We demonstrate a simple method for controlling the nonlinear oscillations by only using a semiconductor laser and photo detectors. The nonlinearity necessary for exhibiting period-doubling bifurcations and chaotic phenomenon was realized by appropriately superposing the threshold characteristics of semiconductor lasers on the saturation characteristics of photodiodes in their electric current vs. light intensity properties. An electro-optical NDFS (nonlinear delayed feedback system) has been composed by making use of this nonlinearity. A low-pass filter was inserted into this NDFS as an electric feedback element, which gave variety to the behavior of the nonlinear oscillations. With this system, multi-stable oscillations and chaotic transitions with various patterns have been observed. In this scheme, an optical dynamical memory function has been demonstrated to perform binary data writing. In addition, we have applied an external light input to the NDFS, for example, some sinusoidal wave modulations with acoustic frequencies. If the external input light effects to the oscillation waveform are to be reproducibly derived, new application to a waveform recognition system and cryptography will be expected.
