Patent ID: 6687037
Filing Date: 2004-02-03
Classification: G02B,G11B

Abstract:
An optical scanning device for scanning optical record carriers with radiation of a first and a second wavelength, the device having a focusing element with a diffractive part, the diffractive part including a pattern of pattern elements having a stepped profile, wherein the total optical paths pertaining to steps of a pattern element are substantially equal to multiples of said first wavelength, such that radiation of said first wavelength is substantially undiffracted by the said diffractive part and such that said device has a first focusing characteristic for said first wavelength, andwherein the steps are arranged such that radiation of the second wavelength is diffracted by said diffractive part and such that said device has a second focusing characteristic, different to said first focusing characteristic, for a selected diffractive order of the radiation of the second wavelength, and the relative step heights between adjacent steps of said pattern element include a relative step height having an optical path substantially equal to a&lgr;1, wherein a is an integer and a>1 and &lgr;1 is said first wavelength, whereby an improved efficiency of transmission for said selected diffractive order of the radiation of the second wavelength is provided.