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Abstract

An optical memory for storing and/or reading data on an optical disk. The optical disk incorporates a material in which holographic gratings can be created at plural locations within the disk. An electro-optical head which is capable of creating these holographic gratings at any one of the plural locations is employed. The head is additionally capable of detecting the presence or absence of a holographic grating at any one of these plural locations. The presence of the holographic grating could indicate a first binary state and the absence of the holographic grating indicate a second state. Alternately, the electro-optical head could be used to vary the diffraction efficiency of the holographic gratings during their creation. In that case, the head would also be capable of detecting this variation in efficiency and produce a proportional detection signal. This signal would be used as an indicator of the value of the stored data element. The material of the optical disk is further capable of having multiple holographic gratings created at each one of the plural locations. These multiple holographic gratings are created via a beam of light from the electro-optical head which has a different wavelength or point of focus. In reading these holographic gratings, a beam of light generated by the electro-optical head is sequentially varied in wavelength or point of focus to correspond to the wavelength or point of focus and the sequence of wavelengths or points of focus employed to record each one of the data elements recorded.

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