Research On The Generation And Performance Optimization Of Supercontinuum In Microstructured Fiber

This work was supported by National Basic Research Program of China (2010CB327600), National Natural Science Foundation of China (61077049), Program for New Century Excellent Talents in University of China (NCET-08-0736) and the111Project of China (B07005).The supercontinuum(SC) has the advantages of both broadband and high-stability. These properties should make the SC an ideal tool for important applications including optical communication system, biomedicine, optical measurement, etc.. In this dissertation, the generation and performance optimization of SC used for optical communication systems are studied both theoretically and experimentally. The main contents and achievements are as follows.1. According to the quantum theory of light field, the nonlinear propagation equation contains spontaneous Raman scattering was deduced to model pulse propagation in fiber. And the numerical method-the Fourth-order Runge-Kutta in the Interaction Picture combined with split-step Fourier method-is discussed to compute the above equation and the generalized nonlinear Schrodinger equation.2. Based on the generalized nonlinear Schrodinger equation, the mechanism of SC generation in normal dispersion regime is demonstrated theoretically. The effect of fiber parameters and pumping conditions on the bandwidth and flatness of SC generation in Microstructured Fiber (MF) are discussed in detail. A dispersion-flattened MF with small normal dispersion and high nonlinear are designed for flat broadband SC generation in1550nm region.3. The effect of shot noise of pump pulse on the broadband amplitude noise of SC generated in fiber is investigated numerically. The relative intensity noise is used to analyze the broadband amplitude noise of SC generated in normal dispersion regime quantitatively, the results show that, the noise suffers twice obvious amplifications in the process of SC generation, the first time is caused by the initial spectral severe split and is inherent, the second time is caused by the nonlinear energy loss in the presence of intrapulse Raman scattering (IRS) and is the main reason of the amplification of broadband amplitude noise during SC generation. The IRS effect can be suppressed by using MF with suitable dispersion characteristics.4. Using high-order soliton compression effect, enhancement of bandwidth of SC generated in MF by using compressed pulse is demonstrated, the measured-lOdB spectral width is broadened from75nm to more than140nm. The low-frequency noise of SC spectrum generated by compressed pulse is analyzed quantitatively. Numerical analysis shows that using the certain peak power pulse compressed by a certain length fiber can increase the spectral bandwidth without making extra low-frequency amplitude noise.5. The dependence of the flatness of SC on the steep degree of pump pulse is discussed in detail. The results show that the flatness of SC spectrum generated by the pulse with more steep pulse is better. The flatness of SC generation in MF is improved by filtered the pump pulse using a double-pass Littman-Metcalf filter before injected into MF.