All-Optical Digital Logic Based on Unidirectional Modes

Standard electronic computing based on nanoelectronics and logic gates has upended our lives in a profound way. However, suffering from, both, Moore's law and Joule's law, further development of logic devices based solely on electricity has gradually stuck in the mire. All-optical logic devices are believed to be a potential solution for such a problem. This work proposes an all-optical digital logical system (AODLS) based on unidirectional (one-way propagation) modes in the microwave regime. In a Y-shaped module of the AODLS, the basic seven logic gates, including OR, AND, NOT, NOR, NAND, XOR, and XNOR gates, are achieved for continuous broadband operation relying on the existence of unidirectional electromagnetic signals. Extremely large extinction and contrast ratios are found in these logic gates. The idea of "negative logic" is used in designing the AODLS. Moreover, the authors further demonstrate that the AODLS can be assembled to multi-input and/or multi-output logical functionalities, which is promising for parallel computation. Besides, numerical simulations perfectly fit with and corroborate the theoretical analyses presented here. The low-loss, broadband, and robust characteristics of this system are outlined and studied in some detail. The AODLS consisting of unidirectional structures may open a new route for all-optical calculation and integrated optical circuits.