Fiber Bragg gratings inscribed using femtosecond laser Bessel beams

Fiber Bragg gratings (FBGs) inscribed by femtosecond (fs) lasers have become an important alternative to ultraviolet laser-based methods, offering flexibility across a wide range of fiber types. However, existing fs laser inscription strategies still face a tradeoff between speed and spectral quality, limiting their application in large-scale photonic systems. In this work, we demonstrate a Bessel-beam-based inscription approach specifically tailored for FBG fabrication. By exploiting the long focus length of the Bessel beam in combination with a time-of-flight line-by-line (LbL) strategy, FBGs can be written at significantly higher speeds than conventional LbL methods while retaining good spectral quality (improved short-wavelength loss). Furthermore, we extend this approach to plane-by-plane (PlbPl) inscription in a commercial multi-cladding, seven-core fiber (SCF), enabling the simultaneous fabrication of multiple FBGs without dedicated core-by-core lateral alignment. The results exhibit the value of Bessel-beam-based inscription under fiber-specific constraints and a practical route toward high-speed, low-loss, and multi-core-compatible FBG fabrication.