Nanophotonic advances shed light on tunable metasurfaces

13 June 2019

The ability to manipulate light with optical metasurfaces has the potential to improve efficiency in technologies ranging from solar cells to virtual reality glasses.

Physicist Dr Howard Lee (Croucher Fellowship 2012), of Baylor University in Texas, has dedicated the past few years to exploring the tiniest of structures – 1,000 times thinner than a human hair – focusing on metasurfaces in optical technologies.

Metasurfaces are nanostructured optical thin films, only a few tens of atoms thick. These films can usefully behave in a similar way to a prism or lens by controlling light to produce a certain phase and amplitude. Indeed, such materials have previously yielded an array of optical components, such as flat lenses and holographic surfaces. But they have not yet provided active manipulation of the wave’s properties.

Now, by successfully applying an electrical voltage to ultra-thin film to steer the light being produced, Lee and his team have developed a dynamically tunable metasurface enabling such control. The discovery could potentially be applied to a range of ultrathin optical technologies.

Today’s light harvesting and high-resolution devices tend to be bulky and suffer from energy loss. It was this situation that led scientists to seek a small and efficient solution, and Lee and his co-researchers to propose tunable zero refractive index metasurfaces. The team’s findings on perfect absorption in ultrathin structures have appeared in an article in ACS Photonics.

Their next goal is to manipulate the metasurfaces to achieve perfect absorption with large tunable operating wavelengths and a wide angle of incidence. One hundred per cent absorption in nano-optic materials could help technologies to be more efficient and thinner, which could then be applied to optical fibres in internet cables.

Fibre-optic technology has been studied for more than 25 years. Yet certain limitations have still to be overcome. For example, optical properties of light transmitted through optical fibres cannot easily be altered. Additionally, the light transmitted is restricted by the fibres’ diffraction limit. Lee’s discoveries in metasurfaces could overcome these limitations by introducing a metalens with engineerable focal length to tailor the fibre’s optical properties for advanced light manipulation.

The scientist says his idea of success is “creating interesting ideas and finding practical applications for his work”. His advances in metasurfaces could potentially make mobile phone cameras less bulky, increase solar cell efficiency, and create more durable spacecraft. Long-term goals include improving virtual reality glasses by enabling lenses to be thinner, providing displays with more functionalities, and giving focus greater adjustability.

Lee was honoured with a 2018 CAREER Award from the National Science Foundation (NSF) and a five-year US$500,000 grant for his work in nano-optics. The award is given to junior faculty who serve as role models in both research and teaching.

Dr Howard Lee and his students.

Lee joined Baylor in 2015 as an assistant professor after completing a Croucher Postdoctoral Fellowship at the California Institute of Technology. He enjoys teaching as well as research and when asked about his students he is quick to relate how the work of the young researchers in his group has been recognised with awards from the International Society for Optics and Photonics, the US National Science Foundation and the Optical Society of America.

Although busy with his research and teaching at Baylor, Lee also manages to make time to organise outreach activities on nanophysics at a nearby museum and a junior college. “We form a team where we figure out a challenging problem together. When we then solve the problem and get good research outcomes, we are all satisfied,” he said.

Dr Howard Ho Wai Lee is an Assistant Professor in the Department of Physics at Baylor University in Texas, US. He is also an IQSE Fellow and Visiting Professor at the Institute for Quantum Science and Engineering (IQSE) at Texas A&M University. He received his BSc (Hons I) in applied physics from City University of Hong Kong in 2006 and earned a PhD in physics at the Max Planck Institute for Science of Light in Germany, under the supervision of Professor Philip Russell. Dr Lee then joined Professor Harry Atwater’s group at California Institute of Technology as a postdoctoral scholar in 2012. There, his research focused on active linear, non-linear, and quantum plasmonic/metasurface/zero-index optics, quantum biophotonics and imaging, “meta”- fibre optics, and hybrid photonic-plasmonic on-chip optical devices. He received a 2018 National Science Foundation CAREER Award, a 2017 Defence Advanced Research Projects Agency (DARPA) Young Faculty Award, and the 2017 American Physical Society’s Robert S Hyer Award. He was also a 2018 Optical Society (OSA) Ambassador. Dr Lee received a Croucher Fellowship in 2012. 

To view Dr Lee’s full Croucher profile, please click here.