  Focusing and guiding light into semiconductor nanostructures can deliver
revolutionary concepts for photonic devices, which offer a practical pathway
towards next-generation power-efficient optical networks. In this review, we
consider the prospects for photonic switches using semiconductor quantum dots
(QDs) and photonic cavities which possess unique properties based on their low
dimensionality. The optical nonlinearity of such photonic switches is
theoretically analyzed by introducing the concept of a field enhancement
factor. This approach reveals drastic improvement in both power-density and
speed, which is able to overcome the limitations that have beset conventional
photonic switches for decades. In addition, the overall power consumption is
reduced due to the atom-like nature of QDs as well as the nano-scale footprint
of photonic cavities. Based on this theoretical perspective, the current
state-of-the-art of QD/cavity switches is reviewed in terms of various optical
nonlinearity phenomena which have been utilized to demonstrate photonic
switching. Emerging techniques, enabled by cavity nonlinear effects such as
wavelength tuning, Purcell-factor tuning and plasmonic effects are also
discussed.
