Optical access system by Y-00 protocol at 2.5-Gb/s data rate for secure optical fiber communication

Recently, optical fiber transmission lines have flows of huge data including confidential information. Presently, the mathematical cipher is employed in some access systems to protect eavesdropping. However, the cipher break history shows such mathematical cipher is not reliable enough. Such fact demands an urgent development of more reliable cipher and drives us to focus actively on the research and development of physical cipher. Y-00 quantum cipher is an encryption scheme combined with physical phenomena and mathematical cipher, and it provides high speed performance and a provable security. So far, we have applied Y-00 quantum cipher to point-to-point transmission systems. However, secure communication system in the multiple remote point access system from a local point is also important. In this work, we propose a secure multiple point access system using the intensity modulated Y-00 quantum cipher. A one-to-three point transmission system using Y-00 quantum cipher in the wavelength division multiplexing (WDM) scheme is experimentally demonstrated where Y-00 quantum ciphers encrypted with three different secret keys are transmitted from a local point to three users in different remote access points. For the first time to our knowledge, Y-00 cipher communications between users with the correct keys are successfully demonstrated at 2.5-Gb/s data rate while users with the different keys are not able to communicate.