All-optical multistability using cross-gain modulation in quantum-dot distributed feedback semiconductor optical amplifier

We propose and theoretically demonstrate a novel type of all-optical multistable device using single quantum dot distributed feedback semiconductor optical amplifier. The device utilizes cross-gain modulation with proper wavelength detuning to obtain multistability in a conventional DFB semiconductor optical amplifier. We find that dual bistability, which can be adjusted vertically or horizontally by applying small probe input, can be obtained in both the pump and the probe characteristics. Adjustable switching with contrast ratio as high as 14 dB is obtained from the probe signal.