Dynamic Frequency Passive Millimeter-Wave Radiometer Based on Optical Up-Conversion

In the proposed effort, we will leverage this extensive experience and capabilities to realize a frequency agile mmW radiometer that can cover the range of DC-110 GHz and can be scaled to DC-200 GHz under Phase II. Ours is a photonic system that multiplies and up-coverts a low-frequency reference signal onto an optical carrier (laser) using EO modulation, then uses the modulation sidebands to injection lock a second laser to a frequency offset from the first by a selectable multiple (harmonic) of the reference. Because the EO modulation process is both (a) coherent, and (b) ultra-broadband, the second laser becomes coherent (phase-locked) to both the first laser and the reference, while oscillating at an offset from the first laser that can be quickly and easily turned over the entire mmW band. An antenna is used to collect the incident mmW energy onto another EO modulator which induces side bands onto the primary laser carrier frequency which are proportional in amplitude to the incident mmW energy. This signal is combined with the second laser on a photodiode which mixes the two signals in a homodyne detection approach. The second laser can be thermally turned to different harmonics which allows it to interrogate the primary laser signal which contains the mmW sidebands. The output at the photodiode is low pass filtered and the DC term is now proportional to the mmW energy at the frequency selected by the second laser.