OTDR在光纤测量中的应用

介绍ＯＴＤＲ工作原理及主要性能参数;详细说明ＯＴＤＲ在光纤测量中参数的设置及测量方法;结合工作实践提出了ＯＴＤＲ在实际光纤测量中的几点经验和技巧。     

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     

Fading rates in coherent OTDR

The fading rates of the backscatter signal from a single-mode optical fibre under quasimonochromatic pulse excitation are measured experimentally using a homodyne OTDR system. A method of increasing the fading rates to facilitate efficient signal averaging is discussed.     

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.     

基于OTDR分布式光纤的海底管道安全检测

提出了一种基于OTDR的分布式光纤传感系统的海底管道安全检测技术,分析了检测系统的组成工作原理,阐述了检测系统定位结构和方法,通过注入脉冲与接收到的信号之间的时间延迟得到扰动的位置。理论分析和测试结果表明,该测试系统具有较高的稳定性和定位精度。     

Statistics of Rayleigh backscatter from a single-mode optical fibre

The probability density function of the intensity of the Rayleigh backscatter signal from a single-mode optical fibre resulting from a short quasimonochromatic pulse excitation is derived for the first time. The result is used to explain the appearance of coherence noise in OTDR systems.     

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     

受激布里渊散射主被动混合调Q光纤激光器

基于瑞利散射和受激布里渊散射(RS-SBS)的被动调Q掺铒光纤(EDF)激光器的输出脉冲序列具有重复频率低、脉宽窄、功率高的特点,适合光时域反射(OTDR)系统对脉冲光源的基本要求,但是输出的脉冲序列不够稳定。提出在被动调Q激光腔中插入声光调制器(AOM)构成主被动混合调Q激光器。实验结果证明,这种混合调Q的方法既保持了声光调制器主动调Q激光器输出脉冲序列重复频率低而且稳定的特点,又发挥了瑞利散射和受激布里渊散射被动调Q机制动态速度快、输出脉冲宽度窄的优势。在120~200 mW的抽运功率条件下,得到的脉冲序列重复频率从30 Hz~90 kHz连续可调,脉冲宽度最小可达20 ns,峰值功率最高可达200 W,脉冲重复频率稳定度优于5%,脉冲幅度起伏不大于10%。脉冲峰值功率和脉冲宽度受抽运功率的影响不大,但随着调制频率增加,脉冲峰值功率降低而脉冲宽度加宽。     

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     

OTDR系统波形的分析及其在光纤测量中的应用

本文利用瑞利散射原理分析了脉冲信号和脉宽大于、小于回波时间的方波信号的回波信号波形,并利用数值模拟得到了其理论波形图。根据原理自主搭建了一套光纤光时域反射仪（Optic Time Domain Reflectometer,简称OTDR）,用通信中通用的1550nm激光波长对样品光纤进行了实际测量,得到了与理论模拟完全一致的实测波形。通过对实测波形进行降噪处理得到了高精度的长度测量值和损耗测量值。长度测量的相对误差仅为0.0085%,与直接测量值比较,光纤传输损耗的相对误差为0.086%,理论与实验表明该OTDR系统完全可以与工程用的OTDR系统相媲美,在工程技术和教学研究中具有一定的应用前景。     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

A novel in-service measurement technique using the same wavelength band as SCM signals

This paper proposes a new technique for measuring in-service optical fibers, that uses an optical time domain reflectometer (OTDR). The feature of the proposed technique is that the OTDR light is in the same wavelength band as the video signal, which is distributed by using the subcarrier multiplexing (SCM) technique. In a 40-channel SCM system operating at a signal wavelength of 1.558 /spl mu/m, we show that the required video quality can be maintained, by using the proposed OTDR operating in the 1.55 /spl mu/m band, even though the measured fiber is in service and the OTDR light enters an optical receiver. Moreover, we clarify the conditions for undertaking measurements, without the need for optical filters designed to prevent OTDR light from degrading the SCM signal quality.     

OTDR performance enhancement through erbium fibre amplification

By employing erbium fibre amplification of both the outgoing transmitter pulses and the returning backscatter signals of an optical time domain reflectometer (OTDR), a substantial increase is achieved in the one-way dynamic measurement range. First experimental results are presented showing almost 10 dB net improvement in OTDR range, with the potential established for performance increases of up to 20 dB one-way. The prospects are discussed for such performance improvements both in high-resolution OTDR applications and for long-distance fault location.<>     

基于菲涅耳反射的准分布式光纤温度传感器

基于菲涅耳反射原理和光时域反射(OTDR)技术,提出了一种新型的、结构简单的准分布式光纤温度传感器.传感器由两个端面抛光的光纤对接构成,并在两端面间隙中填充温敏材料.传感器周围温度变化改变温敏材料的折射率,从而引起菲涅耳反射强度的变化.将三个传感头串联,利用OTDR探测各传感器菲涅耳反射的微弱变化实现温度传感和传感器定位.在-30～80℃范围内,随着温度升高,该系统各个传感头的菲涅耳反射强度单调增大,且温度传感特性具有良好的重复性,同时具有极低的附加损耗.     

An Optically Linked Telemetry System for Use with Electromagnetic-Field Measurement Probes

A battery-powered optical telemetry transmitter, 2.5 X 2.5 X 3 cm, has been developed for use with various electromagneticfield hazard probes. The electrical outputs from one of these probes, containing three orthogonal sensors, are electrooptically converted to three separate optical pulse trains so that a dc to 2-kHz information bandwidth is established in the transmitter using frequency-modulation techniques. The three optical pulse tains are transmitted over a 4.6-m fiber-optics bundle to one of two types of receivers. These units reconvert the information to either an analog replica of the transmitter input waveform, or to a three-digit, scaled numerical display of the time-averaged value of the input signal. Practical applications involving field-strength measurements in the 1-MHz to 12-GHz region are presented. Advantages over hardwire data links are discussed, and significate reductions in RF interference and cable backscatter during field-strength measurements are described.     

Ultra-Wideband Waveform Generator Based on Optical Pulse-Shaping and FBG Tuning

We propose and demonstrate experimentally a prototype for ultra-wideband (UWB) waveform generator based on optical pulse shaping. The time-domain pulse shape is written in the frequency domain, and a single-mode fiber performs frequency-to-time conversion. A U.S. Federal Communications Commission (FCC)-compliant power efficient pulse shape is inscribed in the frequency domain by a fiber Bragg grating (FBG) with an excellent match between optimized and measured pulses. Two other popular UWB pulse shapes (Gaussian monocycle and doublet pulses) are achieved by proper tuning of two FBG-based variable optical filters. A balanced photodetector removes an unwanted rectangular pulse superimposed on the desired waveform, assuring compliance at low frequency.     

一种基于小波变换的OTDR事件分析算法的研究

简单分析了用 OTDR卡进行光纤检测的原理 ,根据小波分析检测信号突变点的理论 ,提出了运用小波分析对光纤断点及反射事件准确定位的方法。理论分析和实例计算表明 ,这种方法对 OTDR曲线中反射事件尤其是断点的定位非常准确 ,是一种行之有效的方法     

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     

Employing the ForWaRD Method to Improve Resolution of Conventional OTDR for Application in SHM

As a fiber sensor,optical time domain reflectometer becomes more and more popular to measure parameters,such as strain and temperature in structural health monitoring(SHM) simultaneously.Since the accuracy of range resolution in optical time domain reflectometer(OTDR) is determined by the pulse width of laser,the range resolution in order of centimeter is achieved by employing of picoseconds lasers which are not commercial.In this paper,to achieve this accuracy with conventional OTDR,Fourier wavelet regular...     

拉曼自频移全光量化中的全光纤脉冲宽度压缩器的设计

通过数值求解广义非线性薛定谔方程,研究了由高非线性光纤分别与3M-FS-PM-7811光纤和SMF-28光纤串联构成的全光纤脉冲宽度压缩器在压缩波长为1550nm的红外光脉冲宽度方面的性能.计算结果表明:采用3M-FS-PM-7811光纤的脉冲宽度压缩器所需要的入射功率小,而采用SMF-28光纤的脉冲宽度压缩器输出的脉冲基座小;两种全光纤脉冲宽度压缩器均能将脉冲宽度为2ps的高斯输入脉冲压缩到200fs～300fs.