Quantum Key Distribution Based on Entanglement at a Distance of 500 Meters in Optical Fiber Substrate

In this research, an optical fiber substrate is used to implement the BBM92 protocol, an entanglement-based QKD system, over a 500-meter distance. Polarization-entangled photon pairs were produced using an optimized Sagnac interferometer construction. Once the Sagnac interferometer setup was properly calibrated, the pump laser was activated at various power levels. It was found that both the degree of entanglement and the visibility of the source were higher at lower pump laser powers. In contrast, at higher pump laser powers, thermal effects caused an increase in the wavelength bandwidth of the output beam. As a result, an increase in the wavelength bandwidth of the visible pump laser led to a decrease in the degree of source entanglement. Utilizing the properties of quantum entanglement for quantum encryption in communication is one of the safest methods for transmitting information. The approach outlined in this article can be used to ensure the security of sensitive information over short distances.