The properties of wavefunctions, such as the ones encoded in the Berry curvature, play a fundamental role in topological photonics. In open photonic systems, where light can radiate into the far field, an intriguing question arises: to what extent can the topology of bulk modes be inferred from the emitted light?

In this work, we employ an effective non-Hermitian model that captures both guided and radiative modes in photonic crystal slabs with diffractive and radiative couplings. Within this framework, we calculate the radiation Berry curvature — a topological quantity defined directly from the far-field emission — and systematically compare it to the conventional bulk Berry curvature from Bloch states.

We explore the bulk-radiation correspondence near high-symmetry points of photonic lattices. Our results reveal that, while the two Berry curvatures can coincide, their correspondence is fundamentally non-universal and can break down in the presence of polarization singularities such as bound states in the continuum.

See the manuscript on arXiv.