Photonic crystals provide a versatile platform to engineer electromagnetic responses through wavelength-scale periodic structures. When both time-reversal and inversion symmetries are broken, these systems can exhibit a quantized axionic θ-term, manifesting at domain walls and leading to protected hinge-localized modes, closely mirroring effects seen in topological condensed matter systems, but realized for light. I will present two realizations in the microwave regime: a theoretical design based on a modulated stack of gyrotropic dielectrics, supporting tunable photonic hinge states that connect and disconnect in response to magnetic biasing; and a macroscopic table-top experimental demonstration of a three-dimensional photonic crystal built from gyrotropic materials, characterized by a gapped axion bulk, hinge modes, and half-quantized Chern surfaces. These systems support massive photons and tightly confined 1D channels, providing a scalable platform to explore axion electrodynamics in photonic settings.
