Based On The Super Fast Signal Processing Research Of Optical Fiber

The fiber-based optical devices, for example in optical sensing and signal processing, have extensive research and application in many areas. Especially in the ultra-fast optical signal processing, the all-optical switching based on the nonlinear long-period fiber gratings, and the analog to digital conversion based on the photonic time-stretched system which depends on the characteristics of the fiber dispersion, have had being the hot spot of academic research after being proposed. The theoretical simulation and experimental verification of the two optical elements have been done in this dissertation, which lays a good foundation for the design of the all-optical switching in the nonlinear long-period fiber grating and the photonic time-stretched analog to digital conversion in the further.Firstly, the coupled mode equations for nonlinear long-period fiber grating, which bases on the coupled mode theory of the long period fiber gratings and combines with the Maxwell equations, are derived, and the characteristics of all-optical switching in nonlinear long-period fiber gratings are numerically simulated, in the dissertation. The calculating results show that the threshold power of all-optical switching in highly nonlinear long-period fiber gratings is nearly four orders smaller than that in an ordinary single-mode (SMF-28) long-period fiber grating. The all-optical switching in nonlinear long-period fiber gratings has been optimized according to the detuning, the grating length, the input pulse peak power and the relationships between them and extinction ratio.Secondly, the principle of the fiber-dispersion-based photonic time-stretched analog to digital converter is described. The impact of the time-stretched system on the signal to noise ratio and the fidelity are analyzed, and are the experimentally validated. In the cases of the time-stretched factor for M=1.11and10, the experimental results are coincident with the theoretical ones, which validates that the photonic time-stretched system can improve the effective sampling rate and the input bandwidth of the analog to digital converter. Finally, the opinions on the experimental improvements and the application of the continuous-time photonic time-stretched analog to digital conversion are proposed in this dissertation.