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In this paper, various aspects of optical storage have been reviewed. First, the author introduces storage needs which will continue to grow exponentially. The advancement of Internet and computer software will accelerate the increase of manageable data and the large storage requirements. This paper introduces discussion topics such as applications, recording density limits and the progress of science and technology. The possibility of optical dynamic random access memory (ORAM) is mentioned in relation to memory hierarchy. To overcome the density growth limit many kinds of attempts have been made including introduction of super resolution, flying head recording, near field recording and dynamic spatial phase control recording. In the future, optical storage with a high recording density of 100 Gbit per square-inch and new amplification or enhancing mechanisms for writing and reading of tiny marks will be important. The author has raised the above issues which will be discussed.

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Experimental results of nonlinear optical image processing by a saturable Fabry-Perot filter are described. Fulgide, a photochromic compound, in toluene is used as a saturable absorber for the green light of an Ar-ion laser. Image thresholding using a steep increase of transmission with a critical power density of 700 mW/cm(2) is demonstrated. The spatial resolution is found to be more than 10 lines/mm over a 30-mm-diameter aperture.