Investigation Of Pulse Coding Technique In Polarization Optical Time Domain Reflectometry

Optical Time Domain Reflectometry(OTDR)is born with the problem of low Signal-to-Noise(SNR)and the trade-off between SNR and spatial resolution.As an effective solution to these problems,pulse coding has attracted much research and been applied to conventional OTDR systems,Raman-based fiber sensing systems and Brillouin-based fiber sensing systems to improve system performance.However,few research has been carried out on pulse coding in polarization-sensitive OTDR(POTDR).To fill this blank,a comprehensive investigation on the availability and performance enhancement of pulse coding in SMF-based POTDR is conducted in this thesis.The main content of the thesis includes:(1)Pulse response theory and coding response theory in POTDR are derived,proving the possibility of direct detection pulse coding in POTDR.By analyzing the temporal depolarization effect,degree of polarization(DOP)is also found to be an important parameter in POTDR that affects the system dynamic range.Then,coding gain,average DOP and coding energy utilization efficiency are proposed to evaluate the performance of pulse coding.(2)Linear combination code represented by Simplex code and correlation code represented by Golay code are investigated in POTDR systems.They are all demonstrated to be feasible in improving the system SNR without sacrificing spatial resolution or DOP.Simulations and experiments are conducted to prove the conclusion.(3)Oversampling effect is investigated in coding OTDR systems.Theoretical analysis predicts that oversampling has no effect in OTDR systems based on linear combination code,but can further improve the SNR enhancement in correlation coding schemes.Experiments are conducted and confirm it.Since oversampling does not need any change in transmitting part,it will have great potential in the improvement of existing systems as well as the design of new OTDR systems.