Abstract: A device for optically scanning an information plane having tracks. Radiation is supplied by a radiation source focused on the information plane by an objective system. The beam reflected by the information plane is incident on a dividing element, for example a grating which divides the beam into two halves along a dividing line. Two sub-gratings at both sides of the dividing line each form a detection beam from one half of the beam, which detection beams are detected each by a detector. A focus error signal is generated from the detector signals by forming a difference signal of the two detector signals and dividing this difference signal by the sum signal of the two detector signals. The focus error signal is relatively insensitive to the position accuracy of the detectors with respect to the detection beams.

Abstract: An optical scanning device using one or more rows of scanning spots for simultaneously scanning a plurality of information tracks of an optical record carrier. The resulting radiation produced from the respective spots is imaged on respective photodetectors, and the detection signals from a plurality of the photodetectors are used to derive focus error and tracking error signals for the corresponding scanning spots. Error signals of the same type are then combined to derive servo control signals for respectively controlling focus and tracking of all scanning spots. The focus error signals can also be combined to derive further servo control signals for controlling tilt of the record carrier and tracking angle. Derivation of the servo control signals from error signals corresponding to a plurality of the scanning spots achieves improved immunity against the effects of dust or other artifacts on the surface of the record carrier.

Abstract: A device for optically scanning an information plane (2) having tracks (5). Radiation supplied by a radiation source (7) is focused on the information plane by an objective system (8). The beam reflected by the information plane is incident on a dividing element, for example, a grating (12), which divides the beam into two halves along a dividing line (17). Two sub-gratings (15, 16) at both sides of the dividing line, respectively, each form a sub-beam from one half of the beam, which sub-beams are detected by a detection system (10), which produces detection signals therefrom. A focus error signal is generated from the detector signals. According to the invention, modulation of the focus error signal by the track structure will be minimal if the dividing line (17) is located at an angle between 15.degree. and 80.degree. to the direction of the tracks.

Abstract: A beam splitter (120) arranged in the radiation path of the scanning beam splits off a reference beam synchronously moving with the scanning spot (21) to a reference plane (140). The movement of the scanning spot (21) can be checked by measuring, with the aid of a radiation detector (160), the movement of a reference spot (121) formed by the reference beam in the reference plane. In this way an accurate determination of the position of the scanning spot (21) is possible while using simple beam-deflecting elements (40,42) having a relatively low accuracy. A cylindrical lens (131) gives the scanning spot the shape of a line, so that sensitivity to dust and other contaminations on the reference plane is reduced considerably.

Abstract: An objective system (20) focusses the radiation from a radiation source (10) to a diffraction-limited spot (A) which is imaged on two point detectors (61, 62) by an imaging system (40) and a beam divider (60). By using this confocal principle, a differential phase contrast microscope is obtained having a low sensitivity to details which are out of focus, an increased resolution in the object plane and little crosstalk between the two detectors.