A new kind of laser, in which light snakes around a cavity of any shape without scattering, has been developed by researchers in the US. They claim that their "toplogical laser", which works at telecom wavelengths, could allow improved miniaturization of silicon photonics or even protect quantum information from scattering.
Topological insulators are materials that do not carry electrical currents in the bulk, but do conduct through edge states. Crucially, these states always travel in one direction, steering neatly around corners and imperfections in the surface without scattering or leaking out.
Such "topologically protected" electric currents can be induced in a thin sheet of any conductor by inducing an electric field across the sheet and a magnetic field perpendicular to it. In the bulk, the electrons simply travel in circles but at the edges they hop along in semicircles.
Although photons have no magnetic moment and so do not respond directly to a magnetic field, an analogous effect can be achieved using electrons excited by incident light. Such electrons respond differently to a magnetic field than if they had not been excited, and in turn influence the light differently.
"The interaction of the photons with the magnetic field is mediated by the material," explains Boubacar Kanté, an applied physicist at the University of California, San Diego. That's the theory – and it works well at low frequencies.
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