| The benefits of imaging using regions of the electromagnetic spectrum outside the visible range have been known for decades. Infrared and radio frequency imaging techniques have achieved great successes in both military and civilian applications. However, there remains a range of the spectrum between these two regimes that remains relatively unexplored. Millimeter waves, or the range of wavelengths between one millimeter and one centimeter, have remained relatively unexplored as an imaging technology, largely due to the lack of sufficiently sensitive, practical detectors for passive imaging in this regime. At these short wavelengths, the diffraction limit imposed by the limited extent of the imaging aperture significantly limits attainable image resolution. Recent developments in semiconductor low-noise amplifiers have demonstrated many desirable applications for such imaging technology, but have, as yet, not been able to demonstrate the economical, small-format imagers necessary to make such imagers practical in most of the conceived applications.; In this regard, I present a new approach to millimeter-wave detection based on optical modulation with subsequent carrier suppression. This approach demonstrates promise in achieving the goal of economical, high-resolution imagers with sufficient sensitivity for passive millimeter-wave imaging. In this thesis, I explain the operational requirements of such detectors, provide theoretical background for their operation, and describe current experimental results obtained using commercially available components in the 35 GHz. In addition, I describe successful efforts to fabricate modulators with improved modulation bandwidths for detection in the 95 GHz atmospheric window. These demonstration systems have attained sufficient single pixel performance to detect thermal emission with a noise equivalent temperature difference (NETD) approaching 1K/ Hz at both 35 and 95 GHz. The NETDs attained correspond to sub-picowatt noise equivalent powers which, to the best of my knowledge, have never before been obtained without the use of millimeter-wave low noise amplifiers or cryogenic cooling.; The described optically-based detection technique has also demonstrated unique advantages to overcoming the resolution limits imposed by aperture size. Since the optical upconversion process preserves the phase of the collected energy, coherent imaging methods are possible. This enables the use of distributed aperture imaging, which could potentially provide large effective apertures for high resolution without the associated volumetric scaling associated with traditional focal plane arrays. Optical fiber can be utilized to provide low-loss, dispersion-free routing of the upconverted energy and optical lenses and cameras can be used to reconstruct the sampled image in a relatively simple manner. The combination of these factors offers potential for a uniquely capable millimeter-wave imaging technology based on optical upconversion. As part of this dissertation, I describe the relevant parameters that must be considered in designing such an imager and present results from a prototype array that has been successfully demonstrated. |
