Photonic Doping of Epsilon‐Near‐Zero Bragg Microcavities

Epsilon‐near‐zero (ENZ) photonics provides a powerful route to extreme dispersion engineering, strong field confinement, and unconventional wave phenomena. A closely related concept, photonic doping , employs subwavelength nonmagnetic dielectric inclusions in ENZ media to enable exotic responses such as perfect‐magnetic‐conductor behavior and simultaneous epsilon‐and mu‐near‐zero states. However, photonic doping has remained limited to microwave and far‐infrared regimes due to intrinsic losses in optical ENZ materials. Here, photonic doping is demonstrated at optical frequencies by embedding a periodic array of dielectric Mie resonators within an ultralow‐loss all‐dielectric ENZ platform based on near‐cutoff Bragg microcavities. The resulting structures support spectrally isolated quasi‐singular coupled Bragg–Mie resonances spanning electric and magnetic multipolar orders and their overtones. These modes exhibit effective near‐zero‐index dispersion, with fields confined either within or between the nanoparticles. A representative ‐scale doped structure exhibits a quality factor of and a magnetic Purcell enhancement exceeding in the near‐infrared. This platform elevates photonic doping from a microwave‐only concept to a fully optical, low‐loss, and multipole‐resolved system, enabling ultra‐narrowband Mie‐like resonances, enhanced magnetic–light interactions, and new opportunities in multipolar‐selective spectroscopy and lasing, low‐threshold nonlinear optics, and engineered spontaneous emission.