Asymmetric topological pumping in nonparaxial photonics

Topological photonics was initially inspired by the quantum-optical analogy between the Schrödinger equation for an electron wavefunction and the paraxial equation for a light beam. Here, we reveal an unexpected phenomenon in topological pumping observed in arrays of nonparaxial optical waveguides where the quantum-optical analogy becomes invalid. We predict theoretically and demonstrate experimentally an asymmetric topological pumping when the injected field transfers from one side of the waveguide array to the other side whereas the reverse process is unexpectedly forbidden. Our finding could open an avenue for exploring topological photonics that enables nontrivial topological phenomena and designs in photonics driven by nonparaxiality.

Electronic Confinement in the Continuum: Leaky Bragg Mirror for Electrons

In this work we present an InGaAs/InAlAs heterostructure lattice matched with InP that holds two leaky electronic states in the continuum. An optical analogy with Bragg mirrors is used to explain the origin and the desired characteristics of the leaky electronic state. Multipass waveguide absorption measurements were performed and theoretical calculations used to determine the energy levels involved in the optical transitions. The comparison between the theoretical and experimental oscillator strength shows the good optical quality of the sample.