To obtain high-angular-resolution (< 1 milliradian) passive millimeter-wave images using traditional imaging techniques requires prohibitively large apertures for most applications. Sparse aperture techniques present a viable alternative by providing large effective aperture without the corresponding cubic increase in imager volume and weight. However, implementing a large field-of-view, high-resolution, sparse-aperture imager presents a number of challenges, namely: (1) the fabrication of a large number of phase-sensitive, ultra-low-noise millimeter-wave detectors, (2) routing and (3) realtime correlation of acquired data across the array, and (4) implementation of true time delays for steering the field-of-view without pronounced fringe-washing effects. In previous work, we have presented optical upconversion techniques as a viable alternative for overcoming these challenges. Converting passive millimeter-wave energy collected at each point in the array into sidebands on a common optical carrier signal allows for (1) recording of broadband complex field values onto the optical carrier, (2) efficient routing of these field values via fiber optics, (3) correlation of the recorded data via optical filtering and simple optics, and (4) implementation of true time delays using fiber optic or integrated
optical switches. Herein, we present continued theoretical and experimental progress toward the realization of such optically based sparse arrays for passive millimeter-wave imaging applications.