Simulative investigations of power penalty for DWDM link in the presence of FWM

In this paper, the eight channels dense wavelength division multiplexing (DWDM) optical communication system has been simulated, and power penalty introduced due to neighboring channels required to compensate the crosstalk has been calculated. It has been observed that the intermediate channels are more affected as compared to the boundary channels and more power is required to compensate the loss of information due to crosstalk.     

Photonic crystal channel drop filter based on ring-shaped defects for DWDM systems

This paper presents a novel configuration of channel drop filters based on two-dimensional photonic crystal slabs in silicon-on-insulator platforms. The structure is composed of two photonic crystal line-defect waveguides as input and output ports, along with an L3 cavity with ring-shaped border holes. The effects of structural parameters and fabrication errors on resonance frequency and drop efficiency are investigated. Band structure and propagation of electromagnetic field through device are calculated by plane wave expansion and finite-difference time-domain methods. The results show that the quality factor and line-width of output signal are ~5690 and 0.27 nm, respectively, indicating that the proposed filter can be properly used in dense wavelength division multiplexing systems with 0.8 nm channel spacing.     

DWDM系统非简并四波混频串扰的分析

考虑到DWDM系统中的比特序列的随机性、信道间脉冲走离效应等多种因素的影响,完善了归零调制格式下的四波混频效率的计算方法,给出了相应的非简并四波混频噪声标准差的计算公式,并利用该公式进行实例分析,计算结果表明,当占空比和信道间隔变小时,不同信道内的随机比特序列的相对初始时延及光纤色散值的取值组合对四波混频效率的影响变得更大,为保证系统的低色散和低四波混频串扰特性,必须对这些量取值组合进行优化. 关键词： 非简并四波混频 脉冲走离 密集波分复用     

DWDM混合光学系统中帧间和信道内四波混频效应的抑制

本文提出了光码多分址（CDMA）和光密集波分复用（DWDM）的混合系统,全面研究了四波混频（FWM）的影响。在这个系统中,主要存在两个四波混频问题：包括多址干扰（MAI）和码间干扰（ISI）的帧间四波混频和信道内四波混频。结果表明,综合考虑信道间和信道内四波混频的影响,最佳发射功率可选为18 dBm。当发射功率大于18 dBm时,混合系统的误码率（BER）将增加。基于此,本文提出了一种电光相位调制器（EOPM）模块,将其放置在波分复用器之后,通过抑制信道内四波混频的影响,同时调制所有波长信号的相位,从而增加混合系统的非线性容限,这极大地改善了基于OOK传输的光学CDMA-DWDM混合系统的性能。此外,由于多对角线（MD）结构具有零互相关特性,通过使用多对角线识别序列码可以减少多址干扰的影响。结果还表明,CDMA技术与色散相结合有助于降低信道间四波混频的影响。此外,识别序列码间隔在减轻码间干扰中起着至关重要的作用,如结果所示,当识别序列码间隔压缩至比特持续时间的25%时,可以避免码间干扰,此时所提出的混合系统的性能最佳。     

All-fiber Mach-Zehnder interferometer for DWDM filter direct group-delay measurement

The group delay of the dense wavelength division multiplexing (DWDM) filter is becoming more important in optical communication. This study proposes a Mach-Zehnder interferometer based on the direct group delay measurement of an optical thin film filter. The interferometer provides a simple, accurate and physically intuitive picture of what happens to broadband optical pulses on common optical materials. A 100 GHz DWDM filter was used as an example in the measurement and showed that the time of measurement and selection of Gaussian window were two important factors.     

A multi-channel full-duplex 60-GHz-band radio-over-fiber system

We propose and simulate a novel full-duplex radio-over-fiber system using a single light source at central station (CS). The scheme is employed to generate 60-GHz optical millimeter wave at CS for down-link transmission while the same optical carrier is reused at base station for up-link connection. There is no additional laser source for the upstream data generation in the base station. The bidirectional full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF). The power penalty for the down-link data after transmission over 40 km SMF is less than 0.6 dB, while for the up-link data, the power penalty after transmission over 40 km SMF is neglected. This system shows good performance over long-distance delivery and has important applicable value in high radio frequency (RF) sector and multi-channel full-duplex system.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　ＴｈｅｒｅｉｓａｇｒｅａｔｄｅａｌｏｆｉｎｔｅｒｅｓｔｉｎｆｉｂｅｒＢｒａｇｇｇｒａｔｉｎｇｓｄｕｅｔｏｔｈｅｉｒｍａｎｙｉｍｐｏｒｔａｎｔａｐｐｌｉｃａｔｉｏｎｓｉｎｔｈｅｆｉｅｌｄｏｆｔｅｌｅｃｏｍｍｕｎｉｃａｔｉｏｎｓａｎｄｆｉｂｅｒｓｅｎｓｏｒｓ .ＢｅｃａｕｓｅｆｉｂｅｒＢｒａｇｇｇｒａｔｉｎｇｓｅｘｈｉｂｉｔｄｉｓｐｅｒｓｉｏｎｂｏｔｈｉｎｒｅｆｌｅｃｔｉｏｎ ,ｅｓｐｅｃｉａｌｌｙｗｈｅｎｔｈｅ ｇｒａｔｉｎｇｉｓｃｈｉｒｐｅｄ[1] ,ａｎｄｉｎｔｒａｎｓｍ…     

一种基于半导体光放大器马赫-曾德尔干涉仪的新型全光信头和净荷分离方案

提出一种新型的光分组信头净荷分离方案.利用一个非对称半导体光放大器马赫－曾德尔干涉仪提取出信头脉冲,然后再利用对称的SOA-MZIs构建异或门,完成信头脉冲和光分组脉冲在差分调制下的逻辑运算,提取出净荷脉冲.在50 Gb/s速率下,数值仿真表明提取出的信头和净荷信号的开关比均超过16 dB.此外通过更改参数设置.该方案还可以应用到不同速率,不同信头长度的信头净荷分离中.     

Analysis of bottlenecks in DWDM fiber optic communication system

This paper deals with the limiting factors like Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS) and Four Wave Mixing (FWM) in DWDM Fiber Optic Communication. The variation of SBS threshold power level for the spectral width of the source is analyzed and it is found that addition of spectral width in the source lowers the SBS effect. By reducing the SBS effect, we could transmit more optical power in a single channel and maintain high OSNR. Similarly the effect of phase mismatching (dispersion) and wavelength spacing on both FWM and SRS are analyzed. This work aims at finding the optimal value of spectral width, dispersion and channel spacing, thereby exploring the possibilities of increasing the overall capacity of the fiber optic trunk line.     

Dispersion Compensators Based on Overlaped Linearly Chirped Fiber Gratings for DWDM Systems

By introducing a convergent lens in the phase mask setup and by tilting appropriately the fiber from the phase mask, a linearly chirped fiber grating with an appropriate chirp can be obtained conveniently. Using this method, two groups of fiber gratings, each of them is composed of 8 overlaped linearly chirped fiber gratings but with different center reflection wavelength separations (～0.8 nm and ～1.6 nm, respectively) are fabricated. Experimental results show that, the compensators based on the two groups of fiber gratings can be used to compensate for the dispersion of 8×2.5 Gb/s transmission over 100 km of standard single-mode fiber for multiple channels in optical time-division multiplexing (OTDM) and densed wavelength division multiplexing (DWDM).     

三光纤干涉型波分复用器的理论分析与实验

本文提出一种由三根长度不等的单模光纤作为干涉臂连接两个3×3耦合器而成的干涉型超窄三波分复用器,并对其进行了理论分析与实验研究文中给出了三角型3×3耦合器的传输矩阵及三根干涉臂的长度之差与复用波长的关系,并由此导出了整个系统的功率传输式理论分析与实验曲线基本一致我们实验样品的使用波段为155μm,波长复用间隔为16nm,插入损耗约06dB,三个端口的隔离度分别在13～16dB之间.     

Tunable Filters with Narrow-Band in Bulk SLA for DWDM Networks

The filter mechanism of a tunable filter with narrow-band in bulk semiconductor laser amplifier (SLA) is analyzed, which is suitable for dense wavelength division multiplexed (DWDM) optical fiber networks. The wavelength selectivity of the filter is derived from nondegenerate four-wave mixing (NDFWM) in semiconductor gain medium. It uses the direction of propagation to separate the desired wave-mixing product from the other light beams. The filters are shown to have very narrow passbands (subangstrom bandwidth) tunable over the entire semiconductor gain bandwidth. We gave the theoretical analysis of NDFWM effect in semiconductor gain medium is given and a set of nonlinear coupled wave equations is deduced, which are processed efficiently by Runge-Kutta method in numerical simulation. The influences of various structural parameters of the filter on the output bandwidth and efficiency were also discussed.     

微机械FP腔可调谐滤波器在WDM系统中的串扰分析

介绍了一种以FP谐振腔为基础,用于波分复用系统的MOEMS器件-电控可调谐FP光滤波器.器件采用微电子机械加工技术研制.研究了FP型解复用器在密集波分复用系统中引入的信道间串扰对系统的影响,并分别讨论了激光器线宽、滤波器带宽、信道间距对串扰的影响.在信道间隔为100GHz,激光器线宽为5GHz,串扰可达到-21dB左右.     

Low cost solution to high capacity 32 × 32 channel FTTH duplex link employing triple play services

In this paper, low cost solution based on RSOAs is proposed for a high capacity 32 × 32 channel, 20 km, FTTH duplex link employing triple play services. Here, downstream transmitters generate a 2.5-Gbps NRZ signal which is routed to both receivers and RSOA-based upstream transmitters. The RSOA modulates this signal with a 1.25-Gbps NRZ signal that effectively overwrites the downstream signal and then it is transmitted back over the same 20 km of bidirectional fiber, where it is routed to receivers at the CO. The proposed model completely eliminates the requirement of separate lasers for upstream communication which makes the system very cost effective. The high-pass filtering effect of the RSOA becomes predominant at higher input powers which has been used as an advantage here to effectively suppress the downstream signal. The impact of RSOA input power and extinction ratio of the downstream signal have been investigated and reported.     

密集波分复用条件下的光轨网络串扰分析与仿真

光轨网络是一种能够利用成熟的光学器件实现带宽灵活分配和信息交换的新型网络.串扰是限制光轨网络的物理层性能及其扩展性的重要因素.本文讨论了典型的光轨网络节点中异频串扰和同频串扰的产生原因,理论分析了两者对光轨网络的物理层传输性能的影响.给出了3种串扰性能的评价方法.以密集波分复用技术为应用背景,分别搭建了器件隔离度为20dB和30dB的、具有3个节点5个波长且单波长速率为2.5Gbps的光轨网络,仿真了串扰在光轨网络中的传播过程,并计算了光轨网络的误码率、功率代价和相对串扰.理论分析和仿真结果表明:光滤波器、解复用器和复用器是光轨网络中串扰产生的关键器件,且提高器件的隔离度等性能对于提高光轨网络的传输性能会有较显著的效果;在密集波分复用条件下,串扰对单波长速率为2.5Gbps的光轨网络的误码率和功率代价具有显著的影响,从而限制了光轨网络实际可用的节点数目.     

Tunable Filters with Narrow Band in Bulk SLA for DWDM Networks

１　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｔｏｄａｙ,ｗｉｔｈｔｈｅｑｕｉｃｋｄｅｖｅｌｏｐｍｅｎｔｏｆｔｈｅｈｉｇｈｄｅｎｓｅｗａｖｅｌｅｎｇｔｈｄｉｖｉｓｉｏｎｍｕｌｔｉｐｌｅｘｉｎｇ,ｔｈｅｌｉｎｋｃａｐａｃｉｔｙｗｉｌｌｂｅｇｒｅａｔｌｙｅｎｈａｎｃｅｄ．Ａｌｔｅｒｎａｔｉｖｅｌｙ,ｔｈｅｅｎｈａｎｃｅｍｅｎｔｏｆｔｈｅｌｉｎｋｃａｐａｃｉｔｙｄｅｐｅｎｄｓｏｎｔｈｅｒｅｌａｔｉｖｅｌｙｈｉｇｈｗａｖｅｌｅｎｇｔｈｒｅｓｏｌｕｔｉｏｎｏｆｔｈｅｗａｖｅｌｅｎｇｔｈｆｉｌｔｅｒｓｉｎｔｈｅｒｅｃｅｉ…     

密集波分复用条件下的光轨网络串扰分析与仿真

光轨网络是一种能够利用成熟的光学器件实现带宽灵活分配和信息交换的新型网络.串扰是限制光轨网络的物理层性能及其扩展性的重要因素.本文讨论了典型的光轨网络节点中异频串扰和同频串扰的产生原因,理论分析了两者对光轨网络的物理层传输性能的影响.给出了3种串扰性能的评价方法.以密集波分复用技术为应用背景,分别搭建了器件隔离度为20 dB和30 dB的、具有3个节点5个波长且单波长速率为2.5 Gbps的光轨网络,仿真了串扰在光轨网络中的传播过程,并计算了光轨网络的误码率、功率代价和相对串扰.理论分析和仿真结果表明:光滤波器、解复用器和复用器是光轨网络中串扰产生的关键器件,且提高器件的隔离度等性能对于提高光轨网络的传输性能会有较显著的效果;在密集波分复用条件下,串扰对单波长速率为2.5 Gbps的光轨网络的误码率和功率代价具有显著的影响,从而限制了光轨网络实际可用的节点数目.     

An intensity-modulation direct-detection radio-over-fiber link with a tunable transfer function

An intensity-modulation direct-detection (IMDD) radio-over-fiber link with a tunable transfer function is presented. It utilizes a bias drift free intensity modulator based on a Sagnac fiber loop interferometer containing an optical phase modulator. By adjusting the polarization controller in the interferometer, the transfer function of the whole system can be tuned. The present method is simple and easy to implement.     

DWDM极窄带干涉滤光片的误差与自动补偿效应

针对现代光通信中的核心元件之一--密集型波分复用(DWDM)系统中极窄带光学薄膜干涉滤光片的指标要求,提出采用基于四分之一波长的规整膜系是实现密集型波分复用功能的最佳选择.对给定的设计方案的各个膜层的误差灵敏度分布、特定膜层的误差成因进行了分析,并对多个膜层进行了随机分布的误差模拟.通过对直接极值法监控中不同误差的补偿机理的研究,指出采用直接极值法监控是目前为止镀制这种滤光片的有效方法.最后讨论了可能存在的两种系统误差.     

Investigation of optimum pulse shape for 112 Gbps DP-DQPSK in DWDM transmission

This paper reports the simulative analyses to investigate the impact of different pulse shapes on DP-DQPSK modulation for high-spectral efficient DWDM transmission at 112 Gbps per channel. In the simulation model we have considered three different pulse shapes viz. NRZ, 50% duty cycle RZ (RZ50) and 67% duty cycle RZ (RZ67) in symbol-aligned and symbol-interleaved format. The analysis has been carried out for various linear and nonlinear system impairments where the pulse is subjected to degradation under the influence of amplified spontaneous emission (ASE) noise, group velocity dispersion (GVD), cross-phase modulation (XPM) and polarization mode dispersion (PMD) and thus, limiting the system performance. Results show that the RZ50 pulse shape for DP-DQPSK with symbol interleaving shows the maximum tolerance for the various system degradations in long haul DWDM transmission. Even the system based on the NRZ pulse shape can gain significant improvement from the symbol-interleaving.