Controlling chaotic oscillation modes in visible semiconductor lasers by external light input and its applications to novel optical communications

Abstract

We have demonstrated a simple method for controlling the nonlinear oscillations using only semiconductor lasers and photodetectors. An electro-optical NDFS (nonlinear delayed feedback system) has been composed by making use of this method. With this system, multi-stable oscillations and chaotic transitions with various patterns have been observed. In addition, some characteristic routing sequences form period-doubling bifurcation to chaos have been reproducibly observed when some external modulations with acoustic frequencies are applied to the NDFS. In this case, we have proved that the harmonic numbers of the multi- stable oscillation modes to appear as system output are to be controlled in terms of timing (phase) as well as frequencies of external input signals at the moment they are applied. And we have also confirmed such remarkable transition behaviors of the multi-stable oscillation modes by numerical analysis based on nonlinear delayed differential equations describing our NDFS. Consequently, we have demonstrated that the oscillation harmonic numbers can be directly chosen from the 1st order up to the 9th by setting the frequencies of the external input signals to be their characteristic values specifying the desired harmonic numbers to appear for output and also by setting the timing of input signals with respect to the phase of original waveform of the oscillating modes. Thus, our system is expected to be a potential for something novel, intelligent communication technique based on chaos.