Optical time-domain reflectometry of discrete fiber Raman amplifiers

Optical time-domain reflectometry is proposed and demonstrated as a means to characterize the signal power evolution in discrete fiber Raman amplifiers. Up to /spl sim/20-dB-gain amplifiers have been characterized comprising different fibers, under copropagating and counterpropagating signal-pump configurations, and under saturated and unsaturated conditions. The results demonstrate the flexibility of this simple and useful amplifier characterization technique. Simulations show good agreement with experimental results, and sustain the reliability of the technique.     

基于相位光时域反射的光纤分布式声波传感研究

文中提出了一种光纤分布式声波传感方案。作用在传感光纤上的声波信号导致后向瑞利散射光的相位变化,将含有声波信息的后向瑞利散射信号注入到迈克尔逊干涉仪,并采用相位载波解调算法解调出相位信息。实验中采用压电拉伸器模拟声波振动,分布式声波传感系统实现了10 m的空间分辨率以及平坦的频响。     

Optical time-domain reflectometry measurements in a 4 km fibre ring laser

The first experimental Rayleigh backscatter measurements in a passively modelocked fibre ring laser are reported. The Rayleigh backscatter data were used to identify and estimate splice losses as well as the back reflection of the intracavity optical isolator.<>     

Determination of conductivity profiles by time-domain reflectometry

A new numerical method for the reconstitution of the inhomogeneous media conductivity is described. The conducting medium is nonmagnetic, and its relative permittivity equals one. Its frequency-independent conductivity varies normally to its interface. The medium is normally illuminated by a transverse electromagnetic (TEM) plane wave of causal time dependence. The reconstruction process is a direct approach to the inverse problem. It is based on a space time discretization of an exact integral equation. The conductivity profile is determined step-by-step without approximations other than numerical. Some examples are given to illustrate the most interesting properties of the method; special attention is given to the simulation of experimental errors.     

Measurement of magnetic field by polarisation optical time-domain reflectometry

The technique of polarisation optical time-domain reflectometry has been used to measure magnetic field through the use of the Faraday effect. A spatial resolution of 0.4 m was achieved, and a sensitivity corresponding to a magnetic field of 10?3 T over a length of 0.5 m was obtained.     

Low-cost high-resolution time-domain reflectometry for monitoringthe range of reflective points

A new OTDR technique to interrogate the range of reflective markers in an optical fiber (or an electrical cable) is presented. The technique has been developed to monitor strain in sections of a fiber over gauge lengths of several meters. Signal-to-noise analysis shows that current OTDR systems do not fully exploit the spatial resolution theoretically available. The available resolution is explored with a new OTDR technique     

Optical transmission in dispersion-shifted single mode spliced fibers and cables

Dispersion-shifted single mode fibers have been fabricated with losses as low as 0.21 dB/km in the zero-dispersion region (lambda_{0} approx 1.5-1.6 mum). Low-loss (average = 0.06-dB) fusion splices have been made with the chlorine-hydrogen flame fusion technique. The recoated splices show strengths in excess of 300 kpsi. The fibers have been incorporated into a cable structure with negligible change in loss.     

Optical power distribution in multimode fibers with angular-dependent mode coupling

An expression for the power flow, in multimode optical fibers, is derived, which is mathematically simple and allows a clear physical interpretation of the effects of mode coupling. Coupling strength is assumed to decrease with increasing axial angle. The solution obtained under this assumption is supported by experimental observations. Following the analysis, an experimental procedure to determine the coupling constant is devised. The theoretical results enable the prediction of the loss due to the mode coupling and the transmission bandwidth of the angular multiplexed channels in step-index optical fibers.     

Measurement of Raman scattering in single-mode optical fiber byoptical time-domain reflectometry

The measurement of the Raman scattering in a single-mode optical fiber using optical time-domain reflectometry (OTDR) is reported. The OTDR technique makes it possible to determine the power level of the pump and Stokes components along the fiber without cutting it back, and to estimate Raman scattering parameters in a reliable manner. The measurement method is described and experimental results are discussed. It is concluded that the power conversion process to higher Stokes components has been clearly displayed without cutting back the fiber     

Determination of structural parameter variations in single-mode optical fibres by time-domain reflectometry

Backscatter measurements on single-mode fibres reveal apparent changes in local attenuation resulting from backscatter factor variations. The detailed shape of the backscatter waveforms is compared to known variations of fibre parameters.     

相位敏感光时域反射系统低频响应性能优化

相位敏感光时域反射系统以其分布式光纤传感技术的优势在分布式水听、压裂微地震检测、自然灾害预警等低频监测领域具有极高的应用前景。文中对系统中脉冲斩波信号与频率调制信号时钟不同源的问题予以验证,并对其产生的影响进行理论分析;设计双路同步时钟源驱动产生脉冲斩波信号和频率调制信号,降低每个脉冲重复周期中频率调制信号的随机低频相位噪声,提高探测脉冲光的相位稳定性;采用时钟同源和时钟非同源两种方式对典型的基于外差相干检测的相位敏感光时域反射系统的声光调制器进行驱动,由信号发生器驱动缠有光纤的压电陶瓷,产生不同频段的扰动信号。实验结果表明:在同一测试条件下,前者在低频段的信噪比、相位解调质量、频率响应方面均优于后者,最小响应频率为0.1 Hz,相对提高两个数量级,降低了系统中低频噪声干扰。该方法易于实现,可与现有的低频性能优化方法或结构兼容,进一步提高系统低频响应性能。     

光模块内置OTDR数据及格式分析

为了满足日益增多的PON 的网络光纤检测需求,光模块内置OTDR 技术正在不断地发展完善,提出了基于光模块内置OTDR的PON系统架构中OTDR相关接口的数据传输接口功能和数据分析功能,确定了OTDR数据文件结构,分析梳理了OTDR的数据内容,定义了OTDR的数据格式,目的是能够实现通用的内置OTDR数据格式,促进内置OTDR技术产业发展成熟。     

利用OTDR准确查找光缆线路障碍点

本文重点讲述光缆故障的产生、判断、OTDR（光时域反射仪）的设置、测试及怎样最快查找光缆故障点。     

Comparative measurement of Rayleigh scattering in single-modeoptical fibers based on an OTDR technique

A technique for comparing the Rayleigh scattering coefficients of single-mode step index fibers is described, and its theoretical limitations are discussed. The validity of the technique is proved using telecommunications-grade fibers. Of particular interest is the variation of scatter found with increasing core index. In addition, the influence of small (<0.1%) quantities of rare-earth dopant ions on the fiber scatter losses is analyzed for the first time     

基于OTDR的分布式光纤传感器原理及其应用

介绍了分布式光纤传感器的当前进展及发展趋势.总结了基于光时域反射(OTDR,BOTDR,ROTDR)的分布式光纤传感器的原理、优缺点、应用领域以及在应用中存在的问题.同时对当前产品的测量精度、测量范围等进行了归纳.     

Evaluation of the performance of dual-order mode couplers usingoptical low-coherence reflectometry

Describes a simple and efficient means of evaluating the performance of deep-ridge dual-order mode couplers, a key component in all-optical Mach-Zehnder wavelength converters. The principal characteristics of these couplers namely, the optimal operation wavelength range and the corresponding mode rejection ratio have been determined for the first time using low-coherence reflectometry measurements performed simultaneously in reflection and transmission modes     

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     

Conformal finite-different time-domain (FDTD) with overlappinggrids

It is shown how to use many overlapping conformal grids in the neighborhood of the scatterer while using a rectangular grid away from the scatterer for solving Maxwell's equations. The locally conformal grids allow better approximation of the boundary condition on the scattering object while the rectangular grid preserves the simplicity and accuracy of the regular finite-difference time-domain (FDTD) algorithm. These grids overlap typically about three zones. It is shown how to connect together the calculations done in different overlapping grids     

Finite-difference time-domain (FDTD) analysis of magnetic diffusion

Problems with very slow waveforms or very long diffusion times may be difficult to treat using finite-difference time-domain techniques because of the Courant stability condition. Problems of this class, however, often prove to have a response which does not depend on the speed of light. The examples presented here show cases where internal fields do not change if c is reduced by as much as five orders of magnitude. This permits Δt to be proportionally increased. For simplicity much of this paper is restricted to one dimension, although generalization to three dimensions is also presented. The author considers an aluminum enclosure. Initially, the transient field will induce eddy currents on the enclosure which exactly cancel the external field and exclude it from the enclosure interior. This scheme has been, in fact, proposed to shield large systems which contain magnetic memories     

Transmission properties of the single mode fiber with a cross-sectional micro-channel investigated using time-domain finite difference (FDTD) method

Light scattering by a micro-channel intersecting core of a single mode fiber (SMF) has been investigated by use of two dimensional time-domain finite difference (2D-FDTD) method and the numerical results are in good agreement with those reported in the experiments. The transmission properties of the SMF with such a micro-channel can be attributed to the combined results of scattering effect and FP resonance effect. It is suggested that the SMF with micro-channel of about 4–6 μm in diameter can be effectively used for refractive index sensing with a high refractive index resolution up to ∼10⁻⁵.