Nonlinear Optical Loop Mirror Switching Properties Of Picosecond And Femtosecond Pulses

With the development of communication technology, nonlinear optical loop mirrors(NOLM) are widely used in high-speed fiber optical communication systems due to their special advantages. Many nonlinear optical effects such as SPM, XPM and FWM play important roles in the evolutions of optical pulses in the loop mirrors. In this paper, we focused on the study of characteristics of pulse evolutions and SPM induced switching effects in the fiber loop mirrors.The achievements of this dissertation are as follows:1. We have investigated the propagating characteristics of picosecond optical pulse in the nonlinear fiber loop mirrors constructed from dispersion decreasing fibers. Using this structure, the compressed pulse with good spectral and temporal quality can be generated in a large range of optimum fiber loop length. And the output pulse can propagate long distance without distortions.2. The propagating characteristics of femtosecond pulse in this type of NOLM are also investigated. The result shows that the optical switching is valid only under certain condition for femtosecond pulse due to the higher-order dispersions and nonlinear effects, especially the stimulated Raman scattering (SRS). Moreover, analysis of the higher-order effects shows that SRS enhances the pulse compression in some conditions.3. The effects of the slopes and profiles of the fiber dispersion on the performance of pulse propagation have been investigated in the NOLM. Three shaped profiles (parabola, linear, and exponential) have been considered. The exponential dispersion profile fiber loop is optimal for the propagation and compression of picosecond pulse. On the contrary, the parabola dispersion profile fiber loop is optimal for femtosecond pulse due to the high order effects such as the third order dispersion (TOD), stimulated Raman scattering (SRS) and self steeping (SS). We also compared the effects of positive and negative third-order dispersion working with SRS. The result shows that the effect of negative third order dispersion working with SRS is more suitable for pulse propagation and compression. As a result, we proposed two methods to facilitate the propagation of optical pulse in NOLM, and hence provided a theoretic guidance to the better design of eight-figure fiber laser.