Plasmonic multi-channel filters with separately tunable pass-bands

A tunable multi-channel plasmonic filter based on the metal-insulator-metal (MIM) structure of rectangular cavities is proposed and numerically investigated by the two-dimensional finite difference time domain (2D FDTD) method. Proper positioning of the output waveguides according to the distribution of the inside fields of the cavity makes it possible to separate modes and output single-wavelength pass-bands. Also, creating a notch in the middle of the cavity changes its effective length for the second mode. Hence, the first and second modes of the cavity can be tuned separately by adjusting the length of the cavity and the height of the central notch. Such a tunable filtering characteristic of the rectangular cavity provides the ability to select all pass-bands of introduced two, four and six-channel filters at telecommunication range using the minimum number of cavities. The proposed structure is efficient and promising for the design of subwavelength tunable multi-channel filters and demultiplexing systems, and has potential applications in nanoscale integrated photonic circuits in optical telecommunications.