Analysis of optical phase-conjugate characteristics of picosecondfour-wave mixing signals in semiconductor optical amplifiers

We have analyzed for the first time the optical phase-conjugate characteristics of picosecond four-wave mixing (FWM) signals in semiconductor optical amplifiers (SOAs) using the finite-difference beam propagation method (FD-BPM). We show that the optical phase-conjugate characteristics of the FWM signals are strongly dependent on input pump pulsewidths. As a typical example, we have demonstrated that SOAs act as an ideal phase-conjugator, within the confines of reversing the chirp of optical pulses, for a 10-ps input pump pulse and a ~2.2-ps linearly chirped input probe pulse. When the pulsewidth of pump pulse becomes short, the minimum compressed pulsewidth is obtained by using a fiber shorter in length than the input fiber, but having the same group velocity dispersion as the input fiber. For a much shorter pump pulse such as 1 ps, the short FWM signal can be obtained via the gating characteristics of the FWM. However, only a part of the phase information is copied to the FWM signal due to such gating characteristics. The phase information is also degraded due to the fast nonlinear effect in the SOA. Thus, the pulsewidth is not compressed by propagation through a dispersive medium     

Characterization of nonlinear switching in a figure-of-eight fiberlaser using frequency-resolved optical gating

The measurement technique of frequency-resolved optical gating is applied to determine the nonlinear switching characteristics of a passively modelocked figure-of-eight erbium-doped fiber laser. By completely characterizing the intensity and phase of the laser output pulses, the intracavity fields in the nonlinear amplifying loop mirror of the laser cavity are determined by numerical propagation using the nonlinear Schrodinger equation. Excellent switching of 95% can be achieved as a result of uniform phase characteristics developed by pulses propagating in the nonlinear amplifying loop mirror     

Characterization and optimization of optical pulse differentiation using spectral interferometry

A simple fiber-based spectral interferometry setup is implemented for characterizing and monitoring the amplitude and phase of ultrafast temporal waveforms generated by optical differentiation with a long-period fiber grating (LPFG). In particular, the system is applied to characterize subpicosecond odd-symmetry Hermite-Gaussian (HG) pulses, consisting of two /spl pi/ phase-shifted temporal lobes, obtained by temporal differentiation of Gaussian-like pulses. This technique is ideally suited for optimizing the experiment conditions (e.g., wavelength shifting between the input pulse and LPFG transmission characteristic) so as to achieve a nearly ideal odd-symmetry HG temporal waveform (with a sharp discrete /spl pi/ phase shift at its center), of potential interest as a higher order soliton in dispersion-managed optical communication systems.     

Reflection of femtosecond optical pulses from multiple-layer dielectric mirrors--Analysis

We present an analytical treatment of the reflection of femtosecond pulses from broad-band multiple-layer dielectric mirrors. In particular, closed-form expressions are given for the reflected pulse amplitude which includes the dispersive effect of the cubic phase term. It is shown that this term is still insufficient to accurately describe certain experimental results obtained with 20-fs optical pulses. We introduce an alternative technique which describes the phase branches analytically and yields accurate closed-form expressions for the reflected pulse amplitude in terms of complementary error functions having real or complex arguments.     

Investigating nonlinear femtosecond pulse propagation withfrequency-resolved optical gating

Frequency-resolved optical gating (FROG) is used to investigate nonlinear pulse propagation in normally dispersive media. We present high-dynamic-range measurements of broad-bandwidth femtosecond pulses that result from nonlinear propagation in fused silica and compare these measurements with a (3+1)-dimensional modified nonlinear Schrodinger equation. We also demonstrate the ability of FROG to provide information about a noninstantaneous nonlinearity in methanol. In this case, the instantaneous nonlinear index and the time response of the noninstantaneous nonlinearity are used as fit parameters in a (1+1)-dimensional model     

分析任意光脉冲传输的矩阵方法

本文用矩阵分析方法讨论了任意时间场分布的光脉冲在一般色散介质中的传输,引入了光脉冲质量因子M_τ~2和一般化的脉冲复参数P~(-1),得到了具有任意形状和任意啁啾的光脉冲在色散光学系统中传输的ABCD定律。     

Theory of sonogram characterization of optical pulses

We derive a formula for retrieving the amplitude and phase of an optical pulse from its sonogram. When the transfer function of the frequency filter is known, the pulse amplitude and phase are completely retrieved from the sonogram without iterative calculations by using the derived formula. Based on this formula, we find that the width of a sampling pulse, which is used for cross-correlation measurement of the sonogram, must be much shorter than the width of the pulse under test, and that it is not necessarily possible to reconstruct the pulse when we use the pulse under test itself as a sampling pulse. Finally, we discuss possible schemes for sonogram characterization of optical pulses     

光纤中光脉冲的直线平移及幅度衰减振荡特性

为了探索初始1阶相位调制对高斯光脉冲光纤中长距离传输特性的影响规律,从光纤中的非线性光演化方程出发,采用分步傅里叶算法,数值研究了初始1阶相位调制的高斯光脉冲在光纤中传输时的形状、幅度、时间轨道的演化特性。结果表明,高斯脉冲在长距离传输中,一方面其幅度呈现出衰减的振荡行为,另一方面其时间轨道则因为1阶相位调制的存在而发生直线平移;直线平移的大小和方向分别取决于相位调制参量的绝对值和正负号。该工作可扩展非孤子脉冲的长距离传输特性研究,并可用于脉冲时间轨道的直线调控。     

利用频率分辨光学门回归超短脉冲振幅和相位

本文首先介绍频率分辨光学门（RFOG）技术的原理和算法。对于倍频情况（SHG-FROG），我们编程实现了利用计算机快速回归。文中给出了利用该程序所获得的回归结果及对传统算法的改进。事实证明，该算法在分析各种性质的超短脉冲时既准确又方便。     

Efficient time gating in ultrafast optical TDM networks

Ultrafast optical communication is the backbone of high-speed global networking infrastructure. Optical time division multiplexing (OTDM) is a popular technique for embedding data from many simultaneous users on a single optical channel. This paper studies the optimal clock signal used in optical time gating to extract the data of the desired user in an OTDM network. We show that the pulse width of the clock signal can be optimized to achieve a minimum bit error rate (BER) in these networks. In this paper, we assume that the optical clock signal used for time gating has jitter, and there is therefore a delay variation between the clock and data signals. We model this delay as a zero mean Gaussian random variable. Using this model, an analytical BER expression is derived for systems with Gaussian pulses. In the numerical results, we find the optimal values of the clock pulse width by evaluating the BER versus the pulse width for different variances of the delay. Simulation results are also presented to evaluate the accuracy of the analytical expression.     

超短光脉冲的频率分辨光学开关法测量研究

为了对二次谐波型和偏振开关型频率分辨光学开关法测量超短光脉冲的研究,利用矩阵的方法对实验系统中几种常见超短光脉冲的二次谐波-频率分辨光学开关和偏振开关-频率分辨光学开关光谱图进行了数值模拟,并采用基于矩阵的主元素广义投影算法从数值模拟的二次谐波-频率分辨光学开关光谱图中恢复了脉冲的振幅和相位,误差达到收敛的标准(G-4)。结果表明,频率分辨光学开关能够精确地测量超短光脉冲。     

Frequency-resolved optical gating characterisation of passively modelocked quantum-dot laser

A unique, ultra-sensitive frequency-resolved optical gating system was constructed, and the pulse shape and chirp of a quantum-dot modelocked laser was unambiguously measured using this technique for the first time. A clear pulse asymmetry was detected, and evidence that the pulses are recompressible to sub-picosecond lengths is presented.     

三阶色散对光纤中高斯型脉冲传输特性的影响

从含修正项的非线性薛定谔方程出发,采用变分法,导出了在三阶色散情况下光学高斯型脉冲参数随传输距离的演化方程组;在此基础上,求出了振幅与脉宽、频率与啁啾、脉宽与啁啾之间的三个重要约束关系;并进一步得出了脉宽随传输距离演化的解析解;讨论了三阶色散对光纤中高斯型脉冲传输特性的影响.     

拉曼效应下飞秒光脉冲间的相互作用及其抑制

数值模拟了Raman自频移效应下fs光脉冲间的相互作用及其抑制,结果表明：Raman效应的存在使得fs脉冲的相互作用与常规的ps脉冲间的相互作用不同,在初始阶段孤子相互吸引,而后一直处于排斥状态,脉冲间距随传输距离增加而增大,脉冲在传输过程中发生漂移,孤子产生能量交换,传输距离显著减小,严重影响了通信质量;同步幅度调制、非线性增益与滤波器相结合可有效抑制Raman效应下fs光脉冲间的相互作用。     

光纤中非线性阻尼对类明孤子传输特性的影响

研究了光纤中非线性阻尼对类明孤子传输特性的影响,导出了类明孤子脉冲参数演化的动力学方程.对于常规单模光纤,光纤非线性阻尼将对类明孤子脉冲的振幅、脉宽、啁啾、频率和相位参数有影响,而对位置参数ξ无影响.     

Complete characterization of ultrashort pulse sources at 1550 nm

This paper reviews the use of frequency-resolved optical gating (FROG) to characterize mode-locked lasers producing ultrashort pulses suitable for high-capacity optical communications systems at wavelengths around 1550 nm, Second harmonic generation (SHG) FROG is used to characterize pulses from a passively mode-locked erbium-doped fiber laser, and both single-mode and dual-mode gain-switched semiconductor lasers. The compression of gain-switched pulses in dispersion compensating fiber is also studied using SHG-FROG, allowing optimal compression conditions to be determined without a priori assumptions about pulse characteristics. We also describe a fiber-based FROG geometry exploiting cross-phase modulation and show that it is ideally suited to pulse characterization at optical communications wavelengths. This technique has been used to characterize picosecond pulses with energy as low as 24 pJ, giving results in excellent agreement with SHG-FROG characterization, and without any temporal ambiguity in the retrieved pulse     

光纤非线性色散对类明孤子传输特性的影响

应用类明孤子在单模光纤中非线性传输特性的微扰理论，研究了光纤非线性色散对类明孤子传输特性的影响，导出了类明孤子参数演化的动力学方程。结果表明：光纤非线性色散微扰对类明孤子脉冲位置、频率和相位参数有影响，而对类明孤子脉冲振幅、脉宽、啁瞅参数无影响。     

光脉冲特性测量和分析的新方法

文章给出并采用了光脉冲特性分析新方法,对10 GHz光脉冲在色散平坦光纤中的线性传输前后的时域波形、相位和时间带宽积等作了深入研究,并与数值计算得到的双曲正割和高斯光脉冲线性传输特性作了比较,对光脉冲的时域波形、啁啾等作出了更准确的判断,进一步证实了光脉冲的二次谐波-频率分辨光学门测量及其分析新方法的可靠性和准确性.     

短脉冲在色散平坦光纤中传输前后波形、相位和啁啾测量的实验研究

二次谐波频率分辨光学门(SHG-FROG)是能够准确测量短脉冲多项特性参量的新技术。利用二次谐波频率分辨光学门脉冲分析仪对在色散平坦光纤中传输前后的短脉冲进行了测量,得到了待测光脉冲的频率分辨光学门(FROG)图、自相关曲线、自相关频谱曲线、波形和相位曲线以及脉宽、谱宽、啁啾等反映短脉冲特性的信息,对实验结果进行了分析,并与高斯脉冲在单模光纤中的线性传输理论进行了比较。结果表明,激光器输出的短脉冲是具有负线性啁啾的近变换极限高斯脉冲,经过12.7 km色散平坦光纤传输后仍然为具有负线性啁啾的高斯脉冲,其谱宽在传输过程中基本保持不变,脉宽展宽了3.1倍,啁啾增大了4倍。实验测量结果和理论预期一致。