Zero-index metamaterial could boost on-chip photonics

On-chip photonics may have gotten a boost thanks to researchers at Harvard and Peking University. “We designed and fabricated an on-chip integrated metamaterial with a refractive index of zero in the optical regime,” they report in a paper in the November issue of Nature Photonics. Such metamaterials exhibit infinite phase velocity and wavelength. The researchers’ implementation consists of low-aspect-ratio gold-film-clad silicon pillar arrays on a silicon-on-insulator (SoI) substrate embedded in a polymer matrix. The structure, they report, can be fabricated using standard planar processes.

The researchers note that previously, zero-index metamaterials have been demonstrated with out-of-plane geometries. Their design enables an in-plane geometry with light confined on-chip, supporting integration with optical elements such as waveguides, resonators, and interferometers.

The researchers conclude, “This design enables direct implementation of zero-index phenomena on a chip, including super-couplers, surface-emitting lasers, and new approaches for phase-matching in nonlinear optics, It can also serve as an on-chip lab to explore fundamental science such as photon entanglement and enhancement of spontaneous emission.”

The paper, “On-chip zero-index metameterials,” by Yang Li, Shota Kita, Philip Muñoz, Orad Reshef, Daryl I. Vulis, Mei Yin, Marko Loncar, and Eric Mazur, can be downloaded here.

Kevin Hartnett in The Boston Globe takes a look at potential practical applications, including optical computing, but the remaining challenges are significant. He quotes Alessandro Salandrino, an electrical engineer at the University of Kansas, as saying, “Changing to a completely photonic system implies computing completely with photons, which obey different laws compared to electrons. We have to rethink the whole process.”

Hartnett quotes Mazur as saying that with the metamaterial, “You can squeeze [light] down instantly, twist it, bend it. It’s the perfect coupling between a nanoscale circuit and ordinary connections. It opens the door to a much better interface between nanophotonics and world we live in.”