Optical element and image sensor

1. An optical element comprising:

a refractive index pattern that is periodically formed by a plurality of media having refractive indices different from each other,

wherein the highest diffraction orders for at least three light beams of wavelength regions that enter the optical element are different from each other, and

wherein the light beams of the wavelength regions are emitted so that each of the light beams of the wavelength regions is periodically localized.

2. The optical element according to claim 1 ,

wherein the light beams of the wavelength regions are localized at positions different from each other.

3. The optical element according to claim 1 ,

wherein the light beams of the wavelength regions are localized at the same position.

4. An optical element comprising:

a refractive index pattern that is periodically formed by a plurality of media having refractive indices different from each other,

wherein the highest diffraction order for a light beam of a first wavelength region that enters the optical element is greater than the highest diffraction order for a light beam of a second wavelength region that is longer than the first wavelength region,

wherein the light beams of the first wavelength region and the second wavelength region are emitted so that each of the light beams of the first wavelength region and the second wavelength region is periodically localized, and

wherein the refractive index pattern includes a refractive index pattern smaller than a center wavelength of the second wavelength region.

5. The optical element according to claim 1 ,

wherein the refractive index pattern includes a plurality of refractive index patterns in a unit period of the refractive index pattern, and

wherein the plurality of refractive index patterns are at least one of different-sized patterns and non-similar patterns.

6. The optical element according to claim 1 ,

wherein the refractive index pattern includes a concave shape.

7. An optical element comprising:

a refractive index pattern that is periodically formed by a plurality of media having refractive indices different from each other,

wherein the highest diffraction order for a light beam of a first wavelength region that enters the optical element is greater than the highest diffraction order for a light beam of a second wavelength region that is longer than the first wavelength region,

wherein the light beams of the first wavelength region and the second wavelength region are emitted so that each of the light beams of the first wavelength region and the second wavelength region is periodically localized, and

wherein the refractive index pattern includes a straight line shape having at least (¼n) times as long as a center wavelength of the first wavelength region for the maximum refractive index n of the refractive index pattern.

8. An optical element comprising:

a refractive index pattern that is periodically formed by a plurality of media having refractive indices different from each other,

wherein the highest diffraction order for a light beam of a first wavelength region that enters the optical element is greater than the highest diffraction order for a light beam of a second wavelength region that is longer than the first wavelength region,

wherein the light beams of the first wavelength region and the second wavelength region are emitted so that each of the light beams of the first wavelength region and the second wavelength region is periodically localized,

wherein the optical element is an element that emits a visible light beam and that has a period of 800 nm to 2500 nm in an x direction and a y direction orthogonal to the x direction,

wherein the plurality of media having the refractive indices different from each other are configured by including a glass and a void,

wherein the refractive index pattern is rotationally symmetrical by 90 degrees on an xy plane and includes the void having a circular shape and an L shape on the xy plane, and

wherein a thickness of the void is 100 nm to 1 μm.

9. An image sensor comprising:

an optical element including a refractive index pattern that is periodically formed by a plurality of media having refractive indices different from each other, wherein the highest diffraction orders for at least three light beams of wavelength regions that enter the optical element are different from each other, and wherein the light beams of the wavelength regions are emitted so that each of the light beams of the wavelength regions is periodically localized; and

a light receiving element that has light receiving regions that the light beams of the wavelength regions enter are periodically disposed.