Femtosecond Laser Plane-By-Plane Inscription of Chirped and Tilted Fiber Bragg Gratings

An innovative method utilizing femtosecond laser plane-by-plane (Pl-b-Pl) fabrication of chirped and tilted fiber Bragg gratings (CTFBGs) within single-mode fibers (SMFs) is proposed and demonstrated. By adding a rotatable slit in the optical path for beam shaping, the beam shaping can be realized to perform Pl-by-Pl inscription. Then the grating chirp is produced by changing the period of grating. The successful fabrication resulted in chirped fiber Bragg gratings (CFBGs) with 3 dB bandwidths of 1.5 nm, 2.2 nm, 3.4 nm, and 7.7 nm. This method was utilized to investigate the influence of geometric parameters such as tilt angle, length of grating, and chirp rate on the CTFBG filter bandwidth and depth, leading to the acquisition of a series of transmission-filtered spectra. Besides, we proposed different structures for the multiplexed CTFBGs (MCTFBGs). CTFBGs with varying tilt angles and Bragg wavelengths were inscribed in cascade, indicating certain regularities. This technology has become a simple and promising solution for manufacturing CFBG and CTFBG, with broad applications in fiber optic sensing, optical filters, and laser systems.