Bowtie Photonic Crystal Allows Extreme Light Concentration with Low Loss

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A new nanostructure that is part bowtie and part funnel has been shown to focus and conduct light powerfully and nearly indefinitely, as measured by a scanning near-field optical microscope. The bow-tie photonic structure, developed by a team at Vanderbilt University, allows light to be squeezed into very small volumes, which yield very high levels of energy. The Vanderbilt team collaborated with researchers at the IBM T.J. Watson Research Center and the University of Technology in Troyes, France, to fabricate the device.

The research is based on Maxwell’s equations, a 19th-century text familiar to college physics students. By applying these equations in a new way and structuring materials at the nanoscale, the size of the bowtie structure is just 12 nm, the researchers developed a low-loss, dielectric bowtie photonic crystal structure that could support mode volumes commensurate with plasmonic elements.

To create the bowtie shape, the researchers combined a nanoscale air slot surrounded by silicon with a nanoscale silicon bar surrounded by air.

The team believes that its approach could open the door to the extremely strong light-matter interaction regime that incorporates both an ultralow mode volume and an ultrahigh quality factor. The strong light-matter interaction platform could be used in a range of applications, including low-power optoelectronics, nonlinear optics, and quantum optics.

“The use of the bowtie shape concentrates the light so that a small amount of input light becomes highly amplified in a small region,” said professor Sharon Weiss. “We can potentially use that for low-power manipulation of information on computer chips.”

Researcher Shuren Hu said there are generally two ways to increase optical energy density: Focus light down to a small tiny space and trap light in that space as long as possible. “It has been a prevailing belief in photonics that you have to compromise between trapping time and trapping space,” said Hu. “The harder you squeeze photons, the more eager they are to escape.”

The researchers will continue work on improvements to the device and explore its possible application in future computer platforms.

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