Volume hologram shrinkage dynamics and compensation strategies under long-term accelerated aging conditions

Volume holographic optical elements (VHOEs) are pivotal for next-generation augmented reality (AR) and virtual reality (VR) systems. However, the dimensional stability of photopolymers under environmental stress remains a critical challenge, as material shrinkage leads to Bragg condition mismatches. This study investigates the long-term shrinkage dynamics of Bayfol HX200 photopolymer based on reflection gratings under accelerated aging conditions (85°C/85% RH) over 100 days. We utilized angular shifting measurements to precisely quantify the Bragg angle deviation. Results demonstrate that high humidity significantly accelerates shrinkage, causing it to converge to a stable limit of approximately 16.5% after 70 days, whereas high temperature alone results in slower, non-convergent shrinkage. Crucially, this humidity-induced shrinkage was found to be irreversible. Leveraging this stability, we propose and experimentally validate a pre-compensation recording strategy. By offsetting the recording angles to account for the predicted terminal shrinkage, the VHOEs achieved the designed Bragg characteristics after stabilization. Additionally, we address the issue of non-uniform efficiency degradation, attributing it to substrate-induced warping rather than photopolymer failure.