We investigate theoretically and numerically a model that can achieve narrow-band plasmonic directional excitation in the near-infrared region. The structure is a silver film modified by two uniform metallic slits with a coupled cavity. Our design method is based on the coupled cavity theory, and surface plasmon polaritons (SPPs) interference. The work wavelength region is chosen when the coupled cavity is in resonance. The distance between the two slits is chosen based on SPPs interference. The directional excitation bandwidth can be only 37.9 nm. The finite-difference time-domain method is carried to verify our design method. (C) 2015 Optical Society of America
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