Real-time and low speckle holographic projection

Holographic projection that utilizes holography to record and reconstruct images to be projected is an attractive technique because it inherently requires no lenses, which could lead to the development of an ultra-small projector. In addition, holographic projection has unique functions that are difficult to perform on other projections: multi-projection that projects a multi-image on plural screens (which are also applicable on tilted screens) and projection on arbitrary surface screens; however, holographic projection has considerable problems: speckle noise, hologram calculation time and zoom without using a zoom lens. In this paper, we begin with basics of holographic projection (how to calculate holograms and reconstruct the projected images, and why we need a random phase), and then describe our latest results: the speckle reduction technique, which is referred to as random phase-free method; multi-projection, and real-time holographic projection with the random phase-free method. In addition, our holographic projection is capable of performing the zoom function without using a zoom lens, using a numerical method called scaled diffraction which can calculate diffraction at different sampling rates on a projected image and hologram.