Optical phase division multiplexing for local communicationsapplications

A local fiber bus system is described wherein many users sequentially phase-modulate the output of a single light source. Since the modulated signal has a constant envelope, optical amplifiers can be used to boost the signal power along the bus to a level sufficient for reliable detection. Also, since a single laser source is used, a higher quality device (for example, with small linewidth) is more readily affordable. This system is analyzed to determine the limits of performance due to noise. The analysis indicates that many wideband signals could be accommodated if noise sources only, rather than signal distortions caused by nonideal optical devices, were the limiting factor. For example, with optical amplifiers distributed along the bus, this system can support 1000 10-MHz users     

光码分多址技术在光接入网中的应用

无源光网络是光接入网的主要发展方向,ＦＴＴＨ是ＰＯＮ的最终方式,将ＯＣＤＭＡ,ＷＤＭ等技术用于光接入网中,是帝现接入网宽带化的途径之一。介绍了ＯＣＤＭＡ的技术报目前光接入网中多址技术的弊端,探讨了ＯＣＭＤＡ用于光接入网的可能性和优势,提出实现无源光网络多址接入的ＷＤＭ／ＣＤＭＡ方案。     

Optical time division multiplexing: systems and networks

The recent advances in optical time division multiplexed (OTDM) systems and components research show the technique to be highly suited to the generation and transmission of high capacity data on a single optical carrier. This approach uses a single wavelength to carry capacities of at least 40 Gb/s. Such systems are based on a clock frequency and tributary data rates which are easily accessible using electronic components. Short optical pulses are used in a return-to-zero data transmission format with temporal interleaving to map a number of optical data channels into a single electronic clock cycle. It is an approach that can be used to achieve extremely high data-rate bit interleaved systems. This article summarizes the developments in this field and outlines a possible methodology to evolve transport networks to encompass the potential that both WDM and OTDM have to offer     

Performance of a power group division scheme for ALOHA systems in afinite capture environment

A method proposed by Metzner (1976) for improving the utilisation in ALOHA systems involves dividing the users into different power groups. This was analysed assuming that a packet can withstand interference from an unlimited number of packets from lower-power groups. The performance of such a scheme when only a limited number of interferers can be tolerated is examined in this paper     

一种光输出功率控制电路

分析了光输出功率控制在光通信中的重要性 ,提出了一种有效的光功率控制电路。实验结果表明 ,该电路对调节和稳定光输出功率非常有效。     

Optical power limiting and stabilization based on a novel polymercompound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by ~810 nm and ~7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d₀=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the ~810-nm laser beam is increased from I₀=15 to 600 MW/cm² . The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I₀≈400 MW/cm² with a Δ≈±25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to Δ≈±8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are σ₂=66, 80, and 101×10^-20 cm⁴/GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes     

Optimum design of a wideband planar N-way fork power divider with arbitrary power division and input-to-output impedance matching

An effective design procedure based on method of least squares is proposed for multi-section and multi-output fork power divider/combiner with arbitrary power division ratios among its outputs in a specified frequency bandwidth together with impedance matching among its arbitrary source/load impedances. Transmission and scattering matrices are obtained for its equivalent circuit. An error function is constructed based on design specifications on its output power division ratios, isolations among output ports, return losses at its input and output ports and source/load impedances in a desired frequency bandwidth. The design procedure is fully developed, which determines the widths and lengths of microstrip line sections and resistor values. A design example is described for unequal power division ratio and unequal input/output impedances. A 3-section and 3-output fork power divider is designed for equal power division and load/source impedances for 2–12 GHz band. It is fabricated and measured. Variations of its transmission coefficients are less than 0.5 dB, isolations at its outputs are better than −15 dB and reflection coefficients at its ports are better than −10 dB. Excellent agreement is observed among the results of the proposed design procedure, full wave computer software and measurement data.     

Optical heterodyne image-rejection receiver for high-densityoptical frequency division multiplexing system

An optical heterodyne image-rejection receiver (IRR) for high-density optical frequency division multiplexing (OFDM) systems is described. The IRR was realized using balanced receivers, which showed more than 18-dB suppression over the 1.5-3.0-GHz IF region. Measured crosstalk penalties in a two-channel 560 Mb/s differential phase-shift keyed (DPSK) heterodyne optical communication system were realized for the first time. The crosstalk penalties in an OFDM system are estimated theoretically with and without the IRR. The required channel spacing and number of channels that can be accommodated in the 10-nm tuning range of the local laser are presented. A particular configuration of the IRR, its operation, and its performance limitations are discussed. The experimental results for image-rejection reception in a two-channel 560-Mb/s DPSK system are also given. Crosstalk penalties are estimated experimentally and compared to the theoretical calculation. Since the conventional configurations of the IRR are very sensitive to the polarization fluctuation of the transmitted signals, polarization-insensitive IRRs are proposed and their features are considered     

PON系统测试用光功率计

文章介绍了一种无源光网络(PON)系统中测试用的光功率计,该功率计通过特殊设计的光路和电路结构来实现PON系统中对信号光功率测试的特殊要求,即要满足线路上3种光信号波长的同时测试、在线测试和1 310 nm信号的突发测试功能,从而大大方便PON系统的安装、管理和维护.     

基于光波分复用的超长距离光缆随路状态监测

在光缆随路状态监测过程中,为避免因光信号波 长分离难度大而影响状态监测的准确 性,本研究在现场监测站采集光信号的基础上,利用光波分复用过程实现对不同波长光信号 的分离处理。根据分离结果,通过OTDR测试获得监测点到光缆故障点之间的距离,再结合小 波变换过程确定最大故障衰减信息。基于此,利用BP算法实现对超长距离光缆随路中存在的 故障点的定位,实现对光缆随路状态的监测。实验结果表明:该方法的监测过程耗时始终保 持在4min之内,且故障定位准确度在80%左右,证明该方法监测过程 耗时短、效率高,且对故障点的定位准确度较高,大大提升了状态监测结果的准确性。     

Uncoded integrated interleave division multiple access systems in presence of power interleavers

Interleaving is one of the most common methods known to eradicate the effects of multiple user interference. Removal of different interferences is one of the major challenges for advanced communication system designers. Several methods of interleaving have been proposed in literature and their performances have been analyzed on different communication systems to prove their worthiness in multiple user interference removal. One of such interleavers is power interleaver, which can be employed in communication systems as a means to control burst errors and reduce the multiple user interference. In this paper, performances of two different integrated interleave division multiple access (IIDMA) techniques i.e. SCFDM-IDMA and OFDM-IDMA have been analyzed. Novelty of this work is in the sense that the entire analysis has been performed in the presence of power interleavers for the above two IIDMA techniques as the conventional IDMA fails to mitigate the problems of inter-carrier and inter-symbol interferences. Hence, the two techniques in presence of power interleavers empower the idea of quality communication without any interference for future generation communication systems.     

基于对数比率放大电路的光功率测量

光功率测量是光纤通信系统最基本的测试参数之一。本文提出一种基于对数比率放大电路的光功率测量方法,相对于线性放大电路具有控制简单、动态范围大和线性度好的优点,是光缆在线监测的最佳选择。     

Optical fibre transmission power meter having self-calibrationfunction

A power meter for measuring transmission power in optical fibres has been developed. A thermistor element is used for the power sensor, and can be calibrated by the calorimetric technique. It is available for power levels of 1 μW~10 mW at wavelengths of 400~1600 nm with an accuracy of 2.5~0.5%     

光缆光功率实时监测

介绍了光缆光功率实时监测系统的组成结构、基本原理和功能，详细介绍了告警信息及控制指令的通信方式及协议，讨论了系统的特点及应用范围．     

Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communications

Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency‐selective fading environment with additive coloured Gaussian noise which is used to model the actual in‐home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC‐CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single‐user and multi‐user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal‐to‐noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd.     

Peak-to-average power reduction in space division multiplexing based OFDM systems through spatial shifting

A new method to reduce the peak-to-average power ratio (PAPR) in space division multiplexing systems applying orthogonal frequency division multiplexing is proposed. The method applies spatial shifting to partial transmit sequences to achieve a decreased PAPR on all transmit branches.     

Optical power distribution in multimode fibers with angular-dependent mode coupling

An expression for the power flow, in multimode optical fibers, is derived, which is mathematically simple and allows a clear physical interpretation of the effects of mode coupling. Coupling strength is assumed to decrease with increasing axial angle. The solution obtained under this assumption is supported by experimental observations. Following the analysis, an experimental procedure to determine the coupling constant is devised. The theoretical results enable the prediction of the loss due to the mode coupling and the transmission bandwidth of the angular multiplexed channels in step-index optical fibers.     

Optical power monitors in Ge monolithically integrated on SOI chips

We report on the fabrication and operation of optical power monitors monolithically integrated on silicon-on-insulator optical chips. The devices consist of near-infrared waveguide pn heterojunction photodiodes in evaporated germanium. The low temperature growth of Ge is compatible with silicon waveguide technology. The photodetectors exhibit typical responsivities of 10-30 mA/W; the power monitors are used with front-end trans-impedance amplifiers based on commercially available operational amplifiers and can operate with optical signals as small as 10 nW, with errors below 0.2% and 2% at 1 and 0.1 μW, respectively.     

光通信网络在电力配电自动化系统中的设计思路构架

本文主要通过对电力配电自动化系统通信网络发展过程中存在的问题进行分析,来分析电力配电自动化系统光通网络设计的思路,已制定出科学的配电自动化系统光通信网络设计方案,以保障电力配电自动化系统光通信网络的正常运行。据此,有利于推动电力配电通信网的自动化发展,充分利用现代计算机信息技术,以提高电力配电自动化系统光通信网络的运行效率,从而保障电力事业的可持续发展。     

ONU buffer reduction for power efficiency in Passive Optical Networks

Power efficiency will be one of the primary factors dictating the choice of future network deployments. Passive Optical Networks (PONs) in general consume less power and are well positioned to be the technology of choice for future access networks. In a PON, the Optical Network Units (ONUs), that provide the interface between the end user and the Optical Line Terminal (OLT), consume a substantial amount of power. Typically, 2 MB or more buffer capacity is used in an ONU for holding upstream packets. This consumes around 1.29 W of leakage power when idle. In the current work, we show the relationship between buffer capacity and leakage power consumption. This motivated us to propose buffer reduction as a strategy to reduce power consumption of an ONU. We propose three schemes viz. Zero Buffers (ZBs), Node Proportional Buffers (NBs) and Rate Proportional Buffers (RBs). They impose aggressive buffer capacity restrictions on the ONU to reduce power consumption. Having said that, these schemes cannot be realized without modifications to the basic network operation. We propose mechanisms required to support the buffer reduction schemes. Through simulations we explore the relationship between power consumption and network performance. We also present the comparison of the proposed schemes in terms of network performance with different network loads. Simulation results indicate that despite buffer size reduction, an acceptable level of application level performance can be achieved. We show that buffer reduction as a strategy is viable and can cut down more than 90% of leakage power consumed by packet buffers at the ONU.