US Patent 7907849 Secure communication system and method for exchanging data units

A communication system, the communication system includes: a first decision entity; and a long laser that includes a first reflector and a second reflector; wherein a lasing characteristic of the long laser is responsive to: (i) first data unit that is provided by a first user and affects a reflection spectrum of the first reflector, and (ii) second data unit that is provided by a second user and affects a reflection spectrum of the second reflector; and wherein the first decision entity is adapted to receive the first data unit and information representative of the lasing characteristic, as well as to determine (i) a relationship between the first data unit and the second data unit, or (ii) a content of the second data unit.