Optical compensator for use in an optical scanning device

Abstract

The present invention provides an optical compensator for use in an optical scanning device for scanning optical record carriers, there being at least two different information layer depths within two different ones of the carriers, the optical record carriers including a first optical record carrier (3'), a second optical record carrier and a third optical record carrier, the scanning device including a radiation source system (7) for producing first, second and third radiation beams for scanning the first, second and third record carriers, respectively, the first, second and third radiationbeams having different predetermined wavelengths. The optical compensator has a non-periodic phase structure through which each of the first, second and third radiation beams are arranged to pass, the non-periodic phase structure including a plurality of stepped annular zones separated by steps, the zones forming a non-periodic radial pattern, the stepped annular zones introducing first, second and third different wavefront modifications into at least part of the first, second and third radiation beams, respectively. The optical compensator includes radial height variations in the plurality of stepped annular zones, the radial height variations being arranged such that non-zero contributions are provided to each of the first, second and third wavefront modifications by the optical compensator in each of the stepped annular zones.

Description

technical field [0001] The invention relates to an optical compensator for an optical scanning device for scanning an optical record carrier having a plurality of information layers, with at least two different information layer depths in two different record carriers. Background technique [0002] The field of data storage using optical record carriers is currently an active area of ​​technical research. A variety of optical record carrier formats exist, including: compact disc (CD), digital versatile disc (DVD), blu-ray disc (BD) and high definition digital versatile disc (HDDVD). These formats are available in different types, including: read-only format (for example, CD-ROM / DVD-ROM / BD-ROM), recordable format (for example, CD-R / DVD-R / BD-R), Rewritable formats (eg, CD-RW, DVD-RW, BD-RE) and audio formats (eg, CD-A). In order to scan different formats of optical record carriers, radiation beams having different wavelengths must be used. The wavelength for scanning CD is ...

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Problems solved by technology

Furthermore, three of these modes include a radiation wavelength of 785 nm and a radiation wavelength of 405 nm, the ratio between these wavelengths is such that the phase change introduced by the NPS steps differs by a factor of about 2 in most optical materials, This results in either poor transmission for one of the wavelengths, or a rather high NPS step, which makes the manufacturing process expensive

[0011] Another shortcoming of the currently proposed solutions is that they rely on the use of gratings with different diffraction orders for each wavelength

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