(3+1)D Printing of Core–Clad Waveguide by Two‐Photon Polymerization

Abstract Optical waveguides are key components in the development of next‐generation photonic circuits, where minimizing propagation losses remains a critical challenge. In this work, an innovative methodology is presented for the fabrication of core–clad waveguides using 3D printing based on femtosecond laser two‐photon polymerization and the hybrid Ormocomp resin. The approach leverages multiple laser passes and power modulation to locally tailor the refractive index of the printed structures. To assess the degree of polymerization and its effect on refractive index modulation, in‐depth Raman spectroscopic analyses are performed. These investigations provide insight into the molecular structure of the polymer and its correlation with optical index changes. Furthermore, several low‐loss core–clad waveguides with refractive index variations achieve through 2 to 6 laser passes are demonstrated. Optical characterization and interface roughness analysis reveal propagation losses as low as 0.16 dB·cm −1 , along with a minimum surface roughness of 28 nm. By combining original 3D printing techniques with detailed spectroscopic analysis and optical characterizations, this work paves the way for new possibilities for the additive manufacturing of integrated photonic waveguiding devices.