Researchers from the University of Amsterdam and Stanford University have created an incredible flat lens that is only three atoms thick. It’s an innovation that could pave the way for the development of next-generation augmented reality (AR) glasses — ones you’ll never notice because they’re so thin — among other exciting applications.

A quantum lens

For centuries, lenses have relied on their curved shape to bend and focus light. This bending allows us to focus light, bringing distant objects into sharp view or magnifying tiny details. This tiny new lens, however, utilizes the power of quantum mechanics to achieve the same effect in a flat, ultra-thin design.

The lens is made from a single layer of tungsten disulphide (WS2) and features a series of concentric rings with gaps in between. This design, known as a Fresnel lens, diffracts light instead of refracting it, achieving focus without the need for curvature. The lens itself is half a millimeter wide and 0.0000006 millimeters thick — the thinnest lens on Earth by far.

What truly sets this lens apart, though, is its exploitation of quantum effects within the WS2 material. These materials exhibit strong light-matter interactions due to exciton resonances. Excitons are bound states of an electron and a hole, which are created when light interacts with a semiconductor. By examining the excitonic decay rates, the researchers found that these rates significantly impact the focusing efficiency of an atomically thin lens carved from WS2.

When light interacts with the lens, it excites electrons within the material, forming the excitons. These excitons play a crucial role in efficiently absorbing and re-emitting light at specific wavelengths, effectively tuning the optical properties of the material. At cryogenic (very cold) temperatures, the lens’s optical efficiency increased, the researchers also found.

Lens of the future

This innovative lens design boasts several advantages that make it ideal for AR applications. Because the lens allows most light to pass through unobstructed, it offers a clear view for the wearer while simultaneously focusing a small portion of light for information processing. This eliminates the potential obstruction of vision that can occur with traditional lenses.

The research team is now looking towards creating more intricate and multifunctional optical coatings. By applying an electrical charge, they hope to dynamically adjust the lens’s properties, such as its focal length.

“Excitons are very sensitive to the charge density in the material, and therefore we can change the refractive index of the material by applying a voltage,” says Jorik van de Groep, the leader of the 2D Nanophotonics at the University of Amsterdam and one of the authors of the new study.

This opens doors for the development of adaptive lenses that can be controlled electronically. The success of this research highlights the exciting potential of quantum materials like WS2.

The findings appeared in the journal Nano Letters.