Plasmonic Waveguide based Filter Design with Demultiplexing and Slow Light Capabilities

A new approach to design plasmonic peak filter, notch filter and wavelength demultiplexer is presented in this paper with detailed numerical investigation using the finite difference time domain (FDTD) method. The basic structure of the proposed devices is made up of two rectangular cavities coupled with input and output metal–insulator-metal (MIM) waveguides. The higher and lower mode resonance wavelengths can be conveniently tuned by simply changing the lengths of lower and upper cavities, respectively. It is demonstrated that by changing the radii of the nanorods placed within the cavities, resonance wavelengths can be tuned without increasing the size of the cavities. The transmittance of the peak filter was obtained as high as 76% while the minimum transmission of the notch filter was as low as 1.3%. The 1 × 2 and 1 × 4 demultiplexers, that had been designed based on the basic filters, achieved minimum cross talks of -26.5 dB and -21.5 dB with maximum Q-factors of 37.12 and 53, respectively. Group delays of the basic filter were 0.06 ps and 0.065 ps at 855 nm and 1025 nm wavelengths demonstrating the slow light properties of the designed devices. The proposed filters exhibit excellent transmission characteristics and narrow FWHM values and the proposed demultiplexers show satisfactory performance in terms of peak transmission, Q-factors, FWHM values and crosstalk.