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 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.