Q Factors Exceeding 10 ⁴ in Wavelength-to-Subwavelength-Scale Free-Space Resonators with Dual Asymmetry Control

Free-space-addressable optical resonators with high quality factors ( Q ) and wavelength-to-subwavelength mode volumes ( V m ) enhance light–matter interactions in sensing, nonlinear optics, and quantum photonics. However, experimental Q factors in this mode volume regime remain limited to ∼10 3 because existing asymmetry-driven designs couple geometric and optical perturbation components, constraining access to high- Q regimes. Here, we show that independently tuning these two asymmetry axes unlocks a biaxial radiative landscape with iso- Q contours connecting geometrically and optically distinct perturbations of equivalent Q . We demonstrate this framework in very-large-scale-integrated Si nanoantenna pixel (VINPix) resonators with 35–150 nm out-of-plane perturbations of amorphous Si, SiN x, and SiO 2 . Experimentally, we achieve Q up to 76 000 at V m of ∼1.7 λ 0 3 n eff –3 across arrays of >80 resonators in water. Computationally, slotted VINPix resonators reach Q of >10 6 at V m of ∼0.2 λ 0 3 n eff –3 . This biaxial framework establishes a generalizable design strategy for ultrahigh- Q free-space nanophotonic resonators.