Patent ID: 7710536

Claim:
A liquid crystal diffraction lens element comprising: a pair of transparent substrates disposed in parallel to each other, 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 each of the first birefringent Fresnel lens member and the second birefringent Fresnel lens member is an annular Fresnel lens formed around an optical axis of the liquid crystal diffraction lens element; 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.