Edge states emerge in diverse areas of science, offering new opportunities for the development of novel electronic or optoelectronic devices, sound and light propagation controls in acoustics and photonics [1,2]. Previous experiments on edge states and exploration of topological phases in photonics were carried out mostly in linear regimes, but the current belief is that nonlinearity introduces new striking features into physics of edge states, leading to the formation of edge solitons [3,4], optical isolation [5], and topological lasing [6-9], to name a few. Here we experimentally demonstrate edge solitons at the zigzag edge of a reconfigurable "photonic graphene" lattice [10-13] created via the effect of electromagnetically induced transparency [14] in an atomic vapor cell with controllable nonlinearity [15]. To obtain edge solitons, Raman gain [16] was introduced to compensate strong absorption experienced by the edge state during propagation. Our observations pave the way to experimental exploration of topological photonics on nonlinear, reconfigurable platform.

The quest for realizing novel fundamental physical effects and practical applications in ambient conditions has led to tremendous interest in microcavity exciton polaritons working in the strong coupling regime at room temperature. In the past few decades, a wide range of novel semiconductor systems supporting robust exciton polaritons have emerged, which has led to the realization of various fascinating phenomena and practical applications. This paper aims to review recent theoretical and experimental developments of exciton polaritons operating at room temperature, and includes a comprehensive theoretical background, descriptions of intriguing phenomena observed in various physical systems, as well as accounts of optoelectronic applications. Specifically, an in-depth review of physical systems achieving room temperature exciton polaritons will be presented, including the early development of ZnO and GaN microcavities and other emerging systems such as organics, halide perovskite semiconductors, carbon nanotubes, and transition metal dichalcogenides. Finally, a perspective of outlooking future developments will be elaborated.

Microcavities with whispering gallery modes (WGM), usually formed by two-dimensional (2D) circular structures, are significant elements in integrated optics, quantum information, and topological photonics. We report three-dimensional (3D) WGM from self-bent-up microdisks consisting of strain-released AlGaN/GaN bilayers, which provide an extra degree of freedom of the WGM photons in the vertical dimension, in contrast with the 2D WGM whose field mainly distributes in the horizontal plane. Despite the ultrathin and deformed cavity layer, the 3D WGM shows a reasonably high quality factor for GaN-based microdisks (∼1300) and exhibits single mode lasing due to the anisotropic feature of the bent-up disk, a unique advantage over the conventional planar microdisks of the same material and size. Such devices provide altitude dependence of emitting direction and are promising for applications in multilevel integrated photonics circuits.

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