Liquid crystal lens and imaging lens device
The present invention provides an imaging lens device, which has a widely extended focusing range and exhibits good resolution over the entire focusing range. The imaging lens device comprises a liquid crystal lens for focusing an object at a prescribed distance, comprising a liquid crystal layer, a first transparent substrate disposed adjacent to one surface of the liquid crystal layer and having a first electrode and having Fresnel lens surface formed on the boundary with the liquid crystal layer, a second transparent substrate disposed adjacent to the other surface of the liquid crystal layer and having a second electrode; a controller for changing the refractive index of the liquid crystal layer for extraordinary ray by changing electric voltage applied between the first electrode and the second electrode; and an imaging element for taking an image of the object. The liquid crystal lens functions as a diffractive optical element for an extraordinary ray when the liquid crystal layer has a prescribed refractive index for an extraordinary ray incident upon the liquid crystal layer.
1 . An imaging lens device comprising:
a liquid crystal lens for focusing an object at a prescribed distance, comprising:
a first liquid crystal layer;
a first transparent substrate disposed adjacent to one surface of said first liquid crystal layer, and having a first electrode and having Fresnel lens surface formed on the boundary with said first liquid crystal layer;
a second transparent substrate disposed adjacent to the other surface of said first liquid crystal layer, and having a second electrode;
wherein, when said first liquid crystal layer has a prescribed refractive index for extraordinary ray incident on said first liquid crystal layer, said Fresnel lens surface functions as a diffractive optical element for said extraordinary ray;
a controller for changing the refractive index of said first liquid crystal layer for extraordinary ray by changing the electric voltage applied between said first electrode and said second electrode; and
an imaging element for taking an image of said object.
2 . The imaging lens device according to claim 1 , wherein steps are formed on said Fresnel lens surface so as to divide said Fresnel lens surface into a plurality of regions, and wherein optical path difference produced at said step for extraordinary ray incident upon said first liquid crystal layer is an integer multiple of wavelength for which said imaging element has sensitivity when the refractive index of said first liquid crystal layer for extraordinary ray has a prescribed value.
3 . The imaging lens device according to claim 1 , wherein said first transparent substrate has a member having said Fresnel lens surface formed thereon.
4 . The imaging lens device according to claim 3 , wherein said first transparent substrate has a flat plate-shaped substrate, said first electrode being disposed between said flat plate-shaped substrate and said member.
5 . The imaging lens device according to claim 1 , wherein said Fresnel lens surface is formed on a portion of said first transparent substrate.
6 . The imaging lens device according to claim 1 , wherein said prescribed refractive index is the minimum value of refractive index included in the range of variable refractive index of said first liquid crystal layer for extraordinary ray.
7 . The imaging lens device according to claim 1 , wherein the refractive index of said first transparent substrate and the refractive index of said first liquid crystal layer for ordinary ray coincide with each other.
8 . The imaging lens device according to claim 1 , wherein said liquid crystal lens functions as a diffractive optical element for ordinary ray incident upon said first liquid crystal layer.
9 . The imaging lens device according to claim 1 , wherein said Fresnel lens surface is aspherical surface.
10 . The imaging lens device according to claim 1 , wherein said second transparent substrate has Fresnel lens surface formed on the boundary with said first liquid crystal layer.
11 . The imaging lens device according to claim 1 , said liquid crystal lens further comprising:
a second liquid crystal layer;
a third transparent substrate disposed adjacent to one surface of said second liquid crystal layer, and having Fresnel lens surface formed on the boundary with said second liquid crystal layer; and
a fourth transparent substrate disposed adjacent to the other surface of said second liquid crystal layer;
wherein the liquid crystal in said first liquid crystal layer and the liquid crystal in said second liquid crystal layer are oriented with respective long axes orthogonal to each other, and
wherein, when said second liquid crystal layer has a prescribed refractive index for extraordinary ray incident on said second liquid crystal layer, said Fresnel lens surface formed on the boundary with said second liquid crystal layer functions as a diffractive optical element for said extraordinary ray.
12 . The imaging lens device according to claim 11 , wherein Fresnel lens surface of said first transparent substrate and Fresnel lens surface of said third transparent substrate respectively have the shape of cylindrical lens arranged such that the respective directions for functioning as Fresnel lens are orthogonal to each other.
13 . The imaging lens device according to claim 1 , wherein said liquid crystal lens is a lens with positive power when it functions as a diffractive optical element.
14 . An imaging lens device comprising:
a liquid crystal lens for focusing an object at a prescribed distance, comprising:
a first liquid crystal layer;
a first transparent substrate disposed adjacent to one surface of said first liquid crystal layer, and having a first electrode and having Fresnel lens surface formed on the boundary with said liquid crystal layer; and
a second transparent substrate disposed adjacent to the other surface of said first liquid crystal layer, and having a second electrode;
wherein said Fresnel lens surface functions as a diffractive optical element for ordinary ray incident upon said first liquid crystal layer;
a controller for changing the refractive index of said first liquid crystal layer for extraordinary ray by changing the electric voltage applied between said first electrode and said second electrode; and
an imaging element for taking an image of said object.
15 . The imaging lens device according to claim 14 , wherein steps are formed on said Fresnel lens surface so as to divide said Fresnel lens surface into a plurality of regions, and wherein optical path difference produced at said step for ordinary ray incident upon said first liquid crystal layer is an integer multiple of wavelength for which said imaging element has sensitivity.
16 . The imaging lens device according to claim 15 , wherein the optical path difference produced at said step for ordinary ray incident upon said first liquid crystal layer is one or two times said wavelength, and wherein said controller changes the refractive index of said first liquid crystal layer for extraordinary ray such that the minimum value of optical path difference produced at said step for extraordinary ray incident upon said first liquid crystal layer is larger than the coherent length of the extraordinary ray.
17 . The imaging lens device according to claim 14 , wherein said first transparent substrate has a member having said Fresnel lens surface formed thereon.
18 . The imaging lens device according to claim 17 , wherein said first transparent substrate has a flat plate-shaped substrate, said first electrode being disposed between said flat plate-shaped substrate and said member.
19 . The imaging lens device according to claim 14 , wherein said Fresnel lens surface is formed on a portion of said first transparent substrate.
20 . The imaging lens device according to claim 14 , wherein said Fresnel lens surface is aspherical surface.
21 . The imaging lens device according to claim 14 , wherein said second transparent substrate has Fresnel lens surface formed on the boundary with said first liquid crystal layer.
22 . The imaging lens device according to claim 14 , said liquid crystal lens further comprising:
a second liquid crystal layer;
a third transparent substrate disposed adjacent to one surface of said second liquid crystal layer, and having Fresnel lens surface formed on the boundary with said second liquid crystal layer; and
a fourth transparent substrate disposed adjacent to the other surface of said second liquid crystal layer;
wherein the liquid crystal in said first liquid crystal layer and the liquid crystal in said second liquid crystal layer are oriented such that respective long axes are orthogonal to each other, and
wherein said Fresnel lens surface formed on the boundary with said second liquid crystal layer functions as a diffractive optical element for said ordinary ray incident upon said second liquid crystal layer.
23 . The imaging lens device according to claim 22 , wherein Fresnel lens surface of said first transparent substrate and Fresnel lens surface of said third transparent substrate respectively have the shape of cylindrical lens arranged such that the respective directions for functioning as Fresnel lens are orthogonal to each other.
24 . The imaging lens device according to claim 14 , wherein said liquid crystal lens is a lens with positive power when it functions as a diffractive optical element.
25 . A liquid crystal lens comprising:
a liquid crystal layer;
a first transparent substrate disposed adjacent to one surface of said liquid crystal layer, and having a Fresnel lens surface formed on the boundary with said liquid crystal layer;
a second transparent substrate disposed adjacent to the other surface of said liquid crystal layer; and
a first electrode and a second electrode for changing electric voltage applied to said liquid crystal layer so as to change the refractive index for extraordinary ray incident upon said liquid crystal layer;
wherein, by applying a prescribed electric voltage between said first electrode and said second electrode such that said liquid crystal layer has a prescribed refractive index for extraordinary ray incident on said liquid crystal layer, said Fresnel lens surface functions as a diffractive optical element for said extraordinary ray.
26 . A liquid crystal lens comprising:
a liquid crystal layer;
a first transparent substrate disposed adjacent to one surface of said liquid crystal layer, and having a Fresnel lens surface formed on the boundary with said liquid crystal layer;
a second transparent substrate disposed adjacent to the other surface of said liquid crystal layer; and
a first electrode and a second electrode for changing electric voltage applied to said liquid crystal layer so as to change the refractive index for extraordinary ray incident upon said liquid crystal layer;
wherein said Fresnel lens surface functions as a diffractive optical element for an ordinary ray incident upon said liquid crystal layer.