“…It is expected that these useful properties improve the device performance. For example, it is possible to fabricate lowthreshold lasers (Shimizu et al 2007), un-cooled lasers (Otsubo et al 2004;Tanaka et al 2009), long-wavelength lasers (Ledentsov et al 2003;Yamamoto et al 2005, high-power lasers (Tanguy et al 2004) and ultra-broadband lasers by using QD structures (Rafailov et al 2007). Additionally, the ultra-broadband semiconductor optical amplifier is also expected to be fabricated by using the QD structure.…”