Electronically tunable color filter with surface plasmon waves

Last year, we reported a novel phenomenon of voltage-induced color-selective absorption with surface plasmons. When a white light is incident on a metal/EO material interface, in certain condition, surface plasmon waves can be excited; those photons in surface plasmon resonance wavelength range would be totally absorbed and these photons out of the surface plasmon resonance wavelength range would be almost totally reflected. This surface plasmon resonance depends on the dielectric constants of both the metal and the EO material. If a voltage is added on the EO material to change its dielectric constant,the surface plasmon resonance spectrum can be shifted from one wavelength to the other, and this is a tunable notch filter. If coupled surface plasmon waves are used, a tunable bandpass filter can be built. A prototype mode has been built using liquid crystal as the EO material. Experiment results, which has excellent agreement with theory, has shown that the wavelength tunable range can cover almost all of the visible when 30-v voltage is applied. Theoretical calculation has shown that this tunable filter can also work in IR range up to at least 10 micrometers .