RZ-DPSK transmission using a 42.7-Gb/s integrated balanced optical front end with record sensitivity

We have demonstrated a record sensitivity of -37.0 dBm (38 photons/bit) for a BER of 10/sup -9/ at 42.7-Gb/s using an integrated balanced optical front end. Results were obtained using optical preamplification of RZ-DPSK modulation and an external delay-interferometer. The OSNR requirement was measured to be 16.9 dB in a 0.1-nm bandwidth. The impact of polarization-mode dispersion (PMD) and chromatic dispersion on the optical front end performance has been measured. Performance for enhanced forward error correction has been projected based on 10/sup -3/ BER performance.     

Research on the transmission performance of turbo codes in DDO-OFDM system

With the rapid development of optical elements with large capacity and high speed,the network architecture is of great importance in determing the performance of wavelength division multiplexing passive optical network(WDM-PON).This paper proposes a switching structure based on the tunable wavelength converter(TWC)and the arrayed-waveguide grating(AWG)for WDM-PON,in order to provide the function of opitcal virtual private network(OVPN).Using the tunable wavelength converter technology,this switch structure is designed and works between the optical line terminal(OLT)and optical network units(ONUs)in the WDM-PON system.Moreover,the wavelength assignment of upstream/downstream can be realized and direct communication between ONUs is also allowed by privite wavelength channel.Simulation results show that the proposed TWC and AWG based switching structure is able to achieve OVPN function and to gain better performances in terms of bite error rate(BER)and time delay.     

Corona Based Optimal Node Deployment Distribution in Wireless Sensor Networks

This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.     

Suppression of optical beat interference-noise in orthogonal frequency division multiple access-passive optical network link using self-homodyne balanced detection

A new technique, which reduces optical beat interference (OBI) noise in orthogonal frequency division multiple access-passive optical network (OFDMA-PON) links, is proposed. A self-homodyne balanced detection, which uses a single laser for the optical line terminal (OLT) as well as for the optical network unit (ONU), reduces OBI noise and also improves the signal to noise ratio (SNR) of the discrete multi-tone (DMT) signal. The proposed scheme is verified by transmitting quadrature phase shift keying (QPSK)-modulated DMT signal over a 20-km single mode fiber. The optical signal to noise ratio (OSNR), that is required for BER of 10⁻⁵, is reduced by 2 dB in the balanced detection compared with a single channel due to the cancellation of OBI noise in conjunction with the local laser.     

扫频相干探测光谱幅度码标记交换系统的传输性能分析

基于光谱幅度码(SAC)标记的生成原理,利用扫频相干探测技术,搭建对156Mbit/s SAC标记进行识别的SAC标记交换系统。加载40Gb/s强度调制(IM)净荷信息后,分别对背靠背、40km和80km传输距离下,本振光源(LO)线宽、发射功率以及净荷与标记频率间隔对标记接收质量的影响进行仿真分析。同时分析接收光功率(ROP)、光信噪比(OSNR)、标记与净荷频率间隔对净荷误码(BER)特性的影响。结果表明:传输40 km、80 km后,标记接收眼高度(EH)与背靠背系统相比差别较小,且都能达到-0.6 dB左右;同时,传输80 km后,当净荷BER为10-9时,其ROP与OSNR分别为-17.8dBm和14.5dB。     

Coherent crosstalk in ultradense WDM systems

We present extensive numerical studies on the determination of coherent wavelength-division multiplexing (WDM) crosstalk penalties for ultradense wavelength-division multiplexed (DWDM) systems, focusing on carrier-suppressed return-to-zero (CSRZ) as well as on 67% duty cycle differential phase-shift keying (67% RZ-DPSK) at a spectral efficiency of 0.8 b/s/Hz. Our analyses reveal large statistical variations in the predicted required optical signal-to-noise ratio (OSNR) when changing the WDM channels' interference conditions, in particular their relative optical phases and their relative time shifts. The strong impact of the exact WDM interference conditions can lead to simulation inaccuracies of many decibels when using standard OSNR simulations techniques. In measurements of DWDM system performance, the long averaging time of bit error ratio (BER) test sets can hide these burst-error generating penalty variations, and may, therefore, lead to wrong interpretations, especially for systems employing forward error correction (FEC). To overcome the DWDM simulation problem, we introduce and thoroughly assess a new simulation technique that allows us to efficiently and accurately capture the average required OSNR penalty for DWDM systems with negligible statistical error.     

40-Gb/s NRZ wavelength conversion with 3R regeneration using an EA modulator and SOA polarization-discriminating delay interferometer

We propose and demonstrate, for the first time, to our knowledge, a 40-Gb/s nonreturn-to-zero wavelength converter with 3R regeneration based on an electroabsorption modulator and semiconductor optical amplifier polarization-discriminating delay interferometer. The results show that the root mean square timing jitter and optical signal-to-noise ratio (OSNR) of the regenerated signal are kept to 0.68 ps and higher than 40 dB/0.1 nm, respectively. In addition, the measured receiver sensitivity (BER=10/sup -9/) is improved from -19 to -25.2 dBm at the input OSNR of 26 dB/0.1 nm.     

Novel Statistical OSNR Budgeting for Optically Amplified DWDM Circuits With Polarization-Dependent Loss

Polarization-dependent loss of optical components used in all-optical network circuits may introduce fast power fluctuations and bursts of high bit-error-rate (BER) impairment at a receiver. The power fluctuation in amplified circuitry manifests as statistics of both power and optical-signal-to-noise-ratio (OSNR) penalty at the receiver. Importantly, the power and OSNR statistics are not directly correlated in a long chain of amplifiers and the impact to BER is rather complicated. We propose the corresponding statistic model for budgeting OSNR to guarantee the probabilistic system availability     

An OSNR monitor for optical packet switched networks

Optical packet switched networks bring about new challenges to the research in optical performance monitoring. We present the first experimental demonstration of an optical signal-to-noise ratio (OSNR) monitor capable of direct OSNR monitoring on the packet basis. By measuring the radio frequency noise from optical packets with a special performance monitoring segment, the OSNR monitoring error is found to be less than 0.6dB for consecutive packets with varying OSNR of 16 to 27 dB. The response time of the OSNR monitor can be around 10 ns.     

In-Band OSNR Monitoring Technique Based on Link-by-Link Estimation for Dynamic Transparent Optical Networks

A cost-effective optical performance monitoring system, based on link-by-link optical signal-to-noise ratio (OSNR) estimation, is proposed for a dynamic transparent optical network. The proposed technique estimates the OSNR by monitoring the channel powers at the input and output of each optical link and the total input power to the inline EDFAs. In-band OSNR monitoring was successfully demonstrated at 42.7 Gb/s RZ-DQPSK signals, reflecting the transmission performance.     

一种改进的ISFA信道估计算法

设计了一种基于符号内频域平均(ISFA)的信道估计算法,用于偏振复用光正交频分复用(PDM-O-OFDM)系统的信道估计和传输信道色散损伤的均衡。算法采用凯撒窗函数对基于导频的ISFA算法进行改进,提高了信道估计后处理的精度,改善了长距离PDM-O-OFDM系统的误码率(BER)和光信噪比(OSNR)性能。通过仿真试验,确定了算法的相关参数,分析了算法对长距离系统中色散损伤的均衡性能。仿真结果表明,改进算法对于传输距离超过700km系统的均衡效果优于原算法,其中900km处的OSNR代价比原算法低0.35dB。     

System Performance of High-Order Optical DPSK and Star QAM Modulation for Direct Detection Analyzed by Semi-Analytical BER Estimation

Recently, higher order modulation formats are intensively investigated to further increase spectral efficiency for building next generation optical transport networks. Direct detection receivers are capable of detecting arbitrary modulation formats with differentially encoded phases such as differentially phase shift keying (DPSK) and star shaped quadrature amplitude modulation (Star QAM) formats. In an earlier publication of the authors (M. Seimetz , “Optical systems with high-order DPSK and star QAM modulation based on interferometric direct detection,” J. Lightw. Technol. , vol. 25, no. 6, pp. 1515–1530, Jun. 2007) a system analysis was performed where performance was mainly characterized by eye opening penalties. Here, these investigations are extended. A tool for semi-analytical BER estimation is developed allowing to calculate the BER down to small values such as $10^{-9}$ for a wide range of modulation formats, as well as for different receiver structures. Using this module, the back-to-back OSNR requirements are calculated. CD and SPM tolerances are characterized by optical signal-to-noise ratio (OSNR) penalties at ${hbox {BER}} = 10^{-9}$ . As far as the authors know, this is the first analysis of the transmission characteristics of optical 16DPSK and Star 16QAM based on the BER. Moreover, further novel aspects such as optimization of the optical and electrical receiver filter bandwidths are investigated.      

Performance degradation induced by polarization-dependent loss in optical fiber transmission systems with and without polarization-mode dispersion

The performance degradation caused by polarization-dependent loss (PDL) in optical fiber transmission systems in both the absence and presence of polarization-mode dispersion (PMD) is studied. First a simple theory is given to show how PDL affects the system performance and then extensive simulation results are presented. We show that PDL causes a much larger fluctuation of optical-signal-to-orthogonal-noise ratio (OSNR/sub ort/) than that of optical-signal-to-parallel-noise ratio (OSNR/sub par/), but OSNR/sub par/ has a much larger impact on the system performance than OSNR/sub ort/. We find that when there is no PMD, the system performance degradation induced by PDL can be effectively reduced by suppressing OSNR/sub par/ fluctuation. However, the presence of PMD in the system could significantly reduce the efficiency of the PDL mitigation technique, especially the mitigation technique that suppresses the OSNR/sub par/ fluctuation.     

Performance evaluation of optical DQPSK using saddle point approximation

In this paper, the authors derive the moment generating function (MGF) of the decision variable for a practical optical differential quadrature phase shift keying (DQPSK) receiver affected by phase noise and the amplifier spontaneous emission noise. The effect of the different optical filters, Gaussian, Fabry-Pe/spl acute/rot (FP), and optical integrator, on the phase noise is examined. Using the saddle point approximation, the authors obtain numerically the bit error rate (BER) for the above system, as a function of the optical-signal-to-noise ratio (OSNR) and the source linewidth. The model is found to agree with previous published simulation results and the Monte Carlo simulations presented in this paper. The authors also calculate the BER floors for DQPSK inflicted by the phase noise and compare its performance with differential phase shift keying (DPSK). Finally, the authors examine the effect of interferometric demodulation on the relative intensity noise (RIN) spectra and the impact on the DQPSK system performance. In particular, the authors examine the influence of system dispersion on the receiver sensitivity.     

基于高维调制的模分复用系统性能研究

为了提高系统的传输容量和传输性能,提出了基于高维调制的模分复用通信技术.通过搭建的基于高维调制的模分复用系统,仿真分析了4b-4D和8b-8D高维信号在不同光信噪比、传输距离和模式耦合系数条件下的传输性能,并与传统的谱效率相同的二维调制信号QPSK进行了对比.实验结果表明,在目标误码率下,4b-4D信号和8b-8D信号所需信噪比分别比QPSK信号降低了2和4 dB,传输距离分别比QPSK信号增加了20和40km.可见,随着信号维度的增大,信号的抗噪声性能及抗色散性能越好.此外,实验结果表明模式耦合对误码率的影响也随着信号维度的增加而减小.     

An improved multiplier-free feed-forward carrier phase estimation for dual-polarization QPSK modulation format

An improved multiplier-free feed-forward carrier phase estimation algorithm is proposed for dual-polarization quad-rature-phase-shift-keying (DP-QPSK) with coherent detection. The bit error rate (BER) performance, block length effect and linewidth tolerance of the proposed algorithm are evaluated for a 112 Gbit/s DP-QPSK system. A linewidth symbol duration product of 2.9×10-4 is demonstrated for 1 dB optical signal-to-noise-ratio (OSNR) penalty at BER of 10-3 for the proposed algorithm. The hardware complexity of the proposed multiplier-free algorithm is demonstrated to be much lower than that of the 4th power algorithm.     

光通信系统Q因子测量和原理

10Gbit/s及其以上速率光传输系统非线性效应很强,对系统最终的BER性能有着举足轻重的影响。人们倾向采用Q因子来衡量系统性能。Q因子被定义为在接收机判决电路信噪比,这种检测到的电SNR最终决定物理层系统BER。可以适用于各种信号格式和速率的数字客户信号,而且不需要解开帧结构,比较简单易行。本具体讨论Q因子的定义及与OSNR之间的关系。同时介绍ITU关于Q因子的测试方法和对测试设备的要求。     

Transmission performance of implicit optical label switching system with coherently detected spectral amplitude code labels

A new optical label switching system with coherently detected implicit spectral amplitude code (SAC) labels is proposed in this paper. The implicit SAC labels are recognized using a frequency-swept local light source oscillator. An explicit SAC-label switching system with 40 Gbit/s intensity modulation (IM) payloads and 156 Mbit/s label and an implicit SAC-label switching system with 2.5 Gbit/s IM payloads and 156 Mbit/s label are both considered. Label and payload bit error rate (BER) performance is assessed and compared by simulations. The results reveal that after 80 km transmission and at the BER of 10-9, the received optical power (ROP) values of label and payload are -8.3 dBm and -23.5 dBm in implicit SAC-label switching system, respectively, while those are -18.2 dBm and -18.6 dBm in explicit SAC-label switching system, respectively. As a result, the payloads of 40 Gbit/s and 2.5 Gbit/s in explicit/implicit SAC-label switching system have little influence on the received payload quality at the BER of 10-9 after 80 km transmission. Finally, a payload of 40 Gbit/s can obtain 12.5 dB optical signal-to-noise ratio (OSNR) after 80 km transmission.     

OSNR comprehensive-awareness model based lightpath control scheme in an OpenFlow controlled all-optical network

To enhance the communication quality of OpenFlow controlled all-optical networks, an optical signal-to-noise ratio comprehensive-awareness (OSNR-CA) model based lightpath control scheme is proposed. This approach transforms main physical-layer optical impairments into OSNR value, and takes this comprehensive OSNR value of the optical signal along the lightpath into consideration, when establishing the lightpath for the connection request using OpenFlow protocol. Moreover, the proposed scheme makes full advantages of the OSNR monitoring function in each node, and assigns the lightpath according to the comprehensive-OSNR value by extending messages of OpenFlow protocol, in order to guarantee the reliable establishment of the lightpath. The simulation results show that the proposed scheme has better performance in terms of packet loss rate and lightpath establishment time.     

光环形网的光信噪比分析与系统设计

文章指出光环形网的设计中必须考虑最长环路保护时的光信噪比(OSNR)计算问题。导出了光分插复用／光交叉连接(OADM／OXC)节点级联的OSNR的计算公式。最后针对链路发生故障点不同的同一业务波长配置的保护倒换情况进行了OSNR的分析，给出了环路保护倒换情况下的OSNR最低条件的模型，并依据此模型建立了光环形网工程设计方法，简化了工程设计中OSNR验证的计算量。