Abstract: An electrically-tunable optical filter has an optical cavity that forms an absorption peak in light that is incident on the filter. The optical cavity includes a layer composed of a material with a high electro-optic coefficient so that the index of refraction of the layer changes in response to a voltage applied by a controller. By adjusting the voltage, the controller can control the index of refraction so that an absorption peak of the filter can be tuned as may be desired without having to alter the physical structure of the filter.

Abstract: An optical filter has a layer of silicon film deposited onto a metallic substrate surface at a silicon film thickness corresponding to a wavelength of light to be filtered from incoming light. The critical coupling of light to the optical cavity formed by the silicon film on metal surface results in a strong and near perfect absorption of the light at a resonance wavelength and strong absorption in the wavelength region near the peak absorption wavelength. Other wavelengths of the incoming wave are reflected by the device so the spectral content of light is changed. By controlling the thickness of the silicon film and/or other factors, such as the extent to which the silicon film is annealed or the type of metal beneath the silicon film, the wavelength of the light absorbed by the silicon film can be precisely controlled.