Indonesian Journal of Electrical Engineering and Computer Science Vol. 39, No. 1, July 2025, pp. 247~257 ISSN: 2502-4752, DOI: 10.11591/ijeecs.v39.i1.pp247-257  247 Journal homepage: http://ijeecs.iaescore.com Evolution of the optical add/drop multiplexer in dense wavelength division multiplexing optical networks Mnotho P. Mkhwanazi 1 , Khumbulani Mpofu 1 , Vusumuzi Malele 2 1 Department of Industrial Engineering, Tshwane University of Technology, Pretoria West, South Africa 2 North-West University, Unit for Data Science and Computing, Vanderbijlpark, South Africa Article Info ABSTRACT Article history: Received Nov 21, 2023 Revised Mar 4, 2024 Accepted Mar 26, 2025 Mobile network operators are facing ever-increasing traffic demands because of the numerous data-hungry applications used by subscribers nowadays. As a result, technologies that support high bandwidth and network availability have become essential. One such technology is dense wavelength division multiplexing (DWDM). This study investigated the evolution of an optical add/drop multiplexer (OADM), which is one of the key components of DWDM technology. The goal of this research was to investigate how the evolution of an OADM has contributed to network survivability and bandwidth enhancement in DWDM optical networks. A thorough search of the literature on an OADM was undertaken using data sources like Google Scholar, Elsevier, ResearchGate, ScienceDirect, Springer, and DWDM vendor manuals. The study found that in order to address present and future DWDM optical network demands, a reconfigurable optical add/drop multiplexer (ROADM) deployed over flex- grid spectrum is essential. The most advanced iteration of a ROADM supports colorless, directionless, contentionless, and flex-grid functionalities, resulting in the most robust, flexible, and future-proof DWDM optical network. The study further found that flex-grid technology supports uplinks with high line rates and has superior spectral efficiency. Keywords: CDC-F ROADM DWDM Flex-grid OADM ROADMs This is an open access article under the CC BY-SA license. Corresponding Author: Mnotho P. Mkhwanazi Department of Industrial Engineering, Tshwane University of Technology Staatsartillirie, Pretoria West, South Africa Emails: mnotho.mkhwanazi@gmail.com 1. INTRODUCTION The increasing use of data-driven applications in business, social media, and entertainment has resulted in a surge in data traffic for mobile network operators. Optical communication addresses this data traffic increase adequately due to its ability to cope with high data volumes [1]. The growing demand for bandwidth propels the rapid advancement of optical fibre communication technology [2], one such technology being dense wavelength division multiplexing (DWDM). DWDM technology is used to increase transmission capacity in optical networks. This technology increases the bandwidth of an existing fibre network by combining and transmitting multiple signals simultaneously at different wavelengths on the same fibre [3]. Each input is produced by a distinct optical source with a specific wavelength. DWDM technology is the most advanced multiplexing technique available today [4]. Prior research on DWDM technology has explored its ability to meet present and future bandwidth demands, without going into great detail on the specific components that make up a DWDM system. As DWDM technology evolved, so did its fundamental components. An optical add/drop multiplexer (OADM) is one such component. The OADM is responsible for three main functions within the DWDM network: optical add, drop, and express switching of the optical