Optical scanning device

A method of designing an optical element for use in an optical scanning device for scanning optical record carriers with radiation of a first and second wavelength, said optical element including a diffractive part,

• designing a first part of said diffractive part to approximate a generally sawtooth-like structure with a height h2 on the highest side of each sawtooth-like pattern element generating a phase change substantially equal to i·2π, where i is an integer, for radiation of said second wavelength, the sawtooth-like structure being approximated by an initially selected stepped profile representing said sawtooth-like structure, and
• approximating the different selected stepped profile for a second part of the diffractive part of the initially selected stepped profile by approximating said different selected stepped profile with steps of a total step height approximately equal to h1′, with h 1 ′ = λ 1 n - 1 ⁢ k
• whereby λ1 is said first wavelength, n is the refractive index of the material from which the optical element is made, n0 is the refractive index of the adjacent medium and k is an integer taking a plurality of different values within one pattern element.

An optical scanning device for scanning optical record carriers with radiation of a first and a second wavelength, the device including a focusing element with a diffractive part, the diffractive part including a pattern of pattern elements having a stepped profile, wherein the step heights are selected:

• such that radiation of said first wavelength passes said diffractive part in zeroth diffractive order substantially unattenuated and is subsequently focused with a first focusing characteristic;
• and
• such that radiation of said second wavelength is diffracted by said diffractive part, resulting in a beam of a selected diffractive order, with a second focusing characteristic different from said first characteristic.

An optical element for use in an optical scanning device for scanning optical record carriers with radiation beams of a first and second wavelength and with a first and second numerical aperture respectively, said optical element including a focusing element with a diffractive part, the diffractive part including a pattern of pattern elements having a stepped profile, wherein the step heights are selected:

• such that radiation of said first wavelength passes said optical element in zeroth diffractive order substantially unattenuated and to provide said device with a first focusing characteristic;
• and
• such that radiation of said second wavelength is diffracted by said optical element, resulting in a beam of a selected diffractive order, and to provide said device with a second focusing characteristic different from said first characteristic.