Provided are a high-speed optical modulator and a method of modulating light by using the same. The optical modulator includes first and second resonance cavities that are sequentially stacked on a transparent substrate, wherein the first and second resonance cavities each include an electric-optical layer. According to the method, first and second voltages having different sizes are simultaneously applied respectively to the first and second resonance cavities, and then for the other configuration of the modulator mutually interchanged voltages are applied.