Three-Dimensionally Confined Optical Modes in Quantum Well Microtube Ring Resonators

We report on microtube ring resonators with quantum wells embedded as an optically active material. Optical modes are observed over a broad energy range. Their properties strongly depend on the exact geometry of the microtube along its axis. In particular, we observe (i) preferential emission of light on the inside edge of the microtube and (ii) confinement of light also in the direction of the tube axis by an axially varying geometry, which is explained in an expanded waveguide model.