METHOD AND DEVICE FOR GENERATION OF INVERTED IMAGE AS WELL AS METHOD AND APPARATUS FOR DETECTION OF FOCUS ERROR MAKING USE OF IT

摘要

PROBLEM TO BE SOLVED: To cancel a signal error due to optical axis change based on the tilt of an optical disk or the shift of an objective lens. SOLUTION: The reverse image generator 10 comprises a translucent surface 18 for dividing an optical beam 9 into first and second optical beams, first and second prisms for phase inverting the second beam into reverse image, and third and fourth prisms 14 for combining the first beam 9a with the phase inverted second beam. The generator also has two 1/4-wavelength plates, optical demultiplexing and multiplexing surfaces to reduce the optical loss. The error due to optical axis change is removed from the focus error signal detected from the multiplexed beam emitted from the generator 10. Accordingly, it is effective to stably drive an optical pickup.