Semiconductor metasurfaces have emerged as a transformative technology for beam steering applications, offering compact, lightweight, and high-performance alternatives to conventional optical components. By leveraging subwavelength nanostructures made of germanium (Ge), silicon (Si), or III-V materials, these metasurfaces enable precise control over light propagation through engineered phase gradients. Their applications span LiDAR, optical communications, and augmented reality (AR), where dynamic and efficient beam manipulation is critical.

The fundamental principle behind semiconductor metasurfaces for beam steering lies in the local phase modulation of incident light. Each nanostructure, or meta-atom, introduces a spatially varying phase shift, creating a phase gradient across the surface. This gradient deflects the incident beam according to the generalized Snell’s law, allowing for arbitrary wavefront shaping. Semiconductor materials are particularly advantageous due to their high refractive indices, low optical losses, and compatibility with existing fabrication processes. Ge and Si operate efficiently in the near-infrared (NIR) and short-wave infrared (SWIR) ranges, while III-V materials like gallium arsenide (GaAs) and indium phosphide (InP) extend functionality into the visible and mid-infrared spectra.

In LiDAR systems, semiconductor metasurfaces provide a solid-state solution for beam steering, eliminating the need for bulky mechanical components. A phase-gradient metasurface composed of Si nanopillars can achieve deflection angles exceeding 60 degrees with efficiencies above 80% at 1550 nm, a wavelength commonly used in automotive LiDAR. The absence of moving parts enhances reliability and reduces power consumption, critical for autonomous vehicles. Additionally, tunable metasurfaces incorporating III-V materials enable dynamic beam steering through carrier injection or thermo-optic effects, allowing real-time adaptation to environmental conditions.

Optical communications benefit from the high-speed and low-loss characteristics of semiconductor metasurfaces. In fiber-optic networks, beam steering elements based on Ge or Si metasurfaces can route signals with minimal insertion loss, improving data transmission efficiency. For free-space optical links, metasurfaces enable precise alignment and multiplexing of optical beams, enhancing bandwidth and reducing cross-talk. Experimental demonstrations have shown that InP-based metasurfaces can achieve sub-degree beam steering accuracy at telecommunication wavelengths, making them suitable for next-generation photonic integrated circuits.

Augmented reality displays require ultra-compact and high-resolution beam steering to project virtual images onto the user’s field of view. Semiconductor metasurfaces address this need by enabling wide-angle deflection with minimal aberrations. For instance, GaAs metasurfaces designed for visible wavelengths can achieve diffraction-limited performance across a 50-degree field of view, critical for immersive AR experiences. The ability to integrate these metasurfaces with micro-LEDs or laser diodes further simplifies the optical architecture, paving the way for lightweight AR glasses.

The design of phase-gradient metasurfaces involves optimizing the geometry and arrangement of nanostructures to achieve the desired phase profile. Common configurations include dielectric nanopillars, nanofins, and grating couplers, where the dimensions of each element are tailored to provide the requisite phase shift. For example, a Si nanofin with a height of 600 nm and varying cross-sectional dimensions can cover the full 2π phase range at 1310 nm. Advanced optimization algorithms, such as inverse design and machine learning, further enhance performance by identifying non-intuitive geometries that maximize efficiency and bandwidth.

Fabrication of semiconductor metasurfaces relies on lithographic techniques such as electron-beam lithography (EBL) or deep ultraviolet (DUV) lithography, followed by dry etching processes. High-aspect-ratio nanostructures with smooth sidewalls are essential to minimize scattering losses. Recent advances in nanoimprint lithography and self-assembly techniques offer scalable alternatives for mass production, though challenges remain in achieving uniformity over large areas.

Despite their promise, semiconductor metasurfaces face several challenges. Material absorption at shorter wavelengths limits efficiency in visible-light applications, while fabrication tolerances become increasingly stringent at smaller feature sizes. Thermal stability is another consideration, particularly for high-power applications where thermo-optic effects may degrade performance. Ongoing research focuses on hybrid designs combining multiple semiconductor materials to mitigate these limitations.

In summary, semiconductor metasurfaces represent a versatile platform for beam steering, with significant potential in LiDAR, optical communications, and AR. Their ability to manipulate light with high precision and efficiency, coupled with compatibility with existing semiconductor technologies, positions them as a key enabler of future optoelectronic systems. Continued advancements in design methodologies and fabrication techniques will further expand their capabilities, driving innovation across multiple industries.