Graphene-based fine-tunable optical delay line for optical beamforming in phased-array antennas.

The design of an integrated graphene-based fine-tunable optical delay line on silicon nitride for optical beamforming in phased-array antennas is reported. A high value of the optical delay time (τ_g=920  ps) together with a compact footprint (4.15  mm²) and optical loss <27  dB make this device particularly suitable for highly efficient steering in active phased-array antennas. The delay line includes two graphene-based Mach-Zehnder interferometer switches and two vertically stacked microring resonators between which a graphene capacitor is placed. The tuning range is obtained by varying the value of the voltage applied to the graphene electrodes, which controls the optical path of the light propagation and therefore the delay time. The graphene provides a faster reconfigurable time and low values of energy dissipation. Such significant advantages, together with a negligible beam-squint effect, allow us to overcome the limitations of conventional RF beamformers. A highly efficient fine-tunable optical delay line for the beamsteering of 20 radiating elements up to ±20° in the azimuth direction of a tile in a phased-array antenna of an X-band synthetic aperture radar has been designed.