There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.

Topological Photonics

This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

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Space-division multiplexing in optical fibres

Rydberg atoms with principal quantum number $n⪢1$ have exaggerated atomic properties including dipole-dipole interactions that scale as ${n}^{4}$ and radiative lifetimes that scale as ${n}^{3}$. It was proposed a decade ago to take advantage of these properties to implement quantum gates between neutral atom qubits. The availability of a strong long-range interaction that can be coherently turned on and off is an enabling resource for a wide range of quantum information tasks stretching far beyond the original gate proposal. Rydberg enabled capabilities include long-range two-qubit gates, collective encoding of multiqubit registers, implementation of robust light-atom quantum interfaces, and the potential for simulating quantum many-body physics. The advances of the last decade are reviewed, covering both theoretical and experimental aspects of Rydberg-mediated quantum information processing.

Quantum information with Rydberg atoms

An overview is presented of the current state-of-the-art in silicon nanophotonic ring resonators. Basic theory of ring resonators is discussed, and applied to the peculiarities of submicron silicon photonic wire waveguides: the small dimensions and tight bend radii, sensitivity to perturbations and the boundary conditions of the fabrication processes. Theory is compared to quantitative measurements. Finally, several of the more promising applications of silicon ring resonators are discussed: filters and optical delay lines, label-free biosensors, and active rings for efficient modulators and even light sources.

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Silicon microring resonators

We study experimentally the role of nonlinearity in adiabatic photonic structures. We realize a three-core structure exhibiting an adiabatic passage of light, and find that nonlinearity has a strong effect on the dynamics.

Nonlinear Effects in Adiabatic Optical Structures

Hybrid integration of photonic membrane and nanowire devices from multiple material platforms is demonstrated using high-accuracy transfer printing. The deterministic assembly technique enables serially printed devices with separations as low as 100 nm.

Transfer-printing enables multi-material assembly of integrated photonic systems

We experimentally demonstrated a silicon photonic cylindrical vector beams emitter, consisting of a micro-ring resonator with angular grating and a resistive heater. The device is capable of generating and tuning azimuthal and radial polarization beams.

On-chip Tunable Cylindrical Vector Beams Emitter

Cascadable, digital all-optical routing by incoherent interactions between a highly confined soliton and two successive control beams of different wavelength was implemented in an AlGaAs waveguide array.

Optical Routing by Sequential Incoherent Blocker Soliton-Control Beam Interactions in Kerr Waveguide Arrays

Fast tuning of the Optical Angular Momentum (OAM) order of a vortex beam is demonstrated with 20μs switching times using a compact silicon photonic device.

Marc Sorel

Papers

Nonlinear Effects in Adiabatic Optical Structures

Transfer-printing enables multi-material assembly of integrated photonic systems

On-chip Tunable Cylindrical Vector Beams Emitter

Optical Routing by Sequential Incoherent Blocker Soliton-Control Beam Interactions in Kerr Waveguide Arrays

Fast switching of optical vortex beam mode orders generated using a fully integrated SOI device