Supercontinuum generation with photonic crystal fibers and its applications

Abstract

Pure silica fibers having periodic arrays of microscopic air holes in the cladding region, photonic crystal fibers are of significant research interest. Femtosecond Ti:sapphire laser pulses that have only a few cycles in duration and a high index contrast between the core and the cladding of solid-core photonic crystal fibers, allowing very tight mode confinement and high optical intensity make it possible to extremely broaden the spectra of laser pulses. Supercontinuum is a complex nonlinear phenomenon, which is characterized by the dramatic spectral broadening over an octave of intense light pulses. In this thesis, we have presented the characteristics of the supercontinuum generation obtained experimentally and numerically. The near- and far-field images of the principal modes of the irregularly microstructured elliptic core fiber were investigated. The long and short axes of the elliptic shape of the far-field image are rotated by π/2 with respect to those of the near-field image. The large aspect ratio of the core axes gives rise to the big difference between the two zero-dispersion wavelengths and the large value of birefringence. The measured zero-dispersion wavelengths using the Mach-Zehnder interferometric method are 740 nm for the long axis mode and 683 nm for the short axis mode. The group birefringence obtained using the wavelength-scanning method is about 0.0055 near 800 nm and increases in proportion to the wavelength. For the supercontinuum generation, the 15-fs input pulse with the center wavelength of 800 nm is launched to a 12-cm long irregularly microstructured elliptic core fiber. The output power after passing the fiber was about 30 mW, when the input power is 300 mW. The spectral components of the output pulses are from 500 to 1200 nm for the long axis mode and from 450 to 1100 nm for the short axis mode, respectively. The big difference of the two dispersion properties of the fundamental modes of the fiber leads to the strong ...