Design and performance analysis of a six-state QKD over FSO and optical fiber utilizing switch-controlled polarization generation for secure optical communications

Abstract Quantum key distribution (QKD) is a process that utilizes the principles of quantum mechanics to securely share a secret key between two parties, ensuring unconditional security. Diverse QKD protocols are established to guarantee the security and integrity of information against any attempts by an eavesdropper monitoring the transferred photons. One of these protocols is the six-state protocol. This work employs OptiSystem 21.1 simulation software to design and emulate the six-state protocol, wherein polarization states are produced through random switching control rather than optical modulators. The protocol’s performance, indicated by quantum bit error rate and secure key rate, is analytically examined for both free space optical (FSO) channel and optical fiber channel, incorporating parameters from two types of commercial single-photon detectors to enhance realism. The maximum secure key rate attains 5.439 Mbps at 10 km of optical fiber, in contrast to 1.674 Mbps at 0.2 km under clear weather conditions in the FSO quantum channel utilizing ID 281 single-photon detector modules across both channels. The maximum distance that guarantees secure key rate with ID 281 for FSO channel is 2 km with 1760 bps with heavy haze compared to 100 km optical fiber with secure key rate of 15,000 bps.