# Integrated Photonics for IoT, RoF, and Distributed Fog-Cloud Computing: A Comprehensive Review
## 4 Photonic Implementations in Fog Computing Domains
### Smart Cities and Urban Infrastructure  
Smart cities face numerous challenges, such as traffic congestion, public safety, energy management, sanitation, and internet connectivity [21; 22; 23]. Fog computing addresses these by enabling localized processing and storage near end devices, reducing reliance on centralized Cloud infrastructure. Key applications include smart parking, smart hospitals, smart healthcare systems, smart transportation, optimized highway usage, smart buildings, and software-defined factories. While cellular networks provide city-wide coverage, their limited capacity often falls short of supporting advanced city services. Integrating Fog computing with Bluetooth, LoRa, WiFi, 5G, and 6G technologies enables a scalable and responsive smart city infrastructure to be developed by offloading workloads to nearby Fog nodes and optimizing bandwidth utilization. Integrated photonic links further support high-speed, low-latency data transfer across urban sensor networks.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Figure of Merit** & **RoF System** & **CS / ODN / BS Considerations** & **PIC Research Opportunities** \\ \hline Cost and Simplicity & Low-cost mm-wave generation and simplified architectures & Use of multiple light sources and integrated components & Explore cost-optimized integrated designs; PICs reduce footprint and simplify maintenance by combining functions on-chip. \\ \hline mm-wave Frequency and Bandwidth & Photonic-based mm-wave generation & Integrated CW lasers; cascading limitations & Develop broadband, compact sources; PICs support efficient mm-wave generation with reduced loss and improved integration. \\ \hline Spectral Purity and Frequency Accuracy & Low-phase-noise LO and frequency stabilization & Narrow linewidth lasers, interleaving techniques & Enhance spectral purity and tone correlation; PICs improve stability via laser and filter integration. \\ \hline Transmission Integrity & Robust modulation and coding & ODN nonlinearities and amplification effects & Optimize transmission quality under distortion; PICs support low-noise integration of key signal processing blocks. \\ \hline RF Output Power and Signal Strength & High-efficiency downlink delivery & Remote generation, mm-wave photodiodes & Improve output power and efficiency; PICs enable high-performance photodiode integration. \\ \hline Scalability & Tunable and flexible downlink techniques & Configurable RN and multi-wavelength sources & Design adaptable, scalable networks; PICs offer compact WDM and fast wavelength tuning. \\ \hline Power Consumption & Energy-efficient transmission schemes & Amplification and BS power optimization & Reduce system-level power use; PICs lower interconnect loss and support compact, low-power designs. \\ \hline Reliability and Availability & Self-healing and monitorable architectures & Minimize failure points; integrate restoration features & Design robust systems; PICs integrate monitoring and switching to improve fault tolerance. \\ \hline Figures of Merit (QoS) & End-to-end system performance control & Bandwidth and spectral integrity & Ensure consistent service quality; PICs allow fine control over optical signal paths and conditions. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Research opportunities for RoF systems with PIC integration. CS stands for Central Station, ODN for Optical Distribution Network, and BS for Base Station.  
Example: Photonic-enabled high-speed fiber backhaul is increasingly being adopted for Roadside Units (RSUs) in intelligent transportation and urban IoT deployments to ensure low-latency and reliable communications over metropolitan-scale networks [25]. Meanwhile, Microsoft's Project Silica explores durable, volumetric photonic storage using femtosecond laser-writing in quartz glass--promising archival data densities of several terabytes in DVD-sized volumes with lifespans measured in millennia [26].