大模场单模增益光纤的研究进展

高功率光纤激光器的发展面临着各种非线性效应和输出模式和功率不稳定等技术瓶颈,而大 模场单模光纤被认为是解决该类问题的主要手段。 本文系统总结了各种典型的大模场单模增益光纤,阐述了各种光纤的 结构特点以及实现原理,重点分析 了光纤的模场面积、输出功率、抗弯曲特性、激光光束质量和制备难度等几项关键指标。最 后介绍了作者最新设计的新型异质包层螺旋侧漏大模场 单模光纤结构模型及其实现路径,该光纤芯径在50～200μm范围内 具有可调控性,且制备相对简单,有望成为大模场单模光纤 发展的一个新的方向。     

GG-IAG大模场光纤制备与增益性能的研究

基于GG-IAG光纤理论模型,设计了掺Nd3＋ 磷酸盐GG-IAG光纤玻璃材料配方;采用管棒法制备了GG-IAG光纤 预制棒,在530℃下拉制了不同直径(200μ m－500μm)的掺Nd磷酸盐GG-IAG大模场光纤;测试了光纤的光谱 参 数与增益性能,然而,由于光纤存在模式泄漏损耗,导致其增益性能不高。为了提高GG-IA G光纤的增益性能,采 取磁控溅射方法,分别在芯径为130μm、160μm和200μm的GG-IAG光纤包层表面蒸镀200 nm的Ag膜作为全反射膜, 使得泵浦光被束缚在光纤中,从而提高了光纤的泵浦效率。实验结果表明,在光纤参数相同 的情况下,镀Ag膜后光 纤的放大效率分别为50%、41.88%、24.33%;而未镀Ag膜光纤的放大效率分别为26.87%、22.8%、 15.87%。说明光 纤表面镀膜能够显著改善GG-IAG光纤的增益性能,研究结果对GG-IAG光纤的应用具有指导 意义。     

流动激光腔中饱和增益的基本变化规律

本文给出在流动激光腔(GDL)中饱和增益系数随场分布沿流动方向变化的基本规律。联系到各振型振动能和振动温度的变化,用激活介质弛豫过程的物理机制对这些规律作了诠释,因而指出例如 Gerry 的单模输出30千瓦的器件还有相当多的可被利用的振动能。     

Measurement of polarization mode dispersion in systems having polarization dependent loss or gain

The principal states of polarization and their propagation characteristics are analyzed for both unitary and nonunitary optical systems in terms of the complex plane representation of polarization. A new method for the estimation of the polarization mode dispersion of the system is proposed together with experimental and simulation results.     

Linear and nonlinear crosstalk suppression for DWDM RZ-DPSK transmitter using a saturated SOA as power booster amplifier

Saturated semiconductor optical amplifiers (SOAs) can be used as booster amplifiers for dense wavelength-division-multiplexing (DWDM) return-to-zero differential phase-shift keying (RZ-DPSK) transmitters. By introducing time interleaving (TI), both linear crosstalk induced by WDM components and nonlinear crosstalk induced by SOA nonlinearities are suppressed. Receiver sensitivities for four-channel DWDM RZ-DPSK signals with 100- and 50-GHz channel spacing were improved 2.2 and 4.2 dB, respectively, by applying proper TI between adjacent channels. A 1-dB gain enhancement was also achieved.     

Dynamics and circuit of a chaotic system with a curve of equilibrium points

Although chaotic systems have been intensively studied since the 1960s, new systems with mysterious features are still of interest. A novel chaotic system including hyperbolic functions is proposed in this work. Especially, the system has an infinite number of equilibrium points. Dynamics of the system are investigated by using non-linear tools such as phase portrait, bifurcation diagram, and Lyapunov exponent. It is interesting that the system can display coexisting chaotic attractors. An electronic circuit for realising the chaotic system has been implemented. Experimental results show a good agreement with theoretical ones.     

Analysis of mode behavior in a waveguide with graded index and gain

Numerical analysis has been carried out for a waveguide with graded index and gain. It is shown that the radiation peak of the fundamental mode is deflected as the gradient of either the index or gain increases. The high-order modes also change their peak intensity ratio as the gradient of index or gain increases. The behavior of the fundamental mode is suitable for use in a beam scanner while that of higher-order modes is suitable for use in a deflection switching of laser beams. The analysis also shows that the modal gain of higher-order modes becomes larger than that of the fundamental mode as the gradient of the index and gain increases, which provides some explanation for the wide laser beam scanning observed by Scifres et al.     

一类非线性系统的模糊神经网络全局滑模控制

文中针对一类非线性系统提出了一种基于模糊神经网络的全局滑模控制策略。设计了模糊神经全局滑模函数,并根据Lyapunov稳定性理论设计出控制器和自适应律。文中以三相并联型有源电力滤波器为实例在MATLAB平台上进行了仿真实验,电网电流谐波畸变率由24. 71%降低到1. 6%,表明所提出的方案具有很好的补偿性能。     

Linear and nonlinear mode interactions in a semiconductor ring laser

In order to understand and explain recently reported nonlinear behaviors in semiconductor ring lasers (SRLs) and to further design novel functional devices, a multimode model has been developed for linear and nonlinear interactions between modes in an SRL lasing unidirectionally. The model includes population pulsation, spectral hole burning, carrier heating, and four-wave mixing effects. Heterodyne detection has been used to make high-resolution measurements of the lasing spectra of an SRL in which the individual resonances associated with the coupled eigenvalues can be observed. By fitting these high-resolution spectra to the model, we have extracted a number of key parameters characterizing the coupling mechanisms in the device and the semiconductor gain medium. Using these parameters, the model generates device characteristics in very good agreement with experimental results, which validate its use for future device design and optimization.     

The effect of transient gain compression in a saturated EDFA onoptical time domain reflectometry testing

This paper examines optical-time-domain-reflectometry (OTDR) pulse distortion due to transient gain compression in a saturated erbium-doped fiber amplifier (EDFA) and the resultant effect on testing long-haul optical fiber systems     

A rapid smart approach for reliability and failure mode analysis of memories and large systems

This paper presents a novel system simulation methodology based on the known Monte Carlo technique, used for reliability and failure mode analysis of complex and large systems. The presented approach, called “state-merging and assorted random-testing” (SMART), is particularly applicable to systems involving different types of clusters of identical components, and is ideally suited for simulation of huge memories and similar systems. Simulators based on this approach are insensitive to the number of system components, system reliability or the number of associated spares or standby units, and thus they afford an extremely small simulation time compared to the accelerated Monte Carlo simulation time.     

Multiple equilibrium points and their significance in the second breakdown of bipolar transistors

Suggests a simple one-dimensional model for the electrical and thermal behavior of a bipolar transistor. The proposed model can be embedded in an external circuit and analyzed by an appropriate circuit analysis program. Existence of multiple equilibrium points for certain biasing conditions is demonstrated and their implication upon the transient behavior of a device is discussed. The triggering mechanism for second breakdown in the case of forward base current, as well as reverse base current, is described in the light of these multiple equilibrium points. Prediction of that part of the safe operating area boundary limited by second breakdown is reported. The results compare favorably with the manufacturer's recommended limit.     

Accuracy considerations in the measurement of the power gain of a large microwave antenna

Accuracy considerations in the measurement of the power gain of a large microwave antenna are discussed. The analysis indicates that, using the power gain comparison method with a standard antenna of nominally 40-dB gain, a large antenna with a power gain of nominally 60 dB could be calibrated to within an error of 0.17 dB (3sigma). The power gain of the standard antenna is considered to be determined via the generalized three-antenna extrapolation method. Individual sources of errors in both the generalized three-antenna extrapolation method and the power gain comparison method are discussed.     

Transverse mode propagation and gain coefficients in a planarwaveguide CO2 laser amplifier

The transverse mode propagation and amplification characteristics of a large electrode area, planar waveguide carbon dioxide laser amplifier have been investigated. Amplification of an imperfectly mode-matched input produces varying output beam quality with changing discharge conditions, through the modification of the propagation constants of the waveguide modes by the gas thermal lens. For improved mode-matching to the amplifier, a near ideal TE₁ output is obtained without discharge-induced variations. The maximum gain coefficient for propagation in the fundamental mode is shown to be dependent on the radio frequency discharge conditions through the frequency dependence of the minimum stable power density. At 81 MHz, a gain coefficient of 0.65 m^-1 at 50 torr pressure is obtained     

Composite one- and two-pass gain saturation in the geometric mode limit of unstable resonators

Design curves, of the geometric mode limit output power of gain-saturated confocal positive branch unstable resonators with mirror separation large compared to mirror diameters, are given as a function of mode magnification, ratio of mean cavity to small signal gain coefficients, and axial and transverse distributions of the small signal gain coefficient.     

Effect of multipath and scattering on array gain of a large adaptive beam forming phased array

An adaptive antenna array system large enough to obtain angular resolving power comparable to common optical systems is called a radio camera. Following an adaptive beam forming procedure the beam is open-loop scanned to get the desired images. Multipath and scattering of the energy reradiated from the target induce phase-front distortions. A theory has been developed showing that the loss in array gain due to the scattered field can be described by a simple relationship involving only two quantities: the strengthSof the scattered field relative to the direct field and a spatial correlation functionrho(theta)associated with the scattering process. The argumentthetais the scanning angle. The array gain isG(theta) = G(0)S[1-rho(theta)]. A series of experiments has been conducted to test the assumptions underlying the development of the theory, which appears to vindicate them. The theory and experiments are described. The theory is then used to determine the degradation in radio camera scanning performance for several important cases of interference caused by reflections.     

WCDMA系统下行链路最优功率和扩频增益分配方案

研究了一种联合优化发射功率和扩频增益的资源分配算法，并就WCDMA系统采用的正交可变扩频因子(OVSF)码和针对其有限的码资源，提出了相应的最优功率和扩频增益分配方案。仿真结果表明，该方案可以显著地提高系统的总数据传输流量，缩短等待服务队列中的等待时间，达到较高的信道利用率。     

Modeling of four-wave mixing and gain peaking in amplified WDMoptical communication systems and networks

A theoretical model is presented for analyzing the propagation of densely spaced WDM optical signals through a cascade of erbium-doped fiber amplifiers and single-mode optical fibers with nonuniform chromatic dispersion. By combining a numerical solution for the EDFA and an analytical expression for FWM components generated through the cascade, the model allows a realistic system analysis which includes gain peaking effect, amplified spontaneous emission accumulation and the effect of dispersion management on the four-wave mixing efficiency. The FWM power distribution at the end of the multi-amplifier transmission link is computed taking into account the phase relation between FWM light amplitudes generated within different sections of the link. The transmission of many WDM channels, evenly spaced around 1547.5 nm, has been analyzed for various dispersion management techniques and propagation distances. Numerical results point out the importance of such a model for a realistic design of WDM optical communication systems and networks. A proper choice of chromatic dispersion, amplifier characteristics, span length, input signal powers and wavelengths, combined with the use of gain equalizing filters, allows to maximize the transmission distance ensuring acceptable signal-to-noise ratio (SNR) and limited SNR variation among channels