All-optical memory based on a two-mode diode laser with optical feedback

In this paper we numerically demonstrate that an optical memory can be based on a two-mode laser diode with optical feedback and injection in the short external cavity regime. For modelling this system we use a two-mode extension of the Lang-Kobayashi rate equations with gain saturation and optical injection. The parameters chosen are consistent with the simultaneous oscillation of the two modes in the free running laser, which is possible for frequency spacings greater than approximately 500 GHz at optical frequencies around 200 THz. For certain values of the system parameters, we have found a hysteresis loop between single-mode equilibrium states for increasing and decreasing feedback strength. Our simulations show that injected optical pulses can switch the system between single mode equilibrium states when the feedback parameters are fixed in this bistable region, demonstrating the function of the optical memory. This system has attractive features such as the absence of a holding beam and the symmetry between the two states of the memory element. These properties along with the external cavity length of 1 cm make the system an interesting candidate for optical integration.