Optical scanning device
AssigneeKoninklijke Philips Electronics N.V.
InventorsBernardus Hendrikus Wilhelmus Hendriks, Jeroen Wals
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Abstract
The present invention provides a scanning device with the following features: the system is capable of writing data to record carriers of a first format because it is corrected for chromatic aberration resulting from fast wavelength variations during write operation; it has a diffractive element with a generally sawtooth-like pattern, such that it may for example be manufactured in a single-step replication process; the system has high efficiency for scanning first optical record carriers (e.g. DVDs) and acceptable efficiency for scanning second optical record carriers (e.g. CDs); and the lens provides limited spherochromatism and the system is thus able to cope with wavelength variations.
Claims11
An optical scanning device for scanning first and second optical record carriers with a first and a second information layer depth by radiation of a first wavelength λ1, and a second wavelength λ2, respectively,
- said device being capable of reading and writing optical record carriers of said first format,
- the device including an objective lens (10) with at least one refractive element and at least one diffractive element (11) and with a numerical aperture NA of NA>0.60 for said first wavelength λ1,
- said diffractive element including a pattern of generally sawtooth-like elements;
- wherein the diffractive and refractive properties of the objective lens are selected:
- such that radiation of said first wavelength is transmitted and focused on optical record carriers of said first thickness;
- such that radiation of said second wavelength is transmitted and focused on optical record carriers of said second thickness;
- and
- such that a variation in wavelength λ1 of 5 nm results in spherochromatism below 0.03λ1.
An optical scanning device for scanning optical record carriers of a first and second format by radiation of a first and second wavelength λ1 and λ2, respectively, the device including an optical objective lens with at least one refractive and one diffractive element,
- wherein the refractive and diffractive properties are selected such that diffractive orders m1 and m2 of wavelength λ1 and λ2 are used to scan optical record carriers of said first and second format respectively with:
- (m1, m2) being one of the following combinations:
- (m1, m2)=(−2, −2), (−3, −2), (−3, −3) or (−4, −3).
Dependencies are inferred from the claim text.