Plasmonic wavelength splitter based on a metal–insulator–metal waveguide with a graded grating coupler

A plasmonic wavelength splitter based on a sub-wavelength metal–insulator–metal (MIM) periodic rectangle wrinkle waveguide with a graded grating coupler is theoretically analyzed and experimentally demonstrated. The surface plasmon polaritons (SPPs), excited in the metal grating with wavelength selection, are deflected by the graded difference according to the aplanatic parametric principle. The wave vector of the deflected SPPs meets the phase-matching condition and couples into the periodic rectangle wrinkle waveguide with a plasmonic bandgap. The characteristic of the plasmonic wavelength splitter is simulated by finite difference time domain (FDTD) simulation, which agrees well with the theoretical analysis. By electron beam lithography and ion beam etching process, the plasmonic wavelength splitter was fabricated. The SPPs excited by incident 650 and 832 nm were successfully split and guided to opposite directions of the MIM waveguide with extinction ratios of 27.5 dB and 32.7 dB, respectively, which was observed under an optical microscope using a CCD camera. The proposed wavelength splitter is simple fabricated and has a large coupling aperture by utilizing the graded grating coupler.