Photonic Processing for Digital Comparison and Full Addition Based on Semiconductor Optical Amplifiers

An N bit all-optical comparator and an all-optical full adder are presented. These complex circuits, which perform photonic digital processing, are implemented cascading a unique basic gate that exploits cross gain modulation and cross-polarization rotation in a single semiconductor optical amplifier (SOA). Since the interacting signals are counterpropagating in the SOA, they can be set at the same wavelength. Photonic processing improves the speed of the optical networks by reducing the packet latency time to the time-of-flight in the nodes. Digital comparison and full-addition are key functionalities for the processing of the packet labels. Integrated realizations are crucial, thus, SOAs represent a suitable mean both because they allow hybrid integrated solutions and fast operation speed. The performances of the basic gate, the comparator, and the full adder are investigated both in terms of bit error rate and eye opening. To the best of our knowledge this is the first time it is reported on the implementation of an all-optical comparator able to compare patterns longer than 1 bit. Previous works demonstrate the comparison of 1 bit patterns. Only few works report on an all-optical full adder implementation, but with different schemes. In our implementation, sum and carry out do not depend directly on the carry in, thus potentially improving the output signal quality when cascading multiple full adders.