Sculping light with extreme spectral, spatial, and polarization selectivity is central to modern nanophotonics and quantum technologies, yet one of the most powerful resources, optical bound states in the continuum (BICs), often remains “hidden in the dispersion” and dark to standard transmission/reflection spectra. Here, we reveal and control these modes via coupled photoluminescence (PL) and quantify how topology governs their spatial-spectral and polarization responses. We engineer a one-dimensional photonic crystal hosting two orthogonally polarized, symmetry-protected BICs, enabling mode-resolved quasi-BIC (qBIC)-coupled PL from on-chip emitters. The two BICs are accessed simultaneously with a single emitter species yet exhibit distinct responses to geometric perturbation. Angle-resolved transmission and FDTD simulations identify BICs at 586 and 670 nm with diverging quality factors, while back-focal-plane Stokes maps confirm polarization-vortex topology. The qBIC-coupled PL forms symmetric lobes that vanish in the normal direction, achieving up to 94% spectral narrowing, 92.8% degree of polarization, 65.5× intensity enhancement, and 0.75° angular fwhm. We show how the collection numerical aperture sets lobe resolvability and signal-to-background, and how the PL profile is tuned via overlayer modification. These results establish mechanism-resolved design rules for spectral, polarization, and momentum selectivity in directional emitters, sensing, and on-chip light sources, leveraging multi-BIC nanophotonic platforms.
Liu et al. (Mon,) studied this question.