A three-dimensional plasmonic wavelength demultiplexer is investigated using slit- and stub-type filters consisting of metal–insulator–metal waveguides. To achieve a narrow bandwidth of the slit-type filter, a dielectric material is inserted into the slit section and the metal thickness is deliberately chosen to be 0 . 2 μ m . Then, a demultiplexer is considered with the two filters being placed in parallel. Numerical results show that a separation of 18.9 dB between the two output ports is obtained at 1 . 31 μ m , while it is only 9.8 dB at 1 . 55 μ m . To improve the separation, stub sections forming an attenuation pole are introduced into the waveguides. It is found that the separation is successfully improved to more than 20 dB at both wavelengths. All calculations are performed using the finite-difference time-domain method based on the trapezoidal recursive convolution technique.
