Abstract: An updatable optical data storage disc for use with a laser includes a substrate and a recording layer. The substrate contains pre-recorded information in the form of concentric or spiral tracks of pits. Recordable tracks are positioned between adjacent pre-recorded tracks, whereby the tracks on the disc alternate in the radial direction. Laser light reflected from the recorded portions of the recording layer has a different phase than does light reflected from the unrecorded portions. This phase difference must be significant enough to be sensed by the detector. The difference in the reflectivity of the unrecorded and recorded portions of the recording layer should be minimized. The invention also includes a method and drive compatible with the disc.

Abstract: An achromatic polarization-rotating right-angle prism system for rotating the plane of polarization of an electric field, E, by 90.degree. while maintaining strict linear polarization at all wavelengths. The direction of travel of the beam may be altered by 90.degree. or the beam may continue on in the same direction and along the same line of travel. One embodiment includes two pairs of right-angle isosceles prisms. The horizontal, H, and vertical components, V, of E each undergo an equal number of s- and p-polarized reflections.

Abstract: A magneto-optic recording medium for use with a recording system including a laser beam operable at at least two different energy levels and magnetic field source(s) for generating two different magnetic fields. The medium includes a substrate and at least two layers: a magneto-optical storage layer and a magnetic biasing layer. The storage layer maintains areas of selected magnetic orientation and is made of a rare earth transition metal alloy, such as terbium-iron-cobalt. The magnetic biasing layer is magnetically exchange-coupled to the storage layer and is made of a rare earth transition metal alloy, such as dysprosium-terbium-iron-cobalt. The Curie temperature of the storage layer is greater than that of the bias layer.

Abstract: A multilayer medium comprising a substrate, a composite dielectric layer, a magneto-optic recording layer, another dielectric layer, and a reflective layer. The composite dielectric layer has two sublayers made of different materials with distinct refractive indices, or alternatively has a single layer with a refractive index gradient. The refractive index of the portion of the composite dielectric layer adjacent the substrate is about 0.3 to 1.0 greater than the refractive index of the portion of the composite dielectric layer adjacent the recording layer.

Abstract: A method for recording on a magneto-optic recording medium having two magneto-optic recording layers having different Curie temperatures. The magneto-optic layers must be capable of existing in two different magnetic states: a first magnetic state in which both magneto-optic layers are magnetized in the same direction and second state in which the layers are magnetized in opposite directions. The phase, .phi., of the magneto-optic film stack is defined as the arctangent of the magneto-optic ellipticity, .epsilon., divided by the magneto-optic rotation, .theta., i.e.,=tan.sup.- (.epsilon./.theta.) for each magnetic state. The phase difference, .DELTA..phi., for the two states should be about 90.degree.. The method includes initializing the media, performing a first recording pass during which laser power is modulated between a high power record level and a low power record level, and performing a second recording pass during which laser power is modulated between read level power and low record level power.

Abstract: A magneto-optic recording medium having two magneto-optic recording layers having different Curie temperatures. The magneto-optic layers must be capable of existing in two different magnetic states: a first magnetic state in which both magneto-optic layers are magnetized in the same direction and second state in which the layers are magnetized in opposite directions. The phase, .phi., of the magneto-optic film stack is defined as the arctangent of the magneto-optic ellipticity, .epsilon., divided by the magneto-optic rotation, .theta.; i.e.,=tan.sup.-1 (.epsilon./.theta.) for each magnetic state. The phase difference, .DELTA..phi., for the two states should be about 90.degree.. The invention also includes a magneto-optic drive for use with the medium described above.

Abstract: A magneto-optic recording medium records data in a single, direct-overwrite step. The medium includes a magneto-optical storage layer and a magnetic biasing layer disposed in selected heat conductive relationship with the storage layer. The first magnetic field is generated externally of the storage layer at a first energy level of a laser to set the magnetic orientation of domains at the storage layer. At a second energy level of the laser, which is higher than the first energy level, the magnetic biasing layer provides a second magnetic field greater than the first magnetic field for setting the magnetic orientation of domains in the storage layer.