A review on all-optical logic adder: Heading towards next-generation processor

In this paper few literatures on all-optical adders, reported approximately in last fifteen years, have been reviewed. Being the key element of arithmetic and logic unit (ALU), adder has attracted stirring attention of the researchers. The reviewed articles are primarily categorized into three broad sections based on the platforms utilized in designing all-optical adder namely semiconductor optical amplifier (SOA), plasmonics and photonic crystal (PhC). SOA based designs offer high contrast ratio between the output logic levels, however; at the cost of high response time and operating power. Plasmonic based designs provide miniaturized physical footprint of the devices owing to the tight optical confinement. Nevertheless, the process of fabrication involved with the plasmonic based designs along with the loss incurred at the metal are among the limiting features. In contrast, PhC based designs are much more advantageous owing to the notable characteristics of light propagation. The operating power and bandwidth of operation are also higher as compared to the other designs. Photonic crystalbased designs are further categorized into linear and nonlinear domains based on their operating principle. The design structures and performances have been summarized and a comparison is made. Some insights have been discussed leading to design of more efficient PhC based all-optical adders for next generation ultra-first optical processors.