Modeling the Copying Accuracy of Two-Dimensional Holographic Gratings in Photopolymer Media

Volume holographic gratings are periodic refractive index structures widely used in sensing and photonic devices. This paper develops a modeling and computational framework for predicting the copying accuracy of two-dimensional gratings recorded in photopolymer materials using interference lithography. A previous mathematical model is generalized to describe material transport, polymer growth, and modulation of the refractive index during exposure, enabling, for the first time, a quantitative assessment of copying accuracy in holographic gratings. High-fidelity finite-element simulations were performed for different optical lattices produced by three-beam interference. The results show that the diffusion–polymerization ratio has a strong impact on pattern accuracy, modulation depth, and polymer distribution. In particular, diffusion-dominated regimes enable high copying accuracy, while polymerization-dominated conditions lead to significant distortions of the recorded structure. Furthermore, the model predictions are experimentally validated by good agreement in the measured diffraction patterns and efficiencies.