We receive two relations, the first relation between refractive index of the critical-angle prism and focus-error signal; the second relation between numerical aperture of object lens and out-of-focus error signal.

The principle of the detection of the focusing error signal in a holographic optic head is dis- cussed.

According to the principle of focusing error for two dimensions laser galvanometer scanning,a dynamic focusing optical model for correcting this error was put forward.

Analysis of the focus error characteristic in high density optical disk driver;