高速光纤网络中的超短光脉冲产生技术

文章综述了高速光纤网络中的超短光脉冲产生技术及其进展,讨论了实现高效率脉冲压缩的途径,介绍了作者利用阶梯色散渐减光纤环镜代替色散渐减光纤环镜的光脉冲压缩方法的研究成果.数值计算表明,该方法的压缩效果与色散渐减光纤环镜的压缩效果基本一致,解决了色散渐减光纤制作和选择困难的问题,给系统设计带来了方便.     

基于色散渐减光纤的光脉冲压缩技术及其进展

综述了基于色散渐减光纤的绝热孤子压缩、高阶孤子压缩和非线性光纤环镜的光脉冲压缩的方法、原理及其进展,介绍了作者最近的研究成果,即采用色散渐减光纤构成的马赫--曾德尔干涉仪压缩光脉冲.     

光纤脉冲压缩技术及其进展

本文系统综述了基于单榄光纤的脉冲压缩方法，原理及其进展，介绍了我们最近的研究结果，讨论了实现高效率脉冲压缩的途径。     

光纤脉冲压缩技术及其进展

本文系统地综述了基于单模光纤的脉冲压缩方法、原理及其进展，介绍了我们最近的研究结果，讨论了实现高效率脉冲压缩的途径。     

一种新型的全光纤超短光脉冲压缩方案

文章提出了一种基于正常色散递减光纤（ND—DDF）、单模光纤（SMF）和非线性环镜（NOLM）组成的全光纤超短脉冲压缩方案。利用光脉冲在正常色散区的色散递减光纤（ND-DDF）中传输时,在脉冲的中心部分将带上较大线性正啁啾（和普通光纤相比）,当脉冲在SMF中传输时色散致啁啾对其进行补偿从而有一个脉冲压缩的过程,最后利用NOLM对压缩后的脉冲进行进一步的压缩和消基座处理。数值模拟的结果表明：半峰全宽为10ps、能量为74pJ的高斯脉冲经过1km的DDF、79m的SMF和20m的NOLM后,可以获得峰值功率为210W,半峰全宽为120fs且几乎无基座的超短脉冲。     

超高斯光脉冲在单模光纤中的传输特性

从光脉冲在光纤中传输演变所满足的基本方程出发,研究了超高斯光脉冲在普通单模光纤中的传输特性。数值模拟的结果表明,超高斯光脉冲入射后脉冲波形、瞬时啁啾以及峰值强度的演变规律与高斯脉冲入射时不同,脉冲波形不再总保持单峰结构,通常将经历一个从近平顶、多峰、最后到单峰的演变过程;从脉冲的前沿到后沿,瞬时啁啾也不再为线性,而是具有多个极值;峰值强度随传输距离的变化趋势也不再为单调递减,而是先增加后减小。这些变化规律还与入射超高斯脉冲的边沿陡峭程度和初始频率啁啾有关。     

光脉冲的初始啁啾对单模光纤的色散效应的影响

在光纤通信中已经有利用光脉冲的初始啁啾来进行色散补偿的运用。文中从理论上分析了光脉冲的初始啁啾与单模光纤的色散效应的关系，并用数值仿真的方法验证了分析结果：线性初始啁啾可以在一定程度上补偿一阶色数，但却加大了高阶色散对传输光脉冲的负面影响。     

利用光纤环形镜开关特性与孤子压缩效应获得无基座超短光脉冲

利用色散渐减光纤中高阶孤子非绝热压缩及非线性环形腔镜的消基座作用获得高质量无基座超短光脉冲.可以把波长为1.55 μm,脉宽为20 ps的光脉冲压缩为1.42 ps无基座超短脉冲.并与直接用色散渐减光纤的非绝热孤子压缩得到的同宽度光脉冲分别在光纤正负色散区传输进行了比较,发现用色散渐减光纤构成的非线性光纤环形腔镜获得的压缩光脉冲具有相对理想的波形和频谱结构,有利于在光纤中长距离稳定传输.     

超短光脉冲技术的研究进展

超短光脉冲在遥测、探索微观世界的规律以及产生高温等离子体等方面有极广泛的用途。介绍了超短光脉中产生的工作原理及国内外发展状态,并介绍了几种获得超短光脉冲的方法。     

Field in Single-Mode Helically-Wound Optical Fibers

The scalar field wave equations of the fundamental mode in single-mode helically-wound optical fibers with circular cross section are obtained by using the Maxwell equations in the local orthogonal curvilinear coordinate system introduced by Tang. Two important results are brought about 1) The field in the above-mentioned fibers maintains a quasi-linear state of polarization while its orientation rotates with a rotation rate close to - tau with respect to the Serret-Frenet frame. 2) The state of polarization (SOP) of the above field changes periodically along the propagation distances from 1 to a value a little less than 1, and, for a fixed s, it changes periodically according to the incident polarized angles with a period/spl pi//2. The theoretical results have been verified by the experimental measurements.     

Single-Mode Pulse Dispersion in Optical Waveguides

The limitations of a widely used method for analyzing pulse distortion in a single-mode waveguiding structure are derived. The results are applied to propagation in optical waveguides, and for cases where material dispersion is dominated by a broad resonance line, pulse attenuation is found to be much more serious than the broadening of the pulse. In extremely low-loss regions, however, other effects may cause the reverse to be true.     

远红外自由电子激光器中超短光脉冲的产生

探讨了射频型远红外波导自由电子激光器（ＦＩＲ—ＦＥＬ）中产生超短光脉冲的可能性。由于短电子束辐射出与其长度相当的光脉冲．因此提出了选择适当的电子束起始相速度来确保正增益和光脉冲折射率沿相对滑移方向单调增加，这样当光脉冲渡越折射率渐变的“增益介质”—电子束团时．光脉冲前后沿将向中心相向移动而使其径向宽度被压缩。则可能获得远红外波段的高功率超短光脉冲。     

基于电吸收调制晶体的超短光脉冲产生的数值模拟

数值模拟了基于电吸收调制晶体（ＥＡＭ）的超短光脉冲源的输出脉冲宽度及消光比与外加反向偏压、射频信号幅度之间的变化关系。数值模拟结果表明,在重复率为１０ＧＨｚ情况下,可以获得的最小脉宽约为１３ｐｓ,其消光比大于２０ｄＢ,脉冲波型接近ｓｅｃｈ＾２孤子波型。因此,基于ＥＡＭ的超短光脉冲源可以满足２０Ｇｂ／ｓ的光时分复用（ＯＴＤＭ）系统的需求,也适合于超长距离的光孤子通信系统。     

单模光纤中啁啾脉冲的分裂机制

采用分步傅里叶算法数值求解非线性薛定谔方程,分析了单模光纤中不同情形下皮秒量级啁啾脉冲的分裂机制。结果表明,对于较短的脉冲(10 ps),啁啾脉冲分裂从高阶孤子压缩导致的脉冲塌陷开始;对于较长的脉冲(200 ps),脉冲分裂主要由调制不稳定性导致;对于介于两者之间的脉冲(50 ps),噪声使得脉冲分裂机制从高阶孤子压缩转向调制不稳定性。初始正、负啁啾能分别加速和延缓短脉冲分裂,而初始啁啾对长脉冲分裂影响很小。初始啁啾对脉冲分裂的影响与其分裂机制密切相关。     

Wave Coupling Between Parallel Single-Mode and Multimode Optical Fibers

A directional coupler composed of a single-mode optical fiber and a multimode optical fiber has been considered to be capable of serving as a drop/insert device of a node in optical fiber Iocal area networks. It should couple almost all the local transmitter power into the multimode fiber bus, while removing only a small fraction of the optical power from the bus through the single-mode fiber. In this paper, the underlying fundamental process of the power transfer between two such optical fibers is analyzed utilizing a coupled-mode theory. Numerical calculations show that wave coupling among the guided modes on the fibers is quite complicated and that the wave amplitude variations along the propagation direction are different from the sinusoidal types resulting from two-mode coupling. The theoretical results do support the expected performance of the proposed couplers and provide an important guide for the design of such devices.     

五阶非线性光纤中光扰动所致超短脉冲串的产生

从光纤中包含五阶非线性效应的扩展非线性薛定谔方程出发,采用分步傅里叶算法,数值模拟了连续光波的幅度受到正弦光扰动的调制后在光纤中演化分裂成超短脉冲串的过程,探讨了五阶非线性效应和正弦调制周期对脉冲串形成和演化特点以及相应频谱的影响.结果表明,与三阶非线性相比,正五阶非线性使形成超短脉冲串的最佳光纤长度缩短,形成的单个脉冲宽度更窄、峰值功率更高,负五阶非线性则相反.正弦调制周期将影响脉冲串的重复率和最佳光纤距离.随传输距离的增加,单个脉冲可能分裂成两个甚至三个分脉冲,在主脉冲之间还可能出现一定数量的峰值功率弱的次脉冲.就频谱特性而言,正(负)五阶非线性可增多(减小)光波频率成分、加宽(窄化)频谱;视主脉冲有无分裂以及次脉冲的存在与否,频谱的形状也会不同.     

Dual-Wavelength Pulse Train Generation Based on Silicon-on-Insulator Optical Waveguides

In this paper, we present and numerically study a method with pump-probe configuration to generate ∼4.17-THz dual-wavelength ultrahigh-repetition-rate pulse train from the continuous-waves (CW) based on the submicron silicon-on-insulator (SOI) optical waveguides. An original ∼4.17 THz repetition rate pulsed pump, with femtosecond pulse duration, at 2900 nm (mid-wave infrared wavelength-MWIR) and 2-channel CW lights at 1450 nm and 1650 nm (near infrared wavelengths) are simultaneously launched into the silicon waveguide. Results show that, when both of CW lights with high intensity pulsed pump are co-propagating along the SOI waveguide, the CW lights will, respectively, experience normal and anomalous group velocity dispersion (GVD) regimes, leading to developing into two inverted ∼4.17 THz repetition rate pulse train by the combined effects of GVD and nonlinear frequency chirp induced by pulsed pump inside the waveguide. Moreover, the outcome pulse trains have short pulse duration and high extinction ratio (ER) comparing with the original pulsed pump if the systems parameters such as input power and waveguide length are judiciously adjusted.     

Ultrashort Optical Pulse Detection for High-Speed Asynchronous Optical CDMA Networks

Like its wireless counterpart, optical code-division multiple access (optical CDMA) offers greater scalability than other optical multiplexing schemes and provides flexible quality of service, physical layer privacy and asynchronous access . However, unlike wireless CDMA, high bit-rate optical CDMA networks use much higher bandwidth, which cannot be effectively processed with modern electronics rendering many earlier developed detection schemes inapplicable. In this paper we show both theoretically and experimentally that conventional electronics-based detection is inefficient in optical CDMA networks and limits the total network throughput by the bandwidth of the photodetector used. As a solution, we show that network performance can be greatly improved using ultrafast all-optical signal processing for signal detection. Recently developed all-optical thresholding devices performing cubic transformation allow for more than seven times increase in throughput for typical network parameters. A comprehensive comparison of different detection methods for optical CDMA including optimized electronics-based and all-optical signal processing-based is given for the first time.