Abstract: A control system for maintaining proper focus of a radiant recording or writing beam, such as a laser beam, with respect to a recording surface, by measurement of the duty cycle of an oscillatory information-carrying signal recorded from the recording surface immediately after recording. The system includes a photodetector for detecting a reading beam used to recover the recorded information, a focusing lens movable with respect to the recording surface to focus the writing and reading beams, a dither oscillator to generate a dither signal employed to move the focusing lens in an oscillatory manner, a duty cycle detector to provide a signal indicative of the duty cycle of the information-carrying signal recovered by the reading beam, and a multiplier for comparing the phases of the duty cycle signal and the dither oscillator signal, and thereby providing a correction signal indicative of the magnitude and polarity focus error.

Abstract: A direct-read-after-write optical recording disc having a pair of transparent, disc-shaped members, each being formed with integral inner and outer ring-shaped bosses on one of its sides. A thin recording layer of a light-sensitive material is coated on each disc-shaped member, in a shallow annular recess formed between its two ring-shaped bosses, and the two members are disposed in a coaxial relationship, with their respective bosses in abutment with each other, whereby the two recording layers are located within a sealed, annular chamber.

Abstract: A multi-layer information recording medium for storing large amounts of information in a prescribed pattern of microscopic pits, formed by focusing onto the medium a beam of radiation having a prescribed wavelength and having an intensity modulated by the information to be recorded. The record medium includes a substrate having a light-reflective surface on its upper side, a light-absorptive dielectric layer overlaying the substrate and having a thickness approximately equal to an odd integral multiple of one fourth the wavelength of the beam of radiation in the dielectric material, and a thin metallic layer overlaying the dielectric layer and having a light-reflective surface on its lower side.

Abstract: A direct-read-after-write optical recording disc having a pair of transparent, disc-shaped members, each being formed with integral inner and outer ring-shaped bosses on one of its sides. A thin recording layer of a light-sensitive material is coated on each disc-shaped member, in a shallow annular recess formed between its two ring-shaped bosses, and the two members are disposed in a coaxial relationship, with their respective bosses in abutment with each other, whereby the two recording layers are located within a sealed, annular chamber.

Abstract: A digital servo system for maintaining a detection device, such as a light beam, centered as closely as possible over an information track, such as an optical track on a video recording disc. The servo system includes circuitry for detecting when the light beam traverses a switching line, which, in the illustrative embodiment, is the track centerline, for applying a constant-magnitude acceleration force to deflect the beam to a corrected position, and for reversing the polarity of the acceleration force when the beam traverses the switching line.

Abstract: Apparatus, and a related method, for maintaining an incident beam of radiation in alignment with the centerline of a movable, optically-readable information track, wherein the track comprises a succession of light-reflecting and light-scattering regions representative of a frequency modulated carrier and the sides of the track are adapted to scatter incident radiation in predetermined directions. The apparatus includes photodetector means for sensing the amount of radiation scattered by each side of the track and for generating an error signal indicative of the deviation of the incident beam relative to the centerline of the track, along with means responsive to the error signal for controllably moving the incident beam into alignment with the centerline of the track.

Abstract: Apparatus for limiting the rotational speed of an internal combustion engine by monitoring the time interval between ignition impulses produced when a breaker switch in the primary circuit of the ignition coil opens. A pair of sequentially operable timers are started for each ignition pulse with the second time interval enabling a delay means coupled between the source of pulses and a control gate of a controlled switch connected across the breaker switch through an impedance. When a following pulse occurs during the second time interval, indicating a limiting rotational speed, the slightly delayed pulse triggers the controlled switch and the ignition pulse is shunted through the impedance with the resulting secondary voltage in the ignition coil being insufficient to cause a spark, thereby limiting the speed of the engine.

Abstract: A videodisc system utilizes a beam of light which tracks the center of an interrupted spiral information channel. The light beam is "dithered" from side to side of the channel in order to determine the relative "direction" of a beam deviating from the center of the channel. The beam oscillates by approximately one-third of the width of the channel. By multiplying the returned signal by the drive signal, a signal is derived whose mean value is positive on one side of the track, negative on the other side and zero when in the center of the track.