Polarisation optical time domain reflectometry

A proposed new optical fibre technique will allow measurement of the spatial distribution of physical fields, and will also allow location of anomalous features in single polarisation state monomode optical fibres such as are under discussion for very high bandwidth communication.     

Raman-assisted long-distance optical time domain reflectometry

The measurement range of long-haul optical time domain reflectometry (OTDR) may be extended substantially by introducing distributed Raman gain in the fibre under test. With semiconductor pump lasers an increase in the fault location range of at least 10 dB one-way is achievable, without requiring the OTDR to have an increased processing dynamic range.<>     

Advances in optical time domain reflectometry

Advances in optical time-domain reflectometry (OTDR), such as enlargement of dynamic range, enhancement in resolution, reduction of noise intrinsic to single-mode fibers, and increase in user friendliness of the equipment, are reviewed. The gated detection technique and recent progress in OTDR are presented. Future optical network diagnostics are discussed     

Optical time domain reflectometry by photon counting

A photon counting technique has been used to extend greatly the range of optical time domain reflectometry or `back-scatter? for fault location in optical fibre systems. A range of more than 40 dB of one-way fibre loss has been achieved even when the break was index-matched to eliminate any reflection.     

Resolution enhancement in time domain reflectometry systems

The resolution enhancement of time domain images obtained from electromagnetic and acoustic TDR systems is reported.     

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     

Application of super-resolution techniques to time domain reflectometry systems

By application of the principles of super timing (i.e. sharpening of the time resolution for a given bandwidth) it is shown that the resolution of a t.d.r. system can be improved beyond the classical limit imposed by the rise time of the step generator. The discussion is supported by experimental results.     

Two signal processing enhancements for optical time domain reflectometry

Because time domain response of the backscattered signal in optical fibers is essentially exponential, there is 6-8 dB signal gain obtainable by using a logarithmic amplifier before any form of averaging, in the weak signal limit. Furthermore, the direct summation averaging of noisy traces (instead of the usual weighted averaging) is simpler because the required OTDR information is essentially relative.     

Fault detection in a photovoltaic plant by time domain reflectometry

A reflectometric technique has been developed for diagnostic monitoring of a photovoltaic plant. Detailed information on the position and type of fault is inferred from the shape of the voltage waveforms resulting when a pulsed voltage excitation is applied to a string consisting of several series-connected modules. When an open circuit or a short circuit to ground are occurring, direct reading of the results is obtained by means of a software tool performing numerical analysis of the digitized waveforms. Extensions of this approach to the case of parallel-connected strings, as well as to the cases of a loaded plant and no illumination, are discussed.     

基于偏振光时域反射技术的分布式光纤传感器

首先介绍了偏振光时域反射技术(POTDR)的基本原理及发展现状,并重点介绍了几种典型调制效应(电光效应、Faraday效应以及弹光效应)的基本原理及其在POTDR分布式光纤传感器中的主要应用模式,以及POTDR分布式光纤传感器对现代监测系统的意义。最后,提出POTDR光纤传感器在实际应用中存在的问题与不足,并对其应用前景和发展方向进行了展望。     

Resolution controllable optical time domain reflectometry based onlow coherence interference

A low-coherence optical time domain reflectometer (OTDR) that can control spatial resolution is proposed to efficiently diagnose waveguides. This is achieved using a light source consisting of a superluminescent diode (SLD), an optical bandpass filter for truncating the SLD output, and an antireflection-coated laser diode booster amplifier. Two resolutions, 44 and 14 μm, were experimentally demonstrated with and without the filter having a 2.7-nm full width at half maximum (FWHM), respectively. The length of the blind space and the minimum detectable reflectivity were respectively <7 mm and <-134 dB at a 3-Hz detection bandwidth, for both resolutions. The noise characteristics of the light source and the system performance are investigated theoretically and experimentally     

Characterization of power electronics system interconnectparasitics using time domain reflectometry

The significance of interconnect parasitics of power electronics systems is their effects on power converters' electromagnetic interference (EMI)-related performances, such as voltage/current spikes, dv/dt, di/dt, conducted/radiated EMI noise, etc. In this paper, a time domain reflectometry (TDR) measurement-based modeling technique is described for characterizing interconnect parasitics in switching power converters. Experiments are conducted on power components of a prototype high-power inverter, including insulated gate bipolar transistor (IGBT) modules, busbar and bulk capacitors. It is shown that the interconnect inductance of the IGBT module can be extracted completely using TDR. It is also shown that the busbar equivalent circuit can be modeled as transmission line segments or L-C filter sections, and the bulk capacitor contains a significant equivalent series interconnect inductance     

基于相位敏感光时域反射计的长距离入侵探测系统

根据受激布里渊散射(SBS)对相位敏感光时域反射计(-OTDR)的监测距离的限制,分析了在使用不同灵敏度的光电探测器时-OTDR系统的监测距离,并根据SBS阈值随着光纤长度的增加而下降的特点,提出了一种新的光路结构以提升系统的监测距离。该光路结构采用环行器将敏感光纤分为多个部分,并对各部分的后向瑞利散射光分别进行探测,避免了各部分光纤产生的斯托克斯光相互叠加,从而提高了SBS阈值,进而实现了提升系统监测距离的目的。在实验室测试中,使用3个环行器将敏感光纤分为了3个部分并实现了66.92 km的监测距离。通过增加环行器的数量,系统的监测距离可以进一步提高。     

Optical time domain reflectometry using an M-ary FSK probe andcoherent detection

This paper proposes a new approach to enhancing the performance of optical time domain reflectometry (OTDR). This approach launches a probe signal modulated in the M-ary FSK format into a test fiber and detects the backscattering by coherent detection, which offers excellent frequency discrimination, followed by simple signal processing to recover the fiber impulse response. Fault location experiments verify the theoretical prediction of that the proposed approach reduces the measurement time to 1/M without sacrificing measurable dynamic range or spatial resolution. They also show that the approach is effective in reducing fluctuations in the OTDR trace. It is experimentally confirmed that OTDR with the proposed approach is feasible for long haul transmission systems     

Polarisation optical time domain reflectometry for statistical evaluation of polarisation mode dispersion

The authors shows that a commercial optical time domain reflectometer can be modified to measure the statistical nature of polarisation mode dispersion along the length of a communications grade fibre with short-length PMDs<4 ps/km.<>     

Optical time domain reflectometry in optical transmission linescontaining in-line Er-doped fiber amplifiers

Optical time domain reflectometry (OTDR) in an optical transmission line containing in-line Er-doped fiber amplifiers is investigated. The proposed Er-doped fiber amplifiers are based on optical circulators, which support both OTDR and digital signal transmission. The measurable limit of OTDR fault location in optical transmission lines containing in-line amplifiers is discussed. Fault location and 1.8-Gb/s digital signal transmission are demonstrated in a 316.9 km, optical transmission line constructed with three in-line Er-doped fiber amplifiers     

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.     

Isolating failing sites in IC packages using time domain reflectometry: Case studies

This paper deals with Time Domain Reflectometry (TDR) technique with the aim to confirm that this tool should not be kept away from a non-destructive failure analysis process flow. An improvement of known comparative TDR methodology, the sequential comparative method, is introduced and several case studies illustrate its better efficiency to isolate complex packaging defects. Also, main limitations of the technique are studied and several hardware improvements are proposed, especially in terms of spatial resolution.     

Time domain reflectometry liquid level sensors

The technique of time domain reflectometry (TDR) has been used by electrical engineers for testing the characteristics of transmission lines and diagnosing faults. Although TDR instruments for testing cable are commonly used today, few instrumentation engineers are aware that the technique can measure liquid levels and fluid interfaces. In this article, I review the theory and principles of time domain reflectometry and present the application of this technology as a liquid level sensor     

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.<>