WDM孤子多通道传输系统稳定性研究

光孤子通信技术是一种非线性全光长距离通信,通过利用光孤子脉冲在传输过程中的非线性压缩和色散之间的平衡来实现光孤子脉冲高速长距离通信。同时考虑三种高阶效应和孤子互作用的条件下,通过变分法综合解析DWDM系统中的非线性薛定愕方程,揭示短皮秒和飞秒孤子脉冲传输演化规律。从理论分析和数值模拟两个方面研究超高速长距离光孤子系统中调制器参数和滤波器参数与系统的稳定性关系,得出系统稳定条件,发现在存在SSFS条件下,采用时域和导频滤波复合控制,实现160Gbit/s光孤子零频移稳定传输是可行的。     

光孤子通信系统的色散控制研究

光纤色散特性是支撑光纤孤子通信的决定性因素。比较了目前的几种色散补偿方案后,着重对相位共轭控制的色散控制方式进行了分析研究,该方式利用光纤非线性四波混频产生与输入光脉冲信号相位共轭的输出光脉冲信号,光脉冲的频谱以泵浦光频为中心进行反转,构建成相位共轭器,实现了对放大自发辐射(ASE)噪声、孤子相互作用与色散波等的控制,达到提高系统传输速率、距离和通信容量的目的。     

浅论光孤子通信技术

光孤子通信利用光纤非线性来抵消光纤色散效应,是下一代超高速、长距离、超大容量光纤通信的优选技术。因此,介绍光孤子通信技术的概念和所具有的优越性,从理论上阐明光孤子在光纤通信中部分关键技术;并且归纳光孤子通信技术的应用前景。     

光纤中光孤子传输演化及相互作用研究

基于非线性薛定谔方程,采用分步傅立叶方法模拟了基阶、二阶和三阶皮秒光孤子以及光孤子对在光纤中的传输演化.结果表明,在长距离传输过程中基阶孤子的幅度和脉宽基本不变,是进行光孤子通信的理想载体.高阶孤子的幅度和脉宽变化较大,并呈现一种周期性的变化;孤子对的传输与两个脉冲的初始相位和输入强度相关.考虑三阶色散的飞秒量级孤子在光纤中的传输将不再出现对称性和周期性,脉冲的中心位置将发生偏移,同时脉冲的波形也会发生扭曲.     

光孤子在光纤通信的基本应用

介绍了光孤子的产生、光孤子通信的基本原理、关键技术及其光孤子通信系统构成,展望了光孤子通信的前景。     

30km 2.5GHz光孤子波传输与压缩实验研究

通过实验研究了光孤子源的产生及光纤孤子的传输。采用增益开关分布反馈半导体激光器作为超短脉冲源，用１．４８μｍ激光泵浦的掺饵光纤放大器作为第一级功放，用Ｆ－Ｐ腔谱窗降啁啾技术产生变换限制脉冲，用另一只１．４８μｍ激光泵浦掺饵光纤放大器作为第二级功放，得到了重复频率为２．５ＧＨｚ的高功率变换限制光孤子脉冲；进行了３０ｋｍ光孤子传输实验，观察了光孤子的传输特性与高阶孤子的压缩特性。     

高非线性光纤的性能特点和应用

光纤中产生的非线性效应可应用于光波长变换、光脉冲整形、光信号处理、宽带光源及光脉冲压缩等方面，高非线性光纤（HNLF）是提高光纤非线性作用的关键介质，在这些应用中，只需要较小的泵浦光功率和较短的HNLF就可以达到高效的非线性作用效果。受实际使用环境的影响，HNLF的紧凑封装是必要的，     

2.5GHZ光孤子传输

报导了我国首次成功地实现了２．５ＧＨｚ光孤子传输。近变换极限的孤子脉冲源是带有Ｆ－Ｐ标准具的增益开关分布反馈激光二极管。孤子脉冲的功率通过分别由１４８０ｎｍ和９８０ｎｍ泵浦的两个掺饵光纤放大器放大，当入纤功率达到一阶孤子功率时，经过２１ｋｍ色散位移光纤传输后，孤子的输出脉宽保持不变。同时还观察到孤子脉冲压缩现象。     

超短孤子脉冲在色散缓变光纤中的时间抖动

通过微扰理论分析了超短孤子在色散缓变光纤(DDF)中传输的时间抖动。结果发现三阶色散和拉曼散射分别影响了孤子的位置和频率,是决定时间抖动大小的重要因素。在光纤的拉曼系数一定的情况下,选择不同的三阶色散参数,系统的时间抖动存在一个最小值。当DDF的三阶色散参数为接近零的一个负值的时候,系统时间抖动最小,这个负值与拉曼系数和传输距离有关,其绝对值随传输距离的增大而增大。在采用色散缓变光纤进行超短孤子传输的系统设计中应该重点考虑三阶色散的影响,当DDF的三阶色散参数较大的时候,必须对系统的三阶色散进行补偿,使时间抖动达到最小,能够极大地增加了孤子的传输距离。     

孤子局域共振激发的一种物理模型

作为非线性领域的重要内容,孤子自从被发现以来就得到了广泛的关注。虽然目前关于孤子的传播及其相互作用性质等方面的研究已经相当成熟,但是对于孤子的产生问题仍然没有系统的认识。孤子产生问题的深入研究,不仅对于理解自然界及物理系统中的非线性现象十分重要,对孤子现象的工程应用也极为重要。基于这些原因,一些孤子激发方法的研究不断被提出。在非线性阵列带隙中的能量超透射现象激发孤子理论的基础上,局域共振孤子激发的方法被提出。该方法通过在半无限长β-FPU链中加入缺陷来引入局域共振机制,不仅有效降低了孤子激发的临界驱动振幅,还实现了孤子激发的可控操作。然而,虽然理论分析与数值模拟都证明了这一方法的可行性,但关于该方法的相关实验验证还是空白。为了进一步将该方法推向实际实验,提出了一种简易可行的实验方案,并做了深入的理论分析与大量的数值模拟。该方案给出一种物理模型,该模型以线性弹簧为基本元件,利用结构的几何非线性来构建β-FPU链,并以耦合摆阵列来实现。通过大量数值模拟证明了该方法的可行,同时研究了孤子释放周期与驱动频率、振幅的关系,结果与前述理论一致。此外,还通过数值模拟研究了孤子的激发周期与缺陷处阻尼大小的关系,以及单元质量不均匀性对孤子激发与传播的影响,为进一步实验提供依据。     

Programmable select multiwavelength gigahertz Raman soliton pulse generation

The generation of programmable multiwavelength pulses based on the self-frequency shift of a Raman soliton is demonstrated. The approach produces tunable multiwavelength picosecond pulses. Only select multiwavelength signals with a tuning range of approximately 50 nm are generated with a repetition rate of 9.95 GHz at each wavelength channel. A bit error rate (BER) of better than 1 x 10(-9) was successfully obtained for all the measured multiwavelength Raman soliton pulses. Furthermore, it was found that the signal has an excellent relative intensity noise (RIN) of better than -135.5 dBc/Hz. The BER and RIN measurements show that the frequency-shifted Raman soliton pulses are promising for use in measurement systems, optical gating, signal processing, and wavelength routing optical packet networks with the ability to provide 1:1 communication and 1:N multicasting.     

天线振动对大气激光通信误码率影响的仿真

大气激光通信系统的误码率不仅受到振动时振幅大小的影响,而且受到光学发射天线孔径的影响。通过数值仿真,分析了孔径分别为 17.5mm, 20mm, 25mm 的光学发射天线,在其振动时对大气激光通信误码率的影响。分析表明,在一定距离下,选取产生大光斑的孔径,能提高系统对振动的抗干扰性。这为合理选择光学发射天线的孔径提供了理论依据。     

Picosecond soliton transmission by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors

Stable picosecond soliton transmission is demonstrated numerically by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors (NALMs). We show that, as compared with previous soliton transmission schemes that use conventional NALMs or nonlinear optical loop mirror and amplifier combinations, the present scheme permits a significant increase of loop-mirror (amplifier) spacing. The broad switching window of the present device and the high-quality pulses switched from it provide a reasonable stability range for soliton transmission. We also show that a soliton self-frequency shift can be suppressed by the gain-dispersion effect in the amplifying fiber loop and that soliton-soliton interactions can be partially reduced by using lowly dispersive transmission fibers.     

正常色散光纤消啁啾的孤子传输实验

利用正常色散光纤消啁啾成功地进行了１Ｇｂｉｔ／ｓ，２３公里的光弧子传输，观察到了一阶和高阶孤子传输现象，通过实验发现：采用适当长度的正常色散光纤消负啁啾，不仅能够压窄负啁啾的脉宽而且能够压窄频谱。     

2.5Gb/s O/E/O光波长变换器

介绍了两种高码率Ｏ／Ｅ／Ｏ光波长变换器。实验表明，这两种光波长变换器都具有优良的光、电技术指标和可靠性，其中２．５Ｇｂ／ｓ Ｏ／Ｅ／Ｏ光波长变换器已经应用在广州＝深圳间１０Ｇｂ／ｓ波分复用光纤通信系统中。     

Enigmas of optical and matter-wave soliton nonlinear tunneling

The method of mathematical analogies opens the possibility to study optical and matter-wave solitons in parallel and, due to the evident complexity of experiments with matter wave solitons, offers remarkable possibilities in studies of the BEC systems by performing experiments in the nonlinear optical systems and vice versa. We discuss previous misinterpretations of the binding soliton energy and investigate all possible scenarios of nonlinear soliton tunneling of Schrödinger solitons including soliton splitting on a potential barrier, leading to partial reflection and partial transmission, sub-barrier soliton tunneling and over-barrier soliton reflection. We reveal the most significant modifications of soliton tunneling scenarios due to increasing the binding energy, and show that the self-compressing soliton resembles more the classical particle case than a quantum mechanical behavior. The enhancement of the soliton binding energy is of decisive importance in the testing of a long-standing theoretical result which predicts that an optical soliton can tunnel between two regions of anomalous dispersion across a forbidden region of normal dispersion (enhanced soliton spectral tunneling effect).     

Phase jitter control of ultrashort soliton in high-speed communication systems with nonlinear gain

An expression is derived for soliton phase jitter in soliton transmission with higher-order effects in the presence of nonlinear gain and filters. It is demonstrated that soliton phase jitter can be suppressed efficiently by nonlinear gain in addition to filters not only for long duration solitons but also for ultrashort solitons provided that the nonlinear gain coefficients satisfy specific conditions. This scheme offers an alternative means for the development of ultralong distance soliton transmission systems using differential phase-shift keying (DPSK), and exploits a robust technique to achieve a higher-speed soliton communication system using DPSK.     

Method of all-optical frequency encoded decimal to binary and binary coded decimal, binary to gray, and gray to binary data conversion using semiconductor optical amplifiers

Conversion of optical data from decimal to binary format is very important in optical computing and optical signal processing. There are many binary code systems to represent decimal numbers, the most common being the binary coded decimal (BCD) and gray code system. There are a wide choice of BCD codes, one of which is a natural BCD having a weighted code of 8421, by means of which it is possible to represent a decimal number from 0 to 9 with a combination of 4 bit binary digits. The reflected binary code, also known as the Gray code, is a binary numeral system where two successive values differ in only 1 bit. The Gray code is very important in digital optical communication as it is used to prevent spurious output from optical switches as well as to facilitate error correction in digital communications in an optical domain. Here in this communication, the author proposes an all-optical frequency encoded method of ":decimal to binary, BCD," "binary to gray," and "gray to binary" data conversion using the high-speed switching actions of semiconductor optical amplifiers. To convert decimal numbers to a binary form, a frequency encoding technique is adopted to represent two binary bits, 0 and 1. The frequency encoding technique offers advantages over conventional encoding techniques in terms of less probability of bit errors and greater reliability. Here the author has exploited the polarization switch made of a semiconductor optical amplifier (SOA) and a property of nonlinear rotation of the state of polarization of the probe beam in SOA for frequency conversion to develop the method of frequency encoded data conversion.     

Large nonlocal nonlinear optical response of castor oil

The nonlocal nonlinearity of castor oil was investigated using the Z-scan technique in the CW regime at 514 nm and in femtosecond regime at 810 nm. Large negative nonlinear refractive indexes of thermal origin, thermo-optical coefficients and degree of nonlocality were obtained for both laser excitation wavelengths. The results indicate that the electronic part of the nonlinear refractive index and nonlinear absorption were negligible. Our results suggest that castor oil is promising candidate as a nonlinear medium for several nonlocal optical applications, such as in spatial soliton propagation, as well as a dispersant agent in the measurement of absorptive properties of nanoparticles.