Multiwavelength fiber lasers based on multimode fiber Bragg gratings using offset launch technique

The reflective characteristics of a multimode fiber Bragg grating (MM-FBG) and the changes of reflective spectra with mode excitation conditions in the multi-mode fiber were investigated. Two multiwavelength fiber laser configurations using offset launch technique to MM-FBG with hybrid gain mediums are proposed and demonstrated. Different multiwavelength outputs were obtained by variation of the spatial launching position of the single-mode fiber against the MM-FBG to achieve different mode group excitation. The first laser employs one MM-FBG in the ring cavity, achieving seven output wavelengths with a wavelength spacing of 0.76 nm. The second laser comprises two MM-FBGs connected in parallel, yielded 10 output wavelengths.