The Research On OTDR About High Dynamic And Lilltle Dead Zone

Since 1980's, Chinese scientists began to develop Optical Time Domain Reflectometer. Although some progresses were made, there are still two common disadvantages in previous technology. Firstly, the dead zone of OTDR is too long to get the position of break point of short fiber. Secondly, the dynamic range of OTDR is too small to suitable for Backbone Network. The purpose of this paper is to solve the two problems.The factors that affect dead zone and dynamic range are analysed, including pulse width, bandwidth of receiving curcuit, sampling frequency, noise of the system, along with the saturation of amplifier, using properly of the digital filter. As a result of the analysis, a series of practicable parameters are provided.An approach to design a portable OTDR is presented in this paper, which uses a high performance embedded PC card as the processor, and transfers data and command with 16-bit width in bidirection via PC/104 bus. All the logic are designed in a single CPLD, such as pulse width setting, delay time controlling, pulse transmitting, clock generating, data acquisition and so on. In pipeline way, the design accomplishs A/D converting, data reading, accumulating, as well as data storing. The paper provides an input device meeting IBM-PC keyboard standard, together with a low power consumpution system.On the basis of the mentioned principle and method, a portable OTDR has been made, which achieved the goal of 5-meter dead zone and 40dB dynamic range simultaneously.