High Temperature Sustainable Tilted Fiber Bragg Gratings via Femtosecond Laser Plane-by-Plane Writing Technology

In this paper, high-quality tilted fiber Bragg gratings (TFBGs) inscribed by using femtosecond laser and the slit beam shaping technique were reported. By adjusting the included angle between the slit and the fiber, we realized a series of tilted gratings with tilt angles of $0^{\circ }$ (FBG), $5^{\circ }$ , $10^{\circ }$ , $15^{\circ }$ , and $20^{\circ }$ in a single-mode-fiber. For a $10^{\circ }$ TFBG, the Bragg resonance was $-1.90$ dB at 1604.51 nm, and the maximum cladding-mode resonance reached 36.17 dB with an insertion loss of 1.44 dB due to the method of Plane-by-Plane (Pl-by-Pl) inscription. The effects of slit widths and different laser pulse energies on the Pl-by-Pl writing of TFBGs were also studied. The refractive index response sensitivity of the $10^{\circ }$ TFBG was measured at 449.45 nm/RIU. Moreover, the TFBG written by this method was a type-II grating, which could withstand a high temperature of $1100\,^{\circ }$ C for a long time.