New concept in long-reach PON Planning: BER-aware wavelength allocation

With the use of arrayed-waveguide grating (AWG) and erbium-doped-fiber amplifier (EDFA), the long-reach passive optical network (LR-PON) can provide enormous bandwidth over large distances. However, these new technologies can also deteriorate the receivers' bit-error rate (BER) performance. By bringing the concept of BER-awareness into network planning, we can alleviate the performance deterioration, which could in turn lead to simpler design of receiver and thus lower the total cost of LR-PON.The effects of AWG and EDFA on BER are studied in this paper. An analytical model of BER performance is developed as a function of the output port location in the AWG and the distance of the receiver from the AWG. Not only does the proposed model capture the power loss caused by AWG, but it also accounts for several transmission impairments, including the beat noise due to inter-channel crosstalk in the AWG, the amplified spontaneous emission (ASE) noise related to EDFA, and the thermal noise related to the receiver. Based on this model, we propose both short-term and long-term distance-aware wavelength allocation schemes, which balance the BER among the optical network units (ONUs) at different distance. Simulation results show that average BER improves and the relative standard deviation decreases.     

基于Nyquist脉冲副载波调制的短距离光纤传输技术研究

提出了一种适用于强度调制直接检测(IM/DD) 光系统的信号调制格式。这种基于Nyquist脉冲half cycle副载波调制(SCM)信号能有效提高频谱效率,为了减少传递函数引起的系统的性能 恶化,采 用了数字预均衡和后均衡实现对光纤损伤的补偿;建立了偏振复用(PDM)IM/DD系统 平台, 分析了Nyquist脉冲SCM信号在系统中的PAPR性能,实现了72Gbit/s 64-QAM N yquist脉冲SCM信号经过20km标准单模光纤(SMF)传输后其误码性能 小于前向纠错(FEC)阀值3．8×10－3。     

Construction and performance analysis of variable-weight optical orthogonal codes for asynchronous OCDMA systems

A construction scheme of variable-weight optical orthogonal codes （VW-OOCs） for asynchronous optical code division multiple access （OCDMA） system is proposed. According to the actual situation, the code family can be obtained by programming in Matlab with the given code weight and corresponding capacity. The formula of bit error rate （BER） is derived by taking account of the effects of shot noise, avalanche photodiode （APD） bulk, thermal noise and surface leakage currents. The OCDMA system with the VW-OOCs is designed and improved. The study shows that the VW-OOCs have excellent performance of BER. Despite of coming from the same code family or not, the codes with larger weight have lower BER compared with the other codes in the same conditions. By taking simulation, the conclusion is consistent with the analysis of BER in theory. And the ideal eye diagrams are obtained by the optical hard limiter.     

三阶色散效应对光码分多址系统误码率的影响

光码分多址(OCDMA)系统的误码率是评价系统性能的重要指标,由于色散和非线性效应会导致超短光脉冲在光纤传输过程中脉宽的展宽,进而影响OCDMA系统的误码率。在基于理想情况的OCDMA系统误码率定义的基础上,研究了三阶色散和三阶非线性效应对系统误码率的影响,进一步分析了有硬限幅器和二维OCDMA系统的误码率。结果表明,三阶色散和三阶非线性效应都会导致OCDMA系统误码率的增大,但三阶非线性效应对系统性能影响没有三阶色散效应明显;在系统参数相同基础上,接收端引入光硬限幅器和系统采用二维编码均可优化系统性能。     

HAP-GEO-HAP全光中继放大链路模型及其误码性能

针对几何传播损耗和指向误差联合效应对空间激光链路性能的影响,研究了HAP-GEO-HAP全光中继放大链路通信模型的误码性能。建立了基于GEO卫星全光中继放大转发的高空平台激光链路通信模型,在考虑背景光辐射与放大器引入的自发辐射等因素的条件下,研究了信道衰减系数的统计特性和各类噪声的强度,获得链路模型的Q因子,推导出误码率表达式。仿真分析了在不同发射功率、抖动标准差和波束宽度等参数条件下,链路误码率与比特速率的关系。研究结果表明:当比特速率较低时,增大发射功率、降低抖动标准差或减小波束宽度,对链路误码率性能的改善程度较为明显;当比特速率大于4 Gbps时,上述措施对链路误码性能的改善程度较为缓慢。     

空间光通信中平台振动对误码率影响的抑制

在自由空间光通信(FSO)中,通信端机所处的平台在各种随机干扰力下发生振动,使正常的通信光路发生偏移,对误码率(BER)产生影响。为了减小振动引起的误码率,提出通过控制接收端光斑形状和大小来抑制误码率,并给出利用像散来获得指定光斑的设计方法和实例。结果表明,在实际通信环境中,通过选取合适的光斑参量可以使振动引起的误码率达到最小,通过调节发射端光学天线参量可以获得指定的光斑参量。对于振动不对称的情况,接收端光斑应该选择为椭圆形。     

Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels

This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at BER = 10^-6 and a scintillation level of sigma = 0.1, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When sigma = 0.2, an optical communication system employing subcarrier BPSK achieves a BER = 10^-6 at SNR = 13.7 dB, while the BER of a comparable system employing OOK can never be less than 10^-4. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation.     

基于DFB激光器实现波长转换误码特性的研究

作为自动交换光网络中的核心器件,全光波长转换器将在全光通信系统中发挥重要作用.根据半导体激光器实现波长转换的理论模型,重点研究了基于DFB实现波长转换器的误码特性.包括工作电流、输入信号光功率等参量对消光比、误码率的影响.并利用自行搭建的基于DFB实现波长转换的实验平台,进行了实验分析,发现理论分析结果和实验数据十分吻合.这对于优化基于DFB结构的全光波长转换器有重要参考价值.     

A 2-Gb/s optical transceiver with accelerated bit-error-ratio test capability

Accelerated bit-error-ratio (BER) measurement techniques using specialized test equipment are widely used for rapidly verifying the low BER (<10/sup -12/) of high-performance optical links. However, once these links are deployed in the field, it takes days to weeks to complete such BER measurements using a conventional testing method. This paper describes an optical transceiver architecture with on-chip accelerated BER measurement mechanics that reduces "in the field" BER testing time to minutes. The approach described in this paper uses an integrated interference generator to degrade receiver performance and raise the BER to a range that allows a substantially reduced measurement time. Values of BER versus the amount of interference are then extrapolated to the point of zero artificial degradation for actual BER. A 0.5-/spl mu/m complementary metal-oxide-semiconductor, 2-Gb/s, four-channel optical transceiver chip was designed, fabricated, and tested to serve as a vehicle for verifying the concept. The experimental results show excellent agreement between the extrapolated and actual BER values. The architecture described here points to a practical built-in self-test capability for optical links within high-performance digital systems, specifically in board- and backplane-level interconnections.     

BER analysis of coherent optical CDMA communication systems with transfer function matrix

We analyze the bit error rate (BER) of coherent optical code-division multiple-access (CDMA) communication systems with a transfer function matrix (TFM). The coherent optical CDMA is a promising system for an access network due to its advantages of asynchronous transmission, information security, multiple-access capability. TFM is defined as the Fourier transform of the impulse response of an optical fiber, which interconnects each CDMA system. TFM has parameters such as the state of polarization (SOP), phase difference, power distribution between two orthogonal modes over an optical frequency range. We first analyze the statistic of a received signal via an optical fiber with TFM, and then apply the statistic to the BER analysis. The analytical results show that BER increases with the bandwidth of a signal, and that selecting a proper center frequency leads to the BER reduction.     

Performance bounds and cutoff rates of quantum limited OOK withoptical amplification

The bit error probability (BER) and the generalized cutoff rate (GCR) of optically amplified, direct-detection on-off keying (OOK) signaling are addressed utilizing the classical theory of Fredholm integral equations. The approach accounts for the impact of optical bandlimiting and upper bounds on the BER are found via Chernoff techniques, which address the resultant intersymbol interference (ISI) incurred by the linear pulse distortion. Simple rigorous upper bounds on the BER are derived in terms of basic system parameters relaxing the need for solving Fredholm related equations. Random coding is used to obtain the GCR of this channel. The theory is demonstrated for the Lorentzian and finite-duration bandpass optical filters and the optical bandwidth which optimally balances the ISI versus the amplified spontaneous emission noise is found     

Noise analysis for optical frequency conversion using nearlydegenerate four wave mixing in semiconductor optical amplifier

For future wavelength-division-multiplexed (WDM) networks, optical frequency conversion will enable the flexible and efficient use of optical frequency bandwidth. However, the signal degradation at frequency converters limits the maximum size of the network. Noise due to optical frequency conversion using nearly degenerate four wave mixing in a semiconductor optical amplifier is investigated, and it is found that the crosstalk from one of the two pump lasers can impose the power penalty on the bit error rate (BER) characteristics after optical frequency conversion. Analytical expressions for BER are developed and used to evaluate the receiver sensitivity penalty caused by optical frequency conversion. On the basis of these results the optimal setting of the frequency difference between the signal and pump lasers and the power ratio of the two pump lasers are discussed. A 155-Mb/s frequency-shift keying (FSK) transmission with 1750-GHz (14 nm) optical frequency conversion has been carried out, using a novel phase noise cancellation method. The BER performance is in good agreement with the calculated results     

Ultimate performance of optical DSB signal-based millimeter-wavefiber-radio system: effect of laser phase noise

It is theoretically shown that the phase noise of laser light source can be automatically eliminated by compensating the differential group delay due to the fiber dispersion between the two sidebands of the optical DSB signal. The bit error rate (BER) measurement of 60 GHz millimeter (mm)-wave subcarrier multiplexed optical double-sideband (DSB) signal transport in dispersion-compensated optical fiber link using fiber Bragg grating (FBG) mill show that the effect of the laser phase noise on the BER is as small as a few % relative to the other additive noise effect, thus realizing almost the ultimate performance     

Modeling and verification of FEC performance for optical transmission systems using a proposed uniformly quantized symbol error probability model

We investigate the estimation of the bit-error rate (BER) performance of optical transmission systems with forward error correction (FEC) coding using a proposed uniformly quantized symbol error probability model. This model has been verified by the measurement of BER characteristics of coded and uncoded 10 Gb/s optical signals transmitted over 100 km. The measured results are very similar to the calculated results from the proposed model as well as Monte Carlo (MC) simulations. Our results suggest that the proposed uniformly quantized symbol error probability model using more than 8-decision levels can be applied to estimate BER performance for coded systems without degrading accuracy.     

A bit error rate analysis for TCP traffic over parallel free space photonics

Inter-satellite links (ISL) are a useful technology to transmit data to space stations and to communicate between satellites. However, there are serious limitations due to long delays and poor channel performance, resulting in high bit error rates (BER). In this paper, parallel transmission and the scaling of the Transport Control Protocol (TCP) window in free space optics (FSO) communications are analyzed in order to overcome these disadvantages in optical inter-satellite links. Latency and BER are the dominant effects that determine link performance. Thus, a physical, link, network and transport cross-layer analysis for FSO over ISL is presented in this paper. This analysis shows the advantages and disadvantages of using optical parallel transmission and TCP window scaling for free space optical links between stations and satellite constellations. The key contribution of this work is to simulate the effects of the BER and to link the results to packet error rate (PER) to determine the goodput for TCP transmissions by using a cross-layering approach. The results give evidence that wavelength division multiplexing (WDM) can mitigate the effects of long delay and high BER for a FSO communication using TCP.     

Optical CDMA with time hopping and power control for multimedia networks

Optical code-division multiple access (OCDMA) for high-speed multimedia transmission is proposed and its performance is investigated. The proposed system introduces time hopping to vary transmission bit rate and power control to control transmission signal performance, which allows various signals with different desired rate and performance. An expression for the bit error rate (BER) of the proposed system is derived and numerical results are shown. An optical power selector (OPS) coupled with a hard limiter are also proposed to improve system performance. The OPS is a device to transmit the instantaneous maximum optical power among input signals. The OPS combined with the optical hard limiter reduces the interference from simultaneous users which results in an improved BER. BER is theoretically derived and numerical results for some parameters are shown. We show that the proposed system significantly improves BER and is an attractive scheme for future multimedia networks.     

OCDM/WDM多跳光网络及其端到端误码率性能研究

采用码分复用与波分复用相结合的技术可以构成基于波长和码字转换的多跳光网络。只考虑码字转换,首先给出了光码分复用/波分复用多跳光网络的构成方法和码字转换器的一般结构,然后分析了网络中端到端的误码率性能。计算结果表明:码字转换次数的增加对端到端误码率的影响较小;当接收端的干扰信道数小于前一码字转换阶段的干扰信道数时,端到端误码率与判决阈值的关系曲线在最小值附近出现一近水平区间。     

40 Gbit/s packet bit error ratio and loss real-time measurement for ultrahigh-speed packet switched network

A novel packet bit error rate (BER) and loss measurement method and system is proposed. A proposed 40 Gbit/s packet BER and loss measurement system is expressed in detail. A 40 Gbit/s BER and loss measurement with various conditions is demonstrated experimentally. In real time, only the payload part of a packet and burst stream with fluctuated guard time is evaluated. The BER and packet loss of a randomly received packet sequence due to routing and buffering can be also evaluated by the measurement system. A 10 Gbit/s packet BER and loss measurement with optical label switching, buffering, and preamble-free optical packet 3R are demonstrated experimentally.     

Bit-error rate of M-QAM signal and its analysis model for compositedistortions in AM/QAM hybrid transmission

In cable television (CATV) systems that deliver digital video services by employing a hybrid fiber and coaxial network, it is important to consider digital channel deterioration due to composite distortions, as well as the amplitude-modulation vestigial-sideband channel. Furthermore, it is essential to clearly estimate a digital channel's quality in designing CATV transmission systems. However, there have been few studies on statistical models and an analysis method to estimate the bit-error rate (BER) of M-ary quadrature amplitude-modulation signals for composite distortions. This paper shows statistical properties of composite distortions and a new BER analysis method to handle them. In the evaluations, the amplitude distributions of composite distortions are given by Weibull distributions with skewness levels of 2.3 for composite second-order distortion and 1.5 for composite triple-beat distortion. We propose a new BER analysis method that uses the Weibull distributions for the composite distortion statistical features and demonstrate the effectiveness of the new BER analysis method in estimating BER by comparing its measurement results to calculation results     

基于非线性光纤环镜的OCDMA全光码字转换方法

提出了一种利用非线性光纤环镜(NOLND实现二维全光码字转换方法,设计了基于NOLM的码字转换方案,并进行了系统性能仿真分析.研究结果表明:该方法能够成功实现系统的数据传输;采用这种码字转换方法,系统误码率性能远远高于没有进行码字转换的系统性能.