Extreme Light Confinement Mediated by the Transverse Kerker Effect

Dielectric nanoparticles can be engineered to scatter light predominantly in the transverse direction, perpendicular to the incident plane wave’s propagation direction, a phenomenon known as the transverse Kerker effect. Although complete cancellation of forward scattering from a single object is forbidden by the optical theorem, we show that a single photonic mode can provide an ideal transverse Kerker effect. When combining several nanoparticles to form a metasurface, the mode evolves into an accidental bound state in the continuum. This enables polarization-independent quasi bound states in the continuum whose quality factors are tunable without symmetry breaking. We experimentally demonstrate our concept in the visible, achieving the first polarization-independent bound state in the continuum without Brillouin-zone folding. These modes maintain large quality factors over a broader region of momentum space than conventional bound states in the continuum. Our results establish a platform for realizing ultranarrow resonances free of conventional design constraints.