Focus controlling apparatus and method, and optical disc drive

A focus controlling method for focusing a light beam and positioning the focused light beam onto a signal recording layer of a signal recording media, comprising the steps of:

• positioning the light beam focused by an objective lens onto the signal recording layer of the recording media;
• periodically moving the objective lens within a predetermined optical-axial range,
• detecting an amplitude of an RF signal read from the recording media at either end of the optical-axial range, and
• adjusting an offset between the signal recording layer of the recording media depending upon a difference between the amplitudes of the detected RF signal;
• wherein during said step of periodically moving, a sinusoidal movement is used.

A focus controlling method for focusing a light beam and positioning the focused light beam onto a signal recording layer of a signal recording media, comprising the steps of:

• positioning the light beam focused by an objective lens onto the signal recording layer of the recording media;
• periodically moving the objective lens within a predetermined optical-axial range,
• detecting an amplitude of an RF signal read from the recording media at either end of the optical-axial range, and
• adjusting an offset between the signal recording layer of the recording media depending upon a difference between the amplitudes of the detected RF signal;
• and
• wherein said positioning and detecting steps are done alternately for at least one period of said signal.

An optical disc drive for recording and/or reproducing a signal by positioning a focused light beam onto a signal recording layer of a signal recording media, comprising:

• a light beam focusing means having a numerical aperture of 0.6 or more;
• a focus controlling means for positioning the light beam focused by said light beam focusing means onto the signal recording layer of the recording media;
• and
• an offset adjusting means for adjusting an offset between the focused light beam positioned by the focus controlling means and the signal recording layer of the recording media depending upon an RF signal read from the recording media;
• wherein the offset adjusting means periodically moves the light beam focusing means within a predetermined optical-axial range to adjust the offset depending upon an amplitude of a signal read from the recording media at either end of the optical-axial range;
• and
• the light beam focusing means moves depicting a sine waveform.