• Achieved multiplexing efficiencies of 99.17% (red), 99.76% (green), and 96.63% (blue), with an average of 98.52% using entropy weight-TOPSIS optimization.
• The directional-coupler-based RGB beam combiner features a compact size of 4.768 mm × 0.062 mm, making it suitable for integration into AR/VR microdisplay systems.
• The entropy weight-TOPSIS method proved effective for multi-parameter optimization, significantly improving device performance compared to single-parameter approaches.
• This design overcomes the low blue-light efficiency (92.1%) of prior directional coupler combiners, enhancing it to 96.63% while maintaining a simple structure and low cost.