| 摘要 |
<p>A focus error correction apparatus for use in a pickup system for reading data in a three-dimensional information carrier is presented. The information carrier is formed with a plurality of spaced-apart data regions, each surrounded by surrounding regions. The data regions are made of a material capable of generating an output excited radiation, when interacting with a predetermined incident exciting radiation. The surrounding regions are substantially optically transparent with respect to the incident and output radiation. A focusing optics defines a focal plane inside the carrier, and is associated with an actuator that provides a relative displacement between the information carrier and the focusing optics along its optical axis. A filter assembly picks up the output radiation to be received by a detection unit. An arrangement is provided for defining at least two spaced-apart focal planes aligned in a preset relationship with the focal plane of the focusing optics, such that the received output radiation is indicative of the relative location of the addressed plane relative to the focal plane.</p> |
