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.<>     

OTDR in monomode fibres at 1.3 ?m using a semiconductor laser

Optical time domain reflectometry (OTDR) in monomode optical fibre using a 1.3 ?m semiconductor laser source is reported for the first time. A nonreflecting fibre defect may be accurately located at a range exceeding 17 dB one-way loss by observing the cessation of the Rayleigh backscattered signal.     

Real-time long range complementary correlation optical time domainreflectometer

The improved performance of an optical time-domain reflectometer (OTDR) through the application of a correlation technique using codes with complementary autocorrelation properties is discussed. The theoretical foundations of the method are presented along with experimental results exhibiting the best one-way range reported to date for a practical long-haul, long-wavelength OTDR system     

OTDR in a 147 km single-mode fibre in 1.55 ?m wavelength region using an LD and GaInAs/InP APD at room temperature

A Rayleigh backscattered signal over 147.7 km of single-mode optical fibre has been observed for the first time by long-range, optical time-domain reflectometry (OTDR) usinga 1.54 ?m high-power semiconductor laser (LD) and a GaInAs/InP APD with a small dark current at room temperature. A one-way backscattered dynamic range of 29.3 dB at room temperature has been achieved.     

1.5-μm-band optical time domain reflectometer for single-modeoptical fiber using a P2O5-highly-doped fiberRaman laser

A wide-dynamic-range 1.5-μm-band optical time-domain reflectometer (OTDR) for single-mode optical fibers using a P₂O₅-highly-doped fiber Raman laser light source and a cooled Ge-p-i-n photodiode is realized for the first time. The stimulated-Raman-scattering properties of P₂O₅-doped single-mode fiber are investigated. Using this fiber and an Nd:YAG laser operating at 1.32 μm, a high-power light pulse at 1.59 μm is generated with high efficiency. Using the stimulated-Raman-scattering light as the light source and a high-sensitivity optical receiver, a 1.5-μm-band OTDR having a one-way dynamic range of 35 dB is realized     

Optical time-domain reflectometer with a semiconductor laser amplifier

An optical time-domain reflectometer (OTDR) using a semiconductor laser as an optical pulse generator and as a back-scattered optical signal amplifier is reported. It is found that the detectable one-way loss of the apparatus is improved by 4.5 dB compared with the conventional OTDR using direct detection.     

Development of a coherent OTDR instrument

Optical time domain reflectometry (OTDR) is a commonly used technique for characterization and fault location of optical fiber transmission systems. It involves measuring the fraction of a probe pulse that is scattered back (by Rayleigh scattering) from a silica fiber. Because of the very small levels of backscatter in single-mode fiber at long wavelengths, very sensitive optical detection is necessary to achieve adequate range performance. This paper gives the principles of operation and performance of a coherent OTDR system designed for use at 1.3 μm and its realization as a robust field-portable instrument with a specified performance of better than 24-dB one-way range, and 0.2-dB fault loss resolution. Coherent detection gives ultimate receiver sensitivity and also reduces the dynamic range requirements of the electronic signal processing. To realize these advantages, a novel technique is used to provide the necessary highly coherent source from a semiconductor laser. Sophisticated Signal processing techniques are employed both pre- and post-detection to integrate the signal out of the noise and also to reduce coherent fading effects. The various components of the system and their development into a robust instrument are described, and the performance of the system over long lengths of fiber both in the laboratory and more importantly on installed transmission links is presented in detail, showing achieved performance considerably better than this specified minimum.     

Design of a 1.65-μm-band optical time-domain reflectometer

The design and performance of a 1.65-μm-band single-mode optical time-domain reflectometer (OTDR) with a laser diode source are described. The approach employs a high-power laser diode with a strained-layer InGaAs/InGaAsP multiple-quantum-well (MQW) structure which is grown by metalorganic vapor phase epitaxy (MOVPE), an InGaAs avalanche photodiode, and methods for reducing the optical wiring loss in an optical unit. A 1.65-μm-band OTDR is realized with a single-way dynamic range of 25 dB at a pulse width of 1.0 μs     

High performance single mode OTDR using coherent detection and fibre amplifiers

A high performance single mode OTDR has been constructed at 1.55 mu m using a DFB laser diode, laser diode pumped fibre amplifiers and a coherent detector, all suited to integration into a robust and portable instrument. A dynamic range of 33 dB has been attained with 1 mu s launch pulses, 1 MHz receiver bandwidth and 10/sup 4/ integrations. This result represents an increase of about 13 dB in performance over the standard version of the OTDR using a laser diode as a light source. It is comparable to the best previously reported value attained using a high power glass laser and a cooled detector.<>     

Optical fiber splice loss predictions from one-way OTDRmeasurements based on a probability model

It is well known that one-way optical time-domain reflectometry (OTDR) measurement contains a false contribution to the splice loss due to statistical fluctuations in light scattering among fibers. Using a large amount of collected data over splice losses from field installations, a two-dimensional probability distribution function with the actual splice loss and the one-way measured OTDR discontinuity as variables was fitted to the data. The five parameters of the chosen probability distribution were determined numerically from the observed data. The probability of keeping the splice loss below a target value based on the observed one-way OTDR reading was calculated and can be displayed in a curve or a table of values. The agreement between theory and experimental values is satisfactory for standard match clad single-mode fibers measured at 1.3-μm wavelength     

Improved-dynamic-range single-mode OTDR at 1.3 ?m

A high-performance single-mode optical time-domain reflector (OTDR) incorporating a new low-noise receiver design utilising a PIN diode detector and a transimpedance amplifier is described. With a 1.3 ?m laser diode source a dynamic range of 30 dB one way is achieved, and using an Nd: YAG laser source the dynamic range is 41 dB one way.     

Simulation method of reflectance measurement error using the OTDR

This letter presents an algorithm relating two different optical time-domain reflectometer (OTDR) reflectance measurement methods. From the impulse response of an OTDR, and the attenuation and reflectance values of a reflective event supplied by the OTDR operating according to a first classical implemented method, the algorithm allows the determination of the reflectance that would be measured according to a second more accurate method. Over a 10-dB comparison range the deviations between experimental results and those obtained with the proposed algorithm do not exceed 0.5 dB     

基于LFM-OTDR的超长跨距光纤电力通信链路监测

为了降低电力通信系统中白噪声和随机多径噪声,提出了2种基于线性调频-光时域反射仪(LFM-0TDR)技术的监测方案,即单频LFM-0TDR方案和频分复用LFM-0TDR(FDM-LFM-0TDR)方案.该监测方案采用LFM光脉冲信号作为探测信号,利用分数阶傅里叶变换将后向散射回来的探测信号变换到分数阶傅里叶域进行信号处...     

Optical reflectometry with micrometer resolution for theinvestigation of integrated optical devices

An optical time-domain reflectometry (OTDR) system using an infrared subpicosecond pulse source in conjunction with balanced heterodyne detection is discussed. Experimental results show a density of more than 100 dB and a resolution of 60 μm in air. Taking advantage of the large tuning range of the laser system, it is possible to improve the resolution to less than 10 μm. The applicability of the OTDR system for the diagnostics of integrated optical devices is demonstrated for a simple GaAs waveguide structure     

A distributed optical fiber sensing system for synchronous vibration and loss measurement

We propose a fully distributed fusion system combining phase-sensitive optical time-domain reflectometry (Φ-OTDR) and OTDR for synchronous vibration and loss measurement by setting an ingenious frequency sweep rate (FSR) of the optical source. The relationships between FSR, probe pulse width and repeat period are given to balance the amplitude fluctuation of OTDR traces, the dead zone probability and the measurable frequency range of vibration events. In the experiment, we achieve synchronous vibration and loss measurement with FSR of 40 MHz/s, the proble pulse width of 100 ns and repeat rate of 0.4 ms. The fluctuation of OTDR trace is less than 0.45 dB when the signal-to-noise ratio (SNR) is over 12 dB for a captured vibration event located at 9.1 km. The proposed method can be used for not only detection but also early warning of damage events in optical communication networks.     

Long dynamic range spread spectrum optical domain reflectometer

The performance of an optical time domain reflectometer (OTDR) is significantly improved using spread spectrum technology. The concept of spread spectrum OTDR (SSOTDR) is proposed, the theoretical basis and simulation results of the new method are given, and the problem of direct application of bipolar spread spectrum codes to OTDR and despreading in the optical domain are solved. The simulation results show the feasibility of the SSOTDR, which exhibits better dynamic range reported to date for a practical long-haul OTDR system without using conventional average technique.     

长距离高精度的线性调频光时域反射仪

为了对西藏人烟稀少地区和单跨段传输距离很长的光纤链路进行检测,文章提出一种用于提高线性调频(LFM)光时域反射仪(OTDR)空间分辨率和测量距离的方法。该方法通过产生一个调频范围为200 MHz、脉冲宽度为20μs的强度调制模拟LFM信号来实现高的空间分辨率和大的探测距离。使用该方法在西藏地区的实际光纤传输链路中进行了实验测试,实验结果表明,该方法能够在长度为240 km的光纤链路上实现0.000 53 km的空间分辨率,与相同测量参数的单脉冲OTDR相比,动态范围提高了8.5 dB。     

Photon timing OTDR: a multiphoton backscattered pulse approach

Time-correlated photon counting with solid state detectors is of considerable interest for high resolution optical time-domain reflectometry (OTDR). Up to now long measurement times were required. A new approach is described, yielding measurement times 50 times shorter and dynamic range enhanced by approximately=20 dB.<>     

工程中遇到的光纤（衰减）均匀性熔接损耗和偏振模色散（PMD）

本介绍了光纤（衰减）不均匀性三种情况和国内标书中常见的一些表述。中指出：要使国内标书中的表述与光纤（衰减）三种不均匀性相容,就要求光纤不连续点（台阶）幅度、衰减波动幅度小于0.05dB,OTDR测两端衰减系数差小于0.05dB/km。光纤（包括衰减和色散）的不均匀性,实质上就是光纤几何（包括折射分布）不均匀性。它导致两根光纤作熔接时产生接头损耗。中对光纤接头损耗的定义、接头损耗的概率分布,以及中楼段链路中n个光纤熔接头的平均损耗计算也作了介绍。此外,中也简要介绍了光纤（缆）的偏振模色散（PMD）。     

Ultra-long-range OTDR in single-mode fibres at 1.3 ?m

A single-mode optical time-domain reflectometer (OTDR) operating at a wavelength of 1.3 ?m with a dynamic range in excess of 26 dB one way is reported. The equipment incorporates a semiconductor laser source and a new low-noise optical receiver design utilising a PIN diode detector and a transimpedance amplifier.