Imaging lens

An imaging lens comprising a liquid crystal lens and a refractive lens laminated together;

• the refractive lens being a refractive lens having a positive refractive power;
• the liquid crystal lens comprising:
• a pair of transparent substrates disposed so as to be opposed to each other, a Fresnel diffraction lens surface and a transparent electrode formed on one of the opposed two surfaces of the pair of transparent substrates, a transparent electrode formed on the other one of the opposed two surfaces of the pair of transparent substrates, and a liquid crystal layer filling the concave/convex portion and sandwiched between the transparent substrates;
• the Fresnel diffraction lens surface having a saw-tooth-shaped cross section and consisting of concentrically arranged annular concave/convex portions;
• wherein the liquid crystal lens is configured so that the alignment state of the liquid crystal layer is changeable by applying a voltage to the liquid crystal layer by supplying a power from an external power source to the transparent electrode;
• wherein the imaging lens is configured so that its focal length is changeable by changing the applied voltage to the liquid crystal lens,
• wherein the liquid crystal lens is a liquid crystal lens in which Δn×d being a product of Δn multiplied by a depth d of the concave/convex portion of the Fresnel diffraction lens satisfies the following formula:
• 390×m≦Δn×d≦650×m
• (wherein m=1, 2 or 3)
• provided that |n1−nF| and |n2−nF|, whichever smaller, is defined as Δn, wherein n1 and n2 are refractive indexes of the liquid crystal layer for linearly polarized light of the predetermined polarization direction at no voltage application and at voltage application respectively, and nF is the refractive index of the Fresnel diffraction lens surface, and
• wherein a phase correction surface having a concave/convex shape consisting of arranged annular shapes is formed on the opposed surface of said the other transparent substrate of the liquid crystal lens on which the Fresnel diffraction lens surface is not formed, so that the center of the phase correction surface agrees with the center of the Fresnel diffraction lens surface, and the transparent electrode is formed on the phase correction surface.

An imaging lens comprising a liquid crystal lens and a refractive lens laminated together;

• the refractive lens being a refractive lens having a positive refractive power;
• the liquid crystal lens comprising:
• a pair of transparent substrates disposed so as to be opposed to each other, a Fresnel diffraction lens surface and a transparent electrode formed on one of the opposed two surfaces of the pair of transparent substrates, a transparent electrode formed on the other one of the opposed two surfaces of the pair of transparent substrates, and a liquid crystal layer filling the concave/convex portion and sandwiched between the transparent substrates;
• the Fresnel diffraction lens surface having a saw-tooth-shaped cross section and consisting of concentrically arranged annular concave/convex portions;
• wherein the liquid crystal lens is configured so that the alignment state of the liquid crystal layer is changeable by applying a voltage to the liquid crystal layer by supplying a power from an external power source to the transparent electrode;
• wherein the imaging lens is configured so that its focal length is changeable by changing the applied voltage to the liquid crystal lens,
• wherein the liquid crystal lens is a laminated liquid crystal lens comprising first and second liquid crystal lenses;
• and
• each of the first and second liquid crystal lenses are configured so that its refractive power for linearly polarized light of predetermined polarization direction is changeable by changing alignment state of liquid crystal layer by applying a voltage to the liquid crystal layer by supplying a power to the transparent electrodes from an external power source respectively;
• wherein the laminated liquid crystal lens comprises the first liquid crystal lens and the second liquid crystal lens laminated so that their predetermined polarization directions are perpendicular to each other,
• wherein the liquid crystal lens is a liquid crystal lens in which Δn×d being a product of Δn multiplied by a depth d [nm] of the concave/convex portion of the Fresnel diffraction lens satisfies the following formula:
• 390×m≦Δn×d≦650×m
• (wherein m=1, 2 or 3)
• provided that |n1−nF| and |n2−nF|, whichever smaller, is defined as Δn, wherein n1 and n2 are refractive indexes of the liquid crystal layer for linearly polarized light of the predetermined polarization direction at no voltage application and at voltage application respectively, and nF is the refractive index of the Fresnel diffraction lens surface,
• wherein a phase correction surface having a concave/convex shape consisting of arranged annular shapes is formed on the opposed surface of said the other transparent substrate of the liquid crystal lens on which the Fresnel diffraction lens surface is not formed, so that the center of the phase correction surface agrees with the center of the Fresnel diffraction lens surface, and the transparent electrode is formed on the phase correction surface.