The Research Of Optical Time Domain Reflective Detection Technique Based On Simplex Codes

The optical time domain reflective detection technique is not only an importantmethod for fiber link loss measurement, but also the main technology for distributedoptical fiber sensors. The traditional optical time domain reflective detection techniqueemploys a single pulse as the detection signal, which is injected into the fiber under testto obtain backscattered optical signal. But there is a contradiction between the systemdynamic range and the spatial resolution.To solve above problems, in this thesis, using simplex codes as the detection signalfor the optical time domain reflectometer was proposed. Combined with a signalprocessing method of matrix computation, it can effectively solve the contradictionbetween the system dynamic range and the spatial resolution. The large dynamic rangeand the high spatial resolution can be achieved with a low-power optical probe pulse.The main works of this thesis were as follows:1. In this thesis, development history and research advances of the coded opticaltime domain reflectometer was introduced. Based on the principle of the optical timedomain reflective detection technique, various factors, which influence the systemdynamic range and the spatial resolution, were analyzed. The program which is usingsimplex codes as the detection signal of the optical time domain reflectometer andcombining with a matrix computation signal processing was proposed.2. The working principle of optical time domain reflectometer based on simplexcodes was analyzed. The system simulation model based on simplex codes and thesystem simulation model based on single pulse were constructed using the mathematicalsimulation software MATLAB. The system dynamic range was analyzed and comparedin different pulse widths and coding lengths.3. According to the principle of optical time domain reflectometer based onsimplex codes, the composition structure and method of optical time domainreflectometer system based on simplex codes were investigated. With VC++6.0, thesystem software module of optical time domain reflectometer based on simplex codeswas written to realize pulse generation and signal processing. 4. Experimental platform for system experimental verification was constructed. Inthe case of pulse width20ns, averaging1000times, simplex codes order7, the dynamicrange of optical time domain reflectometer based on simplex codes was higher thanconventional single pulse optical time domain reflectometer by3.5dB in the samemeasuring number. It was only0.7dB less than the theoretical value.Simulation and experimental results show that the new method which wasproposed in this thesis can effectively improve the dynamic range of the optical timedomain reflectometer.