Otdr Signal Processing Based On Dsp

Optic Time Domain Reflectometry (OTDR) is the instrument as a token of transmission characteristic of fiber. Compare with the traditional sensors, The distributed fiber sensor based on the principle of the OTDR has many good characters, such as high resist of EMI, low cost of unit-information, high Spatial Resolution and precision. And it can work in the atrocious conditions too.In this paper, the principle, the history and developing trends of OTDR are discussed. A new kind of OTDR system based on DSP is studied. DSP as the main control unit of the system controls the laser emitting the narrow pulse light. The back-rayleigh-information is changed into the electric information by the detector. Then the electric information is sampled by the ADC and the data is processed by DSP, such as the digital filter. Lastly, the data is transmitted to PC. In the system, the parameters are setted and the result is displayed in PC. So PC has more time to process the other important business.In the paper, kinds of the methods used to enhance the precision of OTDR are discussed. It expatiates on the sum-and-average method effecting the quantization precision and signal-noise-ratio. It also discusses the different noise effectting the quantization precision and it provide the base theory that high precision quantization are obtained using the ADC with less bits.In the OTDR system, the whole information of fibers is needed. In result of it, the numbers of sampling-data of OTDR system are large. Compare with the traditional system, the data are processed by DSP in the system. In the result, the time of data-process and data-transmission is reduced. In some sense (the same measuring time), the precision is enhanced.The main electrical circuit components, including DSP, power detector, ADC, memory, communication interface, are discussed and practically designed. In the same time, the software of the system is discussed.Finally, the practical pictures, such as electrical circuit and measuring-fiber, are displayed in the paper. The paper also points out the next step and direction to improve the system.