Valley-Hall Nanoscale Lasers

Topological photonics underpins a promising paradigm for robust light mani­pulation and smart design of optical devices with improved reliability and advanced func­tionalities governed by the nontrivial band topology. 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.

Scanning electron microscope image of the fabricated sample. The false-colour triangle marks the interior of the topological cavity. (Source: D. Smirnova et al., ANU)

Now, 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”. (Source: LPC-CAS)

Reference: D. Smirnova et al.: Room-temperature lasing from nanophotonic topological cavities, Light Sci. Appl. 9, 127 (2020); DOI: 10.1038/s41377-020-00350-3

Link: Nonlinear Physics Center, Research School of Physics, Australian National University, Canberra, Australia

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