Hybrid‑2D optical modulator. a Illustration of the concept: the electrical tunability of a monolayer 2D semiconductor in a heterostructure cavity is combined with the strong light‑matter interaction of a dielectric non‑local metasurface to achieve strong intensity modulation of the reflected beam. b Experimentally measured photoluminescence (PL) intensity for a bare heterostructure cavity as a function of gate voltage (color). The inset shows a micrograph of the heterostructure, with the monolayer outlined in blue and the measurement position indicated by the red cross. Scale bar: 5 µm. c Schematic of the detailed geometry of the modulator design (not to scale). d Electric‑field intensity enhancement for a transverse‑electric (TE) polarized normal‑incident wave at free‑space wavelength λ₀ = 621 nm. The blue line represents the monolayer. e Calculated reflectance spectra for the device with an intrinsic (Rᵢ, blue) and n‑doped (Rₙ, red) monolayer. f The corresponding modulation depth (10·log₁₀(Rᵢ/Rₙ), magenta) extracted from e. Credit: Light: Science & Applications (2026). DOI: 10.1038/s41377‑025‑02079‑3

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Controlling light is an important technological challenge

Not just at the large scale of microscopes and telescopes, but also at the nanometer scale. Recently, physicists at the University of Amsterdam published a clever quantum trick that allows them to make a nanoscale mirror that can be turned on and off at will.

The work is published in the journal Light: Science & Applications.

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A light switch on the nanoscale

In modern laboratory experiments, light can be controlled at small scales in remarkable ways. To achieve this, physicists use ultrathin optical coatings called metasurfaces. These structures are typically just a few tens to hundreds of nanometers thick—about a thousand times thinner than a human hair. Despite their tiny size, these cleverly designed nanostructures can bend light, focus it, or otherwise manipulate it in unprecedented ways.

These recent developments make optics at the nanoscale achievable, but the possibilities are still somewhat limited. Most metasurfaces are “static”: once they are made, their behavior cannot be changed. For future technologies, scientists need optical components that can be actively tuned—turned up or down, switched on or off—to achieve with light what we now only achieve with electronic circuits.

In the new research, physicists Tom Hoekstra and Jorik van de Groep from the UvA‑Institute of Physics describe an important breakthrough. Using a new approach, they realized an actively tunable metasurface whose heart is a single two‑dimensional layer of tungsten disulfide (WS₂). The unique properties of this 2D material allowed the researchers to build a nanoscale mirror for red light that can be turned on and off at will—a true light switch on the nanoscale.

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Excitons

In technical terms, the device that Hoekstra and Van de Groep constructed is an optical modulator. The idea of using 2D materials for optical modulation had been proposed shortly after these materials were discovered in 2004, but making the effect work at room temperature proved extremely difficult.

The key to the researchers’ success was a metasurface that traps light right where the WS₂ monolayer resides. This strong confinement makes the interaction between light and matter unusually strong; so strong, in fact, that quantum effects within the WS₂ layer persist at room temperature, giving the device record‑breaking efficiency.

When WS₂ absorbs light, an electron is excited to a higher energy level. Because of confinement in the atomically thin layer, the negatively charged electron and the positively charged “hole” it leaves behind remain bound together by electrostatic attraction, forming an exciton.

Excitons are at the heart of the device’s tunability. In the “on” state, excitons enable the device to reflect red light like a nanoscale mirror. Because excitons are highly sensitive to the charge density in the material, applying a voltage suppresses them. In the “off” state the red light is absorbed instead of reflected.

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A new era of photonics

The work by Hoekstra and Van de Groep shows that excitons in 2D materials can be harnessed for compact, active optical components with many potential applications.

Looking ahead, their approach could be used wherever light needs to be controlled quickly and precisely—e.g., in optical communication links, where beams of light transmit data wirelessly, or in optical computing, where photons rather than electrons carry information at high speeds and low energy cost. Excitons may well spark a new era of photonics.

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Publication details

Tom Hoekstra et al., “Electrically tunable strong coupling in a hybrid‑2D excitonic metasurface for optical modulation,” Light: Science & Applications (2026). DOI: 10.1038/s41377‑025‑02079‑3

Citation: Quantum phenomenon enables a nanoscale mirror that can be switched on and off (2026, January 8) retrieved 18 January 2026 from https://phys.org/news/2026-01-quantum-phenomenon-enables-nanoscale-mirror.html