The optical multiplexer was created at a nanoscale plasmonic structure utilizing the finite element method (FEM) with COMSOL version 5.5 software to enable maximum light confinement, high-speed optical systems, and a tiny structure. The metal-insulator-metal technology at a nanoscale dimension is used for creating the 4×1 multiplexer. In this design, the transmission threshold (T t h r e s h o l d ) is selected to be 100% for separating between logic "1" and logic "0" at a 1310 nm operating wavelength. The modulation depth (MD), contrast ratio (CR), and insertion loss (IL) characteristics were explained to evaluate the performance of the multiplexer. The CR has 3.48 dB, the MD offers an ideal performance with 95.28 %, and the IL has 3.31 dB.