  We demonstrate that thousands of periodic nano-craters are fabricated on a
subwavelength-diameter tapered optical fiber, an optical nanofiber, by
irradiating with just a single femtosecond laser pulse. A key aspect of the
fabrication is that the nanofiber itself acts as a cylindrical lens and focuses
the femtosecond laser beam on its shadow surface. We also demonstrate that such
periodic structures on the nanofiber, act as a 1-D photonic crystal (PhC). Such
PhC structures on the nanofiber will strongly enhance the field confinement in
such a tapered fiber-based system and may open new avenues in nanophotonics and
quantum information technology.
