Side‐DBR Guided Exciton‐Polariton Lasing With Near‐Field Mode Imaging in an InGaN Thin‐Film Ridge Waveguide

ABSTRACT Guided exciton‐polariton devices promise compact coherent sources, yet achieving strong coupling, low thresholds, and controlled feedback in ridge geometries remains challenging. Here, a room‐temperature exciton‐polariton edge‐emitting laser is realized on a thin‐film InGaN/GaN platform using a ridge waveguide that employs distributed Bragg reflectors along both longitudinal sides. These side DBRs provide in‐plane Bragg confinement and feedback independent of end facets, enabling guided polariton lasing with a vacuum Rabi splitting of approximately 25 meV. Micro‐photoluminescence reveals a polariton‐lasing threshold of with a Q factor of around 5000, comparable to thresholds in GaN vertical microcavity polariton lasers and far below those of GaN ridge polariton lasers, highlighting the role of the thin‐film InGaN/GaN platform combined with lateral side‐DBR confinement. Scanning near‐field optical microscopy directly images the photon‐like and polariton modes in the same device, and finite‐element simulations reproduce the observed mode profiles. Together, the side‐DBR cavity and near‐field mode imaging provide a platform for integrated polariton photonics.