  Recent development of the fifth-generation (5G) of cellular networks has led
to their deployment worldwide. As part of the implementation, one of the
challenges that must be addressed is the skip-zone problem, which occurs when
objects obstruct the transmission of signals. A signal obstruction can
significantly reduce the signal-to-noise ratio in radio frequency (RF) and
indoor visible light communications (VLC) systems, whereas the obstruction can
completely disrupt data transmission in free-space optical (FSO) systems.
Therefore, the skip-zone dilemma must be resolved to ensure the efficient
operation of 5G and beyond networks. In recent years, reconfigurable
intelligent surfaces (RISs) that are more efficient than relays have become
widely accepted as a method of mitigating skip-zones and providing
reconfigurable radio environments. However, there have been limited studies on
RISs for optical wireless communication (OWC) systems. This paper aims to
provide a comprehensive tutorial on indoor VLC systems utilizing RISs
technology. The article discusses the basics of VLC and RISs and reintroduces
RISs for OWC systems, focusing on RIS-assisted indoor VLC systems. We also
provide a comprehensive overview of optical RISs and examine the differences
between optical RISs, RF-RISs, and optical relays. Furthermore, we discuss in
detail how RISs can be used to overcome line-of-sight blockages and device
orientation issue in VLC systems while revealing key challenges such as RIS
element orientation design, RIS elements to access point/user assignment
design, and RIS array positioning design problems that need to be studied.
Moreover, we discuss and propose several research problems on integrating
optical RISs with other emerging technologies and highlight other important
research directions for RIS-assisted VLC systems.
