Multiple-bit all-optical logic based on cross-gain modulation in a semiconductor optical amplifier

In this paper we have evaluated the non-linear response of a semiconductor optical amplifier (SOA) in terms of Cross Gain Modulation effect (XGM). The different ranges of optical power that make the SOA work as a logic gate have been determined, as well as the optimum relation between inputs to obtain the best response. Taking into account the SOA response, a schematic model for an all-optical 4-input NOR gate using a single SOA has been proposed. Our experimental set-up has been tested with four streams of 10 Gbps RZ data to verify the proper and stable operation of the NOR gate under diverse power levels for each data input. The logic output has been evaluated for different inputs using an optical eye diagram to verify its quality; in addition, the possibility of using the NOR output as the input to other logical semiconductor structures, which would allow to chain multiple gates, has been demonstrated. The concatenation of NOR gates allows to build more complex all-optical devices which will permit the design of advanced mechanisms in the field of transparent networks, such as comparators or look-up tables for switching nodes, without the necessity of optical-electrical conversion.