Display device comprising a display panel having a Lambertian light emission distribution and a viewing angle modulator including a diffraction structure

1. A display device comprising:

a display panel including a display surface having a Lambertian light emission distribution; and

a viewing angle modulator disposed on the display panel, wherein

the viewing angle modulator includes:

a first refractive layer including a diffraction structure on a surface;

a refractive index conversion layer disposed on the first refractive layer and including an electro-optical material having a refractive index that changes when a voltage is applied to the electro-optical material; and

a second refractive layer disposed on the refractive index conversion layer, and the refractive index conversion layer includes:

a base layer; and

an optical structure disposed on the base layer that changes a path of light incident on a surface facing the second refractive layer.

2. The display device of claim 1 , wherein the optical structure is one of a prism structure and a convex lens structure.

3. The display device of claim 1 , wherein the viewing angle modulator includes:

a normal mode that sets a viewing angle of the display panel to a reference viewing angle when the voltage is not applied to the electro-optical material of the refractive index conversion layer; and

a private mode that sets the viewing angle of the display panel to be narrower than the reference viewing angle when the voltage is applied to the electro-optical material of the refractive index conversion layer.

4. The display device of claim 3 , wherein the refractive index conversion layer divides incident light incident on a first interface between the first refractive layer and the refractive index conversion layer into first exit light traveling in a first path and second exit light traveling in a second path, through the diffraction structure when the voltage is applied to the electro-optical material of the refractive index conversion layer.

5. The display device of claim 4 , wherein

the first exit light is incident on a second interface between the optical structure and the second refractive layer in a first incident angle range, and

the second exit light is incident on the second interface in a second incident angle range having an angle smaller than an angle of the first incident angle range.

6. The display device of claim 5 , wherein

the first exit light does not pass through the display surface of the display panel,

the second exit light passes through the display surface of the display panel, and

an exit angle of the second exit light is smaller than an exit angle range of the reference viewing angle.

7. The display device of claim 1 , wherein

the first refractive layer has a first refractive index,

the second refractive layer has a second refractive index, and

the first refractive index and the second refractive index are same.

8. The display device of claim 7 , wherein the electro-optical material is a liquid crystal including a material having a birefringence having an ordinary ray refractive index and an extraordinary ray refractive index.

9. The display device of claim 8 , wherein the liquid crystal has the extraordinary ray refractive index when the voltage is applied to the electro-optical material of the refractive index conversion layer and has the ordinary ray refractive index when the voltage is not applied to the electro-optical material of the refractive index conversion layer.

10. The display device of claim 8 , wherein the first refractive index, the second refractive index, and the ordinary refractive index are same.

11. The display device of claim 7 , wherein

the refractive index conversion layer includes the electro-optical material only in the base layer, and

the optical structure has a third refractive index.

12. The display device of claim 11 , wherein the electro-optical material is a liquid crystal including a material having a birefringence having an ordinary ray refractive index and an extraordinary ray refractive index.

13. The display device of claim 12 , wherein the liquid crystal has the extraordinary ray refractive index when the voltage is applied to the electro-optical material of the refractive index conversion layer and has the ordinary ray refractive index when the voltage is not applied to the electro-optical material of the refractive index conversion layer.

14. The display device of claim 12 , wherein

the first refractive index, the second refractive index, and the ordinary refractive index are same, and

the third refractive index is greater than the first refractive index and the second refractive index and smaller than the ordinary ray refractive index.

15. The display device of claim 7 , wherein the electro-optical material is a Polymer Network Liquid Crystal (PNLC) including a liquid crystal stabilized by a polymer network having a three-dimensional net structure from an outer surface to an inside of the electro-optical material.

16. The display device of claim 15 , wherein the liquid crystal includes a material having a birefringence having an ordinary ray refractive index and an extraordinary ray refractive index.

17. The display device of claim 16 , wherein the PNLC is divided into domains including the liquid crystal by the polymer network.

18. The display device of claim 17 , wherein

the domains have the extraordinary ray refractive index when the voltage is applied to the PNLC, and

a first domain of the domains has the ordinary ray refractive index and a second domain of the domains has the extraordinary ray refractive index when the voltage is not applied to the PNLC.

19. The display device of claim 18 , wherein the second domain scatters incident light.

20. The display device of claim 16 , wherein the first refractive index, the second refractive index, and the ordinary ray refractive index are same.