Enhanced three-dimensional imaging with large depth of field using pre-processing in optical scanning holography

Optical scanning holography (OSH) emerges as a groundbreaking single-pixel real-time holographic recording technique, charting new territory beyond conventional digital holography. A notable challenge in OSH, as with all three-dimensional (3D) imaging methods, is the susceptibility of reconstructed images corrupted by defocus noise. The noise is an unintended result of diffraction on the focused plane from out-of-focus planes of the three-dimensional object, which can degrade image quality upon holographic reconstruction. Current methods, however, all use some algorithms to post-process holographic data to achieve the purpose of eliminating out-of-focus noise, which is difficult to meet the requirements of real-time image processing. We propose an innovative pre-processing approach in optical scanning holography that not only eliminates defocus noise but also significantly enhances image quality. Preprocessing is accomplished by the utilization of a focus-tunable lens (FTL) to refocus the optical scanning beam according to the depth of the occlusion-free object. Complex holograms are then captured without the artifacts associated with defocus through real-time holographic data pre-processing. Numerical simulations and experimental results demonstrate that our proposed method can directly obtain high-quality reconstructed images with all the 3D information being in focus simultaneously.