Improved all-optical modified signed-digit adders using semiconductor optical amplifier and Mach–Zehnder interferometer

In this paper, we present improved all-optical circuits that implement ultra-fast adders based on the carry-free property of the modified signed-digit (MSD) number representation. The all-optical realizations are based on semiconductor optical amplifier (SOA) and Mach–Zehnder interferometer (MZI) switches, which represent one of the most promising solutions due to their compact size, thermal stability and low power operation. Several all-optical circuit designs are proposed with the objective to minimize the number of the SOA–MZI switches, the time delay in the adders and some other optical elements. The proposed circuits are more efficient comparing to previously published ones in terms of the number of optical components (less by 50%) as well as the operational speed (faster by 50%).