High-order fiber Bragg gratings in the visible range inscribed with femtosecond laser and a phase mask

Visible fiber lasers play an important role in underwater optical communication, laser display and so on, but most visible fiber laser oscillators are not of all-fiber structure due to the lack of fiber Bragg gratings (FBG). Using FBGs to realize all-fiber laser oscillators could remarkably improve their compactness, simplicity and robustness. However, the period of low-order FBG in the visible range is too short to be inscribed easily. To simplify the inscription setup and procedure, we analyze the high order Bragg harmonics with Rouard’s method and Fourier components, and then demonstrate a method to obtain high-order FBG operating at visible wavelength by femtosecond laser and a phase mask with a long period of 1-1.5 μm. By increasing the exposure time and grating length, the 6th-order FBGs with the center wavelength of 717.2 nm and controllable reflectivity from -8.8 dB to -0.4 dB were fabricated. This work contributes to mitigating the shortage of FBG at visible wavelengths and promoting the development and application of monolithic visible fiber lasers.