A prism device includes: a prism material having substantially the same index of refraction at first and second wavelengths; a first anti-reflection coating for reducing reflection of a first signal beam at the first wavelength; and a second anti-reflection coating for reducing reflection of a second signal beam at the second wavelength. The prism material can be silicon, which has substantially the same index of refraction at IR and RF wavelengths. In this case, the RF anti-reflection coating can be a layer of silicon dioxide (fused silica), which can be sandwiched between two IR anti-reflection coatings designed to minimize IR reflections between the surrounding air and the RF anti-reflection coating and between the RF anti-reflection coating and the prism material, respectively. Two or more of the prism devices can be used in a beam steering system to simultaneous direct the first and second signal beams in substantially the same direction.