Abstract: Disclosed is a system for optically recording information on a disc-shaped record carrier body along an information track, with the write spot being accurately guided in the radial and tangential directions. The record carrier body comprises a servo track formed by a constant and large number of servo areas per revolution of the servo track. In addition to a write spot, the write apparatus also projects a servo spot on the servo track. The tangential speed and the radial position of the servo spot relative to the servo track are determined from the modulated servo beam and used to correct the tangential speed and the radial position of the write spot, which is locked to the servo spot.

Abstract: Disclosed is a system for optically recording information on a disc-shaped record carrier body along an information track, with the write spot being accurately guided in the radial and tangential directions. The record carrier body comprises a servo track formed by a constant and large number of servo areas per revolution of the servo track. In addition to a write spot, the write apparatus also projects a servo spot on the servo track. The tangential speed and the radial position of the servo spot relative to the servo track are determined from the modulated servo beam and used to correct the tangential speed and the radial position of the write spot, which is locked to the servo spot.

Abstract: An electro-optical apparatus comprising an objective (7) scans an optical disc (3) having a transparent protective layer (5) by means of a radiation beam (10) which, through the transparent layer, is focussed on a reflecting recording surface (4). The objective moves along the optical axis (19) for focussing the radiation beam on the recording layer and moreover performs limited pivotal movements. The position of the optical axis of the objective is corrected for obliquity of the surface of the optical disc, correction means (22A, B) being provided to tilt the objective through a correction angle, so that the angle between the optical axis and the normal to the disc surface is reduced.

Abstract: "Method of coding data bits on a recording medium, arrangement for putting the method into effect and recording medium having an information structure."The so-called Miller modulation has the disadvantage that a direct current is generated in the information channel. When this modulation method is used for magnetical or optical recording, the result is that the amplitude values and the zero crossings are deformed as these channels cannot transmit direct current.According to the invention, in order to obtain, a d.c. free modulation, the Miller modulation concept is modified such that sequences of data bits which, after coding, result in the introduction of a d.c. component are coded differently. It appears that, the frequency zero excepted, a good suppression of the response is obtained also in a fairly wide low-frequency portion of the spectrum.

Abstract: Disclosed is a method and apparatus for recording information on a disc-shaped record carrier body with a single beam of radiation. The record carrier body is provided with a servo track which preferably exhibits a phase structure and which contains a multitude of sector addresses each associated with a portion provided with a radiation sensitive layer. Before the information is recorded, the beam is switched to a low, read level and the desired address is located. Simultaneously, the radial position and tangential speed of the radiation spot and the focusing of the radiation beam are checked. Once the desired address is located, the beam is switched to a higher, write intensity and the information is recorded on the radiation sensitive layer of the portion associated with that address. During recording, the radiation returning from the record carrier can be used to check whether the information is recorded correctly.

Abstract: An optical read unit for reading radiation-reflecting video discs comprises a semiconductor laser which with the aid of a scan wobbler and a focussing wobbler is moved at high frequency in two directions relative to the video disc, a radial direction for tracking purposes and a direction normal to the disc for the purpose of automatic focussing. The semiconductor diode laser is mounted on a metal radiation source carrier which is connected to a heat sink for carrying off the heat with a low temperature gradient, and is driven by piezo-electric plates.

Abstract: An optical scanning device which scans a rotary video disc with the aid of a light beam comprises an objective which performs focussing movements, for focussing a light spot on a recording surface of the video disc, as well as tilting tracking movements and time-error correction movements. Near its lower end the objective is suspended in an impregnated corrugated loudspeaker diaphragm of fabric fibre which enables the various movements of the objective to be made without giving rise to annoying resonant effects. The tracking movements and the time-error correction movements are obtained with the aid of coils which are connected to the objective near the upper end and which are disposed in air gaps of associated permanent magnetic stators.