Chromatically resolved infrared light localization in a 3D chirped woodpile photonic structure

Engineering materials with tailored optical properties remain a key challenge in photonics. We report the design, fabrication, and experimental characterization of a three-dimensional chirped woodpile photonic crystal with nanometric features, produced via two-photon laser lithography. The structure exhibits wavelength-dependent light localization and intensity enhancement in the near-infrared regime, achieved through group velocity reduction. This effect arises from a gradual lattice-period chirp along the propagation direction, inducing a frequency-dependent bandgap shift and spatial separation of localized wavelengths. We propose an experimental technique capable of sensing the infrared light localization inside the crystal through the measurement of the transversely scattered light. We confirm, for the first time to our knowledge, strong localization in the 1400 to 1700 nm range, with longer wavelengths penetrating deeper into the crystal, consistent with numerical simulations. These findings open new opportunities for infrared photonic applications requiring enhanced light–matter interactions, including optical sensing, photoluminescence, advanced light sources, and nonlinear optical processes.