Generation Of Broadband And Flattened Supercontinuum Using Photonic Crystal Fiber

Because of a very wide range of applications in fields such as biological, medical, information, measurement, military and so on, supercontinuum has attracted widespread interests in the scientific community since it appeared. The flexible structural characteristics, highly nonlinear, controlled zero dispersion point and the unique dispersion characteristics of photonic crystal fiber (PCF) determine that it is a good media to generate supercontinuum. In recent years, PCF-based supercontinuum research has been developing rapidly. In this paper, we consider the 3dB bandwidth of supercontinuum as a standard to theoretically analyze the impact on flatness and width of supercontinuum with different parameters.Through the split-step Fourier method to solve the generalized nonlinear Schrodinger (GNLS) equation, we simulated the nonlinear propagation and supercontinuum (SC) generation of a femtosecond Gaussian pulse in a PCF. Through the analysis and Comparison of supercontinuum generated in PCFs with different dispersion properties, we found that the supercontinuum generated in PCF with normal dispersion had good flatness. While the flatness of supercontinuum generated in PCF with abnormal dispersion was bad. The impact on supercontinuum of structural parameters (air hole pitch A and hole pitch ratio f) was researched in PCF with normal dispersion. It indicated that:the 3dB bandwidth of supercontinuum increased with the A or f increased. Therefore, large A or f is favorable for the flatness of supercontinuum. On the other hand, when the A or f increases to a certain value the dispersion of PCF changes negative, so it is not conducive to generate flat supercontinuum. Through analysis supercontinuum generated in PCFs, the PCF can be optimized.The impacts of Gaussian pulse's peak power (P0) and pulse width(TFWHM) on the supercontinuum generation are investigated through analysis the supercontinuum generated by different pulses in the optimized PCF. Analytical results indicate that when the TFWHM=100fs, the 3dB bandwidth first increases and then decreases. Therefore, in order to obtain high-quality supercontinuum generation, the peak power of the ultra-short pulse must be taken account. While when P0=100W, the 3dB bandwidth enlarges with the TFWHM becomes smaller. So small pulse width is benefit for large bandwidth and highly flat supercontinuum. In summary, in order to produce large bandwidth and highly flat supercontinuum, we must reasonably choose the pulse characteristics.Based on the above obtained supercontinuum, we can optimize it generated in PCF. The 3dB and lOdB bandwidth of the supercontinuum generated by different pulses in the optimized PCF is calculated to obtain the diagram of width with the Pulse characteristics. The best Gaussian pulse can be got from the 3dB bandwidth diagram.