双折射光纤中克尔效应及光纤—光学逻辑门

本文详细地研究了单模双折射光纤中的克尔效应。讨论了其应用于光纤－光学逻辑门的优点，给出了有关的理论分析和计算结果以实验装置，确定了强度型逻辑门的“１／０”状态，测出了输出光脉冲宽度。理论分析和实验结果符合良好。     

双折射光纤中克尔效应及光纤－光学逻辑门

本文详细地研究了单模双折射光纤中的克尔效应．讨论了其应用于光纤－光学逻辑门的优点,给出了有关的理论分析和计算结果以实验装置,确定了强度型逻辑门的“１／０”状态,测出了输出光脉冲宽度．理论分析和实验结果符合良好．     

基于信号抽运的光纤光参量放大的全光3R再生系统

本文研究了利用恶化信号作为抽运的光纤光参量放大效应(FOPA)进行全光判决的全光3R(再放大、再整形、再定时) 再生实验方案,理论上分析了在不同的抽运功率条件下时(分别对应"0"和"1"码)参量放大抑制噪声的不同机理,表明选用合理的实验参数可以同时对"0","1"码噪声进行抑制.实验中利用高Q值的法布里-珀罗(F-P)滤波器提取了均方根(RMS)抖动仅为180 fs的40 GHz时钟;完成了对40 bit/s的单波长恶化信号的全光判决实验,将恶化信号的信噪比从4.52改善为11.43.实验验证了理论分析的 关键词： 光纤通信 3R再生 光纤光参量放大 全光判决     

色散效应对光纤自相位调制全光再生器性能的影响

针对基于光纤自相位调制效应的全光再生技术,分析了色散效应对再生器转移函数和Q因子改进量的影响以及再生器中色散和自相位调制的相互作用,提出一种通过改变再生器光纤结构实现转移函数平坦区改善的方法。数值结果表明:全光再生器中色散会抑制自相位调制引起的频谱展宽,使Q因子改进量减小;对于色散,非线性系数和长度等参量不同的光纤介质,如果色散与长度的乘积与最大非线性相移的比值一定,再生器的性能基本不变;在两段高非线性光纤间增加适当长度色散补偿光纤,可以改善转移函数平坦区,使平坦区范围显著增加。     

基于非线性光纤环形镜的少模脉冲幅度调制再生器

随着网络带宽需求的快速增加,波分复用系统的容量已接近非线性香农极限.为了适应未来网络的发展,空分复用技术引起了越来越多的关注.本文首次提出基于少模非线性光纤环形镜(FM-NOLM)的脉冲幅度调制(PAM)全光再生器,描述了其工作原理和具体设计过程.采用COMSOL软件对组成FM-NOLM的硫化物高非线性光纤进行了模式特性仿真.以LP01,LP11,LP21三个光纤模式为例,确定了再生器的参数,计算出每个模式的功率转移函数曲线.仿真分析了该少模PAM-4全光再生器的噪声抑制(NRR)性能,并与单模情形进行了比较.研究表明,1)对于每个空间模式的PAM信号,所有再生电平具有一致的功率转移性能;2)当输入信噪比(SNR)约大于20 dB时,三种模式的噪声抑制比均可超过3 dB,并随着输入信噪比线性增加,其斜率约为1.2;3)在相同输入SNR条件下,三种模式的噪声抑制比相差不大,不超过1.1 dB.为了说明再生器的再生性能,当输入SNR为25 dB时,我们还给出了再生前后PAM-4信号的功率分布直方图.与现有的再生方案相比,本文方案的均匀多电平再生转移性能,使其更适合高频谱效率的长距空分复用系统和任意电平数的PAM信号再生.此外,该方案也能够扩展到波长域,有效提高光通信系统的传输容量.     

色散效应对光纤自相位调制全光再生器性能的影响

针对基于光纤自相位调制效应的全光再生技术,分析了色散效应对再生器转移函数和Q因子改进量的影响以及再生器中色散和自相位调制的相互作用,提出一种通过改变再生器光纤结构实现转移函数平坦区改善的方法。数值结果表明：全光再生器中色散会抑制自相位调制引起的频谱展宽,使Q因子改进量减小;对于色散,非线性系数和长度等参量不同的光纤介质,如果色散与长度的乘积与最大非线性相移的比值一定,再生器的性能基本不变;在两段高非线性光纤间增加适当长度色散补偿光纤,可以改善转移函数平坦区,使平坦区范围显著增加。     

基于高非线性微结构光纤的全光再生研究

提出了利用高非线性微结构光纤自相位调制效应进行全光再生的研究方案。分析了一组微结构光纤的色散和非线性特性。结果显示光纤的非线性系数与光纤结构有密切关系。通过减小有效模面积,可以提高光纤的非线性系数。采用一种高空气填充比的高非线性微结构光纤作为非线性介质,进行了基于自相位调制效应的全光再生研究。结果表明,由于微结构光纤的高非线性,采用较短的光纤长度就可以实现较好的再生效果。同时,输入微结构光纤的峰值功率、滤波器的参量选择对光再生的效果有重要的影响,它们必需满足一定要求,才能实现光再生。此外,对再生器的传输特性进行了研究。通过调整输入峰值功率和滤波器的参量,可以对不同宽度的光脉冲信号进行全光再生。     

光纤延迟线型全光缓存器的研究

概括了本课题组在近十年中进行的光纤延迟线型全光缓存器的研究工作,介绍了基本的基于3×3平行排列耦合器的基本缓存单元——双环耦合全光缓存器(DLOB),并以此为基础,构建出缓存时间为1～9999 T(时间单位)的大动态范围、多波长等全光缓存器,速率都在2.5 Gb/s以上,并研制出基于偏振的全光缓存器.对这些缓存器的原理...     

基于光子晶体光纤中的自相位调制的全光再生

利用高非线性光子晶体光纤中的自相位调制效应产生的超连续谱,理论上推导了超窄脉冲信号的再生机制。分别从频域和时域上形象的解释了脉冲再生的原理,该本再生方法可以适用于OTDM的信号再生。实验上对劣化了的脉冲宽度为1.7ps的携带信息的超窄脉冲信号进行了再生,再生之后的信号峰值均衡,消光比达到了15dB。再生前信号中心波长是1548.2nm,重复频率是9.96872GHz。实验中,在1554nm—1570nm和1530nm—1543nm范围内都可以得到10dB以上的再生质量。同时拟合了信号峰值功率和波长关系,得到的曲线和超连续谱曲线相吻合。     

基于半导体光纤环形腔激光器的新型全光AND门和NOR门

提出了一种新型的基于半导体光纤环形腔激光器(SFRL)中同时发生的四波混频效应和交叉增益调制效应同时实现全光AND门和NOR门方案，并建立了这种全光逻辑门完整的宽带理论模型.通过数值模拟的方法，研究了输入信号光峰值功率及SFRL中两个耦合器的耦合比对这种全光逻辑门输出特性的影响. 关键词： 半导体光纤环形腔激光器 全光逻辑门 四波混频 交叉增益调制     

基于光克尔门空间扫描单次激光信噪比测量

提出一种基于光克尔门空间扫描的单次激光信噪比测量方法.在该方法中,门光和探测光在光克尔介质中正交传输,通过光克尔门对探测光的空间扫描实现激光信噪比测量.采用该测量方法进行了单次激光信噪比测量的实验研究,测得时间窗口和分辨率分别为88.2ps、2.7ps.由于取样门是由光克尔效应来控制,因此该激光信噪比测量方法对于待测激光的波长没有限制.     

Longitude magneto optical Kerr effect of Fe/GaAs (0 0 1) with Al overlayers

The longitude magneto optical Kerr effect (LMOKE) is investigated on ultrathin Fe film grown on GaAs (0 0 1) substrate with Al overlayer. The formula of the longitude magneto optical Kerr effect is derived to find out the influence of the Al overlayer on the magneto optical properties of Fe/GaAs (0 0 1) sample. Results obtained from this formula fit very well with the experimental data. The change of the Kerr rotation as a function of the incident angle is also given, which can be used to find a proper angle in sample measurement. A numerical simulation was carried out to find out the relation between Kerr rotation and optical properties of the overlayer. Results from this simulation can be used to select the best overlayer material to protect the Fe/GaAs (0 0 1) sample.     

Partial compensation of Kerr nonlinearities by optical phase conjugation in optical fiber transmission systems without power symmetry

We investigate the suppression of Kerr nonlinearities by optical phase conjugation (OPC) in a fiber transmission system without power symmetry by including all the manifestations of the Kerr nonlinearities. We found that OPC cannot completely compensate for all Kerr nonlinearities in absence of power symmetry, and some nonlinearities may become even worse if one of the nonlinearities is fully compensated. Therefore, it is necessary to optimize the compensation system to eliminate the most dominating nonlinearity. Simulation results are presented to demonstrate the interplay of various kinds of nonlinearities. The need of proper design for transmission systems to suppress the dominating nonlinear effect is shown when all manifestations of Kerr nonlinearity are not compensated simultaneously.     

振荡流下回热器压降特性的实验研究

研制了一种简单实用的实验装置,用于振荡流回热器压降特性的研究。在活塞提供的振荡流作用下,研究了回热器孔隙率、长度、堆叠方式及温差对回热器动态压降的影响。实验结果显示,丝网型回热器的动态压降与回热器的长度及孔隙率几乎呈线性关系,而在相同条件下与丝网的堆叠方式无明显的关联;此外,回热器的动态压降随回热器两端温差的增加而增大,与温差变化方向无明显联系。本文研究的目的是为斯特林回热器的设计提供相关的实验数据。     

Distortions of the statistical distribution of Barkhausen noise measured by magneto-optical Kerr effect

In magneto-optical Kerr measurements of the Barkhausen noise, a magnetization jump ΔM due to a domain reversal produces a variation ΔI of the intensity of a laser beam reflected by the sample, which is the physical quantity actually measured. Due to the non-uniform beam intensity profile, the magnitude of ΔI depends both on ΔM and on its position on the laser spot. This could distort the statistical distribution p(ΔI) of the measured ΔI with respect to the true distribution p(ΔM) of the magnetization jumps ΔM. In this work the exact relationship between the two distributions is derived in a general form, which will be applied to some possible beam profiles. It will be shown that in most cases the usual Gaussian beam produces a negligible statistical distortion. Moreover, for small ΔI the noise of the experimental setup can also distort the statistical distribution p(ΔI), by erroneously rejecting small ΔI as noise. This effect has been calculated for white noise, and it will be shown that it is relatively small but not totally negligible as the measured ΔI approaches the detection limit.     

用两级方向耦合器组成的光纤反射器

提出了用级联方向耦合器组成光纤反射器的设想，给出了其基本结构形式，推导了各种结构的光场量和强度的反射和传输系数，并对其特性进行了分析和比较。     

Study of the Performance of an All-Optical Half-Adder Based on Three-Core Non-Linear Directional Fiber Coupler Under Delayed and Instantaneous Non-Linear Kerr Responses

Abstract

Recently, much attention has been given to the influence of the relaxation process of the non-linear response, because the usual assumption of instantaneous non-linear response fails for ultra-short pulses, and additional contributions coming from non-linear dispersion and delayed non-linearity have to be taken into account. This article presents a numerical analysis of the symmetric planar and asymmetric planar three-core non-linear directional fiber couplers operating with a soliton pulse, where effects of both delayed and instantaneous non-linear Kerr responses are analyzed for implementation of an all-optical half-adder. To implement this all-optical half-adder, eight configurations were analyzed for the non-linear directional fiber coupler, with two symmetric and six asymmetric configurations. The half-adder is the key building block for many digital processing functions, such as shift register, binary counter, and serial parallel data converters. The optical coupler is an important component for applications in optical-fiber telecommunication systems and all integrated optical circuit because of its very high switching speeds. In this numerical simulation, the symmetric/asymmetric planar presents a structure with three cores in a parallel equidistant arrangement, three logical inputs, and two output energy. To prove the effectiveness of the theoretical model for generation of the all-optical half-adder, the best phase to be applied to the control pulse was sought, and a study was done of the extinction ratio level as a function of the Δ > parameter, the normalized time duration, and the Sum and Carry outputs of the (symmetric planar/asymmetric planar) non-linear directional fiber coupler. In this article, the interest is in transmission characteristics, extinction ratio level, normalized time duration, and pulse evolution along the non-linear directional fiber coupler. To compare the performance of the all-optical half-adders, the figure of merit of the logic gates was used. All results were obtained numerically, considering a simple model for generation of an all-optical half-adder.     

Output Characteristics of High-Power Continuous Wave Raman Fiber Laser at 1239 nm Using Phosphosilicate Fiber

A high-power singlemode Raman fiber laser (RFL) with maximum output power of 4.11 W and maximum power conversion efficiency of 47.40% at 1239 nm is realized using continuous wave 8.4 W Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and a Raman cavity formed by a pair of fiber Bragg grating mirrors at 1239 nm. The output characteristics of the RFL at 1239 nm for different fiber lengths and output mirror reflectance are reported. Theoretical simulation is done to numerically optimize for fiber length and output coupler reflectivity to obtain maximum first Stokes power.     

活性炭吸附氦气式回热器的吸附特性研究

回热式低温制冷机在空间探测和地面实验中都有重要应用,但是在液氦温区工质氦气的体积比热容高于目前几乎所有的蓄冷材料,导致回热器效率低下.直接使用活性炭吸附一部分工质氦气作为蓄冷填料是一种潜在的解决方案.基于4～J10 K温度区间内吸附量的实验数据,建立了低温动态吸附计算模型,分析了液氦温区动态吸附特性对回热器性能参数的影...