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All-optical logic gates (AO-LGs) are the key elements that play a pivotal role in the development of future all-optical networks and all-optical computing. A complete overview of the seven all-optical logic gates (i.e., AND, OR, NOT, XOR, XNOR, NAND, and NOR) based on their design techniques and applications are covered, including the latest technologies, such as topological photonics and artificial intelligence-based designs techniques. In addition, we have further categorized the AO-LGs as reconfigurable gates, simultaneous gates, reversible gates, modulation-based gates, and data rate-based gates. The techniques to implement these different classes of gates are reviewed and their limitations are discussed. We also discuss in brief the various simulation tools used to design and analyze the AO-LGs. Finally, the most feasible techniques for constructing optical integrated circuits based on the existing fabrication technologies and available resources are explored, and future prospects are outlined.

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In this work, an optimized structure of an XOR gate working in the optical domain is put for-ward to achieve high contrast ratio and extremely compact dimensions using a photonic crystal platform. The above structure employs silicon rods in a hexagonal lattice configuration. The design works purely on linear interference effect between the incoming light signals and does not involve any non-linear materials. The Finite Difference Time Domain based simulations are utilized to study the propagation of light within the structure and the Plane Wave Expansion Method is applied to generate bandgap structure. After optimization of the various design parameters, a contrast ratio of 31.76 dB is attained by the proposed structure along with a response time of 0.46 ps and a footprint of 42.24 μm 2 . The device can be operated in the C Band with optimum performance at 1550 nm, which is the telecommunication wavelength. The operating bit rate for the proposed structure is 2.17 Tbps. All-optical XOR gate being a universal gate forms the building blocks of various sequential and combinational logic designs suitable for optical computing and communication applications.

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