A bright dot in a shadow has turned into a shortcut for making one of light’s stranger structures.
Scientists at Nanyang Technological University in Singapore said they have found a simpler way to produce optical skyrmions, unusual swirling patterns in light that researchers see as promising for future data storage, communications and computing technologies.
The team generated the structures by shining a laser at a small circular disc, instead of using expensive, highly engineered metamaterials that have traditionally been needed to create them.
The findings were published in the journal Optica and led by Nanyang Assistant Professor Shen Yijie from NTU’s School of Physical and Mathematical Sciences and School of Electrical and Electronic Engineering.
“What is remarkable is that optical skyrmions can now be generated using a simple effect where light bends around an object, without relying on expensive, complex man-made metamaterials or highly specialized techniques,” Asst Prof Shen said.
“This could make optical skyrmions much more accessible to researchers. By lowering the technical barrier to creating and studying them, the method opens up new possibilities for scientists to study how they could be used in future optical, materials and computing research.”
The work builds on the Poisson spot, an optical phenomenon in which a bright point appears at the centre of the shadow cast by a circular object when it is illuminated by a coherent light source such as a laser.
The Poisson spot was part of an early 19th century debate over the nature of light. Wave theory predicted that a bright point should appear in the centre of the disc’s shadow, where complete darkness would otherwise be expected. Observing the Poisson spot provided evidence that light undergoes diffraction, meaning it bends and spreads as it passes around objects or through small openings.
NTU said optical skyrmions are tiny, stable swirling patterns formed within the properties of light. Their structure has often been compared to the spines of a hedgehog.
The researchers also found their Poisson spot setup naturally produced up to four related topological field patterns at the same time: spin skyrmions, Stokes skyrmions, electric field skyrmions and magnetic field skyrmions.
Spin refers to the rotation-like properties of light, while the Stokes parameters describe polarization, or the direction in which light waves vibrate as they travel.
The university said generating the four types together could give scientists a way to compare how different optical skyrmions form, evolve and interact within the same light field.
Computer simulations showed the structures as swirling arrays of arrows illustrating how different properties of light change direction across the Poisson spot.
Light has characteristics that researchers can manipulate, including intensity, phase, polarization, spin, and its electric and magnetic field vectors. These can be arranged into topological structures, patterns that remain stable even when stretched or distorted.
Asst Prof Shen said several types of optical vectors could form topological structures at the same time in the light spot created by the team.
“These different components of light are closely connected, but they do not necessarily form identical topological patterns,” he said.
“Being able to produce and compare several skyrmions within one system could help researchers uncover new links between light’s electric, magnetic and other physical properties.”
Earlier methods for producing optical skyrmions relied on metamaterials, artificially engineered microscopic structures designed to manipulate light in ways that conventional materials cannot.
The paper is titled Optical skyrmions in Poisson spots.
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