Research On Portable Optical Time-domain Reflectometer

With the exponential growth of telecommunication services, the gradual opening telecommunication market will enjoy a prospect development in the near future. Furthermore,by substituting the traditional electrical communication techniques(such as the electrical switch, transmission and access), the full-optical communication is the tendency of the future communication field. As we can see, the fiber fault monitoring is the key and even the core part among the techniques in the full-optical communication. And the necessary instrument for fiber fault monitoring is the Optical Time-domain Reflectometer(OTDR), which can detect the fault point, the melting point and the connecting point of a fiber-link. The research on the OTDR is valuable and significant for the practical application of the all-optical network.In this paper, the wide application of OTDR in the optical communication was introduced after a brief on the advantages and the potential of the optical communication. Then, by comparing the previous research on OTDM at home and abroad, this paper demonstrated the basic Rayleigh scattering and Fresnel reflection theories the applied on the OTDR. Later, the structure of a novel portable OTDR based on FPGA and ARM was proposed. In the end,the principles of different modules in the OTDR were introduced at two parts: the hardware part including a laser drive circuit, an optical detective circuit, a differentiating circuit, an A/D sampling circuit and a power supply circuit; and the software part containing a Digital Signal Processing, a Noise-removal Processing, a Synthetic Data Processing and a Cumulative Average Algorithm Processing. The designed OTDR in this paper is innovative in the improvement in Laser power and detection sensitivity of APD, the reduction in hardware circuit noise, the filter of digital signal at the FPGA and the cumulative average algorithm,elc.The experiment on this OTDR in the research proved that all the circuits achieve theexpected results and all the software simulation parts are operated in smooth situation. And the experiment further proved that this OTDR is stable in the performance with high-resolution and wide-measuring range. In addition, the OTDR designed in this paper is simple in its structure and thus portable. In conclusion, this paper has achieved the expected function of the OTDR.