Micro/nano fiber gratings and polarimeters

Air-cladding micro/nano fibers can be taper-drawn from standard SMF-28 fibers. Firstly, highly birefringent (Hi-Bi) noncircular air-clad silica microfibers (MFs) with wavelength and sub-wavelength scale transverse dimensions are studied. These Hi-Bi MFs are also taper-drawn from the SMF-28 fibers that are "pre-processed" by "cutting away" parts of the silica cladding on opposite sides of the fiber with a femtosecond infrared laser. Such Hi-Bi MFs have approximately elliptical cross-sections. Experiments with an air-clad elliptical fiber with a major diameter of 0.9 μm and a minor/major ratio of 0.9 demonstrated a group birefringence of ~ 0.015. Secondly, long period gratings (LPGs) are fabricated in the circular air-cladding silica microfiber by use of a femtosecond infrared laser to periodically modify the surface of the fibers. These LPGs have grating periods of a few tens of micrometers, much smaller than those in conventional optical fibers. Such a LPG has small temperature sensitivity and is truly a compact device with a grating length of only -150 μm.