Research On Flat Visible Supercontinuum Generation In Normal Dispersion Fibers

The flat visible supercontinuum(SC) generation in the normal dispersion fiber has good spatial coherence and conservation of a single ultrashort pulse in the time domain. It is important for these applications in broadband time-resolved spectroscopy and ultrahigh resolution spectroscopy frequency comb generation etc. As a result, the coherent SC generation based on the normal dispersion fibers is very attractive recently. In this paper, the flat visual SC generation in the normal dispersion fibers is numerically analyzed based on the generalized nonlinear Schrodinger equation (GNLSE). The detailed contents are as follows:Firstly, the group velocity dispersion (GVD) profiles in the photonic crystal fiber(PCF) is numerically simulated by tuning the structure parameters, including the ratio of hole diameter to the space and air hole diameter. The results show that the GVD profile in the visible wavelengths can be flattened by adjusting the geometric parameters in the PCF. Additionally, the relationship between the GVD properties in the suspended core fiber(SCF) and the core diameter is analyzed. When the wall thickness remained unchanged, different GVD profiles in the SCF can be obtained by adjusting the fiber core diameter. When the fiber core diameter is 520nm, the absolute value of the GVD slope is less than 30ps3/km in the wavelength range from 500 nm to 1000 nm.Secondly, the influence of the parameters of the initial pump pulse on the SC generation is analyzed numerically in the normal dispersion region. The numerical results in the cases of the PCF and SCF are analyzed and compared with the femtosecond laser as the pumping source. The results show that, for the spectral flatness of 5dB. the designed PCF and SCF can output SC with the bandwidths of 680nm (420nm-1000nm) and 456nm (326nm-782nm), respectively. The corresponding pump wavelengths are 700 nm and 520 nm, respectively.Finally, the hollow core PCF with filling liquid material is proposed. The carbon tetrachloride is chosen as the filling liquid because of the high nonlinear index, which is about 6 times higher than that of quartz. The results show that the SC generation in wavelength range of 429nm-1083nm can be obtained in the liquid-core optical fiber. The corresponding flatness is 3dB.