Design Of ?-OTDR High-speed Synchronization Pulse Generator

Phase sensitive optical time domain reflectometer(?-OTDR)is one of the distributed optical fiber sensing detection methods and it becomes a hot issue research because of the advantages like distributed,high sensitivity,wide detection range,disaffected by topography interference and so on.In ?-OTDR sensing system,the performance of the detection light pulse will directly affect signal-to-noise ratio,dynamic range and other performance index of the sensing system.People usually use acousto-optic modulator(AOM)to modulate continuous laser light,and choose external signal generators to use single pulse as the pulse signal source of acousto-optic modulator and they take no account of the influence of parameter of pulse signal to extinction ratio and signal-to-noise ratio of the output light pulse.To solve the limitations of traditional methods and to get light pulse of high quality,the article designs pulse signal generators based on embedded high-speed pulse.Analyzing the principle of distributed optical fiber and the position principle and researching the influence of test light pulse to the performance of ? – OTDR system,this paper shows the quantitative relation between input pulse parameter and signal-tonoise ratio of the system.Through analyzing the principle and performance parameter of acousto-optic modulator,the paper gives constraint condition to input pulse signal.For the requirement of time to pulse signal increasing of acousto-optic modulator,the thesis designs high-speed buffering circuit,and it realize 8.8ns increasing time of pulse signal.To realize the function of shielding invalid input,the thesis designs effective input algorithm,and it improves the signal-to-noise ratio of the system ? – OTDR.The generators of pulse also provide the generation functions which are from several kinds of pulse coding series.The signal generators uses human-computer interaction to set up pulse output module in flexibility.Researching the principle of realization of pulse coding technology and the application ways of ? – OTDR,the thesis shows lifting capacity of signal-to-noise ratio which corresponds to different ways of coding.Comparing the method of pulse coding with the method of traditional superposition average,we uses the method of pulse coding series to test ?-OTDR,and then we obtain high signal-to-noise ratio light-time domain signal.By positioning experimental verification of coding pulse better than single pulse signal.With experiments,the paper analyzes the influence to actual output of acoustooptic modulator from pulse parameter.The thesis gives the influence of different pulse period to time-domain signal waveform and to positioning results,and then finds that the longer period the worse positioning results.Using the definition of the ratio between square of peak value and square of average value,the paper describes the influence of pulse period to system positioning.Through the positioning experiments,the pulse generators acquire 2 meter space resolution.In the experiment of positioning accuracy,compared with the standard of traditional signal generators' positioning,the pulse generators reduce deviation with 0.72 meter.The pulse generator in these designs has the character of stable outputs,fast response,short increasing time,and could output pulse coding series.It satisfies the requirement of the ?-OTDR system.