Leaky-wave metasurfaces: A perfect interface between free-space and integrated optical systems

Because the devices are so thin, transparent, and compatible with (PICs), they can be used to improve optical displays, LIDAR (Light Detection and Ranging), optical communications, and quantum optics.

"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."

Bridging free-space optics and integrated photonics

The key challenge of interfacing PICs and free-space optics is to transform a simple waveguide mode confined within a waveguide—a thin ridge defined on a chip—into a broad free-space wave with a complex wavefront, and vice versa. Yu's team tackled this challenge by building on their invention last fall of "nonlocal metasurfaces" and extended the devices' functionality from controlling free-space light waves to controlling guided waves.

Left: Schematic showing the operation of a leaky-wave metasurface. Right: A 2D array of optical spots forming a Kagome pattern that is produced by a leaky-wave metasurface. Credit: Heqing Huang, Adam Overvig, and Nanfang Yu/Columbia Engineering

Left: Photo of two leaky-wave metasurfaces for generating Kagome lattices. Right: SEM image of a portion of a leaky-wave metasurface, which is composed of nano-apertures etched into a polymer layer on top of a silicon nitride thin film. Credit: Heqing Huang, Adam Overvig, and Nanfang Yu/Columbia Engineering

Left two figures: Two holographic images produced by a leaky-wave metasurface at two different distances from the device surface. Right four figures: Four distinct holographic images produced by a single leaky-wave metasurface at two different distances from the device surface and at two orthogonal polarization states. Credit: Heqing Huang, Adam Overvig, and Nanfang Yu/Columbia Engineering