Integrated Optical True Time Delay Network Based on Grating-Assisted Contradirectional Couplers for Phased Array Antennas

Phased array antennas (PAAs) play a key role in many fields such as radar systems and wireless communication systems. Since PAAs based on optical methods outperform the electronic counterparts in beam directivity and instantaneous bandwidth, optical PAAs have aroused wide research interests. Here, we report and experimentally demonstrate an integrated 4-channel optical true time delay network for PAAs. The true time delay unit is based on a grating-assisted contradirectional coupler, assisted by index chirp engineering and asymmetric apodization. A linear group delay with both positive and negative dispersion coefficients can be obtained. For the 4-channel time delay network, the measured dispersion coefficient of each channel is 10.35, 4.00, -4.32 and -14.38 ps/nm with 7 nm available bandwidth, respectively. The calculated beam scanning angle can range from 36.4 degree to -33.9 degree for the beam steering. This time delay network can be extended to large scale with more delay units and cascaded structures, thus wider scanning range and better beam directivity can be achieved.