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Volume 578 Issue 7794, 13 February 2020

Triangular momentum

Electrically driven semiconductor lasers are one of the most common types of laser and are widely used in our daily lives, from optical-fibre communication to laser printing and barcode readers. But the performance of these lasers is affected by semiconductor defects — damage or imperfections introduced during fabrication and packaging. In this week’s issue, Qi Jie Wang, Yidong Chong, Baile Zhang and their colleagues present a terahertz laser based on a quantum cascade laser that suggests such problems might be solved by taking advantage of the topological properties of light. By creating a triangular interface between two differently oriented photonic crystal lattices (as shown on the cover), the authors create topological edge states that can emit terahertz radiation even if there are sharp corners and defects present. As the laser is driven electrically, it could open the way for topological systems to find practical applications.

Cover image: Songdi Technology (Beijing) Co, Ltd.

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