The extraordinary transmission of light through a vertical nanoslit in a metal film is enhanced by introducing a nanocavity antenna formed by a nearby metallic nanostrip over the slit opening. For a fixed wavelength, the width of the metallic nanostrip should be chosen to make the horizontal metal–insulator–metal waveguide of finite length resonant as a Fabry–Perot cavity. When such a cavity antenna is used to enhance the transmission through a nonresonant nanoslit, the slit should be opened at a position with a maximal magnetic field in the horizontal resonant cavity. It is shown that an optimized cavity antenna can enhance greatly the transmission of light through a nonresonant nanoslit (by about 20 times) or a resonant nanoslit (by 124%). Such a transmission enhancement with a nanocavity antenna is studied for the first time, and the physical mechanism is explained.
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