Nanohole induced microfiber Bragg gratings.

We demonstrate the fabrication of high-index-contrast microfiber Bragg gratings (MFBGs) using phase-mask technique under seconds' femtosecond laser ablation to drill periodic nanoholes in microfibers and study the aging properties of the gratings at room temperature. These sub-micrometer-diameter holes, benefited from the resolution of femtosecond laser micromachining beyond-diffraction limit, results in an effective negative refractive index change Δn ~-10(-3). Transmission dips over -23 dB are achieved for the gratings with excellent Gaussian apodization and 3-dB reflection bandwidths up to 1.14 nm. Moreover, the grating reflectivity increased by 3 dB, the resonant wavelength blue-shifted 1.35 nm after two weeks' placement of grating at room temperature and these gratings exhibit excellent stability in the following time. This makes them attractive elements in sensing, nanophotonics and nonlinear optics.