Autofocusing control system.

摘要

An autofocusing control system makes a position of focusing spot (Si) follow for itself a displacement of an information medium (5). In the autofocusing control system, a single mode semiconductor laser (1) is excited in a multi oscillation mode by returning part of a reflected light beam from the information medium, and a focusing lens (20) having chromatic aberration is used which focuses a laser beam from the semiconductor laser onto a different position along the optical axis of the lens in association with a different laser wavelength.