A type II interband cascade gain medium including a thick and indium-rich GaInSb hole well, two or more GaSb hole wells, electron and hole injectors are separated by a thick AISb barrier, the thickness of the firs InAs electron well in the electron injector, as well as the total thickness of the electron injector and the number of cascaded stages is reduced, transition regions are inserted at the interfaces between the various regions of the gain medium, thick separate confinement layers comprising Ga(InAIAs)Sb are disposed between the active gain region and the cladding, and the doping profile of the cladding layers is optimized to minimize the overlap of the optical mode with the most heavily-doped portion of the InAs/AISb SL cladding layers.
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