Researchers at Columbia Engineering have invented a highly efficient method to control light propagating in confined pathways, also known as waveguides, by using nano-antennas.
Photonic integrated circuits (ICs) are based on light propagating in optical waveguides. Controlling light propagation is currently a major obstacle when it comes to building the chips. These chips use light instead of electrons to transport data and the method the team has developed could lead to faster, more powerful and efficient optical chips that could transform optical communications and signal processing.
The optical power of light waves spreading along waveguides is limited within the core of the waveguide. Currently, researchers can only access the guided waves by way of the small evanescent “tails” that exist near the waveguide surface. These guided waves are difficult to work with, For this reason, photonic integrated devices have been large and take up space, limiting the device integration density of a chip. Creating these photonic integrated devices in smaller sizes is the main challenge that researchers long to overcome within their work.
"We have built integrated nanophotonic devices with the smallest footprint and largest operating bandwidth ever," said Nanfang Yu Applied Physics Assistant Professor, Columbia University. "The degree to which we can now reduce the size of photonic integrated devices with the help of nano-antennas is similar to what happened in the 1950s when large vacuum tubes were replaced by much smaller semiconductor transistors. This work provides a revolutionary solution to a fundamental scientific problem: How to control light propagating in waveguides in the most efficient way?"
What Yu’s team discovered is that the most efficient way to control light in waveguides is to decorate the waveguides with optical nano-antennas. Using this method, the miniature antennas pull light from the waveguide core, modify the light’s properties, and release light into the waveguides. The effect of a densely packed array of nano-antennas is so strong that they could achieve functions such as waveguide mode conversion with propagation distance no more than twice the wavelength.
What the researchers have created are waveguide mode converters that change a certain waveguide mode to another waveguide mode. These key enablers of a technology are called “mode-division multiplexing” (MDM). An optical waveguide can support a fundamental waveguide mode and a set of higher-order modes. MDM is a strategy that substantially augments and optical chip’s information processing power.
Next, Yu aims to incorporate actively tunable optical materials into photonic integrated devices to enable active control of light propagating in waveguides, which would lay the foundation for These fully functional augmented reality glasses. In addition, he aims to explore the conversion of waves propagating in waveguides into strong surface waves, which could be used for on-chip chemical and biological sensing.
The study, titled “Controlling Propagation and Coupling of Waveguide Modes Using Phase-Gradient Metasurfaces” has been published online in Nature Nanotechnology.