Design of a four channel green-wavelength multiplexer based on multicore polymer optical fiber

The growing demand for compact photonic systems in the green spectral range necessitates fully integrated wavelength division multiplexing (WDM) solutions. Conventional multiplexers often rely on bulky components, resulting in high insertion losses and limited integration potential. Concurrently, advances in neuromorphic photonic computing require novel devices that support both spectral multiplexing and optical weighting within a unified platform. This study introduces a compact four-channel green-wavelength optical multiplexer based on a multi-core polymer optical fiber (MC-POF) embedded with polycarbonate (PC) cores. The device passively multiplexes light via engineered coupling between adjacent cores, operating across the 500–560 nm range without the need for external optics. Beam propagation method (BPM) simulations, combined with MATLAB-based optimization, confirm that a 20 mm fiber segment enables low insertion losses (0.13–0.55 dB), sharp channel isolation, and high thermal stability. A single optimized coupling region enables 20 nm channel spacing across four wavelengths and acts analogously to a synaptic junction, allowing simultaneous signal convergence. This design not only supports efficient green-spectrum transmission but also lays the groundwork for integrated neuromorphic photonic networks. Experimental validation was performed using a two-channel PC-MC-POF with 500 nm and 540 nm green laser sources. Collimated beams were coupled into separate fiber cores, and the multiplexed output was directly imaged using a CMOS camera. The measured far-field intensity profile closely matches simulation results, confirming effective spatial multiplexing and validating the theoretical model. The proposed PC-MC-POF multiplexer offers a scalable, low-loss, and energy-efficient solution for green-wavelength WDM systems. It serves both as a functional optical multiplexer and a foundational building block for photonic neural architectures, contributing to the development of next-generation integrated optical communication and computing technologies.