All-optical logic gates are essential elements for the optical processing of information, since they overcome the fundamental difficulties of their electronic counterparts, in particular the limited data transfer speed and bandwidth.

Recently, silicon has been used as a basic element in making passive and active photonic devices owing to its high thermal and mechanical properties, stability, high quality, low loss, and large bandwidth extending from 1.55 μm to nearly 7 μm.

In a new study, Amer Kotb and LI Wei at Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) and Kyriakos Zoiros at the Democritus University of Thrace in Greece have designed seven basic logic operations, i.e., NOT, XOR, AND, OR, NOR, NAND and XNOR, using silicon-on-silica waveguides operated at 1.55 μm.

These logic operations are realized based on the constructive and destructive interferences between the input beams. The operations’ performance is evaluated against the contrast ratio (CR).

With the convolutional perfectly matched layer as an absorbing boundary condition, a Lumerical finite-difference-time-domain is run to simulate and demonstrate the operation of the proposed logic operations.

The simulation results published in Physica Scripta suggested that compact waveguide can be used to realize all-optical logic gates with higher CRs and a speed as high as 120 Gb/s compared with previously designs.