The Research On Ultra-short Pulse Generation Technology With High Extinction Ratio In Time Correlated Single Photon Counting-OTDR

With the development of optical communication technology,optical fiber has become a new medium of data transmission and has been widely used due to its wide bandwidth and large transmission capacity.The avionics system network based on optical fiber communication gradually replaces the traditional copper bus.Compared with the ordinary optical fiber communication network,the fiber length of the avionics network is shorter,the link is more complex,and the minimum distance between adjacent nodes is usually around 10 cm.Therefore,in the avionics network maintenance and detection,high-precision optical fiber optic cable testing equipment is crucially.So,a OTDR based on time correlated single photon counting technique is very suitable for optical cable detection in avionics network due to its high response,simple structure,easy integration and non-destructive detection.At the same time,as the core module of OTDR,the optical pulse generator fundamentally determines the performance of OTDR.Therefore,a research on the high extinction ratio and narrow pulse-width optical pulse generator is performed in this thesis.The main work of the thesis is listed as follows:1.Firstly,the numerical model of TCSPC-OTDR is established,and the simulation analysis is carried out.It is proved that the high extinction ratio and narrow pulse signal can not only improve the dynamic range,but also improve the distance resolution of the OTDR.2.A new method of generating high extinction ratio pulse signal based on feedback structure is proposed,then the influence of system parameters on output pulse signal is analyzed,and the system parameter setting method satisfying the expected output is given.The simulative experimental results show that the output of the pulse signal with high extinction ratio and high power is achieved by the MZ modulator with low extinction ratio.3.The output characteristics of semiconductor lasers based on gain switch technology are analyzed,and the effects of modulation pulse width,modulation current,bias current and modulation frequency on the impulse extinction ratio and pulse width are studied.Then,the schemes of using segmented rectangular wave and sawtooth wave as modulation signal of gain switching laser are proposed to further improve pulse width and extinction ratio.The simulation results show that,when the step rectangular wave is used as the modulation signal,the performance of the laser output pulse is better than that of the rectangular wave.At the same time,under the same pulse width,the performance of sawtooth wave is better than that of rectangular wave,and the requirement of pulse width is reduced.4.The prototype of a portable multi-channel high-precision OTDR system is designed and fabricated with an 850 nm gain switch laser and a time dependent single photon detector,and the characteristics of 32-core airborne optical cables are measured.The test results show that the spatial resolution of the OTDR is less than 9 cm,the dynamic range of the system is greater than 18 dB,which accords with the performance demand of the airborne electro-optic network for the optical cable detection equipment.