Monolithically integrated optical waveguide devices for microwave beamforming

The Army is developing an optically controlled phased-array antenna using waveguide systems for SatCom and terrestrial communication purposes. This system uses a simpler optical phase-shifting scheme to produce the microwave beamforming in the optical domain. The optical beamforming unit receives two perpendicularly polarized light beams separated by the microwave frequency from a laser heterodyne source. The beamforming waveguide circuit y-splits them into n channels and makes individual relative phase-shifts between the two beams at the end of each waveguide channel. At the output of each channel, via a fiber, the light beams beat at a photodetector near each microwave-radiating patch element to generate the heterodyne microwave signal with an appropriate phase for beamforming. The antenna may require from 100 to more than 1000 antenna elements. Therefore, the major challenge for this photonic system is to integrate a large number of passive optical waveguide devices such as splitters with active optical devices like amplifiers and modulators.