Nanophotonics Looks to Engineering for Improved Efficiency

04 January 2018
Polaritons propagating through a flake of hexagonal boron nitride (hBN). Image credit: U.S. Naval Research Laboratory.

Nanophotonic devices, which confine light to very small dimensions, have a broad range of direct applications including ultra-high-resolution microscopes, solar energy harvesting, optical computing and targeted medical therapies.

It was recently learned that hexagonal boron nitride (hBN), a compound with an atomically-thin lattice consisting of boron and nitrogen atoms, is an ideal substrate for two-dimensional materials. It also holds a great deal of promise as an optical material for use in infrared nanophotonics.

Yet previous work with hBn showed limits to its transmission efficiency. That may change thanks to the work of a team of physicists headed by the U.S. Naval Research Laboratory.

"We have demonstrated that the inherent efficiency limitations of nanophotonics can be overcome through the careful engineering of isotopes in polar semiconductors and dielectric materials," said Dr. Alexander J. Giles, research physicist, NRL Electronics Science and Technology Division.

Why Mess with the Isotopes?

Naturally-occurring boron is comprised of two isotopes, boron-10 and boron-11, which have a 10 percent difference in atomic masses. That may not sound like a lot, but this difference results in photon scattering that translates to substantial efficiency losses.

By engineering pure samples of hBN that consist almost entirely of one isotope or the other, however, the research team has seen a dramatic reduction in optical losses. With vibrational modes that travel up to three times farther and persist for up to three times longer than natural hBN, the team's findings have implications for advances in hBN applications such as near-field optics and chemical sensing. They also provide a strategic approach to exploit and build upon for other materials systems.

"Controlling and manipulating light at nanoscale, sub-diffractional dimensions is notoriously difficult and inefficient," said Giles. "Our work represents a new path forward for the next generation of materials and devices."

Contributors to this research also include scientists from the University of California San Diego, Kansas State University, Oak Ridge National Laboratory, Columbia University and Vanderbilt University.

To contact the author of this article, email tony.pallone@ieeeglobalspec.com

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