Ultralong multimode optical fibre fault location using Raman optical time domain reflectometry

The OTDR technique using the stimulated Raman scattering effect (ROTDR) is applied to ultralong multimode optical fibre fault location. In experiment, Stokes light pulses at 1.6 ?m wavelength, which are the most advantageous for fault location, are used. It is shown that the multimode fibre break, more than 80 km long, is locatable, and fibre loss at 1.6 ?m is measurable by the ROTDR technique.     

Ultra-long graded-index multimode optical-fiber fault location using Raman optical time-domain reflectometry

Ultra-long graded-index (GI) multimode fiber fault location has been carried out using Raman optical time-domain reflectometry (ROTDR), where the Stokes' light pulses generated by the stimulated Raman scattering effect in a measured fiber are used as probe pulses. For basic investigation, spectral power distributions of the Stokes' pulses in a multimode fiber pumped by a 1.06-μmQ-switched Nd:YAG laser have been measured. Maximum locatable distance for a fiber break using the ROTDR technique has been estimated by the measurement results, and it has been shown that a more-than-100-km-long multimode fiber break is locatable. On the basis of these results, a 86-km-long multimode fiber fault-location experiment has been carried out, and the break without Fresnel reflection has been located.     

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     

Fault location in optical fibers using optical frequency domain reflectometry

This paper describes the experimental and analytical investigations performed on another backscattering technique named "Optical Frequency Domain Reflectometry" (OFDR). In this approach the temporal signatures of graded-index multimode fibers are obtained as the inverse Fourier transform of the OFDR data. In the employed OFDR system the entire process is automated, and the modulation frequency is changed stepwise to obtain an exact inverse Fourier transform. The effects of starting frequency, frequency increment, and highest modulation frequency on OFDR temporal response are considered. The experimental results are in good agreement with those obtained by computer simulations. Also, a synchronous detection type of filtering process is suggested for signal-to-noise ratio improvement in OFDR technique.     

First field demonstration of in-service fault location/supervisory using optical time domain reflectometry

In-service fault location using optical time domain reflectometry is demonstrated for the first time over an installed submarine, fibre-optic cable. Results are presented showing simultaneous fault location and 565 Mbit/s data transmission on one fibre of the UK-Channel Islands no.7 fibre-optic cable. In addition, laboratory experiments indicate that the technique could prove to be invaluable in supervising wavelength-routed networks incorporating both passive and active optical components.<>     

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.<>     

Analysis of power budget performances of digital transmissionsystems with an optical amplifier

Explicit expressions for the power budget of a direct detection transmission system when an optical amplifier changes its location along the span are presented. The analysis is in good agreement with experimental data obtained at 565 Mbit/s and 2.5 Gbit/s     

Optical time domain reflectometry on optical amplifier systems

The use of optical time-domain reflectometry (OTDR) on long-span fiber transmission systems containing in-line optical amplifiers is discussed. Having identified the specific requirements for OTDR equipment, measurements were carried out on systems of up to 300 km in length, containing three semiconductor laser amplifiers. The results demonstrate that OTDR can be used not only for fault location on fiber links several hundred kilometers in length but also as an alternative to standard system supervisory techniques, thus providing the potential for minimizing the hardware in the optical amplifier stages of future long-span fiber optic transmission systems     

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.<>     

WDM upgrading of an installed submarine optical amplifier system

This paper describes the WDM upgrading of a submarine optical amplifier system installed for single-channel transmission in commercial use. The key technologies used include 10-Gb/s high-speed forward error correction, preemphasis to overcome the optical passband-width constraint, optimized signal pulse format that leads to partial return-to-zero (PRZ) signaling, and dispersion compensation to suppress the degradation caused by fiber nonlinearity and dispersion. It also reports field experimental results on upgraded system performance. The results confirm that simply upgrading the terminal equipment allows the transmission capacity of a submersed line consisting of submarine repeaters and cables to be flexibly increased from 10 Gb/s to 40 Gb/s per fiber pair     

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/.<>     

Research on fault location technology based on BP neural network in DWDM optical network

BP neural network is introduced to the fault location field of DWDM optical network in this paper. The alarm characteris-tics of the optical network equipments are discussed,and alarm vector and fault vector diagrams are generated by analyzing some typical instances. A 17×14×18 BP neural network structure is constructed and trained by using MATLAB. By comparing the training performances,the best training algorithm of fault location among the three training algorithms is chosen. Numerical simulation results indicate that the sum squared error (SSE) of fault location is less than 0.01,and the processing time is less than 100 ms. This method not only well deals with the missing alarms or false alarms,but also improves the fault location accuracy and real-time ability.     

Research on fault location technology based on BP neural network in DWDM optical network

BP neural network is introduced to the fault location field of DWDM optical network in this paper. The alarm characteristics of the optical network equipments are discussed, and alarm vector and fault vector diagrams are generated by analyzing some typical instances. A 17 × 14 × 18 BP neural network structure is constructed and trained by using MATLAB. By comparing the training performances, the best training algorithm of fault location among the three training algorithms is chosen. Numerical simulation results indicate that the sum squared error （SSE） of fault location is less than 0.01, and the processing time is less than 100 ms. This method not only well deals with the missing alarms or false alarms, but also improves the fault location accuracy and real-time ability.     

基于开放光传送网络的域间故障定位技术研究与实践

目前,不同专业设备的网络管控系统相对独立,如何快速恢复域间光网络故障是当下网络运维需要解决的问题。针对域间光网络的故障定位方案展开研究,域间网络发生故障后,先通过链路自动发现协议和光模块调顶技术获取完整的链路信息和模块数据,再利用性能实时监控技术和根因分析功能找到当前故障的根告警。综合运用这些方法并通过开发的传输网络运行质量分析原型系统将光传送网络的管理域外延,从而形成包含远端客户侧在内的端到端的开放光传送综合管控系统。     

Coherent optical tapping using semiconductor optical amplifier

Semiconductor optical amplifiers are attractive not only as optical repeaters but also as functional devices, since carrier density modulation in amplifiers causes a nonlinear phenomenon. Utilizing the effect of the carrier density modulation on the semiconductor optical amplifier junction voltage, a coherent optical tapping is proposed for signal monitoring or control signal extraction. A 155 Mb/s FSK (frequency shift keying) signal tapping was realized with a simple configuration using heterodyne single-filter detection with -24.4 dBm sensitivity. Many applications for this coherent optical tapping are discussed, and basic characteristics for frequency-selective tapping from FDM (frequency division multiplexing) signals and optical amplifier gain control are examined     

海缆布里渊光时域反射信号的去噪方法研究

为了从噪声背景中有效地提取光电复合海缆的布里渊光时域反射信号,根据信号的特点,提出了采用小波阈值法对实时信号进行去噪处理。针对小波阈值去噪参量设置的基础性问题,通过理论分析和实验对比确定了适于海缆布里渊光时域反射信号去噪处理的最优参量,并与中值滤波、均值滤波的去噪效果进行了对比。结果表明,相对于两种传统的滤波方法,最优参量下的小波阈值法能有效去除噪声,不仅信噪比提高了14.1dB,而且能检测出100με的应变变化。该研究对于探索海缆布里渊光时域反射信号的高效处理方法具有重要参考价值。     

光纤参量放大器技术及其最新进展

介绍和论述了一种非常有实用前景的基于光纤非线性效应的光参量放大器(OPA)及其最新技术进展．最新发展揭示了它的很多技术特性优于传统的掺铒光纤放大器(EDFA)、半导体光放大器(SOA)和近年来很热门的光纤拉曼放大器(FRA)，如对信号的调制形式、比特率的完全透明性、相位共轭、超宽的增益带宽、很低的噪声指数和具备优异的全光波长转换功能．     

Millimeter-resolution optical time-domain reflectometry using afour-wave mixing sampling gate

We report an optical time-domain reflectometer that employs an ultrafast optical switch based on nondegenerate four-wave mixing in a semiconductor laser amplifier. Two-point spatial resolution on the order of 1 mm over 2 m is demonstrated; Fresnel reflections with optical return losses greater than 53 dB are detected. Submillimeter-resolution optical time-domain reflectometry over a 100-m range should be possible with modifications to the pulse sources     

Noise in optical low-coherence reflectometry

It is theoretically and experimentally shown that Fresnel end reflection at a waveguide under test can degrade the sensitivity of an optical low-coherence reflectometer (OLCR) with a balanced detection scheme. Optical mixing of the local oscillator (LO) light and the end reflection produces beat noise whose current noise spectral density is represented by 2(1+P²)〈I₁〉〈I₂ 〉/δν, where P and δν are the degree of polarization and the effective linewidth of the light, respectively, and 〈I₂〉 and 〈I₂〉 are the total mean photocurrents of the LO light and the end reflection at the balanced mixer, respectively. The balanced detection technique suppresses the intensity noise of the light and the beat noise becomes the dominant source of sensitivity degradation. The minimum detectable reflectivity is derived which includes the effect of sensitivity degradation caused by beat noise     

Multiwavelength laser source using linear optical amplifier

We propose and demonstrate a high-performance multiwavelength ring laser based on a linear optical amplifier (LOA) for potential applications in dense wavelength-division-multiplexing communication systems. Experimental results indicate that the inhomogeneous gain medium provided by the LOA reduces the gain competition and leads to stable multiwavelength lasing. Thirty-eight wavelengths covering C+L-band with 0.8-nm channel spacing are generated at room temperature. Simultaneous tuning of multiwavelengths is demonstrated and a stability test shows a power fluctuation of less than 0.2 dB during a 3-h test.