ObjectiveLidar systems based on metasurfaces are currently popular research topics. The development of lidar systems relying on traditional optical components has encountered a bottleneck, and the stacked optical component structure limits further miniaturization and integration. Recent advancements in metasurface research are seen as a promising alternative to traditional lidar technology. Metasurface-based lidar systems are expected to integrate lidar functionalities—such as light emission, scanning, and detection—into a single CMOS chip, paving the way for compact chip-level lidar sensors. However, existing infrared lidar-band metasurfaces typically use high refractive index materials, such as titanium oxide, as the antenna material, which limits their integration on CMOS-compatible chips. To address this issue, this paper explores the design of metasurfaces using CMOS-compatible materials for the 905 nm lidar band.
MethodsUsing the electromagnetic simulation software FDTD, we performed scans to determine the optimal period and antenna height for metasurfaces designed with the CMOS-compatible material silicon nitride. Additionally, we replaced cylindrical pillars with square posts to increase the antenna duty cycle. Furthermore, we simulated the performance of metasurfaces with different focal lengths under the same aperture, analyzing how their performance varied with the
f-number. We also investigated the impact of dispersion on the focusing ability of the metasurfaces under broadband conditions.
Results and DiscussionsComparing the focusing performance of the metasurfaces with the same aperture but different focal lengths (Fig.5), it is evident that when the f-number of the metasurface is in the range of 0.6 to 5, the metasurfaces exhibits minimal focal length deviation, high focusing efficiency, and a resolution close to the diffraction limit. The broadband dispersion results of the metasurfaces (Fig.6) show that within the bandwidth and central wavelength shift range of the existing lidar source, the metasurface is able to achieve imaging close to the diffraction limit.
ConclusionsIn this paper, we have introduced a method for designing metasurfaces using the low-contrast material silicon nitride, which is compatible with CMOS technology in the 905 nm lidar band. We employed square posts instead of the commonly used cylindrical nanopillars as antennas to increase the maximum duty cycle, achieving a low aspect ratio design. The framework we developed is applicable for designing arbitrary spatial phase profiles, similar to previous designs, and brings metasurface optics fully into the lidar spectrum. We then simulated metasurfaces with different focal lengths under the same aperture to analyze their performance in terms of focal length deviation, focusing ability, and efficiency with respect to
f-number. Additionally, we examined the impact of laser source bandwidth and dispersion on metasurface performance. The use of silicon nitride extends the material options for metasurface optical devices, enabling the fabrication of metasurfaces compatible with widely used CMOS manufacturing processes. This advancement is crucial for the further integration and miniaturization of lidar systems, facilitating the realization of ultra-compact chip-level lidar sensors and opening up new possibilities for a wide range of applications.