Controlling nanolasers with magnets lays the groundwork for more
robust optical signaling.
A magnetic field can be used to switch nanolasers on and off, shows new
research from Aalto University. The physics underlying this discovery paves
the way for the development of optical signals that cannot be disturbed by
external disruptions, leading to unprecedented robustness in signal
processing.
Lasers concentrate light into extremely bright beams that are useful in a
variety of domains, such as broadband communication and medical diagnostics
devices. About ten years ago, extremely small and fast lasers known as
plasmonic nanolasers were developed. These nanolasers are potentially more
power-efficient than traditional lasers, and they have been of great
advantage in many fields—for example, nanolasers have increased the
sensitivity of biosensors used in medical diagnostics.
So far, switching nanolasers on and off has required manipulating them
directly, either mechanically or with the use of heat or light. Now,
researchers have found a way to remotely control nanolasers.
“The novelty here is that we are able to control the lasing signal with an
external magnetic field. By changing the magnetic field around our magnetic
nanostructures, we can turn the lasing on and off,” says Professor
Sebastiaan van Dijken of Aalto University.
The team accomplished this by making plasmonic nanolasers from different
materials than normal. Instead of the usual noble metals, such as gold or
silver, they used magnetic cobalt-platinum nanodots patterned on a
continuous layer of gold and insulating silicon dioxide. Their analysis
showed that both the material and the arrangement of the nanodots in
periodic arrays were required for the effect.
Photonics advances towards extremely robust signal processing
The new control mechanism may prove useful in a range of devices that make
use of optical signals, but its implications for the emerging field of
topological photonics are even more exciting. Topological photonics aims to
produce light signals that are not disturbed by external disruptions. This
would have applications in many domains by providing very robust signal
processing.
“The idea is that you can create specific optical modes that are
topological, that have certain characteristics which allow them to be
transported and protected against any disturbance,” explains van Dijken.
“That means if there are defects in the device or because the material is
rough, the light can just pass them by without being disturbed, because it
is topologically protected.”
So far, creating topologically protected optical signals using magnetic
materials has required strong magnetic fields. The new research shows that
the effect of magnetism in this context can be unexpectedly amplified using
a nanoparticle array of a particular symmetry. The researchers believe their
findings could point the way to new, nanoscale, topologically protected
signals.
“Normally, magnetic materials can cause a very minor change in the
absorption and polarization of light. In these experiments, we produced very
significant changes in the optical response— up to 20 percent. This has
never been seen before,” says van Dijken.
Academy Professor Päivi Törmä adds that “these results hold great potential
for the realization of topological photonic structures wherein magnetization
effects are amplified by a suitable choice of the nanoparticle array
geometry.”
These findings are the result of a long-lasting collaboration between the
Nanomagnetism and Spintronics group led by Professor van Dijken and the
Quantum Dynamics group led by Professor Törmä, both in the Department of
Applied Physics at Aalto University.
Reference:
Freire-Fernández, F., Cuerda, J., Daskalakis, K.S. et al. Magnetic on–off
switching of a plasmonic laser. Nat. Photon. 16, 27–32 (2022).
DOI: 10.1038/s41566-021-00922-8
Tags:
Physics