Metamaterial for Ultrathin Optical Cavities

New ultrathin nanocavities with embedded silver strips have streamlined color production, and therefore broadened possible bandwidth, for both today’s electronics and future photonics. (Source: A. Kildishev, Purdue U.)

Only using one color of light at a time on an elec­tronic chip currently limits techno­logies based on sensing changes in scattered color, such as detecting viruses in blood samples, or processing airplane images of vege­tation when monitoring fields or forests. Putting multiple colors into service at once would mean deploying multiple channels of infor­mation simul­taneously, broadening the bandwidth of not only today’s elec­tronics, but also of the even faster upcoming nano­photonics rather than slow and heavy electrons to process infor­mation with nanoscale optical devices.

As researchers engineer solutions for even­tually replacing elec­tronics with photonics, a Purdue Univer­sity-led team has simplified the manu­facturing process that allows uti­lizing multiple colors at the same time on an electronic chip instead of a single color at a time. The researchers also addressed another issue in the transition from elec­tronics to nano­photonics: The lasers that produce light will need to be smaller to fit on the chip.

“A laser typically is a mono­chromatic device, so it’s a challenge to make a laser tunable or poly­chromatic,” said Alexander Kildishev, asso­ciate professor of electrical and computer engi­neering at Purdue Uni­versity. “Moreover, it’s a huge challenge to make an array of nano­lasers produce several colors simul­taneously on a chip.” This requires downsizing the optical cavity, which is a major component of lasers. For the first time, researchers from Purdue, Stanford Uni­versity and the Uni­versity of Maryland embedded silver meta­surfaces in nano­cavities, making lasers ultrathin.

“Optical cavities trap light in a laser between two mirrors. As photons bounce between the mirrors, the amount of light increases to make laser beams possible,” Kildishev said. “Our nano­cavities would make on-a-chip lasers ultra­thin and multi­color.” Currently, a different thickness of an optical cavity is required for each color. By embedding a silver meta­surface in the nano­cavity, the researchers achieved a uniform thickness for producing all desired colors.

“Instead of adjusting the optical cavity thickness for every single color, we adjust the widths of meta­surface elements,” Kildishev said. Optical meta­surfaces could also ulti­mately replace or complement tradi­tional lenses in electronic devices. “What defines the thick­ness of any cell phone is actually a complex and rather thick stack of lenses,” Kildishev said. “If we can just use a thin optical meta­surface to focus light and produce images, then we wouldn’t need these lenses, or we could use a thinner stack.” (Source: Purdue U.)

Reference: A. M. Shaltout et al.: Ultrathin and multicolor optical cavities with embedded metasurfaces, Nat. Commun. 9, 2673 (2018); DOI: 10.1038/s41467-018-05034-6

Link: Birck Nanotechnology Center, Purdue University, West Lafayette, USA

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