  Free-space optical (FSO) systems are able to offer the high data-rate,
secure, and cost-efficient communication links required for applications such
as wireless front- and backhauling for 5G and 6G communication networks.
Despite the substantial advancement of FSO systems over the past decades, the
requirement of a line-of-sight connection between transmitter and receiver
remains a key limiting factor for their deployment. In this paper, we discuss
the potential role of intelligent reflecting surfaces (IRSs) as a solution to
relax this requirement. We present an overview of existing optical IRS
technologies; compare optical IRSs with radio-frequency IRSs and optical
relays; and identify various open problems for future research on IRS-assisted
FSO communications.
