【作者】 刘莉；

【导师】 何祖源；

【作者基本信息】 上海交通大学 ， 电子科学与技术， 2015， 硕士

【摘要】 光反射仪是测量光纤传输特性的仪器,现已经广泛应用于光纤通信系统的诊断中。近年来,有关光反射仪的技术发展迅速,如光时域反射仪(OTDR,Optical Time Domain Reflectometry)、光相干域反射仪(OCDR,Optical Coherent Domain Reflectometry)、光频域反射仪(OFDR,Optical Frequency Domain Reflectometry)等。相干光时域反射仪(COTDR)是在OTDR的基础上,对光纤中返回的光信号采用相干接收的方式,进一步提升了检测信号的动态范围和探测距离。利用OCDR,不需要高速光电探测和信号采集设备就可以实现高空间分辨率,但是其测量距离受光源相干长度的限制,而且需要很长的延时光纤,其测量距离一般只有几千米。COTDR的测量距离可以达到几十公里到上百公里,但是其空间分辨率比较低(难以超过1米),空间分辨率与测量距离是一对相互矛盾的量,随着空间分辨率的提高,可测量的光纤的距离会相应地缩短。为了克服COTDR中空间分辨率和测量距离之间的矛盾,本文提出了一种基于外部调制啁啾脉冲方案的COTDR技术,采用声光调制器,将探测光脉冲调制为具有线性频率啁啾的脉冲,而本地探测光为没有调制的连续光。该技术的空间分辨率取决于频率啁啾的范围,而与脉冲的持续时间无关,克服了传统COTDR技术中空间分辨率与测量距离之间的矛盾。在实验中,利用该技术实现了58.6 km测量距离下1.2 m的空间分辨率,动态范围超过20 d B。在此基础上,啁啾脉冲调制方案进一步应用于OCDR技术,将探测光和本地振荡光分别调制成为具有线性频率啁啾的脉冲,并且探测光脉冲和本地振荡光脉冲的时间延迟可以通过数字信号进行精确调整。该方案不需要高速数据采集设备,且克服了传统OCDR技术中频率调制速率与测量距离之间的矛盾,在验证实验中,OCDR的测量距离达到24.6 km,其空间分辨率为3.9 m。更多还原

【Abstract】 Optical reflectometer is a measuring instrument to characterize the optical fiber transmission, which has already been widely used for the diagnosis of optical fiber communication networks. Techniques for the reflectometry are developing rapidly in recent years, such as Optical Time Domain Reflectometry(OTDR)、Optical Coherent Domain Reflectometry(OCDR) 、Optical Frequency Domain Reflectometry(OFDR) and so on. Coherent OTDR(COTDR) is based on OTDR, and it greatly enhances the dynamic range and detection distance of the probe signal by using coherent reception in the backscattered signal in the fiber. OCDR can realize high spatial resolution without high speed photoelectric detection and acquisition device, but its measurement distance is restricted to several kilometers because it is restricted by the coherence length of light source and it often needs long delayed optical fiber. The measurement distance for COTDR can be from tens of kilometers to hundreds of kilometers, but its spatial resolution is difficult to be better than 1m. Moreover, the measured distance will be short with the improvement of spatial resolution due to the tradeoff between them.In order to break the contradiction between spatial resolution and measured distance of COTDR, this paper presents a novel COTDR technique based on external dual chirp pulse modulation, in which the probe beam is linear frequency modulated by acousto-optic modulators while the local is continuous light without modulation. The spatial resolution depends on the range of frequency chirp other than pulse width. The new COTDR technique overcomes the contradiction between spatial resolution and the measured distance with the realization of 1.2m in spatial resolution of 58.6 km fiber. Its dynamic range is more than 20 d B.On the basis of the above scheme, the technique of external dual chirp pulse modulation is applied to OCDR. However, the probe and local oscillator beams are linear frequency modulated independently. Moreover, the time delay between the probe and local beams can be adjusted digitally precisely. This technique not only doesn’t need high-speed data acquisition device but also overcomes the contradiction between frequency modulation rate and the measured distance with the realization of 3.9 m in spatial resolution of 24.6 km fiber.更多还原