An interband cascade gain medium, comprising: an active gain region, the active gain region having a first end and a second end opposite the first end and having a cladding layer (108a, 108b) at each of the first and second ends, the active gain region comprising a plurality of cascading stages, each of the cascading stages including: an active gain quantum well region (101a, 201); a hole injector region (101b, 202) adjacent the active gain quantum well region; and an electron injector region (101c, 203) adjacent the hole injector region; each of the active gain quantum well region, the hole injector region, and the electron injector region comprising a plurality of electron barriers and at least one of an electron quantum well and a hole quantum well, the active gain region having an active gain quantum well region of a first stage at the first end thereof and an electron injector region of a last stage at the second end thereof, characterized in that at least one hole injector region of at least one stage of the active gain region is separated from an adjacent electron injector region by an AlSb electron barrier having a thickness of between 2.0 and 2.5 nm, and wherein at least one electron injector region (101c, 203) of at least one stage of the active gain region has a thickness of less than 25 nm; and further comprising a high-refractive-index separate confinement layer (106a, 106b) disposed between the active gain region and a corresponding cladding layer, the separate confinement layer comprising one of GaSb, GaInSb, GaAlSb, GaAsSb, GaAlAsSb, GaInAsSb, GaAlInSb, and GaAlInAsSb and having a total thickness of at least 0.8 μm. an active gain region, the active gain region having a first end and a second end opposite the first end and having a cladding layer (108a, 108b) at each of the first and second ends, the active gain region comprising a plurality of cascading stages, each of the cascading stages including: an active gain quantum well region (101a, 201); a hole injector region (101b, 202) adjacent the active gain quantum well region; and an electron injector region (101c, 203) adjacent the hole injector region; an active gain quantum well region (101a, 201); a hole injector region (101b, 202) adjacent the active gain quantum well region; and an electron injector region (101c, 203) adjacent the hole injector region; each of the active gain quantum well region, the hole injector region, and the electron injector region comprising a plurality of electron barriers and at least one of an electron quantum well and a hole quantum well, the active gain region having an active gain quantum well region of a first stage at the first end thereof and an electron injector region of a last stage at the second end thereof, characterized in that at least one hole injector region of at least one stage of the active gain region is separated from an adjacent electron injector region by an AlSb electron barrier having a thickness of between 2.0 and 2.5 nm, and wherein at least one electron injector region (101c, 203) of at least one stage of the active gain region has a thickness of less than 25 nm; and further comprising a high-refractive-index separate confinement layer (106a, 106b) disposed between the active gain region and a corresponding cladding layer, the separate confinement layer comprising one of GaSb, GaInSb, GaAlSb, GaAsSb, GaAlAsSb, GaInAsSb, GaAlInSb, and GaAlInAsSb and having a total thickness of at least 0.8 μm.