  Since the advent of optogenetics, technology development has focused on new
methods to optically interact with single nervous cells. This gave rise to the
field of photonic neural interfaces, intended as the set of technologies that
can modify light radiation in either a linear or non-linear fashion to control
and/or monitor cellular functions. These include the use of plasmonic effects,
up-conversion, electron transfer and integrated light steering, with some of
them already implemented in vivo. This article will review available approaches
in this framework, with a particular emphasis on methods operating at the
single-unit level or having the potential to reach single-cell resolution.
