Researchers from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, in collaboration with the Institute of Semiconductors of CAS, developed a double-layer silicon-based optical phased array (OPA) that significantly expands the scanning range of chip-scale LiDAR systems. The study was published in Scientific Reports.

LiDAR, short for Light Detection and Ranging, enables machines to perceive their surroundings by emitting laser pulses and analyzing the reflected signals. It plays a central role in autonomous driving, intelligent robotics, and high-precision mapping. Conventional LiDAR systems often rely on mechanically rotating mirrors to scan the environment, which increases system size and reduces long-term reliability. Optical phased arrays offer a solid-state alternative. By precisely adjusting the phase of light emitted from many microscopic antennas on a chip, OPAs can steer laser beams electronically at high speed, without moving parts.

Despite this advantage, traditional two-dimensional silicon OPAs have faced a structural limitation. As engineers increase the number of antennas to improve resolution and widen the field of view, the dense network of waveguides needed for independent phase control occupies much of the chip surface. This routing congestion forces the antennas to be spaced farther apart. When antenna spacing becomes too large, unwanted diffraction effects—known as grating lobes—emerge in the far field. These parasitic beams reduce the effective scanning range and degrade beam quality, placing a practical limit on planar integration.

To overcome this bottleneck, the research team adopted a three-dimensional integration strategy. They designed a hierarchical double-layer architecture in which the complex waveguide routing and part of the phase-control system were placed in a lower layer, while the two-dimensional nanoantenna array was arranged in an upper layer. By separating control components from the light-emitting aperture, the design freed valuable in-plane space and enabled a much denser antenna layout. The vertical signal transfer between layers was achieved through optimized interlayer coupling structures, allowing each antenna to maintain independent phase control.

With this approach, the antenna pitch was reduced to 5 micrometers, a compact spacing that is difficult to achieve in conventional single-layer designs. The reduced spacing effectively suppressed grating lobes and expanded the grating-lobe-free scanning range. Performance evaluation demonstrated that the device achieved beam steering over approximately ±18 degrees in the far field. The steered beams showed a well-defined main lobe and controlled side-lobe intensity, indicating stable and predictable optical interference across the array.

Beyond demonstrating a wider scanning angle, the study highlights the broader value of vertical photonic integration. By moving from a purely planar architecture to a stacked configuration, the researchers provided a practical solution to the spatial constraints that have limited high-density OPA development. The design is compatible with established silicon-on-insulator and CMOS fabrication processes, suggesting realistic prospects for large-scale integration.