Communication with chaotic Lasers

I am interested in assessing the potential use of chaos and chaos synchronization for communication. The use of chaotic signals on which to modulate and demodulate information may be attractive from the point of view of the efficiency of the use of communications channel bandwidth or possibly for reasons of power efficiency in the design and use of the transmitter.

Single mode semiconductor lasers with feedback exhibit chaos. Without feedback semiconductor lasers can be modeled as a system with just two dynamical degrees of freedom (and therefore no chaos); one degree of freedom for the carrier density and one for the photon density in the cavity. The feedback on the other hand has a certain time delay associated with it which introduces the possibility of chaos. One observes that the complexity of the dynamics increases with the amount of time-delay in the feedback and can thus study both low and high dimensional chaos with the same system.

As part of my disseration research I studied semiconductor lasers with electro-optical feedback, that is a setup where one detects part of the output power of the semiconductor laser and then changes the pump current of the semiconductor laser accordingly. In this work, which was done in collaboration with Henry Abarbanel and Matt Kennel, we show numerically the existence of chaos and compare the route to chaos to the one seen in experiments. This gives us some confidence in the model. We then propose a scheme to synchronize two chaotic lasers and investigate the robustness of this synchronization with respect to noise and parameter mismatches of the two lasers.

In the regimes where chaos synchronization exists, one can then modulate information at the transmitter and retrieve it on the receiver side by comparing at each instance in time the signal one expects to the one which is received. Since the lasers are synchronized, the difference of expected and received signal is due to the modulation of information onto the chaotic carrier waveform, which we can then decode. This is of course only true for an ideal channel. We compute the performance curves of one such communication scheme in a noisy optical channel. Although the performance of the scheme with chaotic carrier signal is worse than the chaos free 'direct signaling' case, in general noise does not cause complete desynchronization and therefore chaos communication is feasible.

Our theoretical investigation on semiconductor lasers was accompanied by experiments by the group of Jia-Ming Liu at UCLA. A short summary of the experimental results and how they fit with our theoretical predictions can be found in the conference proceedings of the 6th Experimental Chaos Conference.

This research is part of the MURI project: Communications with Chaos

Publications

• L. Illing , "Chaos Synchronization and Communications in Semiconductor Lasers", Thesis (Ph.D.), University of California, San Diego (2002)
• S. Tang, L. Illing , J. M. Liu, H. D. I. Abarbanel, M. Kennel Communication using Synchronization of Chaos in Semiconductor Lasers with optoelectronic feedback, American Institute of Physics Conference Proceedings of the 6th Experimental Chaos Conference, no.622, pp.224-9, (2002)
• H. D. I. Abarbanel, M. Kennel, L. Illing, S. Tang, H.F. Chen and J.M. Liu, "Synchronization and Communication Using Semiconductor Lasers With Optoelectronic Feedback", IEEE J. Quantum Electron., vol. 37, 1301 (2001)

• Clifford Tureman Lewis, Henry D. I. Abarbanel, Matthew B. Kennel, Michael Buhl, and Lucas Illing, "Synchronization of chaotic oscillations in doped fiber ring lasers",Phys. Rev. E, vol.63, pp. 016215 (2001)
• Henry D. I. Abarbanel, Matthew B. Kennel, Michael Buhl, and Clifford Tureman Lewis, "Chaotic dynamics in erbium-doped fiber ring lasers", Phys. Rev. A, vol.60, no. 3, pp. 2360-2374, (1999)
• Henry D. I. Abarbanel and Matthew B. Kennel, "Synchronizing High-Dimensional Chaotic Optical Ring Dynamics", (Phys. Rev. Lett. , vol. 80, pp.3153-3156, (1998)

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