The Research On Supercontinuum Generation In Photonic Crystal Fibers By Optical Pulses

Because of the nonlinearly characteristic of the fiber, frequency spectrum will been broaden when ultra-short pulses propagate in nonlinear media, which is called the supercontinuum. Comparing with the conventional fibers, Photonic crystal fibers (PCFs), which were demonstrated in recent years, have some unique characteristics, such as endlessly single mode, controllable dispersion and rich optical nonlinearity. So they have become one of the good medium for the generation of supercontinuum. Supercontinuum generation in photonic crystal fibers has also become a hot research topic in optical communication. The mechanism of supercontinuum generation in photonic crystal fibers has been investigated experimentally and numerically in the present dissertation. The main contents are summarized as follows:1. Based on light-wave equations, we derived a basic equation--- the nonlinear Schr?dinger equation that governs propagation of optical pulses in fibers. We have also described numerical simulation techniques used to study the pulse-propagation problem in photonic crystal fibers with emphasis on the split-step Fourier method.2. By using the nonlinear polarization rotation passively mode-locked fiber laser, a stable ultra-short pulse with the central wavelength of 1556.0nm, the 3dB bandwidth of 5.5 nm, the pulse width of 462.0fs, and the pulse repetition rate of 28.6MHz was obtained experimentally, and by delivering this ultra-short pulse into the PCF, a supercontinuum with the 20dB bandwidth about the 140nm has been obtained when the pump power is 90mW. We particularly investigated supercontinuum generation in different pump power and analyzed the mechanism of supercontinuum generation.3. The thesis report on a numerical study of supercontinuum generation in PCF with the anomalous dispersion region. It is show that the solitons orders, the input pulse chirp, the input pulse form, the input pulse duration, higher-order dispersion, higher-order nonlinearity and fiber length are all responsible for the generation of supercontinuum. We have found a suitable fiber length for the flat, broad SC.4. By using the passively mode-locked fiber laser, a femtosecond optical pulse with the central wavelength of 1557.8nm, the 3dB bandwidth of 5.0nm, the pulse width of 509.0 fs, and the pulse repetition rate of 28.2MHz has been obtained, and by delivering this short pulse into the PCF after being amplified in the erbium-ytterbium co-doped fiber amplifier, a supercontinuum with the 20dB bandwidth about 530nm, the power of 530mW has been obtained. We particularly investigated supercontinuum generation in different pump power and analyzed the mechanism of supercontinuum generation. We also gave the reason of generating higher power SC.5. A new method of generating supercontinuum through modulation instability in single mode fibers has been proposed. This method used quasi-continuous wave to generate supercontinuum. We numerically analyzed the mechanism of supercontinuum generation. We also numerically investigated the impacts of the quasi-continuous wave orders, the input pulse duration, and the fiber length on the supercontinuum generation. The possibility of its experimental research has also been proposed.