To explore the critical role and technological trends of optical communication networks in smart city development, this study systematically analyzes the application scenarios and performance of three key technologies: free-space optical communication (FSO), integrated sensing and communication (ISAC) optical networks, and visible light communication (VLC). Furthermore, based on the latest advancements in novel optical fibers, optoelectronic device manufacturing, and quantum communication technologies, future development directions are proposed. The analysis reveals that FSO offers high-speed transmission advantages for cross-domain connectivity and emergency communications but suffers from weather-dependent instability. ISAC-enabled optical networks facilitate real-time monitoring in scenarios such as traffic and seismic activity through fiber-optic sensing, yet exhibit high false alarm rates in complex environments. VLC achieves centimeter-level precision and interference-free transmission in indoor positioning and medical applications but faces challenges in hardware cost. Looking ahead, hybrid hollow-core and multi-core fiber architectures, co-packaged optics (CPO), and quantum key distribution (QKD) are expected to drive smart city advanc ements in network infrastructure, energy-efficient device interconnection, and security enhancement, respectively.