Due to waveguiding silicon's high refractive index (n_silicon = 3.48) in comparison to air (n_air = 1) or the silica cladding layer (n_silica = 1.44), the strong optical guiding is ensured for all signals around the typical near-infrared wavelength of 1.55 μm. Additionally, due to silicon's strong optical confinement, which allows for bending waveguide radii of only a few micrometers and functional waveguide elements of just ten to a few hundred micrometers, incredibly compact optical devices can be created.

On the contrary, all-optical logic gates (AOLGs) overcome the disadvantages of their electronic counterparts, namely the low bandwidth and slow data transit speed, thus enabling more effective data processing.

Amer Kotb from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) and his co-authors, Kyriakos Zoiros from the Democritus University of Thrace, Antonios Hatziefremidis from National Kapodistrian University of Athens, and Chunlei Guo from the University of Rochester, have employed Z-shaped silicon-on-silica waveguide to demonstrate AOLGs, including XOR, AND, OR, NOT, NOR, NAND, and XNOR, that operate at 1.55 μm.

This unique design won the admiration of all the reviewers as well as the Journal Editors, and they were highly praised for its results, which were quickly published in Micromachines.

Three slots, grouped in the shape of the letter Z, make up the suggested waveguide. The function of the target logic gates is based on constructive and destructive interferences that result from the phase difference experienced by the launched input optical beams.

These gates are evaluated against the contrast ratio by investigating the impact of key operating parameters on this metric. Moreover, the dependence of the spectral transmission on the waveguide’s key operating parameters is investigated and assessed.

The simulation results reveal that owing to the devised waveguide-based structure, the target AOLGs can be executed with improved performance at a faster rate than other design counterparts described in the literature, which is technologically feasible. To this end, these AOLGs can serve as the key modules in fundamental- and system-oriented level modern applications.