Patent ID: 6363039
Filing Date: 2002-03-26
Classification: G11B

Abstract:
An optical information recording and playback apparatus comprising:a light source; a focusing optical system for focusing a light beam from said light source into a microscopic light spot on a recording surface of an optical information recording medium having a transparent protective layer; a light detector for receiving the light beam reflected or diffracted at the recording surface of said optical information recording medium, and for converting said received light beam into an electrical signal; signal circuit for converting said electrical signal into a playback information signal; a signal circuit for generating from said electrical signal a phase difference tracking error signal which is independent of variation in the amount of tilt in the recording medium indicating a positional displacement between an information track and the light spot on the recording surface of said optical information recording medium; and driving means of causing said light spot to follow said information track on said optical information by using said phase difference tracking error signal, said optical information recording and playback apparatus characterized by the inclusion of: means of measuring the tilt of said optical information recording medium relative to said focusing optical system; an off-tracking circuit for displacing said light spot in a direction that reduces jitter of a playback signal obtained by playing back information recorded on said optical information recording medium from said information track, by adding an offset signal, based on a result of measuring the tilt, to said phase difference tracking error signal in order to drive the light spot to a certain direction being a direction parallel to said optical information recording medium and perpendicular to a scanning direction of said light spot, said phase difference tracking error signal being supplied to said driving means for causing said light spot to follow said information track on said optical information; and wherein said off-tracking circuit includes: means of determining an off-track direction, the direction in which said light spot is to be displaced, as (1) a direction moving toward an inner circumference of said optical information recording medium when said inner circumference of said optical information recording medium, compared with an outer circumference thereof, is positioned closer to an incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system and (2) a direction moving toward said outer circumference of said optical information recording medium when said outer circumference, compared with said inner circumference, is positioned closer to the incidence side of said focusing optical system because of the tilting of said optical information recording medium relative to said focusing optical system.