Abstract This study presents the design and analysis of metal-insulator-metal (MIM) waveguide based optical demultiplexers for optical communication wavelengths. Numerical analyses have been performed using finite-difference time-domain (FDTD) method. The calculated transmission efficiencies are 0.68, 0.66, 0.63, 0.60, and 0.58 at wavelengths of 1241 nm, 1281 nm, 1323 nm, 1368 nm, and 1405 nm, respectively. These wavelengths are highly significant for optical communications. Firstly, a basic ban