FEEDBACK DEVICE IN DEFLECTING SYSTEM

摘要

An acousto-optic deflector may selectively deflect an applied light beam. The remaining undeflected zero-order beam varies considerably in power depending upon whether the beam is deflected. The zero-order beam is modulated and directed at a detection arrangement to detect a characteristic of the beam other than the selective deflection power variation. The modulation and detection is best employed to detect position feedback for an informational writing beam. An exemplary detection arrangement having a defined ringing frequency with a long shift time constant detects an amplitude modulation of the beam having a significantly higher frequency than that of the selective deflection power variation. The feedback may be in the form of an oscillation representing the position of the deflected beam as it is swept in a raster format and the detection arrangement detects the amplitude oscillations as indicative of the feedback.