Optical structure, light guide, and a display device

1. An optical structure that changes a traveling direction of light and emits the light, the optical structure comprising:

a first surface formed of a flat surface and configured to change a traveling direction of light; and

a second surface formed adjacent to the first surface and having a surface in a curved shape corresponding to a side surface of a cylinder,

wherein the curved shape is formed at each of both ends of the second surface,

wherein each of the curved shapes has a first curved surface corresponding to a side surface of a first cylinder as the cylinder and a second curved surface corresponding to a side surface of a second cylinder as the cylinder,

wherein when the first surface is seen from a direction along a perpendicular line on the first surface, a center of a bottom surface of the first cylinder and a center of a bottom surface of the second cylinder are located on mutually opposite sides across a boundary of the first surface and the second surface, and

wherein, when

a virtual plane including an outer edge not adjacent to the second surface, out of outer edges of the first surface, and an outer edge not adjacent to the first surface, out of outer edges of the second surface, is defined as a reference plane;

a maximum value of a distance between the reference plane and a boundary of the first surface to the second surface is D;

an angle between the first surface and the reference plane is θ; and

a radius of a bottom surface of the cylinder is R,

the following equation (1) is held:

D<R sin θ  (1).

2. The optical structure according to claim 1 , wherein incident light is reflected or refracted on the first surface to change a path of the light.

3. The optical structure according to claim 1 , wherein when

a virtual plane including an outer edge not adjacent to the second surface, out of outer edges of the first surface, and an outer edge not adjacent to the first surface, out of outer edges of the second surface, is defined as a reference plane, and

out of the outer edges of the first surface, an outer edge adjacent to the second surface is a first outer edge, and an outer edge adjacent to the reference plane is a second outer edge straight line,

a maximum value of a length of a perpendicular line from a point on the first outer edge to the second outer edge straight line is shorter than a radius of a bottom surface of the cylinder.

4. The optical structure according to claim 1 , wherein when

a virtual plane including an outer edge not adjacent to the second surface, out of outer edges of the first surface, and an outer edge not adjacent to the first surface, out of outer edges of the second surface, is defined as a reference plane, and

out of the outer edges of the first surface, an outer edge adjacent to the second surface is a first outer edge, and an outer edge adjacent to the reference plane is a second outer edge straight line,

an inclination of a tangent of a curve indicated by the first outer edge with respect to the second outer edge straight line at an intersection of the first outer edge and the second outer edge straight line is smaller than 90 degrees.

5. The optical structure according to claim 1 , wherein the second surface includes the curved shape at each of both ends, and the two curved shapes are adjacent to each other.

6. The optical structure according to claim 1 , wherein the second surface includes a surface in the curved shape at each of both ends and includes a plane between the surfaces in the curved shape.

7. A light guide that guides light entering inside and emits a part of the light from a light exit surface, the light guide comprising a plurality of the optical structures according to claim 1 .

8. A display device comprising:

the light guide according to claim 7 ; and

a light source configured to emit light into the light guide.

9. The display device according to claim 8 , wherein display is performed using directivity of light emitted from the light guide.