Tunable chromatic dispersion based on uniform fiber Bragg gratings in helical multicore fiber inscribed by femtosecond laser

A novel method for controlling the chromatic dispersion of uniform fiber Bragg gratings (FBGs) in helical multicore fiber (HMCF) is proposed and experimentally demonstrated. By precisely manipulating the 3D shape of the grating, including local curvature and bending orientation, varying strain gradients are induced, leading to tunable bandwidth and group delay. FBGs were inscribed in HMCF using the femtosecond laser point-by-point (PbP) technique. When the grating was shaped into an arc with a radius of 1 cm, a tuning bandwidth of 8.3 nm and a dispersion of 5.7 ps/nm were achieved. Furthermore, a misalignment fabrication method is introduced, ensuring that gratings in different cores exhibit consistent tunable dispersion characteristics through curvature adjustment. This proposed method offers significant potential for chromatic dispersion control in optical transmission systems based on multicore fiber.