Optoelectronic modulation of mm-wave beams using a a semiconductor substrate

Modulation of millimeter and submillimeter-wave beams via an optically excited semiconductor substrate is a potentially powerful technique, but typically requires high optical illumination densities. Various methods are outlined that yield reduced illumination levels and enable optimization of the substrate. As an example device, the photo-injected Fresnel zone plate antenna (piFZPA) is presented, and we discuss the realization of this spatial modulating device at millimeter-wave frequencies. Preliminary data is presented demonstrating the realization of a 100-mm aperture F/1.2 piFZPA at 94 GHz, using a retail visible data projector as a programmable broadband light source and spatial light modulator. The demonstrated antenna can be steered precisely in two dimensions and yielded a 36-dBi directivity with excellent mainlobe symmetry, and a 12-dB peak sidelobe level.