We propose a simple, compact and high-security holographic optical memory system using Ulexite in order to produce random patterns of reference beam. 100 hologram multiplexing was achieved by multiplexing exposure, rotating Ulexite by 0.2 degrees every time with LiNbO3 crystal as a recording medium. Moreover, with this system, animation readout images can play for approximately 8 seconds by continuous rotation of Ulexite. As a natural stone, the exactly same Ulexite is very difficult to be found or replicated. Basic experimental results show that Ulexite can be used as a security key for its image-reproducibility and BER calculations.
We fabricated a large size (110x106mm2) Volume Phase Holographic (VPH) grism which was extremely high efficiency and dispersion. In June 2003, the VPH grism with straight wavelength of 450nm and the resolution 2500, installed in Subaru telescope used for the Faint Object Camera And Spectroscopic (FOCAS) for a test observation. As a result of this performance assessment, it was verified that our optimal design and fabrication process was valid. Liquid photopolymer is used for VPH grating as photosensitive materials. We design the optimal parameters such as grating thickness and strength of the refractive index modulation, which is crucial in obtaining a well performing grism, by reference to Rigorous Coupled Wave Analysis (RCWA). Here, the optimal design and fabrication procedure, and the evaluation of high performance VPH grism (wavelength:520nm, resolution:3000, grating period:1μm) will be discussed.