Unidirectional All-Optical Absorption Switch Based on Optical Tamm State in Nonlinear Plasmonic Waveguide

We demonstrate that unidirectional absorption can be achieved and efficiently tuned in an asymmetrical and nonlinear metal-dielectric-metal plasmonic waveguide by inserting a one-dimensional photonic crystal and a metal layer into the waveguide core. We show that optical Tamm state is excited when the surface impedance of the photonic crystal and that of the metallic layer match with each other. Owing to the strong field confinement induced by the optical Tamm state, high absorption of the surface plasmon can be achieved in the proposed waveguide. The geometric asymmetry of the considered system makes its absorption performance quite different for different incident directions, which is useful for the design of unidirectional plasmonic absorber. Furthermore, Fano resonance, originating from the quantum interference between the optical Tamm state and the traveling waveguide mode, occurs and can be tuned through the nonlinear optical effect. Based on the tunable Fano asymmetric line shape of the considered system, absorption contrast ratio up to 43.5 dB is achieved by varying the intensity of the pumping light, which can be used for all-optical Fano absorption switching. Our results may find potential applications in integrated optical circuits and photodetection.