We demonstrated ultra-violet (UV) generation by launching 1040-nm picosecond pulses into a step-index fused-silica
fiber without tapering. Even in a conventional step-index fiber, the phase mismatching between LP01 mode of the
fundamental wave and higher-order mode of the third-harmonic wave can be reduced by increasing the index contrast. In addition, in the cladding mode, Cherenkov-type phase matching is made possible. Thus, although the phase-matching is not achieved rigorously, THG can occur locally enough to observe the third-harmonic signal clearly at the output. In the experiment, we launched a picosecond pulse train from a 1040-nm fiber laser into a commercially available stepindex fiber with high index contrast. The UV light was observed in the wavelength range of 347-390 nm, and the output power of UV components was increased with the third- and fourth-order dependence. Also, we observed the bright bluelight emission along the fiber, which was originated from the fluorescence due to the defect of SiO2/GeO2 radiated by UV light (generated by THG).