Generation of a narrow linewidth mm-wave signal from two phase-locked DFB lasers that are mutually coupled via four wave mixing

Wireless communication systems require compact sources for the generation of mm-wave signals, that must have high spectral purity (linewidth < 100 kHz, phase noise < 100 dBc @ 100 kHz offset), tuneability, low power consumption and low cost. Other important applications for mm-wave signals are: i) anti-collision car-borne radars (60 GHz); ii) local oscillators for astronomic investigations (100-900 GHz range); iii) THz applications (300-3000 GHz range). The optoelectronic approach based on photomixing is tuneable and scalable, and allows for the propagation along an optical fiber. The major limitation lies in the spectral purity of the generated RF signal that can be hardly reduced below 1 MHz. To achieve a better spectral purity, complex systems have been proposed, that include a reference RF signal source and an opto-electronic feedback loop.