Scientists demonstrate innovative perovskite waveguides with edge lasing

Integrated photonic circuits operating at room temperature and combined with nonlinear optical effects could revolutionize classical and quantum signal processing. Scientists from the Faculty of Physics of the University of Warsaw, in collaboration with other institutions in Poland, Italy, Iceland and Australia, have demonstrated the creation of perovskite crystals with predefined shapes that can be used as waveguides, couplers, splitters and modulators in nonlinear photonics.

The research results, published in the journal Natural materialsdescribe the fabrication of these innovative structures and the edge laser effect. This effect is notably associated with the formation of the exciton-polariton condensate, which are quasiparticles behaving partly like light and partly like matter.

Barbara Piętka, professor at the Faculty of Physics of the University of Warsaw, one of the initiators of the project and head of the research process, emphasizes: “Perovskites are very versatile: from polycrystalline layers, nano- and microcrystals to massive crystals. They can be used in various applications, from solar cells to lasers.

“Some, like CsPbBr₃ (cesium-lead bromide) that we used are also ideal semiconductors for optical applications because of their high exciton binding energy and oscillator strength. These effects help to enhance light interactions, significantly reducing the energy required for nonlinear light amplification.

The researchers applied reproducible and scalable synthesis methods to obtain perovskite crystals with precisely defined dimensions and shapes. They used a microfluidic approach, where the crystals are grown from solution in narrow polymer molds onto which any shape can be printed from a template.

A key element was to control the solution concentration and growth temperatures while maintaining an atmosphere of saturated solvent vapors. This approach, combined with the use of nearly atomically smooth gallium arsenide templates fabricated using electron beam lithography and plasma etching at the Łukasiewicz Research Network – Institute of Microelectronics and Photonics under the direction of Anna Szerling, made it possible to produce high-quality single crystals.

In this way, CsPbBr₃ The crystals can be formed into any shape, from simple angles to gentle curves, a real feat in the world of crystalline materials. They can be fabricated on any substrate, improving their compatibility with existing photonic devices.

Mateusz Kędziora, a PhD student at the Faculty of Physics of the University of Warsaw and first author of the paper who developed the crystal synthesis methods, adds: “These crystals, due to their high quality, form Fabry-Pérot-type resonators on their walls, allowing to observe strong nonlinear effects without the need for external Bragg mirrors,” which offers hope for the application of these materials in integrated photonic circuits.

The demonstration of polaritonic laser emission from microwire interfaces and corners marks another advance.

“The wavelength of the emitted light is modified by the effects of strong light-matter interactions, which indicates that the emission is due to the formation of a non-equilibrium Bose-Einstein condensate of excitons-polaritons. This is therefore not a conventional laser effect due to the Purcell effect (weak coupling), but an emission from a condensate in the regime of strong light-matter coupling,” explains Piętka.

“The strong coherence between the different signals of edge and corner light, confirmed by far-field photoluminescence and angle-resolved spectroscopy, indicates the formation of a macroscopically extended and coherent polariton condensate,” adds Dr Helgi Sigurðsson from the Faculty of Physics, University of Warsaw and the Institute of Science, University of Iceland in Reykjavik.

Further confirmation of nonlinear effects is the increase in energy with increasing population of a given mode (known as blueshift), which results from interactions within the condensate. Due to the unique properties of perovskite structures, the condensate can travel long distances within the crystals and the emitted light can propagate through air gaps to neighboring structures.

“Our simulations show how naturally formed resonators for light modes and scattering affect edge and curvature emission in crystals,” adds Dr. Andrzej Opala from the Faculty of Physics, University of Warsaw and the Institute of Physics, Polish Academy of Sciences, one of the lead authors of the paper and the developer of the theoretical model showing how numerical aperture and spatial confinement in microwires affect the observed effects.

“In addition, thanks to calculations based on solving Maxwell’s equations in three-dimensional structures with complex shapes, we were able to visualize photonic modes and show how their image is formed in the far field,” says Professor Tomasz Czyszanowski from the Lodz University of Technology, who specializes in simulations of photonic and laser structures. This discovery allows them to be used in compact “on-chip” systems capable of handling both classical and quantum computing tasks.

“We expect that our findings will open the door to future devices capable of operating at the single-photon level, integrating nanolasers with waveguides and other elements on a single chip,” concludes Professor Michał Matuszewski from the Centre for Theoretical Physics of the Polish Academy of Sciences.

Perovskites could play a key role in the future development of optical technologies, and the UW physicists’ findings could significantly increase the chances of using perovskite crystals in nonlinear photonics operating at room temperature. In addition, the structures developed could be compatible with silicon technology, further improving their commercialization potential.