Method for Quantum Key Establishment through a Multimode Fiber

Secure communication became extremely important in the Information Age. Quantum communication protocols have been developed to provide absolutely secure transmission of information. Historically, quantum key distribution (QKD) uses the two-dimensional polarization basis to encode information and the key element of long-distance communication is single-mode optical fiber. However, it intrinsically limits the information content to 1 bit per photon. Nowadays, significant effort is devoted to increase the data carrying capacity of a single quantum secure optical line. Large-core multimode fibers support a multitude of transverse optical modes and can potentially transfer information at much higher density.