Optical disk pickup device with focusing correction by electrostriction

An optical pickup for recording/reproducing signals on or from an optical recording medium by radiating a high beam from a light source to the optical recording medium via an object lens along an optical axis, the optical pickup comprising:

• co-focal point detecting optical means for receiving a return light from the optical recording medium;
• focusing error detection means for detecting a focusing error by signals from said co-focal point detecting optical means, said focusing error signal representing an amount of deviation of the focal point of said object lens along the optical axis;
• and
• an electrostriction device arranged in an outgoing light path from said light source to said recording medium, said electrostriction device having a central region and a peripheral region, and wherein the focusing error signal is applied between the central region and the peripheral region to produce a phase difference between the central region and the peripheral region in an amount corresponding to a voltage magnitude of the focusing error signal, wherein said electrostriction device includes a piezoelectric plate and electrodes arranged on both sides of said piezoelectric plate, one of the electrodes of said piezoelectric plate having a central electrode and a peripheral electrode.

A focusing servo device for controlling the focal point along the optical axis of an optical pickup for recording/reproducing signals on or from an optical recording medium by radiating a light beam from a light source to the optical recording medium via an object lens along an optical axis, the focusing servo device comprising:

• object lens driving means for moving said object lens along the optical axis;
• focusing error detection means for detecting a focusing error by signals from a light receiving element for receiving a return light from the optical recording medium, said focusing error detection means generating a error detection signals which are representative of an amount of deviation of the focal point along the optical axis;
• an electrostriction device arranged in an outgoing light path from said light source to said recording medium, said electrostriction device having a central region and a peripheral region exhibiting a phase difference corresponding to an applied voltage;
• control means for effecting, responsive to the error detection signals from said focusing error detecting means, a rough servo up to the vicinity of the depth of focus by said object lens driving means and applying one of the error detection signals to the electrostriction device to effect a fine servo within the depth of focus by said electrostriction device;
• a beam splitter for separating a light beam from the light source from a return beam from the optical recording medium and directing the return light beam to said light receiving element;
• and
• pinholes provided between said beam splitter and said light receiving element and ahead and behind a focal point of said return light beam.

A focusing servo device for controlling the focal point along the optical axis of an optical pickup for recording/reproducing signals on or from an optical recording medium by radiating a light beam from a light source to the optical recording medium via an object lens along an optical axis, the focusing servo device comprising:

• object lens driving means for moving said object lens along the optical axis;
• focusing error detection means for detecting a focusing error by signals from a light receiving element for receiving a return light from the optical recording medium, said focusing error detection means generating error detection signals which are representative of an amount of deviation of the focal point along the optical axis;
• an electrostriction device arranged in an outgoing light path from said light source to said recording medium, said electrostriction device having a central region and a peripheral region exhibiting a phase difference corresponding to an applied voltage;
• control means for effecting, responsive to the error detection signal from said focusing error detecting means, a rough servo up to the vicinity of the depth of focus by said object lens driving means and applying one of the error detection signals to the electrostriction device to effect a fine servo within the depth of focus by said electrostriction device;
• a beam splitter for separating a light beam from the light source from a return beam from the optical recording medium and directing the return light beam to said light receiving element;
• and
• said light receiving element receiving said return light beam separated by said beam splitter and having a light receiving surface made up of a circular central light receiving section and a peripheral light receiving section around said central light receiving section.