Spatiotemporal characterization of supercontinuum extending from the visible to the mid-infrared in a multimode graded-index optical fiber.

We experimentally demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat supercontinuum generation with a uniform bell-shaped spatial beam profile extending from the visible to the mid-infrared at 2500 nm. We study the development of the supercontinuum along the multimode fiber by the cut-back method, which permits us to analyze the competition between the Kerr-induced geometric parametric instability and stimulated Raman scattering. We also performed a spectrally resolved temporal analysis of the supercontinuum emission.

Large temporal narrowing of subnanosecond pulses in a low-birefringence optical fiber.

A temporal shortening by a factor higher than 10 of subnanosecond pulses launched into a low-birefringence optical fiber is achieved by polarization filtering at the output. By means of the theoretical approach, in good agreement with experimental measurements, the impact of the nonlinear polarization rotation and of the coherent coupling phenomena is pointed out.

Nondestructive analysis of the transverse structure of novel optical fibers by third-harmonic-generation microscopy.

We demonstrate the suitability of the third-harmonic-generation technique as a new nonlinear microprobe for nondestructive determination of the index profile of optical fibers. Photonic bandgap (Bragg-type) and air-silica microstructure (ASM) fibers were tested. The complete spatial characteristics, such as hole diameter and spacing into ASM fibers or sandwiched layer thickness into Bragg fibers, were demonstrated to be attainable anywhere along a bare fiber.