A new strategy for active metasurface design provides a full 360DEG
phase tunable metasurface

Date:
May 2, 2022
Source:
The Korea Advanced Institute of Science and Technology (KAIST)
Summary:
An international team of researchers has demonstrated a widely
applicable methodology enabling a full 360DEG active phase
modulation for metasurfaces while maintaining significant levels
of uniform light amplitude. This strategy can be fundamentally
applied to any spectral region with any structures and resonances
that fit the bill.



FULL STORY ==========================================================================
An international team of researchers led by Professor Min Seok Jang of
KAIST and Professor Victor W. Brar of the University of Wisconsin-Madison
has demonstrated a widely applicable methodology enabling a full 360DEG
active phase modulation for metasurfaces while maintaining significant
levels of uniform light amplitude. This strategy can be fundamentally
applied to any spectral region with any structures and resonances that
fit the bill.


========================================================================== Metasurfaces are optical components with specialized functionalities indispensable for real-life applications ranging from LIDAR and
spectroscopy to futuristic technologies such as invisibility cloaks and holograms. They are known for their compact and micro/nano-sized nature,
which enables them to be integrated into electronic computerized systems
with sizes that are ever decreasing as predicted by Moore's law.

In order to allow for such innovations, metasurfaces must be capable of manipulating the impinging light, doing so by manipulating either the
light's amplitude or phase (or both) and emitting it back out. However, dynamically modulating the phase with the full circle range has been
a notoriously difficult task, with very few works managing to do so by sacrificing a substantial amount of amplitude control.

Challenged by these limitations, the team proposed a general methodology
that enables metasurfaces to implement a dynamic phase modulation with
the complete 360DEG phase range, all the while uniformly maintaining significant levels of amplitude.

The underlying reason for the difficulty achieving such a feat is that
there is a fundamental trade-off regarding dynamically controlling the
optical phase of light. Metasurfaces generally perform such a function
through optical resonances, an excitation of electrons inside the
metasurface structure that harmonically oscillate together with the
incident light. In order to be able to modulate through the entire
range of 0-360DEG, the optical resonance frequency (the center of the
spectrum) must be tuned by a large amount while the linewidth (the width
of the spectrum) is kept to a minimum. However, to electrically tune the optical resonance frequency of the metasurface on demand, there needs to
be a controllable influx and outflux of electrons into the metasurface
and this inevitably leads to a larger linewidth of the aforementioned
optical resonance.

The problem is further compounded by the fact that the phase and the
amplitude of optical resonances are closely correlated in a complex,
non-linear fashion, making it very difficult to hold substantial control
over the amplitude while changing the phase.

The team's work circumvented both problems by using two optical
resonances, each with specifically designated properties. One resonance provides the decoupling between the phase and amplitude so that the phase
is able to be tuned while significant and uniform levels of amplitude
are maintained, as well as providing a narrow linewidth.

The other resonance provides the capability of being sufficiently tuned to
a large degree so that the complete full circle range of phase modulation
is achievable. The quintessence of the work is then to combine the
different properties of the two resonances through a phenomenon called
avoided crossing, so that the interactions between the two resonances
lead to an amalgamation of the desired traits that achieves and even
surpasses the full 360DEG phase modulation with uniform amplitude.

Professor Jang said, "Our research proposes a new methodology in
dynamic phase modulation that breaks through the conventional limits
and trade-offs, while being broadly applicable in diverse types of metasurfaces. We hope that this idea helps researchers implement
and realize many key applications of metasurfaces, such as LIDAR and
holograms, so that the nanophotonics industry keeps growing and provides
a brighter technological future." The research was funded by the Samsung Research Funding & Incubation Center of Samsung Electronics.


========================================================================== Story Source: Materials provided by The_Korea_Advanced_Institute_of_Science_and_Technology_ (KAIST). Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ju Young Kim, Juho Park, Gregory R. Holdman, Jacob T. Heiden,
Shinho Kim,
Victor W. Brar, Min Seok Jang. Full 2p tunable phase modulation
using avoided crossing of resonances. Nature Communications, 2022;
13 (1) DOI: 10.1038/s41467-022-29721-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220502120458.htm

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