The Development Of High-speed Optical Time Domain Reflectometer

Optical Time Domain Reflectometer(OTDR) is an important test equipment used widely in optical fiber communication system for measuring the physical properties of optical fiber including the length,the attenuation coefficient,the connection loss. Besides, it is also used to locate the position of faults and connection precisely along optical fiber.Conventional OTDR uses single pulse as detection signal, since the laser power is limited, pulse width must be increased in order to improve the measurement dynamic range,but the increase of pulse width makes the measurement resolution lower.So the trade-off between measurement dynamic range and response resolution is a problem all the conventional OTDRs have to face.This paper describes a new approach to OTDR that applies correlation techniques. By using Golay complementary codes as detection signal and correlating it with the echo signalwhich, this technique can get the characteristics of optical fiber and at the same time it increases the dynamic range of the OTDR and significantly reduce the required measurement time without sacrificing resolution.According to the principle of autocorrelation of Golay complementary codes, a solution is created considering FPGA as the core. Functions such as the generating of Golay complementary codes,the processing of signals, the measurement and display of distance as well as communication are intergrated in a single FPGA and a experimental sample is created. On the process of signals, due to the realization of autocorrelation algorithm by hardware, processing speed is improved.The technique of Recursive and assembly line is applied which make the sampling and process of signals realize seamless connection.In this way,it improves the algorithm efficiency and truely real-time on-line measurement is obtained. The simulation and experiments confirm the conclusions.