PHOTONIC CRYSTAL FIBERS SUPERCONTINUUM GENERATION AND POLARIZATION

We investigate the propagation of femtosecond pulses in the anomalous dispersion region of a birefregent photonic crystal fiber and the effect of its polarization on the broadening of the generated supercontinuum. It is found that the generated supercontinum exhibits a good linear polarization when the femtosecond pulse is coupled into the fiber with its polarization along the fast or slow axis of the photonic crystal fiber. When the angle between the polarization of the input femtosecond pulse and the fast axis is equal to 45 degree, the output supercontinum is circularly polarized. Since photonic crystal fibers with large birefringence usually possess high nonlinearity and third-order dispersion, they can be employed to produce supercontinuum with good polarization. The spectrum of supercontinum changes regularly when the angle between the pulse polarization and the fast aixs of the photonic crystal fiber is varied. A flat spectrum is observed when the angle is close to 45 degree. The experimental observations indicate that solid-core photonic crystal fibers with large birefregent can be used to generate supercontinuum with good linear polarization.