Research On Nonlinear Effects In Microstructure Fibers

The research work of this dissertation is supported by the National Basic Research Program of China (973 Project, Grant 2003CB314906), the Foundation for the Key Program of Ministry of Education of China (Grant 104046), the National 863 High Technology Project of China (2003AA311010) and the Foundation from the Education Commission of Beijing (Grant XK100130437).Microstructure fiber (MF) is a silica fiber with an array of air holes running down its length, and is also called photonic crystal fiber. It has many unusual properties compared to standard fibers, such as endless single mode operation, flexible tailorability of dispersion and modal area, high birefringence etc. The adjustable properties of MF suggest a lot of potential applications in the field of optical communications. For example, MF can be used for broadening operation wavelength range, dispersion compensation, pulse compression, short wavelength soliton transmission and ultra-broadband continuum generation etc. and can also be used to make optical devices based on MF.In this dissertation, the nonlinear properties of microstructured fibers are studied both theoretically and experimentally. The main research results are listed below:1. The supercontinuum phenomena are theoretically and experimentally studied. A theoretical investigation with the method of split- step Fourier is presented on the nonlinear propagation of a femtosecond laser pulse with 800nm central wavelength in a microstructure fiber. A supercontinuum generation caused by femtosecond pulse in a microstructure fiber is demonstrated. The generation of a flat supercontinuum spectrum of over 70nm in the 1.55μm region by injecting 10GHz rate picosecond pulses into a nonlinear dispersion-flattened MF is demonstrated. It can serve as a broadband light source and has an important application in fiber grating experiment.2. The FWM coupled amplitude equation is numerically studied. The evolution of optical powers transmitting along the fiber is studied under different phase dismatch conditions. Experimental research on FWM in microstructure fiber is performed.3. The optimization design of parametric gain in OPA is demonstrated. Some parameters such as fiber length, dispersion slope, nonlinearity coefficient, and pump power have important impact on gain and bandwidth in optical fiber amplification system. By way of using improved effective index method, we have designed a dispersion-flattened microstructure fiber to get high efficiency optical parametric amplification. The effect caused by pump depletion is theoretically studied and numerical simulation is carried out. From the simulation result, high pump depletion (83%) could be obtained in a CW fiber optical parametric amplification in a dispersion-flattened microstructure fiber.4. The FWM phase matching condition is studied in conventional single fiber. And the single-pump OPA phase matching curves in MF for pump wavelengths of 1550 and 800 nm are given.