A photodetector is divided into a pair of first segments and a pair of second segments by a common line. A total area of the first segments is larger than an area of a spot reflected from an optical disk onto the first segments. The second segments are provided within the first segments. A total area...http://www.google.de/patents/US5253240?utm_source=gb-gplus-sharePatent US5253240 - Tracking error detecting system for removing an offset in an optical disk player
