SCEN103 CD Focusing Based on Astigmatism

A cylindrical lens introduces astigmatism into the optics. The shape of the cross section of the beam changes on moving through the principal focus. The different relative intensities on the four-quandrant detector generates a signal which is used to correct the focus of the objective lens.

Focusing mechanism based on astigmatism

Source: "The physics of the compact disc" by John A. Cope, Physics Education 28, 1993.

Last updated May 17, 1999.
Copyright George Watson, Univ. of Delaware, 1996.