Femtosecond laser fabrication of long period fiber gratings by a transversal-scanning inscription method and the research of its orientational bending characteristics

In order to make the whole fiber core modified, an improved point-by-point inscription method (called a transversal-scanning inscription method) is proposed to fabricate long period fiber gratings (LPFGs) by using femtosecond laser. LPFGs with an attenuation depth of 16 dB are achieved within the wavelength range of 1580-1680 nm. We have compared the bending properties of LPFGs fabricated by the line-by-line scanning inscription method and the transversal-scanning inscription method at the orthogonal directions. It is found that increasing scanning area using the transversal-scanning method can enhance the bend sensitivity obviously. The resulting curvature sensitivities are −4.82 nm/m−1 and −1.63 nm/m−1 at the 0° and 90° bend orientations respectively, within the curvature range from 1.75 m−1 to 3 m−1 in the experiment. The LPFG-I fabricated by the line-by-line scanning inscription method experiences red-shift, while the LPFG-II fabricated by the transversal-scanning inscription method experiences blue-shift.