Abstract: Turntable (10) has a turntable bottom (19) and a turntable wall (20) which together define a locating space (21) in which the hub (7) of an information disc is engageable, and in which it is centered by means of a centering member (12) and clamped by magnetic clamping means. At the circumference of the locating space a centering wall (26) is provided, which wall has an inwardly sloping surface (27). The dimensions of the various parts, the field strength of the magnetic means and the coefficients of friction of the cooperating materials of the hub and the turntable are selected in such a way that, once an information disc has reached a position in which the free end of the centering member (22) has engaged the centering hole (17) of the information disc, the outer wall (28) of the hub (7) is situated above the sliding surface (27) of the turntable.

Abstract: The recording surface of an optical record carrier (1) is divided into a succession of first (A) and second (B) annular zones, each including a plurality of substantially concentric information tracks. The tracks in each zone (A) include radially aligned first control words (13) and the tracks in the annular zones (B) include radially aligned second control words (14), the structures of the first and second control words being distinguishable from each other. An optical scanning device projects a beam which as it scans the tracks reads the control words and a detection circuit generates a measurement signal V.sub.m upon each passage of the beam from one zone to another. The measurement signal can be utilized to rapidly address the scanning beam to any of the annular zones.

Abstract: An information-transmission system including an encoder for converting n-bit information words (D7, . . . , D0) into transmitted m-bit code words (C10, . . . , C0), and a decoder which reconverts the received code words (C'10, . . . , C'0) into information words (D*7, . . . , D*0) corresponding to the original information words. For a first group the encoder converts a first portion (D7, . . . , D3) into a first portion of a code word, such portion comprising q bits (C10, . . . , C5) thereof; and converts a second portion (D2, . . . , D0) of the information word into a second portion of the code word, such portion comprising s bits (C4, . . . , C0) thereof. For a second group the encoder converts a first portion (D7, . . . , D3) into a second portion comprising q bits (C'5, . . . , C'0) of a code word, and converts a second portion (D2, . . . , D0) of the information word into a first portion comprising s-bits of (C'10, . . . , C'6) such code word.

Abstract: Method of providing a substrate of an optically readable information disc with an optically detectable structure, mould for use in the method, apparatus for carrying out the method, and information disc manufactured in accordance with the method.Substrate (3) is provided with a disc hub (8) comprising disc-centering means (9) which serve to center the finished information disc (17) on the drive spindle (27) of a drive apparatus. The intermediate product comprising the substrate (3) and the disc hub (8) is centered on the base (1A) of the mould by cooperation between the base-centering means (17) and the disc-centering means (9). This may be effected by the use of an auxiliary centering means (12) which is in contact with a wall (14) of a central centering hole (11) in the disc hub (8) and with a wall (13) of a central centering recess (10) in the base (1A).

Abstract: The invention relates to a method of providing a substrate with a centered optically detectable structure, such as a servo structure on a transport substrate of an optical information disc. The method uses a mould (1) having a base (1A) carrying a mould structure (2) which is covered with a reproduction layer (4) of a transparent radiation-curable resin, which after curing is detached from the mould together with the substrate. In its center the base (1A) of the mould is provided with base-centering means (7) relative to which the mould structure is centered accurately. Before it is placed on the mould a substrate (3) is provided with a disc hub (8) comprising separate disc-centering means (9) which serve to center the finished information disc (17) on the drive spindle (27) of a drive apparatus. The intermediate product comprising the substrate (3) and the disc hub (8) is centered on the base (1a) of the mould by cooperation between the base-centering means (17) and the disc-centering means (9).

Abstract: An interchangeable optically readable storage disk has a substrate with a recording surface, and a cover thereon which may comprise a second substrate with a further recording layer. The disk includes a protecting arrangement at the circumference of the substrate, which includes a balancing arrangement. The balancing may be effected by apertures in the protecting arrangement, or balancing masses affixed thereto.

Abstract: Disclosed is an apparatus for detection of write protect data written on an optical disk by simultaneously reading the data during writing using differential detection and disabling further writing if write protect data is present. The write protect data is the same format as other data written on the optical disk and is written as the first byte of data on all data fields. The data is written in a fixed-block format defining a symbol having a predetermined number of symbol positions and a predetermined number of holes which may be written at the symbol positions, an equal number of holes at odd and at even positions. The write protect symbol has holes written at symbol position numbers two and five. During the writing of a write protect symbol, the laser is operated at read power before it is operated at write power and a signal associated with the hole associated power of the reflected beam is sampled at position number eight of the previous symbol and at position number one of the write protect symbol.

Abstract: Disclosed is an apparatus for verifying data written on an optical disk by simultaneously reading the data during writing and using differential detection to verify that the data has been written correctly. The data is written in a fixed-block format defining a symbol having a predetermined number of symbol positions and a predetermined number of holes which may be written in the symbol positions, an equal number of holes in the odd positions and in the even positions. In this regard, the holes written in the odd positions are independently verified from the holes written in the even positions. Immediately after the laser has been operated at write power, it is returned to read power and a signal associated with the hole associated power of the reflected beam is sampled. This signal is compared to the signal power generated at the previous even or odd position. The highest signal is retained and compared to the next even or odd position's signal.

Abstract: A circuit is shown for rapidly enabling and disabling a high current laser diode through a coaxial cable responsive to a data signal received at the circuit input. At the circuit input are two switching transistors, one or the other of which is forward biased while its counterpart is reverse biased, depending upon the level of the incoming data signal. The output of one of the switching transistors is fed to the base inputs of two emitter follower transistors, one PNP and the other NPN. The emitter terminals of the follower transistors are connected to the gate terminal of an enhancement mode VMOS field effect transistor. When the VMOS FET is enabled, current flows in the laser diode to energize it. The voltage level at the input to the follower transistors determines the voltage to the gate input of the FET. When the incoming data signal is low, the gate-to-source potential difference is near zero, thus preventing the FET from conducting current.

Abstract: Two thick film resistors calibrate the output of the feedback light detector circuit for monitoring the light power of a laser diode. The output is connected to the power control circuit for the laser diode. Calibration of the feedback output during manufacture permits replacement of the laser diode/feedback light detector combination in the field without recalibration of the power control circuit.

Abstract: Disclosed is a Reed-Solomon error correction apparatus which is programmable to perform several distinct error correction functions. The apparatus performs the following functions: encoding, error detection, syndrome generation, burst error trapping, and Chien searching.

Abstract: Disclosed is a sector mark decoder for an optical recorder. Sector marks are prerecorded on the optical recording surface and comprise a series of evenly spaced marks. Data is recorded on the media in a fixed block code via holes burned into the optical recording surface. Both sector marks and data are detected by common apparatus, but are distinguished from each other by their different recording format. The location of a hole or a prerecorded mark is determined by comparing two sample and hold cells in a comparator. One holds the read signal value received at one disk position and compares it to the signal value held in the other sample and hold cell received at the previous position. If the comparison results in a new higher valued signal being found, the output of the comparator changes. The new higher valued signal is retained and the other sample and hold cell samples at the next disk position. This sequence continues until a sector mark has been decoded.

Abstract: A wedge/taper alignment ring is used to hold the objective lens of a laser light pen in place. The ring is free to move in the axial direction under forces of thermal expansion and shock, decreasing distortion and misalignment to the objective. Moreover, it centers the mechanical axis of the objective to that of the housing. A spring with a high restoring force moves the ring back into place.