Characterization of Long Period Grating With a Screw Shape Fabricated by a Single-Path Scanning of Femtosecond Laser

We propose a manufacturing process for fabrication of long period grating (LPG) with a screw shape by a single-path scanning of femtosecond laser. The optical fiber was rotating in radial direction and traveled along the fiber-axis simultaneously while femtosecond laser irradiation. Several screw-shaped LPGs were fabricated under different parameters, such as laser power, index change length and grating period, and their transmission characteristics were investigated. Moreover, the screw-shaped LPG with complicated pitches of the screw were fabricated by adjusting the rotating speed and travelling speed. The screw-shaped LPG sensor with complex pitches had reverse bending effect that the transmission dip becomes deeper as bending curvature increases. Consequently, it was found that the screw-shaped LPG with multiple pitches of grating has a potential as the sensors for monitoring of the structural characteristics such as bending or curvature under harsh environment.