Researchers from the 4th Physics Institute of the University of Stuttgart and the Istituto Italiano di Tecnologia (IIT) in Milan have demonstrated a new mechanism for directing light in a naturally hyperbolic van der Waals material without the need for conventional nanofabricated waveguides. The discovery opens new possibilities for integrated photonics, on-chip optical communication, and future quantum technologies. DOI : 10.1038/s41565-026-02243-9
Channeling light without complex waveguides
When a stone is dropped into water, circular waves spread outward from the point of impact. Light behaves similarly: when emitted from a localized source, it naturally propagates as spherical or circular wavefronts within a material. While this isotropic propagation is a fundamental property of waves, it is often undesirable in photonic applications where light must be guided efficiently along predefined paths.
Conventional optical technologies overcome this challenge using waveguides. In optical fiber communications, for example, glass fibers confine laser light and transport it over long distances with minimal loss. Similarly, photonic integrated circuits rely on nanoscale waveguides fabricated by complex lithographic processes, including resist coating, lithography, and etching. These fabrication steps are technologically demanding and contribute significantly to manufacturing costs.
A collaborative team led by Professor Harald Giessen from the 4th Physics Institute of the University of Stuttgart and Dr. Antonio Ambrosio from the Istituto Italiano di Tecnologia (IIT) in Milan has now demonstrated an alternative approach that eliminates the need for artificially fabricated waveguides.
Biaxial material with unique properties
The researchers employed the two-dimensional material molybdenum oxy-dichloride (MoOCl₂). By placing a nanoscale gold antenna on the surface and illuminating it with infrared laser light, they generated highly confined optical waves that propagated exclusively along a single direction. Remarkably, the light remained naturally confined to a narrow channel, behaving as though it was guided by an invisible waveguide embedded within the material itself.
The experimental work was carried out by Farid Aghashirinov, doctoral researcher at the 4 th Physics Institute, and Andrea Mancini, postdoctoral fellow at the ITT, using scattering-type scanning near-field optical microscopy (SNOM). A key advantage of the approach is that the material does not require any nanostructuring. Instead, its intrinsic crystal properties determine the direction of light propagation.
MoOCl₂ belongs to the class of biaxial materials, whose optical response differs strongly along different crystallographic directions. Along one axis, the material exhibits metallic behavior that supports collective oscillations of electrons known as surface plasmons, which efficiently transport electromagnetic energy. Along the orthogonal direction, however, the electronic response is dielectric, strongly suppressing plasmon propagation.
This pronounced anisotropy naturally confines plasmonic waves to a narrow propagation channel, analogous to water being forced through a canal. The researchers therefore describe the phenomenon as plasmon canalization.
New effect to be used for integrated optics, photonic chips and quantum technologies
The experiments revealed a strong wavelength dependence of the phenomenon. At an excitation wavelength of approximately 4 μm, the researchers observed highly directional canalized propagation. When the wavelength was increased to 5 μm, the wavefront went back to the familiar ring-like shape resembling isotropic propagation of water waves, while at a wavelength to 3 μm it transitioned to an open hyperbolic wavefront. The canalization condition can be pictured as originating from the extreme stretching of an elliptical wavefront where the foci of the ellipse are brought to infinity. These observations demonstrate that the topological character of propagating waves in MoOCl 2 can be tuned from open to closed going through the critical point of canalized propagation by simply adjusting the excitation wavelength.
The experiments were performed using a tunable infrared laser developed by Stuttgart Instruments GmbH, a spin-off company from the University of Stuttgart. Near-field optical images were acquired with a SNOM microscope manufactured by attocube systems AG, another technology company originating from academic research.
The researchers anticipate that plasmon canalization in naturally hyperbolic materials could provide a fundamentally new platform for integrated photonics. By enabling directional light transport without lithographically fabricated waveguides, the approach has the potential to simplify photonic chip fabrication while expanding the design possibilities for optical interconnects, nanoscale photonic circuits, and integrated quantum technologies.
Nature Nanotechnology
Nano-optics: New mechanism for channeling light waves discovered in natural hyperbolic materials
3-Aug-2026