Design of GST Phase Only Pixel Metasurfaces for Beam Steering at Optical Telecom wavelength

Metasurfaces are pivotal in developing miniaturized beam steerers and optical elements capable of precise light manipulation. This work details the design and optimization of tunable reflective metasurfaces based on the phase-change material GeSeTe (GST) for beamforming applications at the telecom wavelength of 1550 nm. The proposed metasurface architecture integrates multi-layered gold and GST structures on a silicon substrate, engineered to achieve almost pure phase control with minimal spurious loss modulation. Utilizing rigorous coupled wave analysis (RCWA) simulations combined with a tailored optimization function, we identified key geometric parameters that maximize reflectance while ensuring a \(\pi\)-phase delay between the amorphous and crystalline states of GST. The far-field beam steering capabilities were validated through finite element method (FEM) simulations for both binary and ternary phase modulation configurations, demonstrating precise angular control and reduced side lobes. Furthermore, a comparative evaluation of various chalcogenide PCM candidates — assessing switching energy, speed, and optical properties — confirmed GST as the most suitable option, despite its relatively higher extinction coefficient. These findings pave the way for high-speed, low-energy, and finely controllable optical beam steering devices, crucial for next-generation photonic systems such as LIDAR and advanced optical transceivers.