All-optical logic processing in a triangular symmetric three-core optical fiber coupler

Research on all-optical fiber-based logic processing is scarce and often focuses on single-function nonlinear devices that are costly, difficult to fabricate, and hard to scale or integrate into larger photonic circuits. In this paper, we investigate the logic-processing capabilities of a linear, dispersion-free triangular symmetric three-core (TSTC) optical fiber coupler propagated by low-power, amplitude-modulated light pulses. Using a model based solely on fiber design, coupled-mode theory, and a custom performance metric, we map all regions of logical operation within the coupler and derive a threshold-line equation that precisely delineates the transition between passive and active processing regimes. We demonstrate the acquisition of several single-function, multi-function, and even configurable all-optical logic devices without relying on nonlinear effects or mechanisms beyond the fiber itself. Our approach stands out for its linearity, simplicity of implementation, and potential for scaling and integration into larger photonic systems, but faces challenges related to design parameter sensitivity and lack of experimental validation under real-world conditions.