A modulator for modulating incident rays of light, the modulator comprising a plurality of equally spaced apart beam elements, each of which includes a light reflective planar surface. The elements are arranged parallel to each other with their light reflective surfaces parallel to each other. The modulator includes means for supporting the beam elements in relation to one another and means for moving the beam elements relative to one another so that the beams move between a first configuration wherein the modulator acts to reflect the incident rays of light as a plane mirror, and a second configuration wherein the modulator diffracts the incident rays of light as they are reflected therefrom. In operation, the light reflective surfaces of the beam elements remain parallel to each other in both the first and the second configurations and the perpendicular spacing between the reflective surfaces of adjacent beam elements is equal to m/4 times the wavelength of the incident rays of light, wherein m=an even whole number or zero when the beam elements are in the first configuration and m=an odd number when the beam elements are in the second configuration.