OPTICAL PICK-UP UNIT FOR USE IN A MULTI-DISC OPTICAL PLAYER AND METHOD FOR CORRECTING OPTICAL ABERRATIONS IN SUCH AN OPTICAL PICK-UP UNIT

摘要

The present invention concerns to an optical pick-up unit for use in a multi- disc system, for scanning a first type of record carriers and at least a second type of record carriers, the second type of record carriers having an information density different from an information density of the first type of record carriers, the optical pick-up unit comprising at least two optical branches (3, 5, 7), a first optical branch (3) having a first radiation source (39) emitting a first radiation beam with a first wavelength, which first radiation beam propagates along a first optical path (4), and a second optical branch (5, 7) having a second radiation source (51, 59) emitting a second radiation beam with a second wavelength, which second radiation beam propagates along a second optical path (6, 8), the first and the second wavelengths and the first and the second optical path (4, 6, 8) being different and the first and the second radiation beam propagating - after having passed the first and the second optical path (4, 6, 8) - along a common optical path (66) comprising an objective lens (73) for focusing the first radiation beam or the second radiation beam at the record carrier (35). The optical pick-up unit is characterized in that at least one of the optical branches (3, 5, 7) comprises an optical component (41, 53, 61) that is movable for correcting an optical aberration in the first or second radiation beam.