  The rise of intelligent reflecting surfaces (IRSs) is opening the door for
unprecedented capabilities in visible light communication (VLC) systems. By
controlling light propagation in indoor environments, it is possible to
manipulate the channel conditions to achieve specific key performance
indicators. In this paper, we investigate the role that IRSs can play in
boosting the secrecy capacity of non-orthogonal multiple access (NOMA) VLC
systems. More specifically, we propose an IRS-based physical layer security
(PLS) mechanism that mitigates the information leakage risk inherent in NOMA.
Our results demonstrate that the achieved secrecy capacity can be enhanced by
up to 105% for a number of 80 IRS elements. To the best of our knowledge, this
is the first paper that examines the PLS of NOMA-based IRS-assisted VLC
systems.
