Holographic resolution and its application in memory and imaging

Citation

Liu, Wenhai (2001) Holographic resolution and its application in memory and imaging. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BDB0-VJ12. https://resolver.caltech.edu/CaltechTHESIS:10152010-092145939

Abstract

Optical information storage and optical information processing are two major applications of holography, with significantly different holographic philosophies. For a holographic memory system, a complex holographic pattern encoded with the storage data is recorded first, and is read out later by a simple pre-designed reference beam. For a holographic information processing system, a pre-designed holographic pattern is stored in the medium first, and is probed by complex incident signal wave fronts. The pre-designed hologram extracts certain components from the complex input and diffract them as specific reference wave fronts. Holographic resolution, or Bragg phase selectivity in spatial and spectral dimensions, plays a key role in both applications. It determines the information capacity to be stored in and reconstructed from the hologram memory, or the information capacity to be extracted and processed by a hologram from the complex signal input. In this thesis, we investigate the holographic resolution in volume holograms and its specific issues in both applications. In a phase conjugate holographic memory system, we demonstrate the recording and reconstruction of a submicron pixel resolution, leading to the potential of storing 1 Gbit in 1 cm^3 volume holographically. Phase conjugate reconstruction eliminates the optical resolution limit by the imaging optics and reduces the system volume and cost. Phase conjugate reconstruction and its multiplexing in a compact holographic module are investigated. In general, a volume hologram has two degenerate Bragg phase-matching dimensions besides the spatial and spectral selectivity, in which significant diffraction is present. They provide a potential ability for optically sectioning a two-dimensional slice from the spatial plus spectral hyperspace and for linearly transferring the information onto a two-dimensional sensor array by a single hologram. The resolution of optical sectioning and information transformation is not only determined by the volume hologram diffraction intensity selectivity but also by the holographic architecture and the transformation aberration. We study two holographic architectures theoretically and experimentally, on issues of optical sectioning and linear transformation for imaging application. By designing a transmission geometry system, we have achieved a linear 2-D optical sectioning and imaging from a 4-D object hyperspace (3-D spatial plus spectral dimension). By optical sectioning of multiplexed holograms, the ability of imaging 3-D spatial information from an object without a scanning mechanism is demonstrated by a holographic imaging system.

Thesis Files