Abstract: In an optical recording system for both reading and writing, the laser beam is projected to the media through a diffraction grating which generates a plus one and minus one order beam ahead of and behind the main zero order beam. The grating is driven by an oscillating driver so as to wobble in a fashion which leaves the zero order beam unaffected but causes the plus one and minus one order beams to move inwardly and outwardly, radially, with respect to the information track on the media in opposite fashions. The wobbling plus one and minus one order beams are used to generate differential signals from separate detectors and are passed through a band pass filter to generate a radial position error signal which may be used to drive the write/read head inwardly or outwardly to remain positioned over a particular information track.