Effect of bias voltage on optically mixed two chaotic oscillators using an X-coupler device

In this experimental work, optoelectronic feedback and optical injection are applied to twin laser diodes. The X-coupler passive optical component device is employed to introduce and mix optical injection as a feed-forward, while a photodetector is used to detect and modulate self-optoelectronic feedback. The generated chaotic signal is modified by the X-coupler, and a broadband carrier with 9.4 MHz is achieved when the case of the first laser diode (LD1) bias current is changed. In the case of the second laser diode (LD2) being controlled, the generated carrier bandwidth frequency range increased to 124 MHz. Justification for chaoticity is carried out by calculating fractal dimension in terms of correlation function. According to calibration, the Lyapunov exponent also confirmed the existence of chaos with selected dimensions and noise with others. The bias voltage level is in correspondence to the laser threshold-based light-current curve. Calibrated attractors corresponding to the resulting dynamics have slightly variable hyperspherical shapes with varied radii and filled areas with modes and trajectories. This technique, named double feeding, finds applications in optical neural networks with which input and hidden and output layers can be simulated and chaotic synchronization can be employed.