Patent Number: 7,710,536

Title: Liquid crystal diffraction lens element and optical head device

Abstract: A liquid crystal diffraction lens element and an optical head device, which can switch focal lengths of both of outgoing light and returning light by a single element, are provided. The liquid crystal lens element comprises transparent substrates 1a, 1b, a liquid crystal 4 sandwiched between the transparent substrates 1a, 1b, transparent electrodes 2a, 2b, birefringent Fresnel lens members 3a, 3b each having a Fresnel lens shape and made of a birefringent material, and a seal 5, wherein the extraordinary refractive index direction A of the birefringent Fresnel lens member 3a and the extraordinary refractive index direction B of the birefringent Fresnel lens member 3b are perpendicular to each other, and the alignment direction of the liquid crystal 4 at the interface between the liquid crystal 4 and the transparent substrate 1a is perpendicular to the alignment direction of the liquid crystal 4 at the interface between the liquid crystal 4 and the transparent substrate 1b.

Inventors: Osawa; Mitsuo (Koriyama, JP), Ooi; Yoshiharu (Chiyoda-ku, JP)

Assignee: Asahi Glass Company, Limited

International Classification: G02F 1/13 (20060101); G11B 7/135 (20060101)

Expiration Date: 5/04/12018