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Hiding image data with a material such as a light-scattering medium is useful as an initial stage of data protection, because the hidden image can be detected only by observation with a specific technique. A light-scattering medium is used to hide the image data, and a low-temporal-coherence interferometer performs the readout processing. A new readout method for detecting pixel values of the image is proposed to overcome spatial variation of the light intensity and distortion of the interference fringes. The introduction of spatial coding further improves the performance by overcoming spatial variations of the light-scattering medium and variations in the reflectance of given pixels.

A new type of 4000-5000 lm-class white lamp system using high-power blue laser diodes and phosphors has been developed for high-luminance lighting applications. Using fibre-optics, the lamps can be arranged separately from a light engine containing the blue laser diodes. One of the new lamp systems achieved much higher luminance of 140 Mcd/m 2 than the conventional white LEDs. Their lighting quality and safety categorization have been discussed based on speckle contrast as an index of coherence. Speckle contrast values less than 2% as low as the LEDs have been obtained, implying that these lamps are considered to be incoherent as well as the conventional white LEDs. Multiple scattering processes in the lamp structure including the phosphor layer are found to be indispensable for reducing speckle contrast completely, adding to multi-longitudinal mode operation of the blue laser diodes.

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