The Research And Application Of Optical Time-domain Reflectometry In Access Network

As the quick development of broadband service and the rapid appearance of various businesses, the demand of broadband access network from users is increasing greatly. As the future technology of broadband access network, passive optical network (PON) is advanced towards TDM-PON and WDM-PON. With the development and application of PON, it demands new challenges to the conventional optical fiber link monitoring device of optical time-domain reflectormetry.This paper introduces the working principle and the technical specification of optical time-domain reflectormetry (OTDR), including the dynamic range, spatial resolution and measurement time. By theoretic analyst, this paper summarizes all kinds of technologies to enhance the OTDR performance, such as accumulating and averaging technology, FSK modulating technology and correlative coding technology. Biorthogonal coding is discussed in details.The complex structure in PON, such as point-to-multi-points structure and multi-wavelength transmission and so on, demands many technical requirements to the conventional monitoring device of OTDR. This paper summaries and analyses current various OTDR monitoring technologies used in optical access network and its development trend. A tunable wavelength of OTDR based on biorthogonal codes is proposed, which is studied theoretically and experimentally. Using 64-bit biorthogonal codes, combining with 512 accumulating and averaging, we can achieve a signal-to-noise (SNR) ratio enhancement of about 14.7dB. It realizes a 2-meter distance resolution and 22.8dB dynamic range measurement with 6dBm input power in optical fiber. The results demonstrate that it can satisfy the requirement for tunable wavelength OTDR to monitor the optical fiber link in WDM-PON system online. Finally, this paper introduces the design and implementation of the embedded OTDR system software based on Windows CE specifically.