The terms "intersubband" (ISB) or "intraband" refer to electronic transitions between confined states in either the conduction band or the valence band of semiconductor heterostructures. In order to observe ISB absorption, the first electronic level must be populated. However, high doping levels may affect the transition energy. The ISB absorption energy exhibits a significant blue shift due to many-body effects, mostly related to the exchange interaction and the depolarization shift. The presence of internal electric fields in polar materials increases the design complexity of ISB devices. Nanowire heterostructures offer a unique situation for devices requiring low defect density in the active region and the combination of materials with large lattice mismatch. The demand for increasing bandwidth in optical communication networks impels the development of all-optical switches at 1.55 µm, which should be capable of sustaining high repetition rates with low switching energy and high modulation depth.