The optical, lasing, and waveguiding capabilities of perovskite make this material a promising platform for integrated photonic circuits for classical and quantum signal processing. A research team from the University of Warsaw, in collaboration with institutions in Europe and Australia, developed a way to efficiently fabricate large-scale waveguiding perovskite crystals in predefined shapes such as couplers, splitters, or microwires. Along with repeatable, scalable synthesis techniques, the researchers used nearly atomically smooth gallium arsenide templates, which they made with electron-beam lithography and plasma etching, to create the crystals. This approach resulted in high-quality single crystals with precisely defined dimensions and shapes, for possible use in nonlinear optics. Researchers led by the University of Warsaw have developed a method to create perovskite waveguides with edge lasing effect. Courtesy of Mateusz Krol, University of Warsaw and the School of Physics at the Australian National University in Canberra. “These crystals, due to their high quality, form Fabry-Pérot type resonators on their walls, allowing strong nonlinear effects to be observed without the need for external Bragg mirrors,” researcher Mateusz Kedziora said. The researchers grew the perovskite crystals from solution in narrow polymer molds using a microfluidics approach. To ensure the success of this approach, they retained control of the solution concentration and growth temperatures while maintaining an atmosphere of saturated solvent vapors. The team used cesium-lead-bromide (CsPbBr3) as its perovskite material. CsPbBr3 perovskites make good semiconductors for optical applications, because of their high exciton binding energy and oscillator strength. “These effects allow for enhanced light interactions, significantly lowering the energy required for nonlinear light amplification,” professor Barbara Pietka said. The predesigned perovskites displayed an edge lasing effect, which is associated with the formation of the condensate of exciton-polaritons — quasiparticles that behave partly like light and partly like matter. “The wavelength of the emitted light is modified by the effects of strong light-matter interactions, indicating that the emission is due to the formation of a non-equilibrium Bose-Einstein condensate of exciton-polaritons,” Pietka said. “This is therefore not conventional lasing due to the Purcell effect (weak coupling), but emission from a condensate in the strong light-matter coupling regime.” When the researchers nonresonantly stimulated a condensate of waveguided exciton-polaritons, the transverse interfaces and corners of the perovskite microstructures exhibited bright polariton lasing. The team used far-field photoluminescence and angle-resolved spectroscopy to confirm the high coherence between different signals of the emitted light from the edges and corners. “Our simulations show how naturally formed resonators for light modes and scattering affect the emission from edges and bends in the crystals,” researcher Andrzej Opala said. The team detected large blueshifts with excitation power and high mutual coherence between the different edge and corner lasing signals in the far-field photoluminescence, indicating that spatially extended condensates of coherent polaritons had formed. Due to interactions within the condensate, the researchers observed an increase in energy with increasing population of a given blueshift, which further confirmed the presence of nonlinear effects. “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 forms in the far field,” professor Tomasz Czyszanowski said. The condensate polaritons were found to propagate over long distances in the wires from the excitation spot and were able to couple to neighboring wires through large air gaps, indicating that they potentially could be used for integrated polaritonic circuitry and on-chip optical devices with strong nonlinearities. The predesigned perovskite waveguides with edge lasing could help advance the use of perovskite crystals in nonlinear photonics that operate at room temperature. Moreover, the perovskite structures could be compatible with silicon technology, which would increase their commercialization potential. The structures can be fabricated on any substrate, enhancing their compatibility with existing photonic devices. Integrated photonic circuits operating at room temperature, combined with optical nonlinear effects, could transform the ability of classical and quantum devices to optically manipulate and analyze signals. “We predict that our discoveries will open the door to future devices that can operate at the level of single photons, integrating nanolasers with waveguides and other elements on a single chip,” professor Michal Matuszewski said. The research was published in Nature Materials (www.doi.org/10.1038/s41563-024-01980-3).
