Superimposed Fiber Bragg Gratings With Comb-Like Reflection Peaks Inscribed by Femtosecond Laser

We propose a novel method for inscribing superimposed fiber Bragg gratings (SIFBGs) with comb-like reflection peaks using femtosecond laser and phase mask method. By superimposing only two uniform fiber Bragg gratings (FBGs) with slightly different periods at the same location within the fiber core, we achieve the formation of a strong SIFBG that exhibits nearly 11 equal spaced reflection peaks. Furthermore, more than 30 reflection peaks can be easily obtained by superimposing only three FBGs. We found that the spacing of the reflection peaks in the SIFBG is determined by its period, while the number of reflection peaks corresponds to the quantity of FBGs that are superimposed. All reflection peaks of the SIFBG demonstrate essentially identical temperature and strain sensitivities. Additionally, these SIFBGs exhibit remarkable high-temperature resistance characteristics.