Abstract: The invention relates to an optical memory in which an optical recording medium is built in a case, and also to a memory apparatus. Recording, reproducing and erasing operations are performed by irradiating light via a transparent portion of the case onto the built-in optical recording medium. The optical recording medium built in the case has face vibrations with respect to the case, because it is moved within the case. The present invention is characterized by employing such a construction for optically mitigating irregular fluctuation in reflectivity caused by this face vibration. In the optical memory of the present invention, the reflectivity fluctuation caused by an interference effect made between reflection light from the case and air, and also reflection light from the optical recording medium and air due to the relative deviation in the face vibrations, may be reduced by antireflection films provided in the case and the optical recording medium.

Abstract: There is provided a compact and thin optical disk unit as a memory unit suitable for a portable computer such as a book type computer and a portable recording/reproducing apparatus. In the optical disk unit, the diameter of an objective lens is limited and a beam shaping prism, a beam splitter, a mirror and a 1/4 wavelength plate are formed into a unitary structure to make easy the optical axis adjustment of an optical head and ensure highly accurate assembling.

Abstract: An optical recording medium, which comprises a recording layer capable of reversibly undergoing a phase change between a crystalline state and an amorphous state by irradiation of an electromagnetic energy, the crystalline state of the recording layer being composed of a single phase of substantially a three-component compound or a higher multi-component compound can attain high speed recording and high speed erasing that cannot be obtained with the conventional optical recording medium.