The objective of this research is to demonstrate chaotic communications systems that are secure and enable high data-rate communications at 10 gigabits per second. The approach is to use semiconductor lasers with optoelectronic time delays to provide chaotic emitters and receivers that when coupled exhibit synchronized chaotic dynamics. By concealing a message in the output of the emitter, it can be transmitted securely and decrypted at the receiver. The work seeks to multiplex several messages for high data rates. Internal and operation parameters are explored to conceal the encryption key to ensure high security.
The intellectual merit of this project is to find ways to optimally utilize the optical bandwidth acknowledging that the chaotic carrier's bandwidth exceeds that of any individual message. By multiplexing several messages within a single chaotic carrier, one can achieve bandwidths compatible with deployed optical communications systems. Preliminary work shows that choosing judicious parameters, chaotic time-delay systems can mask the encryption key, offering high security. One aim is to see if this holds for more complex systems for practical applications.
The broader impacts of this work include increasing security in optical communications in a manner that is compatible with existing communications infrastructure and new systems. Chaos encryption is a form of physical layer security; the only layer rarely used. Chaos encryption can, thus, be combined with software encryption. The research provides a mechanism for multidisciplinary training. The work involves an international collaboration between Georgia Tech in Atlanta and in Metz and Supélec in Metz, France.
This project addresses the use of external-cavity semiconductor lasers (laser diodes with time-delayed feedback) operating in a chaotic regime and their application for encrypted chaos communications. The project also addresses scientific and engineering questions in support of the main project aim. Intellectual Merit: Key results obtained under this project are the forllowing. (1) Theoretical prediction that the time delay--a key parameter in ensuring security--can be concealed (i.e., not easily extracted by means of low-order statisics obtained from the time-dependent intensity output) provided the time delay is chosen to be near the relaxation-oscillation time. (2) Theoretical schemes for multiplexed chaos encrypted communications using single external-cavity semiconductor lasers for the emitter and the receiver where the bandwidths of the channels strongly overlap. (3) Building an experimental capability to explore chaos in these lasers. (4) Obtaining the first experimental bifurcation diagrams as a function of feedback strength in these lasers. (5) Detecting bifurcations by means of the laser-diode terminal voltage. (6) Measuring and computing the first- and second-order statistics of the time-dependent intensity and drawing attention to discrepancies between theory and experiment. (7) Several photonic-crystal structures for possible future on-chip photonic integration of the external cavity. Broader Impacts: The key broader impacts of this program were in education and training of graduate students, specifically in an international context. Under this program, the first student to earn a dual PhD degree under a program between the Georgia Institute of Technology and Supelec, France conducted his research. This student subsequently was appointed to a faculty position at Supelec. This and other students supported in part by the program have spent a portion of their PhD studies at Georgia Tech Lorraine in Metz, France.
