Received 22 December 2022, accepted 23 January 2023, date of publication 25 January 2023, date of current version 31 January 2023. Digital Object Identifier 10.1109/ACCESS.2023.3239807 Wireless and Optical Convergent Access Technologies Toward 6G HUGO RODRIGUES DIAS FILGUEIRAS 1,2 , (Associate Member, IEEE), EDUARDO SAIA LIMA 2 , MATHEUS SÊDA BORSATO CUNHA 2 , CELSO HENRIQUE DE SOUZA LOPES 2 , LETÍCIA CARNEIRO DE SOUZA 2 , RAMON MAIA BORGES 3 , LUIZ AUGUSTO MELO PEREIRA 2 , TIAGO HENRIQUE BRANDÃO 2 , TOMÁS POWELL VILLENA ANDRADE 2 , LUCIANO CAMILO ALEXANDRE 2 , GERALDO NETO 4 , AGOSTINHO LINHARES 5 , LUCIANO LEONEL MENDES 6 , (Member, IEEE), MURILO ARAUJO ROMERO 7 , (Senior Member, IEEE), AND ARISMAR CERQUEIRA S. JR. 2 1 VS Telecom, São Paulo 04213-001, Brazil 2 Laboratory Wireless and Optical Convergent Access (WOCA), National Telecommunications Institute (Inatel), Santa Rita do Sapucaí, Minas Gerais 37540-000, Brazil 3 Institute of Systems Engineering and Information Technology, Federal University of Itajubá, Itajubá, Minas Gerais 37500-903, Brazil 4 TMG, Vancouver, WA 98662, USA 5 Brazilian Ministry of Communications, Brasília, Distrito Federal 70044-900, Brazil 6 Radiocommunications Reference Center (CRR), National Telecommunications Institute (Inatel), Santa Rita do Sapucaí 37540-000, Brazil 7 Department of Electrical and Computer Engineering, University of São Paulo (USP), EESC/USP, São Carlos, São Paulo 13566-590, Brazil Corresponding author: Arismar Cerqueira S. Jr. (arismar@inatel.br) This work was supported in part by the National Education and Research Network (RNP) with resources from Ministry of Science, Technology, Innovation and Communication (MCTIC) under the 6G Mobile Communications Systems Project of the Radiocommunication Reference Center [Centro de Referência em Radiocomunicações (CRR)] of the National Institute of Telecommunications (Instituto Nacional de Telecomunicações—Inatel), Brazil, under Grant 01245.020548/2021-07; in part by the National Scientifc and Technological Development Council (CNPq); in part by the Higher Education Personnel Improvement Coordination (CAPES); in part by the Financier of Studies and Projects (FINEP); and in part by the Research Support Foundation of the State of Minas Gerais (FAPEMIG). ABSTRACT The sixth generation of mobile communication (6G) systems is recently rising a lot of interest, introducing new futuristic and challenging use cases that will demand much more than just communications to become a reality. Higher throughput, lower latencies, higher number of connections will push the requirement of the future mobile networks to a new level, but also sensing, positioning and imaging will play an important role in the new foreseen use cases. The integration of techniques developed for wireless communications with those conceived for optical links will be essential to provide the infrastructure for the 6G networks. In this context, this paper presents a review on wireless and optical convergent access solutions towards the 6G systems. The manuscript brings the use cases, requirements and enablers for 6G networks including a discussion about the state-of-the-art on THz and sub-THz communications, wireless and optical convergence, visible light communication, integrated and free-space optics, new antenna designs, power- over-fber deployments and the use of machine learning in the physical layer of future networks. By reviewing the most relevant contributions available in the literature for wireless and optical communications and presenting their main contributions, this paper clearly shows that, more than a technological trend, the convergence of wireless and optical technologies is a fundamental step towards the development of the 6G network infrastructure. INDEX TERMS 6G, antennas, FSO, optical-wireless convergence, physical layer, PIC, PoF, THz, VLC. I. INTRODUCTION The evolution from the frst generation of mobile com- munications (1G) to the fourth generation of mobile com- The associate editor coordinating the review of this manuscript and approving it for publication was Leo Spiekman . munications (4G) has been mainly focused on increasing the system capacity in terms of data rate and number of users. The ffth generation of mobile network (5G), on the other hand, has been designed to support three main scenar- ios according with international mobile telecommunications (IMT)-2020 vision [1], [2], [3]: enhanced mobile broadband 9232 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ VOLUME 11, 2023