Research On The Coherence Properties Of Supercontinuum Source

Supercontinuum (SC) generated in photonic crystal fibers (PCFs) has many applications in various fields such as spectroscopy, pulse compression and tunable ultrafast femtoseconds laser sources. In the recent decade, it has been researched widely and deeply. Coherence property is an important physical characteristic of SC source and this dissertation analyzes it theoretically and experimentally.Firstly, the historical development and research state of SC generation are summarized and also the research of coherence of SC is concluded. The theoretical foundation and numerical model of SC generation in PCFs are described, and the role of dispersion and nonlinear effects in the process of SC generation is analyzed. The SC generation in PCFs is numerically simulated.Secondly, because of the importance of the dispersion in the SC generation, its measurement methods are compared and the theory of interference method is illustrated. Broadband dispersion measurement apparatus based on supercontinuum was constructed. The existing apparatus which was used to measure the dispersion of PCFs has been improved with high measurement precision and automation. The dispersion characteristics of two kinds of special fibers all solid photonic bandgap fiber and fluoride ZBLAN fiber are measured. The experimental results match well with the calculation results; as a result, the validity of the dispersion measurement system is clarified.Thirdly, coherence characteristics of SC source are illustrated to distinguish the distinction between the coherence of the conventional white light and SC source. Adding noise in the generalized nonlinear Schr?dinger equation (GNLSE) models the coherence of SC. Degree of mutual coherence is introduced to quantify the coherence of SC. The coherence properties of SC generated under various pump conditions are calculated; from the results, modulation instability is the main effect to degrade the coherence of SC. To obtain coherent broadband SC, the PCF need to be pumped by short pulses which are far from zero dispersion wavelength in anomalous dispersion region.Finally, degree of self-coherence is introduced to quantify the coherence of SC generated by long pulse. High precision Mach-Zehnder interferometer is built to measure the coherence length and degree of self-coherence of SC generated in PCFs. The results show that above the whole SC spectral range the coherence is comparatively good, and the average self-coherence degree is 0.461. The coherence lengths and degree of self-coherence of different wavelengths are different. The coherence length of the longer side of the pump wavelength is better and it presents better coherent property.