LIQUID CRYSTAL DIFFRACTION LENS ELEMENT AND OPTICAL HEAD DEVICE

• US 20070182915A1
• Filed: 04/19/2007
• Published: 08/09/2007
• Est. Priority Date: 10/19/2004
• Status: Active Grant

• Current Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: Ooi, Yoshiharu, Osawa, Mitsuo
• Granted Patent: US 7,710,536 B2
• Time in Patent Office: Days
• US Class Current: 349/201
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 3/14 of variable focal length
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02F 1/133526 Lenses, e.g. microlenses or Fresnel lenses
• CPC Class Codes: G02F 1/29 for the control of the position or the direction of light beams, i.e. deflection
• CPC Class Codes: G02F 1/294 Variable focal length devices
• CPC Class Codes: G11B 2007/0006 adapted for scanning different types of carrier, e.g. CD & DVD
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1369 Active plates, e.g. liquid crystal panels or electrostrictive elements
• CPC Class Codes: G11B 7/1378 Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
• CPC Class Codes: G11B 7/13925 active, e.g. controlled by electrical or mechanical means

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.

Claims

1. A liquid crystal diffraction lens element comprising a pair of transparent substrates disposed in parallel, a liquid crystal sandwiched between the pair of transparent substrates, transparent electrodes for applying an electric field to the liquid crystal, a first birefringent Fresnel lens member formed between a first one of the transparent substrates and the liquid crystal, having a Fresnel lens shape and made of a birefringent material, and a second birefringent Fresnel lens member formed between a second one of the transparent substrates opposed to the first one of the transparent substrates and the liquid crystal, having a Fresnel lens shape and made of a birefringent material;

wherein the extraordinary refractive index direction of the first birefringent Fresnel lens member and the extraordinary refractive index direction of the second birefringent Fresnel lens member are perpendicular to each other; and

wherein the alignment direction of the liquid crystal at the interface between the liquid crystal and the first birefringent Fresnel lens member or the transparent electrode, and the alignment direction of the liquid crystal at the interface between the liquid crystal and the second birefringent Fresnel lens member or the transparent electrode, are perpendicular to each other.

2. The liquid crystal diffraction lens element according to claim 1, wherein at least one of the birefringent material of the first birefringent Fresnel lens member and the birefringent material of the second birefringent Fresnel lens member, is a polymer liquid crystal.

3. The liquid crystal diffraction lens element according to claim 1, wherein the liquid crystal and the birefringent Fresnel lens members have the same ordinary refractive index and the same extraordinary refractive index.

4. The liquid crystal diffraction lens element according to claim 1, wherein the shape of the first birefringent Fresnel lens member and the shape of the second birefringent Fresnel lens member are the same.

5. The liquid crystal diffraction lens element according to claim 1, wherein the extraordinary refractive index directions of the first birefringent Fresnel lens member and the second birefringent Fresnel lens member, are parallel with the transparent substrate surfaces and twisted from each other about an axis perpendicular to the transparent substrate surfaces.

6. The liquid crystal diffraction lens element according to claim 1, wherein the liquid crystal diffraction lens element is integrated with a phase plate producing a phase difference of an odd number times of n/2 of wavelength of transmission light.

7. The liquid crystal diffraction lens element according to claim 1, wherein the alignment direction of the liquid crystal agrees with the extraordinary refractive index direction of each of the birefringent Fresnel lens members in the vicinity of the interface between the liquid crystal and the birefringent Fresnel lens member.

8. The liquid crystal diffraction lens element according to claim 1, wherein a part of each of the birefringent Fresnel lens members is made of an isotropic material.

9. The liquid crystal diffraction lens element according to claim 1, wherein a phase adjustment surface of concave-convex shape is integrated with at least one of the transparent substrates.

10. The liquid crystal diffraction lens element according to claim 9, wherein the phase adjustment surface is made of a plurality of materials having refractive indexes of different temperature coefficients.

11. An optical head device comprising a light source, a light-converging means for converging light emitted from the light source on an optical recording medium, the liquid crystal diffraction lens element as defined in claim 1 disposed in an optical path between the light source and the light-converging means, and a photodetector for reading out an information from the optical recording medium.

12. The optical head device according to claim 11, wherein the polarization direction of outgoing light incident into the liquid crystal diffraction lens element from the light source side, agrees with or is perpendicular to the extraordinary refractive index direction of the first birefringent Fresnel lens member disposed on the side of the liquid crystal diffraction lens element where the outgoing light is incident among the birefringent Fresnel lens members of the liquid crystal diffraction lens element.