Topological nanoscale lasers
Topological photonics promises robust light manipulation and smart design of optical devices such as topological nanolasers.
Nanostructures made of high-index dielectric materials with judiciously designed resonant elements and lattice arrangements show special promise for implementation of topological order for light at the nanoscale and optical on-chip applications. High-index dielectrics such as III-V semiconductors that can contain strong optical gain further enhanced by topological field localization form a promising platform for active topological nanophotonics.
A team of scientists, led by Yuri Kivshar from the Australian National University and Hong-Gyu Park from the Korea University, and co-workers have implemented nanophotonic cavities in a nanopatterned InGaAsP membrane incorporating III-V semiconductor quantum wells. The nanocavities exhibit a photonic analogue of valley-Hall effect. Researchers demonstrated room-temperature low-threshold lasing from a cavity mode hosted within the topological bandgap of the structure.
The cavity is based on the closed valley-Hall domain wall created by inversion of staggering nanoholes sizes in a bipartite honeycomb lattice. In the topological bandgap frequency range, the cavity supports a quantized spectrum of modes confined to the domain wall. The images show real-space emission profiles below and above the threshold.
The scientists explain: "In experiment, we first observe spontaneous emission from the cavity. The emission profile shows the enhancement along the entire perimeter of the triangular cavity associated with edge states. When increasing a pump power, we observe a threshold transition to lasing with a narrow-linewidth where the emission gets confined at the three corners."
When two spots are isolated, coherence of the emission is confirmed by interference fringes observed in the measured far-field radiation patterns. An isolated corner emits a donut-shaped beam carrying a singularity. These findings make a step topologically controlled ultrathin light sources with nontrivial radiation characteristics. The researchers forecast: "The proposed all-dielectric platform holds promise for the versatile design of active topological metasurfaces with integrated light sources. Such topological nanocavities has vast potential for advances in nonlinear nanophotonics, low-power nanolasing and cavity quantum electrodynamics".
[Smirnova, D., Tripathi, A., Kruk, S. et al. Room-temperature lasing from nanophotonic topological cavities. Light Sci Appl 9, 127 (2020). https://doi.org/10.1038/s41377-020-00350-3]