  The anticipated launch of the Sixth Generation (6G) of mobile technology by
2030 will mark a significant milestone in the evolution of wireless
communication, ushering in a new era with advancements in technology and
applications. 6G is expected to deliver ultra-high data rates and almost
instantaneous communications, with three-dimensional coverage for everything,
everywhere, and at any time. In the 6G Radio Access Networks (RANs)
architecture, the Fronthaul connects geographically distributed Remote Units
(RUs) to Distributed/Digital Units (DUs)pool. Among all possible solutions for
implementing 6G fronthaul, optical technologies will remain crucial in
supporting the 6G fronthaul, as they offer high-speed, low-latency, and
reliable transmission capabilities to meet the 6G strict requirements. This
survey provides an explanation of the 5G and future 6G optical fronthaul
concept and presents a comprehensive overview of the current state of the art
and future research directions in 6G optical fronthaul, highlighting the key
technologies and research perspectives fundamental in designing fronthaul
networks for 5G and future 6G. Additionally, it examines the benefits and
drawbacks of each optical technology and its potential applications in 6G
fronthaul networks. This paper aims to serve as a comprehensive resource for
researchers and industry professionals about the current state and future
prospects of 6G optical fronthaul technologies, facilitating the development of
robust and efficient wireless networks of the future.
