A plasmonic switching device and method of providing a plasmonic switching device. An example device includes a resonant cavity and an electromagnetic radiation feed arranged to couple electromagnetic radiation into the resonant cavity and at least one plasmonic mode. The resonant cavity is arranged to be switchable between: a first state in which the resonant cavity has an operational characteristic selected to allow resonance of the electromagnetic radiation at a frequency of the at least one plasmonic mode; and a second state in which the operational characteristic of the resonant cavity is adjusted to inhibit resonance of the electromagnetic radiation at a frequency of the at least one plasmonic mode.