SIGNAL DETECTING SYSTEM AT A OPTICAL INFORMATION APPARATUS

摘要

The detection system has a light detector having 4 light receiving regions arranged in a far field of an information track. The regions are divided about an optical axis of an incident light beam in orthogonal directions. Output signals are obtained from the diagonally aligned regions and supplied to a first adder to produce a sum. Two other signals are supplied to a second adder from the other two regions to obtain a sum. The two sum signals are connected to an adder and a subtractor to produce a sum singal and a difference signal. The latter has a polarity depending upon a direction of deviation of a light spot w.r.t. the track.