The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 31, 2013
Filed:
Dec. 07, 2010
Stephan Knappmann, Rottweil, DE;
Frank Przygodda, Friedrichshafen, DE;
Stephan Knappmann, Rottweil, DE;
Frank Przygodda, Friedrichshafen, DE;
Thomson Licensing, Issy les Moulineaux, FR;
Abstract
An apparatus for reading from or writing to a near-field optical recording medium capable of detecting tilt and spherical aberration is described. The apparatus comprises a light source for generating a reading light beam, a near-field lens, an aberration compensation element, and a diffractive optical element. The diffractive optical element is switchable between a far-field mode and a near-field mode and is adapted to generate a main light beam and four or more sub-beams from the reading light beam for determining at least a cover layer thickness error signal. For this purpose it has an outer region with a first grating period and an inner region having a diameter smaller than an effective numerical aperture of the near-field lens, which in the near-field mode has a second grating period and which has a switchable inner area having a diameter smaller than a far-field numerical aperture of the near-field lens, which in the far-field mode has the first grating period. The aberration compensation element is adapted to be adjusted based on the thickness error signal when the diffractive optical element is in the near-field mode.