Metasurfaces are advancing our ability to manipulate light in various ways, but so far, their applications have been mostly limited to controlling light in free space. Researchers have tried integrating metasurfaces on guided-wave photonic systems, which allow for more precise control of light scattering off-chip, including manipulation of its amplitude, phase, or polarization. However, these attempts have only been able to control one or two optical degrees of freedom at best and often result in more complex device configurations compared to conventional grating couplers.
In this study, researchers from Columbia University introduce leaky-wave metasurfaces, a new material platform constructed from specially designed photonic crystal slabs with modified symmetry. This alteration enables them to possess unique light-related properties that exist continuously within a specific range, known as quasi-bound states. These metasurfaces offer a compact form factor, similar to that of grating couplers, but provide full control over the amplitude, phase, and polarization (four optical degrees of freedom) across large apertures. They have developed devices that can control phase and amplitude at a fixed polarization state, as well as devices that can control all four optical degrees of freedom for operation at a wavelength of 1.55 micrometers.
By merging the fields of guided and free-space optics through the hybrid nature of quasi-bound states in the continuum, these leaky-wave metasurfaces could have applications in various fields such as imaging, communications, augmented reality, quantum optics, LIDAR, and integrated photonic systems.
“We are excited to find an elegant solution for interfacing free-space optics and integrated photonics–these two platforms have traditionally been studied by investigators from different subfields of optics and have led to commercial products addressing completely different needs,” said Nanfang Yu, associate professor of applied physics and applied mathematics who is a leader in research on nanophotonic devices. “Our work points to new ways to create hybrid systems that utilize the best of both worlds–free-space optics for shaping the wavefront of light and integrated photonics for optical data processing–to address many emerging applications such as quantum optics, optogenetics, sensor networks, inter-chip communications, and holographic displays.”
By leveraging the unique properties of leaky-wave metasurfaces, researchers may be able to develop more efficient, high-resolution, and compact holographic display systems in the future. This could lead to advancements in areas such as entertainment, virtual reality, augmented reality, and various other visual technologies.
Reference
Huang, H., Overvig, A. C., Xu, Y., Malek, S. C., Tsai, C.-C., Alù, A., & Yu, N. (2023). Leaky-wave metasurfaces for integrated photonics. Nature Nanotechnology, 1–9. https://doi.org/10.1038/s41565-023-01360-z
