On-chip metalens-based beamformer enabling in-situ beamforming in a silicon optical phased array

This study proposes a Si-based optical phased array integrated with an on-chip metalens-based beamformer (OCMB) that enables in-situ beamforming, resorting to no external imaging systems. The OCMB is connected to a grating antenna array and comprises a diffraction region, an on-chip metalens (OCM), and multiple monitoring ports. The residual beam that remains after emission from the antenna is guided into the OCMB to monitor the free-space far-field patterns. The OCM possesses a relatively high numerical aperture, enabling it to focus the beam within the diffraction region and thereby determine its overall length. The focused beam then propagates toward monitoring ports that are located at the beam positions corresponding to phase differences of 0, ±π/2, and ±π between adjacent channels. The monitoring performance was experimentally verified by comparing the far-field patterns emitted from the grating antenna with the intensity distribution radiated from the monitoring ports. The proposed structure simultaneously enables in-situ beamforming and miniaturization of monitoring systems, with potential for practical implementation in compact photonic platforms.