  The proliferation of mobile Internet and connected devices, offering a
variety of services at different levels of performance, represents a major
challenge for the fifth generation wireless networks and beyond. This requires
a paradigm shift towards the development of key enabling techniques for the
next generation wireless networks. In this respect, visible light communication
(VLC) has recently emerged as a new communication paradigm that is capable of
providing ubiquitous connectivity by complementing radio frequency
communications. One of the main challenges of VLC systems, however, is the low
modulation bandwidth of the light-emitting-diodes, which is in the megahertz
range. This article presents a promising technology, referred to as "optical-
non-orthogonal multiple access (O-NOMA)", which is envisioned to address the
key challenges in the next generation of wireless networks. We provide a
detailed overview and analysis of the state-of-the-art integration of O-NOMA in
VLC networks. Furthermore, we provide insights on the potential opportunities
and challenges as well as some open research problems that are envisioned to
pave the way for the future design and implementation of O-NOMA in VLC systems.
