Abstract: A switchable optical unit, capable of controlling a beam of radiation (b) passing through an optically active portion (8) of the unit, comprises a fluid chamber (10) including an electrically conductive liquid (18), which chamber comprises at least one first electrode (20,22) fixed to the chamber inner walls (12,14) at the position of the optically active portion and second electrode means (24) fixed to inner walls of the chamber outside the optically active portion and a third electrode (28) connected to the conductive liquid. By applying a voltage (V) to the at least one first electrode and the second electrode means, respectively the conductive liquid can be moved in and out the optically active portion so that the unit (1) is switched between a least two discrete states.

Abstract: A device for reading and/or writing a disc-shaped information carrier which comprises a support element of a magnetizable material along its circumference. An electromagnetic unit cooperates with the support element and a scanning unit for reading and/or writing the information carrier, which can be rotated about an axis of rotation and positioned with respect to the scanning unit in five degrees of freedom except for the rotational degree around the axis of rotation.

Abstract: The invention relates to a method of manufacturing a master mold (1), which is used to manufacture an optical information disc, such as a CD or DVD. According to the method, a substrate (3) is provided with a photosensitive layer (5), which is subsequently irradiated by means of a radiation beam (7), which is focused to a scanning spot (11) on said layer by means of an optical lens system (9). A liquid, such as water, is supplied into a gap (53) present between the photosensitive layer and an auxiliary lens (59) of the lens system facing said layer. As a result, the size of the scanning spot is decreased and the information density of the information disc to be manufactured is increased. According to the invention, the liquid is supplied via a supply opening (69) which is positioned immediately adjacent the auxiliary lens (59), in a direction which, viewed from the scanning spot (11), is contrary to a direction (Z) wherein the substrate (3) is moved with respect to the lens system (9).

Abstract: The invention relates to a device for reading and/or writing a disc-shaped information carrier (17), which comprises a support element (25) of a magnetizable material along its circumference. The device comprises an electromagnetic unit (27) for co-operation with the support element and a scanning unit (23) for reading and/or writing the information carrier. By co-operation between the electromagnetic unit and the support element, the information carrier can be rotated about an axis of rotation (73) and positioned with respect to the scanning unit (23) in five degrees of freedom, i.e. in all degrees of freedom except the rotational degree of freedom around the axis of rotation.

Abstract: The invention relates to a method of manufacturing a master mold (1), which is used to manufacture an optical information disc, such as a CD or DVD. According to the method, a substrate (3) is provided with a photosensitive layer (5), which is subsequently irradiated by means of a radiation beam (7), which is focused to a scanning spot (11) on said layer by means of an optical lens system (9). A liquid, such as water, is supplied into a gap (53) present between the photosensitive layer and an auxiliary lens (59) of the lens system facing said layer. As a result, the size of the scanning spot is decreased and the information density of the information disc to be manufactured is increased.

Abstract: A tracking mirror device, in particular for a video disc player, in which for following an information track on a video disc with a beam of radiation, use is made of a mirror which oscillates at a high frequency, which causes the beam of radiation, which serves for scanning the information track, to oscillate transversely to the information track at a high frequency and a small amplitude, while the filtered out high-frequency signal, as a function of its amplitude and its phase relationship with the high frequency voltage which is applied to the oscillating mirror, yields a control signal for following the information track. In accordance with the invention, use is made of an oscillating mirror which is driven electromagnetically and which is connected to oscillation compensation elements by means of springs which elements oscillate in phase opposition to the mirror. Thus, an oscillator mirror is obtained which can readily be excited to natural resonance and thus requires little power.

Abstract: A playing apparatus, more specifically a video player for playing round records with a central hole, which are made of a transparent material, which records at one side have a transparent surface and at their other side are provided with information tracks which are optically readable with the aid of a read beam, which tracks are covered by a light-reflecting layer. In order to enable both relatively thick rigid records and relatively thin flexible records to be played on one playing apparatus, the invention provides a transparent adapter disc, which together with a flexible record can be positioned on the playing apparatus and driven in a rotary fashion. In order to prevent dust particles from being trapped between the flexible record and the transparent adapter disc, the adapter disc may be provided with a central recess with a number of air admission apertures at the circumference thereof, so that during operation a thin film of air is formed between the flexible record and the adapter disc.

Abstract: An automatic optical focussing system, suitable for a video disc player, comprising an optical focussing device with an objective which is moved to and fro at high frequency in the direction of its optical axis by electro-dynamic drive means, the superimposed high frequency component of the signal which has been modulated by the information tracks on the video disc being employed for automatic control of the position of the objective. In view of a low power consumption the objective is connected to an oscillation-compensation element by means of at least one resilient element, for example a circular plate, which compensation element is axially movable or relative thereto, and which together with the objective and the resilient element constitutes a mechanical resonant system. On the resonant system a piezo-electric acceleration transducer may be mounted with the aid of which the mechanical resonant system can be included in a self-oscillating loop.

Abstract: In an opto-electronic focus detection system for determining a deviation between the plane of focussing of an objective and a radiation-reflecting surface the path of a focussing beam which is reflected by said surface includes an assembly of two radiation-sensitive detection elements. The difference in the output signals of said elements is proportional to said deviation. By disposing a lenslike element of which only the outer zone has a lens action before the detection elements, the measuring range can be extended while maintaining the sensitivity for small deviations.

Abstract: A device for writing information in a disk-shaped record carrier, and/or for reproducing the recorded information, the transducer being radially movable relative to the record carrier, which transducer is disposed on a tubular member, which at its one end is provided with a drive coil and at its other end with a tachometer coil, which coils are movable in an air gap of a stationary magnet system.