Applications of optical upconversion to sparse aperture millimeter-wave imaging

Passive millimeter-wave imagers have shown significant potential for use in applications that require penetration through atmospheric obscurations such a fog and smoke. However, the large apertures required to achieve sufficient diffraction-limited resolution in such systems often prohibit their use for many applications. One possible technique to circumvent this limitation is to use sparse-aperture imaging techniques. To date, such systems have not been realized because they require a high number of phase-sensitive, low-noise detectors spread over a large physical area. Collection and correlation processing of the data from this large array of sensors has not been practical using available technologies. Herein, we present the potential of optical upconversion detectors for sparse aperture imaging. The optical signals generated in such detectors preserve the phase information of the detected signal up until photodetection and may be easily routed to a central processor using low-loss optical fiber. Potential architectures for sparse aperture imagers using optical upconversion are discussed and compared to more traditional down-converted approaches. In addition, experimental results demonstrating the viability of such imagers are presented.