Overview of DWDM/ODC Project

This article introduces the main achievements resulting from the DWDM/ODC project. The five areas of research activity within the DWDM/ODC project cover some of the main issues of design and development of dense wavelength division multiplexing systems for transparent optical networks. These issues are: performance assessment with arbitrary optical filtering; performance of signaling formats; dispersion compensation strategies for directly and externally modulated systems in presence of nonlinear transmission-induced degradation; and the impact of noise and crosstalk in the extent of transparent optical networks. All five areas of research activity have contributed significantly to a better understanding of the limitations present in dense wavelength division multiplexing systems.     

Analysis of Pulse Tolerance to Pump Depletion Induced Noise in DWDM Systems Using Distributed Fiber Raman Amplifiers

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Analysis of Pulse Tolerance to Pump Depletion Induced Noise in DWDM Systems Using Distributed Fiber Raman Amplifiers

In distributed optical fiber Raman amplifiers,instantaneous pump power depletion is related to patterns of input DWDM signals and results in extra optical noise and crosstalk.This noise has different effects on non-return-to-zero (NRZ) and return-to-zero (RZ) pulse forms.These phenomena are compared with present simulation results.     

多级全通均衡器对介质薄膜滤波器进行色散补偿的探讨

讨论了介质薄膜滤波器的色散特点,并推导了单级全通滤波器的理论色散。比较理论色散曲线与实际测量色散曲线,两者吻合较好。但由于单级全通滤波器的色散带宽及斜率不能满足实际所需的色散补偿曲线,因此提出了多级全通滤波器,通过控制级连的单级全通滤波器的谐振波长及反射率,可以增大色散带宽,改善色散斜率,使之满足实用的要求。文中给出了四级全通滤波器的理论色散曲线。     

一种有效提高薄膜滤光片型密集波分复用器器件性能的方法及其实验研究

对光梳状滤波器加薄膜滤光片型模块制作密集波分复用器(DWDM)的两种应用方案进行了研究,提出了一种提高插损一致性、信道隔离度及减小串扰的结构方案。对新结构方案与常规结构方案进行了理论分析及实验研究,结果表明新结构可将级联次级峰由大于-30dB降至-50dB以下。用16波50GHz的密集波分复用器件拼接进行的实验表明最终器件的插损减小0．869dB,插损一致性减小2．005dB,相邻信道隔离度提高1．004dB,非相邻信道隔离度提高42．903dB．总串扰提高1．68dB。该方案不仅可以应用到光梳状滤波器与薄膜滤光片型模块拼接高性能的超密集波分复用器件．同样也可适用于阵列波导光栅等类型的密集波分复用器件中以降低工艺难度,提高性能指标。     

Characterization of phase modulated non-return-to-zero (PM-NRZ) format for DWDM long reach PONs

A technique which has been shown to be effective to mitigate the Rayleigh backscattering (RB) noise and potentially suited for use in the carrier distributed passive optical networks (PONs), uses a phase modulator (PM) at the reflective optical networking unit (RONU) to reshape the spectrum of the upstream non-return-to-zero (NRZ) signal, named PM-NRZ. Since the PM-NRZ signal has a much wider spectrum than the conventional NRZ signal, it would be very interesting to know its performance when applied to the multiple channels, or dense wavelength division multiplexed (DWDM) environment. Here, we, for the first time, show how close the neighboring channels can be located in the network by means of numerical simulations. We also provide solutions to reduce the crosstalk produced by neighboring PM-NRZ channels. Since in the WDM-PON system the distances between different ONUs and the head-end office vary, we also analyze the network performance when the powers of adjacent PM-NRZ signals change.     

偏振模色散及非线性效应对40 Gbit/s密集波分复用系统的影响

高速率、大容量的密集波分复用系统是光纤通信系统的最终发展方向 ,单信道速率达到 4 0Gbit/s时 ,光纤的非线性效应、偏振模色散现象对系统的影响更加突出。在综合考虑群速度色散、自相位调制、交叉相位调制、四波混合、偏振模色散等因素的基础上 ,推导了密集波分复用系统中任意信道的耦合非线性薛定谔方程组。利用扩展的分步傅里叶方法对该方程进行了数值计算 ,通过对 8× 4 0Gbit/s密集波分复用系统的仿真 ,分别研究了非线性效应和偏振模色散对密集波分复用系统的影响。发现由于交叉相位调制和四波混合作用 ,多波长的密集波分复用系统比单波系统受非线性效应影响严重 ;系统受偏振模色散与非线性效应的影响程度与输入信号功率有关 ,在入射光单信道平均功率较低 0 .1mW时 ,偏振模色散是影响系统性能的主要因素 ;当入射光单信道平均功率较高1mW时 ,系统受非线性效应影响严重。而偏振模色散在使信号脉冲展宽的同时 ,类似于非零色散位移光纤中的微小色散 ,对非线性效应又有一定的抑制作用。     

Experimental realization of a novel dispersion- compensating optical fiber amplifier for simultaneous compensation of positive dispersion and losses

Erbium-doped dispersion-compensating optical fiber (EDCF) has been theoretically simulated and experimentally fabricated using Modified Chemical Vapor Deposition (MCVD) for optimum operation at 5.0km. It is optimized for both gain as well as negative dispersion. The erbium has been doped into the cladding region while the core of the optical fiber is chosen to be narrow so as to have a high negative dispersion. Measured gain of 3.1 dB at 200 m using 100 mW pumping power (980 nm wavelength) at 1550 nm has been obtained and the gain of 32 dB at 5.0 km using same pumping scheme has been predicted. The chromatic dispersion of this EDCF has been also measured to be –43.5 ps/km-nm at 1550 nm and thus, providing the dispersion of –217.5 ps/nm at 5 km. The bend-induced losses are found to be negligible. We are the first to report the experimental realization of EDCF.     

Beyond 90-km Reach of a 16 × 2.5 Gb/s C/L-band Dense Wavelength-Division Multiplexing Metropolitan Network Based on Self-Seeded Reflective Semiconductor Optical Amplifiers

Abstract

This article reports the operation of a cost-effective, colorless, dense wavelength-division multiplexing metropolitan network based on self-seeded reflective semiconductor optical amplifiers. All reflective semiconductor optical amplifiers used in the experiments are packaged in commercial small form-factor pluggable modules. The proposal architecture is simple and symmetric thanks to utilization of two cyclic array waveguide gratings. Downstream link functions in the C-band wavelength range and the upstream link functions in the L-band wavelength range. By using erbium-doped fiber amplifiers to extend the reach, an error-free transmission over 90 km for 16 channels at 2.5 Gb/s was experimentally demonstrated for both directions, and an optical budget over 35 dB was obtained.     

112 Gbit/s信号混传多种速率信号的非线性效应影响

主要研究在波长间隔50GHz的密集波分复用系统中,112Gbit/s偏分复用差分四相移键控信号在不同速率的相邻信道影响下经过长距离传输后的非线性容忍度。实验结果表明,112Gbit/s信号结合43Gbit/s信号或者10Gbit/s信号传输时系统得到较好的非线性容忍度,验证了在严重的非线性效应存在的情况下同步传输系统的可行性。     

Impact of a Post-OTDM-Demultiplexing Optical Filter on Dense OOK OTDM-WDM Transmission

The impact of a post-OTDM-demultiplexing optical filter on the performance of dense on-off keying (OOK) optical time division multiplexing (OTDM)—wavelength division multiplexing (WDM) systems was studied. For return-to-zero (RZ) modulation, it was found that the additional filter working in a double-tier filter configuration did not offer any significant improvements to performance when the signal pulse width is optimized. Improvements generally increase only when the signal pulse width deviates from its optimal value and only for low spectral densities. For ideal non-return-to-zero (NRZ) modulation, however, significant improvements of around 1 dB are obtained using the double-tier configuration over a large range of spectral densities.     

Nonlinear Crosstalk Suppression in WDM-SCM Systems

The mechanism of nonlinear crosstalk in WDM-SCM fiber communication systems is investigated. Then the crosstalk suppression method of complementary modulation of twin carriers is introduced and discussed. Aiming at the limitation of this method, a new method named symmetric carrier complementary modulation is presented, and it has shown satisfactory effect in crosstalk reduction.     

自相位调制和交叉相位调制共同作用下抽运探测波结构中的信号扰动研究

针对强度调制直接检测波分复用系统研究了抽运探测波结构中自相位调制和交叉相位调制共同作用下的光信号传输,给出了确定任意抽运信号下的探测波时域波形及强度调制率的理论解析方法,分析了信道间隔、传输速率对于交叉相位调制的影响,发现抽运波自相位调制的作用主要体现在使探测波时域强度调制率有所增大,解析结果和数值仿真能较好地吻合。     

Tbit/s超大容量光纤通信系统的研究进展

Tbit/s超大容量光纤传输系统促进了光纤通信技术的发展。综述了采用波分复用技术(WDM)、光时分复用技术(OTDM)和WDM/OTDM混合方式的Tbit/s超大容量光传输系统的研究现状、技术实现方式及研究的最新进展。对各种传输系统的优缺点进行了评价,对Tbit/s光纤通信系统的前景作了展望。     

混沌光通信与OC-48光纤通信的波分复用

数值证实并分析了混沌激光通信与现行光通信的波分复用传输,对于100 GHz的信道间隔,混沌激光通信系统实现了传输速率为1 Gbit/s数字信号的保密传输,现行光通信系统实现了传输速率为2.5 Gbit/s数字信号的传输.研究表明,当现行光通信中脉冲光信号的峰值功率不超过17 dBm时,混沌激光通信可在传输距离80 km内实现并行传输.此外,当现行光通信中脉冲光信号的峰值功率为7 dBm时,系统接收到的信号质量受混沌激光通信的干扰很小,当光纤传输距离从80 km增加到160 km时,对应的眼图开启度从82% 关键词： 混沌光通信 混沌同步 波分复用 信道串扰     

Investigations on order and width of RZ super Gaussian pulse in different WDM systems at 40 Gb/s using dispersion compensating fibers

In optical wavelength division multiplexed (WDM) systems the dispersion management is a key issue. In optical systems a lot of research is going on to reduce dispersion by selecting proper dispersion compensating techniques and proper modulation format for input data. One way to reduce dispersion is by using dispersion compensating fibers in the WDM systems. This paper analyzes the use of RZ super Gaussian pulse inputs for different WDM systems i.e. for conventional, dense and ultra dense WDM systems employing dispersion compensating fibers. The pulse width and the order of the RZ super Gaussian pulse was varied to evaluate the performance at 40 Gb/s. The experiment showed that to get minimum BER, pulse width of 7.5 ps and 10 ps along with third-order RZ super Gaussian pulse were found suitable and recommended to be used.     

Optimal Configuration of Multiple Pump Powers and Wavelengths for Balanced Pre- and Post-pumped Raman Fiber Amplifiers

A novel configuration algorithm for bi-directionally pumped Raman amplifier is developed by adopting simulated annealing algorithm. Automatic design of optical fiber Raman amplifier using 10 laser diode pumps with different wavelengths and powers is demonstrated for 64 channels DWDM systems. The resulted gain ripple is less than 2.6 dB in amplification bandwidth of more than 50 nm for a transmission span of more than 300 km. The algorithm can be practically applied to desired signal channel number and gain profile.     

Optimal Configuration of Multiple Pump Powers and Wavelengths for Balanced Pre- and Post-pumped Raman Fiber Amplifiers

A novel configuration algorithm for bi-directionally pumped Raman amplifier is developed by adopting simulated annealing algorithm. Automatic design of optical fiber Raman amplifier using 10 laser diode pumps with different wavelengths and powers is demonstrated for 64 channels DWDM systems. The resulted gain ripple is less than 2.6 dB in amplification bandwidth of more than 50 nm for a transmission span of more than 300 km. The algorithm can be practically applied to desired signal channel number and gain profile.     

光纤光栅和环形器组成的光分插复用器同频串扰特性研究

对三种不同结构的光纤光栅和环形器组成的光分插复用器的同频串扰进行了实验研究。实验表明，与常规的I型结构光分插复用器相比，Ⅱ型和Ⅲ型结构中由上载端泄漏到下载端的同频串扰分别减少了24．4dB和39．3dB，由下载端泄漏到上载端的同频串扰分别减少了23．6dB和24．6dB。     

Analysis of all optical cascaded XGM wavelength converter using CW-holding beam

In this paper, we propose and analyze a wavelength conversion using an cross-gain modulation (XGM) with two semiconductor optical amplifiers and CW-holding beam for improvement of wavelength conversion speed and frequency chirp characteristics. Wavelength conversion characteristics of the cascaded XGM with a CW-holding beam are investigated in time domain. From the simulation, we have observed that the proposed scheme provides a non-inverted efficient wavelength conversion and frequency chirp reduction at higher bit rate operation.