Materials science

Optoelectronics

Engineering

Physics

Topology (electrical circuits)

Photonic crystal

Optics

Topological insulator

Optical communication

Computer science

Computer graphics (images)

Band gap

Electrical engineering

Condensed matter physics

Wavelength

Planar

Photonics

Nature Nanotechnology

Photonic topological insulators offer the possibility to eliminate backscattering losses and improve the efficiency of optical communication systems. Despite considerable efforts, a direct experimental demonstration of theoretically predicted robust, lossless energy transport in topological insulators operating at near-infrared frequencies is still missing. Here, we combine the properties of a planar silicon photonic crystal and the concept of topological protection to design, fabricate and characterize an optical topological insulator that exhibits the valley Hall effect. We show that the transmittances are the same for light propagation along a straight topological interface and one with four sharp turns. This result quantitatively demonstrates the suppression of backscattering due to the non-trivial topology of the structure. The photonic-crystal-based approach offers significant advantages compared with other realizations of photonic topological insulators, such as lower propagation losses, the presence of a band gap for light propagating in the crystal-slab plane, a larger operating bandwidth, a much smaller footprint, compatibility with complementary metal–oxide–semiconductor fabrication technology, and the fact that it allows for operation at telecommunications wavelengths. Thanks to its topological properties, a CMOS-compatible photonic crystal shows reflectionless transmission of light at telecommunication wavelengths even along a path with sharp turns.

Robust topologically protected transport in photonic crystals at telecommunication wavelengths