光频域反射在光通信网络检测中应用分析

光频域反射计(OFDR)相对于光时域反射计(OTDR)而言,其动态范围与空间分辨率无制约关系,可以在不损失动态范围的情况下获得高的空间分辨率,因而可以被广泛应用于光纤传输特性检测和集成光路诊断等领域.本文分析了OFDR在光通信网络检测中的基本原理、OFDR相对于OTDR的优点,并讨论了限制OFDR使用的各种因素和目前的发展现状.     

浅议高分辨率光频域反射计的发展及优点

光频域反射计(OFDR)作为高分辨率测量仪器的主要代表性产品之一,具有动态范围大,测量范围光等优点,被广泛使用于我国的光纤故障监测中,同时也为我国光纤领域的发展和建设提供了有利的保障。文章在分析OFDR技术的基本原理和光源调制方式之后,总结了此项技术的发展现状及优点,以供各位读者参考。     

基于窄带光纤激光器的光频域反射计研究

光频域反射计(OFDR)是一种强大的光通信网络检测工具,能对光纤中微弱反射进行探测、定位和量化,利用这种特性可以实现对光纤长度的高精度测量。主要介绍了OFDR的工作原理,对OFDR系统的空间分辨率的限制因素进行了讨论,理论分析了空间分辨率与光频调谐范围之间的关系,以及光源非线性扫频对光纤长度测量结果的影响。利用测试干涉仪和辅助干涉仪实现了对光纤的高精度、高空间分辨率的长度测量。     

柔性光纤压力传感器的制备工艺与参数研究

为了提高柔性光纤压力传感器的灵敏度和稳定性,对压力传感器结构设计、结构参数及制作工艺进行了研究。制作了基于不同浓度配比和不同固化时间的PDMS柔性光纤压力传感器,对比了不同参数下传感器的性能,得出了最佳的配比和固化参数,最后利用光频域反射计(OFDR)测量了光纤应变变化。结果表明,在PDMS基底厚度和固化温度恒定的情况下,浓度配比和固化时间均对柔性光纤压力传感器的灵敏度有影响,并验证了当施加压力的范围为0～276.2 kPa,加压的步长为27.6 kPa时,PDMS配比为8∶1,固化时间为2 h的传感器灵敏度最高,可达6.250 59με/kPa。同时,柔性压力传感器具有柔韧、轻薄、可测量复杂曲面等优点,为航天航海领域弧形物体表面压力测量提供了可靠的解决方案。     

分布式光纤传感技术在蜗壳模型试验中的应用

分布式光纤传感器与传统应变片和光纤光栅传感器相比,具有分布式测量的显著特点,成为传感器领域的研究热点。随着技术的进步,基于瑞利散射的光频域反射技术(OFDR)得到了迅速的发展。该文介绍了OFDR的测量原理,并将分布式光纤传感器应用于蜗壳模型试验中。为检验蜗壳充水后的变形规律,检查蜗壳和混凝土的整体安全性和设计的合理性,对蜗壳试验过程中外围混凝土应变进行监测。通过分布式光纤传感器在每级水压加载下产生的应变,获得蜗壳模型外部变形以及裂缝发展的情况。实验结果表明,分布式光纤传感器能够真实地反应结构物的应变分布,及时准确地监测蜗壳模型在加压作用下混凝土变形及开裂情况,对结构的损伤进行识别。     

基于光频域反射技术的拱桥模型应变分布试验研究

为得到拱桥拱肋在不同受力情况下的应变分布规律,通过建立有限元模型和采用基于光频域反射(OFDR)的分布式光纤传感技术2种方法研究了不同荷载情况下的拱肋应变分布.结果表明:在拱肋表面粘贴的基于OFDR的分布式光纤传感器不仅能准确地反映不同荷载情况下拱肋的应变分布规律,还可以得到拱肋在吊杆损伤前后的应变分布变化,且能定位吊...     

复杂配线系统中绝缘缺陷诊断与定位技术

本文介绍了国内外绝缘缺陷诊断与定位技术的几种典型方法。重点分析了目前国外最新研究并成功应用于飞机配线系统检测的脉冲火花放电（PASD）法。最后总结了几种绝缘缺陷诊断与定位技术方法的应用范围和局限性，并对PASD法的应用前景做出展望。     

时域反射测量技术在“CATV”系统工程中的应用

本文是要是从“ＣＡＴＶ”系列电缆故障维护难题出发，引出了时域反射测量技术。使这一项非常有用的测量手段，在计算机时代又获得了新的生命力。同时对时域反射测量技术的工作原理、应用举例及在“ＣＡＴＶ”系统中的故障判断，也做了较详细的介绍。     

采用“芯吸”法制造的掺铒光纤

采用最新开发的名为“芯吸”的技术制造出一种石英包层中含有锗酸铅铒玻璃纤芯的掺铒光纤预制棒。然后将这种预制棒拉制成光纤,并测量光纤的剖面、损耗谱和折射率分布。采用商用接续机将制造的一根30cm长光纤与一根标准石英光纤连接。然后用这根接续光纤构建掺铒光纤放大器（EDFA）,并测量该放大器的增益谱。采用基于光后向散射反射计（OBR）的光频域反射测量技术（OFDR）测量所制造掺铒光纤的增益分布。结果证实,“芯吸”法可以用于制作与普通石英光纤相兼容的高增益放大器。     

基于柔性基的高灵敏度无损光纤压力传感器

为了简化光纤压力传感器的制作方法，降低制作成本，提出了一种柔性基应变式无损光纤压力传器，将未进行过任何处理的单模光纤嵌入在两片柔性的聚二甲基硅氧烷(PDMS)薄膜中，制作成“三明治”结构压力传感器，采用光频域反射计(OFDR)技术进行解调，测试传感器在不同压力下的光谱漂移与光纤的微应变的关系。实验结果表明:在受力面积为 ２.３７５ ｍｍ２ ，压力范围0~ 5kgf(０~ 20ＭＰａ)时，传感器的灵敏度达到194 /kgf，是裸单模光纤的6.47倍，同时压力测量范围提高5 倍，在0~ 2kgf(０~ 8ＭＰａ)范围内传感器具有很高的重复性与线性度，另外进行了分布式压力测试，证实传感器输出响应明显，空间分辨率较高。     

基于OFDR技术的深层土体水平位移场监测研究

深层土体水平位移场监测是基坑安全开挖的重要指标,现有测斜法耗费大量人力,且精度较低,但仍是当前获得水平位移的主要方法。该文提出了一种基于光频域反射(OFDR)技术的分布式光纤测量法,推导了应变-挠曲变形转换关系,通过室内实验进行了验证,证实了分布式光纤测斜的可行性和准确性,且基于OFDR的测量方法在苏州某基坑工程中得到了应用,准确详细地获取了基坑在开挖过程深层土体位移信息。     

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.     

Coherent frequency-domain reflectometry for characterization ofsingle-mode integrated-optical waveguides

Based on the principles of optical frequency domain reflectometry (OFDR), a highly resolving and sensitive technique suitable for detecting, localizing, and quantifying weakly reflecting irregularities in single-mode optical waveguides is developed. A distributed feedback (DFB)-laser diode at λ₀≅1.3 μm tuned within a range of Δλ≅6 nm and Δv≅1 THz, respectively, is used as a source in the experimental arrangement. An auxiliary interferometer is employed so that the tuning need not be linear in time, in contrast to early implementations. At present, with waveguide structures on InP under test, a spatial resolution of 50 μm and a dynamic range of about 60 dB are obtained. These data surpass OFDR results published so far. Prospects of closing the gap to coherence-domain reflectometric results and specific advantages make OFDR a promising technique     

A method for nonlinearity compensation of OFDR based on polynomial regression algorithm

A method based on polynomial regression algorithm(PRA) is proposed in this paper to compensate the nonlinear phase noise in optical frequency domain reflection(OFDR) systems. In this method, the nonlinear phase of OFDR systems is represented by the polynomial phase function, and then the coefficients of the polynomial phase function are estimated by PRA. Finally, the nonlinearity is compensated by match Fourier transform(MFT). Simulation results demonstrate that the proposed algorithm has good performance in compensating both weak and strong nonlinear phase noises of OFDR systems.     

Coherent optical frequency domain reflectometry (OFDR) using afiber grating external cavity laser

An optical frequency domain reflectometry (OFDR) system containing a narrow linewidth fiber grating external cavity laser is demonstrated to have 62-dB of sensitivity when detecting Fresnel backreflection and 2 m of resolution at a 115 m range in optical fiber. With this system we were able to detect Rayleigh backscattering in optical fiber with 20-dB signal-to-noise ratio. The phase noise limitation on the distance range for the OFDR was investigated, and the measured signal-to-noise ratio (SNR) data followed the theoretical simulation over the ranges measured. This technique has potential to be applied to the OFDR at 1550 mm with very high dynamic range by using an erbium doped fiber laser     

OFDR diagnostics for fibre and integrated-optic systems

Optical frequency-domain reflectometry (OFDR) shows promise as a diagnostic tool for high-resolution ranging in fibre/integrated-optic systems, and in high-resolution distributed fibre-optic sensors. We discuss some signal processing aspects of this technology, potential performance and application.     

Optical frequency domain ranging by a frequency-shifted feedbacklaser

This paper describes the theoretical and experimental study of a new technique for optical frequency domain ranging (OFDR) by a frequency-shifted feedback (FSF) laser. In conventional OFDR, a frequency chirped single-mode laser is used as a light source to convert a distance into a beat frequency, and a tradeoff exists between measurement range and resolution. The FSF laser output consists of periodically generated chirped frequency components whose chirp rate is faster than 100 PHz/s (P=10¹⁵), By use of the FSF laser, the tradeoff is removed and long-distance high-resolution OFDR is realized In the experiment, a distance of 18.5 km was measured with a resolution of 20 mm     

Nonlinearity-Compensation-Free Optical Frequency Domain Reflectometry Based on Electrically-Controlled Optical Frequency Sweep

A nonlinearity-compensation-free optical frequency domain reflectometry (OFDR) scheme is proposed and experimentally demonstrated based on the electrically-controlled optical frequency sweep. In the proposed scheme, the linear frequency sweep light is generated by propagating an ultra-narrow-linewidth continuous-wave (CW) light through an electro-optic frequency shifter which consists of a dual-parallel Mach-Zehnder modulator (DPMZM) and an electronic 90° hybrid, where the electro-optic frequency shifter is driven by a linear frequency modulated signal generated by a direct digital synthesizer (DDS). Experimental results show that the spatial resolution and signal-to-noise ratio (SNR) of the proposed OFDR scheme without the nonlinear phase compensation are comparable to those of OFDR employing a commercial tunable laser source (TLS), an auxiliary interferometer, and a software-based nonlinear phase compensation method. The proposed OFDR scheme is helpful to reduce the complexity of the optical structure and eliminate the difficulty of developing the nonlinear phase compensation algorithm.     

PMD measurement based on delayed self-heterodyne OFDR andexperimental comparison with ITU-T round robin measurements

A new measurement method of polarisation mode dispersion (PMD) in optical fibres based on delayed self-heterodyne optical frequency domain reflectometry (OFDR) technology is proposed and demonstrated on an automatic measurement system. The results of intercomparison of the ITU-T international PMD round robin measurements on two polarisation-maintaining fibre specimens are presented