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Abstract

Apparatus and methods are disclosed for acquiring and maintaining focus of a coherent light source used to read and write data in an optical disk data storage device. The system uses a conventional astigmatic focus system in conjunction with a signal processor to detect proximity of focus. After proximity of focus is detected, the signal processor enables a fine focus servo system to maintain focus of the coherent light on the disk surface. The system includes a coherent light source for reading and writing data on the optical disk storage medium, a condenser lens for focusing the coherent light on the recording surface of the disk, a cylindrical lens for passing light reflected from the recording surface, a quad light detector responsive to the reflected light from the cylindrical lens for providing an output signal, a controller responsive to the quad detector output signal for providing a control signal when proximity of focus is detected, and a fine servo system for controlling the position of the condenser lens. The system also includes a method of avoiding a false focus on any transparent overcoat layer placed over the recording surface of the optical disk storage medium.

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First Claim