Fabrication and characterization of a broadband long-period grating on a hollow optical fiber with femtosecond laser pulses

Abstract

We have fabricated broadband long-period gratings (LPGs) on hollow optical fibers (HOFs) by 15 corrugating slots with various widths by point-by-point exposure of a Ti:sapphire femotosecond laser. The corrugated LPGs showed unique broadband rejection whose FWHM extended to 190 nm with a low insertion loss of less than 1 dB. The maximum coupling strength was 8.5 dB, which is a significant improvement in comparison with previous HOF acousto-optic tunable filters (AOTFs). The center wavelength and coupling strength of the resonant peak could be systematically controlled by modulating the width of the corrugation.