Sea trial of submarine optical amplifier repeater system using travelling-wave semiconductor laser amplifier

An optical amplifier repeater system consisting of semiconductor laser amplifiers was evaluated in 3000 m deep sea at 820 Mbit/s in the 1.5 mu m wavelength region using 23.5 km of optical submarine cable. The repeater output power was stabilised by an APC system monitoring amplified optical signal power. The authors confirmed stable digital signal transmission and the reduction of variation in the repeater output power for changes in the polarisation of the input signal.<>     

First field demonstration of optical submarine cable system using LD-pumped Er-doped optical fibre amplifier

The authors report on the first field demonstration of an optical submarine cable system using an in-line Er-doped optical fibre amplifier pumped by a 1.47 mu m laser diode. The experiment was performed at an ocean depth of 3000 m. With a maximum optical repeater gain of 20 dB, 1.2 Gbit/s intensity-modulated optical signals were transmitted stably during and after installation and also during recovery of the system. Furthermore, the effectiveness of an automatic-gain-control (AGC) scheme proposed for optical amplifiers was confirmed in a practical environment.<>     

Field demonstration of 195 km-long coherent unrepeatered submarine cable system using optical booster amplifier

Results of a field demonstration of a 1.187 Gbit/s coherent CPFSK system using a booster amplifier over an unrepeatered length of 195 km are shown. A span-loss margin of 51.9 dB was confirmed by a 15 day measurement at a bit-error rate of 4.55*10/sup -15/.<>     

Time evolution of polarisation mode dispersion in 120 km installed optical submarine cable

The timewise evolution of polarisation mode dispersion (PMD) is measured. PMD varies very slowly in 120 km installed optical submarine cable. The measured timewise evolution of PMD suggests that compensation with a response time shorter than a few minutes can greatly reduce the system performance degradation caused by PMD.<>     

Bidirectional optical amplifier for time transfer using bidirectional WDM transmission

In this letter, we propose a bidirectional optical amplification scheme for fiber-optic time transfer based on bidirectional wavelength-division multiplexing (WDM) transmission. The proposed scheme employs single unidirectional erbium-doped fiber amplifier (Uni-EDFA) for commercial optical networks to implement bidirectional optical amplification. Since including isolators, the effect of backscattering due to the accumulated amplification can be efficiently suppressed by the proposed amplifier. The proposed scheme is validated over different length fiber links in laboratory. Experimental results show that the proposed amplifier can support fiber-optic time transfer over several thousands of kilometers with an additional bidirectional delay difference fluctuation at picosecond magnitude.     

Polarization mode dispersion measurements in an installed opticalfiber submarine cable

Highly accurate polarization mode dispersion (PMD) measurement using an interferometric detection technique with AC modulation is discussed. This technique, which searches for the interference fringe signal, was used to measure PMD in a 60 km long installed optical submarine cabled fiber 2500 m sea depth and to determine the fiber-length dependence of PMD. PMD measurement in 60-km-long installed optical submarine cabled fibers was confirmed to be less than about 0.7 ps. It was found that the fiber length dependence of the PMD measurement in the less than ~20-km-long cascaded uncabled fibers was proportional to √L; however, the PMD data in the long-length (over ~50 km long) fibers were slightly scattered     

Investigation of system upgradability over installed fiber-optic cable using 40-Gb/s WDM signals toward multiterabit optical networks

An investigation of system upgradability of installed fiber-optic cable was conducted using 40-Gb/s wavelength-division-multiplexing (WDM) signals toward multiterabit optical networks. A field trial of 63-channel 40-Gb/s dispersion-managed soliton WDM signal transmission was successfully demonstrated over 320-km (4 /spl times/ 80-km) installed nonzero-dispersion-shifted fibers. The average Q factor of 15.4 dB was obtained, and very stable long-term bit-error-ratio performance was confirmed without polarization-mode dispersion compensation. This system upgradability investigation in the field environment provided the confidence to introduce 40-Gb/s technologies and effectively to construct multiterabit optical networks following the demand increase in the future.     

Novel coherent heterodyne optical time domain reflectometry forfault localization of optical amplifier submarine cable systems

A coherent, heterodyne-detection, optical time-domain reflectometry technique suitable for an all-optical repeater system is proposed. Rayleigh backscatter measurement through a 309-km bidirectional optical transmission line with six cascaded in-line semiconductor laser amplifiers is demonstrated using this technique. The possibility of fault localization on an optical amplifier system with optical isolators is shown     

Margin measurements in optical amplifier system

The margin, or the difference between the received signal-to-noise (SNR) and the SNR required to maintain a given bit error ratio (BER), is important to the design and operation of optical amplifier transmission systems A new tehnique is described for estimating the SNR at the receiver's decision circuit when the BER is too low to be measured in a reasonable time. The SNR is determined from the behavior of the BER as a function of the decision threshold setting in the region where the BER is measurable. The authors obtain good agreement between the BER predicted using the measured SNR value and the actual measured BER     

海底光缆通信系统标准化初探

探讨了海底光缆通信系统标准化的必要性与可行性,介绍了海底光缆通信系统的基本构成与特征,分析了国内外海底光缆通信系统的标准化状况,最后提出了我国应如何开展标准化工作的建议。     

喇曼光纤放大器特性及其在WDM系统中的应用

简述喇曼光纤放大器的工作原理，增益和噪声性能，重点探讨了分布式喇曼光纤放大器（DRA）在波分复用系统中的应用。DRA用于DSF DWDM传输实验系统，经过8段80km的传输，所有信道误差率均达到10^-9；用于1.6Tbps DWDM系统，经过4段100km传输，高于其它商用长距离系统所采用的80km的放大距离，可兼容目前的商用网络。     

High-accurate fault location technology using FSK-ASK probebackscattering reflectometry in optical amplifier submarine transmissionsystems

This paper proposes a new modulation format for optical time domain reflectometry (OTDR) to eliminate optical surge and improve OTDR performance in optical amplifier submarine transmission systems. The modulation format, FSK-ASK, uses a short high-power probe pulse and a long dummy pulse. Thanks to the slow gain dynamics of erbium-doped fiber amplifiers, both pulses experience an identical gain, equal to the loss of a span, so that the probe pulse maintains its high power and does not develop into an optical surge. Fault location experiments verify a theoretical prediction that FSK-ASK improves the signal-to-noise ratio (SNR) of OTDR by an amount as large as the power ratio of the probe to dummy signal. They also confirm the elimination of the optical surge caused by conventional OTDR using a solitary probe pulse. An FSK-ASK OTDR is applied in a commercial submarine amplifier transmission system which has a total transmission length of 890 km and a repeater spacing of 90 km. These field trial results show that subtle fiber anomalies can be located, with a spatial resolution of 1 km, along the entire length of the amplifier transmission system from a terminal end     

Dynamic range of an optical amplifier cascade in an ASK system withsignificant phase noise

The authors present detailed results concerning the dynamic range of an amplitude-shift keyed (ASK) heterodyne optical communication system where the transmitted signal is impaired by significant amounts of laser phase noise. Theoretical results are evaluated for a system with up to ten in-line optical amplifiers and a significant influence of the laser phase noise is found for the maximum allowable transmission span and the dynamic range. With ten amplifiers, a linewidth of 11% of the bit rate causes the span to be reduced by 12.2 dB and the dynamic range to be reduced by 5.7 dB. The results have been confirmed using two amplifiers in a field trial experiment at a bit rate of 636 Mb/s with an IF linewidth of 70 MHz     

长距离海底光缆系统的技术动向

随着全球经济一体化和各国实现自身信息化的需求,国际间的通信和信息流量激增,尤其是以因特网为首的多媒体通信急剧发展,４５Ｍｂ／ｓ、１５５Ｍｂ／ｓ国际数字专用线业务的需求量逐年增加,造成了通信容量不足,因此为海底光缆通信提供了广阔的市场空间。本文将对长距离光放大海底光缆系统的开发现状、主要技术和发展动向进行探讨。     

一种新的海底光缆监测系统的研究

建立海底光缆监测系统对保障已经成为当代洲际通信主要手段之一的海底光纤通信非常重要.文章提出了一种新的基于BOTDR和声纳的海底光缆事件监测系统,并讨论了其测量方法.     

Low detection penalty in an optical DPSK heterodyne system using asaturated optical amplifier as phase modulator

A model established from the rate equations of a near traveling-wave optical amplifier (NTWOA) used as a phase modulator shows that the modulation rate is limited by the carrier lifetime to 500 Mb/s and that the worst-case detection penalty is about 0.7 dB. It is then experimentally demonstrated that close control of the injected light polarization can reduce the detection penalty in a DPSK (differential phase-shift keying) heterodyne system, using an NTWOA phase modulator instead of an LiNbO₃ modulator, to 0.6 dB. This device and a balance receiver have allowed the implementation of 282-Mb/s DPSK link operating at 1.522 μm over 242 km of fiber with a 3-dB margin     

Large-signal effects in an optical BSO amplifier

It is shown that the gain obtainable by coherent amplification using two-wave mixing in BSO crystals is limited by nonlinear effects. A model based on a generalisation of existing theories is presented, giving the dependence of gain coefficient on input beam ratio and leading to good agreement with experimental results.     

光纤光栅滤波器在水下光通信系统中的应用

文章提出了一种基于光纤Bragg光栅(FBG)的用于水下光通信系统接收机前站的滤光方案，并采用耦合模理论分析了FBG的传输特性，数值模拟了Bragg波长为532nm、窄带、高反射率的均匀周期高斯切趾FBG。     

Traffic grooming in an optical WDM mesh network

In wavelength-division multiplexing (WDM) optical networks, the bandwidth request of a traffic stream can be much lower than the capacity of a lightpath. Efficiently grooming low-speed connections onto high-capacity lightpaths will improve the network throughput and reduce the network cost. In WDM/SONET ring networks, it has been shown in the optical network literature that by carefully grooming the low-speed connection and using wavelength-division multiplexer (OADM) to perform the optical bypass at intermediate nodes, electronic ADMs can be saved and network cost will be reduced. In this study, we investigate the traffic-grooming problem in a WDM-based optical mesh topology network. Our objective is to improve the network throughput. We study the node architecture for a WDM mesh network with traffic-grooming capability. A mathematical formulation of the traffic-grooming problem is presented in this study and several fast heuristics are also proposed and evaluated     

Large-capacity optical path cross-connect system for WDM photonictransport network

This paper demonstrates our previously developed large-capacity optical path cross-connect (OPXC) system. The major hurdles to be cleared are (1) establishment of a highly modular architecture that facilitates hardware design and upgrading and (2) the development of an OPXC demonstrator designed to achieve 320-Gbit/s throughput capacity. Due to the use of planar lightwave circuit technologies, compact size packaging for an 8×16 delivery-and-coupling type optical switch and an arrayed-waveguide grating for a wavelength-demultiplexer are achieved. The dense packaging of the four-channel optical regenerators (3-R function regenerator) makes it possible to realize a large-capacity OPXC that can offer high quality transmission and ensure robustness in terms of multiple node connection. Performance test results confirm the validity of the system design and the feasibility of 320-Gbit/s OPXC implementation