The present invention relates to a tri wavelength diffraction modulator (TWDM) and a method of tri wavelength diffraction modulation. The tri wavelength diffraction modulator includes: a stationary substrate with a bottom electrode plate formed on top of the stationary substrate; a first electrode plate comprising a first suspended beam suspended in parallel above the stationary substrate and a first connection anchored onto the stationary substrate; and a second electrode plate comprising a second suspended beam suspended in parallel above the first electrode plate and a second connection anchored onto the stationary substrate. The diffraction modulator and the method for diffraction modulation are suitable to projection system.