High flexibility FBG inscribing by point-by-point method via femtosecond laser: Technology, progress, and challenges

FBG is a reflective structure present in the fiber with periodically perturbed effective refractive index. With the emergence of femtosecond lasers, the point-by-point method has been proven to have high flexibility in inscribing FBGs. However, specialized literature reviews are currently unavailable in the areas of inscribing FBGs by point-by-point method via femtosecond lasers, preventing researchers from accessing a comprehensive understanding. Herein, point-by-point technology via femtosecond lasers and recent progress for inscribing FBGs are reviewed. Its high flexibility characteristics have been summarized in detail, including in different types of optical fiber, FBG location and special spectra. The current development of equipment related to the high flexibility characteristic has also been proposed simultaneously, along with the challenges and perspectives on the FBG inscription by point-by-point method. Integrating the insights of this review with in-depth theoretical and experimental research, the fabricated FBG is expected to have a significant impact on industrial applications in extreme environment sensing, advanced fiber laser, artificial intelligence and robotics, biomedicine detection, and so on.