A semiconductor laser device with an active layer having a multi-quantum well structure including more than one well layer and more than one barrier layer and having a cavity length of more than 800 m is disclosed, wherein the active layer includes a doped region which includes at least one well layer and at least one barrier layer adjacent to the well layer. The entire active region, comprising all of the well and active layers may be doped. Adjacent to the active layer are upper and lower optical confinement layers falls having a thickness within a range of from about 20 to about 50 nm. A optical fiber amplifier incorporating the semiconductor laser is also disclosed, including the semiconductor laser device sealed within a package disposed over a cooler, and wherein a light incidence facet of an optical fiber is optically coupled to the optical output power facet of the semiconductor laser device.