A plasmonic laser is turned on (top) and off (bottom) by switching the magnetization of a nanodot array. The zoomed insets show the magnetic field around a single nanodot. Image: Jenna Rantala.
A plasmonic laser is turned on (top) and off (bottom) by switching the magnetization of a nanodot array. The zoomed insets show the magnetic field around a single nanodot. Image: Jenna Rantala.

By taking advantage of novel materials, researchers at Aalto University in Finland have produced nanolasers that can be switched on and off with a magnetic field. 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 communications and medical diagnostics devices. About 10 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 proved of great advantage in many fields—for example, they 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 through the use of heat or light. Now, as they report in a paper in Nature Photonics, the 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," explains Sebastiaan van Dijken from Aalto University. "By changing the magnetic field around our magnetic nanostructures, we can turn the lasing on and off."

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 utilized 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.

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 affected 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," says 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 study shows that the effect of magnetism in this context can be unexpectedly amplified by using a nanoparticle array with 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%. This has never been seen before," says van Dijken.

"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," adds Päivi Törmä from Aalto University.

This story is adapted from material from Aalto University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.