Numerical and optical reconstruction of digital off-axis Fresnel holograms

Abstract

Setup for recording digital off-axis Fresnel holograms is described. Obtained digital holograms were reconstructed both numerically and optically. Results of optical and numerical reconstructions are compared. Digital off-axis Fresnel holograms with a pixel size 9 μm and number of pixels up to 2048 × 2048 for the scene depth up to 480 mm at distances 700÷1400 mm were recorded. Experimental setup allows to record holograms in both modes of object's illumination: "on transmission" and "on reflection". For hologram numerical reconstruction various methods were implemented in programming environment MATLAB: direct calculation of Fresnel diffraction (DC), Fresnel diffraction calculation through fractal Fourier transform (FrFT), angular spectrum propagation and others. Under numerical testing it was found that the best quality of reconstructed images is provided by the FrFT method. The DC method yielded the best results for numerical reconstruction of recorded digital holograms. For optical reconstruction recorded digital holograms were binarized by the threshold and printed on transparent film with a resolution of 100 dots/mm using laser imagesetter. The optically reconstructed images have higher noise level than numerically reconstructed ones. This is primarily because of holograms binarization. Also digital holograms were optically reconstructed using LCOS SLM HoloEye PLUTO VIS. Resolutions of displayed digital holograms were limited to 1920 × 1080 (SLM resolution). Quality of reconstructed images is close to quality of numerically reconstructed images. Real time holographic video of remote volumetric scenes was experimentally demonstrated through combination of the setup for digital holograms recording and the setup with SLM for their optical reconstruction.