共查询到20条相似文献,搜索用时 31 毫秒
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超连续谱的相干性直接影响到很多光学测量器件的分辨率及准确性, 如何获得高相干度的超连续谱是当前非线性光学领域的研究热点之一. 本文首先分析超连续谱产生的机理, 认为调制不稳现象是降低超连续谱相干性的重要因素. 因此抑制调制不稳定性, 利用其他非线性效应(如自相位调制)是得到高相干性超连续谱的有效方法. 最后设计了一种全波段正常色散光子晶体光纤,仿真结果表明, 在脉宽400 fs无啁啾高斯脉冲抽运, 50 cm长该光子晶体光纤的条件下, 产生的超连续谱具有在相对功率大于-80 dB的全波段高度相干的特性. 相似文献
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We have investigated both experimentally and numerically the characteristics of wavelength tunable femtosecond soliton pulse generation using a pulse width variable fiber laser and two different types of polarization maintaining fibers. The generated soliton shows the feature of the pulsewidth becoming almost constant at - 250 fs under any conditions of the pump pulse for 220m fiber. High conversion efficiency from pump pulse to a generated soliton pulse accounting for as much as 73% can be obtained. This efficiency decreases with increase in the input power or wavelength shift. A superior conversion efficiency and broad wavelength shift can be obtained by using a more shortened pump pulse. In the numerical calculations, it is predicted that under a condition of constant power of pump pulse, the maximum wavelength shift is achieved when the soliton number N is -1.4. The difference of mode field diameter and the group velocity dispersion (GVD) coefficient β2 affect the wavelength shift and conversion efficiency. Using the fiber with small mode field diameter and small absolute value of GVD coefficient β2, a high conversion efficiency and large wavelength shift can be obtained. 相似文献
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We investigate the dynamics of femtosecond solitons in photonic crystal fibers (PCFs) by including high-order dispersion terms until to sixth-order in the generalized nonlinear Schrödinger equation, in addition to the nonlinear effects of the self phase modulation, self steepening and Raman scattering. We calculate theoretically the pulse parameters using the moment method. In the case of the fundamental soliton, our computed equations are coupled and difficult to solve analytically. However, we use the finite difference method to calculate numerically pulse parameters using an initially hyperbolic secant pulse at 1550-nm with different peak powers along 10m-PCF. Our numerical results show that the nonlinear regimes allow obtaining pulse compressions and initial pulse amplitudes. Furthermore, we remark a pulse broadening, and weak shifts of the peak power positions and frequencies in the critical and dispersive regimes. The use of an initial chirp provides a better pulse compressions and especially for low input powers. Also, the initial positive chirp reduces the optimal compression position lengths, while the negative one increases them. Therefore, we conclude that our theoretical calculations and numerical simulation results show that the moment method associated with the finite differences method is effective for the study of femtosecond pulse dynamics in PCFs. 相似文献
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We propose an ultrafast optical time-to-two-dimensional (2-D) space conversion system using a crystal of β-BaB2O4. The proposed system can optically retrieve a 2-D spatial distribution (an image signal) from an ultra-short laser pulse modulated by an image. The fundamentals are the time-to-space transform and the spatial time-frequency transform. Optical time gating using a nonlinear optical crystal is applied for the time-to-space transform. The experimental system can convert modulated temporal signals into 2-D spatial distribution at the bit rate of 8 Tbit/s. 相似文献
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本文基于变系数的非线性薛定谔方程,数值地讨论高峰值脉冲在色散渐减光纤中的激发和传输。首先,基于变系数非线性薛定谔方程的Peregrine孤子解,解析和数值地讨论精确的Peregrine孤子在色散渐减光纤中的传输特性。其次,通过输入不同的平面波背景上的局域脉冲,研究高峰值脉冲在非线性色散渐减光纤中的激发和传输。结果显示Peregrine孤子在色散渐减光纤中传输时,会产生一个空间和时间都局域化的高峰值单脉冲,并且当啁啾为负时,脉冲的幅值增加,脉宽被压缩。若光纤系统存在增益,脉冲的幅值也会增加。由于非线性光纤中的调制不稳定性过程,不同平面波背景上的小局部扰动都可激发出高峰值脉冲,除了峰值和宽度略有不同外,激发脉冲的形状几乎相同。 相似文献
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基于动量守恒和光参变过程中的三波耦合波方程,和负单轴非线性光学晶体CsLiB6O10的色散方程,研究了在光参变效应中超短激光脉冲由于群速度色散引起的展宽和形变。数值模拟显示,在超短脉冲波形为双曲正割形和无啁啾调制时,高阶群速度色散引起的超短脉冲为50fs时,晶体长度为10mm,紫外光213nm作为基波入射时的脉冲展宽是波长为532nm绿光在同等条件下的1.6倍。脉冲展宽程度与入射波长和晶体长度有关,波长越短和晶体长度越长则脉冲展宽和波形变化越严重,高阶色散引起的超短高斯脉冲展宽,将破坏其波形对称性并引起旁瓣现象。 相似文献
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A project of ultrafast pulse generation has been presented and demonstrated by utilizing the combined nonlinear effects of
stimulated Raman scattering (SRS) and non-degenerate two-photon absorption (TPA) based on silicon nanophotonic chip, in which
a continuous wave (CW) and an ultrafast dark pulse are co-propagating in the silicon chip so that the CW will be modulated
inversely by the dark pulse during the propagation. As a result, an ultrafast bright pulse is achieved using the technique.
Simulation results show that an ultrafast pulse with a pulsewidth (full-width at half-maximum (FWHM)) of about 50 fs is generated
at the end of a 5-mm long silicon chip, when the initial conditions, including an input maximum of 0.5 W and FWHM of ∼176
fs for dark pulse, and CW with power of 5 W, are chosen.
相似文献
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WENO有限差分格式有较高的分辨精度,适合复杂流场的计算,在国际上被广泛采用。本文利用WENO有限差分格式求解2维守恒型欧拉方程,实现了对无粘流体中Kelvin-Helmholtz不稳定性的数值模拟。速度剪切方向采用周期边界条件;扰动增长方向采用嵌边出流边界条件,一个不稳定波长分布64个网格。数值模拟给出的扰动幅值线性增长率与线性稳定性分析给出的结果很好符合,显示了该格式的有效性和精度。数值模拟给出了清晰的密度等值线,表明该方法还具有较好的界面变形捕捉能力。 相似文献
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Dynamics of the plane and solitary waves in a Noguchi network:Effects of the nonlinear quadratic dispersion
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We consider a modified Noguchi network and study the impact of the nonlinear quadratic dispersion on the dynamics of modulated waves. In the semi-discrete limit, we show that the dynamics of these waves are governed by a nonlinear cubic Schrodinger equation. From the graphical analysis of the coefficients of this equation, it appears that the nonlinear quadratic dispersion counterbalances the effects of the linear dispersion in the frequency domain. Moreover, we establish that this nonlinear quadratic dispersion provokes the disappearance of some regions of modulational instability in the dispersion curve compared to the results earlier obtained by Pelap et al.(Phys. Rev. E 91 022925(2015)). We also find that the nonlinear quadratic dispersion limit considerably affects the nature, stability, and characteristics of the waves which propagate through the system. Furthermore, the results of the numerical simulations performed on the exact equations describing the network are found to be in good agreement with the analytical predictions. 相似文献
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由速率方程和功率传输方程得到信号脉冲平均功率和增益系数随脉冲传输距离的变化关系.利用Ginzburg-landau方程,在信号脉冲功率的不断增强和增益系数的不断变化的情况下,研究超短脉冲的传输演化特性,发现信号脉冲平均功率、能量和增益系数等参量受到色散和非线性效应的影响相对较小,而信号脉冲的峰值功率、时域和频域特性则易受到色散和非线性效应的影响.探讨了在非线性作用下,脉冲分裂和展宽等所导致的脉宽不稳定性对传输特性的影响,表明研究脉冲传输问题时,引入脉宽不稳定性有利于提高数值模拟准确度. 相似文献
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Higher-order nonlinear Schr\"{o}dinger equation with the Hirota
constraint conditions is considered, and an analytic solution, which
can describe the modulational instability process, is presented.
Based on the solution, a new pulse train without continuous wave (CW)
background is generated in quadratures and the propagation of the
pulse train is discussed in detail by simulating numerically. The
results show that, unlike the propagation of the picosecond pulse
train, under the effects of the higher-order terms, the pulse train
cannot propagate along the fibre when the energy is very high;
however, for some medium energy the pulse train can stably propagate.
We also investigate the stability of the pulse train against
violation of the Hirota conditions, and the results show that the
pulse train can still propagate stably when the Hirota conditions are
broken. 相似文献
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基于Drude模型研究了异向介质的色散磁导率对调制不稳定性的影响. 结果表明,在反常色散情形,赝五阶非线性在异向介质的负折射区中增大了调制频谱的范围及增益值,这与常规正折射介质中出现的现象正好相反;自陡峭效应在异向介质中有可能为负值,但无论正负,也无论在正折射区还是负折射区,它都抑制调制不稳定性的产生;二阶非线性色散效应在正、负折射区中分别促进和抑制调制不稳定性的产生. 在正常色散情形,由于二阶非线性色散效应的作用,使本来在常规正折射介质中不可能出现的调制不稳定性现象也能出现,这一特性为在正常色散区形成孤
关键词:
异向介质
调制不稳定性
色散磁导率
二阶非线性色散 相似文献