All optical fiber polarization controlling devices fabricated by femtosecond laser irradiation

Abstract

This paper reports the stress-induced birefringence generated in an optical fiber using femtosecond laser (fs) irradiations and the fabrication of in-fiber waveplates and polarizers. Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core and along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4×10-4 at the optical wavelength of 1550 nm. By controlling the length of the stress rods, waveplates of the desired retardance can be fabricated. The stress-induced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure. For the in-fiber polarizer based on low order mode LPFG, a polarization extinction ratio of more than 25 dB was observed at the wavelength of 1527.8 nm. A high order mode LPFG based in-fiber polarizer, with a broad bandwidth of 100 nm near 1550 nm, was investigated as well. The in-fiber polarization devices with low insertion loss may be useful in optical communications and fiber optic sensing applications.