## 5 Conclusions  
### Discussion  
In the current study, the researchers used a network analysis method to explore the key technologies of 5G optical networks. The empirical results revealed that the focuses of such technologies are mostly on wireless communication network facilities and multiplex communication systems. The maturation of optical component technology paved the way for multiplex communication system technology to flourish, and made it one of the key technologies in the development of 5G. Additionally, an analysis of the top patentees revealed that information technology companies such as Huawei Technologies Co., Ltd. and Telefonaktiebolaget LM Ericsson (publ) hold a relatively high number of patents; this indicates that information technology companies in the private sector are the main force in developing 5G optical network technologies compared with universities and the public sector, which implies the potential of 5G optical networks in future market development. As stated in the 5G Business Potential report, 5G has the potential to generate high revenue for agencies worldwide [40]. Furthermore, driven by the market, 5G optical communication has become the technical focus of the private sector. In terms of technical trends over the years, the researchers found that key technologies in 5G optical networks have shifted from network topologies and security arrangements to transmission systems employing electromagnetic waves other than radio waves, as well as multiplex communication systems. In particular, multiplex communication systems have become one of the pillar technologies in the development of 5G optical networks. In this age of 5G, the volume of digital data being transmitted has increased exponentially. The purpose of multiplex systems is to make 5G available to all people without them interfering with each other. In short, multiplex systems could increase data rate and fulfill the needs of each user or object. For example, the key technology of dense wavelength-division-multiplexed passive optical network (DWDM-PON) is the provision of different wavelengths to the optical network units connecting to a central office, which facilitates the simultaneous transmission of multiple users. It also reduces the number of optical fibers that have to be deployed by enabling the sharing of existing \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Centrality** & **Focuses in the** & **Focuses in the** & **New Technology** & **Elimated** \\
**Indicators** & **Early Stage** & **Later Stage** & **Domains** & **Technology** \\ \hline Closeness & H04W88, H04W84, H04W72, H04W40, H04Q11, H04L5, H04Q11 & H04W72 & H04B10, H04L5 & H04W84, H04W40 \\ \hline Betweenness & H04W88, H04B10, H04W84, H04W72, H04Q11, H04L5, H04W12 & H04Q11, H04L5, H04W72, H04W12 & H04Q11, H04L5 & H04W72, H04W12 \\ \hline Fragmentation & H04W88, H04W84, H04W8, H04B10, H04B10, H04W72, H04Q11, H04L5, H04W72 & H04Q11 & H04W84 \\ centrality & H04L5 & H04W72 & & \\ \hline \hline \end{tabular} Note: 49 patents with 80 CPC codes were observed in the early stage (2014–2016).  
\end{table} 
Table 5: Key trends in technical developments for 5G optical networks. optical network infrastructures. As a result, considerable network construction and maintenance costs are saved. The innovative integration of DWDM-PON and millimeter-wave wireless transmission will become mainstream in the foreseeable future, given that they enhance user data rate, end-to-end connectivity, connection density, and traffic volume density at a reduced cost. Such a development trend is similar to the predictions made by other scholars [14; 41]. In conclusion, the results of the current study correspond with the development trends of this emerging domain. Relevant studies on 5G optical networks have predominantly focused on discussions on the technical [6; 7; 8] or market aspects [4; 9]; however, their findings have not provided a detailed understanding of the key technologies and technical development trends in 5G optical networks.