Noise Reduction in Holographic Reconstruction by Combining Two Spatial Light Modulators

Abstract

One of the issues in holographic display is the presence of the zeroth order and the twin image, which degrade quality of reconstructed objects. A common solution is to use an off-axis configuration. However, the spatial separation of the three contributions imposes constraints on the resolution and the size of holograms that can be displayed. In addition, the spatial light modulators (SLM) available present limitations in term of resolution and fill factor. Recently, different methods have been proposed to display complex information and therefore get rid of the twin image. One approach is to use a grating to combine the real and imaginary parts of the holographic data. It requires only one SLM, but the resolution is low as the SLM is divided in two to display the two components of the data. The grating period that should be used also strongly depends on the wavelength and the hologram size. As a result, the tolerance of the system is very low. Another method is to combine two SLMs. In this study, we used a polarizing beam splitter and a wave-plate to exploit the polarization properties of the light and combine the wavefronts coming from two SLMs. One was used to display the hologram while the second compensated the background noise coming from the diffusion of the input light by the pixels and the intrinsic periodic structure of the SLM. A key point is to align precisely the two SLMs to optimize the noise reduction without losing the object's information.