Purcell Effect in Epsilon-Near-Zero Microcavities

Epsilon-near-zero (ENZ) photonics offers a compelling platform for integrated photonic systems, enabling a range of novel and extraordinary functionalities. However, the practical deployment of ENZ-based devices is constrained by high material losses and severe impedance mismatch, which are detrimental to applications requiring coherent light manipulation and efficient light-matter interaction. To address these challenges, we demonstrate that all-dielectric Bragg-reflection microcavities operated near their cutoff frequency, offer an ultralow-loss platform for enhancing light-matter interaction and exploring emission processes in the ENZ regime. While Bragg cavities are well-established, their potential as ENZ resonant microcavities remains largely unexplored. We investigate the Purcell effect and quality factor in these structures, comparing their performance with those of the perfect-electric-conductor and metallic counterparts. Through analytical derivations based on Fermi's golden rule and field quantization in lossless dispersive media, we establish scaling laws that distinguish these ENZ cavities from conventional resonators. Frequency domain simulations validate our counterintuitive findings, demonstrating that in all-dielectric ENZ Bragg-reflection microcavities, the Purcell and quality factors scale as <i>L</i>/λ₀ and (<i>L</i>/λ₀)³, respectively, where <i>L</i> is the cavity length and λ₀ is the resonance wavelength. Our results offer key insights into the design of ENZ-based photonic systems, paving the way for enhanced light-matter interactions in nonlinear optics and quantum photonics.