Photonic terahertz phased array via selective excitation of nonlinear Pancharatnam-Berry elements.

Phased arrays are crucial in various technologies, such as radar and wireless communications, due to their ability to precisely control and steer electromagnetic waves. This precise control improves signal processing and enhances imaging performance. However, extending phased arrays to the terahertz (THz) frequency range has proven challenging, especially for high-frequency operation, broadband performance, two-dimensional (2D) phase control with large antenna arrays, and flexible phase modulation. Here, we introduce a photonic platform to realize a THz phased array that bypasses the above challenges. Our method employs 2D phase coding with 2-bit across a broad THz frequency range from 0.8 to 1.4 THz. The core of our design is a pixelated nonlinear Pancharatnam-Berry (PB) metasurface driven by a spatially modulated femtosecond laser for selective excitation of the desired PB elements, allowing precise phase and wavefront control of the emitted THz signals. We showcase the effectiveness of our method through four proof-of-concept applications: single beamforming, dual beamforming, imaging, and vortex beam generation. The realized photonic platform provides a promising pathway for developing broadband phased arrays in the THz regime.