空分复用光纤放大器增益均衡技术研究进展

随着第五代移动通信技术的正式商用,全球网络流量的需求呈爆炸式增长,传统单芯单模光纤通信系统的容量已接近香农极限,实现通信系统的升级扩容迫在眉睫.空分复用光纤通信系统基于空间维度复用,可有效解决未来通信系统的扩容难题,而空分复用光纤放大器是不可或缺的核心器件和研究焦点之一.当多信道功率增益不均衡时,功率差将会随传输距离的...     

Acousto-electro-optic demultiplexers in high data-rate optical communication systems

Acousto-electro-optic scanners are introduced as time-division demultiplexing devices in optical fibre communication systems. These devices can time-demultiplex digital signals with multiple Gb s⁻¹ data rates into a large number of channels. Acousto-electro-optic scanners combine the advantages of the large throughputs of acousto-optic scanners and the wide bandwidth of electro-optic scanners. Two-cell scanners are also introduced as a mean of increasing the time resolution by a factor of two compared with one-cell scanners.     

WDM-PON upstream transmission using Fabry–Perot laser diodes externally injected by polarization-insensitive spectrum-sliced supercontinuum pulses

We propose, a novel upstream transmission scheme for high speed wavelength division multiplexed passive optical networks. Upstream transmission at bit rate of 2.5 Gb/s was demonstrated using a Fabry–Perot (FP) laser diode (LD) externally injected by a spectrum-sliced polarization-insensitive supercontinuum pulse source, located at central office. The impact of Rayleigh backscattering on transmission performance is also investigated. The proposed scheme is expected to be cost-effective since low-cost FP LDs are used for light sources.     

Remotely Pumped Hybrid Amplifiers for Extended Bidirectional Passive Optical Networks

In this contribution, we optimize design parameters of hybrid optical amplifiers utilizing distributed Raman amplification in transmission fiber and gain of discrete, remotely pumped erbium-doped fiber amplifier (EDFA) for wideband, bidirectional operation in metropolitan area networks (MAN). The design is based on an application of a numerical model, which takes into account pump-to-pump and signal-to-signal interactions and generation of amplified spontaneous emission in the Raman amplifier and solves the standard rate-propagation equations in an erbium-doped fiber (EDF). We predict 12 dB gain across 72 nm of optical bandwidth with gain ripple better than 10%. The recently proposed serial topology of EDFA is considered; this enables the wideband, bidirectional operation of a hybrid amplifier with only two pump laser diodes emitting in the 1430 and 1480 nm bands.     

Characterizing pattern dependence in transmitters and receivers for modeling optical communication systems

We study the pattern dependences in 10 Gbit/s return-to-zero (RZ) transmitters and receivers. We describe a procedure to characterize and separate out the individual contributions from the transmitter and receiver to the pattern dependences in a 10 Gbit/s RZ system, and we validate the procedure experimentally using a transmitted pseudo-random bit string of length 2⁷ − 1.     

Control of chaos

We review the subject of control of chaotic systems paying special attention to exponential control. We also discuss the application of synchronization of chaotic systems to security in communications.     

All-optical amplification via the interaction among guided and leaky propagation modes in lithium niobate waveguides exploiting the cascaded second-order nonlinearity

The aim of this paper consists of performing a theoretical investigation of an all-optical amplifier and discussing the problems for a realistic implementation. An original periodically poled lithium niobate channel waveguide, having the optical c-axis opportunely oriented on the xz plane was considered. The waveguiding structure, designed to operate in the second communication window of optical fibers, shows versatile properties as was theoretically demonstrated. In fact, it enables both the selection and the coupling strength of four different propagation modes, two guided and two leaky, interacting via the cascaded second-order nonlinearity. The coupling among guided and leaky modes is obtained by means of two different techniques: (i) birefringence phase-matching (BPM) via a suitable orientation of the optical c-axis crystal on the xz plane and (ii) quasi-phase-matching by periodical inversion of the lithium niobate ferroelectric domains. A strong diffusion of magnesium in the region external to the periodically poled waveguiding channel is needed in order to achieve the suitable BPM and to maximize the bounding of the electromagnetic field and, thus, the overlapping integrals. Finally, a powerful refinement of device operation via the use of the seeded second harmonic waves is proposed. Gains of the order of 20 dB are achieved with reduced bias powers. The order of magnitude of the bias power decreases, with respect to the unseeded second harmonic operation, from 145 to 32 W.     

Three stage tandem queue with blocking

An analysis is given of the state and first-come, first-served waiting time processes for a three stage queueing system with no waiting space between stages, but with limited space before the first. Although the basic processes are exponential, no detailed analysis in this generality appears to have been made before; the nearest analyses entail the simplifying assumption that the first stage is never empty. A sufficient condition is derived easily for equilibrium to exist and it can be asserted with virtual certainty that it is also necessary; the complexity of calculation has so far excluded a proper proof, though this is in principle a possibility.The objective is to provide a theoretical framework easily adaptable for a numerical assessment of system performance to be made. Some typical tables with comments are given.     

部分相干光在大气湍流中的光强闪烁效应

以修正Rytov方法为基础,利用部分相干高斯-谢尔(GSM)光束模型并结合Andrews的唯像闪烁模型,研究部分相干光在大气湍流中的光强闪烁效应。推导出适用于不同湍流情形的部分相干光对数光强起伏方差表达式,系统分析了部分相干光在大气湍流中的光强起伏方差。结果表明:在同等的湍流环境下,部分相干光比完全相干光的光强起伏方差要小;光束相干性越差,光强起伏越小,抗湍流能力越强。在不同大气湍流情形下,光源相干性、大气折射率常数等参数对光强起伏都有不同程度的影响。     

航空飞机计算机通信中滤波器的优化设计

航空飞机计算机通信系统进行通信的过程中,由于航空飞机上的电子设备相互之间的电磁干扰严重,导致信道中存在大量的干扰信号。提出基于小波变换算法的抗干扰滤波器设计方法。根据小波变换算法相关原理,综合航空飞机通信中特有的软阀值特点,利用自适应调整参数的方法得到高空通信中的最优小波系数阀值,使得高空噪声过滤阀值函数具有更强的适应性。利用新的阀值函数设计了新的滤波器,对行滤波模块和列滤波模块的设计进行了详细阐述。实验结果表明。利用设计的滤波器能够对航空飞机计算机通信过程中的干扰信号进行有效滤波,缩短了滤波时间,提高了高空通信系统的抗干扰能力。