Abstract: Disclosed is a wavelength multiplexing optical recording apparatus comprising laser sources radiating a plurality of laser beams of different wavelengths, an optical system for focusing the laser beams, and an optical recording medium having a plurality of optical recording layers with wavelength sensitivities for selective recording by said laser beams focused by said optical system. The optical recording layers of recording medium are laminated with distances between adjacent layers being made consistent with biased focal positions of the laser beams attributable to the chromatic aberration of the optical system, so that the laser beams are focused on the optical recording layers of corresponding wavelength sensitivities.

Abstract: An information recording and reproducing apparatus is disclosed, which makes use a recording medium made of a metal or alloy having phases different in their crystalline structures at at least two temperature regions in the solid state and capable of causing phase transformation by heating and quenching. Information such as signals, letters, patterns and symbols are recorded in a distinctive manner and erased by making use of a change in the spectral reflectance owing to the phase transformation. Rewriting can be made easily by making use of the energy of a light beam such as a laser beam.

Abstract: An optical recording medium and an optical recording process using such a medium are provided. The optical recording medium comprises a photopolymerizable monomer having a hydrophilic group, a hydrophobic group, and at least one unsaturated bond in the molecule.

Abstract: Optical data storage members in which the guard bands present between data-carrying tracks of conventional data storage members are used to carry information recorded in a manner which avoids the danger of cross-talk between adjacent tracks. One preferred arrangement consists of an optical data storage member comprising an optically recordable surface having a plurality of tracks in which information may be recorded in analogue or digital form, the tracks being of a first type in which the material constituting the track is sensitive to radiation of a first predetermined characteristic and a second type in which the material thereof is sensitive to radiation of a second predetermined characteristic, wherein tracks of the first type alternate across the surface of the second type. The tracks may be constituted by a surface region (1,2,3,4,5) carrying a plurality of closely spaced grooves (11,12,13,14,15), the grooves of one track being orthogonally directed with respect to those of its adjacent tracks.

Abstract: An apparatus for improving the focus of a digital optical record and playback system is described which provides plural simultaneous focal paths of different lengths for playing back or recording a digital optical data record. These focal paths may interact a common bit portion on a data record, successive bit positions in the same row of data on the record, or bit portions on adjacent tracks of data on the record. In certain embodiments, a selection circuit is utilized for evaluating the focal paths and selecting one which results in an improved focus. Data records having recorded bits of data of extended depth are also described to facilitate focusing during playback of the data record.