High capacity optical beam forming for phased arrays with fiber gratings and frequency conversion for beat noise control

A new wavelength division multiplexing grating-based beam-forming architecture for phased arrays that can achieve the minimum possible number of optical interconnects is presented. A reduction in interconnect hardware of 99.6% is obtained for a 512-beam array, which is, as far as we know, the lowest number of interconnects reported to date. Analysis of the ultimate beam capacity limit of the beam former shows that the beat noise interference limitation is the most important factor. We present a new hybrid frequency-converting optical beam former that removes the fundamental beat noise limitation. This frequency downconverts the rf signal to an intermediate frequency before performing the true-time-delay equalization in the optical domain. The resulting advantage of reduced optical bandwidth per channel enables more wavelengths to be used for a given wavelength span, resulting in an increased beam capacity. A greater than sevenfold increase in beam capacity is demonstrated through the use of the frequency conversion technique, with 960 beams synthesized at 12.4 GHz, showing a 99.8% reduction in required interconnects.