模分配噪声对光纤通信系统的影响

模分配噪声是由于激光器纵模功率瞬时波动和光纤的材料色散引起的。它与激光器光谱宽度和光纤材料色散有关。模分配噪声对于高速率的光纤传输系统,尤其对于单模光纤通信系统性能的影响是重要的。模分配噪声也限制了波分复用系统的性能。本文分析了模分配噪声的表示方法及其对光纤通信系统的影响,并讨论了减小模分配噪声的方法。     

半导体激光器模分配噪声的实验研究

本文分析比较了半导体激光器(SL)模分配系数的各种测量方法。提出了测试条件最接近LD实际工作条件的统计比较法。在560 Mbit/s单模光纤传输系统上对SL模分配噪声进行了测试。     

一种基于过模波导的高功率8 mm微波传输系统

过模波导是一种突破传统单模波导功率容量的波导结构。在高功率微波系统中,基于过模波导的模式过渡器和模式滤波器都是传输系统的关键器件。本文讨论了这些器件的理论设计依据,并设计了一套包括过模波导、模式过渡器、模式滤波器的8 mm 高功率过模波导传输系统,其中,模式滤波器分别通过膜片和窄缝滤除高次模。并用 CST Microwave Studio建模并仿真。仿真结果表明,该过模传输系统能够有效抑制高次模带来的谐振效应,提高微波的传输效率。     

模分配噪声与色散功率代价的计算及测量（下）

模分配噪声与色散功率代价的计算及测量（下）彭承柱五、模分配噪声计算的例子一个４０５Ｍｂ／ｓ单模光缆通信系统，它将９个４５Ｍｂ／ｓ（ＤＳ—３）光电复用组成光端机，与３Ｒ光中继机构成线路传输系统，其系统参数如表２所示。系统设计时考虑由于噪声带宽的增加会使...     

偏振模色散对级联PSA高速光纤通信系统性能的影响

根据耦合非线性薛定谔方程,在考虑不同大小光纤偏振模色散时,通过计算机系统仿真,对分别采用EDFA和PSA作为在线放大器在不同传输速率下的系统传输性能进行了分析。结果表明,在不同系统速率和不同偏振模色散下,采用PSA作为在线放大器的系统性能优于EDFA系统性能。     

140Mb/s、565Mb/s光纤通信系统的传输考虑

一、前言一般认为单模光纤的带宽是很宽的,但是由于单模光纤中存在材料色散和波导色散,以及系统的光源在高速调制下谱线变宽,而且具有随机性质,与光纤的色散相互作用后产生模分配噪声,限制了系统的传输带宽和通信距离。目前的办法是使系统工作在石英光纤的零色散波长(1.3μm),这样可以减免模分配噪声。但光纤在1.3μm的衰减不是最小,衰减最小的波长是在1.55～1.6μm处。     

GPON系统中基于QoS的动态带宽分配算法的研究

为了实现吉比特无源光网络(GPON)带宽分配的公平性,降低网络的丢包率及传输延时,研究了GPON系统传输汇聚层的帧结构及带宽分配的实现方法,提出了一种新的动态带宽分配(DBA)算法--基于QoS的二层动态带宽分配算法.性能分析与对比表明,这种算法对不同用户和不同等级的业务都具有很好的公平性,并可以降低低等级业务的传输延时.     

光纤密码术

虽然现有的量子密钥分配系统取得了很大的进步，速度越来越快，传输距离越来越远，但由于传输中的光子损失而无法实现相互兼容。美国研究者基于波长变换技术开发了一种新的高速光纤量子密钥分配系统，在目前的商用通信基础设施上实现了不可破解的保密通讯，实现了长距离、快速分配下的实际应用。他们的量子密钥分配系统使用不同偏振方向的单光子产生连续的二进制密码，给信息加密，传输距离超过了10km。     

半导体激光器—多模光纤传输的模式噪声实验与分析

光纤通信系统除了光电检测器的噪声之外,还有光源的量子噪声、激光器输出功率曲线“扭折”噪声、反射噪声、模分配噪声与模式噪声等。半导体激光器多模光纤传输容易出现模式噪声而影响传输的正常进行,本文报告模式噪声的实验观察及其有关的计算分析问题。一、实验观察     

WiMAX系统的带宽请求与分配问题的研究

详述了WiMAX系统的各种带宽请求与分配策略，并重点分析了基于竞争的请求与分配机制。通过对竞争请求的冲突概率进行分析，推出了回退窗口和竞争窗口的最佳分配尺寸。并计算了不同业务流数量下系统可达到的最大传输效率。计算机仿真表明以此尺寸进行分配。可有效减小请求冲突，提高系统的传输效率和带宽使用效率。     

Laser mode partition noise in optical wideband transmission links

Laser mode partition noise is an important source of noise in optical transmission systems operating with multimode lasers and dispersive fibres, e.g. single-mode fibres with non-zero material dispersion. The letter describes investigations which confirm the importance of considering laser mode partition noise when practical optical systems are projected. It also gives theoretical estimations and measurement results which are in good agreement, and demonstrates the influence of laser mode partition noise on the transmission quality of an analogue optical system.     

Laser Mode Partition Noise Evaluation for Optical Fiber Transmission

An evaluation of the influence of mode partition noise on error rate performance in a high bit rate optical fiber transmission system is presented. First, it is experimentally clarified that the intensity in each longitudinal mode of a laser diode fluctuates, although the intensity for the total mode is constant. It is also established that this fluctuation causes degradation of the error rate performance after transmission through a long optical fiber. The fluctuation is named "mode partition noise." Next a simple model for the fluctuation is proposed. The characteristics of the fluctuation are discussed on the basis of this model. Optical waveform fluctuation is found to be introduced by mode partition noise in the course of transmission through a long despersive transmission medium. This optical waveform fluctuation and its frequency spectrum are calculated. Finally, the error rate performance is evaluated and specifications required for a laser spectrum to attain a given repeater spacing are clarified.     

Repeater spacing of 280 Mbit/s single-mode fiber-optic transmission system using 1.55 µm laser diode source

This paper describes an attainable repeater spacing for a high bit-rate single-mode fiber-optic transmission in the 1.55 μm wavelength region where laser mode partition noise comes to be significant. An expression for evaluating mode partition noise is given as the form involving the influence of laser spectral fluctuations under high bit-rate modulation, together with the intersymbol interference and the equalized pulse shape in tile optical receiver. After the validity of its numerical results is confirmed experimentally, the resulting evaluation of laser mode partition noise is connected to a systematic discussion on the attainable repeater spacing of a 280 Mbit/s fiber-optic transmission system operating at 1.55 μm, along with fiber loss versus dispersion tradeoffs. This discussion permits the attainable repeater spacing to be 60-70 km for the combination of a laser diode with 1.5-2.0 nm spectrum broadening and a fiber with the loss of 0.5 dB/km and the dispersion of 4-6 ps/km - nm.     

The influence of mode partition fluctuations in nearly single longitudinal mode lasers

A simple relationship between the mode ratio of a two-mode laser and an empirical mode partition coefficient is derived. The effects of the mode ratio of a two-mode laser on the bit-error-rate floor of an optical fiber system are calculated, and the power penalties due to mode partitioning in the presence of Gaussian receiver noise are evaluated. The analysis provides a simple way to calculate the effects of mode ratio on the sensitivity of optical receivers.     

Measurement of mode partition in DFB lasers

Some DFB (distributed feedback) laser diodes have a satellite mode beside a main DFB mode even if FP modes are suppressed. In this paper, the mode partition noise is presented for several DFB lasers operating in multilongitudinal modes. The results show that under modulation at 140 Mbit/s, the mode partition coefficient k²of multimode DFB lasers is very small and at most 0.02 while that of FP lasers biased at the threshold level is 0.03 to 0.12. The numerical evaluation of the mode partition effect in two-mode DFB lasers suggests that a 20- dB suppression of the satellite mode power is enough to achieve a repeater spacing of over 100 km in the 280 Mbit/s fiber-optic transmission system with less than 0.1-dB power penalty.     

Bidirectional SCM Transmission Using a Noise-Suppressed Fabry–Pérot Laser Diode and a Reflective Semiconductor Optical Amplifier in a WDM/SCM-PON Link

We have proposed and experimentally demonstrated a bidirectional hybrid wavelength-division-multiplexed/subcarrier-multiplexed (SCM)-passive optical network based on a noise-suppressed Fabry-Peacuterot laser diode (FP-LD) and a reflective semiconductor optical amplifier (RSOA). For downlink data transmission, an FP-LD with multiple wavelength characteristics was used, and the mode partition noise of the FP-LD was reduced using a gain-saturated SOA with high-pass filter characteristics. For uplink data transmission, the downlink optical source was reused and remodulated by an SCM method, using an RSOA. A bidirectional SCM link with radio frequencies (RFs) of 2.4 GHz in the downlink and 1.0 GHz in the uplink was implemented. To confirm the validity of the proposed configuration, a 16-quadrature amplitude modulation transmission experiment was performed on a 10-km bidirectional optical access link. The transmission performance was investigated by means of the error vector magnitude and RF spectrum     

Uni- and bidirectional 4λ×560 Mb/s transmissionsystems using WDM devices based on wavelength-selective fusedsingle-mode fiber couplers

Four-wavelength-channel wavelength-division multiplexing (WDM) lab transmission system experiments with buried heterostructure (BH) lasers at 1200-, 1240-, 1280-, and 1320-nm wavelengths, all-fiber WDM devices, and 20-km single-mode link fiber at a 560-Mb/s bit rate demonstrated that unidirectional and bidirectional WDM transmission systems could be operated successfully by using all-fiber 4λ multiplexing, 4λ demultiplexing, or 4λ multiplexing/demultiplexing devices with a low insertion loss per wavelength channel (2.1-4.7 dB), enough optical far-end crosstalk attenuation (18-37 dB), and high optical near-end crosstalk attenuation (43-49 dB). It is concluded that the four-wavelength-channel WDM lab transmission system at 560 Mb/s mainly used as a test bed is not representative of future unidirectional trunk WDM systems. Such systems favor distributed feedback (DFB) lasers in the 1500-1560-nm wavelength range where fiber attenuation is lower than in the 1200-1320 nm wavelength range and where 1500-nm DFB lasers with a smaller linewidth do not limit the repeater distance as much because of mode partition noise     

椭圆光波导和圆形光波导单模传输分析比较

文章利用入射线偏振光在柱坐标系下对椭圆光波导进行了严格求解,得到了模场的精确解析解,导出了模式特征方程.光只在长轴方向的子午面内单模传播时,即可实现单模单偏振传输.在给定相同条件下单模传输时,与圆形光波导相比,椭圆光波导传播常数变化很小.文章还简要分析了波长、椭圆率和相对折射率差对传播常数的影响.     

A WDM-PON Employing Fabry–PÉrot Laser Diodes Without a Seed Light Injection

We propose and demonstrate a wavelength-division-multiplexed passive optical network by employing double-contact Fabry-Perot laser diodes (F-P LDs) without a seed light injection. To avoid the high mode partition noise at low frequency, we use a binary phase-shift keying as a modulation format at a low relative intensity noise window. An error-free transmission is achieved by compensating a lasing envelope shift due to temperature variation with the double-contact F-P LD.     

基于嵌入式技术的超低功耗红外光通信系统设计

为了解决红外光通信存在传输方向单一和消耗功率高问题,设计基于嵌入式技术的超低功耗红外光通信系统,系统单片机使用改进型STM32,将超低功耗红外发射装置嵌入到红外光通信系统中,该装置通过固定载波频率将输入音频信号,通过发送校准模式和音频传输模式调制为高频方波信号后,采用红外光管向外发射信号,并在电路中增加功率负载电流实现限流,降低红外光发射电路功耗。红外接收装置通过共射级放大电路接收信号,采用脉冲宽度调制(PWM)调制信号,实现信号高质量、低功率传输。红外通信模块实现红外发射装置和接收装置间信号的双向传输。系统采用保护驱动模式、中断模式与用户模式的红外通信协议栈,最大程度降低系统通信能耗,提高系统通信效率。实验结果表明:该系统能够实现信号和温度信号的有效传输,在休眠和正常运行时的功耗均较低,误码率低,是一种功率消耗低、通信质量高的红外光通信系统。