All-optical logic gates have been studied intensively owing to their potential to enable broadband, low-loss and high-speed communications. However, poor tunability has remained a key challenge in this field. In this work, we propose a Y-shaped structure composed of Yttrium Iron Garnet (YIG) layers that can serve as tunable all-optical logic gates, including, but not limited to, OR, AND and NOT gates, by applying external magnetic fields to magnetize the YIG layers. Our findings reveal that these logic gates are founded on protected one-way edge modes, where by tuning the wavenumber k of the operating mode to a sufficiently small (or even zero) value, the gates can become nearly immune to nonlocal effects. This not only enhances their reliability but also allows for maintaining extremely high precision in their operations. Furthermore, the operating band itself of the logic gates is also shown to be tunable. We introduce a straightforward and practical method for controlling and switching these gates between "work", "skip", and "stop" modes. These findings have potentially significant implications for the design of high-performance and robust all-optical microwave communication systems.

Extraordinary optical transmission (EOT) is a hallmark of surface plasmons and a precursor to nanoplasmonics and metamaterials. However, to the best of our knowledge, this effect has never been topologically protected in three dimensions, leaving it vulnerable to structural imperfections, nonlocal effects, and backreflections. We report broadband, three-dimensional unidirectional structures that allow for EOT (normalized transmission > 1) through deep-subdiffractional single holes, immune to these deleterious effects. These structures avoid unnecessary propagation losses and achieve maximum transmission through a single hole, limited only by unavoidable dissipative losses. In the limit of vanishing losses, the transmission through a deep-subdiffractional hole can approach unity, significantly surpassing existing devices, and rivaling the performance of negative-index ‘perfect’ lenses. The topological stability of these structures renders them robust against surface roughness, defects, and nonlocality, without the need for elaborate meta-structures or tapering.

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 elec-tricity 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 unidi-rectional 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.