Emerging landscape of photonic bound states in the continuum for next-generation metadevices
Bound states in the continuum (BICs) have emerged as a central paradigm in nanophotonics, offering theoretically unbounded quality factors (Q) and topologically protected mode confinement within the radiative continuum. This review critically examines the trajectory of BIC research from foundational predictions by Wigner and von Neumann (1929) and semiconductor superlattice observations by Capasso et al. (1992) to contemporary metasurface implementations. We analyze design methodologies including machine learning and inverse design, and survey emergent BIC classes: super-BICs, chiral BICs, flatband BICs, and Moiré BICs. The integration of phase-change materials and liquid crystals enables dynamic control over emission and absorption, while strong light-matter interaction, ultrafast dynamics, and exceptional points are assessed for device relevance. Key application domains—lasing, optical sensing, and nonlinear optics—are evaluated with emphasis on conversion efficiency and sensitivity thresholds. We identify persistent challenges in fabrication tolerance, material loss, and scalable integration. The review concludes with perspectives on multilayer metasurfaces, quantum emitter interfacing, and pathways toward commercial BIC metadevices, providing a rigorous framework for researchers and engineers targeting high-performance photonic systems.