Impact Of Chromatic Dispersion On The Performance Of Cotdr

Optical time domain reflectometer is main technology for modern optical fiber fault diagnosis. Conventional optical time domain reflectometer in dynamic range and spatial resolution can not improve. Chaotic time domain reflectometry(COTDR) in laboratory can effectively solve this problem, namely,the spatial resolution can not be affected in increasing the dynamic range at the same time.COTDR realize optical fiber fault diagnosis through detection signal in optical fiber link detection, the returning echo signal and the reference signal for cross-correlation. Experimental study found that, in the COTDR, the spread of detection signal in fiber link due to fiber dispersion will cause the detection signal pulse broadening, timing distortion. The detection signal will be different from the reference signal.So cross-correlation echo signal and the reference signal will decrease, namely chaotic time domain reflectometry dynamic range will be reduced. In the experiments, simple dispersion compension can reaches a minimum in signal distortion and improve the performance of COTDR remarkably. Especially in the diagnosis of long distance fiber link,the dispersioncompensation effect is more significant due to an accumulation of more dispersion.In this paper, we use the VPI software simulation and verification of the experimental method, to study the influence of dispersion compensation in dynamic range of COTDR. Firstly,we simulation the influence of the dispersion of chaotic signal timing by VPI software, secondly we demonstrates the effect of dispersion compensation of dynamic range in COTDR by experiments.The major works in this article are as follows:1.The developments, advantages and disadvantages of different optical time domain reflector are introduced, and the COTDR is also introduced. The generation of original chaotic source without bandwidth-enhancement(3.5GHz)and the high bandwidth original chaotic source with bandwidth-enhancement(7GHz).2.The method is proposed to improve the OTDR dynamic range in the paper, which includes improve signal detection power and improve the receiver sensitivity to enhance the dynamic range.Some researchers improve the dynamic range through the data signal processing, such as repeated average, wavelet transform,discrete elimination algorithm.We come up with a dispersion compensation method which improves the similarity between the detection signal and the reference signal, to improve the peak of the cross-correlation peak,to improve the dynamic range of the COTDR.3.We simulation to generate chaotic signal by VPI software.It is dividedinto two parts, One into 12-km fiber which neglects loss and other nonlinear effect, the other is reference signal.We compare the two signals in the timing of distortion.We demonstrated effects due to the fiber dispersion.4.We conduct experiments with the dispersion compensation unit(DCU).The experiments results show that DCU can increase significantly the COTDR dynamic range,which is in agreement with the theoretical estimates. We also performed the single-fault and multi-faults detection.We verify the correctness of the theory through the experiment.5.Summary and Outlook...