Abstract
A two-element objective lens which is compatible with for digital versatile disk (DVD) and Blu-ray Disc (BD) and has adequate optical performances in terms of off-axis wavefront and on-axis chromatic aberration for both optical heads has been designed. The first-order diffracted light is used for DVD and the second-order one is used for BD. We analyzed chromatic spherical aberration and found that using first- and second-diffracted lights causes 20 mλ/nm chromatic spherical aberration at a wavelength of 400 nm. However, using 5λ and 10λ phase steps can reduce chromatic spherical aberration to 7 mλ/nm. The designed two-element lens consists of the first plastic lens, on which there is diffractive optical element, and the second plano-convex glass molded lens.
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