Chaotic optical data encryption using external-cavity VCSELs

Optical synchronisation of chaos in unidirectionally coupled external cavity vertical-cavity surface-emitting semiconductor lasers (VCSELs) has been experimentally achieved. The polarisation of the injected beam is perpendicular to that of the free-running receiver (x-polarisation). Normal (positive-slope) synchronisation is observed between the injected beam and the y-polarized component of the receiver. However, due to the anti-phase dynamics of the receiver, an inverse (negative-slope) synchronisation is found between the injected beam and the x-polarized component of the receiver. A 200 MHz message has been successfully encoded in an external-cavity VCSEL transmitter and decoded in a receiver. Message recovery has been achieved with about 9 dB signal-to-noise ratio.