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.     

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.     

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.     

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。     

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     

Spectral dependence of differential gain, mode shift, and linewidthenhancement factor in a InGaAs-GaAs strained-layer single-quantum-welllaser operated under high-injection conditions

Strained-layer quantum-well lasers, when operated at moderate injection levels, are known to exhibit a reduced linewidth enhancement factor, α, an important parameter in the design of semiconductor lasers. Under increased loss conditions, when spill-over of carriers into the barrier becomes significant, they can also be operated in a quasi-double-heterostructure mode at the barrier wavelength. Thus, by proper control of loss, lasing at different wavelengths is possible, at least in principle. An investigation has been carried out to determine explicitly the spectral dependence of the differential gain, spectral shift, and α of a narrow-stripe InGaAs-GaAs separate-confinement strained-layer single-quantum-well laser operated near the wavelength of the GaAs barrier under extremely high injection. Despite the carrier spill-over, α was found to be remarkably low, about 1.7 at the spectral gain peak (877 nm), which was also the lasing wavelength     

移动通信系统中宽带功放线性化设计与仿真

自适应数字预失真技术能够解决宽带高峰均比信号经过功放产生的非线性失真问题.主要介绍了自适应数字预失真的结构、预失真器的数学模型及相关的自适应算法.仿真结果表明采用自适应数字预失真技术能够显著地改善功放输出信号的带外频谱失真,是一种有效、灵活的技术.     

Electrical impedance as a source of information in man-machine systems

Electrical impedance as measured with the four-electrode technique on the skin over active muscles was investigated as a control signal in man-machine systems. The impedance level showed well-defined relationships to mechanical parameters. This control method is suggested to have distinct advantages as compared to current techniques.     

The state observer and compensator of a large class of 2-D acceptable singular systems

Under the assumption of nonexistence of the jump-mode, this paper gives a simple form of a large class of 2-D singular systems. This class of systems includes all the systems resulted from the linear state transformations of 2-D singular Roesser models and hence we called it the extended singular Roesser models. The criteria are presented for testing that via some suitable invertible linear state transformations, the given 2-D singular systems in the extended Roesser models can be converted equivalently to the classical Roesser models. Some results on 2-D classical singular Roesser model such as the reduced order regular observer and compensator design are generalized to the extended models.