Speckle noise is an important issue in electro-holographic displays. We propose a new method for suppressing speckle noise in a computer-generated hologram (CGH) for 3D display. In our previous research, we proposed a method for CGH calculation using ray-sampling plane (RS-plane), which enables the application of advanced ray-based rendering techniques to the calculation of hologram that can reconstruct a deep 3D scene in high resolution. Conventional techniques for effective speckle suppression, which utilizes the time-multiplexing of sparse object points, can suppress the speckle noise with high resolution, but it cannot be applied to the CGH calculation using RS-plane because the CGH calculated using RS-plane does not utilize point sources on an object surface. Then, we propose the method to define the point sources from light-ray information and apply the speckle suppression technique using sparse point sources to CGH calculation using RS-plane. The validity of the proposed method was verified by numerical simulations.

Holographic scattering (HS) is a phenomenon that occurs when a scattered light wave is recorded on a holographic recording medium and is important for applications using volume holograms, such as holographic data storage, three-dimensional displays, and waveguides for head-mounted displays. We investigated the occurrence mechanism and characteristics of HS occurring in angular-multiplex recording of plane-wave holograms on a photopolymer. First, the reconstruction condition of the hologram formed by scattered light waves during multiplex recording is formulated. Then the diffracted light waves are visualized as the intensity distribution on a virtual screen. Using these results, we proposed a model of the HS-generation mechanism by the superposition of diffracted light waves and self-amplification of hologram reconstruction. The validity of the model is confirmed through experiments, and the diffraction efficiency of HS is measured and discussed.

A holographic 3D printer produces a high-quality 3D image reproduced by a full-color, full-parallax holographic stereogram with high-density light-ray recording. In order to produce a high-resolution holographic stereogram, we have to solve the problem of speckle noise in this system. For equalizing an intensity distribution inside the elementary hologram, the object beam is modulated by a diffuser. However the diffuser typically generates speckles, which is recorded in the holographic stereogram. It is localized behind the reconstructed image as a granularity noise. First we show the problems of some conventional ways for suppressing the granularity noise using a band-limited diffuser, and then we analyze an approach using a moving diffuser for the reduction of this noise. In the result, it is found that recording with a moving diffuser is effective for reducing the granularity noise at infinity of reconstructed image, although an alternative noise occurs. Moreover we propose a new method introducing multiple exposures to suppress the noise effectively.

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We have enabled the superimposition of multiplexed images on the same screen at the same time with tangible and stable equipment. Our multiplex images can be seen by wearing special configured polarized glasses, and the image projection method is designed to be based on current 3D stereoscopic technology, which is now prevalent and making rapid progress, thus high compatibility with current contents industries is retained. Therefore our system enables the wide range of applications with new expressions and can easily be put into production.