A tunable plasmonic filter or an optical filtering method discloses plasmonic filter structure and a voltage or current source. An intensity or wavelength of light transmitted through the filter structure is modulated by the intensity of a voltage or current from the voltage or current source. The plasmonic filter structure is located between electrodes electrically connected to the voltage or current source. The plasmonic filter structure is configured such that the incident light is resonant with at least one plasmonic mode on the structure, and a predetermined wavelength will perturb the metallic plasmonic structure in surface plasmon on energy bands for the wavelength selective transmission of light.