Output power optimization in 980-nm pumping lasers wavelength-locked using fiber Bragg gratings

When erbium-doped fiber amplifiers are pumped by 980-nm laser, fluctuations in the pumping wavelength result in large variations in the gain and amplified output in the 1550-nm band - a phenomenon known as pump-mediated inhomogeneity (PMI) - resulting in stricter requirements with respect to wavelength variation in 980-nm laser modules. Pumping lasers have been developed that use a fiber Bragg grating (FBG) to suppress these pumping wavelength fluctuations, but output power levels using an FBG for wavelength feedback tend to be lower than without an FBG. This output power drop must be kept as low as possible, and to this end the authors have carried out an analysis involving FBG reflectivity, laser front-facet reflectivity, the wavelength pulling effect and the spatial hole-burning (SHB) effect. This paper discusses the concept of output power optimization for 980-nm laser modules with FBGs, and presents a theoretical analysis and simulation results.