摘要 |
An optical system is described for scanning optical record carriers of different types. The optical system includes a compensator having a number of optical elements (NPS 1 , NPS 2 ). The optical elements (NPS 1 , NPS 2 ) are non-periodic phase structures (NPS) having annular areas separated by steps, forming a non-periodic pattern of optical paths of different lengths. By including these multiple optical elements (NPS 1 , NPS 2 ) having NPS surfaces in the lens system of an optical system, it is possible to compensate for the effect of variation of a parameters such as temperature, angle of incidence, polarisation of radiation incident on the system and wavelength of radiation, without causing sensitivity to variation of another such parameter.
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