Millimeter‐Scale Grating Antenna Harnessing Bosund State in the Continuum for Sub‐mrad‐Resolution Lithium Niobate Optical Phased Array

Optical phased arrays (OPAs) with high‐resolution and high‐speed beam steering are highly desirable for next‐generation light detection and ranging (LiDAR) and free‐space optical (FSO) communication systems. However, conventional thin‐film lithium niobate (TFLN) OPAs exhibit relatively large beam divergence due to their limited antenna apertures. Here, we propose and experimentally demonstrate an sub‐mrad‐resolution and high‐speed 64‐channel TFLN OPA, harnessing bound state in the continuum (BIC) enabled millimeter‐scale waveguide grating antenna for the first time. By leveraging the diffraction modulation capabilities of BIC, parasitic sidewall emission is effectively suppressed, which allows for an enlarged effective aperture while maintaining high radiation efficiency. Moreover, all elements are fabricated via only a single‐step etching process, which significantly reduces fabrication complexity. Experimental characterization demonstrates an ultra‐narrow beam divergence of 0.698 mrad, enhancing the far‐field resolution by an order of magnitude compared to all reported high‐speed OPAs to date. Over the entire steering range, the side lobe suppression ratio (SLSR) averages 8.69 dB and reaches a peaking value of 12.17 dB. Prototype verification demonstrates a 24 Gbps non‐return‐to‐zero (NRZ) on‐off‐keying (OOK) FSO communication system using the fabricated TFLN OPA, revealing its potential for low‐power‐consumption, high‐data‐rate optical communication.