Quantum Key Distribution in Multiple Fiber Networks and Its Application in Urban Communications: A Comprehensive Review

Information security faces unprecedented challenges in the digital age, particularly in the face of cyber threats and the emergence of quantum computing. This research examines QKD as a solution for secure communications in urban fiber networks. The study analyzes QKD protocols, including BB84 and Twin-Field QKD, implementing a 46-node metropolitan quantum network and key distribution over distances greater than 1002 kilometers. Various transmission media, such as multicore optical fibers and free-space communication, were evaluated, demonstrating high-capacity quantum communication with advanced noise mitigation techniques. The results reveal significant advances in quantum communication security, highlighting the potential of QKD to provide theoretically secure key distribution based on quantum mechanical principles. The research addresses challenges such as transmission loss, environmental disturbances, and network scalability, laying the groundwork for future implementations in metropolitan networks. This work contributes significantly to the standardization of evaluation protocols and metrics, which is crucial for the global adoption of QKD in a world increasingly dependent on cybersecurity, especially in developing smart cities.