Top-left
: SEM image of the micropillar optophononic resonator, and fibered device.
Top-right: Acoustic spectrum of the nanomechanical resonator. Bottom: time
trace measured using a fibered pump-probe coherent phonon generation scheme.
Courtesy: Centre for Nanoscience and Nanotechnology
From taut
strings vibrating in musical instruments to micro-electro-mechanical systems
for optoelectronics, vibrations cover an extensive range of applications. At
the nanoscale, the study of mechanical vibrations poses several challenges and
opens up a virtually infinite playground for nanotechnologies. Exciting
potential benefits of controlled vibrations in the GHz-THz frequency range
include better thermal transport management, novel quantum acoustic
technologies, improved optoelectronic devices, and the development of novel
nanoscale sensors.
However,
the standard optical techniques used to generate, detect and manipulate these
vibrations suffer from mechanical stability issues, limited reproducibility of
experimental results, and usually require large optical power densities that
many samples do not withstand. Researchers from the Center de Nanosciences et
de Nanotechnologies—C2N (CNRS / University Paris Saclay) and Quandela SAS, have
proposed a novel strategy that simultaneously solves these problems by
integrating fibered systems into pump-probe experiments, replacing complex
optical alignments protocols with a plug-and-play device.
The
researchers tested the new approach with a single-mode fiber glued onto an
opto-phononic micropillar. They realized pump-probe experiments without the
need for any further optical alignment beyond plugging fiber connectors by
spatially overlapping the micropillar's optical mode with the core of the fiber
and gluing them together. A critical requirement in pump-probe experiments is
to detect the probe beam exclusively and reject any contribution from the pump
beam on the optical detector. The usual way to achieve this condition is to use
cross-polarized pump and probe beams. To overcome the polarization rotation due
to the single-mode fiber, the researchers combined their fiber approach with
optical polarization control, resulting in a fibered cross-polarization scheme.
The fibered device allows stable pump-probe signals for more than forty hours
and can operate at very low excitation powers below 1mW to detect vibrations at
the nanoscale. The work was published in Applied Physics Letters.
The
fibered optophononic micropillar constitutes a much-improved platform for
reproducible plug-and-play pump-probe experiments in individual
microstructures. It lifts the necessity of complex optical setups to couple
into microstructures. In addition, the demonstrated stability and the
convenience of a fiber connector as the only necessary element to interface a
sample with an existing experimental setup make it transportable and allows
obtaining consistent measurements from the same device at any laboratory in the
world. These results demonstrate the synergy present at the C2N, where united
efforts of internationally leading nanofabrication facilities, research groups
and private companies create a remarkable impact in the science world.