Discrete wavelength generation using modal interference in a diode-laser-pumped Tm3+-doped few-mode fibre

By employing a few-mode core fibre in a symmetric cladding-pumped fibre laser arrangement, intermodal interference occurs between the first two symmetric modes that are excited simultaneously. In free-running mode, without the placement of dielectric mirrors, the Tm3+-doped silica fibre laser oscillates on a number of fringes simultaneously. In a grating-tuned arrangement, the tuning curves comprise of a number of discrete fringes consistent with the theory associated with interference between the two excited symmetric modes propagating the length of the fibre.