The fluorescence spectra of trivalent samarium doped glass fibres are described. In silica glass Sm3+has a narrow fluorescence of 2.2 nm f.w.h.m. at a wavelength of 650 nm. The influence of fluorescence line narrowing and large external electric fields on this line is reported. Visible laser emission is obtained at this wavelength when the fibre is pumped in a Fabry Perot cavity. The performance of the laser in continuous,Q-switched and self mode-locked operation is described. The basic theory of self-mode-locking is presented.