The Implementation And Application Of Optical Time-Domain Reflectometry With Large Dynamic Range

Optical time-domain reflectometry (OTDR) is an instrument to measure the transmission characteristics of fiber-link. It not only can measure the attenuation and report its detail with respect to distance along the fiber-link but also can monitor, locate and quantify any kind of events along the fiber such as slice loss, end point reflection and so on. In practical engineering application, the OTDR can be used in the installation and maintenance work in the long-haul fiber-optic communication system. It could accurately and rapidly locate the broken point along the fiber from one end without breaking the fiber.This paper introduces the history of development of OTDR and its status quo of research, analyzes the working principle and main technical specifications of OTDR. These technical specifications boil down to the improvement of dynamic range of OTDR and its capability of detecting weak signal as well. The dynamic range increase of OTDR could be achieved by coherent OTDR, co-related OTDR, sampling integration, pulse coding and so on.In this design we implement a new type of OTDR based on the embedded system. The hardware of this OTDR bears the strengths of low noise, high AD sample rate and high sample resolution, which promotes the dynamic range, distance resolution and loss value resolution of OTDR respectively; On the other hand, with the help of high performance device such as ARM processor and FPGA, we implement and high-rate data sampling and complicated digital processing, which improve the dynamic range and distance resolution of OTDR on a software bases. As shown by the experiments, the OTDR could boast itself among the advanced level in terms of dynamic range both at home and abroad. The achievement, strength in design and limits of this OTDR not only provide the methodology for improving in later version of development, but also offer the valuable technical reference for the manufacture of such kind of hand-held OTDR product.This OTDR is also put into use in the surveillance of PON architecture, which verifies the method of waveform comparison in the locating of fault events along the branches in PON. The experimental results also set higher requirements for the technical specifications and new function of OTDR such as dynamic range and waveform comparison. The OTDR is faced with more challenges in such kind of application.