Method for quantum key establishment through a multimode fiber

Secure communication became extremely important in the Information Age [1]. Quantum communication protocols have been developed to provide absolutely secure transmission of information [2]. 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 [3]. Large-core multimode fibers support a multitude of transverse optical modes and can potentially transfer information at much higher density