Chaos on a Chip

For the first time physicists have shown that well-structured chaos can be initiated in a photonic integrated circuit. Furthermore, this represents the first time scientists have been able to study optical chaos at gigahertz rates.

The output of a semiconductor laser is normally regular. However, if certain laser parameters are tweaked, such as by modulating the electric current pumping the laser or by feeding back some of the laser's light from an external mirror, the overall laser output will become chaotic; that is, the laser output will be unpredictable.

To make the chaos even more dramatic -- and exploitable -- Mirvais Yousefi and his colleagues at the Technische Universiteit Eindhoven, in the Netherlands, use paired lasers, lasers built very close to each other on a chip in such a way that each affects the operation of the other. The Eindhoven chip, using the paired-laser mutual-perturbation approach to triggering chaos, is the first to exhibit chaos directly-revealing telltale strange attractors on plots of laser power at one instant versus laser power at a slightly later instant-rather than indirectly through recording laser spectra.

Looking ahead to the day when opto-photonic chips are covered with thousands or millions of lasers, the Eindhoven approach could allow troubleshooters to pinpoint the whereabouts of misbehaving lasers---not only that but possibly even exploit localized chaotic effects to their advantage.

According to Yousefi (m.yousefi@tue.nl) other possible uses for chip-based chaos will be the business of encryption, tomography, and possibly even in the establishment of multi-tiered logic protocols, those based not on just on the binary logic of 1s and 0s but on the many intensity levels corresponding to the broadband output of the chaotic laser system.

Yousefi et al., Physical Review Letters, 26 January 2007
Contact Mirvais Yousefi
Technische Universiteit Eindhoven
m.yousefi@tue.nl