。同时,还研究了同一脉冲不同横向空间位置处的超连续谱的变化规律,在中心频率两侧均有新频率产生。最后,通过实验证实了超连续谱的产生。     

Soliton and rogue wave statistics in supercontinuum generation in photonic crystal fibre with two zero dispersion wavelengths

Stochastic numerical simulations are used to study the statistical properties of supercontinuum spectra generated in photonic crystal fibre with two zero dispersion wavelengths. For picosecond pulse excitation, we examine how the statistical properties of solitons generated on the long wavelength edge of the supercontinuum (``optical rogue waves") are modified by energy transfer to dispersive waves across the second zero dispersion wavelength. The soliton statistics (characterized in terms of peak power, wavelength and pulse duration) are shown to be strongly modified by the mechanism of dispersive wave generation, with the detailed form of the probability distribution depending strongly on input pulse energy.     

Highly nonlinear chalcogenide glass micro/nanofiber devices: Design, theory, and octave-spanning spectral generation

In this review we consider the basic elements of tapering chalcogenide optical fibers for the generation of extreme spectral broadening through supercontinuum generation. Creating tapered nanofiber devices in chalcogenide fiber, which has an intrinsic nonlinearity that is two orders of magnitude higher than silica, has resulted in the demonstration of octave-spanning spectra using record low power. We first present a brief theoretical understanding of the tapering process that follows from the basic principle of mass conservation, and a geometric construction tool for the visualization of the shape of tapered fibers. This is followed by a theoretical treatment of dispersion engineering and supercontinuum generation in a chalcogenide nanofiber. In the final section, we cover the experimental implementation of the chalcogenide nanofiber and demonstrate an octave-spanning spectrum created with 150 W of peak power.     

高非线性光纤正常色散区产生超连续谱的数值研究

基于广义非线性薛定谔方程,通过数值计算对高非线性光纤正常色散区产生超连续谱进行了研究.结果表明,抽运脉冲的峰值功率、脉冲宽度以及脉冲初始啁啾对该光纤正常色散区超连续谱的形成有极其重要的影响;在高非线性光纤正常色散区产生超连续谱的过程中,三、四阶群速度色散甚至更高阶群速度色散对超连续谱的影响完全可以忽略,但与其他高非线性效应相比,自陡峭效应对超连续谱产生的影响更为明显.高功率超短光脉冲在高非线性光纤正常色散区,得到了没有泵浦成份残余、－20 dB谱宽达400 nm以上而频谱强度起伏小于10 dB的超宽而平坦超连续谱.     

Pulse collapse and blue-shifted enhanced supercontinuum in a photonic crystal fiber

The blue-shifted supercontinuum generation in a photonic crystal fiber pumped by high peak power femtosecond pulses with a wavelength located in the anomalous dispersion region is investigated experimentally and numerically.The formation of a blue-shifted enhanced supercontinuum due to the pulse collapse is demonstrated.The process of the pulse collapse is measured by using the grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique(GRENOUILLE).Numerical simulations in spectral and temporal domains are conducted.The data from the numerical simulations are in good agreement with the experimental results.Our experimental results and numerical simulations show that pulse collapse is the determining factor in the generation of a blue-shifted supercontinuum.     

Optimization of supercontinuum generation in photonic crystal fibers for pulse compression

A theoretical study of super generation in photonic crystal fiber and its application to pulse compression is presented. The evolution of the spectrum can be divided into three stages: initial broadening below a certain threshold propagation distance, dramatic broadening to a supercontinuum at a threshold distance, and, finally, saturation of the spectral width on propagation. It is found that the group delay and group-delay dispersion of the supercontinum are sensitive to the input pulse peak power after further propagation at the third stage. Fluctuations from the input pulse are amplified and translated into fluctuations and time shift of the compressed pulses. There exists an optimum compressed distance at which compressed pulses with negligible fluctuation and time shift can be obtained.     

Generation of an acoustic supercontinuum under conditions of the hypersound intrapulse scattering mode

The nonlinear generation of an acoustic supercontinuum in a solid doped with impurity paramagnetic ions is studied theoretically. It is shown that generation can be the most efficient at two certain carrier frequencies of input pulses lying above the resonance spin-phonon absorption line and determined by the time and spatial dispersions, respectively. The generated supercontinuum lies well below the resonance absorption line. Generation of the supercontinuum in the single-frequency regime is accompanied by a shift of the input pulse spectrum mainly to the red. In the two-frequency regime, cross scattering is possible when a higher-frequency pulse is scattered by the powerful supercontinuum generated by a pulse with a different, lower carrier frequency. As a result, the spectrum of the high-frequency pulse experiences a strong modulation and broadening both to the red and blue. The efficiency of supercontinuum generation both in the single-frequency and two-frequency regimes can be on the order of 1%.     

Pulse collapse and blue-shifted enhanced supercontinuumin photonic crystal fiber

The blue-shifted supercontinuum generation in a photonic crystal fiber pumped by high peak power femtosecond pulses with wavelength located in the anomalous dispersion region is investigated experimentally and numerically. The formation of a blue-shifted enhanced supercontinuum due to the pulse collapse is demonstrated. The process of the pulse collapse is measured by using the grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields technique (GRENOUILLE). Numerical simulations in spectral and temporal domains are conducted. The data from numerical simulations are in good agreement with the experimental results. Our experimental results and numerical simulations show that the pulse collapse is the determining factor in the generation of blue-shifted supercontinuum.