Frequency-Agile Heterodyne-Driven MMW Signal Generator

Conventional generation of a high-quality RF carrier (signal) beyond 50GHz requires high precision cavity engineering that inherently restricts contiguous bandwidth coverage. Worse, even if one were capable of fabricating a set of such stabilized, frequency-dense cavities to mimic discrete 30-120GHz band coverage, the absence of wideband electrical gain in this range would invalidate such an approach. Recognizing this basic limitation, the proposed work will generate a high-quality tunable signal by heterodyning phase-correlated optical tones combining high power and low noise. In contrast to conventional RF-photonics approaches, a high quality tunable RF signal will be derived from a single, shot-noise-limited master oscillator. The new technique unifies, for the first time, the low-noise characteristics of highly coherent master oscillators and high-power heterodyning. In simple terms, the approach combines high-power emitters with very low RIN characteristics, without resorting to high-resonance cavity construction. Specifically, the novelty of the proposed work is reflected in: (a) the first use of tunable injection locking to guarantee true frequency agility to the 300GHz range and beyond; (b) combined phase-noise inhibition and high-power scaling that is otherwise not possible in conventional shot-noise-limited oscillators; and (c) nearly lossless, fiber distribution of the tunable RF carrier with absolute phase reference.