Abstract: An optical spherical Luneburg lens is described which is also useful for millimeter wave and microwave operation, which can provide a multitude of simultaneously acting receiving beams over a hemispherical or spherical field of view. When used in conjunction with surface mounted optical/radio frequency pickup elements, the lens can be employed in a passive target detection system of unique field of coverage and sensitivity. The lens comprises a center sphere of refractive index of approximately .sqroot.2, around which are arranged in concentric shells of aerogel material. The aerogel material of the respective shells is fabricated to obtain a particular index of refraction approximately equal to (2-(r/r.sub.0).sup.2).sup.1/2, where r is the radius of the shell and r.sub.0 is the radius of the lens assembly. The lens can be employed in a system providing dual mode simultaneous optical and radio frequency operation with a single aperture.