  In this paper, we investigate the use of intelligent reflecting surfaces
(IRSs) (i.e., smart mirrors) to relax the line-of-sight requirement of free
space optical (FSO) systems. We characterize the impact of the physical
parameters of the IRS, such as its size, position, and orientation, on the
quality of the end-to-end FSO channel. In addition, we develop a statistical
channel model for the geometric and the misalignment losses which accounts for
the random movements of the IRS, transmitter, and receiver due to building
sway. This model can be used for performance analysis of IRS-based FSO systems.
Our analytical results shows that depending on the angle between the beam
direction and the IRS plane, building sway for the IRS has either a smaller or
larger impact on the quality of the end-to-end FSO channel than building sway
for the transmitter and receiver. Furthermore, our simulation results validate
the accuracy of the developed channel model and offer insight for system
design.
